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

Abstract

The present disclosure relates to a method and device 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 can comprise the steps of determining to initiate an LTM configuration for a terminal; and transmitting, to a first distributed node among distributed nodes of the base station, a first message related to a terminal based timing advance (TA) measurement, wherein the first message comprises information indicating at least one candidate cell for which the terminal based TA measurement is to be applied.

Description

Technical Field

[0001] The following description relates to wireless communication systems, and more specifically, to devices and methods in wireless communication systems that support uplink synchronization during handover. Background Technology

[0002] Wireless access systems are being widely deployed to provide various types of communication services, such as voice and data. Typically, a wireless access system is a multiple access system that can support communication with multiple users by sharing available system resources (bandwidth, transmission power, etc.). 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] Specifically, due to the need for large communication capacity in many communication devices, enhanced mobile broadband (eMBB) communication technologies have been proposed that improve upon existing radio access technologies (RAT). Furthermore, communication systems have been proposed that consider not only connecting multiple devices and objects to provide various services anytime, anywhere, but also reliability and latency-sensitive services / user equipment (UE). Various technical configurations for this purpose are being proposed. Summary of the Invention

[0004] Technical issues

[0005] This disclosure relates to devices and methods for efficiently supporting L1 / L2 triggered mobility (LTM) handover in wireless communication systems.

[0006] This disclosure relates to apparatus and methods for optimizing the early uplink synchronization process during LTM in wireless communication systems.

[0007] This disclosure relates to apparatus and methods for optimizing the early uplink synchronization process within a centralized unit (CU) in a wireless communication system using LTM.

[0008] This disclosure relates to apparatus and methods for optimizing the early uplink synchronization process between distributed units (DUs) within the same CU in a wireless communication system.

[0009] This disclosure relates to apparatus and methods for providing information related to timing advance (TA) measurements based on the UE to the current serving DU in a wireless communication system.

[0010] This disclosure relates to devices and methods for skipping or omitting the early TA acquisition process for at least one candidate cell in a wireless communication system, in preparation for LTM.

[0011] This disclosure relates to apparatus and method for instructing a serving DU to apply UE-based TA measurements to at least one candidate cell in a wireless communication system.

[0012] This disclosure relates to an apparatus and method in a wireless communication system for obtaining valid TA information for at least one candidate cell from a previous serving DU during LTM cell handover.

[0013] This disclosure relates to an apparatus and method for utilizing TA information of at least one candidate cell obtained through an early TA acquisition process triggered by a previous TA in a new serving DU in a wireless communication system.

[0014] This disclosure relates to an apparatus and method in a wireless communication system, wherein, when an LTM cell handover occurs between DUs within the same CU, TA information of at least one valid candidate cell of the serving DU is delivered to the new serving DU.

[0015] This disclosure relates to an apparatus and method in a wireless communication system for requesting valid TA information from a previous serving DU when an LTM cell handover between DUs within the same CU is detected.

[0016] The technical objectives to be achieved by this disclosure are not limited to those mentioned above, and those skilled in the art to which the technical configuration of this disclosure applies may consider other technical problems not mentioned below based on the embodiments of this disclosure described below.

[0017] Technical solution

[0018] As an example of this disclosure, a method may include the following steps: a control node of a base station determines to initiate L1 / L2 triggered mobility (LTM) configuration for a UE; and the control node of the base station sends a first message related to UE-based timing advance (TA) measurements to a first distributed node among the base station's distributed nodes. The first message may include information indicating at least one candidate cell for which UE-based TA measurements are to be applied.

[0019] As an example of this disclosure, a method may include the steps of: receiving, by a first distributed node of a base station, a first message related to UE-based advance timing (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 process for at least one of a plurality of candidate cells for L1 / L2 triggered mobility (LTM) based on the first message. The first message may include information indicating at least one candidate cell to which the UE-based TA measurement is to be applied.

[0020] As an example of this disclosure, an apparatus may include: a transceiver; and a processor connected to the transceiver. The processor may control a control node of a base station to determine and initiate L1 / L2 triggered mobility (LTM) configuration for a UE, and control the control node of the base station to send a first message related to a UE-based timing advance (TA) measurement to a first distributed node among the base station's distributed nodes. The first message may include information indicating at least one candidate cell for which the UE-based TA measurement is to be applied.

[0021] As an example of this disclosure, an apparatus may include: a transceiver; and a processor connected to the transceiver. The processor may control a first distributed node of a base station to receive a first message related to UE-based timing advance (TA) measurements from a control node of the base station, and control the first distributed node of the base station to skip an early TA acquisition process for at least one of a plurality of candidate cells for L1 / L2 triggered mobility (LTM) based on the first message. The first message may include information indicating at least one candidate cell to which UE-based TA measurements are to be applied.

[0022] As an example of this disclosure, a communication device may include: 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 UE to perform an operation. The operation may include: a control node of a base station determining to initiate an L1 / L2 triggered mobility (LTM) configuration for the UE; and the control node of the base station sending a first message related to a UE-based timing advance (TA) measurement to a first distributed node among the base station's distributed nodes. The first message may include information indicating at least one candidate cell for which the UE-based TA measurement is to be applied.

[0023] As an example of this disclosure, a non-transitory computer-readable medium stores at least one program instruction. The at least one program instruction, when executed by at least one processor, can cause a UE to perform operations. These operations may include: a control node of a base station determining to initiate an L1 / L2 triggered mobility (LTM) configuration for the UE; and the control node of the base station sending a first message related to a UE-based timing advance (TA) measurement to a first distributed node among the base station's distributed nodes. The first message may include information indicating at least one candidate cell for which the UE-based TA measurement is to be applied.

[0024] The above aspects of this disclosure are merely some preferred embodiments of this disclosure, and those skilled in the art can deduce and understand various embodiments reflecting the technical features of this disclosure based on the detailed description described below.

[0025] Beneficial effects

[0026] The embodiments based on this disclosure can provide the following effects.

[0027] This disclosure can optimize the early uplink synchronization process during L1 / L2 triggered mobility (LTM) in a wireless communication system.

[0028] The effects obtainable from the embodiments of this disclosure are not limited to those described above, and those skilled in the art to which the technical configuration of this disclosure applies can clearly obtain and understand other effects not mentioned below based on the following description of the embodiments of this disclosure. In other words, those skilled in the art can also obtain unexpected effects from implementing the configurations described in this disclosure based on the embodiments of this disclosure. Attached Figure Description

[0029] The accompanying drawings are provided to aid in understanding this disclosure and to provide embodiments of the disclosure as well as a detailed description. However, the technical features of this disclosure are not limited to the specific drawings, and the features disclosed in each drawing can be combined with each other to form new embodiments. Reference numerals in each drawing may indicate structural elements.

[0030] Figure 1 Examples of communication systems applied to this disclosure are illustrated.

[0031] Figure 2 Examples of UEs applicable to this disclosure are illustrated.

[0032] Figure 3 An example of functional separation between NG-RAN and fifth-generation core (5GC) applicable to this disclosure is illustrated.

[0033] Figure 4 An example of a general architecture applicable to the fifth-generation (5G) system of this disclosure is illustrated.

[0034] Figure 5a and Figure 5b This is an example of the DU-LTM process applicable to this disclosure.

[0035] Figure 6a and Figure 6b This is an example of a process for optimizing the early uplink synchronization process during LTM within the CU, according to an embodiment of this disclosure.

[0036] Figure 7 An example of a process for sending TA measurement-related information according to an embodiment of this disclosure is illustrated.

[0037] Figure 8 An example of a process for receiving TA measurement-related information according to an embodiment of the present disclosure is illustrated. Detailed Implementation

[0038] The following embodiments are combinations of the components and features of this disclosure in a predetermined form. Unless otherwise explicitly stated, each component or feature may be considered optional. Each component or feature may be implemented without combination with other components or features. Furthermore, embodiments of this disclosure can be configured by combining some components and / or features. The order of operations described in the embodiments of this disclosure may be changed. Some configurations or features of one embodiment may be included in another embodiment, or may be replaced by corresponding configurations or features of another embodiment.

[0039] In the description of the accompanying drawings, processes or steps that may obscure the essential points of this disclosure are not described, nor are processes or steps that can be understood by those skilled in the art.

