Apparatus and method for supporting handover in wireless communication system

Abstract

The present disclosure relates to an apparatus and a method for supporting handover in a wireless communication system and may comprise: a step of determining initiation of an L1L2 triggered mobility (LTM) configuration for at least one cell belonging to at least one other base station; a step of exchanging, between the base stations, a configuration of candidate cells for the LTM, resource allocation information for early TA acquisition, and information related to support for a cell change according to subsequent performing of the LTM; a UE reconfiguration completion step of an LTM candidate cell; a step of performing an early TA acquisition procedure, notifying a cell change between the base stations, and performing data forwarding according to the cell change; and the like.

Description

Device and method for supporting 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 LTM (L1L2 triggered mobility) 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 supporting LTM between centralized units (CUs) in a wireless communication system.

[0006] The present disclosure relates to a device and method for a serving CU to initiate LTM setup between CUs in a wireless communication system.

[0007] The present disclosure relates to a device and method for proposing LTM between CUs based on an L3 or L1 measurement report message in a wireless communication system.

[0008] The present disclosure relates to a device and method for proposing candidate cells for LTM between CUs based on an L3 or L1 measurement report message in a wireless communication system.

[0009] The present disclosure relates to a device and a method for proposing a preparation and setup procedure for LTM between CUs in a wireless communication system.

[0010] The present disclosure relates to a device and method for supporting early TA acquisition between CUs in a wireless communication system.

[0011] The present disclosure relates to a device and a method for proposing an LTM execution procedure between CUs in a wireless communication system.

[0012] The present disclosure relates to a device and method for transmitting and receiving information required for LTM operation between CUs in a wireless communication system.

[0013] The present disclosure relates to a device and method for instructing a terminal to change to a cell of a CU other than a serving CU in a wireless communication system.

[0014] 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.

[0015] As an example of the present disclosure, a method performed by a first control node of a first base station in a wireless communication system includes the steps of determining initiation of LTM (L1L2 triggered mobility) setup, and transmitting a first message related to setup of candidate cells for the LTM, wherein the candidate cells for the LTM include at least one cell belonging to at least one other base station, and wherein the first message can be transmitted to a second control node of a second base station included in the at least one other base station.

[0016] As an example of the present disclosure, a method performed by a first distributed node of a first base station in a wireless communication system includes the steps of receiving a measurement report message from a terminal, and transmitting a message proposing LTM (L1L2 triggered mobility) to a first control node of the first base station based on the measurement report message, wherein the measurement report message includes an L1 measurement report message, and the LTM may include an LTM between base stations.

[0017] As an example of the present disclosure, a method performed by a second control node of a second base station in a wireless communication system may include the steps of receiving a first message related to configuration of candidate cells for LTM (L1L2 triggered mobility) from a first control node of a first base station, performing configuration for the LTM for at least one of the candidate cells based on the first message, and transmitting a second message including information related to the at least one candidate cell to the first control node.

[0018] As an example of the present disclosure, a method performed by a terminal in a wireless communication system includes the steps of transmitting a measurement report message to a first distributed node of a first base station, and receiving a cell change message from the first distributed node, wherein the cell change message can instruct a cell change to a target cell belonging to a second distributed node of a second base station.

[0019] As an example of the present disclosure, in a wireless communication system, a first control node of a first base station includes a transceiver and a processor connected to the transceiver, the processor controlling the initiation of LTM (L1L2 triggered mobility) setup and transmitting a first message related to setup of candidate cells for the LTM, the candidate cells for the LTM including at least one cell belonging to at least one other base station, and the first message can be transmitted to a second control node of a second base station included in the at least one other base station.

[0020] As an example of the present disclosure, in a wireless communication system, a first distributed node of a first base station includes a transceiver and a processor connected to the transceiver, wherein the processor receives a measurement report message from a terminal and controls transmission of a message proposing LTM (L1L2 triggered mobility) to a first control node of the first base station based on the measurement report message, wherein the measurement report message includes an L1 measurement report message, and the LTM may include an LTM between base stations.

[0021] As an example of the present disclosure, in a wireless communication system, a second control node of a second base station includes a transceiver and a processor connected to the transceiver, wherein the processor is configured to receive a first message related to configuration of candidate cells for LTM (L1L2 triggered mobility) from a first control node of a first base station, perform configuration for the LTM for at least one of the candidate cells based on the first message, and transmit a second message including information related to the at least one candidate cell to the first control node.

[0022] As an example of the present disclosure, in a wireless communication system, a terminal includes a transceiver and a processor connected to the transceiver, wherein the processor controls to transmit a measurement report message to a first distributed node of a first base station and to receive a cell change message from the first distributed node, wherein the cell change message can instruct a cell change to a target cell belonging to a second distributed node of a second base station.

[0023] As an example of the present disclosure, a communication device includes at least one processor, and at least one computer memory coupled to the at least one processor and storing instructions that, when executed by the at least one processor, direct operations, the operations including: determining to initiate LTM (L1L2 triggered mobility) setup; and transmitting a first message related to setup of candidate cells for the LTM, wherein the candidate cells for the LTM include at least one cell belonging to at least one other base station, and wherein the first message can be transmitted to a second control node of a second base station included in the at least one other base station.

[0024] As an example of the present disclosure, a non-transitory computer-readable medium storing at least one instruction includes at least one instruction executable by a processor, the at least one instruction controlling a device to determine to initiate LTM (L1L2 triggered mobility) setup and to transmit a first message related to setup of candidate cells for the LTM, the candidate cells for the LTM including at least one cell belonging to at least one other base station, and the first message can be transmitted to a second control node of a second base station included in the at least one other base station.

[0025] The following effects may be achieved by embodiments based on the present disclosure.

[0026] The present disclosure can support LTM (L1 / L2 triggered mobility) between different NG-RAN nodes in a wireless communication system.

[0027] 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 resulting 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.

[0028] Figure 1 illustrates an example of a communication system applicable to the present disclosure.

[0029] FIG. 2 illustrates an example of a user equipment (UE) applicable to the present disclosure.

[0030] 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.

[0031] FIG. 4 illustrates an example of a general architecture of a 5G (5th generation) system applicable to the present disclosure.

[0032] Figures 5a and 5b illustrate examples of handover procedures between MNs regardless of whether SN changes are initiated by the MN.

[0033] Figure 6 illustrates an example of a successful procedure for preparing to add an S-NG-RAN node.

[0034] Figure 7 illustrates an example of a failure procedure for preparing to add an S-NG-RAN node.

[0035] FIG. 8 illustrates an example of an overall procedure for LTM between CUs according to an embodiment of the present disclosure.

[0036] FIGS. 9A to 9C illustrate examples of LTM preparation and setup procedures between CUs according to embodiments of the present disclosure.

[0037] FIG. 10A and FIG. 10B illustrate examples of an early TA acquisition procedure between CUs according to an embodiment of the present disclosure.

[0038] FIGS. 11A to 11C illustrate examples of LTM execution procedures between CUs according to embodiments of the present disclosure.

[0039] FIG. 12 illustrates an example of a procedure for triggering LTM according to an embodiment of the present disclosure.

[0040] FIG. 13 illustrates an example of an LTM preparation procedure according to an embodiment of the present disclosure.

[0041] FIG. 14 illustrates an example of an LTM preparation procedure according to an embodiment of the present disclosure.

[0042] FIG. 15 illustrates an example of a cell change procedure according to LTM settings according to an embodiment of the present disclosure.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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).

[0049] 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.

[0050] 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.

[0051] 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 be applied to systems implemented after the 3GPP 5G NR system and are not limited to a specific system.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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).

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Hereinafter, this specification is described based on the terms defined above.

[0060] 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).

[0061] 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.

[0062]

[0063] Communication system applicable to the present disclosure

[0064] 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.

[0065] 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.

[0066] Figure 1 illustrates an example of a communication system applied to the present disclosure.

[0067] 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.

[0068] 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).

[0069] 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 communication between base stations (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.

[0070] Figure 2 illustrates an example of a UE applicable to the present disclosure.

[0071] 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).

[0072] 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).

[0073] 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.

[0074] 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.

[0075] 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).

[0076] 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).

[0077] 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.

[0078] 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).

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 5G system architecture applicable to the present disclosure

[0084] 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.

[0085] 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.

[0086] - 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).

[0087] 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.

[0088] 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).

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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).

[0093] 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.

[0094] 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).

[0095] 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.

[0096] 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.

[0097] Figure 3 illustrates an example of functional separation of NG-RAN and 5GC (5th generation core) applicable to the present disclosure.

[0098] 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.

[0099] The UPF node functions as a gateway through which user data is transmitted and received.

[0100] The authentication server function (AUSF) authenticates and manages UEs. The Network Slice Selection Function (NSSF) is a node for network slicing, as described below.

[0101] The network exposure function (NEF) provides a mechanism to securely expose the services and functions of the 5G core.

[0102]

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] In the TS 37.340 standard document, the MR-DC procedure is described as follows:

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

[0110] 10.7.2 MR-DC (multi-radio dual connectivity) with 5GC

[0111] Inter-MN handover (with / without SN change) is used to transfer UE context data from a source MN to a target MN while the UE context is kept in one SN or moved to another SN. During an inter-MN handover, the target MN decides whether to keep or change the SN (or release the SN as described in Section 10.8). Only intra-RAT inter-MN handover is supported (e.g., not switching from NGEN-DC to NR-DC) regardless of SN change.

[0112] Figures 5a and 5b illustrate examples of handover procedures between MNs regardless of whether SN changes are initiated by the MN.

[0113] Note 1: For handover between master nodes without change of secondary node, the source SN and target SN shown in FIGS. 5a and 5b are the same nodes.

[0114] 1. The source MN initiates the handover procedure by initiating the Xn handover preparation procedure, which includes both MCG and SCG configuration. The source MN includes the source SN UE XnAP ID, SN ID, and the UE context of the source SN in the handover request message.

[0115] Note 2: The source MN can trigger an MN-initiated SN modification procedure (for the source SN) to retrieve the current SCG configuration and allow provision of data forwarding related information prior to step 1.

[0116] 2. If the target MN decides to keep the UE context in the source SN, the target MN sends an SN add request to the SN, which includes the SN UE XnAP ID as a reference to the UE context of the SN established by the source MN. If the target MN decides to change the SN allowing delta setup, the target MN sends an SN add request to the target SN, which includes the UE context of the source SN established by the source MN. Otherwise, the target MN may send an SN add request to the target SN, which does not include the SN UE XnAP ID or the UE context of the source SN established by the source MN.

[0117] 3. The (target) SN responds with an SN addition request confirmation. The (target) SN may include an indication of full or delta RRC configuration.

[0118] Note 2a0: In a CHO using SCG configuration, it is up to the target MN implementation to ensure that the CG-Config provided by the (target) SN is available for all CHO preparations.

[0119] 3a. For SN termination bearers using MCG resources, the target MN provides Xn-U DL TNL address information in the Xn-U Address Indication message.

[0120] 4. The target MN may include the MN RRC reconfiguration message to be transmitted to the UE to perform the handover in the handover request acknowledge message and provide the forwarding address to the source MN. If the target side performs PDU session splitting during the handover procedure, two or more data forwarding addresses corresponding to each node are included in the handover request acknowledge message. If the target MN and SN decide to maintain the UE context in the SN in steps 2 and 3, the target MN indicates to the source MN that the UE context in the SN is maintained.

[0121] 5a / 5b. The source MN sends an SN release request message to the source SN, which includes the cause indicating MCG mobility. The source SN confirms the release request. If the source MN receives an indication from the target MN, it indicates to the source SN that the SN's UE context is maintained. If the SN includes an indication that the UE context is maintained, the SN maintains the UE context.

[0122] 5c. The source MN transmits data forwarding information by sending an XN-U Address Indication message to the (source) SN. If the PDU session is fragmented at the target side, more than one data forwarding address may be provided.

[0123] 6. The source MN triggers the UE to perform a handover and apply the new settings.

[0124] 7 / 8. The UE synchronizes with the target MN and responds with an MN RRC Reset Complete message.

[0125] 9. If bearers requiring SCG radio resources are configured, the UE synchronizes with the (target) SN.

[0126] Note 2a1: The order in which the UE performs the random access procedure to the MN (step 7) and the random access procedure to the SN (step 9) is not defined.

