Apparatus and method for supporting uplink synchronization during handover in wireless communication system

Abstract

The present disclosure relates to a method and an apparatus for efficiently supporting L1L2 triggered mobility (LTM) handover in a wireless communication system. A method of a control node of a base station for optimizing an uplink synchronization procedure may comprise the steps of: determining initiation of LTM configuration for a terminal; and transmitting a first message related to terminal-based timing advance (TA) measurement to a first distributed node among distributed nodes of the base station, wherein the first message includes information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

Description

Device and method for supporting uplink synchronization during handover in a wireless communication system

[0001] The following description relates to a wireless communication system, and more particularly, to a device and method for supporting uplink synchronization during handover in a wireless communication system.

[0002] Wireless access systems are widely deployed to provide various types of communication services, such as voice and data. Typically, wireless access systems are multiple access systems that support communications with multiple users by sharing available system resources (e.g., bandwidth, transmission power). Examples of multiple access systems include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), and single-carrier frequency division multiple access (SC-FDMA).

[0003] In particular, as numerous communication devices demand greater communication capacity, enhanced mobile broadband (eMBB) communication technologies are being proposed, improving upon existing radio access technology (RAT). Furthermore, massive machine type communications (mMTC), which connects numerous devices and objects to provide diverse services anytime and anywhere, as well as communication systems that consider reliability and latency-sensitive services / user equipment (UE), are being proposed. Various technological configurations are being proposed for these purposes.

[0004] The present disclosure relates to a device and method for efficiently supporting LTM (L1L2 triggered mobility) handover in a wireless communication system.

[0005] The present disclosure relates to a device and method for optimizing an early uplink synchronization procedure during LTM in a wireless communication system.

[0006] The present disclosure relates to a device and method for optimizing an early uplink synchronization procedure for LTM within a centralized unit (CU) in a wireless communication system.

[0007] The present disclosure relates to a device and method for optimizing an early uplink synchronization procedure for LTM between DUs (distributed units) within the same CU in a wireless communication system.

[0008] The present disclosure relates to a device and method for providing information related to terminal-based TA (timing advance) measurement to a current serving DU of a terminal in a wireless communication system.

[0009] The present disclosure relates to a device and method for skipping or omitting an early TA acquisition procedure for at least one candidate cell prepared for LTM in a wireless communication system.

[0010] The present disclosure relates to a device and method for indicating to a serving DU in a wireless communication system at least one candidate cell to which terminal-based TA measurement will be applied.

[0011] The present disclosure relates to a device and method for obtaining valid TA information for at least one candidate cell from a previous serving DU when switching LTM cells in a wireless communication system.

[0012] The present disclosure relates to a device and method for using TA information of at least one candidate cell acquired through an early TA acquisition procedure triggered by a previous serving DU in a wireless communication system in a new serving DU.

[0013] The present disclosure relates to a device and method for transmitting TA information of at least one valid candidate cell of a serving DU to a new serving DU when LTM cell switching occurs between DUs within the same CU in a wireless communication system.

[0014] The present disclosure relates to a device and method for requesting valid TA information from a previous serving DU when an LTM cell switch between DUs within the same CU is detected in a wireless communication system.

[0015] The technical objectives to be achieved in the present disclosure are not limited to those mentioned above, and other technical tasks not mentioned can be considered by a person having ordinary skill in the technical field to which the technical configuration of the present disclosure is applied from the embodiments of the present disclosure described below.

[0016] As an example of the present disclosure, the method includes a step in which a control node of a base station determines to initiate LTM (L1L2 triggered mobility) setup for a terminal, and a step in which the control node of the base station transmits a first message related to terminal-based TA (timing advance) measurement to a first distributed node among distributed nodes of the base station, wherein the first message may include information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

[0017] As an example of the present disclosure, the method includes the steps of: receiving, by a first distributed node of a base station, a first message related to terminal-based timing advance (TA) measurement from a control node of the base station; and controlling, by the first distributed node of the base station, to skip an early TA acquisition procedure for at least one candidate cell among a plurality of candidate cells for LTM (L1L2 triggered mobility) based on the first message, wherein the first message may include information indicating the at least one candidate cell to which the terminal-based TA measurement is to be applied.

[0018] As an example of the present disclosure, a device includes a transceiver and a processor connected to the transceiver, wherein the processor controls a control node of a base station to determine initiation of LTM (L1L2 triggered mobility) setup for a terminal, and the control node of the base station to transmit a first message related to terminal-based TA (timing advance) measurement to a first distributed node among distributed nodes of the base station, wherein the first message may include information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

[0019] As an example of the present disclosure, a device includes a transceiver and a processor connected to the transceiver, wherein the processor is configured to cause a first distributed node of a base station to receive a first message related to terminal-based timing advance (TA) measurement from a control node of the base station, and to control the first distributed node of the base station to skip an early TA acquisition procedure for at least one candidate cell among a plurality of candidate cells for LTM (L1L2 triggered mobility) based on the first message, wherein the first message may include information indicating the at least one candidate cell to which the terminal-based TA measurement is to be applied.

[0020] As an example of the present disclosure, a communication device includes at least one processor, and at least one memory connected to the at least one processor and storing instructions that, when executed by the at least one processor, cause a terminal to perform operations, the operations including: a step of a control node of a base station determining initiation of LTM (L1L2 triggered mobility) setup for a terminal; and a step of the control node of the base station transmitting a first message related to terminal-based TA (timing advance) measurement to a first distributed node among distributed nodes of the base station, wherein the first message may include information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

[0021] As an example of the present disclosure, a non-transitory computer-readable medium storing at least one program instruction, wherein the at least one program instruction, when executed by at least one processor, causes a terminal to perform operations, the operations including: a step of a control node of a base station determining initiation of LTM (L1L2 triggered mobility) setup for a terminal; and a step of the control node of the base station transmitting a first message related to terminal-based TA (timing advance) measurement to a first distributed node among distributed nodes of the base station, wherein the first message may include information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

[0022] The above-described aspects of the present disclosure are only some of the preferred embodiments of the present disclosure, and various embodiments reflecting the technical features of the present disclosure can be derived and understood by a person having ordinary skill in the art based on the detailed description of the present disclosure to be described below.

[0023] The following effects may be achieved by embodiments based on the present disclosure.

[0024] The present disclosure can optimize an early uplink synchronization procedure during LTM (L1L2 triggered mobility) in a wireless communication system.

[0025] The effects that can be obtained from the embodiments of the present disclosure are not limited to the effects mentioned above, and other effects that are not mentioned can be clearly derived and understood by those skilled in the art to which the technical configuration of the present disclosure is applied, from the description of the embodiments of the present disclosure below. In other words, unintended effects that result from implementing the configuration described in the present disclosure can also be derived by those skilled in the art from the embodiments of the present disclosure.

[0026] The accompanying drawings are intended to aid in understanding the present disclosure and, together with detailed descriptions, may provide embodiments of the present disclosure. However, the technical features of the present disclosure are not limited to specific drawings, and the features disclosed in each drawing may be combined with each other to form new embodiments. Reference numerals in each drawing may indicate structural elements.

[0027] Figure 1 illustrates an example of a communication system applicable to the present disclosure.

[0028] FIG. 2 illustrates an example of a user equipment (UE) applicable to the present disclosure.

[0029] FIG. 3 illustrates an example of functional separation of a next generation radio access network (NG-RAN) and a 5th generation core (5GC) applicable to the present disclosure.

[0030] FIG. 4 illustrates an example of a general architecture of a 5G (5th generation) system applicable to the present disclosure.

[0031] Figures 5a and 5b are examples of LTM procedures between DUs applicable to the present disclosure.

[0032] FIGS. 6A and 6B are examples of a procedure for optimizing an early uplink synchronization procedure during LTM within a CU according to an embodiment of the present disclosure.

[0033] FIG. 7 illustrates an example of a procedure for transmitting TA measurement related information according to an embodiment of the present disclosure.

[0034] FIG. 8 illustrates an example of a procedure for receiving TA measurement related information according to an embodiment of the present disclosure.

[0035] The following embodiments combine components and features of the present disclosure in a predetermined form. Each component or feature may be considered optional unless explicitly stated otherwise. Each component or feature may be implemented without being combined with other components or features. Furthermore, some components and / or features may be combined to form embodiments of the present disclosure. The order of operations described in the embodiments of the present disclosure may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment.

[0036] In the description of the drawings, procedures or steps that may obscure the gist of the present disclosure are not described, and procedures or steps that can be understood by a person skilled in the art are also not described.

