Method and apparatus for managing conditional handover and conditional pscell replacement in wireless communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. A method for a terminal in a wireless communication system according to one embodiment of the present disclosure comprises the steps of: receiving configuration information related to a conditional handover from a source network node; selecting a first cell in response to detection of failure in a master cell group (MCG); and determining the selected first cell as a target cell of a radio resource control (RRC) reestablishment procedure on the basis of candidate cell information included in the configuration information related to the conditional handover.

Description

Method and device for managing conditional handover and conditional PSCELL replacement in a wireless communication system

[0001] The present technology relates to a method and device for managing conditional handover of a terminal and conditional PSCell replacement in a mobile communication system.

[0002] 5G mobile communication technology defines a wide frequency band to enable fast transmission speeds and new services, and can be implemented not only in the sub-6GHz frequency band such as 3.5 gigahertz (3.5GHz), but also in the ultra-high frequency band called millimeter wave (mmWave) such as 28GHz and 39GHz ('Above 6GHz'). In addition, for 6G mobile communication technology, which is called the system after 5G communication (Beyond 5G), implementation in the terahertz band (for example, the 3 terahertz (3THz) band at 95GHz) is being considered to achieve a transmission speed that is 50 times faster than 5G mobile communication technology and an ultra-low latency time that is reduced to one-tenth.

[0003] In the early stages of 5G mobile communication technology, the goal is to support services and satisfy performance requirements for enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (URLLC), and massive Machine-Type Communications (mMTC). These include beamforming and massive MIMO to mitigate path loss of radio waves in ultra-high frequency bands and increase the transmission distance of radio waves, support for various numerologies (such as operation of multiple subcarrier intervals) and dynamic operation of slot formats for efficient use of ultra-high frequency resources, initial access technology to support multi-beam transmission and wideband, definition and operation of BWP (Bidth Part), new channel coding methods such as LDPC (Low Density Parity Check) codes for large-capacity data transmission and Polar Code for reliable transmission of control information, and L2 pre-processing (L2). Standardization has been made for network slicing, which provides dedicated networks specialized for specific services, and pre-processing.

[0004] Currently, discussions are underway to improve and enhance the initial 5G mobile communication technology in consideration of the services that 5G mobile communication technology was intended to support, and physical layer standardization is in progress for technologies such as V2X (Vehicle-to-Everything) to help autonomous vehicles make driving decisions and increase user convenience based on their own location and status information transmitted by vehicles, NR-U (New Radio Unlicensed) for the purpose of system operation that complies with various regulatory requirements in unlicensed bands, NR terminal low power consumption technology (UE Power Saving), Non-Terrestrial Network (NTN), which is direct terminal-satellite communication to secure coverage in areas where communication with terrestrial networks is impossible, and Positioning.

[0005] In addition, standardization of wireless interface architecture / protocols is in progress for technologies such as intelligent factories (Industrial Internet of Things, IIoT) to support new services through linkage and convergence with other industries, Integrated Access and Backhaul (IAB) that provides nodes for expanding network service areas by integrating wireless backhaul links and access links, Mobility Enhancement technology including Conditional Handover and Dual Active Protocol Stack (DAPS) handover, and 2-step random access (2-step RACH for NR) that simplifies random access procedures. Standardization is also in progress for system architecture / services such as 5G baseline architecture (e.g., Service-based Architecture, Service-based Interface) for grafting Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) that provides services based on the location of the terminal.

[0006] Once these 5G mobile communication systems are commercialized, an explosive increase in connected devices will be connected to the communication network, necessitating enhanced functionality and performance of 5G mobile communication systems and integrated operation of these connected devices. To this end, new research will be conducted on improving 5G performance and reducing complexity, supporting AI services, supporting metaverse services, and drone communications by utilizing eXtended Reality (XR), Artificial Intelligence (AI), and Machine Learning (ML) to efficiently support Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR).

[0007] In addition, the development of these 5G mobile communication systems includes new waveforms to ensure coverage in the terahertz band of 6G mobile communication technology, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), Array Antenna, and Large Scale Antenna, metamaterial-based lenses and antennas to improve the coverage of terahertz band signals, high-dimensional spatial multiplexing technology using Orbital Angular Momentum (OAM), Reconfigurable Intelligent Surface (RIS) technology, as well as full duplex technology to improve the frequency efficiency and system network of 6G mobile communication technology, satellite, AI (Artificial Intelligence) from the design stage and AI-based communication technology that realizes system optimization by internalizing end-to-end AI support functions, and ultra-high-performance communication and computing resources to provide services with complexity that exceeds the limits of terminal computing capabilities. It can serve as a basis for the development of next-generation distributed computing technologies that can be realized by utilizing them.

[0008] As described above and with the development of mobile communication systems, various services have become available, and methods for effectively providing these services are required.

[0009] The disclosed embodiment seeks to provide a method and device capable of effectively managing the mobility of a terminal in a wireless communication system.

[0010] In accordance with one embodiment of the present disclosure, a method of a terminal in a wireless communication system includes the steps of: transmitting, to a source network node, a first indicator indicating that use of conditional handover and simultaneous setting of conditional primary secondary cell (PSCell) addition and change (CHO+CPAC setting) is supported when selecting a first target network node of an RRC (radio resource control) reestablishment procedure; receiving, from the source network node, a second indicator related to use of the CHO+CPAC setting; and selecting, in response to detecting a failure in a master cell group (MCG), the first target network node of the RRC reestablishment procedure based on the second indicator.

[0011] According to one embodiment of the present disclosure, a method of a network node in a wireless communication system includes the steps of: receiving, from a terminal, a first indicator indicating that conditional handover and simultaneous configuration of conditional primary secondary cell (PSCell) addition and change (CHO+CPAC configuration) are supported when selecting a first target network node of an RRC (radio resource control) reestablishment procedure; and transmitting, to the terminal, a second indicator related to the use of the CHO+CPAC configuration; wherein the second indicator is characterized in that it is used to select the first target network node of the RRC reestablishment procedure in response to detecting a failure in a master cell group (MCG).

[0012] According to one embodiment of the present disclosure, in a wireless communication system, a terminal includes a transceiver; and at least one processor; wherein the processor is configured to transmit, to a source network node, a first indicator indicating that use of conditional handover and simultaneous setting of conditional primary secondary cell (PSCell) addition and change (CHO+CPAC setting) is supported when selecting a first target network node of an RRC (radio resource control) reestablishment procedure, receive, from the source network node, a second indicator related to use of the CHO+CPAC setting, and select, in response to detecting a failure in a master cell group (MCG), the first target network node of the RRC reestablishment procedure based on the second indicator.

[0013] In accordance with one embodiment of the present disclosure, in a wireless communication system, a network node includes a transceiver; and at least one processor, wherein the processor receives, from a terminal, a first indicator indicating that conditional handover and simultaneous configuration of conditional primary secondary cell (PSCell) addition and change (CHO+CPAC configuration) are supported when selecting a first target network node of an RRC (radio resource control) reestablishment procedure, and transmits, to the terminal, a second indicator related to the use of the CHO+CPAC configuration, wherein the second indicator is used to select the first target network node of the RRC reestablishment procedure in response to detecting a failure in a master cell group (MCG).

[0014] The present disclosure can improve service quality by applying setting information to resolve connection failure of a terminal.

[0015] The present disclosure can improve service quality by performing connection to another PCell and PSCell without additional delay when a terminal fails to connect to a master cell group.

[0016] The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present disclosure pertains from the description below.

[0017] FIG. 1 illustrates the structure of an LTE system according to an embodiment of the present disclosure.

[0018] FIG. 2 illustrates a wireless protocol structure of an LTE system according to an embodiment of the present disclosure.

[0019] FIG. 3 illustrates the structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0020] FIG. 4 illustrates a wireless protocol structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0021] FIG. 5 is a block diagram illustrating the internal structure of a terminal according to an embodiment of the present disclosure.

[0022] FIG. 6 is a block diagram showing the configuration of an NR base station according to an embodiment of the present disclosure.

[0023] Figure 7 illustrates setting information according to an embodiment of the present disclosure.

[0024] Figure 8 illustrates the operation sequence of a terminal and a network according to an embodiment of the present disclosure.

[0025] Figure 9 illustrates the operation of a terminal according to an embodiment of the present disclosure.