[0040] Throughout this specification, when a part is referred to as “comprising” or “including” a component, it means that it may also include other components rather than exclude them, unless explicitly stated to the contrary. Furthermore, terms such as “unit,” “apparatus,” and “module” described in the specification refer to a unit that performs at least one function or operation, which may be implemented by hardware, software, or a combination of hardware and software. Additionally, the words “a,” “an,” “the,” and similar related terms may be used in the context of describing this disclosure (particularly in the context of the appended claims) to mean both singular and plural, unless otherwise stated herein or clearly contradicted by the context.

[0041] In this specification, embodiments of the present disclosure have been described regarding the data transmission and reception relationship between a base station and a mobile station. Here, a base station is understood as a terminal node of a network that communicates directly with a mobile station. Specific operations described herein as being performed by the base station may, in some cases, be performed by upper-layer nodes of the base station.

[0042] In other words, various operations for communicating with a mobile station in a network consisting of multiple network nodes, including a base station, can be performed by the base station or other network nodes besides the base station. In this case, "base station" can 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.

[0043] Furthermore, in embodiments of this disclosure, the term "terminal" may be replaced by terms such as User Equipment (UE), Mobile Station (MS), Subscriber Station (SS), Mobile Subscriber Station (MSS), Mobile Terminal, or Advanced Mobile Station (AMS).

[0044] Furthermore, the transmitting end refers to a fixed and / or mobile node that provides data or voice services, and the receiving end refers to a fixed and / or mobile node that receives data or voice services. Therefore, in the uplink case, the mobile station can be the transmitting end, and the base station can be the receiving end. Similarly, in the downlink case, the mobile station can be the receiving end, and the base station can be the transmitting end.

[0045] Implementations of this disclosure may be supported by standard documents disclosed in at least one of the radio access systems including the IEEE 802.xx system, the 3rd Generation Partnership Project (3GPP) system, the 3GPP Long Term Evolution (LTE) system, the 3GPP 5th Generation (5G) New Radio (NR) system, and the 3GPP2 system. Specifically, implementations of this disclosure may be supported by 3GPP Technical Specification (TS) 38.211, 3GPP TS 38.212, 3GPP TS 38.213, 3GPP TS 38.321, and 3GPP TS 38.331 documents.

[0046] Furthermore, the embodiments of this disclosure can be applied to other wireless access systems and are not limited to the systems described above. For example, they can be applied to systems subsequently used after 3GPP 5G NR systems, and are not limited to any particular system.

[0047] In other words, obvious steps or parts not described in the embodiments of this disclosure can be referred to the descriptions in the aforementioned documents. Furthermore, all terms disclosed in this document can be described using the aforementioned standard documents.

[0048] In the following, preferred embodiments according to this disclosure will be described in detail with reference to the accompanying drawings. The preferred embodiments will be described below in conjunction with the accompanying drawings. Figure 1 The detailed description disclosed herein is intended to describe exemplary embodiments of this disclosure and is not intended to represent the only implementation of the technical configurations of this disclosure.

[0049] In addition, specific terminology used in the embodiments of this disclosure is provided to aid in understanding this disclosure, and the use of such specific terminology may be changed to other forms without departing from the technical spirit of this disclosure.

[0050] The following technologies can be applied to various wireless access systems, such as 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).

[0051] For clarity, the following description is based on 3GPP communication systems (e.g., LTE, NR, etc.), but the technical spirit of this disclosure is not limited thereto. LTE can refer to technologies from 3GPP TS 36.xxx version 8 onwards. Specifically, LTE technologies from 3GPP TS 36.xxx version 10 onwards can be referred to as LTE-A, and LTE technologies from 3GPP TS 36.xxx version 13 onwards can be referred to as LTE-A pro. 3GPP NR can refer to technologies from TS 38.xxx version 15 onwards. 3GPP 6G can refer to technologies from TS version 17 and / or version 18 onwards. "xxx" refers to the detailed standard document number. LTE / NR / 6G can be collectively referred to as the 3GPP system.

[0052] For background information, terminology, abbreviations, etc., used in this disclosure, please refer to the descriptions in previously published standard documents. For example, refer to standard documents 36.xxx and 38.xxx.

[0053] For the terminology, abbreviations, and other background technologies that may be used in this document, please refer to the following standard documents previously published. Specifically, for LTE / Evolved Packet System (EPS) related terminology, abbreviations, and other background technologies, please refer to the 36.xxx series, 23.xxx series, and 24.xxx series; and for New Radio (NR) / 5G System (5GS) related terminology, abbreviations, and other background technologies, please refer to the 38.xxx series, 23.xxx series, and 24.xxx series.

[0054] In the following text, this specification is described based on the terminology defined above.

[0055] The three main demand areas for 5G include (1) enhanced mobile broadband (eMBB), (2) massive machine-type communications (mMTC) and (3) ultra-reliable and low-latency communications (URLLC).

[0056] Some use cases may require multiple regions for optimization, while others may focus on only one key performance indicator (KPI). 5G supports these diverse use cases in a flexible and reliable manner.

[0057] Communication systems applicable to this disclosure

[0058] While not limited thereto, the various descriptions, functions, processes, proposals, methods and / or operation flowcharts disclosed in this document can be applied to various fields requiring wireless communication / connectivity between devices (e.g., 5G).

[0059] More specific examples are illustrated below with reference to the accompanying drawings. In the following drawings / description, the same reference numerals may refer to the same or corresponding hardware blocks, software blocks, or functional blocks, unless otherwise described.

[0060] Figure 1 Examples of communication systems applied to this disclosure are illustrated.

[0061] Reference Figure 1 The communication system 100 applied in this disclosure includes wireless devices, base stations, and networks. Here, a wireless device refers to a device that performs communication using wireless access technologies (e.g., 5G NR, LTE) and may be referred to as a communication / wireless / 5G device. While not limited thereto, wireless devices may include robots 100a, vehicles 100b-1 and 100b-2, extended reality (XR) devices 100c, handheld devices 100d, home appliances 100e, Internet of Things (IoT) devices 100f, and artificial intelligence (AI) devices / servers 100g. For example, vehicles may include vehicles equipped with wireless communication capabilities, autonomous vehicles, vehicles capable of performing vehicle-to-vehicle communication, etc. Here, vehicles 100b-1 and 100b-2 may include unmanned aerial vehicles (UAVs) (e.g., drones). XR device 100c includes augmented reality (AR) / virtual reality (VR) / mixed reality (MR) devices, and can be implemented as a head-up display (HUD) installed in vehicles, televisions, smartphones, computers, wearable devices, home appliances, digital signage, vehicles, robots, etc. Handheld device 100d can include smartphones, smart tablets, wearable devices (e.g., smartwatches, smart glasses), computers (e.g., laptops, etc.). Home appliance 100e can include TVs, refrigerators, washing machines, etc. IoT device 100f can include sensors, smart meters, etc. For example, base station 120 and network 130 can also be implemented as wireless devices, and a specific wireless device 120a can operate as a base station / network node for other wireless devices.

[0062] Wireless devices 100a to 100f can connect to network 130 via base station 120. AI technology can be applied to wireless devices 100a to 100f, and wireless devices 100a to 100f can connect to AI server 100g via network 130. Network 130 can be configured using 3G, 4G (e.g., LTE), or 5G (e.g., NR) networks, etc. Wireless devices 100a to 100f can communicate with each other via base station 120 / network 130, but can also communicate directly (e.g., sidelink communication) without going through base station 120 / network 130. For example, vehicles 100b-1 and 100b-2 can perform direct communication (e.g., vehicle-to-vehicle (V2V) / vehicle-to-everything (V2X) communication). Furthermore, IoT device 100f (e.g., sensor) can communicate directly with other IoT devices (e.g., sensors) or other wireless devices 100a to 100f.