[0037] Throughout the specification, when a part is said to "comprising" or "including" a component, this does not mean that other components may be included, but rather that other components may be excluded, unless otherwise specifically stated. In addition, terms such as "...part," "...unit," and "module" described in the specification mean a unit that processes at least one function or operation, which may be implemented by hardware, software, or a combination of hardware and software. In addition, the words "a" or "an," "one," "the," and similar related words may be used in the context of describing the present disclosure (especially in the context of the claims below) to include both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

[0038] Embodiments of the present disclosure described herein focus on the data transmission and reception relationship between a base station and a mobile station. Here, the base station is understood as a terminal node of a network that directly communicates with the mobile station. Certain operations described herein as being performed by the base station may, in some cases, be performed by an upper node of the base station.

[0039] That is, in a network consisting of multiple network nodes including a base station, various operations performed for communication with a mobile station may be performed by the base station or other network nodes other than the base station. In this case, the term 'base station' may be replaced by terms such as fixed station, Node B, eNB (eNode B), gNB (gNode B), ng-eNB, advanced base station (ABS), or access point.

[0040] Additionally, in embodiments of the present disclosure, the term terminal may be replaced with terms such as user equipment (UE), mobile station (MS), subscriber station (SS), mobile subscriber station (MSS), mobile terminal, or advanced mobile station (AMS).

[0041] Additionally, a transmitter refers to a fixed and / or mobile node that provides data or voice services, and a receiver refers to a fixed and / or mobile node that receives data or voice services. Therefore, for uplink, a mobile station can be the transmitter, and a base station can be the receiver. Similarly, for downlink, a mobile station can be the receiver, and a base station can be the transmitter.

[0042] Embodiments of the present disclosure are wireless access systems such as IEEE 802.xx system, 3rd Generation Partnership Project (3GPP) system, 3GPP Long Term Evolution (LTE) system, 3GPP 5G (5 th generation) NR (New Radio) system and 3GPP2 system, and in particular, embodiments of the present disclosure may be supported by 3GPP TS (technical specification) 38.211, 3GPP TS 38.212, 3GPP TS 38.213, 3GPP TS 38.321 and 3GPP TS 38.331 documents.

[0043] Furthermore, the embodiments of the present disclosure can be applied to other wireless access systems and are not limited to the aforementioned systems. For example, they can also be applied to systems implemented after the 3GPP 5G NR system, and are not limited to a specific system.

[0044] That is, obvious steps or parts not described in the embodiments of the present disclosure can be explained by referring to the above documents. In addition, all terms disclosed in this document can be explained by the above standard documents.

[0045] Hereinafter, preferred embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. The detailed description set forth below, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the present disclosure and is not intended to represent the only embodiments in which the technical configurations of the present disclosure may be implemented.

[0046] Additionally, specific terms used in the embodiments of the present disclosure are provided to aid in understanding the present disclosure, and the use of such specific terms may be changed to other forms without departing from the technical spirit of the present disclosure.

[0047] The following technology can be applied to various wireless access systems such as CDMA (code division multiple access), FDMA (frequency division multiple access), TDMA (time division multiple access), OFDMA (orthogonal frequency division multiple access), and SC-FDMA (single carrier frequency division multiple access).

[0048] For clarity, the following description is based on a 3GPP communication system (e.g., LTE, NR, etc.), but the technical spirit of the present invention is not limited thereto. LTE may refer to technology after 3GPP TS 36.xxx Release 8. Specifically, LTE technology after 3GPP TS 36.xxx Release 10 may be referred to as LTE-A, and LTE technology after 3GPP TS 36.xxx Release 13 may be referred to as LTE-A pro. 3GPP NR may refer to technology after TS 38.xxx Release 15. 3GPP 6G may refer to technology after TS Release 17 and / or Release 18. "xxx" refers to a standard document detail number. LTE / NR / 6G may be collectively referred to as a 3GPP system.

[0049] For background information, terms, abbreviations, etc. used in this disclosure, reference may be made to standard documents published prior to the present invention. For example, reference may be made to the 36.xxx and 38.xxx standard documents.

[0050] For terms, abbreviations, and other background technologies that may be used in this document, please refer to the following standard documents published prior to this document. In particular, terms, abbreviations, and other background technologies related to LTE / EPS (Evolved Packet System) can refer to the 36.xxx series, 23.xxx series, and 24.xxx series, and terms, abbreviations, and other background technologies related to NR (new radio) / 5GS (5G system) can refer to the 38.xxx series, 23.xxx series, and 24.xxx series.

[0051] Hereinafter, this specification is described based on the terms defined above.

[0052] The three key requirement areas for 5G include (1) Enhanced Mobile Broadband (eMBB), (2) Massive Machine Type Communication (mMTC), and (3) Ultra-reliable and Low Latency Communications (URLLC).

[0053] Some use cases may require optimization across multiple domains, while others may focus on just one Key Performance Indicator (KPI). 5G supports these diverse use cases in a flexible and reliable manner.

[0054]

[0055] Communication system applicable to the present disclosure

[0056] Although not limited thereto, the various descriptions, functions, procedures, proposals, methods and / or operational flowcharts of the present disclosure disclosed in this document may be applied to various fields requiring wireless communication / connectivity (e.g., 5G) between devices.

[0057] Hereinafter, more specific examples will be provided with reference to the drawings. In the drawings / descriptions below, the same drawing reference numerals may represent identical or corresponding hardware blocks, software blocks, or functional blocks, unless otherwise described.

[0058] Figure 1 illustrates an example of a communication system applied to the present disclosure.

[0059] Referring to FIG. 1, a communication system (100) applied to the present disclosure includes a wireless device, a base station, and a network. Here, the wireless device refers to a device that performs communication using a wireless access technology (e.g., 5G NR, LTE) and may be referred to as a communication / wireless / 5G device. Although not limited thereto, the wireless device may include a robot (100a), a vehicle (100b-1, 100b-2), an XR (extended reality) device (100c), a hand-held device (100d), a home appliance (100e), an IoT (Internet of Things) device (100f), and an AI (artificial intelligence) device / server (100g). For example, the vehicle may include a vehicle equipped with a wireless communication function, an autonomous vehicle, a vehicle capable of performing vehicle-to-vehicle communication, etc. Here, the vehicles (100b-1, 100b-2) may include unmanned aerial vehicles (UAVs) (e.g., drones). The XR devices (100c) include augmented reality (AR) / virtual reality (VR) / mixed reality (MR) devices, and may be implemented in the form of head-mounted devices (HMDs), head-up displays (HUDs) installed in vehicles, televisions, smartphones, computers, wearable devices, home appliances, digital signage, vehicles, robots, etc. The portable devices (100d) may include smartphones, smart pads, wearable devices (e.g., smartwatches, smart glasses), computers (e.g., laptops, etc.), etc. The home appliances (100e) may include TVs, refrigerators, washing machines, etc. The IoT devices (100f) may include sensors, smart meters, etc. For example, the base station (120) and the network (130) may also be implemented as wireless devices, and a specific wireless device (120a) may act as a base station / network node to other wireless devices.

[0060] Wireless devices (100a to 100f) can be connected to a network (130) via a base station (120). AI technology can be applied to the wireless devices (100a to 100f), and the wireless devices (100a to 100f) can be connected to an AI server (100g) via a network (130). The network (130) can be configured using a 3G network, a 4G (e.g., LTE) network, a 5G (e.g., NR) network, etc. The wireless devices (100a to 100f) can communicate with each other via the base station (120) / network (130), but can also communicate directly (e.g., sidelink communication) without going through the base station (120) / network (130). For example, vehicles (100b-1, 100b-2) can communicate directly (e.g., V2V (vehicle to vehicle) / V2X (vehicle to everything) communication). In addition, IoT devices (100f) (e.g., sensors) can communicate directly with other IoT devices (e.g., sensors) or other wireless devices (100a to 100f).

[0061] Wireless communication / connection (150a, 150b, 150c) can be established between wireless devices (100a to 100f) / base stations (120), and base stations (120) / base stations (120). Here, the wireless communication / connection can be established through various wireless access technologies (e.g., 5G NR) such as uplink / downlink communication (150a), sidelink communication (150b) (or D2D communication), and base station-to-base station communication (150c) (e.g., relay, IAB (integrated access backhaul)). Through the wireless communication / connection (150a, 150b, 150c), the wireless device and base station / wireless device, and base stations and base stations can transmit / receive wireless signals to / from each other. For example, the wireless communication / connection (150a, 150b, 150c) can transmit / receive signals through various physical channels. To this end, based on various proposals of the present disclosure, at least some of various configuration information setting processes for transmitting / receiving wireless signals, various signal processing processes (e.g., channel encoding / decoding, modulation / demodulation, resource mapping / demapping, etc.), resource allocation processes, etc. may be performed.

[0062] Figure 2 illustrates an example of a UE applicable to the present disclosure.

[0063] Referring to FIG. 2, the UE (200) may include a processor (202), memory (204), a transceiver (206), one or more antennas (208), a power management module (241), a battery (242), a display (243), a keypad (244), a SIM (Subscriber Identification Module) card (245), a speaker (246), and a microphone (247).