[0026] The operating principles of the present invention will be described in detail below with reference to the attached drawings. In the following description of the present invention, detailed descriptions of known functions or components will be omitted if they are deemed to unnecessarily obscure the gist of the invention. Furthermore, the terms described below are defined based on their functions in the present invention and may vary depending on the intentions or practices of the user or operator. Therefore, their definitions should be based on the overall content of this specification.

[0027] In this disclosure, phrases such as "A / B", "A or B", "at least one of A and B", "at least one of A or B", "A, B, or C", "at least one of A, B, and C", and "at least one of A, B, or C" can each include any one of the items listed together in that phrase, or all possible combinations thereof. Terms such as "first", "second", or "first" or "second" may be used simply to distinguish the corresponding component from other corresponding components and do not limit the corresponding components in any other respect (e.g., importance or order).

[0028] The terms used in the following description to identify connection nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, and terms referring to various identification information are provided for convenience of explanation. Therefore, the present invention is not limited to the terms described below, and other terms referring to objects with equivalent technical meanings may be used.

[0029] Hereinafter, the base station is an entity that performs resource allocation of the terminal, and may be at least one of a gNode B, an eNode B, a Node B, a BS (Base Station), a wireless access unit, a base station controller, or a node on a network. The terminal may include a UE (User Equipment), an MS (Mobile Station), a cellular phone, a smartphone, a computer, or a multimedia system capable of performing a communication function. In the present disclosure, downlink (DL) refers to a wireless transmission path of a signal transmitted from a base station to a terminal, and uplink (UL) refers to a wireless transmission path of a signal transmitted from a terminal to a base station. In addition, although the LTE or LTE-A system may be described below as an example, the embodiments of the present disclosure may also be applied to other communication systems having similar technical backgrounds or channel types. For example, the 5th generation mobile communication technology (5G, new radio, NR) developed after LTE-A may be included in a system to which the embodiments of the present disclosure may be applied, and 5G below may also be a concept that includes existing LTE, LTE-A, and other similar services.

[0030] Furthermore, the present disclosure may be applied to other communication systems with some modifications, as determined by a person skilled in the art, without significantly departing from the scope of the present disclosure. It will be appreciated that each block of the processing flow diagrams and combinations of the flow diagrams can be executed by computer program instructions.

[0031] These computer program instructions may be installed in a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus, so that the instructions executed by the processor of the computer or other programmable data processing apparatus create means for performing the functions described in the flowchart block(s). These computer program instructions may also be stored in a computer-available or computer-readable memory that can be directed to a computer or other programmable data processing apparatus to implement functions in a particular manner, so that the instructions stored in the computer-available or computer-readable memory can produce an article of manufacture that includes instruction means for performing the functions described in the flowchart block(s). The computer program instructions may also be installed on a computer or other programmable data processing apparatus, so that a series of operational steps are performed on the computer or other programmable data processing apparatus to create a computer-implemented process, so that the instructions executing on the computer or other programmable data processing apparatus can provide steps for performing the functions described in the flowchart block(s).

[0032] Additionally, each block may represent a module, segment, or portion of code that contains one or more executable instructions for executing a specific logical function(s). It should also be noted that in some alternative implementation examples, the functions mentioned in the blocks may occur out of order. For example, two blocks shown in succession may in fact be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order depending on the corresponding function. In this case, the term '~unit' used in the present embodiment means software or a hardware component such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit), and the '~unit' may perform certain roles. However, the '~unit' is not limited to software or hardware. The '~unit' may be configured to be on an addressable storage medium and may be configured to execute one or more processors. Thus, as an example, the '~ unit' includes components such as software components, object-oriented software components, class components, and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functionality provided within the components and '~ units' may be combined into a smaller number of components and '~ units' or further separated into additional components and '~ units'. In addition, the components and '~ units' may be implemented to reproduce one or more CPUs within a device or a secure multimedia card. Also, in an embodiment, the '~ unit' may include one or more processors.

[0033] For convenience of explanation, the present invention uses terms and names defined in the 5GS and NR standards, which are standards defined by the 3rd Generation Partnership Project (3GPP) among the existing communication standards. However, the present invention is not limited to the above terms and names and can be equally applied to wireless communication networks that follow other standards. For example, the present invention can be applied to the 3GPP 5GS / NR (5th generation mobile communication standard).

[0034] FIG. 1 is a diagram illustrating the structure of an LTE system according to an embodiment of the present disclosure.

[0035] Referring to FIG. 1, as illustrated, a wireless access network of an LTE system may be composed of next-generation base stations (evolved Node Bs, hereinafter eNBs, Node Bs or base stations) (105, 110, 115, 120), a mobility management entity (MME) (1-5) and an S-GW (130, Serving-Gateway). A user equipment (UE or terminal) (135) may access an external network through the eNBs (105 to 120) and the S-GW (130).

[0036] In Fig. 1, eNBs (105 to 120) may correspond to existing Node Bs of a UMTS (universal mobile telecommunication system) system. The eNBs are connected to UEs (135) via a wireless channel and may perform more complex roles than existing Node Bs. In the LTE system, all user traffic, including real-time services such as VoIP (Voice over IP) via the Internet Protocol, can be serviced through a shared channel. Therefore, a device that collects status information such as buffer status, available transmission power status, and channel status of UEs and performs scheduling is required, and the eNBs (105, 110, 115, 120) may be responsible for this. One eNB can typically control multiple cells. For example, in order to implement a transmission speed of 100 Mbps, the LTE system may use, for example, Orthogonal Frequency Division Multiplexing (OFDM) as a wireless access technology in a 20 MHz bandwidth. In addition, an adaptive modulation and coding (AMC) method that determines a modulation scheme and channel coding rate according to the channel condition of the terminal can be applied. The S-GW (130) is a device that provides a data bearer and can create or remove a data bearer according to the control of the MME (125). The MME is a device that is responsible for various control functions as well as mobility management functions for the terminal and can be connected to multiple base stations.

[0037] FIG. 2 is a diagram showing a wireless protocol structure of an existing LTE system according to an embodiment of the present disclosure.

[0038] Referring to FIG. 2, the wireless protocol of the LTE system may be composed of Packet Data Convergence Protocol (PDCP) (205, 240), Radio Link Control (RLC) (210, 235), and Medium Access Control (MAC) (215, 230) in the terminal and eNB, respectively. PDCP may be responsible for operations such as IP header compression / decompression. The main functions of PDCP may be summarized as follows.

[0039] - Header compression and decompression (ROHC only)

[0040] - User data transfer function

[0041] - In-sequence delivery of upper layer PDUs at PDCP re-establishment procedure for RLC AM

[0042] - Order reordering function (For split bearers in DC (only support for RLC AM): PDCP PDU routing for transmission and PDCP PDU reordering for reception)

[0043] - Duplicate detection function (Duplicate detection of lower layer SDUs at PDCP re-establishment procedure for RLC AM)

[0044] - Retransmission function (Retransmission of PDCP SDUs at handover and, for split bearers in DC, of ​​PDCP PDUs at PDCP data-recovery procedure, for RLC AM)

[0045] - Encryption and decryption functions (Ciphering and deciphering)

[0046] - Timer-based SDU discard in uplink.

[0047] Radio Link Control (RLC) (2-10, 2-35) can perform ARQ operations, etc. by reconfiguring PDCP packet data units (PDUs) to an appropriate size. The main functions of RLC can be summarized as follows.

[0048] - Data transfer function (Transfer of upper layer PDUs)

[0049] - ARQ function (Error Correction through ARQ (only for AM data transfer))

[0050] - Concatenation, segmentation and reassembly of RLC SDUs (only for UM and AM data transfer)

[0051] - Re-segmentation of RLC data PDUs (only for AM data transfer)

[0052] - Reordering of RLC data PDUs (only for UM and AM data transfer)

[0053] - Duplicate detection (only for UM and AM data transfer)

[0054] - Error detection function (Protocol error detection (only for AM data transfer))

[0055] - RLC SDU discard function (RLC SDU discard (only for UM and AM data transfer))

[0056] - RLC re-establishment function

[0057] MAC (215, 230) is connected to multiple RLC layer devices configured in a single terminal, and can perform operations of multiplexing RLC PDUs into MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The main functions of MAC can be summarized as follows.