[0127] 10. If the RRC connection re-establishment procedure is successful, the target MN notifies the (target) SN through an SN re-establishment complete message.

[0128] 11a. The source SN sends a Secondary RAT Data Usage Report message to the source MN, containing the data volume received and delivered to the UE over NR / E-UTRA radio as described in Section 10.11.2.

[0129] Note 2a2: The order in which the source SN sends the Secondary RAT Data Usage Report message and performs data forwarding with the MN / target SN is not defined. The SN may send the report when transmission of the relevant QoS is suspended.

[0130] 11b. The source MN sends a Secondary RAT Report message to the AMF, providing information about the NR / E-UTRA resources used.

[0131] 12. For bearers using RLC AM, the source MN sends an SN status transfer message containing the SN status received from the source SN to the target MN, if necessary. If necessary, the target SN forwards the SN status to the target SN.

[0132] 13. Data forwarding occurs on the source side, if applicable. If the SN is maintained, data forwarding for SN-terminating bearers or QoS flows stored in the SN may be omitted.

[0133] 14-17. The target MN initiates the path switching procedure. If the target MN includes multiple DL TEIDs for a single PDU session in the path switching request message, multiple UL TEIDs in the UPF for the PDU session must be included in the path switching confirmation message if there is a TEID update in the UPF.

[0134] Note 3: If the UPF for the SN contains new UL TEIDs, the target MN performs the SN modification procedure initiated by the MN and provides it to the SN.

[0135] 18. The target MN initiates a UE context release procedure for the source MN.

[0136] 19. Upon receiving a UE context release message from the source MN, the (source) SN releases the C-plane resources associated with the UE context for the source MN. Any ongoing data forwarding can continue. The SN does not release the UE context associated with the target MN if the SN release request message in step 5 includes a UE contest maintenance indication.

[0137] ----------------------------------------------------------------

[0138] Figure 6 illustrates an example of a successful procedure for preparing an S-NG-RAN node addition, and Figure 7 illustrates an example of a failed procedure for preparing an S-NG-RAN node addition. The S-NG-RAN node addition preparation is defined in the TS 38.423 specification document and is described as follows.

[0139] ----------------------------------------------------------------

[0140] 8.3.1. Preparing to Add S-NG-RAN Nodes

[0141] 8.3.1.1 General

[0142] The purpose of the S-NG-RAN node addition preparation procedure is to request the S-GN-RAN node to allocate resources for dual connectivity operation for a specific UE.

[0143] This procedure uses UE-related signaling.

[0144] 8.3.1.2 Successful operation

[0145] The M-NG-RAN node initiates the procedure by sending an S-NODE addition request message to the S-NG-RAN node.

[0146] When the M-NG-RAN node sends an S-NODE addition request message, timer TXn DCprep Start.

[0147] Resource allocation according to the values ​​of the Allocation and Retention Priority IE included in the QoS Flow Level QoS Parameters IE for each QoS flow shall follow the principles specified for the PDU Session Resource Establishment Procedure in TS 38.413 [5].

[0148] The S-NG-RAN node shall select an encryption algorithm based on the information in the UE Security Capabilities IE and the local preference list of AS encryption algorithms and apply the key indicated in the S-NG-RAN node Security Key IE as specified in TS 33.501

[0028] .

[0149] When the TSC Traffic Characteristics IE is included in the QoS flow of the S-NODE Addition Request message, the S-NG-RAN node shall behave identically to the NG-RAN node in the PDU session resource setup procedure specified in TS 38.413 [5].

[0150] When the Additional QoS Flow Information IE is included in the QoS flow of the S-NODE Addition Request message, the S-NG-RAN node shall behave identically to the NG-RAN node in the PDU session resource setup procedure specified in TS 38.413 [5].

[0151] For each GBR QoS flow, if the Alternative QoS Parameters Sets IE is included in the GBR QoS Flow Information IE, the S-NG-RAN node shall behave identically to the NG-RAN node in the PDU session resource setup procedure specified in TS 38.413 [5], if supported.

[0152] For each PDU session, if a Network Instance IE is included in the PDU Session Resources To Be Added List IE and the PDU Session Resource Setup Info - SN terminated IE is included in the PDU Session Resources To Be Added List IE and there is no Common Network Instance IE, the S-NG-RAN node shall use it when selecting transport network resources as specified in TS 23.501 [7], if supported.

[0153] For each GBR QoS flow, if the Offered GBR QoS Flow Information IE is included in the QoS Flows To Be Setup List IE contained in the PDU Session Resource Setup Info - SN terminated IE, the S-NG-RAN node may request the M-NG-RAN node to configure a DRB in which the corresponding QoS flow is mapped to an MCG resource.

[0154] For each PDU session, if the Non-GBR Resources Offered IE is included in the PDU Session Resources To Be Added List IE and is set to "true", the S-NG-RAN node may request the M-NG-RAN node to configure a DRB where the non-GBR QoS flows of the PDU session are mapped to MCG resources.

[0155] For each PDU session, if the PDU Session Resources To Be Added List IE contains a Common Network Instance IE in the PDU Session Resource Setup Info - SN terminated IE, the S-NG-RAN node shall use it when selecting transport network resources as specified in TS 23.501 [7], if supported.

[0156] Duplicate transmission:

[0157] - For each PDU session, if the Redundant UL NG-U UP TNL Information at UPF IE is included in the PDU Session Resource Setup Info - SN terminated IE, the S-NG-RAN node shall, if supported, use it as an uplink termination point for the user plane data of this PDU session for redundant transmission and shall include the DL NG-U UP TNL Information at NG-RAN IE in the PDU Session Resource Setup Response Info - SN terminated IE as described in TS 23.501 [7].

[0158] - For each PDU session, if a Redundant Common Network Instance IE is included in the PDU session resource configuration information - SN Termination IE, the S-NG-RAN node shall use it when selecting transport network resources for redundant transmission as specified in TS 23.501 [7], if supported.

[0159] - For each PDU session that contains a Redundant QoS Flow Indicator IE in the QoS Flows To Be Setup List IE included in the S-NODE Add Request message, the S-NG-RAN node shall store and use the Redundant QoS Flow Indicator IE, if supported, as specified in TS 23.501 [7].

[0160] - For each PDU session, if the Redundant PDU Session Information IE is included in the PDU Session Resource Setup Info - SN terminated IE of the S-NODE Add Request message, the S-NODE-RAN node shall store the received information in the UE context, if supported, and establish redundant user plane resources for that PDU session as specified in TS 23.501 [7].

[0161] - For each PDU session resource successfully established with a duplicate PDU Session Information IE included in the S-NODE Add Request message, the S-NG-RAN node shall include the Used RSN Information IE in the PDU Session Resource Setup Response Info - SN terminated IE of the S-NODE Add Request Acknowledge message, if supported. If the duplicate PDU Session Information IE includes a PDU Session Pair ID IE, the S-NG-RAN node may store it and use it to identify the paired PDU session.

[0162] If the S-NODE Addition Request message includes a Selected PLMN IE, the S-NG-RAN node may use it for RRM purposes.

[0163] If the S-NODE Addition Request message includes an Expected UE Behaviour IE, the S-NG-RAN node may store this information and use it to optimize resource allocation, if supported.

[0164] If the S-NODE Add Request message contains a Mobility Restriction List IE, the S-NG-RAN node stores this information, if supported, and uses it to select an appropriate SCG.

[0165] If the S-NODE Add Request message contains an index to the Index to RAT / Frequency Selection Priority IE, the S-NG-RAN node may use it for RRM purposes.

[0166] If the S-NG-RAN node is a gNB and the S-NODE ADD REQUEST message includes a PCell ID IE, the S-NG-RAN node shall search for a target NR cell among the NR neighbor cells of the specified PCell as specified in TS 37.340 [8].

[0167] If the S-NODE Add Request message includes an S-NG-RAN node PDU Session Aggregate Maximum Bit Rate IE, the S-NG-RAN node may use it for RRM purposes.

[0168] If the S-NODE ADD REQUEST message includes the MR-DC Resource Coordination Information IE, the S-NG-RAN node shall forward it to lower layers and may use it for resource coordination purposes with the M-NG-RAN node or to coordinate sidelink resources used by the M-NG-RAN node. The S-NG-RAN node shall consider the value of the received UL Coordination Information IE to be valid until it receives a new update of the IE for the same UE. The S-NG-RAN node shall consider the value of the received DL Coordination Information IE to be valid until it receives a new update of the IE for the same UE.

[0169] If the E-UTRA Coordination Assistance Information IE or the NR Coordination Assistance Information IE is included in the MR-DC Resource Coordination Information IE, the S-NG-RAN node uses that information, if supported, to determine additional coordination of resource utilization between the S-NG-RAN node and the M-NG-RAN node.

[0170] If the S-NODE Add Request message contains the NE-DC TDM Pattern IE, the S-NG-RAN node must forward it to lower layers for use as a single uplink transmission. The S-NG-RAN node must consider the value of the received NE-DC TDM Pattern IE valid until it receives a new IE update for the same UE.

[0171] If the S-NODE Add Request message includes a QoS Flow Mapping Indication IE, the S-NG-RAN node may consider that only uplink or downlink QoS flows are mapped to the DRB.

[0172] For each bearer for which PDCP entity allocation is requested at the S-NG-RAN node:

[0173] - The M-NG-RAN node may propose to apply downlink data forwarding by including a DL forwarding IE in the DL Forwarding IE within PDU Session Resource Setup Info - SN terminated IE of the S-NODE addition request message. For each bearer that it decides to accept, the S-NG-RAN node may indicate that it accepts the proposed downlink data forwarding for this bearer by including a DL Forwarding GTP Tunnel Endpoint IE in the PDU Session Resource Setup Response Info - SN terminated IE of the S-NODE addition request acknowledge message.

[0174] - The S-NG-RAN node may indicate that it requests data forwarding of uplink packets to be performed for the corresponding bearer by including a UL Forwarding GTP Tunnel Endpoint IE for each bearer in the PDU Session Resource Setup Response Info - SN terminated IE.

[0175] - The M-NG-RAN node shall include an RLC Mode IE for each bearer offloaded from the M-NG-RAN node to the S-NG-RAN node in the DRBs to QoS Flow Mapping List IE within the PDU Session Resource Setup Info - SN terminated IE of the S-NODE Addition Request message, where the RLC Mode IE indicates the mode used by the M-NG-RAN for the DRB when hosted on the M-NG-RAN node.

[0176] For each bearer in the M-NG-RAN node, the PDCP entity:

[0177] - The M-NG-RAN node includes an RLC mode IE for each bearer in the DRBs To Be Setup List IE within the PDU Session Resource Setup Info - MN terminated IE of the S-NODE Add Request message, indicating that the RLC mode has been configured in the M-NG-RAN node, so the S-NG-RAN node must configure the same RLC mode for this MN terminated split bearer.

[0178] The M-NG-RAN node may also propose to apply UL data forwarding when offloading QoS flows for which forwarding is requested in order by including a UL Forwarding Proposal IE in the Data Forwarding and Offloading Info from source NG-RAN node IE in the PDU Session Resource Setup Info - MN terminated IE of the S-NODE Addition Request message. The S-NG-RAN node may indicate that it accepts the proposed forwarding by including a PDU Session Level UL Data Forwarding UP TNL Information IE in the Data Forwarding Info from target NG-RAN node IE in the PDU Session Resource Setup Response Info - SN terminated IE of the S-NODE Addition Request Confirmation message.

[0179] If the S-NODE Add Request message includes the Masked IMEISV IE, the S-NG-RAN node shall use it to verify the UE's characteristics for further processing, if supported.

[0180] If the UE Radio Capability ID IE is included in the S-NODE Addition Request message, the S-NG-RAN node shall store this information in the UE context, if supported, and use it as defined in TS 23.501 [7] and TS 23.502

[0013] .

[0181] The S-NG-RAN node shall report the results for all requested PDU session resources to the M-NG-RAN node in the S-NODE Add Request Confirmation message in the following manner:

[0182] - The list of successfully established PDU session resources must be included in the PDU Session Resources Admitted To Be Added List IE.

[0183] - The list of PDU session resources for which establishment failed must be included in the PDU Session Resources Not Admitted List IE.

[0184] Upon receiving the S-NODE addition request confirmation message, the M-NG-RAN node sets the timer TXn DCprep must be stopped.