[0064] The processor (202) may be configured to implement the descriptions, functions, procedures, proposals, methods, and / or flowcharts disclosed herein. The processor (202) may be configured to control one or more other components of the UE (200) to implement the descriptions, functions, procedures, proposals, methods, and / or flowcharts disclosed herein. A layer of a radio interface protocol may be implemented in the processor (202). The processor (202) may include an ASIC, other chipset, logic circuit, and / or data processing device. The processor (202) may be an application processor. The processor (202) may include at least one of a DSP, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), and a modem (modulator and demodulator).

[0065] Memory (204) is operatively coupled to the processor (202) and can store various information for operating the processor (202). Memory (204) may include ROM, RAM, flash memory, memory cards, storage media, and / or other storage devices. When the implementation is implemented in software, the techniques described herein may be implemented using modules (e.g., procedures, functions, etc.) that perform the descriptions, functions, procedures, suggestions, methods, and / or operational flowcharts disclosed herein. The modules may be stored in memory (204) and executed by the processor (202). Memory (204) may be implemented within the processor (202) or external to the processor (202), in which case it may be communicatively coupled to the processor (202) via various methods known in the art.

[0066] A transceiver (206) is operably coupled to the processor (202) and is capable of transmitting and / or receiving wireless signals. The transceiver (206) may include a transmitter and a receiver. The transceiver (206) may include baseband circuitry for processing radio frequency signals. The transceiver (206) may control one or more antennas (208) to transmit and / or receive wireless signals.

[0067] The power management module (241) can manage the power of the processor (202) and / or the transceiver (206). The battery (242) can supply power to the power management module (241).

[0068] The display (243) can output the results processed by the processor (202). The keypad (244) can receive input to be used by the processor (202). The keypad (244) can be displayed on the display (243).

[0069] A SIM card (245) is an integrated circuit that securely stores an International Mobile Subscriber Identity (IMSI) and associated keys, and can be used to identify and authenticate subscribers in mobile devices such as mobile phones and computers. Additionally, many SIM cards can store contact information.

[0070] The speaker (246) can output sound-related results processed by the processor (202). The microphone (247) can receive sound-related input to be used by the processor (202).

[0071] In implementations of this specification, a UE may operate as a transmitter in the uplink and as a receiver in the downlink. In implementations of this specification, a base station may operate as a receiver in the uplink and as a transmitter in the downlink. In this specification, a base station may be referred to as a Node B (Node B), an eNode B (eNB), or a gNB, and may not be limited to a specific form.

[0072] In addition, for example, the UE may be implemented in various forms depending on the use case / service. The UE may be composed of various components, devices / parts, and / or modules. For example, each UE may include a communication device, a control device, a memory device, and additional components. The communication device may include a communication circuit and a transceiver. For example, the communication circuit may include one or more processors and / or one or more memories. For example, the transceiver may include one or more transceivers and / or one or more antennas. The control device is electrically connected to the communication device, the memory device, and the additional components, and may control the overall operation of each UE. For example, the control device may control the electrical / mechanical operation of each UE based on a program / code / command / information stored in the memory device. The control device may transmit information stored in the memory device to an external device (e.g., another communication device) via the communication device via a wireless / wired interface, or may store information received from an external device (e.g., another communication device) via the communication device via a wireless / wired interface in the memory device.

[0073] Additional components may be configured in various ways depending on the type of UE. For example, the additional components may include at least one of a power unit / battery, an input / output (I / O) device (e.g., an audio I / O port, a video I / O port), a driving device, and a computing device. In addition, the UE is not limited thereto, and may be implemented in the form of a robot (100a in FIG. 1), a vehicle (100b-1 and 100b-2 in FIG. 1), an XR device (100c in FIG. 1), a portable device (100d in FIG. 1), a home appliance (100e in FIG. 1), an IoT device (100f in FIG. 1), a digital broadcasting terminal, a hologram device, a public safety device, an MTC device, a medical device, a fintech device (or a financial device), a security device, a climate / environmental device, an AI server / device (100g in FIG. 1), a base station (120 in FIG. 1), or a network node. UE can be used in mobile or fixed locations depending on the use case / service.

[0074] The various components, devices / parts, and / or modules of the UE may all be connected to each other via a wired interface, or at least some of them may be connected wirelessly via a communication device. In addition, each component, device / part, and / or module of the UE may further include one or more elements. For example, the control device may be configured by a set of one or more processors. For example, the control device may be configured by a set of a communication control processor, an application processor (AP), an electronic control unit (ECU), a graphics processing unit, and a memory control processor. As another example, the memory device may be configured by a random access memory (RAM), a dynamic random access memory (DRAM), a read-only memory (ROM), a flash memory, a volatile memory, a non-volatile memory, and / or a combination thereof.

[0075] 5G system architecture applicable to the present disclosure

[0076] The 5G system is an advanced technology from the 4th generation LTE mobile communication technology. It supports new radio access technology (RAT: Radio Access Technology), extended LTE (eLTE) as an extended technology of LTE (Long Term Evolution), and non-3GPP (e.g., WLAN) access through the evolution or clean-state structure of the existing mobile communication network structure.

[0077] 5G systems are defined as service-based, and the interactions between network functions (NFs) within the architecture for 5G systems can be expressed in two ways as follows.

[0078] - Reference point representation: Represents the interaction between NF services within NFs described by a point-to-point reference point (e.g., N11) between two NFs (e.g., AMF and SMF).

[0079] Service-based representation: Network functions (e.g., AMF) within the control plane (CP) allow other authorized network functions to access their services. This representation also includes point-to-point reference points, if necessary.

[0080] 5GC (5G Core) can include various components, some of which include access and mobility management function (AMF), session management function (SMF), policy control function (PCF), user plane function (UPF), application function (AF), unified data management (UDM), and non-3GPP interworking function (N3IWF).

[0081] The UE connects to the data network via the UPF via the next-generation radio access network (NG-RAN) that includes the gNB. The UE can receive data services via untrusted non-3GPP access points, such as wireless local area networks (WLANs). To connect non-3GPP access points to the core network, an N3IWF may be deployed.

[0082] The N3IWF manages interworking between non-3GPP access and 5G systems. When a UE is connected to a non-3GPP access (e.g., WiFi, also known as IEEE 802.11), it can connect to a 5G system via the N3IWF. The N3IWF performs control signaling with the AMF and connects to the UPF via the N3 interface for data transmission.

[0083] AMF can manage access and mobility in 5G systems. It can also manage non-access stratum (NAS) security. It can also handle mobility in idle states.

[0084] The UPF functions as a gateway for transmitting and receiving user data. A UPF node can perform all or part of the user plane functions of a 4G mobile communications S-GW (serving gateway) and P-GW (packet data network gateway).

[0085] The UPF acts as a boundary point between the next generation RAN (NG-RAN) and the core network, and is an element that maintains the data path between the gNB and the SMF. In addition, the UPF acts as a mobility anchor point when the UE moves across the area served by the gNB. The UPF can perform the function of handling PDUs. For mobility within the NG-RAN (e.g., NG-RAN defined after 3GPP Release-15), the UPF can route packets. In addition, the UPF can also act as an anchor point for mobility with other 3GPP networks (e.g., RAN defined before 3GPP Release-15), such as UTRAN (UMTS (universal mobile telecommunications system) terrestrial radio access network), E-UTRAN (evolved-UTRAN), or GERAN (GSM (global system for mobile communication) / EDGE (enhanced data rates for global evolution) radio access network). A UPF may correspond to the termination point of a data interface toward a data network.

[0086] The PCF is a node that controls the operator's policies. The AF is a server that provides various services to UEs. The UDM is a server that manages subscriber information, similar to the HSS (home subscriber server) of 4G mobile communications. The UDM (460) stores and manages subscriber information in a unified data repository (UDR).

[0087] The SMF can perform the function of assigning an IP (Internet protocol) address to the UE. In addition, the SMF can control the PDU (protocol data unit) session.

[0088] For convenience of explanation below, the drawing symbols for AMF, SMF, PCF, UPF, AF, UDM, N3IWF, gNB, or UE may be omitted, and operation may be performed by referring to the matters described in standard documents published prior to this document.

[0089] Figure 3 illustrates an example of functional separation of NG-RAN and 5GC (5th generation core) applicable to the present disclosure.

[0090] Referring to Figure 3, the UE connects to a data network (DN) via a next-generation RAN. The control plane function (CPF) node performs all or part of the functions of the mobility management entity (MME) of 4G mobile communications, and all or part of the control plane functions of the serving gateway (S-GW) and the PDN gateway (P-GW). The CPF node includes the AMF and the SMF.

[0091] The UPF node functions as a gateway through which user data is transmitted and received.