[0058] - Mapping function (Mapping between logical channels and transport channels)

[0059] - Multiplexing and demultiplexing function (Multiplexing / demultiplexing of MAC SDUs belonging to one or different logical channels into / from transport blocks (TB) delivered to / from the physical layer on transport channels)

[0060] - Scheduling information reporting function

[0061] - HARQ function (Error correction through HARQ)

[0062] - Priority handling between logical channels of one UE

[0063] - Priority handling between UEs by means of dynamic scheduling

[0064] - MBMS service identification function

[0065] - Transport format selection function

[0066] - Padding function

[0067] The PHY (physical layer) (220, 225) can perform an operation of channel coding and modulating upper layer data, converting it into OFDM symbols and transmitting it through a wireless channel, or demodulating and channel decoding OFDM symbols received through a wireless channel and transmitting them to a higher layer.

[0068] FIG. 3 is a diagram illustrating the structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0069] Referring to FIG. 3, a wireless access network of a next-generation mobile communication system (hereinafter referred to as NR or 5g) may be composed of a next-generation base station (New Radio Node B, hereinafter referred to as NR gNB or NR base station) (310) and a next-generation radio core network (New Radio Core Network, NR CN) (305). A next-generation radio user equipment (NR UE or terminal) (315) may access an external network through the NR gNB (310) and the NR CN (305).

[0070] In Fig. 3, the NR gNB (310) may correspond to an eNB (evolved Node B) of an existing LTE system. The NR gNB is connected to an NR UE (315) via a wireless channel and may provide a service superior to that of an existing Node B. In the next-generation mobile communication system, all user traffic may be serviced through a shared channel. Therefore, a device that collects status information such as buffer status, available transmission power status, and channel status of UEs and performs scheduling is required, and the scheduling may be performed by the NR NB (310). A single NR gNB may control multiple cells.

[0071] In next-generation mobile communication systems, bandwidths exceeding the typical maximum bandwidth may be applied to achieve ultra-high-speed data transmission compared to conventional LTE. Furthermore, beamforming technology may be additionally incorporated into Orthogonal Frequency Division Multiplexing (OFDM) as a wireless access technology. Furthermore, Adaptive Modulation & Coding (AMC), which determines the modulation scheme and channel coding rate based on the terminal's channel conditions, may be applied.

[0072] The NR CN (305) can perform functions such as mobility support, bearer setup, and QoS setup. The NR CN (305) is a device that handles various control functions as well as mobility management functions for terminals and can be connected to multiple base stations. In addition, the next-generation mobile communication system can be linked with the LTE system, and the NR CN (305) can be connected to the MME (325) through a network interface. The MME (325) can be connected to an eNB (330), which is an LTE base station.

[0073] Meanwhile, a single NR gNB (310) can generally transmit and receive multiple carriers across multiple frequency bands. For example, when a carrier with a forward center frequency of f1 and a carrier with a forward center frequency of f3 are transmitted from a base station, an NR UE (315) with carrier aggregation capabilities can simultaneously transmit and receive data through multiple carriers.

[0074] The NR gNB (310) can increase the transmission speed of the NR UE (315) by allocating more carriers to the NR UE (315) with carrier aggregation capabilities, depending on the situation. Aggregating forward carriers and uplink carriers transmitted and received by a single base station as described above is called "carrier aggregation within the base station." However, in some cases, unlike as illustrated in FIG. 3, it may be necessary to aggregate forward carriers and uplink carriers transmitted and received by different base stations.

[0075] When an NR gNB (310) transmits / receives a carrier having a center frequency of f1 and another base station transmits / receives a carrier having a center frequency of f2, and an NR UE (315) aggregates (combines) a carrier having a forward center frequency of f1 and a carrier having a forward center frequency of f2, this results in one terminal aggregating carriers transmitted / received from two or more base stations, and in one embodiment of the present disclosure, this is called “inter-base station carrier aggregation (or inter-base station CA).”

[0076] In one embodiment of the present disclosure, carrier aggregation between base stations is referred to as Dual Connectivity (DC, hereinafter referred to as “DC”). For example, setting up DC may mean that carrier aggregation between base stations is set up, that one or more cell groups are set up, that a Secondary Cell Group (SCG, hereinafter referred to as “SCG”) is set up, that at least one Secondary Cell (SCell, hereinafter referred to as “SCell”) under the control of a base station other than a serving base station is set up, that a pSCell (primary SCell) is set up, that a MAC entity for a serving base station is set up, and that two MAC entities are set up in a terminal.

[0077] Meanwhile, terms frequently used in describing embodiments of the present invention are briefly explained as follows.

[0078] In the traditional sense, when a single forward carrier transmitted by a base station and a single uplink carrier received by the base station constitute a single cell, carrier aggregation can be understood as a terminal simultaneously transmitting and receiving data through multiple cells. In this case, the maximum transmission speed and the number of aggregated carriers are positively correlated.

[0079] In the embodiments of the present invention, when a terminal receives data through an arbitrary forward carrier or transmits data through an arbitrary uplink carrier, it means the same as transmitting / receiving data using a control channel and a data channel provided by a cell corresponding to a center frequency and frequency band that characterize the carrier. In the embodiments of the present disclosure, carrier aggregation will be expressed as 'multiple serving cells being configured', and terms such as primary serving cell (hereinafter PCell), secondary serving cell (hereinafter SCell), or activated serving cell will be used. In the embodiments of the present invention, terms such as carrier, component carrier, and serving cell may be used interchangeably.

[0080] In embodiments of the present invention, a set of serving cells controlled by the same base station is defined as a cell group or carrier group (CG, hereinafter referred to as "CG"). The cell group is further divided into a master cell group (MCG, hereinafter referred to as "MCG") and a secondary cell group (SCG, hereinafter referred to as "SCG").

[0081] The above MCG refers to a set of serving cells controlled by a base station (hereinafter referred to as a master base station) that controls one primary cell (PCell) and up to N secondary cells (SCells). The above SCG refers to a set of serving cells controlled by a base station (hereinafter referred to as a slave base station) that controls one primary secondary cell (PSCell) and up to N SCells. Whether a specific serving cell belongs to an MCG or an SCG is notified to the terminal by the base station during the process of configuring the serving cell.

[0082] One MCG and one or more SCGs may be set for one terminal, and in the embodiments of the present invention, for the convenience of explanation, only the case where one SCG is set is considered, but even if two or more SCGs are set, the contents of the present invention can be applied as is without any particular addition or subtraction.

[0083] There are several differences between PCell and SCell. For example, PCell is always active, while SCell alternates between active and inactive states based on the base station's instructions. UE mobility is controlled around the PCell, and SCell can be understood as an additional serving cell for data transmission and reception. In the embodiments of the present invention, the PCell and SCell may refer to the PCell and SCell defined in 3GPP TS 36.331 or TS 36.321.

[0084] In the following description, other terms may be used in place of MCG and SCG for clarity. For example, terms such as primary set and secondary set, or primary carrier group and secondary carrier group, may be used. It should be noted that although these terms may be used differently, the meaning remains the same, with only the terminology used being different.

[0085] FIG. 4 is a diagram showing a wireless protocol structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0086] Referring to FIG. 4, the wireless protocol of the next-generation mobile communication system is composed of NR Service Data Adaptation Protocol (SDAP) (401, 445), NR PDCP (405, 440), NR RLC (410, 435), NR MAC (415, 430), and NR PHY (420, 425) in the terminal and NR base station, respectively.

[0087] The main functions of NR SDAP (401, 445) may include some of the following functions:

[0088] - Transfer of user plane data

[0089] - Mapping function between QoS flow and data bearer for both DL and UL

[0090] - QoS flow ID marking function for uplink and downlink (marking QoS flow ID in both DL and UL packets)

[0091] - Ability to map relective QoS flow to data bearer for uplink SDAP PDUs (reflective QoS flow to DRB mapping for the UL SDAP PDUs).

[0092] For an SDAP layer device, a terminal can be configured by a Radio Resource Control (RRC) message for each PDCP layer device, per bearer, or per logical channel, whether to use the header of the SDAP layer device or whether to use the function of the SDAP layer device. When the SDAP header is configured, the terminal can instruct the terminal to update or reset the mapping information for the QoS flow and data bearer of the uplink and downlink by using a 1-bit indicator for reflecting the Non-Access Stratum (NAS) Quality of Service (QoS) in the SDAP header (NAS reflective QoS) and a 1-bit indicator for reflecting the Access Stratum (AS) QoS in the SDAP header. The SDAP header can include QoS flow ID information indicating QoS. The QoS information can be used as data processing priority, scheduling information, etc. to support a smooth service.