[0185] If the S-NODE Add Request Confirm message includes the MR-DC Resource Coordination Information IE, the M-NG-RAN node may use it for resource coordination with the S-NG-RAN node. The M-NG-RAN node shall consider the value of the received UL Coordination Information IE as valid until it receives a new update of the IE for the same UE. The M-NG-RAN node shall consider the value of the received DL Coordination Information IE as valid until it receives a new update of the IE for the same UE. If the E-UTRA Coordination Assistance Information IE or the NR Coordination Assistance Information IE is included in the MR-DC Resource Coordination Information IE, the M-NG-RAN node uses that information, if supported, to determine additional coordination of resource utilization between the M-NG-RAN node and the S-NG-RAN node.

[0186] The S-NG-RAN node may include a PDCP SN Length IE indicating the PDCP SN length for each bearer in the DRBs To Be Setup List IE of the S-NODE Add Request Confirmation message.

[0187] If the S-NG-RAN node UE XnAP ID IE (S-NG-RAN node UE XnAP ID IE) is included in the S-NODE addition request message, the S-NG-RAN node stores this information, if supported, and uses it as defined in TS 37.340 [8].

[0188] If the S-NODE Addition Request message contains a PDCP SN Length IE, the S-NG-RAN node stores this information, if supported, and uses it in the lower layer configuration of the relevant MN termination bearer.

[0189] If the S-NODE addition request message includes an SN Addition Trigger Indication IE, the S-NG-RAN node shall include an RRC config indication IE in the S-NODE addition request acknowledge message to inform the M-NG-RAN node whether the S-NG-RAN node has applied the full or delta configuration as specified in TS 37.340 [8].

[0190] If the S-NODE Add Request message contains an S-NG-RAN node Maximum Integrity Protected Data Rate Uplink IE or an S-NG-RAN node Maximum Integrity Protected Data Rate Downlink IE, the S-NG-RAN node shall use the received information when applying the maximum integrity protected data rate to the UE.

[0191] When a Security Indication IE is included in the PDU Session Resource Setup Info-SN terminated IE of an S-NODE Addition Request message, the behavior of the S-NG-RAN node shall be the same as specified for the same IE in the PDU Session Resources To Be Setup List IE of the handover preparation procedure for that PDU session, and the S-NG-RAN node shall include the Security Result IE in the PDU Session Resource Setup Response Info - SN terminated IE.

[0192] If the Security Result IE is included in the PDU Session Resource Setup Info - SN terminated IE of the S-NODE Addition Request message, the S-NG-RAN node may consider that information when deciding whether to perform user plane integrity protection or ciphering for the DRB established for the relevant PDU session. However, if the Split Session Indicator IE is included in the PDU Session Resource Setup Info - SN terminated IE and is set to "Split", the S-NG-RAN node shall perform user plane integrity protection or ciphering based on the information in the Security Result IE.

[0193] An S-NG-RAN node may consider this information when deciding whether to perform user plane integrity protection or ciphering for a DRB established for that PDU session. However, if the Split Session Indicator IE is included in the PDU Session Resource Configuration Information - SN Termination IE and set to "Split", then it shall perform user plane integrity protection or ciphering based on the information in the Security Result IE. If the S-NG-RAN node is an ng-eNB, it shall reject any PDU session for which the Integrity Protection Indication IE is set to "required" as specified in TS 33.501

[0028] . If the S-NG-RAN node or M-NG-RAN node is an ng-eNB, the S-NG-RAN node shall act according to clause 6.10.4 of TS 33.501

[0028] for PDU sessions established with the Integrity Protection Indication IE set to "preferred".

[0194] An S-NG-RAN node may include the S-NODE's Location Information IE (Location Information at S-NODE IE) in the S-NODE addition request confirmation message if such information is available from the S-NG-RAN node (Location Information at S-NODE IE).

[0195] If the S-NODE reporting location information IE (Default DRB Allowed IE) set to "pscell" is included in the S-NODE addition request, the S-NG-RAN node shall start providing information about the UE's current location. If the S-NODE location information IE is included in the S-NODE addition request confirmation, the M-NG-RAN node shall store the included information, which may be forwarded to the AMF.

[0196] If the Default DRB Allowed IE is included in the PDU Session Resource Setup Info - SN terminated IE of the S-NODE Add Request message and is set to "true", the S-NG-RAN node can configure a default DRB for the PDU session.

[0197] If the S-NODE Add Request confirmation message includes the DRB IDs taken into use IE, the M-NG-RAN node shall operate as specified in TS 37.340 [8], if applicable.

[0198] If a Trace Activation IE has been previously received for this UE, it shall be included in the S-NODE Addition Request message. If the Trace Activation IE is included in the S-NODE Addition Request message, the S-NG-RAN node shall initiate the requested trace functionality as described in TS 32.422

[0023] , if supported.

[0199] If the S-NODE add request message includes the trace enable IE

[0200] - If the MDT Activation IE is set to “Immediate MDT and Tracking”, the S-NG-RAN node initiates the requested tracking session and MDT session as described in TS 32.422

[0023] , if supported.

[0201] - If the MDT Activation IE is set to “Immediate MDT only”, the S-NG-RAN node initiates the requested MDT session as described in TS 32.422

[0023] , if supported, and the S-NG-RAN node ignores the Interfaces To Trace IE and the Trace Depth IE.

[0202] - For MDT Location Information IE within MDT Configuration IE, S-NG-RAN node stores this information if supported and considers it in the requested MDT session.

[0203]

[0204] - If the MDT Activation IE is set to “Immediate MDT only” and the Signaling based MDT PLMN List IE is included in the MDT Configuration IE, the S-NG-RAN node can use it to propagate the MDT configuration as described in TS 37.320

[0043] .

[0205] - For the Bluetooth Measurement Configuration IE within the MDT Configuration IE, the S-NG-RAN node shall consider it for MDT configuration as described in TS 37.320

[0043] , if supported.

[0206] - For the WLAN Measurement Configuration IE within the MDT Configuration IE, the S-NG-RAN node shall consider it for MDT configuration as described in TS 37.320

[0043] , if supported.

[0207] - For the Sensor Measurement Configuration IE within the MDT Configuration IE, the S-NG-RAN node shall consider it for MDT configuration as described in TS 37.320

[0043] .

[0208] - MDT Configuration IE and if the S-NG-RAN node is a gNB, at least MDT Configuration-NR IE must exist, and if the S-NG-RAN node is an ng-eNB, at least MDT Configuration-EUTRA IE must exist.

[0209] If the Requested Fast MCG recovery via SRB3 IE is set to "true" and included in the S-NODE Addition Request message and the S-NG-RAN node decides to configure fast MCG link recovery via SRB3 as specified in TS 37.340 [8], the S-NG-RAN node shall include the Available fast MCG recovery via SRB3 IE set to "true" in the S-NODE Addition Request Confirmation message, if supported.

[0210] If the QoS Monitoring Request IE is included in the QoS Flow Level QoS Parameters IE for a QoS flow included in the DRBs To Be Setup List IE of the PDU Session Resource Setup Info - MN terminated IE, the S-NG-RAN node shall use it to configure lower layers for delay measurement and QoS monitoring purposes as specified in TS 23.501 [7], if supported. If the QoS Monitoring Reporting Frequency IE is included in the QoS Flow Level QoS Parameters IE for a QoS flow included in the DRBs To Be Setup List IE of the PDU Session Resource Setup Info - MN terminated IE, the S-NG-RAN node shall use it for RAN partial delay reporting, if supported.

[0211] For each QoS flow successfully established at an S-NG-RAN node, if the QoS Monitoring Request IE is included in the QoS Flow Level QoS Parameters IE contained in the PDU Session Resource Setup Information - SN Termination IE, the S-NG-RAN node shall store this information and, if supported, perform delay measurement and QoS monitoring as specified in TS 23.501 [7]. If the QoS Monitoring Reporting Frequency IE is included in the QoS Flow Level QoS Parameters IE contained in the PDU Session Resource Setup Information - SN Termination IE, the S-NG-RAN node shall store this information and, if supported, use it for RAN partial delay reporting. If these QoS flows are included in the DRBs to be Established List IE of the PDU Session Resource Setup Response Information - SN Termination IE, the M-NG-RAN node shall use it to configure lower layers for the purposes of delay measurement and QoS monitoring, if supported. If the QoS Monitoring Reporting Frequency IE is included in the PDU Session Resource Setup Response Information - DRBs to be Set IE of the SN Termination IE, the M-NG-RAN node shall use it for RAN Partial Delay Reporting, if supported.

[0212] For each DRB configured as MN-Terminated Split Bearer / SCG Bearer, if the QoS Mapping Information IE is included in the DRB Allow List IE of the PDU Session Resource Setup Response Information - MN Termination IE of the S-NODE Add Request Confirmation message, the M-NG-RAN node shall use it, if supported, to set the DSCP and / or IPv6 Flow Label fields for downlink IP packets transmitted from the M-NG-RAN node to the S-NG-RAN node over the GTP tunnel specified in the UP Transport Layer Information IE.

[0213] If the Source NG-RAN Node ID IE is included in the S-NODE Add Request message, the S-NG-RAN node shall use it to determine the availability of a direct data path with the specified source NG-RAN node, if supported, and if a direct data forwarding path is available, the S-NG-RAN node shall include a Direct Forwarding Path Availability IE in the S-NODE Add Request Confirm message.

[0214] For a given QoS flow, if the Source DL Forwarding IP Address IE or both, the Source DL Forwarding IP Address IE and the Source Node DL Forwarding IP Address IE, are included in the PDU Session Resource Setup Information - Data Forwarding and Offload Information in the Source NG-RAN Node IE of the SN Termination IE included in the S-NODE Addition Request message, the S-NG-RAN node shall store this information if supported and use it as part of the ACL feature configuration task if the ACL feature is deployed.

[0215] If the Source DL Forwarding IP Address IE for a given QoS Flow is included in the QoS Flows IE mapped to the DRB list of the PDU Session Resource Setup Response Information - SN Termination IE included in the S-NODE Add Request Confirmation message, the M-NG-RAN node, if supported, stores this information and uses it as part of the ACL functionality to identify the source TNL address for data forwarding when preparing for a subsequent handover (if the ACL functionality is deployed).

[0216] If a Management Based MDT PLMN List IE is included in the S-NODE Addition Request message, the S-NG-RAN node, if supported, stores the received information in the UE context and uses this information to allow subsequent UE selection for the Management Based MDT as defined in TS 32.422

[0023] .

[0217] Upon receiving an S-NODE addition request message, the S-NG-RAN node starts collecting SCG information, if supported, and continues collecting it while the UE remains in one of the cells.

[0218] If the UE History Information from the UE IE is included in the S-NODE Addition Request message, the S-NG-RAN node stores this information if supported.

[0219] When the PSCell Change History IE (PSCell Change History IE) set to "Report Full History" is included in the S-NODE Addition Request message, the S-NG-RAN node signals the M-NG-RAN node the latest SCG UE history information on each PSCell change using the S-NG-RAN node initiated S-NG-RAN node modification procedure, if supported.

[0220] If the IAB Node Indication IE is included in the S-NODE Addition Request message, the S-NG-RAN node considers dual connectivity operation to the IAB node to be requested, if supported. In addition:

[0221] - If the No PDU Session Indication IE is included in the S-NODE Addition Request message, the S-NG-RAN node, if supported, considers the UE as an IAB node with no PDU session active, ignores the PDU Session Resources To Be Added List IE, and takes no action with respect to PDU session establishment. The M-NG-RAN node then ignores the PDU Session Resources Admitted To Be Added List IE in the S-NODE Addition Request Confirmation message, if supported.

[0222] - If the F1-terminating IAB-donor Indicator IE is included in the S-NODE Addition Request message, the S-NG-RAN node shall assume that it will be the F1-terminating IAB-donor of the IAB node, if supported, and shall behave as described in TS 38.401 [2].

[0223] If the CHO Information SN Addition IE is included in the S-NODE Addition Request message, the S-NG-RAN node shall consider that the S-NG-RAN node addition preparation procedure is triggered as part of a conditional handover. The Source M-NG-RAN Node ID IE and the Source M-NG-RAN Node UE XnAP ID IE may be used to identify other active S-NG-RAN node addition preparations associated with this UE. If the Estimated Arrival Probability IE is included in the CHO Information SN Addition IE included in the S-NODE Addition Request message, the S-NG-RAN node may use this information to allocate required resources to the UE.