[0063] Wireless communication / connections 150a, 150b, and 150c can be established between wireless devices 100a to 100f / base station 120 and between base stations 120 / 120. Here, the wireless communication / connection can be implemented through various wireless access technologies (e.g., 5G NR), such as uplink / downlink communication 150a, sidelink communication 150b (or D2D communication), and inter-base station communication 150c (e.g., relay, integrated access backhaul (IAB)). Through wireless communication / connections 150a, 150b, and 150c, wireless devices and base stations / wireless devices, as well as base stations and base stations, can transmit / receive wireless signals to each other. For example, wireless communication / connections 150a, 150b, and 150c can transmit / receive signals through various physical channels. Therefore, based on various proposals of this disclosure, at least some of the following can be performed: various configuration information setting processes for wireless signal transmission / reception, various signal processing processes (e.g., channel coding / decoding, modulation / demodulation, resource mapping / demapping, etc.), resource allocation processes, etc.

[0064] Figure 2 Examples of UEs applicable to this disclosure are illustrated.

[0065] Reference Figure 2 The UE 200 may include a processor 202, a 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 subscriber identification module (SIM) card 245, a speaker 246, and a microphone 247.

[0066] Processor 202 may be configured to implement the descriptions, functions, processes, proposals, methods, and / or operational flowcharts disclosed herein. Processor 202 may be configured to control one or more other components of UE 200 to implement the descriptions, functions, processes, proposals, methods, and / or operational flowcharts disclosed herein. A wireless interface protocol layer may be implemented in processor 202. Processor 202 may include an ASIC, other chipsets, logic circuits, and / or data processing devices. Processor 202 may be an application processor. Processor 202 may include at least one of a DSP, a central processing unit (CPU), a graphics processing unit (GPU), and a modem (modulator and demodulator).

[0067] Memory 204 is operatively coupled to processor 202 and can store various information for operating processor 202. Memory 204 may include ROM, RAM, flash memory, memory card, storage medium, and / or other storage devices. When implemented in software, the techniques described herein can be implemented using modules (e.g., processes, functions, etc.) that perform the descriptions, functions, processes, proposals, methods, and / or operation flowcharts disclosed herein. Modules may be stored in memory 204 and executed by processor 202. Memory 204 may be implemented within or outside processor 202, in which case it may be communicatively coupled to processor 202 using various methods known in the art.

[0068] Transceiver 206 is operatively coupled to processor 202 and can transmit and / or receive wireless signals. Transceiver 206 may include a transmitter and a receiver. Transceiver 206 may include baseband circuitry for processing radio frequency signals. Transceiver 206 may control one or more antennas 208 to transmit and / or receive wireless signals.

[0069] The power management module 241 can manage the power used for the processor 202 and / or transceiver 206. The battery 242 can supply power to the power management module 241.

[0070] The display 243 can output the results processed by the processor 202. The keypad 244 can receive input for use by the processor 202. The keypad 244 can be displayed on the display 243.

[0071] The SIM card 245 is an integrated circuit used to securely store the International Mobile Subscriber Identity (IMSI) and related keys, and can be used to identify and authenticate subscribers in mobile devices such as mobile phones or computers. Furthermore, contact information can be stored on multiple SIM cards.

[0072] Speaker 246 can output sound-related results processed by processor 202. Microphone 247 can receive sound-related input for use by processor 202.

[0073] In the implementation described herein, the UE can operate as a transmitting device in the uplink and as a receiving device in the downlink. In the implementation described herein, the base station can operate as a receiving device in the UL and as a transmitting device in the DL. In this specification, the base station can be referred to as Node B, eNode B (eNB), or gNB, and is not limited to any specific form.

[0074] Furthermore, for example, the UE can be implemented in various forms depending on the use case / service. The UE can be configured from 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 communication circuitry and transceivers. For example, the communication circuitry 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, memory device, and additional components, and can control the overall operation of each UE. For example, the control device can control the electrical / mechanical operation of each UE based on programs / code / instructions / information stored in the memory device. The control device can transmit information stored in the memory device to external sources (e.g., other communication devices) via a wireless / wired interface through the communication device, or store information received from external sources (e.g., other communication devices) in the memory device via a wireless / wired interface through the communication device.

[0075] Additional components can be configured differently depending on the type of UE. For example, additional components may include at least one of a power unit / battery, input / output (I / O) devices (e.g., audio I / O ports, video I / O ports), drive units, and computing units. Furthermore, the UE can be implemented in, but is not limited to, the following forms: robot (…). Figure 1 100a in the middle), vehicles ( Figure 1 100b-1 and 100b-2 in the series), XR device ( Figure 1 100c in the middle), portable device ( Figure 1 100d in the middle), household appliances ( Figure 1 100e in the middle), IoT devices ( Figure 1 100f), digital broadcasting terminals, holographic devices, public safety devices, MTC devices, medical devices, fintech devices (or financial devices), security devices, climate / environment devices, AI servers / devices ( Figure 1 100g in the middle), base station ( Figure 1(120 in the middle) network nodes. The UE can be used in mobile or fixed locations depending on the use case / service.

[0076] All the various components, devices / parts, and / or modules of the UE can be connected to each other via wired interfaces, or at least some can be wirelessly connected via communication devices. Furthermore, each component, device / part, and / or module of the UE may include one or more elements. For example, the control unit may be configured with one or more processor groups. For instance, the control unit may be configured with a group of communication control processors, application processors (APs), electronic control units (ECUs), graphics processing units, and memory control processors. As another example, the memory device may be configured with RAM, dynamic RAM (DRAM), ROM, flash memory, volatile memory, non-volatile memory, and / or combinations thereof.

[0077] 5G system architecture applicable to this disclosure

[0078] 5G systems are advanced technologies derived from fourth-generation LTE mobile communication technology. They support new radio access technologies (RATs), extended LTE (eLTE) as an extension of LTE, and non-3GPP (e.g., WLAN) access through the evolution or clean state architecture of existing mobile communication networks.

[0079] 5G systems are service-defined, and the interaction between network functions (NFs) within the 5G system architecture can be represented in the following two ways: - Reference point representation: Represents the interaction between NF services within an NF described by a point-to-point reference point (e.g., N11) between two NFs (e.g., AMF and SMF).

[0080] - Service-based representation: Network functions within the control plane (CP) (e.g., AMF) allow other authorized network functions to access their services. This representation may also include point-to-point reference points where necessary.

[0081] The 5G core (5GC) can include various components, including 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 Interoperability Function (N3IWF).

[0082] The UE connects to the data network via a UPF through a Next Generation Radio Access Network (NG-RAN) including a gNB. The UE can receive data services through untrusted non-3GPP access, such as a Wireless Local Area Network (WLAN). To connect non-3GPP access to the core network, an N3IWF can be deployed.

[0083] The N3IWF manages interoperability between non-3GPP access points and 5G systems. When a UE connects to a non-3GPP access point (e.g., WiFi known as IEEE 802.11), the UE can connect to the 5G system via the N3IWF. The N3IWF communicates with the AMF (Advanced Management Function) for control signaling and connects to the UPF (Uplink Function) via the N3 interface for data transmission.

[0084] AMF can manage access and mobility in 5G systems. AMF can perform functions to manage Non-Access Stratum (NAS) security. AMF can perform functions to handle mobility in idle states.

[0085] UPF performs gateway functions for sending and receiving user data. UPF nodes can perform all or part of the user plane functions of a Serving Gateway (S-GW) and Packet Data Network Gateway (P-GW) for fourth-generation mobile communications.

[0086] The UPF serves as the 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. Furthermore, the UPF acts as a mobility anchor point when the UE moves across an area served by the gNB. The UPF can perform the function of disposing of PDUs. For mobility within the NG-RAN (e.g., NG-RAN defined after 3GPP Release 15), the UPF can route packets. Additionally, the UPF can serve as an anchor point for mobility with other 3GPP networks (e.g., RANs defined before 3GPP Release 15), such as UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network (UTRAN), Evolved UTRAN (E-UTRAN), or GSM (Global System for Mobile Communications) / EDGE (Global Evolution Enhanced Data Rate) Radio Access Network (GERAN). The UPF can correspond to the termination point of the data interface toward the data network.

[0087] PCF is the node that controls operator policies. AF is the server that provides various services to UE. UDM is the server that manages subscriber information, such as the Home Subscriber Server (HSS) in fourth-generation mobile communications. UDM 460 stores and manages subscriber information in the Unified Data Repository (UDR).