[0092] The authentication server function (AUSF) authenticates and manages UEs. The Network Slice Selection Function (NSSF) is a node for network slicing, as described below.

[0093] The network exposure function (NEF) provides a mechanism to securely expose the services and functions of the 5G core.

[0094]

[0095] The reference points shown in Fig. 3 are as follows. N1 represents a reference point between the UE and the AMF. N2 represents a reference point between the (R)AN and the AMF. N3 represents a reference point between the (R)AN and the UPF. N4 represents a reference point between the SMF and the UPF. N5 represents a reference point between the PCF and the AF. N6 represents a reference point between the UPF and the DN. N7 represents a reference point between the SMF and the PCF. N8 represents a reference point between the UDM and the AMF. N9 represents a reference point between the UPFs. N10 represents a reference point between the UDM and the SMF. N11 represents a reference point between the AMF and the SMF. N12 represents a reference point between the AMF and the AUSF. N13 represents a reference point between the UDM and the AUSF. N14 represents a reference point between the AMFs. N15 represents a reference point between a PCF and an AMF in a non-roaming scenario, and a reference point between an AMF and a PCF of a visited network in a roaming scenario. N16 represents a reference point between SMFs. N22 represents a reference point between an AMF and an NSSF. N30 represents a reference point between a PCF and an NEF. N33 may represent a reference point between an AF and an NEF, and the entities and interfaces described above may be configured with reference to those described in standard documents published before this document. N58 represents a reference point between an AMF and an NSSAAF. N59 represents a reference point between a UDM and an NSSAAF. N80 represents a reference point between an AMF and an NSACF. N81 represents a reference point between an SMF and an NSACF.

[0096] The radio interface protocol is based on the 3GPP radio access network standard. Horizontally, the radio interface protocol consists of the physical layer, data link layer, and network layer. Vertically, it is divided into the user plane for data information transmission and the control plane for control signaling.

[0097] Protocol layers can be divided into L1 (layer-1), L2 (layer-2), and L3 (layer-3) based on the three lower layers of the open systems interconnection (OSI) standard model, which is widely known in communication systems.

[0098] Below, the present disclosure describes each layer of the wireless protocol. Figure 4 illustrates an example of a general architecture of a 5G (5th generation) system applicable to the present disclosure.

[0099] Referring to FIG. 4, the AS (access stratum) layer may include a physical (PHY) layer, a medium access control layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a radio resource control (RRC) layer, and operations based on each layer may be performed by referring to matters described in standard documents published prior to this document.

[0100]

[0101] Specific embodiments of the present disclosure

[0102] The present disclosure relates to a device and method for supporting LTM handover in a wireless communication system. Specifically, the present disclosure relates to a device and method for optimizing an early UL synchronization procedure during LTM (L1L2 triggered mobility) within a centralized unit (CU) in a wireless communication system.

[0103]

[0104] In the following description, a CU is a logical node that hosts RRC and PDCP protocols of an en-gNB, or RRC, SDAP, and PDCP protocols of a gNB, which control the operation of at least one DU (distributed unit), and a DU is a logical node that hosts RLC, MAC, and PHY layers of an en-gNB or a gNB. The DU is partially controlled by a CU connected to it via an F1 interface, and supports at least one cell.

[0105] LTM is a cell switching procedure for PCell (or PSCell) triggered by the network via MAC CE based on L1 measurements. PCell is the primary cell of the master cell group, and PSCell is the primary cell of the secondary cell group.

[0106] Timing advance (TA) is the offset between the start of a downlink subframe received by the UE and the start of a transmitted uplink subframe, and time alignment timer (TAT) is a timer that controls the period for which a MAC entity considers serving cells belonging to an associated timing alignment group (TAG) to be aligned with respect to uplink time. Time alignment error (TAE) is the largest timing difference between two different NR signals.

[0107]

[0108] According to the Network Mobility Improvement Work Item (WI) of Rel-18, the following was documented to support LTM to reduce latency, overhead, and interruption time during serving cell changes.

[0109] ---------------------------------------------------------------------

[0110] 3. Justification

[0111] When a UE moves from one cell's coverage area to another, a serving cell change must occur. Currently, serving cell changes are triggered by L3 measurements, additional release of the secondary cell (SCell), synchronization for changing the primary cell (PCell) and primary secondary cell (PSCell), and RRC signaling trigger reset. In such cases, L2 (and L1) resets must be completed, resulting in longer delays, higher overhead, and longer downtime than beam switch mobility. The goal of improving L1 / L2 mobility is to enable serving cell changes via L1 / L2 signaling, thereby reducing delays, overhead, and downtime.

[0112] In Rel-17 conditional PSCell change (CPC) and / or conditional PSCell addition (CPA), a CPC / CPA-configured UE must release its CPC / CPA configuration upon completing random access to the target PSCell. Therefore, the UE does not have the opportunity to perform subsequent CPC / CPA operations without prior CPC / CPA reconfiguration and re-initialization in the network. This increases the delay and signaling overhead for cell changes, especially when SCGs are frequently changed during FR2 operation. Therefore, MR-DC, which selectively activates cell groups, aims to enable subsequent CPC / CPA operations after an SCG change without requiring the network to reconfigure and re-initialize CPC / CPA preparation. This reduces signaling overhead and downtime for SCG changes.

[0113] Currently, CHO and MR-DC cannot be configured simultaneously. This limits the usefulness of CHO and MR-DC when MR-DC is configured. If this has not been completed in Rel-17, a mechanism for configuring CHO and MR-DC simultaneously needs to be defined in Rel-18. However, this alone may not be sufficient to optimize MR-DC mobility, as the radio link quality of the conditionally configured PSCell may not be sufficiently good or the conditionally configured PSCell may not be the optimal candidate PSCell when the UE accesses the target PCell. This may impact UE throughput. To mitigate the impact on UE throughput, Rel-18 CHO+MR-DC may consider a CHO that includes a target MCG and multiple candidate SCGs for CPC / CPA.

[0114] 4. Objective

[0115] 4.1 SI or core part WI or testing part WI purpose

[0116] The detailed objectives of the research item are as follows:

[0117] 1. Define the mechanism and procedure of L1 / L2-based inter-cell mobility to reduce mobility delay:

[0118] - Configuration and maintenance of multiple candidate cells to enable rapid application of settings to candidate cells [RAN2, RAN3]

[0119] o Dynamic switching mechanism between candidate serving cells (including SpCell and SCell) for potentially applicable scenarios based on L1 / L2 signaling [RAN2, RAN1]

[0120] o L1 improvements for inter-cell beam management, including L1 measurements and reporting, and beam indications [RAN1, RAN2]

[0121] - Note 1: Early RAN2 engagement is needed, including the possibility of further clarifying the interactions between this bullet and previous bullets.

[0122] - Note 2: Only SSB-based L1 measurements are supported in this release.

[0123] o Timing advance management [RAN1, RAN2]

[0124] o CU-DU interface signaling to support L1 / L2 mobility, if required [RAN3]

[0125] Note 3: If there are specific improvements to FR2, this is not ruled out.

[0126] Note 4: L1 / L2 based inter-cell mobility procedures are applicable to the following scenarios:

[0127] - In standalone mode, CA, and NR-DC cases where there is a change in serving cell within a CG, MCG is given priority.

[0128] - For intra-DU cases and intra-CU inter-DU cases (applicable to standalone mode and CA; no new RAN interfaces are expected)

[0129] - Both within and between frequencies

[0130] - Both FR1 and FR2

[0131] - Source and target cells may or may not be synchronized.

[0132] ---------------------------------------------------------------------

[0133] To achieve rapid serving cell switching, early DL / UL synchronization before cell switching and handover based on L1 measurement reports triggered by MAC CE have been agreed upon for LTM. This work is in progress in Rel-18 for intra-CU LTM. Intra-CU LTM may include inter-DU LTM or intra-DU LTM.

[0134] Figures 5a and 5b illustrate examples of inter-DU LTM procedures applicable to the present disclosure. The procedures of Figures 5a and 5b may be utilized when a UE moves from one DU within a CU of a gNB to another DU within a CU of the same gNB during NR operation for LTM.

[0135] Referring to FIGS. 5A and 5B, in step 1, L3 measurement control and reporting are performed. The UE (510) transmits an L3 measurement report message including measurement results for a neighboring cell to the source gNB-DU (520-1). The source gNB-DU (520-1) transmits the received L3 measurement report message to the gNB-CU (530). The source gNB-DU (520-1) may transmit a UL RRC MESSAGE TRANSFER message including the L3 measurement report message to the source gNB-DU (520-1).

[0136] In step 2, the gNB-CU (530) determines the LTM configuration. The gNB-CU (530) determines to initiate the LTM configuration for the UE (510) based on the L3 measurement report message.