[0224] If the SCG Activation Request IE is included in the S-NODE Add Request message, the S-NG-RAN node may use it to configure SCG resources as specified in TS 37.340 [8] and, if supported, shall include the SCG Activation Status IE in the S-NODE Add Request Confirm message. If the SCG Activation Request IE in the S-NODE Add Request message is set to "SCG Activated", the S-NG-RAN node shall activate SCG resources, if supported, and set the SCG Activation Status IE in the S-NODE Add Request Confirm message to "SCG Activated".

[0225] If a Conditional PSCell Addition Information Request IE is included in the S-NODE addition request message, the S-NG-RAN node shall consider the request as CPAC-related as described in TS 37.340 [8], if supported. Therefore, the S-NG-RAN node shall include a Conditional PSCell Addition Acknowledge IE in the S-NODE addition request acknowledge message, if supported.

[0226] If the conditional PSCell additional information confirmation is included in the S-NODE additional request confirmation message, the M-NG-RAN node shall consider the designated PSCell selected by the target SN as a candidate PSCell for CPAC, if supported.

[0227] If CG-CandidateList is included in the S-NG-RAN node to M-NG-RAN node container IE of the S-NODE Addition Request Confirmation message, the M-NG-RAN node shall use it for CPAC purposes, if supported.

[0228] If the Estimated Arrival Probability IE is included in the Conditional PSCell Additional Information Request IE contained in the S-NODE Additional Request message, the candidate target S-NG-RAN node can use this information to allocate resources required for the incoming CPAC procedure.

[0229] If an S-NG-RAN node UE Slice Maximum Bit Rate IE for a particular S-NSSAI is included in the S-NODE Addition Request message, the S-NG-RAN node shall store and use the received S-NG-RAN node UE Slice Maximum Bit Rate for all PDU sessions associated with the S-NSSAI for that UE as defined in TS 23.501 [7], if supported.

[0230] Interaction with the S-NG-RAN node reconfiguration completion procedure:

[0231] If the S-NG-RAN node allows at least one PDU session resource, the S-NG-RAN node sends an S-NODE addition request confirmation message to the M-NG-RAN node, except for the CPAC request, when the timer TXn DCoverall . When receiving the S-NODE reconfiguration complete message, TXn DCoverall If this is running, timer TXn DCoveral l is stopped.

[0232] Interacting with the activity notification process

[0233] Upon receiving an S-NODE Addition Request message containing a Desired Activity Notification Level IE, the S-NG-RAN node uses this information, if supported, to decide whether to trigger subsequent activation notification procedures based on the requested notification level.

[0234] 8.3.1.3 Unsuccessful Operations

[0235] If the S-NG-RAN node cannot accept any bearers or a failure occurs during the preparation of adding an S-NG-RAN node, the S-NG-RAN node sends an S-NODE Addition Request Reject message to the M-NG-RAN node with an appropriate cause value.

[0236] 8.3.1. Unsuccessful conditions

[0237] If an S-NG-RAN node receives an S-NODE addition request message that does not contain a PDU Session Resource To Be Added Item IE containing a PDU Session Resource Setup Information - SN Termination IE or a PDU Session Resource Setup Information - MN Termination IE, the S-NG-RAN node fails the S-NG-RAN node addition preparation procedure with an appropriate cause.

[0238] If the encryption support algorithms defined in the NR UE Security Capabilities IE (NR Encryption Algorithms IE) and the mandatory support of NEA0 in all UEs (TS 33.501

[0028] ) do not match the algorithms defined in the list of allowed encryption algorithms configured in the S-NG-RAN node (TS 33.501

[0028] ), the S-NG-RAN node rejects the procedure using an S-NODE Addition Request Reject message.

[0239] If the supported algorithms for integrity defined in the NR Integrity Protection Algorithms IE of the NR UE Security Capabilities IE do not match the algorithms defined in the S-NG-RAN node's list of allowed integrity protection algorithms (TS 33.501

[0028] ), the S-NG-RAN node shall reject the procedure using an S-NODE Add Request Reject message.

[0240] If an S-NG-RAN node receives an S-NODE Addition Request message containing a S-NG-RAN node UE XnAP ID IE that does not match an existing UE context with that ID, the S-NG-RAN node shall reject the procedure using an S-NODE Addition Request Reject message.

[0241] If an M-NG-RAN node receives an S-NODE Add Request Confirmation message containing a PDU Session ID value in the PDU Session Resources Admitted List IE and the PDU Session Resources Not Admitted List IE, the M-NG-RAN node considers the S-NG-RAN node resource setup for that PDU session to have failed.

[0242] If an S-NG-RAN node receives an S-NODE Add Request message containing a PDU Session Resource Configuration Information - SN Termination IE that includes a Split Session Indicator IE for a PDU session set to "Split", but does not include a Security Result IE and has either the Integrity Protection Indication IE or the Confidentiality Protection Indication IE set to "Preferred", it rejects the PDU session.

[0243] Interaction with the S-NG-RAN node release procedure initiated by the M-NG-RAN node:

[0244] If an M-NG-RAN node receives an S-NODE Add Request Confirm message that does not contain a PDU Session Resource Setup Response Information - SN Termination IE or a PDU Session Resource Setup Response Information - MN Termination IE in the PDU Session Resource Admitted To Be Added Item IE, the M-NG-RAN node triggers an M-NG-RAN node initiated S-NG-RAN node release procedure indicating an appropriate cause.

[0245] Timer TXn before the M-NG-RAN node receives the S-NODE addition request confirmation message DCprep If expires, the M-NG-RAN node considers the S-NG-RAN node addition preparation procedure as failed and triggers the M-NG-RAN node initiated S-NG-RAN node release procedure.

[0246] Interaction with the S-NG-RAN node reconfiguration completion and S-NG-RAN node decommissioning procedure initiated by the S-NG-RAN node:

[0247] Timer TXn before the S-NG-RAN node receives the S-NODE reconfiguration complete or S-NODE release request message. DCoverall Upon expiration, the S-NG-RAN node considers the requested RRC connection reconfiguration not applied by the UE and triggers an S-NG-RAN node release procedure initiated by the S-NG-RAN node.

[0248] -----------------------------------------------------------------------

[0249] Specific embodiments of the present disclosure

[0250] The present disclosure is directed to supporting LTM (L1L2 triggered mobility) handover in a wireless communication system. Specifically, the present disclosure relates to a device and method for supporting handover for LTM (inter-CU LTM) between centralized units (CUs) in a wireless communication system.

[0251]

[0252] 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.

[0253] ---------------------------------------------------------------------

[0254] 3. Justification

[0255] When a UE moves from one cell's coverage area to another, a serving cell change must occur at some point. 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.

[0256] 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.

[0257] 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.

[0258] 4. Objective

[0259] 4.1 SI or core part WI or testing part WI purpose

[0260] The detailed objectives of the research item are as follows:

[0261] 1. Define the mechanism and procedure of L1 / L2-based inter-cell mobility to reduce mobility delay:

[0262] - Configuration and maintenance of multiple candidate cells to enable rapid application of settings to candidate cells [RAN2, RAN3]

[0263] o Dynamic switching mechanism between candidate serving cells (including SpCell and SCell) for potentially applicable scenarios based on L1 / L2 signaling [RAN2, RAN1]

[0264] o L1 improvements for inter-cell beam management, including L1 measurements and reporting, and beam indications [RAN1, RAN2]

[0265] - Note 1: Early RAN2 engagement is needed, including the possibility of further clarifying the interactions between this bullet and previous bullets.

[0266] - Note 2: Only SSB-based L1 measurements are supported in this release.

[0267] o Timing advance management [RAN1, RAN2]

[0268] o CU-DU interface signaling to support L1 / L2 mobility, if required [RAN3]

[0269] Note 3: If there are specific improvements to FR2, this is not ruled out.

[0270] Note 4: L1 / L2 based inter-cell mobility procedures are applicable to the following scenarios:

[0271] - In standalone mode, CA, and NR-DC cases where there is a change in serving cell within a CG, MCG is given priority.

[0272] - For intra-DU cases and intra-CU inter-DU cases (applicable to standalone mode and CA; no new RAN interfaces are expected)

[0273] - Both within and between frequencies

[0274] - Both FR1 and FR2

[0275] - Source and target cells may or may not be synchronized.

[0276] ---------------------------------------------------------------------

[0277] To achieve fast serving cell change, early DL / UL synchronization before cell switch and LTM handover based on L1 measurement report triggered by MAC CE have been defined.

[0278] The LTM scenario in Rel-18 was limited to intra-CU cases, i.e., cases where a serving cell change occurs within cells belonging to a single CU. However, a serving cell change can also occur across multiple NG-RAN nodes. Therefore, the present disclosure proposes mechanisms to support LTM between different NG-RAN nodes, i.e., inter-CU LTM.

[0279] In the following description, a centralized unit (CU) is a logical node that hosts RRC, SDAP, and / or PDCP protocols, and a distributed unit (DU) is a logical node that hosts RLC, MAC, and / or PHY layers. A DU is controlled by a CU connected via the F1 interface and supports at least one cell.

[0280] The S-CU (source-CU) is a CU of the NG-RAN node currently serving the UE, and the S-DU (source-DU) is a DU that is connected to the S-CU via the F1 interface and manages the current UE serving cell. In addition, the C-CU (candidate-CU) is a CU of a candidate NG-RAN node that is not the NG-RAN node currently serving the UE, and the C-DU (candidate-DU) is a DU that is connected to the C-CU via the F1 interface and manages at least one of the candidate cells for the UE. The S-CU and C-CU are connected via the X2 or Xn interface.

[0281] FIG. 8 illustrates an example of an overall procedure for supporting LTM between different NG-RAN nodes according to an embodiment of the present disclosure.

[0282] Referring to FIG. 8, in step S801, the UE (810) transmits an L3 measurement report message to the S-CU (820-1). In step S803, the UE (810) transmits an L1 measurement report message to the S-DU (820-2). The L3 measurement report message and / or the L1 measurement report message may include measurement results for neighboring cells. In step S805, the S-DU (820-2) proposes an LTM for the UE to the S-CU (820-1) based on the received L1 measurement report message and proposes candidate cells. The candidate cells may be determined based on the L1 measurement report message. Depending on the embodiment, step S801 may be omitted, or steps S803 and S805 may be omitted. For example, the S-CU (820-1) may receive an L3 measurement report message or an LTM proposal based on an L1 measurement report message from the S-DU (820-2).

[0283] At step S807, the S-CU (820-1) determines candidate cells for LTM preparation. The S-CU (820-1) may decide to initiate LTM setup based on the L3 measurement report message from the UE (810) or the LTM proposal from the S-DU (820-2), and may determine candidate cells for LTM preparation. The candidate cells may be determined based on measurement results for neighboring cells included in the L3 measurement report message or candidate cells proposed by the S-DU (820-2). At least some of the determined candidate cells may be cells of another NG-RAN node (e.g., C-CU1 (830-1) or C-CU2 (840-1)).

[0284] In step S809, an inter-CU LTM preparation and setup procedure may be performed. The inter-CU LTM preparation and setup procedure may be initiated by the S-CU (820-1). According to one embodiment, the inter-CU LTM preparation and setup procedure may include a pre-preparation procedure for LTM and a post-preparation procedure for LTM. The pre-preparation procedure for LTM may be a procedure for checking whether LTM is approved for each candidate cell and performing LTM setup for at least one approved candidate cell, and the post-preparation procedure for LTM may be a procedure for sharing information necessary for performing an inter-CU LTM operation between CUs of at least one approved candidate cell. The inter-CU LTM preparation and setup procedure may be configured as in Embodiment #1 described below.

[0285] At step S811, an early TA (timing advance) acquisition procedure may be performed. For example, an early TA acquisition procedure may be performed for at least one candidate cell. The early TA acquisition procedure may be configured as in Example #2, described below.

[0286] At step S813, an inter-CU LTM execution procedure may be performed. For example, a procedure may be performed to change the serving DU of the UE (810) to a DU belonging to a CU other than the current serving CU based on an L1 measurement report message. The inter-CU LTM execution procedure may be configured as in embodiment #3 described below.