[0088] The SMF can perform the function of allocating Internet Protocol (IP) addresses to UEs. Furthermore, the SMF can control Protocol Data Unit (PDU) sessions.

[0089] For ease of description below, reference numerals for AMF, SMF, PCF, UPF, AF, UDM, N3IWF, gNB, or UE may be omitted, and reference may be made to the descriptions in standard documents previously published in this document.

[0090] Figure 3 An example of functional separation between NG-RAN and fifth-generation core (5GC) applicable to this disclosure is illustrated.

[0091] Reference Figure 3 The UE connects to the data network (DN) via the next-generation RAN. Control plane function (CPF) nodes perform all or part of the functions of the mobility management entity (MME) for fourth-generation mobile communications, as well as all or part of the control plane functions of the serving gateway (S-GW) and PDN gateway (P-GW). CPF nodes include the AMF and SMF.

[0092] UPF nodes perform the functions of a gateway through which user data is sent and received.

[0093] The Authentication Server Function (AUSF) authenticates and manages the UE. The Network Slice Selection Function (NSSF) is a node used for network slicing as described below.

[0094] Network Open Function (NEF) provides a mechanism to securely open up 5G core services and functions.

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

[0096] The radio interface protocol is based on the 3GPP radio access network specification. The radio interface protocol consists of a physical layer, a data link layer, and a network layer horizontally, and is vertically divided into a user plane for data information transmission and a control plane for control signal (signaling) transmission.

[0097] The protocol layer can be divided into L1 (layer-1), L2 (layer-2), and L3 (layer-3) based on the three layers of the Open Systems Interconnection (OSI) reference model, which is widely known in communication systems.

[0098] Each wireless protocol layer is described below. Figure 4 An example of a general architecture applicable to the fifth-generation (5G) system of this disclosure is illustrated.

[0099] Reference Figure 4 The access layer (AS) may include the physical (PHY) layer, the medium access control layer, the radio link control (RLC) layer, the packet data convergence protocol (PDCP) layer, and the radio resource control (RRC) layer, and the operation of each layer can be referenced to the descriptions in the standard documents previously published in this document.

[0100] Specific Implementation Methods of This Disclosure

[0101] This disclosure relates to apparatus and methods supporting LTM handover in wireless communication systems. More specifically, this disclosure relates to apparatus and methods for optimizing the early uplink synchronization process during L1 / L2 triggered mobility (LTM) within a centralized cell (CU) in a wireless communication system.

[0102] In the following description, a CU is a logical node that manages the RRC and PDCP protocols of an en-gNB or the RRC, SDAP, and PDCP protocols of a gNB, controlling the operation of at least one distributed unit (DU), and a DU is a logical node managing the RLC, MAC, and PHY layers of an en-gNB or gNB. The DU is partially controlled in operation by a CU connected via an F1 interface and supports at least one cell.

[0103] LTM is a cell handover process for a PCell (or PSCell) triggered by the network via MAC CE based on L1 measurements. The PCell is the primary cell of the primary cell group, and the PSCell is the primary cell of the secondary cell group.

[0104] Timing advance (TA) is the offset between the start of a downlink subframe received at the UE and the start of a transmitted uplink subframe, and the time alignment timer (TAT) is a timer that controls the uplink time alignment period for serving cells that the MAC entity considers to belong to the associated timing alignment group (TAG). Time alignment error (TAE) refers to the maximum timing difference between two different NR signals.

[0105] According to the Rel-18 Network Mobility Enhancement Research Project (WI), the following has been documented to support LTM, thereby reducing latency, overhead, and downtime during service cell changes.

[0106]

[0107] 3. Judgment

[0108] When a UE moves from the coverage area of ​​one cell to another, a serving cell change is required. The current serving cell change is triggered by L3 measurements and completed via a reconfiguration triggered by RRC signaling, which synchronizes changes for PCell and PSCell, and releases / additions for SCells where applicable. All cases involve a full L2 (and L1) reset, resulting in longer latency, greater overhead, and longer downtime compared to beam-switching mobility. The goal of L1 / L2 mobility enhancement is to enable serving cell changes via L1 / L2 signaling to reduce latency, overhead, and downtime.

[0109] In Rel-17 Conditional PSCell Change (CPC) / Conditional PSCell Addition (CPA), a UE configured with CPC / CPA must release the CPC / CPA configuration upon completing random access to the target PSCell. Therefore, the UE has no opportunity to perform subsequent CPC / CPA without prior CPC / CPA reconfiguration and reinitialization from the network. This increases cell change latency and signaling overhead, especially with frequent SCG changes during FR2 operation. Therefore, MR-DC with selective activation of cell groups aims to enable subsequent CPC / CPA after an SCG change without requiring reconfiguration and reinitialization of CPC / CPA preparation from the network. This results in reduced signaling overhead and shorter downtime for SCG changes.

[0110] Currently, CHO and MR-DC cannot be configured simultaneously. This limits the usefulness of both features when MR-DC is configured. If this was not addressed in Rel-17, Rel-18 should specify a mechanism for configuring CHO and MR-DC simultaneously. However, this alone may not be sufficient to optimize MR-DC mobility, as the radio link quality of the conditionally configured PSCell may be insufficient or not the optimal candidate PSCell when the UE accesses the target PCell, potentially impacting UE throughput. To mitigate this throughput impact, Rel-18 CHO+MRDC can consider CHO for CPC / CPA, including the target MCG and multiple candidate SCGs.

[0111] 4. Objectives

[0112] 4.1 Target of SI or core WI or test WI

[0113] The specific objective of this work project is: 1. To specify the mechanisms and processes for L1 / L2-based inter-cell mobility for mobility latency reduction: - Configure and maintain multiple candidate cells to allow for rapid application of configurations for candidate cells [RAN2, RAN3] Dynamic handover mechanisms in candidate serving cells (including SpCell and SCell) based on potential L1 / L2 signaling application scenarios [RAN2, RAN1] L1 enhancements for inter-cell beam management include L1 measurement and reporting, as well as beam indication [RAN1, RAN2]. - Note 1: Early RAN2 involvement is necessary, including further clarifying the possibility of interaction between this project symbol and previous project symbols. - Note 2: Only SSB-based L1 measurements are supported in this version.

[0114] Scheduled advance management [RAN1, RAN2] If needed, CU-DU interface signaling is used to support L1 / L2 mobility [RAN3]. Note 3: FR2-specific enhancements (if any) are not excluded.

[0115] Note 4: The L1 / L2-based inter-cell mobility process is applicable to the following scenarios: - For independent, CA, and NR-DC cases involving changes to the serving cell within a CG, the MCG takes precedence. - Intra-DU and intra-CU DU scenarios (applicable to standalone and CA: no new RAN interfaces expected) - Both within and between frequencies - Both FR1 and FR2 - The source cell and the target cell can be synchronous or asynchronous.

[0116]

[0117] To enable rapid service cell changes, agreements have been made regarding early DL / UL synchronization prior to handover of designated cells under LTM and handover based on L1 measurement reports triggered by MAC CE. Corresponding work is underway for intra-CU LTM in Rel-18. Intra-CU LTM can include inter-DU LTM or intra-DU LTM.

[0118] Figure 5a and Figure 5b This is an example of an inter-DU LTM procedure applicable to this disclosure. When a UE moves from one DU within a CU of a gNB to another DU within the same gNB during an NR operation for LTM, it can use... Figure 5a and Figure 5b The process.

[0119] Reference Figure 5a and Figure 5b In step 1, L3 measurement control and reporting are performed. UE 510 sends an L3 measurement report message, including measurement results for neighboring cells, to source gNB-DU 520-1. Source gNB-DU 520-1 sends the received L3 measurement report message to gNB-CU 530. Source gNB-DU 520-1 may send a UL RRC message transmission message, including the L3 measurement report message, to source gNB-DU 520-1.

[0120] 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.

[0121] In step 3, gNB-CU 530 sends a UE Context Establishment Request message to candidate gNB-DU 520-2. The UE Context Establishment Request message may include the cell ID of a candidate target cell. gNB-CU 530 uses the UE Context Establishment Request message to indicate the ID of source gNB-DU 520-1 to candidate gNB-DU 520-2 and request PRACH resources. gNB-CU 530 may request candidate gNB-DU 520-2 to provide information related to lower-layer configuration to generate reference configuration information to be used for LTM.

