Method and apparatus for supporting condition-based mobility technology in wireless communication

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. The present disclosure relates to a method by which a terminal performs communication in a wireless communication system and an apparatus therefor. A terminal according to one embodiment of the present disclosure can receive configuration information related to conditional handover (CHO) and conditional PSCELL change (CPC). A terminal according to one embodiment of the present disclosure can identify whether a condition for performing CHO and CPC is satisfied on the basis of the configuration information related to CHO and CPC, and transmit a radio link failure (RLF) report including information about an identification result.

Description

Method and device for supporting condition-based mobility technology in wireless communication

[0001] The present disclosure relates to a method and apparatus for supporting condition-based mobility technology in a wireless 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 could serve as a basis for the development of next-generation distributed computing technologies that can be realized by utilizing this technology.

[0008] The present disclosure seeks to provide a method and device for supporting condition-based mobility technology in a wireless communication system.

[0009] A method for a terminal to perform communication in a wireless communication system according to one embodiment of the present disclosure may receive configuration information related to a conditional handover (CHO) and a conditional PSCELL change (CPC). The method may identify whether conditions for performing the CHO and CPC are met based on configuration information related to the CHO and CPC. The method may transmit a radio link failure (RLF) report including information regarding the identification result.

[0010] In a wireless communication system according to one embodiment of the present disclosure, a terminal performing communication may include a transceiver and at least one processor connected to the transceiver. The at least one processor may receive configuration information related to a conditional handover (CHO) and a conditional PSCELL change (CPC). The at least one processor may identify whether conditions for performing the CHO and CPC are met based on configuration information related to the CHO and CPC. The at least one processor may transmit a radio link failure (RLF) report including information regarding the identification result.

[0011] FIG. 1a is a diagram illustrating the structure of a wireless communication system according to one embodiment of the present disclosure.

[0012] FIG. 1b is a diagram for explaining a wireless connection state transition in a wireless communication system according to an embodiment of the present disclosure.

[0013] FIG. 1c is a flowchart of a process for performing a condition-based handover operation in a mobile communication system according to an embodiment of the present invention.

[0014] FIG. 1d is a flowchart of a process for simultaneously performing condition-based handover and condition-based PSCell change according to one embodiment of the present invention.

[0015] FIG. 1e is a flowchart of a process for releasing a condition-based PSCell change operation when a condition-based handover fails according to an embodiment of the present invention.

[0016] FIG. 1f is a diagram for explaining a condition-based PSCell change operation during a CHO Failure Recovery operation according to an embodiment of the present invention.

[0017] FIG. 1g is a flowchart of a first process for performing a condition-based PSCell change operation during a CHO Failure Recovery operation according to an embodiment of the present invention.

[0018] FIG. 1h is a flowchart of a second process for performing a condition-based PSCell change operation during a CHO Failure Recovery operation according to an embodiment of the present invention.

[0019] FIG. 1i is a flowchart of a third process for performing a condition-based PSCell change operation during a CHO Failure Recovery operation according to an embodiment of the present invention.

[0020] FIG. 1j is an example of a process for performing a condition-based PSCell change operation during a CHO Failure Recovery operation according to an embodiment of the present invention.

[0021] FIG. 1k is a diagram for explaining a CPC Failure Recovery operation according to one embodiment of the present invention.

[0022] FIG. 11 is a flowchart of a process for performing a CHO Failure Recovery operation according to an embodiment of the present invention.

[0023] Figure 1m is a block diagram showing the internal structure of a terminal according to one embodiment of the present invention.

[0024] FIG. 1n is a block diagram showing the configuration of a base station according to one embodiment of the present invention.

[0025] In the following description of the present invention, detailed descriptions of known functions or configurations will be omitted if they are deemed to unnecessarily obscure the gist of the present invention. Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.

[0026] In the following description of the present invention, detailed descriptions of related known functions or configurations will be omitted if they are deemed to unnecessarily obscure the gist of the present disclosure. Furthermore, the terms described below are defined based on their functions within the present disclosure and may vary depending on the intent or custom of the user or operator. Therefore, their definitions should be based on the overall content of this specification.

[0027] In the following description of the present disclosure, detailed descriptions of related known functions or configurations will be omitted if they are deemed to unnecessarily obscure the gist of the present disclosure. Hereinafter, embodiments of the present disclosure will be described with reference to the attached drawings.

[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 as examples for convenience of explanation. Therefore, the present disclosure is not limited to the terms described below, and other terms referring to objects with equivalent technical meanings may be used.

[0029] For convenience of explanation, this disclosure uses terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP) LTE standard. However, this disclosure is not limited to the above terms and names, and can be equally applied to systems conforming to other standards. In this disclosure, eNB may be used interchangeably with gNB for convenience of explanation. That is, a base station described as an eNB may represent a gNB. Figure 1a is a diagram illustrating the structure of a wireless communication system.

[0030] Referring to Fig. 1a, as illustrated, a wireless access network of a wireless communication system is composed of a next-generation base station (New Radio Node B, hereinafter referred to as gNB) (1a-10) and an AMF (1a-05, New Radio Core Network). A user terminal (New Radio User Equipment, hereinafter referred to as NR UE or terminal) (1a-15) can access an external network through the gNB (1a-10) and the AMF (1a-05).