[0287]

[0288] Example #1: Procedures to support preparation and setup of LTM between CUs

[0289] FIGS. 9A to 9C illustrate examples of LTM preparation and setup procedures between CUs according to an embodiment of the present disclosure. The procedures of FIGS. 9A to 9C can be understood as detailed procedures of step S809 of FIG. 8 .

[0290] Referring to FIGS. 9A to 9C, in step S901, the S-CU (920-1) transmits a UE context modification message to the S-DU (920-2) to retrieve reference configuration information to be used for LTM. After determining LTM for the UE as in step S807 of FIG. 8, the S-CU (920-1) may request provision of reference configuration information for LTM by transmitting a UE context modification message to the S-DU (920-2).

[0291] In step S903, the S-DU (920-2) transmits a UE context modification response message to the S-CU (920-1). The UE context modification response message may include reference configuration information for LTM. The reference configuration information may include information related to the latest lower-layer configuration of the UE.

[0292] In step S905, the S-CU (920-1) transmits a handover request message for each candidate cell to the C-CU1 (930-1), which is a CU of the NG-RAN node to which at least one of the candidate cells determined for LTM belongs. The handover request messages for each candidate cell may be transmitted and processed in parallel. The handover request message for each candidate cell may include information related to a data forwarding proposal, an LTM indication indicating that the message is for LTM, and reference configuration information to be used for LTM. The information related to the data forwarding proposal may include information related to an uplink and / or downlink forwarding proposal for S-CU terminated PDU sessions and / or DRBs (S-CU terminated PDU sessions / DRBs). In addition, the handover request message for each candidate cell may include the UE's current serving cell ID or serving S-DU ID. The current serving cell ID or serving S-DU ID can be used to allocate RACH (random access channel) resources for early TA acquisition, i.e., early TA RACH resources, in C-CU1 (930-1).

[0293] In step S907, C-CU1 (930-1) transmits a UE context setup message for LTM preparation to C-DU (930-2) to which at least one candidate cell belongs. The UE context setup message is transmitted for each candidate cell and may include reference configuration information to be used for LTM. In step S909, C-DU (930-2) transmits a UE context setup response message for LTM preparation to C-CU1 (930-1). The UE context setup response message is transmitted for each candidate cell and may include information related to RS (reference signal) configuration and information related to early TA RACH resources. In other words, in steps S907 and S909, C-CU1 (930-1) performs admission control for the corresponding C-DU (930-2) and each candidate cell based on the handover request message for each candidate cell, and may establish a UE context for LTM preparation. C-DU (930-2) can perform LTM setup based on the reference setup information to be used for LTM included in the UE context setup message.

[0294] If at least one other candidate cell among the candidate cells determined for LTM belongs to at least one other DU (e.g., C-DU2) connected to C-CU1 (930-1), C-CU1 (930-1) may perform admission control for the corresponding at least one other DU and the candidate cell in step S911, and establish a UE context for LTM preparation. Step S911 may be configured to perform the same operations as steps S907 and S909, and may be performed in parallel. For example, step S911 may be performed at least temporally at the same time as steps S907 and S909. In one embodiment, if at least one other DU (e.g., C-DU2) connected to C-CU1 (930-1) does not manage any cell among the candidate cells proposed for LTM, step S911 may be omitted.

[0295] At step S913, the C-CU1 (930-1) transmits a handover response message for each candidate cell to the S-CU (920-1). The handover response message may include at least one of information related to forwarding TNLs (transport network layer addresses), information related to a data forwarding proposal to be used for a subsequent LTM, information related to a reference configuration used for LTM configuration, information related to RS configuration prepared for the requested candidate cells, and information related to early TA RACH resources. The forwarding TNLs may be allocated by the C-CU (930-1) based on the information related to the data forwarding proposal of the S-CU (920-1) received at step S905, and the information related to the forwarding TNLs may include at least one of a target GTP-U TEID (GPRS tunneling protocol - user plane tunnel endpoint identifier) ​​or a target IP address. Information related to a data forwarding proposal to be used for a subsequent LTM may include information related to an uplink and / or downlink forwarding proposal for C-CU terminated PDU sessions and / or DRBs (S-CU terminated PDU sessions / DRBs). For example, information related to a data forwarding proposal to be used for a subsequent LTM may include information related to a data forwarding proposal to be used when the C-CU becomes a new serving CU later through inter-CU LTM. The reference configuration information used for LTM setup is reference configuration information prepared in C-CU1 (930-1) and may be different from the reference configuration information provided in the S-CU (920-1) or may be provided to the S-CU (920-1) by being included in a handover response message when the reference configuration information is not provided from the S-CU (920-1).If at least one of the candidate cells for which a handover has been requested is not approved by admission control, a handover failure message may be transmitted in response to the handover request.

[0296] At step S915, the C-CU (930-1) may perform the LTM preparation procedure as described in steps S905 to S913 for each candidate cell in another NG-RAN node. For example, if at least one other candidate cell among the candidate cells for LTM belongs to C-CU2 (940-1), the LTM preparation procedure may be performed between C-CU2 (940-1) and the C-DU connected to C-CU2 (940-1) by transmitting a handover request message for LTM to C-CU2 (940-1).

[0297] At step S917, the S-CU (920-1) transmits a UE context modification message for LTM preparation for each candidate cell to the S-DU (920-2), and at step S919, the S-DU (920-2) transmits a UE context modification response message for LTM preparation for each candidate cell to the S-CU (920-1). The UE context modification message and the UE context modification response message are transmitted and received for each candidate cell. In addition, the UE context modification message may include reference configuration information to be used for LTM establishment, and the UE context configuration response message may include information related to RS establishment and information related to early TA RACH resources. That is, for at least one candidate cell belonging to the S-DU (920-2), the S-CU (920-1) may perform admission control with the S-DU (920-2), establish a UE context, and prepare LTM.

[0298] In step S921, the S-CU (920-1) transmits a UE context setup message for LTM preparation to another DU connected to the S-CU (920-1), and receives a UE context setup response message for LTM preparation from the other DU. The other DU may be another DU connected to the S-CU, other than the S-DU, that manages at least one candidate cell among the candidate cells determined for LTM. Step S921 may be configured to perform the same operations as steps S907 and S909, and may be performed in parallel with steps S917 and S919. For example, step S921 may be performed at least temporarily at the same time as steps S917 and S919. According to one embodiment, if the other DU connected to the S-CU (920-1) does not manage any cell among the candidate cells determined for LTM, step S921 may be omitted.

[0299] In step S923, the S-CU (920-1) transmits a UE context modification message to the S-DU (920-2). The UE context modification message may include information necessary for performing the LTM operation. The information necessary for performing the LTM operation may include a list of approved and / or prepared candidate cells, information related to the RS configuration of the candidate cells, or information related to the early TA RACH resources of the candidate cells.

[0300] At step S925, the S-DU (920-2) transmits a UE context modification response message to the S-CU (920-1). The UE context modification response message includes information related to L1 measurement reporting configuration for each candidate cell in the S-DU (920-2) and transmission configuration indication (TCI) state configuration information for all candidate cells. For example, for the approved candidate cells of the S-DU (920-2), the S-DU (920-2) may generate information related to L1 measurement reporting configuration for each candidate cell and provide information related to the generated L1 measurement reporting configuration to the S-CU (920-1). In addition, the S-DU (920-2) may generate information related to TCI state configuration for approved and / or prepared candidate cells and provide information related to the generated TCI state configuration to the S-CU (920-1).

[0301] In step S927, the S-CU (920-1) transmits an LTM post-preparation request message to the C-CU1 (930-1). The LTM post-preparation request message includes information necessary for performing an LTM operation. The information necessary for performing an LTM operation includes a list of all approved and / or prepared candidate cells, information related to RS configuration of the candidate cells prepared in at least one other CU, and information related to early TA RACH resources of the candidate cells prepared in at least one other CU. The LTM post-preparation request message may further include TCI state configuration information generated by the S-DU (920-2). In addition, the LTM post-preparation request message may include information related to data forwarding TNLs allocated by the other CU. Information related to data forwarding TNLs may be used for data forwarding operations from the C-CU1 to other CUs when LTM is performed on one of the candidate cells under the C-CU1.

[0302] At step S929, C-CU1 (930-1) transmits a UE context modification message to C-DU (930-2). The UE context modification message includes information required to perform LTM operation. The information required to perform LTM operation may include at least one of a list of all approved and / or prepared candidate cells, information related to RS configuration for candidate cells prepared by at least one other DU, and information related to early TA RACH resources for candidate cells prepared by at least one other DU. C-CU1 (930-1) may also transmit information related to TCI state configuration generated by S-DU (920-2) to C-DU (930-2) using the UE context modification message.

[0303] At step S931, the C-DU (930-2) transmits a UE context modification response message to the C-CU1 (930-1). The C-DU (930-2) can generate information related to L1 measurement report configuration for approved candidate cells within the C-DU (930-2) and provide information related to the generated L1 measurement report configuration to the C-CU (930-1).

[0304] In step S933, C-CU1 (930-1) transmits a UE context modification message to another C-DU connected to C-CU1 (930-1) and receives a UE context modification response message from the other C-DU. The other C-DU may be a C-DU to which at least one other candidate cell that has been approved and / or prepared among the candidate cells proposed for LTM belongs. Step S933 may be performed in parallel with steps S929 and S931. For example, step S933 may be performed at least temporarily at the same time as steps S929 and S931. According to one embodiment, if no approved and / or prepared candidate cell belongs to another C-DU connected to C-CU1 (930-1), step S933 may be omitted.

[0305] At step S935, C-CU1 (930-1) transmits an LTM post-preparation response message to S-CU (920-1). The LTM post-preparation response message may include information related to the L1 measurement report configuration of at least one candidate cell approved by C-CU1 (930-1).

[0306] At step S937, the C-CU (930-1) may perform the LTM post-preparation procedure as described in steps S927 to S935 for at least one candidate cell in another NG-RAN node. For example, if at least one approved and / or prepared candidate cell belongs to C-CU2 (940-1), the LTM post-preparation procedure may be performed with C-CU2 (940-1) and the C-DU connected to C-CU2 (940-1) by transmitting an LTM post-preparation request message to C-CU2 (940-1).

[0307] At step S939, a UE context modification procedure may be performed for a candidate cell that has been approved and / or prepared in another DU connected to the S-CU (920-1). The S-CU (920-1) transmits a UE context modification message to another DU connected to the S-CU and receives a UE context modification response message from the other DU. The other DU may be another DU connected to the S-CU, other than the S-DU to which the approved and / or prepared candidate cell belongs. In one embodiment, if the approved and / or prepared candidate cell does not belong to another DU connected to the S-CU (920-1), step S939 may be omitted.

[0308] At step S941, the S-CU (920-1) configures an LTM handover command including the LTM configuration information generated for all approved and / or prepared candidate cells and the corresponding lower layer configuration information for the LTM, and resets the UE via the S-DU (920-2). The lower layer configuration information includes at least one of information related to RS configuration, information related to L1 measurement report configuration, TCI status, or information related to RACH configuration.

[0309] At step S943, the S-CU (920-1) may perform early data forwarding based on information related to data forwarding TNLs allocated by other CUs.

[0310] In the embodiment #1 described with reference to FIGS. 9a to 9c, it is assumed that information related to the final TCI state configuration set in the UE is generated by the S-DU, and information related to the generated final TCI state configuration is propagated to all other relevant DUs for the LTM operation. However, the TCI state configuration information corresponding to each approved and / or prepared candidate cell may be determined by each DU (e.g., C-DU) responsible for the candidate cell. In this case, information related to the TCI state configuration may be provided to the corresponding CU (e.g., C-CU) in step S909, and may be forwarded to the S-CU through step S913. Information related to the TCI state configuration generated by the S-DU may be provided to the S-CU in step S917 or step S919, and information related to the TCI state configuration generated by a DU other than the S-DU may be provided to the S-CU in step S921.

[0311] For LTM operation, information related to TCI state setup collected from the S-CU may be additionally propagated to all relevant DUs through steps S923 and S925, steps S927 to S935, and / or step S939.

[0312] In the embodiment #1 described with reference to FIGS. 9a to 9c, steps S901 to S921 may correspond to pre-preparation procedures for LTM, and steps S923 to S941 may correspond to post-preparation procedures for LTM.