[0093] The main functions of NR PDCP (405, 440) may include some of the following functions:

[0094] - Header compression and decompression (ROHC only)

[0095] - User data transfer function

[0096] - In-sequence delivery of upper layer PDUs

[0097] - Out-of-sequence delivery of upper layer PDUs

[0098] - PDCP PDU reordering for reception

[0099] - Duplicate detection of lower layer SDUs

[0100] - Retransmission function (Retransmission of PDCP SDUs)

[0101] - Encryption and decryption functions (Ciphering and deciphering)

[0102] - Timer-based SDU discard in uplink.

[0103] In the above, the reordering function of the NR PDCP device may refer to a function of reordering PDCP PDUs received from a lower layer in order based on a PDCP SN (sequence number). The reordering function of the NR PDCP device may include a function of transmitting data to an upper layer in the reordered order, or a function of transmitting data directly without considering the order, a function of recording lost PDCP PDUs by reordering the order, a function of reporting a status of lost PDCP PDUs to the transmitting side, and a function of requesting retransmission of lost PDCP PDUs.

[0104] The main functions of NR RLC (410, 435) may include some of the following functions:

[0105] - Data transfer function (Transfer of upper layer PDUs)

[0106] - In-sequence delivery of upper layer PDUs

[0107] - Out-of-sequence delivery of upper layer PDUs

[0108] - ARQ function (Error Correction through ARQ)

[0109] - Concatenation, segmentation and reassembly of RLC SDUs

[0110] - Re-segmentation of RLC data PDUs

[0111] - Reordering of RLC data PDUs

[0112] - Duplicate detection function

[0113] - Protocol error detection

[0114] - RLC SDU discard function

[0115] - RLC re-establishment function

[0116] In the above, the in-sequence delivery function of the NR RLC device may refer to the function of sequentially delivering RLC SDUs received from the lower layer to the upper layer. If a single RLC SDU is originally received divided into multiple RLC SDUs, the in-sequence delivery function of the NR RLC device may include the function of reassembling and delivering them.

[0117] The in-sequence delivery function of the NR RLC device may include a function to reorder received RLC PDUs based on the RLC SN (sequence number) or PDCP SN (sequence number), a function to record lost RLC PDUs by reordering them, a function to report status of lost RLC PDUs to the transmitter, and a function to request retransmission of lost RLC PDUs.

[0118] The in-sequence delivery function of the NR RLC device may include a function to sequentially deliver only the RLC SDUs up to the lost RLC SDU to the upper layer when there is a lost RLC SDU.

[0119] The in-sequence delivery function of the NR RLC device may include a function to deliver to the upper layer in sequence all RLC SDUs received before a predetermined timer starts if there are lost RLC SDUs and a predetermined timer has expired.

[0120] The in-sequence delivery function of the NR RLC device may include a function to deliver all RLC SDUs received so far to the upper layer in order if a predetermined timer has expired, even if there are lost RLC SDUs.

[0121] An NR RLC device can process RLC PDUs in the order they are received and deliver them to an NR PDCP device, regardless of the order of the sequence number (out-of-sequence delivery).

[0122] When an NR RLC device receives a segment, it can receive segments that are stored in a buffer or will be received later, reconstruct them into a complete RLC PDU, and then transmit them to the NR PDCP device.

[0123] The NR RLC layer may not include concatenation functionality, and the functionality may be performed by the NR MAC layer or replaced by the multiplexing functionality of the NR MAC layer.

[0124] In the above, the out-of-sequence delivery function of the NR RLC device may refer to the function of directly delivering RLC SDUs received from a lower layer to an upper layer regardless of the order. The out-of-sequence delivery function of the NR RLC device may include the function of reassembling and delivering the RLC SDUs when an original RLC SDU is received fragmented into multiple RLC SDUs. The out-of-sequence delivery function of the NR RLC device may include the function of storing and arranging the RLC SN or PDCP SN of the received RLC PDUs to record the lost RLC PDUs.

[0125] NR MAC (415, 430) can be connected to multiple NR RLC layer devices configured in one terminal, and the main functions of NR MAC can include some of the following functions.

[0126] - Mapping function (Mapping between logical channels and transport channels)

[0127] - Multiplexing / demultiplexing of MAC SDUs

[0128] - Scheduling information reporting function

[0129] - HARQ function (Error correction through HARQ)

[0130] - Priority handling between logical channels of one UE

[0131] - Priority handling between UEs by means of dynamic scheduling

[0132] - MBMS service identification function

[0133] - Transport format selection function

[0134] - Padding function

[0135] The NR PHY layer (420, 425) can perform operations of channel coding and modulating upper layer data, converting it into OFDM symbols and transmitting it through a wireless channel, or demodulating and channel decoding OFDM symbols received through a wireless channel and transmitting them to a higher layer.

[0136] Figure 5 is a block diagram showing the structure of a terminal according to an embodiment of the present invention.

[0137] Referring to the above drawing, the terminal may include a transceiver (500), a storage unit (530), and a control unit (540). The transceiver (500) may include an RF processing unit (510) and a baseband processing unit (520). The transceiver (500) may be referred to as a communication unit. The control unit (540) may include a multi-connection processing unit (542).

[0138] The RF processing unit (510) included in the transceiver unit (500) may perform functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. The RF processing unit (510) may up-convert a baseband signal provided from the baseband processing unit (520) into an RF band signal and transmit the up-converted signal through an antenna, and may down-convert an RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (510) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital to analog convertor (DAC), an analog to digital convertor (ADC), etc. In the drawing, only one antenna is illustrated, but the terminal may be equipped with multiple antennas. In addition, the RF processing unit (510) may include multiple RF chains. Furthermore, the RF processing unit (510) may perform beamforming. For the above beamforming, the RF processing unit (510) can adjust the phase and size of each signal transmitted and received through multiple antennas or antenna elements. In addition, the RF processing unit can perform MIMO, and can receive multiple layers when performing the MIMO operation.

[0139] The baseband processing unit (520) included in the transceiver unit (500) can perform a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the system. For example, when transmitting data, the baseband processing unit (520) can generate complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (520) can restore a reception bit stream by demodulating and decoding a baseband signal provided from the RF processing unit (510). For example, in the case of following the OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processing unit (520) can generate complex symbols by encoding and modulating a transmission bit stream, map the complex symbols to subcarriers, and then configure OFDM symbols through an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion. In addition, when receiving data, the baseband processing unit (520) divides the baseband signal provided from the RF processing unit (510) into OFDM symbol units, restores signals mapped to subcarriers through FFT (fast Fourier transform), and then restores the received bit string through demodulation and decoding.

[0140] The baseband processing unit (5-20) and the RF processing unit (5-10) can transmit and receive signals as described above. Furthermore, at least one of the baseband processing unit (520) and the RF processing unit (510) may include a plurality of communication modules to support a plurality of different wireless access technologies. In addition, at least one of the baseband processing unit (520) and the RF processing unit (510) may include different communication modules to process signals of different frequency bands. For example, the different wireless access technologies may include wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. In addition, the different frequency bands may include a super high frequency (SHF) (e.g., 2.NRHz, NRhz) band, a millimeter wave (mm wave) (e.g., 60GHz) band.

[0141] The storage unit (530) can store data such as basic programs, application programs, and setting information for the operation of the terminal. In particular, the storage unit (530) can store information related to a second access node that performs wireless communication using a second wireless access technology. In addition, the storage unit (530) can provide the stored data at the request of the control unit (540).

[0142] The control unit (540) can control the overall operations of the terminal. For example, the control unit (540) can transmit and receive signals through the baseband processing unit (520) and the RF processing unit (510). In addition, the control unit (540) can record and read data in the storage unit (530). For this purpose, the control unit (540) can include at least one processor. For example, the control unit (540) can include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as application programs.

[0143] Figure 6 is a block diagram showing the configuration of an NR base station according to one embodiment of the present invention.

[0144] As shown in the drawing, the base station may include a transceiver (600), a backhaul communication unit (630), a storage unit (640), and a control unit (650). The transceiver (600) may include an RF processing unit (610) and a baseband processing unit (620). The transceiver (600) may be referred to as a communication unit. The control unit (650) may include a multi-connection processing unit (652).