[0137] In step 3, the gNB-CU (530) transmits a UE context setup request (UE CONTEXT SETUP REQUEST) message to the candidate gNB-DU (520-2). The UE context setup request message may include one candidate target cell ID. The gNB-CU (530) uses the UE context setup request message to indicate the ID of the source gNB-DU (520-1) to the candidate gNB-DU (520-2) and request PRACH resources. The gNB-CU (530) may request the candidate gNB-DU (520-2) to provide information related to lower layer configuration in order to generate reference configuration information to be used for LTM.

[0138] In step 4, the candidate gNB-DU (520-2) transmits a UE context setup response (UE CONTEXT SETUP RESPONSE) message to the gNB-CU (530). If the candidate gNB-DU (520-2) accepts the LTM setup request for the candidate target cell, the candidate gNB-DU (520-2) may respond to the gNB-CU (530) with a UE context setup response message including information related to the generated lower layer RRC setup and information related to the RS (reference signal) setup for the accepted candidate target cell. For example, the information related to the RRC setup may include at least one of information related to the TCI (transmission configuration indication) state setup or information related to the RACH (random access channel) setup.

[0139] If there is at least one candidate target cell in the candidate gNB-DU (520-2), the UE context setup of steps 3 and 4 may be performed individually for each candidate target cell.

[0140] In step 5, the gNB-CU (530) transmits a UE context modification request message to the source gNB-DU (520-1). The gNB-CU (530) may transmit the UE context modification request message to the source gNB-DU (520-1) including at least one of information related to collected RS configuration for at least one accepted candidate target cell of other gNB-DUs (e.g., candidate gNB-DU (520-2)), information related to TCI state configuration, or information related to RACH configuration.

[0141] In step 6, the source gNB-DU (520-1) transmits a UE context modification response message to the gNB-CU (530). The UE context modification response message may include at least one of information related to RS configuration of the source cell, candidate cells prepared for LTM, or information related to generated CSI reporting configuration.

[0142] In step 7, the gNB-CU (530) transmits a UE context modification request message to the candidate gNB-DU (520-2). The UE context modification request message may include at least one of a cell ID of at least one prepared candidate cell, or information related to an associated RS configuration for each candidate cell in at least one other candidate gNB-DU. The gNB-CU (530) may provide lower layer configuration information among the reference configuration information to the candidate gNB-DU (520-2). Here, the candidate cell may be the same cell as the source cell.

[0143] In step 8, the candidate gNB-DU (520-2) responds to the gNB-CU (530) using a UE context modification response message. The UE context modification response message includes updated lower layer configuration information including information related to the generated CSI reporting configuration.

[0144] In step 9, the gNB-CU (530) transmits a DL RRC MESSAGE TRANSFER message to the source gNB-DU (520-1). The DL RRC MESSAGE TRANSFER message may include a generated RRCReconfiguration message including the LTM configuration.

[0145] In step 10, the source gNB-DU (520-1) forwards the received RRCReconfiguration message to the UE (510), and in step 11, the UE (510) transmits an RRCReconfigurationComplete message to the source gNB-DU (520-1). In step 12, the source gNB-DU (520-1) transmits a UL RRC MESSAGE TRANSFER message including the RRCReconfigurationComplete message to the gNB-CU (530).

[0146] In step 13, early synchronization is performed. The early synchronization procedure may include an early TA acquisition procedure. The early TA acquisition procedure may be performed as defined in TS 38.300.

[0147] In step 14, the candidate gNB-DU (520-2) transmits a notification message regarding TA information to the source gNB-DU (520-1) via the gNB-CU (530). The notification message regarding TA information may include at least one of the TA, associated CFRA resource information, the candidate cell ID, or the source gNB-DU ID.

[0148] In step 15, the UE (510) transmits a report message regarding the lower layer measurement results to the source gNB-DU (520-1). In step 16, the source gNB-DU (520-1) determines an LTM cell switch. That is, the source gNB-DU (520-1) determines an LTM execution for cell switch to a candidate target cell.

[0149] In step 17, the source gNB-DU (520-1) transmits an LTM command to the UE (510).

[0150] In step 18, the source gNB-DU (520-1) transmits a notification message for an LTM cell change to the gNB-CU (530). The notification message for an LTM cell change may include a message indicating that an LTM command to the UE (510) has been initiated. For example, the notification message for an LTM cell change may include at least one of a target cell ID or a TCI state ID. The TCI state ID may indicate selected beam information.

[0151] In step 19, the gNB-CU (530) transmits a notification message for an LTM cell change including a target cell ID and a TCI state ID to the candidate gNB-DU (520-2).

[0152] In step 20, the candidate gNB-DU (520-2) detects access of the UE (510) as a target gNB-DU, and in step 21, transmits an access success message to the gNB-CU (530). The access success message may include the cell ID of the target cell.

[0153] In step 22, the gNB-CU (530) transmits a UE context release command to the source gNB-DU (520-1). The UE context release command may request resource release of a prepared cell.

[0154] In step 23, the source gNB-DU (520-1) transmits a UE context release complete message to the gNB-CU (530). The source gNB-DU (520-1) can release resources of the prepared cell and respond to the gNB-CU (530) using the UE context release complete message.

[0155] As described with reference to FIG. 5, uplink TA values ​​for some candidate cells are acquired through an early TA acquisition procedure. However, according to the present discussion, the uplink TA values ​​for some candidate cells acquired as described above can only be used by the current serving DU that triggered the procedure, and cannot be reused by other serving DUs in subsequent LTM operations. For example, if the source DU triggers a cell switch for one of the candidate cells of the candidate DU, as in step 17 of FIG. 5, the cell successfully accessed by the UE becomes the new serving cell, as in step 20 of FIG. 5. At this time, the UE undergoes another handover to other candidate cells, including the previous serving cell, for subsequent LTM operations.

[0156] For a fast serving cell change, early uplink synchronization for candidate cells may be performed again from the current serving cell. However, TA acquisition procedures for some of the candidate cells may have already been performed, and uplink TA values ​​for some of the candidate cells may have already been provided in a previous serving DU (e.g., the source DU in FIG. 5 ). Of course, these previously acquired TA values ​​may no longer be valid due to UE mobility. However, depending on (1) network deployments, (2) how quickly the UE is affected by the serving cell change, and (3) the TAT of the candidate cells configured for the UE, previously calculated uplink TA values ​​for some candidate cells may still be valid. Here, the TAT value of the candidate cells may be a maximum of 10.240 seconds, and may be set to infinity according to TS 38.331. If previously computed uplink TA values ​​for some candidate cells are still valid, early TA acquisition procedures to obtain those TA values ​​do not need to be triggered again in the new serving DU.

[0157] Additionally, the UE may be configured by the network to perform UE-based TA measurements from its current serving cell toward a candidate cell. At this time, the UE measures or derives TA for the candidate cell based on the Rx timing difference between the current serving cell and the candidate cell, and the current TA value (e.g., the TA value for the current serving cell). In this way, when the UE is configured to perform UE-based TA measurements from its current serving cell toward a candidate cell, when the serving cell of the UE switches from the current serving cell to the candidate cell, it is agreed to apply the pre-measured TA value for the candidate cell and perform LTM without RACH (RACH-less LTM). In this case, the early TA acquisition procedure for the candidate cells does not need to be triggered in the serving DU for RACH-less LTM. However, during the current LTM preparation phase, the serving DU is unaware of whether the UE is configured to perform UE-based TA measurements. Of course, during the LTM preparation phase, the DU may be requested by the CU to prepare lower layer configurations for UE-based TA measurements on a candidate cell basis (e.g., setting reference signals for measuring the received signal time difference between the current serving cell and candidate cells). However, a request for lower layer configurations from the CU does not necessarily mean that the UE must always be configured in this manner. That is, it is entirely up to the CU to decide whether to configure UE-based TA measurements and for which candidate cells to configure UE-based TA measurements.

[0158] If the serving cell changes during the LTM, the CU may determine to reset UE-based TA measurements for each candidate cell based on which cell the UE is currently being served by. For example, as illustrated in FIGS. 5A and 5B , if the serving cell changes from a source DU (e.g., source gNB-DU 520-1) to any one of the candidate cells of a candidate DU (e.g., candidate gNB-DU 520-2), the CU may determine to reset UE-based TA measurements for the UE for subsequent LTM for at least some of the other candidate cells of the candidate DU. For example, if some candidate cells in the candidate DU were co-located with the current new serving cell in the candidate DU, or if they all operate within the FR1 frequency and can maintain the UE's downlink TAE between the serving cell and the candidate cells within 260 ns (as agreed upon by RAN4), the CU may decide to reset the UE-based TA measurements for the candidate cells. In this case, early TA acquisition for those candidate cells in the candidate DU is unnecessary. However, there is currently no mechanism for the CU to notify the DU of this.

[0159] Therefore, the present disclosure proposes mechanisms to optimize the early uplink synchronization procedure during intra-CU LTM.