[0313]

[0314] Example #2: Early TA Acquisition Procedure

[0315] FIGS. 10A and 10B illustrate examples of an early TA acquisition procedure according to an embodiment of the present disclosure. The procedures of FIGS. 10A and 10B can be understood as detailed procedures of step S811 of FIG. 8.

[0316] Referring to FIGS. 10A and 10B , in step S1001, the S-CU (1020-1) determines early TA acquisition for at least some of the candidate cells. In this case, the S-CU (1020-1) may perform at least one of steps S1003, S1005, or S1007, which will be described later. In step S1003, the S-CU (1020-1) may request the S-DU (1020-2) to perform early TA acquisition for some of the candidate cells. In step S1005, the S-CU (1020-1) may transmit a message to the S-DU (1020-2) indicating that early TA acquisition for some of the candidate cells is not necessary. For example, the S-CU (1020-1) may instruct the S-DU (1020-2) that TA acquisition for some cells co-located with the cell for which the TA value is known is not necessary. In step S1007, the S-CU (1020-1) may provide the TA value to the S-DU (1020-2). For example, if the S-CU (1020-1) knows the TA value of a specific candidate cell, it may provide the corresponding TA value to the S-DU (1020-2).

[0317] At step S1009, the S-DU (1020-2) decides to acquire early TA for a candidate cell within another DU.

[0318] In step S1011, the S-DU (1020-2) transmits an early TA acquisition command message to the UE (1010). The early TA acquisition command message may include information instructing the UE to perform early TA acquisition for a candidate cell within another DU.

[0319] At step S1013, the S-DU (1020-2) transmits a message to the DU of the candidate cell, i.e., C-DU1 (1030-2), informing the UE that early TA acquisition has been requested. For example, the S-DU (1020-2) may transmit a message to C-DU1 (1030-2) via the S-CU (1020-1) and C-CU1 (1030-1), informing the UE that early TA acquisition has been requested for the candidate cell of C-DU1 (1030-2).

[0320] In step S1015, the UE (1010) performs RACH for the designated candidate cell. The UE (1010) may obtain information about the candidate cell designated as the early TA acquisition target based on the early TA command message, and transmit a random access preamble based on the information about the designated candidate cell. The UE (1010) may perform contention-free random access (CFRA) or contention-based random access (CBRA) based on the LTM configuration information.

[0321] At step S1017, C-DU1 (1030-2) calculates the TA value of the candidate cell based on the RACH of UE (1010) and transmits the TA value of the candidate cell to S-DU (1020-2). At this time, the TA value of the candidate cell is transmitted to S-DU (1020-2) through C-CU1 (1030-1) and S-CU (1020-1).

[0322] At step S1019, C-CU1 (1030-1) shares the TA value of the candidate cell with another DU connected to C-CU1 (1030-1), i.e., C-DU2 (1030-3), for subsequent LTM operations. At steps S1021 and S1023, S-CU (1020-1) may share the TA value of the candidate cell with at least one other DU of S-CU (1020-1) and C-CU2 (1040-1) of another NG-RAN node for subsequent LTM operations.

[0323] In step S1025, the S-DU (1020-2) determines early TA acquisition for a candidate cell within the S-DU. In step S1027, the S-DU (1020-2) transmits an early TA acquisition command message for the candidate cell of the S-DU (1020-2) to the UE (1010). The early TA acquisition command message may include information related to the candidate cell of the S-DU (1020-2).

[0324] In step S1029, the UE (1010) performs RACH for the designated candidate cell. The UE (1010) may transmit a random access preamble based on information related to the designated candidate cell included in the early TA command message. The UE (1010) may perform contention-free random access (CFRA) or contention-based random access (CBRA) based on LTM configuration information.

[0325] In step S1031, the S-DU (1020-2) calculates the TA value of the candidate cell based on the RACH of the UE (1010) and transmits the TA value of the candidate cell to the S-CU (1020-1). At this time, the TA value of the candidate cell transmitted to the S-CU (1020-1) may be shared with at least one other DU for subsequent LTM operation. The other DU may include at least one of another DU connected to the S-CU (1020-1), C-DU1 (1030-2), C-DU2 (1030-3) connected to C-CU1 (1030-1), or DU connected to C-CU2 (1040-1).

[0326] In the embodiment described with reference to FIGS. 10A and 10B, the early TA acquisition procedure may be initiated by a DU other than the C-CU or S-DU as the serving cell changes during the LTM process.

[0327]

[0328] Example #3: Supporting LTM execution across CUs

[0329] Figures 11a to 11c illustrate examples of LTM execution procedures between CUs according to embodiments of the present disclosure. The procedures of Figures 11a to 11c can be understood as detailed procedures of step S813 of Figure 8.

[0330] Referring to FIGS. 11a to 11c, in step S1101, the cell of the S-DU (1120-2) operates as the serving cell of the UE (1110). In step S1103, the UE (1110) transmits an L1 measurement report message to the S-DU (1120-2), which is the current serving DU, based on the LTM configuration information set in the UE.

[0331] At step S1105, the S-DU (1120-2) determines a cell switch of the UE (1110) and transmits an LTM handover command message to the UE (1110) to command a handover to a target cell in another CU. The target cell in the other CU may be one of the prepared candidate cells and may be selected based on the measurement results for the adjacent cells, i.e., the candidate cells, included in the L1 measurement report message.

[0332] In step S1107, the S-DU (1120-2) transmits an LTM cell change notification message to the C-DU1 (1130-2) to which the target cell belongs. The LTM cell change notification message can be provided to the C-DU1 (1130-2) through the S-CU (1120-1) and the C-CU1 (1130-1). The LTM cell change notification message can include the target cell ID and selected beam information. The selected beam information can be obtained based on the L1 measurement report message and can be provided from the S-DU (1120-2) to the C-DU1 (1130-2) for appropriate uplink scheduling.

[0333] In step S1109, the UE (1110) performs RACH and accesses the target cell. If the early TA acquisition procedure has already been performed in the target cell, RACH may be omitted in step S1109.

[0334] In step S1111, C-DU1 (1030-2) transmits an access success message to C-CU1 (1130-1). In other words, if UE (1110) successfully accesses the target cell, C-DU1 (1130-2) may transmit an access success message to C-CU1 (1130-1). The access success message may include a target cell ID and a TA value for the target cell. The TA value for the target cell may be acquired based on the RACH of step S1109 or step S811 of FIG. 8, which performs early TA acquisition. In step S1113, C-DU1 (1130-2) may operate as a new serving DU for UE (1110).

[0335] In step S1115, the current serving CU, C-CU1 (1130-1), transmits a handover success message to the previous serving CU, S-CU (1120-1), informing the access of the UE (1110) and the cell accessed by the UE. The handover success message includes at least one of the ID of the target cell accessed by the UE, the TA value for the target cell, and information related to the data forwarding proposal of C-CU1 (1130-1). The target cell ID includes identification information of the cell accessed by the UE. C-CU1 (1130-1), the new serving CU of the UE (1110), can share the TA value for the target cell with at least one other DU for subsequent LTM operations.

[0336] In step S1117, the previous serving CU, S-CU (1120-1), transmits an access success message to the previous serving DU, S-DU (1120-2), notifying the access of the UE (1110) and the cell accessed by the UE. The access success message may include the target cell ID accessed by the UE. In step S1119, the previous serving CU, S-CU (1120-1), transmits an SN status transfer message to the new serving CU, C-CU1 (1130-1), and performs late data forwarding in step S1121. That is, the previous serving CU, S-CU (1120-1), may trigger SN status transfer for DRBs requiring PDCP preservation.

[0337] In steps S1123, S1125, and S1127, the previous serving CU, S-CU (1120-1), and the new serving CU, C-CU1 (1130-1), share the TA value for the cell accessed by the UE for subsequent LTM operations with at least one other DU other than the new serving DU. The at least one other DU may include at least one of the DUs connected to S-DU (1120-2), C-DU2 (1130-3), or C-CU2 (1140-1).

[0338] In step S1129, S-CU (1120-1) transmits a data forwarding request message to C-CU2 (1140-1), which is not a new serving CU. The data forwarding request message may include information related to the data forwarding proposal of C-CU1 (1130-1), which is a new serving CU. In step S1131, C-CU2 (1140-1) transmits a data forwarding response message to S-CU (1120-1). The data forwarding response message may include information related to data forwarding TNLs newly allocated by C-CU2 (1140-1) based on information related to the data forwarding proposal of C-CU1 (1130-1).

[0339] At step S1133, the S-CU (1120-1) transmits a data forwarding response message including information related to newly assigned data forwarding TNLs to the new serving CU, C-CU1 (1130-1), based on information related to the data forwarding proposal of C-CU1 (1130-1). The data forwarding response message may include at least one of information related to forwarding TNLs newly assigned by C-CU2 (1140-1) or information related to forwarding TNLs newly assigned by S-CU (1120-1). At step S1135, the C-CU1 (1130-1) may perform early data forwarding based on the newly assigned forwarding TNLs.

[0340] At step S1137, an early TA acquisition procedure may be initiated from a new serving DU, C-DU1 (1130-2). The early TA acquisition procedure may be performed as described in Example #2.

[0341] At step S1139, the UE (1110) transmits an L1 measurement report message to the current serving DU, C-DU1 (1130-2), as set in the UE.

[0342] In step S1141, the current serving DU, C-DU1 (1130-2), determines a cell switch of the UE (1110) and transmits an LTM handover command message to the UE (1110) to command a handover to a target cell in another CU. The target cell in the other CU may be one of the prepared candidate cells, and may be selected based on the measurement results for the adjacent cells, i.e., the candidate cells, included in the L1 measurement report message.

[0343] In step S1143, the current serving DU, C-DU1 (1130-2), transmits an LTM cell change notification message to C-CU2 (1140-1) to which the target cell belongs. The LTM cell change notification message may include the target cell ID and selected beam information. The LTM cell change notification message may be delivered to C-CU2 (1140-1) and the DU connected to C-CU2 (1140-1) via C-CU1 (1130-1) and S-CU (1120-1).

[0344] In step S1145, the UE (1110) performs RACH and accesses the target cell. If the early TA acquisition procedure has already been performed in the target cell, RACH may be omitted in step S1145.

[0345] In step S1147, C-CU2 (1140-1) transmits a handover success message to C-CU1 (1130-1). C-CU2 (1140-1) receives an access success message from a DU connected to C-CU2 (1140-1), i.e., a DU of a target cell successfully accessed by UE (1110), and in response transmits a handover success message to C-CU1 (1130-1) via S-CU (1120-1). The access success message includes a target cell ID and a TA value for the target cell. The TA value for the target cell can be acquired based on the RACH of step S1145 or step S811 of FIG. 8, which performs early TA acquisition. The handover success message includes at least one of the ID of the target cell accessed by the UE, the TA value for the target cell, and information related to a data forwarding proposal of C-CU2 (1140-1). The target cell ID includes identification information of the cell accessed by the UE. In step S1149, C-CU2 (1140-1) may act as a new serving CU for the UE (1110). C-CU1 (1130-1) becomes the previous serving CU.

[0346] In step S1151, the previous serving CU, C-CU1 (1130-1), transmits an access success message to the previous serving DU, C-DU1 (1130-2), notifying the access of the UE (1110) and the cell accessed by the UE. The access success message may include the target cell ID accessed by the UE. In step S1153, the previous serving CU, C-CU1 (1130-1), transmits an SN status transfer message to the new serving CU, C-CU2 (1140-1), and performs late data forwarding in step S1155. That is, the previous serving CU, C-CU1 (1130-1), may trigger SN status transfer for DRBs requiring PDCP preservation.

[0347] In steps S1157 and S1159, the S-CU (1120-1), the previous serving CU C-CU1 (1130-1), and the new serving CU C-CU2 (1140-1) share the TA value for the cell accessed by the UE for subsequent LTM operations with at least one other DU other than the new serving DU. The at least one other DU may include at least one of the S-DU (1120-2), C-DU1 (1130-2), C-DU2 (1130-3), or another DU connected to C-CU2 (1140-1).

[0348] In step S1161, S-CU (1120-1) transmits a data forwarding request message to C-CU1 (1130-1), which is a previous serving CU. The data forwarding request message may include information related to a data forwarding proposal of C-CU2 (1140-1), which is a new serving CU. In step S1163, C-CU1 (1130-1) transmits a data forwarding response message to S-CU (1120-1). The data forwarding response message may include information related to data forwarding TNLs newly allocated by C-CU1 (1130-1) based on information related to the data forwarding proposal of C-CU2 (1140-1).