[0031] In Figure 1a, the gNB corresponds to the eNB (Evolved Node B) of the existing LTE system. The gNB (1a-10) is connected to the NR UE (1a-15) via a wireless channel and can provide a service superior to the existing Node B (1a-20). In a wireless communication system, all user traffic is serviced through a shared channel, so a device that collects status information such as the buffer status of the UEs, the available transmission power status, and the channel status and performs scheduling is required, and this is handled by the gNB (1a-10). A single gNB can typically control multiple cells. In order to implement ultra-high-speed data transmission compared to the existing LTE, it can have a bandwidth higher than the existing maximum, and beamforming technology can be additionally grafted using the orthogonal frequency division multiplexing (OFDM) method as a wireless access technology. In addition, it applies the Adaptive Modulation & Coding (AMC) method that determines the modulation scheme and channel coding rate according to the channel condition of the terminal. AMF (1a-05) performs functions such as mobility support, bearer setup, and QoS setup. AMF (1a-05) is a device that is in charge of various control functions as well as mobility management functions for the terminal and can be connected to multiple base stations. In addition, the next-generation mobile communication system can be linked with the existing LTE system, and AMF (1a-05) can be connected to MME (1a-25) through a network interface. MME (1a-25) is connected to eNB (1a-30), which is an existing base station. Terminals that support LTE-NR Dual Connectivity can transmit and receive data while maintaining a connection to not only gNB but also eNB (1a-35).

[0032] Figure 1b is a diagram for explaining a wireless connection state transition in a wireless communication system.

[0033] In next-generation mobile communication systems, a terminal can have three radio connection states (RRC states). Connected mode (RRC_CONNECTED, 1b-05) is a radio connection state in which the terminal can transmit and receive data. Idle mode (RRC_IDLE, 1b-30) is a radio connection state in which the terminal monitors whether a paging is being transmitted to it. These two modes are radio connection states that are also applied to existing LTE systems, and the detailed technology is identical to that of the existing LTE system. In next-generation mobile communication systems, a new inactive (RRC_INACTIVE) radio connection state (1b-15) has been defined. In this inactive (RRC_INACTIVE) radio connection state (1b-15), the UE context is maintained between the base station and the terminal, and RAN-based paging can be supported. The characteristics of this inactive (RRC_INACTIVE) radio connection state (1b-15) are as follows.

[0034] - Cell re-selection mobility;

[0035] - CN-NR RAN connection (both C / U-planes) has been established for UE;

[0036] - The UE AS context is stored in at least one gNB and the UE;

[0037] - Paging is initiated by NR RAN;

[0038] - RAN-based notification area is managed by NR RAN;

[0039] - NR RAN knows the RAN-based notification area to which the UE belongs;

[0040] The new inactive (RRC_INACTIVE) radio connection state (1b-15) can be transitioned to connected mode or standby mode using a specific procedure. The inactive mode (RRC_INACTIVE, 1b-15) is transitioned to connected mode (RRC_CONNECTED, 1b-05) through the Resume procedure, and the connected mode (RRC CONNECTED, 1b-05) is transitioned to inactive mode (RRC_INACTIVE, 1b-15) through the Release procedure including suspend configuration information (1b-10). The procedure consists of one or more steps, with one or more RRC messages transmitted and received between the terminal and the base station. In addition, the inactive mode (RRC_INACTIVE 1b-15) can be transitioned to standby mode (RRC_IDLE, 1b-30) through the Release procedure after Resume (1b-20). Transitions between connected mode (RRC_CONNECTED, 1b-05) and standby mode (RRC_IDLE, 1b-30) follow existing LTE technology. That is, transitions between the above modes are made through establishment or release procedures (1b-25).

[0041] FIG. 1c is a flowchart of a process for performing a condition-based handover operation in a mobile communication system according to an embodiment of the present invention.

[0042] A terminal (1c-05) can report its capability information to a source cell (1c-10) (1c-25). The capability information can indicate whether the terminal supports conditional handover. The terminal can receive a predetermined RRC message including measurement configuration information from the source cell (1c-30). The terminal (1c-05) can apply the measurement configuration information to measure the signal quality of a serving cell and neighboring cells, and periodically or when a configured event occurs (1c-35), report the collected cell measurement information to the source cell (1c-10) (1c-40). The source cell (1c-10) can determine whether to trigger a conditional handover operation based on the reported cell measurement information (1c-45). In order to configure the conditional handover, the terminal (1c-05) must be able to support the conditional handover. If it is decided to trigger the condition-based handover, the source cell (1c-10) can request the condition-based handover to one or more target cells (1c-20) via a predetermined inter-node message (1c-50). The target cells (1c-20) that receive the request can accept it and transmit handover configuration information required for the condition-based handover operation to the source cell (1c-10) (1c-55). Target cells that do not accept the request are excluded from the condition-based handover. The source cell (1c-10) can store the handover configuration information and additional configuration information received from the target cells (1c-20) in a predetermined RRC message, RRCReconfiguration, and transmit the RRC message to the terminal (1c-05) (1c-60).The above configuration information includes the IDs of target cells, frequency information, configuration information required for random access operations to the target cells (dedicated preamble information, dedicated radio resource information, etc. for each target cell), transmission power information, C-RNTI information used in each target cell, conditions for triggering random access operations to each target cell, etc. Each of the above conditions may be different for each target cell, and multiple conditions may be set for one target cell. In the Rel-16 NR system, up to two conditions may be set for each target cell, and when all of the set conditions are satisfied, the terminal (1c-05) may perform a handover operation to the target cell corresponding to the conditions. The conditions that can be set are as follows. In the present invention, the following conditions are referred to as conventional received signal quality-based conditions.