[0160]

[0161] The present disclosure describes a method and apparatus for optimizing an early uplink synchronization procedure during intra-CU LTM by sharing pre-acquired TA values ​​of some candidate cells when the serving cell changes between DUs and informing the current serving DU whether the UE is configured and / or reset to perform UE-based TA measurements for some candidate cells.

[0162] FIGS. 6A and 6B are examples of a procedure for optimizing an early uplink synchronization procedure during LTM within a CU according to an embodiment of the present disclosure.

[0163] Referring to FIGS. 6A and 6B, in step S601, the S-DU (source-DU) (620) operates as the current serving DU of the UE (610). The S-DU (620) is connected to the CU (630) via the F1 interface and manages the current serving cell of the UE (610). At this time, the C-DUs (candidate-DUs) (640-1, 640-2) are connected to the CU (630) via the F1 interface and manage at least one candidate cell that is not the current serving cell of the UE (610).

[0164] In step S603, the CU (630) determines the LTM for the UE (610). For example, the CU (630) may receive an L3 measurement report message from the UE (610) and determine to initiate LTM configuration based on the L3 measurement report message. The L3 measurement report message may include measurement results of the UE for neighboring cells. Specifically, the UE (610) may transmit the L3 measurement report message to the S-DU (620), and the S-DU (620) may transmit a UL RRC MESSAGE TRANSFER message including the received L3 measurement message to the CU (630). The CU (630) may determine to initiate LTM configuration for the UE (610) based on the L3 measurement report message.

[0165] At step S605, the CU (630) determines candidate cells to be prepared for LTM and checks whether the UE (610) can perform UE-based TA measurements.

[0166] In step S607, LTM is prepared using candidate cells in S-DU (620), C-DU1 (640-1), and / or C-DU2 (640-2), and the prepared LTM is configured in the UE. During the LTM preparation step, S-DU (620), C-DU1 (640-1), and / or C-DU2 (640-2) may be requested to prepare lower-layer configuration information for UE-based TA measurement for each candidate cell. For example, the lower-layer configuration information may include reference signal configuration information for measuring the received signal time difference between the serving cell and the candidate cells.

[0167] According to one embodiment, step S607 may include the following operations (e.g., operations 3 to 12 of FIGS. 5A and 5B ). Specifically, the CU (630) may transmit a UE context setup request message to C-DU1 (640-1) and / or C-DU2 (640-2), and receive a UE context setup response message from C-DU1 (640-1) and / or C-DU2 (640-2). The UE context setup request message may include a cell ID of a candidate target cell, indicate an ID of the S-DU (620), and include information requesting PRACH resources. The candidate target cell may be determined based on an L3 measurement report message. The UE context setup request message may request C-DU1 (640-1) and / or C-DU2 (640-2) to provide information related to lower layer setup in order to generate reference setup information to be used for LTM. The UE context setup response message may include information related to lower layer RRC configuration for LTM setup and information related to RS configuration for a candidate target cell accepted for LTM. For example, the information related to RRC configuration may include at least one of information related to TCI state setup or information related to RACH setup.

[0168] Thereafter, the CU (630) may transmit a UE context modification request message to the S-DU (620) and receive a UE context modification response message from the S-DU (620). The UE context modification request message may include at least one of information related to collected RS configuration for at least one accepted candidate target cell of other candidate DUs (e.g., C-DU1 (640-1), C-DU2 (640-2)), information related to TCI state configuration, or information related to RACH configuration. The UE context modification response message may include at least one of information related to RS configuration of a source cell, prepared candidate cells, or information related to generated CSI reporting configuration.

[0169] Additionally, the CU (630) may transmit a UE context modification request message to C-DU1 (640-1) and / or C-DU2 (640-2), and receive a UE context modification response message from C-DU1 (640-1) and / or C-DU2 (640-2). The CU may use the UE context modification request message to provide lower layer configuration information (e.g., information related to RS configuration, TCI state, or information related to RACH configuration) among the reference configuration information for LTM to C-DU1 (640-1) and / or C-DU2 (640-2). For example, the UE context modification request message may include at least one of a cell ID of at least one prepared candidate cell, and information related to an associated RS configuration for each candidate cell in at least one other candidate DU. Here, the candidate cell may be the same cell as the source cell. The UE context modification response message may include updated lower layer configuration information including information related to the generated CSI reporting configuration.

[0170] The CU (630) may transmit a downlink RRC message transmission message including an RRC reconfiguration message including reference setting information for LTM to the S-DU (620), and the S-DU (620) may transmit the received RRC reconfiguration message to the UE (610). The UE (620) may transmit an RRC reconfiguration complete message to the S-DU (620), and the S-DU (620) may transmit an uplink RRC message transmission message including an RRC reconfiguration complete message to the CU (630).

[0171] At step S609, the CU (630) transmits a notification message for UE-based TA measurement to the S-DU (620). The notification message for UE-based TA measurement may be transmitted for some candidate cells. According to one embodiment, if the UE can perform UE-based TA measurement and the UE-based TA measurement is configured by RRC for some candidate cells at step S607, the CU (630) may transmit a UE-based TA measurement notification message for some candidate cells to the S-DU (620), which is the current serving DU. Accordingly, the early TA acquisition procedure for some candidate cells may be skipped. Alternatively, when the UE-based TA measurement configuration is set to the UE by the LTM cell switching command, the CU (630) may notify the S-DU (620) of candidate cells to which the UE-based TA measurement is applicable, thereby allowing the S-DU (620), which is the current serving DU, to skip the early TA acquisition procedure for some candidate cells. In addition, this may enable the UE to be set to perform UE-based TA measurement by the LTM cell switching command when some candidate cells are triggered for mobility.

[0172] In step S611, an early TA acquisition procedure is performed. The early TA acquisition may be performed by the S-DU (620) for RACH-less LTM. The early TA acquisition procedure may be performed for at least one other candidate cell in other DUs (e.g., C-DU1 (640-1) and / or C-DU2 (640-2)) in the S-DU (620). In this case, the early TA acquisition procedure for some candidate cells indicated by the notification message for UE-based TA measurement may be skipped or omitted. For example, the early TA acquisition procedure may be performed for at least one other candidate cell excluding some candidate cells indicated by the notification message for UE-based TA measurement. According to one embodiment, TA information for some candidate cells indicated by the notification message for UE-based TA measurement may be acquired based on a UE-based TA measurement operation.

[0173] According to one embodiment, step S611 may include the following operations (e.g., operations 13 and 14 of FIGS. 5A and 5B ). Specifically, an early TA acquisition procedure may be performed for at least one other candidate cell, and the S-DU (620) may acquire TA information for at least one other candidate cell acquired through the early TA acquisition procedure. For example, C-DU1 (640-1) and / or C-DU2 (640-2) corresponding to at least one other candidate cell may acquire TA information for the candidate cell through the early TA acquisition procedure, and transmit a notification message including the acquired TA information of the at least one candidate cell to the S-DU (620). The notification message including the TA information may further include at least one of related CFRA resource information, a cell ID of the candidate cell, or an ID of the S-DU.

[0174] At step S613, the UE (610) receives a message commanding cell switching to a candidate target cell of C-DU1 (640-1). At this time, the UE (610) can access the candidate target cell of C-DU1 (640-1) based on the command message.

[0175] According to one embodiment, step S613 may include the following operations (e.g., operations 15 to 19 of FIGS. 5A and 5B ). For example, the UE (610) may transmit a report message about the lower layer measurement result to the S-DU (620). The S-DU (620) may determine an LTM cell switch based on the report message about the lower layer measurement result, and may transmit an LTM command instructing the UE (610) to switch cells to a candidate target cell. In addition, the S-DU (620) may transmit a notification message about an LTM cell change to the CU (630) indicating that the LTM command has been transmitted to the UE (610), and the CU (630) may transmit the notification message about the LTM cell change to a DU (e.g., C-DU1 (640-1)) to which the candidate target cell belongs. The notification message for LTM cell change is a message for indicating that an LTM command to the UE (610) has been initiated, and may include at least one of a cell ID of a candidate target cell or a TCI state ID. The TCI state ID may indicate selected beam information. The notification message for LTM cell change may further include valid TA information for at least one candidate cell possessed by the S-DU (620), which is the current serving DU. Here, the valid TA information is acquired through an early TA acquisition procedure triggered by the S-DU (620), and may include at least one valid TA value corresponding to at least one candidate cell.

[0176] At step S615, C-DU1 (640-1) transmits an access success message to CU (630). C-DU1 (640-1) can detect access of UE (610) and transmit an access success message including the ID of the target cell that UE (610) successfully accessed to CU (630). At step S617, C-DU1 (640-1) can initiate operation as a serving DU of UE (610).