[0349] At step S1165, S-CU (1120-1) transmits a data forwarding response message including information related to newly assigned forwarding TNLs to C-CU2 (1140-1), which is a new serving CU, based on information related to the data forwarding proposal of C-CU2 (1140-1). The data forwarding response message may include at least one of information related to the newly assigned forwarding TNLs by C-CU1 (1130-1) or information related to the newly assigned forwarding TNLs by S-CU (1120-1). At step S1167, C-CU2 (1140-1) may perform early data forwarding based on the newly assigned forwarding TNLs.

[0350] At step S1169, an early TA acquisition procedure may be initiated from a DU connected to C-CU2 (1140-1). The early TA acquisition procedure may be performed as described in Example #2.

[0351] In the embodiment described with reference to FIGS. 11a to 11c, steps S1101 to S1137 correspond to inter-CU LTM execution procedures when the serving DU of the UE changes from S-DU (1120-2) connected to S-CU (1120-1) to C-DU1 (1130-2) connected to C-CU1 (1130-1), and steps S1139 to S1169 correspond to inter-CU LTM procedures when the serving DU of the UE changes from C-DU1 (1130-2) connected to C-CU1 (1130-1) to DU connected to C-CU2 (1140-1). That is, when the serving DU is changed to a DU under another CU by the L1 measurement report message of the UE, the inter-CU LTM execution procedure described in steps S1101 to S1137, or steps S1139 to S1169, may be performed.

[0352] In the embodiment described with reference to FIGS. 11a to 11c, the path switching procedure according to the change of serving DU is omitted for brevity, but may be performed after the LTM procedure between each CU is executed.

[0353] In the embodiment described with reference to FIGS. 11A to 11C, steps S1129 to S1133, and / or steps S1161 to S1165 may be omitted. For example, if information related to a data forwarding proposal of a CU of a target cell and information related to TNLs allocated by another CU based thereon are exchanged during the inter-CU LTM preparation and setup procedure of Embodiment #1, steps S1129 to S1133, and / or steps S1161 to S1165 may be omitted.

[0354]

[0355] As described above, the present disclosure proposes a procedure for supporting LTM in a network system. According to one embodiment, the network system may include networks interconnected by an X2 or Xn interface to support LTM of a UE. Each network node may include a CU and at least one DU connected to the CU.

[0356] According to one embodiment, the serving DU may receive an L1 measurement report message for neighboring cells from the UE, propose an LTM to the serving CU, and propose candidate cells for the LTM.

[0357] According to one embodiment, a serving CU determines an LTM configuration for a UE and transmits a handover request message to another CU for LTM preparation and configuration between CUs. The serving CU may determine the LTM configuration for the UE based on an L3 measurement report message from the UE or an LTM proposal from a serving DU. The handover request message may include at least one of an indication indicating that the handover request message is for LTM, information related to candidate cells proposed for LTM, information related to a data forwarding proposal, reference configuration information to be used for generating LTM configuration information, or a current serving cell ID and / or serving DU ID of the UE to be used for early TA RACH resource allocation.

[0358] According to one embodiment, a CU that receives a handover request message performs admission control and LTM preparation with the corresponding DUs of candidate cells proposed for LTM, and then transmits a handover response message to the serving CU. The handover response message may include at least one of information related to an LTM configuration prepared for the UE, information related to data forwarding TNLs, information related to a data forwarding proposal to be used for a subsequent LTM operation when LTM is executed for one of the candidate cells under the CU that received the handover request message, reference configuration information used for the prepared LTM configuration, information related to RS resource configuration, information related to early TA RACH resources allocated by the prepared candidate cells, and information related to TCI state configuration of candidate cells generated by at least one DU connected to the CU that received the handover request message. Here, the information related to the data forwarding TNLs may include information related to forwarding TNLs allocated by the corresponding CU based on the information related to the data forwarding proposal included in the handover request message. That is, if the CU and at least one DU connected to the CU have accepted the data forwarding proposal provided by the serving CU, information related to the data forwarding TNLs allocated based on the data forwarding proposal may be included in the handover response message.

[0359] According to one embodiment, a serving CU transmits an LTM post-preparation request message to a CU that has received a handover request message. The LTM post-preparation request message may include information necessary for performing an LTM operation. The information necessary for performing an LTM operation may include a list of all approved and / or prepared candidate cells, information related to RS configurations of candidate cells prepared by at least one other CU and information related to early TA RACH resources, information related to TCI state configurations generated by at least one other CU and at least one DU connected to the serving CU, or information related to forwarding TNLs allocated by at least one other CU. The information related to forwarding TNLs allocated by at least one other CU may be used for data forwarding when LTM is performed for one of the candidate cells under the CU that has received the LTM post-preparation request message.

[0360] According to one embodiment, a CU that receives an LTM post-preparation request message may perform a UE context modification procedure with at least one DU connected to the CU, and then transmit an LTM post-preparation response message to the serving CU. The LTM post-preparation response message may include information related to setting the TCI state of candidate cells generated by at least one DU connected to the CU and information related to setting the L1 measurement report.

[0361] In one embodiment, a serving CU may transmit an LTM handover command message to a terminal. The LTM handover command message may include information related to LTM configurations generated for all candidate cells prepared by the serving CU and at least one other CU.

[0362] In one embodiment, the serving CU may request the serving DU to perform early TA acquisition for the UE. In one embodiment, the serving CU may indicate to the serving DU that early TA acquisition is not required for at least one candidate cell. In one embodiment, the serving CU may provide the TA value of at least one candidate cell to the serving DU.

[0363] According to one embodiment, after the serving DU commands the UE to acquire early TA for a candidate cell, the serving DU may notify the DU of the candidate cell that the early TA acquisition for the candidate cell has been requested from the UE. The serving CU and / or the CU of the candidate cell may forward information received from the serving DU to the DU of the candidate cell. The DU of the candidate cell may calculate a TA value of the candidate cell and transmit the calculated TA value of the candidate cell back to the serving DU. Information from the DU of the candidate cell may be forwarded to the serving DU via the serving CU and / or the CU of the candidate cell. The serving CU or the CU of the candidate cell may share the calculated TA value of the candidate cell with at least one other DU for subsequent LTM operations. The serving DU and the DU of the candidate cell may be the same entity.

[0364] In one embodiment, the serving DU may determine cell switching and instruct the UE to handover to the target cell. The target cell may be one of the prepared candidate cells. The serving DU may transmit an LTM cell change notification message to the DU of the target cell. The LTM cell change notification message may include selected beam information. The serving CU or the CU of the target cell may forward information from the serving DU to the DU of the target cell.

[0365] According to one embodiment, a DU of a target cell may transmit an access success message notifying a UE of access to a CU of the target cell. The access success message may include a TA value calculated while the UE accesses the target cell. The CU of the target cell may share the calculated TA value of the target cell with at least one other DU connected to the CU of the target cell. The CU of the target cell may forward information provided from the DU of the target cell to a source CU or a serving CU. The CU of the target cell may forward data forwarding proposals from the target cell accessed by the UE and the CU of the target cell to the source CU and / or the serving CU. The source CU and / or the serving CU may forward information provided from the CU of the target cell to at least one other DU for subsequent LTM operations.

[0366] A source CU may request data forwarding from at least one other CU other than the CU of the target cell, and may search for and / or allocate a new forwarding TNL based on a data forwarding proposal from the CU of the target cell. The source CU may forward information related to data forwarding TNLs allocated by at least one other CU other than the CU of the target cell to the CU of the target cell. Here, the serving DU and the DU of the target cell may be the same entity. The serving CU and the CU of the target cell may be the same entity. Alternatively, the source CU and the serving CU may be the same entity.

[0367]

[0368] Fig. 12 illustrates an example of a procedure for triggering an LTM according to an embodiment of the present disclosure. Fig. 12 illustrates a method performed by a first control node of a first base station. The first base station includes a first NG-RAN node, and the first control node may include a first CU of the first NG-RAN node. The first control node may be connected to at least one distributed node (e.g., DU) via an F1 interface, and may be connected to a control node (e.g., a second CU) of at least one other base station (e.g., a second base station) via an X2 or Xn interface.

[0369] Referring to FIG. 12, in step S1201, the first control node of the first base station determines to initiate LTM configuration. The first control node may determine to initiate LTM configuration between base stations based on an L3 measurement report message received from a terminal or an LTM proposal message from a first distributed node. The LTM between base stations may include an LTM between CUs. The L3 measurement report message may include measurement results for adjacent cells. The LTM proposal message of the first distributed node may include information related to proposed candidate cells. The proposed candidate cells may be determined based on an L1 measurement report message transmitted from the terminal to the first distributed node. The first distributed node may be a logical node connected to the first control node via an F1 interface and managing a serving cell of the terminal under the control of the first control node. The first control node may determine to initiate LTM configuration between base stations and determine candidate cells for LTM. Candidate cells for LTM may be determined based on measurement results for adjacent cells included in the L3 measurement report message or candidate cells suggested by the first distributed node. Candidate cells for LTM may include at least one cell belonging to the second base station.

[0370] In step S1203, the first control node of the first base station transmits a first message for LTM. The first control node may transmit the first message for LTM to a second control node of a second base station to which at least one candidate cell among candidate cells for LTM belongs. The first message for LTM may be transmitted to the second control node of the second base station via an X2 or Xn interface. The first message for LTM is a message for preparing and establishing LTM between base stations and may include a handover request message for each of the candidate cells for LTM. The handover request message for each of the candidate cells for LTM may include at least one of information related to a data forwarding proposal, an LTM indication indicating that the message is for LTM, reference configuration information to be used for LTM, or information related to a current serving cell of a terminal to be used for early TA RACH resource allocation. Here, the reference configuration information to be used for LTM may be obtained from the first distributed node of the first base station using a terminal context modification request and response message. Information related to the serving cell may include at least one of a serving cell ID or a serving DU ID. Handover request messages for each candidate cell may be transmitted and processed in parallel.

[0371] According to one embodiment, the first control node of the first base station may be an S-CU of Embodiment #1, Embodiment #2, and / or Embodiment #3 described with reference to FIGS. 8A to 11C. The first control node may further perform at least one operation of the S-CU described in Embodiment #1, Embodiment #2, and / or Embodiment #3.

[0372]

[0373] FIG. 13 illustrates an example of an LTM preparation procedure according to an embodiment of the present disclosure. FIG. 13 illustrates a method performed by a first distributed node of a first base station. The first base station may include a first NG-RAN node. The first distributed node may include a first DU of the first NG-RAN node. The first distributed node may be connected to a first control node (e.g., a first CU) of the first base station via an F1 interface.

[0374] Referring to FIG. 13, in step S1301, the first distributed node receives an L1 measurement report message from the terminal. The L1 measurement report message may include measurement results for adjacent cells.

[0375] In step S1303, the first distributed node transmits an LTM proposal message. The LTM proposal message may include information related to proposed candidate cells for LTM. Specifically, the first distributed node may determine proposed candidate cells for LTM based on the L1 measurement report message, and transmit an inter-base station LTM proposal message including information related to the determined proposed candidate cells to the first control node. At least one of the proposed candidate cells may be a cell belonging to the second base station. The inter-base station LTM may include an inter-CU LTM.

[0376] According to one embodiment, the first distributed node may be an S-DU of Embodiment #1, Embodiment #2, and / or Embodiment #3 described with reference to FIGS. 8A to 11C. The first distributed node may further perform at least one operation of the S-DU described in Embodiment #1, Embodiment #2, and / or Embodiment #3.

[0377]

[0378] Fig. 14 illustrates an example of an LTM preparation procedure according to an embodiment of the present disclosure. Fig. 14 illustrates a method performed by a second control node of a second base station. The second base station includes a second NG-RAN node, and the second control node may include a second CU of the second NG-RAN node. The second control node may be connected to at least one distributed node (e.g., DU) via an F1 interface, and may be connected to a first control node (e.g., a first CU) of at least one other base station (e.g., the first base station) via an X2 or Xn interface.