[0122] In step 4, candidate gNB-DU 520-2 sends a UE context establishment response message to gNB-CU 530. When an LTM configuration request for a candidate target cell is accepted, candidate gNB-DU 520-2 can respond to gNB-CU 530 using a UE context establishment response message, which includes information related to the generated lower-layer RRC configuration and information related to the reference signal (RS) configuration for the accepted candidate target cell. For example, the information related to the RRC configuration may include at least one of information related to the Transport Configuration Indicator (TCI) state configuration or information related to the Random Access Channel (RACH) configuration.

[0123] When there is at least one candidate target cell among the candidate gNB-DU 520-2, the UE context establishment in steps 3 to 4 can be performed separately for each candidate target cell.

[0124] In step 5, gNB-CU 530 sends a UE context modification request message to source gNB-DU 520-1. gNB-CU 530 may send a UE context modification request message to source gNB-DU 520-1a, which includes at least one of the following: information related to RS configuration, messages related to TCI state configuration, or information related to RACH configuration collected for at least one accepted candidate target cell (e.g., candidate gNB-DU 520-2) of other gNB-DUs.

[0125] In step 6, the source gNB-DU 520-1 sends a UE context modification response message to the gNB-CU 530. The UE context modification response message may include at least one of the following: information related to the RS configuration of the source cell, candidate cells prepared for LTM, or information related to the configuration of the generated CSI report.

[0126] In step 7, gNB-CU 530 sends a UE context modification request message to candidate gNB-DU 520-2. The UE context modification request message may include at least one of the following: the cell ID of at least one prepared candidate cell or information related to the associated RS configuration for each candidate cell in at least one other candidate gNB-DU. gNB-CU 530 may provide lower-layer configuration information from the reference configuration information to candidate gNB-DU 520-2. Here, the candidate cell may be the same cell as the source cell.

[0127] In step 8, candidate gNB-DU 520-2 responds to gNB-CU 530 using a UE context modification response message. The UE context modification response message includes updated lower-layer configuration information, which includes information related to the generated CSI report configuration.

[0128] In step 9, gNB-CU 530 sends a DL RRC message transmission message to the source gNB-DU 520-1. The DL RRC message transmission message may include a generated RRCReconfiguration message with LTM configuration.

[0129] 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 sends an RRCReconfigurationComplete message to the source gNB-DU 520-1. In step 12, the source gNB-DU 520-1 sends a UL RRC message transmission message including the RRCReconfigurationComplete message to the gNB-CU 530.

[0130] In step 13, early synchronization is performed. The early synchronization process may include an early TA acquisition process. The early TA acquisition process may be performed as defined in TS38.300.

[0131] In step 14, candidate gNB-DU 520-2 sends a notification message regarding TA information to source gNB-DU 520-1 via gNB-CU 530. The notification message regarding TA information may include at least one of the following: TA value, associated CFRA resource information, candidate cell ID, or source gNB-DU ID.

[0132] In step 15, UE 510 sends a report message regarding the lower-layer measurement results to source gNB-DU 520-1. In step 16, source gNB-DU 520-1 determines LTM cell handover. That is, source gNB-DU 520-1 determines to perform LTM to handover to the candidate target cell.

[0133] In step 17, the source gNB-DU 520-1 sends an LTM command to the UE 510.

[0134] In step 18, the source gNB-DU 520-1 sends a notification message for LTM cell change to the gNB-CU 530. The notification message for LTM cell change may include a message indicating that an LTM command has been initiated to the UE 510. For example, the notification message for LTM cell change may include at least one of a target cell ID or a TCI status ID. The TCI status ID may indicate the selected beam information.

[0135] In step 19, gNB-CU 530 sends a notification message for LTM cell change to candidate gNB-DU 520-2, including the target cell ID and TCI status ID.

[0136] In step 20, candidate gNB-DU 520-2 detects UE 510 as the target gNB-DU access, and in step 21, sends an access success message to gNB-CU 530. The access success message may include the cell ID of the target cell.

[0137] In step 22, gNB-CU 530 sends a UE context release command to source gNB-DU 520-1. The UE context release command can request the release of resources of the prepared cell.

[0138] In step 23, the source gNB-DU 520-1 sends a UE context release complete message to the gNB-CU 530. The source gNB-DU 520-1 can release the resources of the prepared cell and respond to the gNB-CU 530 with the UE context release complete message.

[0139] As described with reference to FIG5, uplink TA values ​​for some candidate cells are obtained through an early TA acquisition process. However, according to the present discussion, the uplink TA values ​​for some candidate cells obtained as described above may only be used by the current serving DU that triggered the process and cannot be reused by another serving DU in subsequent LTM operations. For example, as shown in step 17 of FIG5, when the source DU triggers a cell handover to one of the candidate cells in the candidate DU, as shown in step 20 of FIG5, the cell that the UE successfully accesses becomes the new serving cell. At this time, the UE experiences another handover to other candidate cells, including the previous serving cell, for subsequent LTM operations.

[0140] For rapid serving cell changes, early uplink synchronization from the current serving cell to candidate cells can be performed again. However, the TA acquisition process for some candidate cells may have already been performed, and the uplink TA values ​​for some candidate cells may have already been provided to the previous serving DU (e.g., the source DU in Figure 5). Of course, due to UE mobility, these previously acquired TA values ​​may no longer be valid. However, depending on (1) network deployment, (2) the speed at which the UE experiences serving cell changes, and (3) the TAT configured for the candidate cells of the UE, the previously calculated uplink TA values ​​for some candidate cells may still be valid. Here, the TAT value of the candidate cell can be as high as 10.240 seconds, and can also be set to infinity according to TS 38.331. If the previously calculated uplink TA values ​​for some candidate cells are still valid, it is not necessary to re-trigger the early TA acquisition process for obtaining those TA values ​​from the new serving DU.

[0141] Additionally, the UE can be configured by the network to perform UE-based TA measurements from the current serving cell toward candidate cells. In this case, the UE measures or derives the 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). Thus, when the UE is configured to perform UE-based TA measurements from the current serving cell toward candidate cells, it is agreed that when the UE's serving cell switches from the current serving cell to the candidate cell, the UE applies the pre-measured TA value for that candidate cell and performs RACH-free LTM. In this case, it is not necessary to trigger an early TA acquisition process for those candidate cells from the serving DU to perform RACH-free LTM. However, during the current LTM preparation phase, the serving DU is unaware whether the UE has been configured to perform UE-based TA measurements. Of course, during the LTM preparation phase, the CU can request the DU to prepare lower-layer configurations (e.g., reference signal configurations for measuring the received signal time difference between the current serving cell and the candidate cell) for each candidate cell based on the UE-based TA measurements. However, a request for lower-layer configuration from the CU does not mean that the UE should always be configured this way. In other words, whether to configure UE-based TA measurement and for which candidate cells to configure UE-based TA measurement are entirely determined by the CU.

[0142] When the serving cell changes during LTM, the CU can determine whether to reconfigure UE-based TA measurements on a per-candidate-cell basis, depending on which cell the UE is currently being served. For example, Figure 5a and Figure 5bAs shown, when the serving cell changes from a source DU (e.g., source gNB-DU 520-1) to one of the candidate cells of a candidate DU (e.g., candidate gNB-DU 520-2), the CU can decide to reconfigure UE-based TA measurements to the UE for subsequent LTMs toward at least some of the other candidate cells of the candidate DU. For example, when some candidate cells in the candidate DU coexist with the current new serving cell in the candidate DU and all operate within the FR1 frequency so that the downlink TAE of the UE between the serving cell and the candidate cells can be maintained within 260 ns (according to the RAN4 convention), the CU can decide to reconfigure UE-based TA measurements to the UE for these 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.

[0143] Therefore, this disclosure proposes a mechanism to optimize the early uplink synchronization process during LTM within the CU.

[0144] This disclosure describes methods and apparatus for optimizing the early uplink synchronization process during LTM within a CU by sharing pre-acquired TA values ​​of some candidate cells when the serving cell changes across DUs, and notifying the current serving DU whether the UE has been configured and / or reconfigured to perform UE-based TA measurements for some candidate cells.