[0177] At step S619, the CU (630) confirms that the serving cell has been successfully changed in the DUs by the LTM. The CU (630) can confirm the changed serving cell of the UE (610) based on the ID of the target cell included in the access success message.

[0178] In step S621, the CU (630) transmits a message requesting valid TA information to the S-DU (620), which is the previous serving DU. In step S623, the S-DU (620), which is the previous serving DU, transmits a response message including valid TA information. For example, the response message may include valid TA values ​​for at least one candidate cell. In step S625, the CU (630) transmits the valid TA information acquired from the S-DU (620), which is the previous serving DU, to the C-DU1 (640-1), which is the new serving DU. In other words, the CU (630) may search for valid TA information for at least one candidate cell from the S-DU (620), which is the previous serving DU, and provide the valid TA information for the at least one retrieved candidate cell to the C-DU1 (640-1), which is the new serving DU. Here, the valid TA information is obtained through an early TA acquisition procedure triggered by the previous serving DU, S-DU (620), and may include at least one valid TA value corresponding to at least one candidate cell.

[0179] In step S627, CU (630) transmits a notification message for UE-based TA measurement to C-DU1 (640-1). The notification message for UE-based TA measurement may be transmitted for some candidate cells. Here, some candidate cells may be the same as or different from some candidate cells in step S609. According to one embodiment, if the UE can perform UE-based TA measurement and UE-based TA measurement is configured by RRC for some candidate cells, CU (630) may transmit a notification message for UE-based TA measurement for some candidate cells to C-DU1 (640-1), which is the current serving DU. Through this, the early TA acquisition procedure for some candidate cells may be skipped. Alternatively, when the UE-based TA measurement configuration is set to the UE by the LTM cell switching command, the CU (630) notifies the C-DU1 (640-1) of candidate cells to which the UE-based TA measurement is applicable, so that the current serving DU, C-DU1 (640-1), can skip the early TA acquisition procedure for some candidate cells. In addition, this can configure the UE to execute the UE-based TA measurement by the LTM cell switching command when some candidate cells are triggered for mobility.

[0180] At step S629, an early TA acquisition procedure is performed. The early TA acquisition may be performed by C-DU1 (640-1), which is a new serving DU, for RACH-less LTM. The early TA acquisition procedure may be performed for at least one other candidate cell in other DUs (e.g., S-DU1 (620), which is a previous serving DU, and / or C-DU2 (640-2)) in C-DU1 (640-1). In this case, the early TA acquisition procedure for some candidate cells indicated by the notification message for UE-based TA measurement may be skipped or omitted. For example, the early TA acquisition procedure may be performed for at least one other candidate cell excluding some candidate cells indicated by the notification message for UE-based TA measurement. According to one embodiment, TA information for some candidate cells indicated by the notification message for UE-based TA measurement may be acquired based on a UE-based TA measurement operation.

[0181] According to one embodiment, step S629 may include the following operations (e.g., operations 13 and 14 of FIGS. 5A and 5B ). Specifically, C-DU1 (640-1) may acquire an early TA acquisition procedure for at least one other candidate cell and TA information for at least one other candidate cell acquired through the early TA acquisition procedure. For example, S-DU1 (620) and / or C-DU2 (640-2) corresponding to at least one other candidate cell may acquire TA information for the candidate cell through the early TA acquisition procedure and transmit a notification message including the acquired TA information of the at least one candidate cell to C-DU1 (640-1), which is a current serving DU. The notification message including the TA information may further include at least one of related CFRA resource information, a cell ID of the candidate cell, or an ID of C-DU1 (640-1), which is a current serving DU.

[0182] At step S631, the UE (610) receives a message commanding switching to a candidate cell of C-DU2 (640-2). At this time, the UE (610) can access the candidate target cell of C-DU2 (640-2) based on the command message.

[0183] According to one embodiment, step S631 may include the following operations (e.g., operations 15 to 19 of FIGS. 5A and 5B ). For example, the UE (610) may transmit a report message about the lower layer measurement result to the current serving DU, C-DU1 (640-1). The current serving DU, C-DU1 (640-1), may determine an LTM cell switch for the UE (610) based on the report message about the lower layer measurement result, and may transmit an LTM command to the UE (610) instructing the cell switch to the candidate target cell. Additionally, C-DU1 (640-1) may transmit a notification message for LTM cell change to CU (630) indicating that an LTM command has been transmitted to UE (610), and CU (630) may transmit the notification message for LTM cell change to a DU (e.g., C-DU2 (640-2)) to which a candidate target cell belongs. The notification message for LTM cell change may include a message for indicating that an LTM command to UE (610) has been initiated. The notification message for LTM cell change may include at least one of a cell ID of a candidate target cell or a TCI state ID. The TCI state ID may indicate selected beam information. The notification message for LTM cell change may further include valid TA information for at least one candidate cell held by C-DU1 (640-1), which is a current serving DU. Here, the valid TA information may include at least one valid TA value corresponding to at least one candidate cell, which is obtained through the early TA acquisition procedure triggered by C-DU1 (640-1), or the valid TA information for at least one candidate cell received from the CU (630) in step S625.

[0184] At step S633, C-DU2 (640-2) transmits an access success message to CU (630). C-DU2 (640-2) can detect access of UE (610) and transmit an access success message including the ID of the target cell that UE (610) successfully accessed to CU (630). At step S635, C-DU2 (640-2) can start operating as a serving DU of UE (610).

[0185] At step S637, the CU (630) confirms that the serving cell has been successfully changed in the DUs by the LTM. The CU (630) can confirm the changed serving cell of the UE (610) based on the ID of the target cell included in the access success message.

[0186] In step S639, the CU (630) transmits a message requesting valid TA information to the previous serving DU, C-DU1 (640-1). In step S641, the previous serving DU, C-DU1 (640-1), transmits a response message including valid TA information. For example, the response message may include at least one valid TA value corresponding to at least one candidate cell. In step S643, the CU (630) transmits the valid TA information acquired from the previous serving DU, C-DU1 (640-1), to the new serving DU, C-DU2 (640-2). In other words, the CU (630) can retrieve valid TA information from the previous serving DU, C-DU1 (640-1), and provide the retrieved valid TA information to the new serving DU, C-DU2 (640-2). Here, the valid TA information may include at least one valid TA value corresponding to at least one candidate cell, which is obtained through an early TA acquisition procedure triggered by the previous serving DU, C-DU1 (640-1), or the previous serving DU, C-DU1 (640-1), which is valid TA information for at least one candidate cell received from the CU (630) in step S625.

[0187] At step S645, CU (630) transmits a notification message for UE-based TA measurement to C-DU2 (640-2). The notification message for UE-based TA measurement may be transmitted for some candidate cells. Here, some candidate cells may be the same as or different from some candidate cells of step S609 or step S627. According to one embodiment, if the UE can perform UE-based TA measurement and UE-based TA measurement is configured by RRC for some candidate cells, CU (630) may transmit a notification message for UE-based TA measurement for some candidate cells to C-DU2 (640-2), which is the current serving DU. Through this, the early TA acquisition procedure for some candidate cells may be skipped. Alternatively, when the UE-based TA measurement configuration is set to the UE by the LTM cell switching command, the CU (630) notifies the C-DU2 (640-2) of candidate cells to which the UE-based TA measurement is applicable, so that the current serving DU, C-DU2 (640-2), can skip the early TA acquisition procedure for some candidate cells. In addition, this can configure the UE to execute the UE-based TA measurement by the LTM cell switching command when some candidate cells are triggered for mobility.

[0188]

[0189] As described above, the present disclosure relates to a method and apparatus for supporting LTM and configuring a UE in a wireless communication system.

[0190] In one embodiment, the CU of the base station can confirm that the terminal can perform UE-based TA measurement for at least one candidate cell. The CU can inform the DU that UE-based TA measurement has been configured for the UE, or that UE-based TA measurement will be applied for at least one candidate cell. In this case, the DU can be the current serving DU of the UE as a DU involved in the process of preparing at least one candidate cell for LTM and configuring LTM for the UE.

[0191] In one embodiment, a CU of a base station can detect a successful cell switch between DUs. Here, the DUs may include DUs involved in the process of preparing a candidate cell for LTM and configuring the LTM for the UE. The CU retrieves valid TA information of at least one candidate cell from a previous serving DU and provides the retrieved TA information to a new serving DU. Here, the valid TA information of at least one candidate cell may be TA information acquired through an early TA acquisition procedure triggered by the previous serving DU.

[0192]

[0193] FIG. 7 illustrates an example of a procedure for transmitting TA measurement-related information according to an embodiment of the present disclosure. FIG. 7 illustrates a method performed by a control node of a base station. The base station includes an NG-RAN node, and the control node may include a CU of the NG-RAN node. The control node may be connected to multiple distributed nodes (e.g., DUs) via an F1 interface.