[0145] The RF processing unit (610) included in the transceiver unit (600) may perform functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. The RF processing unit (610) may up-convert a baseband signal provided from the baseband processing unit (620) into an RF band signal and transmit the up-converted signal through an antenna, and may down-convert an RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (610) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. In the drawing, only one antenna is illustrated, but the first access node may have multiple antennas. In addition, the RF processing unit (610) may include multiple RF chains. Furthermore, the RF processing unit (610) may perform beamforming. For the above beamforming, the RF processing unit (610) can adjust the phase and magnitude of each signal transmitted and received through multiple antennas or antenna elements. The RF processing unit (610) can perform a downlink MIMO operation by transmitting one or more layers.

[0146] The baseband processing unit (620) included in the transceiver unit (600) may perform a conversion function between a baseband signal and a bit stream according to the physical layer standard of the first wireless access technology. For example, when transmitting data, the baseband processing unit (620) may generate complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (620) may restore a reception bit stream by demodulating and decoding a baseband signal provided from the RF processing unit (610). For example, in the case of following the OFDM method, when transmitting data, the baseband processing unit (620) may generate complex symbols by encoding and modulating a transmission bit stream, map the complex symbols to subcarriers, and then configure OFDM symbols through an IFFT operation and CP insertion. In addition, when receiving data, the baseband processing unit (620) can divide the baseband signal provided from the RF processing unit (610) into OFDM symbol units, restore the signals mapped to subcarriers through FFT operation, and then restore the received bit string through demodulation and decoding. The baseband processing unit (620) and the RF processing unit (610) can transmit and receive signals as described above.

[0147] The backhaul communication unit (630) may provide an interface for communicating with other nodes within the network. The backhaul communication unit (630) may convert a bit string transmitted from the main base station to another node, such as an auxiliary base station or a core network, into a physical signal, and may convert a physical signal received from the other node into a bit string.

[0148] The storage unit (640) can store data such as basic programs, application programs, and setting information for the operation of the base station. In particular, the storage unit (640) can store information on bearers assigned to connected terminals, measurement results reported from connected terminals, and the like. In addition, the storage unit (640) can store information that serves as a judgment criterion for whether to provide or terminate multiple connections to a terminal. In addition, the storage unit (640) can provide stored data at the request of the control unit (650).

[0149] The control unit (650) can control the overall operations of the base station. For example, the control unit (650) can transmit and receive signals through the baseband processing unit (620) and the RF processing unit (610) or through the backhaul communication unit (630). In addition, the control unit (650) records and reads data in the storage unit (640). For this purpose, the control unit (650) can include at least one processor.

[0150] In the following, terms used in this disclosure are defined as follows.

[0151] - CHO: conditional handover.

[0152] - CPAC: conditional PSCell addition and change.

[0153] - CHO+CPAC: Simultaneous configuration and execution of conditional handover of terminals and conditional PSCell addition and exchange operations.

[0154] - Target Cell Configuration: For CHO+CPAC operation, target cell configuration may mean one RRCReconfiguration message including MCG configuration including one target PCell configuration and SCG configuration including one target PSCell configuration. This message may include radio bearer configuration, measurement configuration, MCG (main cell group) configuration, and SCG (secondary cell group) configuration, which can be included in a conventional RRCReconfiguration message.

[0155] - Condition: Unless otherwise specified, refers to a performance condition, and one condition may include multiple measIds, each consisting of one measurement object and one report configuration set in the measurement configuration.

[0156] CHO settings refer to settings required for conditional handover, and CHO+CPAC settings refer to simultaneous settings of conditional handover of the terminal and conditional PSCell addition and exchange operations.

[0157] In the present disclosure, CHO may include CHO discussed in 3GPP Release 16, and CHO+CPAC may include CHO+CPAC discussed in 3GPP Release 18, but is not limited thereto.

[0158] When the network configures CHO+CPAC for a terminal, the terminal can perform movement to a specific target PCell and a specific target PSCell associated with the conditions when specific association conditions are satisfied. At this time, if conditions corresponding to the target PCell and conditions corresponding to the target PSCell are given for each CHO+CPAC, the terminal determines whether the conditions are satisfied. If both the conditions corresponding to the target PCell and the conditions corresponding to the target PSCell are satisfied, the terminal can perform a single CHO+CPAC configuration.

[0159] The above target PCell settings and target PSCell settings may be interdependent. That is, one target PCell setting may depend on another target PSCell setting. Additionally, the CPAC setting may depend on the CHO setting.

[0160] In the following, if both the CHO setting and the CHO+CPAC setting are given to the terminal, and if the terminal fails the procedure in the MCG, whether the CHO+CPAC setting will be used when the cell selected during the RRC Reestablishment operation corresponds to the PCell of one of the CHO+CPAC settings will be described. In other words, if both the CHO setting and the CHO+CPAC setting are given to the terminal, and if the terminal fails the procedure in the MCG, whether the CHO+CPAC setting will be used together with the CHO setting will be described.

[0161] Figure 7 illustrates setting information according to an embodiment of the present disclosure.

[0162] More specifically, FIG. 7 is a diagram showing detailed information when CHO settings and CHO+CPAC settings are given to a terminal.

[0163] Referring to Figure 7, in a CHO configuration, the target PCell is unique across all configurations. For example, PCells 1, 2, and 3 each have their own CHO configurations, each associated with a specific ID. Some CHO configurations also include configurations for a specific PCell, such as ID 2.

[0164] As illustrated in Fig. 7, additionally, when the network configures CHO+CPAC, each CHO+CPAC configuration information always includes configuration information for a specific target PCell and a specific target PSCell. At this time, the CHO+CPAC configurations may overlap for the PCell and may overlap for the PSCell, but there can be only one CHO+CPAC when the PCell and PSCell are the same at the same time.

[0165] As shown in Fig. 7, if the CHO setting and CHO+CPAC setting are given to the terminal, when the cell selected by the terminal during RRE operation is PCell 1, the terminal must select one of the settings Id 1 among the CHO settings and one of the settings ID 4, 5, 6, and 7 among the CHO+CPAC settings.

[0166] In the case where cell 1 is set as a PCell candidate cell in the CHO configuration, cell 2 is set as a PCell candidate, and cell 3 is set as a PSCell candidate in the CHO+CPAC configuration, when the UE experiences a failure in the MCG and the cell selection result is cell 2, the existing CHO candidate cell use failure recovery mechanism cannot be used and only the RRC Reestablishment procedure can be performed. In this case, the above CHO+CPAC configuration can be used. In this case, the connection interruption time is shortened.

[0167] In this disclosure, in the case described above, the following method is proposed for determining whether to use the CHO+CPAC setting in the case of MCG failure.

[0168] Method 1: How to use the CHO+CPAC setup even in the case of MCG failure

[0169] Method 2: How to not use CHO+CPAC settings in case of MCG failure.

[0170] Below, the details of each method are explained.

[0171] Method 1: How to use the CHO+CPAC setup even in the case of MCG failure

[0172] In this case, the failure conditions for the terminal to use the above CHO+CPAC settings may be as follows.

[0173] - Radio link failure (RLF) on MCG

[0174] - Reconfiguration failure

[0175] -ReconfigurationWithsync failure

[0176] - Ciphering failure

[0177] - Security failure

[0178] - Integrity protection failure

[0179] Additionally, the following conditions may apply. The sections indicated here refer to the sections based on the 3GPP RAN RRC specification (TS38.331-v17.2.0).