[0145] Figure 6a and Figure 6b This is an example of a process for optimizing the early uplink synchronization process during LTM within the CU, according to an embodiment of this disclosure.

[0146] Reference Figure 6a and Figure 6b In step S601, the source DU (S-DU) 620 operates as the current serving DU of UE 610. S-DU 620 is connected to CU 630 via the F1 interface and manages the current serving cell of UE 610. At this time, candidate DUs (C-DUs) 640-1 and 640-2 are connected to CU 630 via the F1 interface and manage at least one candidate cell that is not the current serving cell of UE 610.

[0147] In step S603, CU 630 determines LTM for UE 610. For example, CU 630 can receive an L3 measurement report message from UE 610 and decide to initiate LTM configuration based on the L3 measurement report message. The L3 measurement report message may include the UE's measurement results for neighboring cells. Specifically, UE 610 may send the L3 measurement report message to S-DU 620, and S-DU 620 may send a UL RRC message transmission message including the received L3 measurement message to CU 630. CU 630 can then determine to initiate LTM configuration for UE 610 based on the L3 measurement report message.

[0148] In step S605, CU 630 determines the candidate cells to be prepared for LTM and checks whether UE 610 can perform UE-based TA measurement.

[0149] In step S607, candidate cells from S-DU 620, C-DU1 640-1, and / or C-DU2 640-2 are used to prepare LTM, and the prepared LTM is configured to the UE. During the LTM preparation phase, 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 measurements based on 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.

[0150] According to the implementation, step S607 may include the following operations (e.g., Figure 5a and Figure 5b (Steps 3 through 12 of the operation). Specifically, CU 630 can send a UE context establishment request message to C-DU1 640-1 and / or C-DU2 640-2, and receive a UE context establishment response message from C-DU1 640-1 and / or C-DU2 640-2. The UE context establishment request message may include the cell ID of the candidate target cell, and may include information indicating the ID of S-DU 620 and requesting PRACH resources. The candidate target cell can be determined based on the L3 measurement report message. The UE context establishment request message may request C-DU1 640-1 and / or C-DU2 640-2 to provide information related to the lower-layer configuration to generate reference configuration information to be used for LTM. The UE context establishment response message may include information related to the lower-layer RRC configuration for LTM configuration and information related to the RS configuration of the candidate target cell for LTM acceptance. For example, the information related to the RRC configuration may include at least one of information related to the TCI state configuration or information related to the RACH configuration.

[0151] Subsequently, CU 630 can send a UE context modification request message to S-DU 620 and receive a UE context modification response message from S-DU 620. The UE context modification request message may include at least one of the following: information related to RS configuration, messages related to TCI state configuration, or information related to RACH configuration collected for at least one accepted candidate target cell for other candidate DUs (e.g., C-DU1 640-1, C-DU2 640-2). The UE context modification response message may include at least one of the following: information related to the RS configuration of the source cell, prepared candidate cells, or information related to the generated CSI report configuration.

[0152] Additionally, CU 630 can send 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 can use the UE context modification request message to provide lower-level configuration information (e.g., information related to RS configuration, TCI status, or RACH configuration) from 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 the following: the cell ID of at least one prepared candidate cell or information related to the associated RS configuration of 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-level configuration information with information related to the generated CSI report configuration.

[0153] CU 630 can send a DL RRC message transmission message to S-DU 620, including an RRCReconfiguration message containing reference configuration information for LTM, and S-DU 620 can send the received RRCReconfiguration message to UE 610. UE 620 can send an RRCReconfigurationComplete message to S-DU 620, and S-DU 620 can send a UL RRC message transmission message to CU 630, including the RRCReconfigurationComplete message.

[0154] In step S609, CU 630 sends a notification message for UE-based TA measurement to S-DU 620. This notification message can be sent for some candidate cells. According to an implementation, when the UE is capable of performing UE-based TA measurement and UE-based TA measurement has been configured via RRC for some candidate cells in step S607, CU 630 can send a notification message for UE-based TA measurement for those candidate cells to S-DU 620, which is the current serving DU. Therefore, the early TA acquisition process for those candidate cells can be skipped. Alternatively, when configuring UE-based TA measurement configuration for the UE via LTM cell handover command, CU 630 can notify S-DU 620 of the candidate cells to which UE-based TA measurement applies, allowing S-DU 620, as the current serving DU, to skip the early TA acquisition process for those candidate cells. Furthermore, this allows the UE to be configured to perform UE-based TA measurement via LTM cell handover command when those candidate cells are triggered for mobility.

[0155] In step S611, an early TA acquisition process is performed. Early TA acquisition can be performed by S-DU 620 for LTM without RACH. The early TA acquisition process can also be performed by S-DU 620 for at least one other candidate cell among other DUs (e.g., C-DU1 640-1 and / or C-DU2 640-2). In this case, the early TA acquisition process for some candidate cells indicated by the notification message for UE-based TA measurement can be skipped or omitted. For example, the early TA acquisition process can be performed for at least one other candidate cell besides those indicated by the notification message for UE-based TA measurement. According to the implementation, TA information for those candidate cells indicated by the notification message for UE-based TA measurement can be obtained based on the UE-based TA measurement operation.

[0156] According to the implementation, step S611 may include the following operations (e.g., Figure 5a and Figure 5b(Steps 13 to 14 of the operation). Specifically, the S-DU 620 can perform an early TA acquisition process for at least one other candidate cell and obtain TA information for at least one other candidate cell obtained through the early TA acquisition process. For example, C-DU1 640-1 and / or C-DU2 640-2 corresponding to at least one other candidate cell can obtain TA information for the candidate cell through the early TA acquisition process and send a notification message to the S-DU 620 including the obtained TA information for at least one candidate cell. The notification message including TA information may also include at least one of the associated CFRA resource information, the cell ID of the candidate cell, or the ID of the S-DU.

[0157] In step S613, UE 610 receives a message commanding the cell to switch to the candidate target cell of C-DU1 640-1. At this time, UE 610 can access the candidate target cell of C-DU1 640-1 based on the command message.

[0158] According to the implementation, step S613 may include the following operations (e.g., Figure 5a and Figure 5b (Steps 15 to 19). For example, UE 610 can send a report message for lower-layer measurement results to S-DU 620. S-DU 620 can determine LTM cell handover based on the report message for lower-layer measurement results and send an LTM command instructing UE 610 to hand over to a candidate target cell. Additionally, S-DU 620 can send a notification message for LTM cell change to CU 630 (indicating that an LTM command has been sent to UE 610), and CU 630 can send a notification message for LTM cell change to the DU to which the candidate target cell belongs (e.g., C-DU1 640-1). The notification message for LTM cell change can include at least one of the candidate target cell's cell ID or TCI status ID as a message indicating that an LTM command has been initiated to UE 610. The TCI status ID can indicate the selected beam information. The notification message for LTM cell change can also include valid TA information for at least one candidate cell maintained by S-DU 620, which is the current serving DU. Here, the valid TA information may have been obtained through an early TA acquisition process triggered by the S-DU 620, and may include at least one valid TA value corresponding to at least one candidate cell.

[0159] In step S615, C-DU1 640-1 sends an access success message to CU 630. C-DU1 640-1 can detect the access of UE 610 and send an access success message to CU 630 including the ID of the target cell to which UE 610 has successfully accessed. In step S617, C-DU1 640-1 can begin serving DU operation as UE 610.

[0160] In step S619, CU 630 confirms that the serving cell has been successfully changed across DU via LTM. CU 630 can confirm the changed serving cell of UE 610 based on the target cell ID included in the access success message.

[0161] In step S621, CU 630 sends a message requesting valid TA information to S-DU 620, which is the previous serving DU. In step S623, S-DU 620, which is the previous serving DU, sends a response message including valid TA information. For example, the response message may include at least one valid TA value for at least one candidate cell. In step S625, CU 630 sends the valid TA information obtained from S-DU 620, which is the previous serving DU, to C-DU1 640-1, which is the new serving DU. That is, CU 630 can retrieve the valid TA information for at least one candidate cell from S-DU 620, which is the previous serving DU, and provide the retrieved valid TA information for at least one candidate cell to C-DU1 640-1, which is the new serving DU. Here, the valid TA information may have been obtained through an early TA acquisition process triggered by S-DU 620, which is the previous serving DU, and may include at least one valid TA value corresponding to at least one candidate cell.