[0194] Referring to FIG. 7, in step S701, the control node initiates LTM configuration for the UE. The control node may determine to initiate LTM configuration within the CU of the base station based on an L3 measurement report message received from the UE. The intra-CU LTM may include at least one of inter-DU LTM within the same CU or intra-CU LTM. The L3 measurement report message may include measurement results for adjacent cells. According to one embodiment, the control node may determine candidate cells to be prepared for LTM and confirm that the UE can perform UE-based TA measurements.

[0195] In step S703, the control node transmits a first message related to terminal-based TA measurement to the first distributed node. At this time, the first distributed node may be the current serving DU of the terminal. The first message may indicate at least one candidate cell to which UE-based TA measurement is to be applied. For example, the first message may include a notification message indicating that UE-based TA measurement may be performed for at least one candidate cell. According to one embodiment, when the UE is configured by RRC to perform UE-based TA measurement for at least one candidate cell, the control node may transmit a notification message related to UE-based TA measurement for at least one candidate cell to the first distributed node, which is the current serving DU. According to one embodiment, when the UE is configured by an LTM cell switching command to perform UE-based TA measurement, the control node may transmit a notification message related to UE-based TA measurement for at least one candidate cell to the first distributed node, which is the current serving DU. Through this, the control node can control to skip or omit the early TA acquisition procedure for at least one candidate cell among the candidate cells prepared for LTM. In addition, the control node can configure the UE via the LTM cell switching command to perform UE-based TA measurements for at least one candidate cell when the candidate cell is triggered for mobility.

[0196] According to one embodiment, the control node of the base station may be the CU (630) of the embodiment described with reference to FIGS. 6A and 6B. The control node may further perform at least one operation of the CU (630) described with reference to FIGS. 6A and 6B.

[0197]

[0198] FIG. 8 illustrates an example of a procedure for receiving TA measurement-related information according to an embodiment of the present disclosure. FIG. 8 illustrates a method performed by a first distributed node of a base station. The base station may include an NG-RAN node. The first distributed node may include a first DU of the NG-RAN node. The first distributed node may be connected to a control node (e.g., CU) of the base station via an F1 interface.

[0199] Referring to FIG. 8, in step S801, a first distributed node receives a first message related to terminal-based TA measurement from a control node. The first distributed node may be the current serving DU of the terminal. The first message may indicate at least one candidate cell to which UE-based TA measurement will be applied. For example, the first message may include a notification message indicating that UE-based TA measurement may be performed for at least one candidate cell.

[0200] In step S803, the first distributed node acquires a TA for at least one other candidate cell based on the first message. The first distributed node can determine at least one other candidate cell for which an early TA acquisition procedure is to be performed among candidate cells prepared for LTM based on the first message. For example, the first distributed node can identify at least one candidate cell for which the early TA acquisition procedure is to be skipped or omitted based on the first message, and control to perform the early TA acquisition procedure for at least one other candidate cell excluding the identified at least one candidate cell. By controlling to perform the early TA acquisition procedure for at least one other candidate cell, the first distributed node can acquire TA information for at least one other candidate cell.

[0201] According to one embodiment, the first distributed node of the base station may be S-DU1 (620), C-DU1 (640-1), or C-DU2 (640-2) of the embodiment described with reference to FIGS. 6A and 6B. The first distributed node may further perform at least one operation of S-DU1 (620), C-DU1 (640-1), or C-DU2 (640-2) described with reference to FIGS. 6A and 6B.

[0202]

[0203] It is clear that the examples of the proposed methods described above can also be considered as a type of proposed methods, as they can be included as one of the implementation methods of the present disclosure. Furthermore, the proposed methods described above can be implemented independently, but they can also be implemented in the form of a combination (or merge) of some of the proposed methods. Information regarding the applicability of the proposed methods (or information regarding the rules of the proposed methods) can be defined by a rule such that the base station notifies the terminal of the application of the proposed methods through a predefined signal (e.g., a physical layer signal or a higher layer signal).

[0204] The present disclosure may be embodied in other specific forms without departing from the technical ideas and essential features described herein. Therefore, the above detailed description should not be construed as limiting in all respects but rather as illustrative. The scope of the present disclosure should be determined by a reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the present disclosure are intended to be included within the scope of the present disclosure. Furthermore, claims that do not explicitly cite each other in the claims may be combined to form embodiments or incorporated into new claims through post-filing amendments.

[0205] Embodiments of the present disclosure can be applied to various wireless access systems. Examples of various wireless access systems include the 3rd Generation Partnership Project (3GPP) or 3GPP2 systems.

[0206] The embodiments of the present disclosure can be applied not only to the various wireless access systems described above, but also to all technical fields that utilize these various wireless access systems. Furthermore, the proposed method can also be applied to mmWave and THz communication systems utilizing ultra-high frequency bands.

[0207] Additionally, embodiments of the present disclosure can be applied to various applications such as autonomous vehicles and drones.

Claims

1. In the method, A step in which the control node of the base station determines to initiate LTM (L1L2 triggered mobility) setup for the terminal; and The control node comprises a step of transmitting a first message related to terminal-based TA (timing advance) measurement to a first distributed node among the distributed nodes of the base station, A method wherein the first message includes information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

2. In claim 1, A method in which the first distributed node comprises a distributed node that manages the current serving cell of the terminal.

3. In claim 1, A method further comprising the step of receiving a second message including TA information of at least one candidate cell from the first distributed node.

4. In claim 3, A step of receiving a second message indicating that the serving cell of the terminal based on LTM cell switching has been changed from the first distributed node to the second distributed node; and A method further comprising the step of transmitting a third message requesting TA information of at least one candidate cell to the first distributed node.

5. In claim 3, A method further comprising the step of transmitting a fourth message including TA information of at least one candidate cell to a second distributed node.

6. In claim 5, Further comprising the step of transmitting a fifth message related to the terminal-based TA measurement to the second distributed node, A method wherein the fifth message includes information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

7. In claim 1, A method wherein the first message is transmitted based on the terminal being configured by RRC to perform terminal-based TA measurement for the at least one candidate cell.

8. In claim 1, A method in which the first message is transmitted based on the terminal being configured to perform terminal-based TA measurement by an LTM cell switching command.

9. In the method, A step in which a first distributed node of a base station receives a first message related to terminal-based TA (timing advance) measurement from a control node of the base station; and A step of controlling the first distributed node to skip an early TA acquisition procedure for at least one candidate cell among a plurality of candidate cells for LTM (L1L2 triggered mobility) based on the first message, A method wherein the first message includes information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

10. In claim 9, A method for controlling the first distributed node to perform an early TA acquisition procedure for other candidate cells except for the at least one candidate cell.

11. In claim 9, A method in which TA information for at least one candidate cell is obtained by terminal-based TA measurement.

12. In claim 9, The first distributed node further comprises a step of receiving valid TA information for some of the plurality of candidate cells for the LTM from the control node, A method in which the above valid TA information includes a TA value acquired through an early TA acquisition procedure triggered by a previous serving distribution node of the terminal.

13. In claim 12, The first distributed node further includes a step of transmitting a notification message regarding successful access of the terminal to the control node, The above valid TA information is received after transmitting the above notification message.

14. In the device, Transmitter and receiver; and A processor connected to the above transmitter and receiver is included, The above processor, The control node of the base station decides to initiate LTM (L1L2 triggered mobility) setup for the terminal, The control node controls the base station to transmit a first message related to terminal-based TA (timing advance) measurement to a first distributed node among the distributed nodes of the base station, A device wherein the first message includes information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

15. In the device, Transmitter and receiver; and A processor connected to the above transmitter and receiver is included, The above processor, A first distributed node of a base station receives a first message related to terminal-based TA (timing advance) measurement from a control node of the base station, The first distributed node controls the early TA acquisition procedure for at least one candidate cell among a plurality of candidate cells for LTM (L1L2 triggered mobility) to be skipped based on the first message, A device wherein the first message includes information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

16. In communication devices, at least one processor; and At least one memory connected to the at least one processor and storing instructions that cause the terminal to perform operations when executed by the at least one processor, The above actions are, A step in which the control node of the base station determines to initiate LTM (L1L2 triggered mobility) setup for the terminal; and The control node comprises a step of transmitting a first message related to terminal-based TA (timing advance) measurement to a first distributed node among the distributed nodes of the base station, A communication device wherein the first message includes information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

17. In a non-transitory computer-readable medium storing at least one program instruction, wherein said at least one program instruction, when executed by at least one processor, causes the terminal to perform operations; The above actions are, A step in which the control node of the base station determines to initiate LTM (L1L2 triggered mobility) setup for the terminal; and The control node comprises a step of transmitting a first message related to terminal-based TA (timing advance) measurement to a first distributed node among the distributed nodes of the base station, A computer-readable medium wherein the first message includes information indicating at least one candidate cell to which the terminal-based TA measurement is to be applied.

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