[0180] 1> upon detecting radio link failure of the MCG and t316 is not configured, in accordance with 5.3.10; or

[0181] 1> upon detecting radio link failure of the MCG while SCG transmission is suspended, in accordance with 5.3.10; or

[0182] 1> upon detecting radio link failure of the MCG while PSCell change or PSCell addition is ongoing, in accordance with 5.3.10; or

[0183] 1> upon detecting radio link failure of the MCG while the SCG is deactivated, in accordance with 5.3.10; or

[0184] 1> upon re-configuration with sync failure of the MCG, in accordance with clause 5.3.5.8.3; or

[0185] 1> upon mobility from NR failure, in accordance with clause 5.4.3.5; or

[0186] 1> upon integrity check failure indication from lower layers concerning SRB1 or SRB2, except if the integrity check failure is detected on the RRCReestablishment message; or

[0187] 1> upon an RRC connection reconfiguration failure, in accordance with clause 5.3.5.8.2; or

[0188] 1> upon detecting radio link failure for the SCG while MCG transmission is suspended, in accordance with clause 5.3.10.3 in NR-DC or in accordance with TS 36.331

[0010] clause 5.3.11.3 in NE-DC; or

[0189] 1> upon reconfiguration with sync failure of the SCG while MCG transmission is suspended in accordance with clause 5.3.5.8.3; or

[0190] 1> upon SCG change failure while MCG transmission is suspended in accordance with TS 36.331

[0010] clause 5.3.5.7a; or

[0191] 1> upon SCG configuration failure while MCG transmission is suspended in accordance with clause 5.3.5.8.2 in NR-DC or in accordance with TS 36.331

[0010] clause 5.3.5.5 in NE-DC; or

[0192] 1> upon integrity check failure indication from SCG lower layers concerning SRB3 while MCG is suspended; or

[0193] 1> upon T316 expiry, in accordance with clause 5.7.3b.5; or

[0194] 1> upon detecting sidelink radio link failure by L2 U2N Remote UE in RRC_CONNECTED, in accordance with clause 5.8.9.3; or

[0195] 1> upon reception of NotificationMessageSidelink including indicationType by L2 U2N Remote UE in RRC_CONNECTED, in accordance with clause 5.8.9.10; or

[0196] 1> upon PC5 unicast link release indicated by upper layer at L2 U2N Remote UE in RRC_CONNECTED.

[0197] If the above failure situation occurs, the terminal can perform cell selection. In this case, cell selection refers to the conventional cell selection operation (i.e., operations related to CHO and CHO+CPAC configurations are not considered).

[0198] After cell selection of the terminal, there are two options for using the CHO+CPAC setting in Method 1 above.

[0199] Option 1. When considering only candidate PCells in the CHO+CPAC configuration

[0200] Option 2. When considering the CHO candidate PCell and the CHO+CPAC configuration candidate PCell together

[0201] Below, options 1 and 2 are described in detail.

[0202] Option 1. When considering only candidate PCells in the CHO+CPAC configuration

[0203] For the above option 1, there are three cases where the terminal distinguishes between the following conditions:

[0204] Case 1) When the CHO+CPAC settings are included in a separate field / IE and transmitted to the terminal:

[0205] This is the case when the selected cell is identical to the target cell in the reconfigurationWithSync field inside the masterCellGroup field of the target cell configuration, i.e., condRRCReconfig, which is included in the CHO+CPAC specific conditional Reconfiguration variable of the MCG.

[0206] Case 2) When the CHO+CPAC setting is set as a separate condReconfig ID set and transmitted to the terminal:

[0207] This is the case when the selected cell is included in the conditional reconfiguration variable of MCG, is a conditional reconfiguration with an id within the range of the id set, and is identical to the target cell of the condRRCReconfig, i.e., the reconfigurationWithSync field included in the masterCellGroup field of the target cell setting.

[0208] Case 3) If the CHO+CPAC settings are included in the same field as the CHO settings and transmitted to the terminal and stored in the same variable:

[0209] This means that the selected cell is identical to the target cell in the reconfigurationWithSync field inside the masterCellGroup field of the target cell configuration, i.e., condRRCReconfig included in the conditional reconfiguration variable of the MCG, and the condRRCReconfig is associated with a condition that includes both condition information for the target PCell and condition information for the target PSCell.

[0210] In the above cases, for the selected target PCell, if only a target cell configuration exists, the terminal can apply the target cell configuration. However, for the selected target PCell, there may be target cell configurations associated with multiple different target PSCells. In this case, an additional "operation regarding which target PSCell among the multiple CPAC target PSCells associated with one CHO target PCell should be selected for the associated target cell configuration" must be performed. This will be explained later.

[0211] Option 2. When considering both the CHO candidate PCell and the CHO+CPAC configuration candidate PCell together: The following additional options are possible:

[0212] Additional Option 1. Selection is made by terminal implementation.

[0213] Specifically, if the cell selected by the terminal in the RRE operation is the same as the target PCell of the CHO configuration, and / or if the cell selected by the terminal in the CHO+CPAC configuration is the same as the target PCell, the terminal determines whether to select the target cell setting of the CHO configuration or the CHO+CPAC target cell setting.

[0214] Additional Option 2. Give priority to PCell in CHO setting over CHO+CPC target cell setting.

[0215] A. If the cell selected by the terminal in RRE operation is identical to the target PCell in the CHO configuration, and if it is identical to the target PCell in the CHO+CPAC configuration, the terminal can apply the CHO configuration. Otherwise, the terminal can apply the same CHO or CHO+CPAC configuration as the selected cell.

[0216] B. The following is an example of the above operation. This may include examples from the specification.

[0217] 1. If The selected cell is the cell for which the reconfigurationWithSync is included in the masterCellGroup field in the MCG VarConditionalReconfig and its execution condition is composed of only Pcell / CHO related ones.

[0218] - Apply that condRRCReconfig;

[0219] 2. else if The selected cell is the cell for which the reconfigurationWithSync is included in the masterCellGroup field in the MCG VarConditionalReconfig and its execution condition is composed of Pcell / CHO and Pscell / CPAC related ones.

[0220] - If there are multiple configurations, Further choose one based on next slide conditions:

[0221] Additional Option 3. CHO+CPAC settings take precedence over CHO settings.

[0222] A. If the cell selected by the UE in RRE operation is identical to the target PCell in the CHO configuration, and if it is identical to the target PCell in the CHO+CPAC configuration, the UE can select the CHO+CPAC configuration. Otherwise, the UE can apply the same CHO or CHO+CPAC configuration as the selected cell. If the CHO+CPAC configuration is selected, each target PSCell can have different configurations. In this case, the "Operation regarding which target PSCell among multiple CPAC target PSCells associated with a single CHO target PCell should select the associated target cell configuration" below is followed.

[0223] B. The following is an example of the above operation. This may include examples from the specification.

[0224] 1. If The selected cell is the cell for which the reconfigurationWithSync is included in the masterCellGroup field in the MCG VarConditionalReconfig and its execution condition is composed of Pcell / CHO and Pscell / CPAC related ones; and

[0225] A. If there are multiple configurations, Further choose one based on next slide conditions: and

[0226] B. Apply that condRRCReconfig;

[0227] 2. Else if the selected cell is the cell for which the reconfigurationWithSync is included in the masterCellGroup field in the MCG VarConditionalReconfig and its execution condition is composed of only Pcell / CHO related ones.

[0228] A. Apply that condRRCReconfig;

[0229] In cases where the above CHO+CPAC target cell configuration is applied, the "action regarding which target PSCell among multiple CPAC target PSCells associated with one CHO target PCell should be selected for the associated target cell configuration" may follow several additional options. Additionally, selecting a target PSCell here means the same as selecting a CHO+CPAC target cell configuration that includes the target PSCell.

[0230] Additional Option 3-1. The terminal may implement the selection of the above multiple PSCells.

[0231] Additional Option 3-2. The network can explicitly inform the above CHO+CPAC target cell settings.

[0232] That is, when a terminal performs cell selection while performing an RRE operation, if there are multiple settings that match the CHO target PCell of the CHO+CPAC configuration among the selected cells, the terminal can explicitly indicate which setting to apply. In this case, the information indicated by the network can indicate to the terminal the conditional Reconfiguration ID of the applicable target or the PCI (physical cell ID) and / or ARFCN (absolute radio frequency channel) information of a specific PSCell among multiple target PSCells.

[0233] Additional Option 3-3. The terminal can select the CHO+CPAC configuration of one of the PSCells among the multiple PSCells that satisfy the associated CPAC condition information. In this case, if there are multiple PSCells that satisfy the CPAC condition information, the terminal can select any PSCell or the one with the strongest received signal strength. Alternatively, the terminal can select the configuration with the lowest conditional Reconfiguration ID among the CHO+CPAC configurations of the PSCells that satisfy the condition.

[0234] Additional Options 3-4. If a terminal has a currently configured PSCell, it can select a CHO+CPAC configuration with that PSCell as the target PSCell. In this case, the PSCell must not be deactivated and transmission / reception must not be suspended.

[0235] Additional options 3-5. The terminal can select the PSCell with the strongest reception signal strength.

[0236] Additional Option 3-6. The terminal can select a specific configuration from among the multiple CHO+CPAC configurations and apply only the PCell settings within that configuration. In this case, the current PSCell configuration can be maintained or a multi-RAT (radio access technology) dual connectivity (MRDC) release operation can be performed.