[0162] In step S627, CU 630 sends a notification message for UE-based TA measurement to C-DU1 640-1. This notification message can be sent for some candidate cells. These candidate cells may be the same as or different from the candidate cells in step S609. According to the implementation, when the UE is capable of performing UE-based TA measurement and has configured UE-based TA measurement for some candidate cells via RRC, CU 630 can send a notification message for UE-based TA measurement for those candidate cells to C-DU1 640-1, which is the current serving DU. This allows skipping the early TA acquisition process for those candidate cells. Alternatively, when configuring UE-based TA measurement configuration for the UE via LTM cell handover command, CU 630 can notify C-DU1 640-1 of the candidate cells to which the UE-based TA measurement applies, allowing C-DU1 640-1, which is the current serving DU, to skip the early TA acquisition process for those candidate cells. Additionally, this allows the UE to be configured to perform UE-based TA measurements via LTM cell handover commands when those candidate cells are triggered for mobility.

[0163] In step S629, an early TA acquisition process is performed. Early TA acquisition can be performed by C-DU1640-1 as a new serving DU for LTM without RACH. The early TA acquisition process can also be performed by C-DU1640-1 for at least one other candidate cell among other DUs (e.g., S-DU1620 and / or C-DU2640-2 as previous serving DUs). In this case, the early TA acquisition process for some candidate cells indicated by the notification message for UE-based TA measurement can be skipped or omitted. For example, the early TA acquisition process can be performed for at least one other candidate cell besides those indicated by the notification message for UE-based TA measurement. According to the implementation, TA information for those candidate cells indicated by the notification message for UE-based TA measurement can be obtained based on the UE-based TA measurement operation.

[0164] According to the implementation, step S629 may include the following operations (e.g., Figure 5a and Figure 5b(Steps 13 to 14 of the operation). Specifically, C-DU1 640-1 can perform an early TA acquisition process for at least one other candidate cell and obtain TA information for at least one other candidate cell obtained through the early TA acquisition process. For example, S-DU1 620 and / or C-DU2 640-2 corresponding to at least one other candidate cell can obtain TA information for the candidate cell through the early TA acquisition process and send a notification message including the obtained TA information for at least one candidate cell to C-DU1 640-1, which is the new serving DU. The notification message including TA information may also include at least one of the associated CFRA resource information, the cell ID of the candidate cell, or the ID of C-DU1 640-1, which is the current serving DU.

[0165] In step S631, UE 610 receives a message commanding the cell to switch to a candidate cell of C-DU2 640-2. At this time, UE 610 can access the candidate target cell of C-DU2 640-2 based on the command message.

[0166] According to the implementation, step S631 may include the following operations (e.g., Figure 5a and Figure 5b(Steps 15 to 19). For example, UE 610 can send a report message for lower-layer measurement results to C-DU1 640-1, which is the current serving DU. C-DU1 640-1, which is the current serving DU, can determine the LTM cell handover for UE 610 based on the report message for lower-layer measurement results and send an LTM command instructing UE 610 to hand over to the candidate target cell. In addition, C-DU1 640-1 can send a notification message for LTM cell change to CU 630 (the notification message indicates that an LTM command has been sent to UE 610), and CU 630 can send a notification message for LTM cell change to the DU to which the candidate target cell belongs (e.g., C-DU2 640-2). The notification message for LTM cell change may include a message indicating that an LTM command has been initiated to UE 610. The notification message for LTM cell change may include at least one of the cell ID or TCI status ID of the candidate target cell. The TCI status ID may indicate the selected beam information. The notification message for LTM cell changes may also include valid TA information for at least one candidate cell maintained by C-DU1 640-1, which is the current serving DU. Here, the valid TA information may include at least one valid TA value corresponding to at least one candidate cell, which may be the valid TA information for at least one candidate cell received by C-DU1 640-1 from CU 630 in step S625, or obtained through an early TA acquisition process triggered by C-DU1 640-1.

[0167] In step S633, C-DU2 640-2 sends an access success message to CU 630. C-DU2 640-2 can detect the access of UE 610 and send an access success message to CU 630 including the ID of the target cell to which UE 610 has successfully accessed. In step S635, C-DU2 640-2 can begin serving DU operation as UE 610.

[0168] In step S637, CU 630 confirms that the serving cell has been successfully changed across DU via LTM. CU 630 can confirm the changed serving cell of UE 610 based on the target cell ID included in the access success message.

[0169] In step S639, CU 630 sends a message requesting valid TA information to C-DU1 640-1, which is the previous serving DU. In step S641, C-DU1 640-1, which is the previous serving DU, sends 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, CU 630 sends the valid TA information obtained from C-DU1 640-1, which is the previous serving DU, to C-DU2 640-2, which is the new serving DU. That is, CU 630 can retrieve the valid TA information from C-DU1 640-1, which is the previous serving DU, and provide the retrieved valid TA information to C-DU2 640-2, which is the new serving DU. Here, the valid TA information may include at least one valid TA value corresponding to at least one candidate cell. The at least one valid TA value may be the valid TA information for at least one candidate cell received from CU 630 in step S625 by C-DU1 640-1 as the previous serving DU or obtained through an early TA acquisition process triggered by C-DU1 640-1 as the previous serving DU.

[0170] In step S645, CU 630 sends a notification message for UE-based TA measurement to C-DU2 640-2. This notification message can be sent for some candidate cells. These candidate cells may be the same as or different from the candidate cells in step S609 or S627. According to the implementation, when the UE is capable of performing UE-based TA measurement and has configured UE-based TA measurement for some candidate cells via RRC, CU 630 can send a notification message for UE-based TA measurement for those candidate cells to C-DU2 640-2, which is the current serving DU. This allows skipping the early TA acquisition process for those candidate cells. Alternatively, when configuring UE-based TA measurement configuration for the UE via LTM cell handover command, CU 630 can notify C-DU2 640-2 of the candidate cells to which the UE-based TA measurement applies, allowing C-DU2 640-2, which is the current serving DU, to skip the early TA acquisition process for those candidate cells. Additionally, this allows the UE to be configured to perform UE-based TA measurements via LTM cell handover commands when those candidate cells are triggered for mobility.

[0171] As described above, this disclosure relates to methods and apparatus for supporting LTM and configuring UE in wireless communication systems.

[0172] According to the implementation method, the CU of the base station can confirm that the UE is capable of performing UE-based TA measurements for at least one candidate cell. The CU can notify the DU that UE-based TA measurements have been configured for the UE, or that UE-based TA measurements will be applicable to at least one candidate cell. Here, the DU can be the UE's current serving DU, as it is involved in the process of preparing at least one candidate cell for LTM and configuring LTM for the UE.

[0173] According to the implementation method, the CU of the base station can detect successful cell handover across DUs. Here, the DU may include the DU involved in the process of preparing candidate cells for LTM and configuring LTM to the UE. The CU retrieves valid TA information of at least one candidate cell from the previous serving DU and provides the retrieved TA information to the new serving DU. Here, the valid TA information of at least one candidate cell may be TA information obtained through an early TA acquisition process triggered by the previous serving DU.

[0174] Figure 7 An example of a process for sending TA measurement-related information according to an embodiment of this disclosure is illustrated. Figure 7 An example of a method performed by a control node of a base station is illustrated. The base station includes NG-RAN nodes, and the control node may include the CU of the NG-RAN nodes. The control node may connect to multiple distributed nodes (e.g., DUs) via an F1 interface.

[0175] Reference Figure 7 In step S701, the control node initiates LTM configuration for the UE. The control node can determine whether to initiate LTM configuration within a CU of the base station based on the L3 measurement report message received from the UE. Intra-CU LTM can include at least one of inter-DU LTM within the same CU or intra-CU LTM. The L3 measurement report message can include measurement results for neighboring cells. According to the implementation, the control node can determine candidate cells to be prepared for LTM and confirm that the UE can perform TA measurements based on the UE.