[0379] Referring to FIG. 14, in step S1401, the second control node of the second base station receives a first message for LTM. The first message for LTM is a message for preparing and setting up LTM between base stations and may include a handover request message. The inter-base station LTM may include inter-CU LTM. In other words, the second control node may receive a handover request message for inter-CU LTM from the first control node of the first base station. The handover request message may be received for each of the candidate cells for LTM. The handover request message for each candidate cell may include at least one of information related to a data forwarding proposal, an LTM indication indicating that the message is for LTM, reference configuration information to be used for LTM, or information related to a current serving cell of a terminal to be used for early TA RACH resource allocation. The information related to the serving cell may include at least one of a serving cell ID or an ID of a serving distributed node (e.g., DU).

[0380] In step S1403, the second control node performs LTM configuration for at least one candidate cell. The second control node may perform admission control on the candidate cells and at least one second distributed node managing the candidate cells for LTM based on the first message, and may establish a UE context for LTM preparation. Specifically, the second control node transmits a UE context configuration message to the second distributed node and receives a UE context response message from the second distributed node. The UE context configuration message is transmitted for each candidate cell and may include reference configuration information to be used for LTM. The UE context configuration response message is received for each candidate cell and may include information related to RS configuration and information related to early TA RACH resources.

[0381] In step S1405, the second control node transmits a second message for LTM. The second message for LTM may include a handover response message. In other words, the second control node may transmit a handover response message for LTM to the first control node of the first base station. The handover response message may be generated and transmitted for each candidate cell. The handover response message for each candidate cell may include at least one of information related to forwarding TNLs, information related to a data forwarding proposal to be used for a subsequent LTM, reference configuration information used for LTM configuration, information related to RS configuration prepared for the requested candidate cells, and information related to early TA RACH resources. The forwarding TNLs may be allocated by the second control node based on the information related to the data forwarding proposal included in the first message, and may include at least one of a target GTP-U TEID (GPRS tunneling protocol - user plane tunnel endpoint identifier), or a target IP address. Information related to a data forwarding proposal to be used in a subsequent LTM may include information related to an uplink and / or downlink forwarding proposal for PDU sessions and / or DRBs (S-CU terminated PDU sessions / DRBs) that terminate at the second control node. For example, information related to a data forwarding proposal to be used in a subsequent LTM may include information related to a data forwarding proposal to be used when the second control node is later determined as a new serving CU by LTM between base stations. The reference configuration information used for LTM setup is reference configuration information used for LTM setup of the second control node, and may be different from the reference configuration information provided by the first control node, or may be included in a handover response message when the reference configuration information is not provided by the first control node.If at least one of the candidate cells is not approved for LTM, a handover failure message may be sent in response to the handover request.

[0382] According to one embodiment, the second control node of the second base station may be a C-CU of Embodiment #1, Embodiment #2, and / or Embodiment #3 described with reference to FIGS. 8A to 11C. The second control node of the second base station may further perform at least one operation of the C-CU described in Embodiment #1, Embodiment #2, and / or Embodiment #3.

[0383]

[0384] Figure 15 illustrates an example of a cell change procedure according to LTM settings according to an embodiment of the present disclosure. Figure 15 illustrates a method performed by a terminal.

[0385] Referring to FIG. 15, in step S1501, the terminal transmits a measurement report message. The measurement report message may include an L1 measurement report message. The terminal may transmit the L1 measurement report message including measurement results for candidate cells configured for LTM to the first distributed node of the first base station. The first distributed node of the first base station is connected to the first control node of the first base station via the F1 interface and manages the serving cell of the terminal under the control of the first control node.

[0386] In step S1503, the terminal receives a cell change message. The cell change message is a message that commands the terminal to perform a handover to a target cell within another base station, and may include an LTM handover command message. The target cell may be a specific candidate cell selected by the distributed node of the first base station based on the L1 measurement report message. The terminal can access the target cell based on the cell change message. For example, the terminal can access the target cell by performing a RACH procedure for the target cell.

[0387] According to one embodiment, the terminal may be a UE of Embodiment #1, Embodiment #2, and / or Embodiment #3 described with reference to FIGS. 8A to 11C. The terminal may further perform at least one operation of the UE described in Embodiment #1, Embodiment #2, and / or Embodiment #3.

[0388]

[0389] 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).

[0390] 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.

[0391] 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.

[0392] 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.

[0393] Additionally, embodiments of the present disclosure can be applied to various applications such as autonomous vehicles and drones.

Claims

1. A method performed by a first control node of a first base station in a wireless communication system, A step for determining the initiation of LTM (L1L2 triggered mobility) setup; and A step of transmitting a first message related to setting up candidate cells for the above LTM, The candidate cells for the above LTM include at least one cell belonging to at least one other base station, A method wherein the first message is transmitted to a second control node of a second base station included in the at least one other base station.

2. In claim 1, Further comprising a step of receiving a measurement report message from the terminal, The above LTM setting initiation method is determined based on the above measurement report message.

3. In claim 1, Further comprising the step of receiving a message proposing LTM between base stations from the first distributed node of the first base station, A method in which a message proposing LTM between the above base stations includes information related to candidate cells proposed for the LTM.

4. In claim 1, The first message includes at least one of information related to a first data forwarding proposal, an indication indicating that the first message is for the LTM, reference setting information to be used for the LTM, or information related to a current serving cell of the terminal to be used for RACH (random access channel) resource allocation for early TA (timing advance) acquisition. The above first message is transmitted to each of the candidate cells.

5. In claim 1, In response to the first message, further comprising the step of receiving a second message related to the LTM from the second control node, A method according to claim 1, wherein the second message comprises at least one of information related to first forwarding TNLs (transport network layer addresses), information related to a second data forwarding proposal to be used for a subsequent LTM, reference configuration information used for configuring the LTM in the at least one other base station, information related to a reference signal (RS) configuration of at least one candidate cell prepared for the LTM, or information related to a RACH resource for early TA acquisition of at least one candidate cell prepared for the LTM.

6. In claim 5, Further comprising the step of transmitting a third message including information necessary for the operation of the LTM to the second control node, The method according to claim 3, wherein the third message includes at least one of a list of candidate cells prepared for the LTM among the candidate cells for the LTM, information related to RS configuration of at least one candidate cell prepared for the LTM in a third control node of a third base station included in the at least one other base station, information related to early TA RACH resources of at least one candidate cell prepared for the LTM in the third control node, information related to TCI state configuration generated by the first distributed node, or information related to second forwarding TNLs allocated by a control node other than the second control node.

7. In claim 6, In response to the third message, further comprising the step of receiving a fourth message from the second control node, A method in which the fourth message includes information related to setting up L1 (layer 1) measurement reporting of at least one candidate cell belonging to the second control node.

8. In claim 1, A step of acquiring TA information for at least one of the candidate cells from a second distributed node connected to the second control node based on an early TA acquisition procedure; and A method further comprising the step of transmitting the acquired TA information to at least one other distributed node.

9. In claim 1, A step of receiving a cell change notification message indicating that a cell change to a target cell has been commanded to the terminal; a step of transmitting the received cell change notification message to the second control node; and A step of receiving a handover success message from the second control node, The above cell change notification message includes at least one of identification information of the target cell or information related to the selected beam, A method in which the handover success message includes at least one of identification information of the target cell accessed by the terminal, TA information of the target cell, or information related to a data forwarding proposal of the second control node.

10. In claim 9, A method further comprising the step of transmitting TA information of the target cell to at least one other distributed node.

11. In a method performed by a first distributed node of a first base station in a wireless communication system, A step of receiving a measurement report message from a terminal; and A step of transmitting a message proposing LTM (L1L2 triggered mobility) to the first control node of the first base station based on the above measurement report message, The above measurement report message includes an L1 measurement report message, The above LTM is a method including LTM between base stations.

12. In claim 11, The message proposing the LTM includes information related to candidate cells proposed for the LTM, A method wherein the above proposed candidate cells are determined based on the L1 measurement report message and include at least one cell belonging to at least one other base station.

13. In claim 11, A step of transmitting an early TA (timing advance) acquisition command for a second distributed node of a second base station to the terminal; and A step of transmitting a message indicating that early TA acquisition has been requested to the terminal to the second distributed node of the second base station through the first control node; and A method further comprising the step of obtaining TA information from a second distributed node of the second base station through the first control node.

14. In claim 13, The above early TA acquisition command is transmitted based on TA-related information acquired from the first control node, A method in which the TA-related information includes at least one of information requesting early TA acquisition for at least one cell among candidate cells for the LTM, information indicating that early TA acquisition for at least one cell among candidate cells for the LTM is not necessary, or TA information for at least one cell among candidate cells for the LTM.

15. In claim 13, A method further comprising the step of transmitting TA information obtained from a second distributed node of the second base station to at least one other distributed node.

16. In claim 11, A step of transmitting a message commanding the terminal to change to a target cell; and A method further comprising the step of transmitting a cell change notification message indicating that a cell change to the target cell has been commanded to the second control node of the second base station to which the target cell belongs through the first control node.

17. In a method performed by a second control node of a second base station in a wireless communication system, A step of receiving a first message related to setting up candidate cells for LTM (L1L2 triggered mobility) from a first control node of a first base station; A step of performing a setting for the LTM for at least one of the candidate cells based on the first message; and A method comprising the step of transmitting a second message including information related to at least one candidate cell to the first control node.

18. In claim 17, A step of receiving a third message including information necessary for the operation of the LTM from the first control node; A step of obtaining information related to setting up L1 (layer 1) measurement reporting of at least one candidate cell based on the third message; and A method further comprising the step of transmitting a fourth message including information related to L1 (layer 1) measurement report settings of at least one candidate cell to the first control node.

19. In a method performed by a terminal in a wireless communication system, A step of transmitting a measurement report message to the first distributed node of the first base station; and A step of receiving a cell change message from the first distributed node, The above cell change message is a method for instructing a cell change to a target cell belonging to a second distributed node of a second base station.

20. In a wireless communication system, in a first control node of a first base station, Transmitter and receiver; and A processor connected to the above transmitter and receiver is included, The above processor, Decide on the initiation of LTM (L1L2 triggered mobility) setup, Controls transmission of a first message related to the configuration of candidate cells for the above LTM, The candidate cells for the above LTM include at least one cell belonging to at least one other base station, The first message is transmitted by the first control node of the first base station to the second control node of the second base station included in the at least one other base station.

21. In a wireless communication system, in a first distributed node of a first base station, Transmitter and receiver; and A processor connected to the above transmitter and receiver is included, The above processor, Receive a measurement report message from the terminal, Control to transmit a message proposing LTM (L1L2 triggered mobility) to the first control node of the first base station based on the above measurement report message, The above measurement report message includes an L1 measurement report message, The above LTM is a first distributed node of a first base station including an LTM between base stations.

22. In a wireless communication system, in a second control node (centralized unit) of a second base station, Transmitter and receiver; and A processor connected to the above transmitter and receiver is included, The above processor, Receive a first message related to setting up candidate cells for LTM (L1L2 triggered mobility) from a first control node of a first base station, Performing a setting for the LTM for at least one of the candidate cells based on the first message; A second control node of a second base station controlling the transmission of a second message containing information related to at least one candidate cell to the first control node.

23. In a wireless communication system, at a terminal, Transmitter and receiver; and A processor connected to the above transmitter and receiver is included, The above processor, Transmit a measurement report message to the first distributed node of the first base station, Control to receive a cell change message from the first distributed node, The above cell change message instructs the terminal to change cells to a target cell belonging to the second distributed node of the second base station.

24. In communication devices, At least one processor; At least one computer memory connected to said at least one processor and storing instructions that direct operations when executed by said at least one processor, The above actions are, A step for determining the initiation of LTM (L1L2 triggered mobility) setup; and A step of transmitting a first message related to setting up candidate cells for the above LTM, The candidate cells for the above LTM include at least one cell belonging to at least one other base station, A communication device in which the first message is transmitted to a second control node of a second base station included in the at least one other base station.

25. In a non-transitory computer-readable medium storing at least one instruction, comprising at least one instruction executable by the processor, At least one of the above commands causes the device to: Decide on the initiation of LTM (L1L2 triggered mobility) setup, Controls transmission of a first message related to the configuration of candidate cells for the above LTM, The candidate cells for the above LTM include at least one cell belonging to at least one other base station, A computer-readable medium in which the first message is transmitted to a second control node of a second base station included in the at least one other base station.

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