[0237] Additional Option 3-7. The above actions can be combined by prioritizing each condition. For example, if a PSCell currently has DC configured among multiple PSCells and its CPAC conditions are met, the CHO+CPAC configuration of that PSCell can be selected. Alternatively, if the current terminal is not configured for DC, the additional option 3-6 can be applied.

[0238] When the terminal completes selection of the above CHO+CPAC settings, it can apply the condRRCReconfiguration, i.e., RRCReconfiguration, message of the corresponding settings.

[0239] After performing the above operation and the terminal applies the message, the terminal can create an RRCReconfigurationComplete message of the selected CHO+CPAC configuration and transmit the message to the gNB of the target PCell of the selected CHO+CPAC, i.e., the T-MN. At this time, the RRCReconfigurationComplete message can include at least one of the selected CHO+CPAC configuration information, the conditional Reconfiguration ID of the selected CHO+CPAC configuration, the PCI and ARFCN information of the target PCell of the corresponding CHO+CPAC configuration, and / or the PCI and AFRCN information of the target PSCell. Since the RRCReconfigurationComplete message including the above information is transmitted to the target MN in the CPAC operation, the T-MN can recognize which cell / which SN node is the new T-SN and can know that the reconfiguration is complete.

[0240] Figure 8 illustrates the operation sequence of a terminal and a network according to an embodiment of the present disclosure.

[0241] Below, the operation of the capability-related signaling system is described.

[0242] Referring to FIG. 8, when a UE (800) is initially connected to a network, or after establishing an RRC connection with a source-master node (S-MN) (803), the UE (800) may transmit a UE capability indication indicating that it supports RRC Reestablishment (RRE) to apply CHO+CPAC settings to the S-MN (803) (810).

[0243] That is, the UE (800) can transmit to the base station (S-MN) a UECapabilityInformaiton message or a UL RRC message including a 1-bit indicator indicating that its CHO+CPAC settings can be used as target cell settings after cell selection of the RRE.

[0244] That is, the UE (800) can transmit, through UE capability information or a corresponding UL RRC message, an indication that it supports the operation of applying the corresponding CHO+CPAC configuration when the selected cell is included in the target cell of the CHO+CPAC configuration after cell selection during the RRC reestablishment operation, especially when it is the same as the target PCell.

[0245] The S-MN (803) can configure the UE (800) to apply features corresponding to the UE capability information transmitted by the UE (800) to the S-MN (803) in step 810 (820).

[0246] That is, the network that has received the indicator can transmit to the UE (800) through a DL RRC message or an RRCRecofiguration message an indicator indicating whether to perform the existing legacy attemptCondReconfiguration for the cell selected during RRE, to use only the CHO+CPAC configuration for application, or to use the existing CHO configuration and CHO+CPAC configuration.

[0247] That is, the network that has received the above indication can then transmit the following indication to the terminal in a separate DL RRC message or RRCReconfiguration message.

[0248] - Existing legacy attemptCondReconfig directive

[0249] - Directive to use only CHO+CPAC settings for candidate settings to be used when selecting RRE cells.

[0250] - A directive to consider both CHO+CPAC and CHO settings simultaneously for candidate settings to be used when selecting an RRE cell (i.e., consider the settings included in the masterCellGroup field of reconfigurationWithSync among condRRCReconfig of conditional Reconfigurations).

[0251] In Fig. 8, for example, it is set assuming that a directive is transmitted to use only the CHO+CPAC setting among the above directives.

[0252] The transmission of the above indicator can be transmitted together with the RRCReconfiguration message when transmitting CHO configuration or CHO+CPAC configuration information.

[0253] After transmitting the CHO and / or CHO+CPAC settings, the UE (800) and S-MN (803) can perform CHO and / or CHO+CPAC settings (830).

[0254] Thereafter, the UE (800) performs measurement and condition evaluation operations, and if a failure occurs with the PCell during the process (the detailed conditions of the failure are described above), the UE (800) can perform an RRC reestablishment operation and, accordingly, perform cell selection (840).

[0255] If the selected cell is the same as the target PCell of CHO among the CHO+CPAC configurations, the UE (800) can select and apply the corresponding CHO+CPAC configuration (or the CHO+CPAC configuration with a specific target PSCell among the configurations) (850).

[0256] Application of the above settings enables mobility operations to be performed on target PCell and target PSCell.

[0257] After the application is performed, the UE (800) can perform random access with the target-master node (T-MN) (807) (860). In addition, the UE (800) can perform random access with the target-secondary node (T-SN) (809) (870). The UE (800) can transmit an RRCReconfigurationComplete message to the target PCell in the configuration (880).

[0258] During this transmission process, the UE (800) can transmit a RACH (random access channel) preamble to the corresponding PCell (or T-MN (807)) and PSCell (or T-SN (target-secondary node) (809)) and receive a RAR (random access response) from the PCell. The RRCReconfigurationComplete message can include information on the CHO+CPAC configuration selected for the RRE process. The RRCReconfigurationComplete message can include a selected condReconfig ID.

[0259] Here, the selected condReconfig ID may be a conditional reconfiguration ID that indicates the PCI and / or ARFCN of a specific target PCell in the CHO configuration or the target PCell configuration in the CHO configuration, if the CHO configuration is selected, according to the application of the above-mentioned option. Alternatively, if the CHO+CPAC configuration is selected, the selected condReconfig ID may be a conditional reconfiguration ID corresponding to a specific CHO+CPAC configuration, and the CHO+CPAC configuration may include PCI and / or ARFCN information of the target PCell of the configuration, and PCI and / or AFRCN information of the target PSCell of the configuration. The T-MN (807) can know that the UE (800) has moved from the S-MN (803) and what the current PSCell and T-SN (809) are through the included configuration information. Accordingly, the T-MN (807) can notify the T-SN (809) that the application of the CHO+CPAC configuration of the UE (800) is complete (890). After this, the UE (800) can operate in a dual connected configuration with the PCell of the new T-MN (807) and the PSCell of the T-SN (809).

[0260] Method 2: How to not use CHO+CPAC settings in case of MCG failure.

[0261] In this case, the terminal does not consider the CHO+CPAC configuration as a setting for application to the selected cell during RRE in case of MCG failure. That is, the terminal can only consider legacy CHO candidate cells.

[0262] In this case, only the CHO settings can be used, and the process works as follows:

[0263] 1> if the cell selection is triggered by detecting radio link failure of the MCG or re-configuration with sync failure of the MCG or mobility from NR failure, and

[0264] 1> if attemptCondReconfig is configured; and

[0265] 1> if the selected cell is not configured with CondEventT1, or the selected cell is configured with CondEventT1 and leaving condition has not been fulfilled; and

[0266] 1> if the selected cell is one of the candidate cells for which the reconfigurationWithSync is included in the masterCellGroup in the MCG VarConditionalReconfig:

[0267] 2> if the UE supports RLF-Report for conditional handover, set the choCellId in the VarRLF-Report to the global cell identity, if available, otherwise to the physical cell identity and carrier frequency of the selected cell;

[0268] 2> apply the stored condRRCReconfig associated to the selected cell and perform actions as specified in 5.3.5.3;

[0269] That is, for the above method 2 to be applied, the selected cell must correspond to the configuration information stored in the variable for conditional reconfiguration of the MCG, and must be a target candidate cell of the reconfigurationWithSync field included in the materCellGroup field of this. However, the CHO+CPAC configuration information can be stored together with the CHO configuration information in the variable for conditional reconfiguration of the MCG. In that case, it is necessary to distinguish whether it is a CHO configuration or a CHO+CPAC configuration, and the case of a CHO+CPAC configuration must be excluded.

[0270] Therefore, the following additional constraints are required. That is, if the selected cell is a target candidate cell for the reconfigurationWithSync field contained in the masterCellGroup field of the configuration information stored in the variable for conditional reconfiguration of the MCG, at least one of the following constraints is required:

[0271] - The saved configuration information will not be CHO+CPAC configuration information;

[0272] - The stored configuration information shall not be the configuration information linked to the CHO condition information and CPAC condition information, i.e., the PCell target condition information and the PSCell target condition information;

[0273] Figure 9 illustrates the operation of a terminal according to an embodiment of the present disclosure.