[0176] In step S703, the control node sends a first message related to UE-based TA measurement to a first distributed node. Here, the first distributed node may be the UE's current serving DU. The first message may indicate at least one candidate cell for 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 for at least one candidate cell can be performed. According to an embodiment, when the UE has been configured via RRC to perform UE-based TA measurement for at least one candidate cell, the control node may send 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 an embodiment, when the UE is configured to perform UE-based TA measurement via LTM cell handover command, the control node may send 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. Thus, the control node can control the skipping or omitting of the early TA acquisition process for at least one candidate cell among the candidate cells prepared for LTM. In addition, the control node may configure the UE via LTM cell handover command such that when at least one candidate cell is triggered for mobility, UE-based TA measurement for the candidate cell is performed.

[0177] According to the implementation method, the control node of the base station can be a reference. Figure 6a and Figure 6b The CU630 described in the implementation instructions. The control node can also execute the reference... Figure 6a and Figure 6b At least one operation of the CU 630 described.

[0178] Figure 8 An example of a process for receiving TA measurement-related information according to an embodiment of the present disclosure is illustrated. Figure 8 An example of a method performed by a first distributed node of a base station is illustrated. 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 the control node (e.g., CU) of the base station via an F1 interface.

[0179] Reference Figure 8 In step S801, the first distributed node receives a first message related to UE-based TA measurement from the control node. The first distributed node may be the UE's current serving DU. 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 can be performed for at least one candidate cell.

[0180] In step S803, the first distributed node obtains the TA (Target Acquisition) for at least one other candidate cell based on the first message. The first distributed node can determine, based on the first message, at least one other candidate cell among the candidate cells prepared for LTM (Large-Term Memory) that requires the early TA acquisition process. For example, the first distributed node can identify at least one candidate cell that needs to skip or omit the early TA acquisition process based on the first message, and can control the execution of the early TA acquisition process for at least one other candidate cell besides the identified candidate cell. The first distributed node can obtain TA information for at least one other candidate cell by controlling the execution of the early TA acquisition process for at least one other candidate cell.

[0181] According to the implementation method, the first distributed node of the base station can be a reference. Figure 6a and Figure 6b The S-DU1 620, C-DU1 640-1, or C-DU2 640-2 are described in the implementation details. The first distributed node can also execute the reference... Figure 6a and Figure 6b At least one operation of the described S-DU1 620, C-DU1 640-1 or C-DU2 640-2.

[0182] Examples of the methods proposed above can also be included as one of the implementation methods of this disclosure; therefore, it is clear that they can be considered as types of proposed methods. Furthermore, the methods proposed above can be implemented independently, but can also be implemented as a combination (or merging) of some proposed methods. Rules can be defined such that the base station notifies the terminal via predefined signals (e.g., physical layer signals or higher layer signals) of information regarding whether to apply the proposed methods (or information about the rules governing the proposed methods).

[0183] This disclosure may be embodied in other specific forms without departing from the technical concept 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 this disclosure should be determined by a reasonable interpretation of the appended claims, and all variations within the equivalent scope of this disclosure are included within its scope. Furthermore, claims that are not explicitly referenced in the claims may be combined to form embodiments, or may be included as new claims by subsequent amendments.

[0184] Industrial applicability

[0185] The embodiments disclosed herein can be applied to a variety of wireless access systems. Examples of various wireless access systems include 3GPP or 3GPP2 systems.

[0186] The embodiments disclosed herein can be applied not only to the various wireless access systems described above, but also to all technical fields employing various wireless access systems. Furthermore, the proposed method can also be applied to millimeter-wave and THz communication systems using the ultra-high frequency band.

[0187] Furthermore, the embodiments disclosed herein can also be applied to various applications, such as autonomous vehicles and drones.

Claims

1. A method comprising the following steps: The control node of the base station determines the initiation of L1 / L2 triggered mobility (LTM) configuration for user equipment (UE); as well as The control node sends a first message related to UE-based timing advance (TA) measurement to the first distributed node among the distributed nodes of the base station. The first message includes information indicating at least one candidate cell for which the UE-based TA measurement is to be applied.

2. The method according to claim 1, wherein, The first distributed node includes a distributed node that manages the current serving cell of the UE.

3. The method according to claim 1, further comprising the following steps: Receive a second message from the first distributed node, which includes the TA information of the at least one candidate cell.

4. The method according to claim 3, further comprising the following step: Receive a second message, the second message indicating that the UE’s serving cell has changed from the first distributed node to the second distributed node based on LTM cell handover; as well as A third message is sent to the first distributed node requesting the TA information of the at least one candidate cell.

5. The method according to claim 3, further comprising the following step: A fourth message including the TA information of the at least one candidate cell is sent to the second distributed node.

6. The method according to claim 5, further comprising the following step: Send a fifth message related to the UE-based TA measurement to the second distributed node. The fifth message includes information indicating the at least one candidate cell for which the UE-based TA measurement is to be applied.

7. The method according to claim 1, wherein, The first message is sent based on the UE being configured via Radio Resource Control (RRC) to perform the UE-based TA measurement for the at least one candidate cell.

8. The method according to claim 1, wherein, The first message is sent based on the UE being configured to perform the UE-based TA measurement via an LTM cell handover command.

9. A method comprising the following steps: The first distributed node of the base station receives a first message related to the timing advance (TA) measurement based on the user equipment (UE) from the control node of the base station; as well as The first distributed node controls, based on the first message, to skip the early TA acquisition process for at least one candidate cell among a plurality of candidate cells for L1 / L2 triggered mobility (LTM). The first message includes information indicating the at least one candidate cell for which the UE-based TA measurement is to be applied.

10. The method according to claim 9, wherein, The first distributed node controls the execution of the early TA acquisition process for candidate cells other than the at least one candidate cell.

11. The method according to claim 9, wherein, The TA information for the at least one candidate cell is obtained through the UE-based TA measurement.

12. The method according to claim 9, further comprising the following step: The first distributed node receives valid TA information for some of the plurality of candidate cells used for the LTM from the control node. The valid TA information includes TA values ​​obtained through an early TA acquisition process triggered by the UE's previous serving distributed node.

13. The method according to claim 12, further comprising the following step: The first distributed node sends a notification message to the control node regarding the successful access of the UE. The valid TA information is received after the notification message is sent.

14. An apparatus, the apparatus comprising: transceiver; as well as The processor is connected to the transceiver. The processor controls: The base station's control node determines whether to initiate L1 / L2 triggered mobility (LTM) configuration for the user equipment (UE); and The control node sends a first message related to UE-based timing advance (TA) measurement to a first distributed node among the distributed nodes of the base station. The first message includes information indicating at least one candidate cell for which the UE-based TA measurement is to be applied.

15. An apparatus, the apparatus comprising: transceiver; as well as The processor is connected to the transceiver. The processor controls: The first distributed node of the base station receives a first message related to timing advance (TA) measurements based on user equipment (UE) from the control node of the base station; and The first distributed node, based on the first message, controls the skipping of the early TA acquisition process for at least one of the multiple candidate cells used for L1 / L2 triggered mobility (LTM). The first message includes information indicating the at least one candidate cell for which the UE-based TA measurement is to be applied.

16. A communication device, the communication device comprising: At least one processor; as well as At least one memory, connected to the at least one processor and storing instructions that, when executed by the at least one processor, cause the UE to perform operations. The operation includes: The base station's control node determines whether to initiate L1 / L2 triggered mobility (LTM) configuration for the UE; and The control node sends a first message related to UE-based timing advance (TA) measurement to the first distributed node among the distributed nodes of the base station. The first message includes information indicating at least one candidate cell for which the UE-based TA measurement is to be applied.

17. A non-transitory computer-readable medium storing at least one program instruction. in, The at least one program instruction causes the UE to perform an operation when executed by at least one processor. The operation includes: The base station's control node determines whether to initiate L1 / L2 triggered mobility (LTM) configuration for the UE; and The control node sends a first message related to UE-based timing advance (TA) measurement to the first distributed node among the distributed nodes of the base station. The first message includes information indicating at least one candidate cell for which the UE-based TA measurement is to be applied.

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