[0274] In one embodiment, the terminal may transmit a first indicator to the source network node indicating that it supports the use of simultaneous configuration of conditional handover and conditional primary secondary cell (PSCell) addition and change (CHO+CPAC configuration) when selecting a first target network node in an RRC (radio resource control) reestablishment procedure (910).

[0275] In one embodiment, the terminal may receive a second indicator related to the use of the CHO+CPAC setting from the source network node (920).

[0276] In one embodiment, the terminal may select the first target network node of the RRC re-establishment procedure based on the second indicator in response to detecting a failure in a master cell group (MCG) (930).

[0277] In one embodiment, the terminal transmits an RRCReconfigurationComplete message to the first target network node, and the RRCReconfigurationComplete message may include at least one of information about a selected CHO+CPAC configuration indicated by the second indicator, a conditional reconfiguration identifier (ID) of the selected CHO+CPAC configuration, and information about a target PCell (primary cell) and a target PSCell (primary secondary cell) indicated by the selected CHO+CPAC configuration. In one embodiment, the second indicator may include one of a third indicator indicating not to consider the CHO+CPAC configuration; a fourth indicator indicating to consider the CHO+CPAC configuration; and a fifth indicator indicating to simultaneously consider the CHO+CPAC configuration and a conditional handover (CHO) configuration.

[0278] In one embodiment, the terminal may select a second target network node in the RRC re-establishment procedure. Furthermore, if the second indicator includes the fourth indicator and the second target network node is identical to the candidate target network node indicated in the CHO+CPAC configuration, the terminal may select the candidate target network node as the first target network node.

[0279] In one embodiment, when the second indicator includes a fourth indicator indicating that the CHO+CPAC configuration is taken into consideration, information about the candidate target network node indicated by the CHO+CPAC configuration may be transmitted to the terminal by being included in a reconfigurationWithSync field, included in a condReconfig ID set, or included in the same field as the CHO configuration.

[0280] In one embodiment, the first target network node of the RRC re-establishment procedure may include a target master network node and a target secondary network node.

[0281] The methods according to the embodiments described in the claims or specification of the present invention may be implemented in the form of hardware, software, or a combination of hardware and software.

[0282] When implemented in software, a computer-readable storage medium storing one or more programs (software modules) may be provided. The one or more programs stored in the computer-readable storage medium are configured for execution by one or more processors within an electronic device. The one or more programs include instructions that cause the electronic device to execute methods according to the embodiments described in the claims or specification of the present invention.

[0283] These programs (software modules, software) may be stored in a non-volatile memory including random access memory, flash memory, read only memory (ROM), electrically erasable programmable read only memory (EEPROM), magnetic disc storage devices, compact disc ROMs (CD-ROMs), digital versatile discs (DVDs) or other forms of optical storage devices, magnetic cassettes, or may be stored in a memory configured as a combination of some or all of these. In addition, each configuration memory may include multiple copies.

[0284] Additionally, the program may be stored in an attachable storage device that is accessible via a communication network such as the Internet, an intranet, a local area network (LAN), a wide local area network (WLAN), a storage area network (SAN), or a combination thereof. Such a storage device may be connected to a device implementing an embodiment of the present invention via an external port. Additionally, a separate storage device on the communication network may be connected to a device implementing an embodiment of the present invention.

[0285] In the specific embodiments of the present invention described above, components included in the invention are expressed in the singular or plural form depending on the specific embodiment presented. However, the singular or plural expressions are selected to suit the presented situation for convenience of explanation, and the present invention is not limited to singular or plural components. Even components expressed in the plural form may be composed of singular elements, or even components expressed in the singular form may be composed of plural elements.

[0286] While the detailed description of the present invention has described specific embodiments, it is clear that various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims but also by equivalents thereof.

Claims

1. In a terminal method in a wireless communication system, A step of receiving configuration information related to conditional handover from a source network node; In response to detecting a failure in a master cell group (MCG), a step of selecting a first cell; and A step of determining the selected first cell as a target cell of an RRC (radio resource control) reestablishment procedure based on candidate cell information included in the configuration information related to the conditional handover; A method characterized in that PSCell (primary secondary cell) target condition information is not set for a candidate cell of the setting information related to the conditional handover corresponding to the first cell.

2. In paragraph 1, A method further comprising the step of transmitting, to the source network node, a first indicator indicating that the source network node supports the use of conditional handover + conditional pscell addition and change (CHO+CPAC configuration) during target cell selection of the RRC re-establishment procedure.

3. In paragraph 2, A method characterized in that the configuration information related to the conditional handover includes at least one of the CHO+CPAC configuration, a conditional reconfiguration identifier (ID) of the selected CHO+CPAC configuration, and information on a target PCell (primary cell) and a target PSCell (primary secondary cell) indicated by the selected CHO+CPAC configuration.

4. In paragraph 1, A method characterized in that the above PSCell target condition information is included in the condExecutionCondPSCell field of the conditional handover related setting information.

5. In a network node in a wireless communication system, A step of transmitting setting information related to conditional handover to a terminal; The candidate cell information included in the configuration information related to the above conditional handover is used to determine the target cell of the RRC (radio resource control) reestablishment procedure in the event of failure in the master cell group (MCG). A method characterized in that PSCell (primary secondary cell) target condition information is not set for a candidate cell of the setting information related to the conditional handover corresponding to the determined target cell.

6. In paragraph 5, A method further comprising: receiving, from the terminal, a first indicator indicating that simultaneous setting of conditional handover and conditional PSCell addition and change (CHO+CPAC setting) is supported when selecting a target cell of an RRC re-establishment procedure.

7. In paragraph 6, A method characterized in that the configuration information related to the conditional handover includes at least one of the CHO+CPAC configuration, a conditional reconfiguration identifier (ID) of the selected CHO+CPAC configuration, and information on a target PCell (primary cell) and a target PSCell (primary secondary cell) indicated by the selected CHO+CPAC configuration.

8. In paragraph 5, A method characterized in that the above PSCell target condition information is included in the condExecutionCondPSCell field of the conditional handover related setting information.

9. In a wireless communication system, at the terminal, Transmitter and receiver; and comprising at least one processor; wherein the at least one processor comprises: Receives configuration information related to conditional handover from the source network node, In response to detecting a failure in the master cell group (MCG), select a first cell, and Based on candidate cell information included in the configuration information related to the above conditional handover, the selected first cell is configured to be determined as a target cell for an RRC (radio resource control) reestablishment procedure. A terminal characterized in that PSCell (primary secondary cell) target condition information is not set for a candidate cell of the setting information related to the conditional handover corresponding to the first cell.

10. In paragraph 9, A terminal further comprising: a step of transmitting, to the source network node, a first indicator indicating that the use of conditional handover + conditional pscell addition and change (CHO+CPAC configuration) is supported when selecting a target cell in an RRC re-establishment procedure.

11. In paragraph 10, A terminal characterized in that the configuration information related to the conditional handover includes at least one of the CHO+CPAC configuration, a conditional reconfiguration identifier (ID) of the selected CHO+CPAC configuration, and information on a target PCell (primary cell) and a target PSCell (primary secondary cell) indicated by the selected CHO+CPAC configuration.

12. In paragraph 9, A terminal characterized in that the above PSCell target condition information is included in the condExecutionCondPSCell field of the conditional handover related setting information.

13. In a network node in a wireless communication system, Transmitter and receiver; and comprising at least one processor; wherein the at least one processor comprises: The terminal is configured to transmit configuration information related to conditional handover, The candidate cell information included in the configuration information related to the above conditional handover is used to determine the target cell of the RRC (radio resource control) reestablishment procedure in case of failure in the master cell group (MCG), and A network node characterized in that PSCell (primary secondary cell) target condition information is not set for a candidate cell of the setting information related to the conditional handover corresponding to the determined target cell.

14. In paragraph 13, Further configured to receive a first indicator from the terminal indicating that the terminal supports the use of conditional handover + conditional pscell addition and change (CHO+CPAC configuration) during target cell selection of the RRC re-establishment procedure, and A network node characterized in that the configuration information related to the conditional handover includes at least one of the CHO+CPAC configuration, a conditional reconfiguration identifier (ID) of the selected CHO+CPAC configuration, and information on a target PCell (primary cell) and a target PSCell (primary secondary cell) indicated by the selected CHO+CPAC configuration.

15. In paragraph 13, A network node, characterized in that the PSCell target condition information is included in the condExecutionCondPSCell field of the conditional handover related setting information.

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