[0043] CondEvent A3: Conditional reconfiguration candidate becomes offset better than PCell / PSCell

[0044] Conditional Event A4 (CondEvent A4): Conditional reconfiguration candidate becomes better than absolute threshold

[0045] CondEvent A5: PCell / PSCell becomes worse than absolute threshold 1 AND Conditional reconfiguration candidate becomes better than another absolute threshold 2

[0046] The terminal (1c-05) that has received the above handover setup information can evaluate whether the provided condition(s) are satisfied (1c-65). If the condition related to a specific target cell is satisfied, a random access process can be performed to the target cell and a T304 timer can be started (1c-70). For example, if CondEvent A3 is set as the above condition and satisfied, the terminal (1c-05) can transmit the provided preamble to the associated target cell (1c-75). If a dedicated preamble has not been provided, the terminal (1c-05) can transmit one of the preambles used in a contention-based manner. The target cell (1c-20) that has received the preamble can transmit a Random Access Response (RAR) message to the terminal (1c-05) (1c-80). The terminal (1c-05) can transmit msg3 to the target cell (1c-20) using the UL grant information stored in the RAR (1c-85). The msg3 stores an RRCConnectionReconfigurationComplete message in the case of an LTE system, and an RRCReconfigurationComplete message in the case of an NR system. If the random access process is successfully completed, the terminal (1c-05) can consider the condition-based handover to have been successfully completed and stop the running T304 timer. If the condition-based handover is not successfully completed before the T304 timer expires, the handover can be considered to have failed.

[0047] When the handover is successfully completed, the terminal (1c-05) can delete the handover configuration information. When the source cell (1c-10) receives a report of the handover success from the target cell (1c-20), the terminal can delete the context information of the terminal. The success can also be determined by a UE context release message, which is an inter-node message transmitted from the target cell to the source cell. In addition, the source cell instructs other candidate target cells included in the handover configuration information to delete the handover configuration information (or UE context information) (or notifies that it is no longer valid). The candidate target cells can delete the handover configuration information on their own after a predetermined period of time has passed since receiving the handover request, even without an instruction from the source cell.

[0048] If a condition related to a specific target cell is satisfied and the terminal (1c-05) performs a handover to the target cell (1c-70), the handover may not be successfully completed until T304 expires. At this time, the terminal (1c-05) searches for a suitable cell through a cell selection operation. If a suitable cell is found, it can be determined whether the found suitable cell is one of the target cell candidates. If it is one of the target cell candidates, the terminal can perform a handover to the suitable cell again. In the present invention, this is called a CHO Failure Recovery operation. If it is not one of the target cell candidates, an RRCReestablishmentRequest message can be transmitted to the suitable cell.

[0049] Similar to the above condition-based handover (Conditional HO, CHO), in wireless communication systems, Conditional PSCell Addition (CPA) or Conditional PSCell Change (CPC) operations have also been introduced, in which a terminal adds or changes a PSCell when a preset condition is satisfied.

[0050] The present invention proposes a method for improving mobility performance when CHO or CPC fails in an operation in which CHO and CPC are set and performed simultaneously.

[0051] FIG. 1d is a flowchart of a process for simultaneously performing condition-based handover and condition-based PSCell change according to one embodiment of the present invention.

[0052] In order to set up an operation in which CHO and CPC are performed simultaneously for a terminal (1d-05), a source MN (1d-10), a source SN (1d-15), a target SN (1d-20), and a target MN (1d-25) may exchange related information with each other and configure setting information for the operation (1d-30). The setting information may include condition information required to perform each of the CHO and CPC operations. In addition, if the CHO execution fails, an indicator indicating whether the terminal can perform CHO Failure Recovery may be included. The source MN (1d-10) may transmit the configured setting information to the terminal (1d-05) (1d-35). The terminal (1d-05) that receives the setting information may evaluate whether the CHO and CPC execution conditions are satisfied (1d-40). Both the CHO execution condition and the CPC execution condition must be satisfied to execute CHO and CPC (1d-45). For example, if only the CPC condition is satisfied, the terminal (1d-05) can maintain the evaluation operation and delay the CPC execution operation until the CHO condition is satisfied. If both the CHO execution condition and the CPC execution condition are satisfied, the terminal (1d-05) can trigger a random access operation to each target PCell and PSCell of CHO and CPC (1d-50, 1d-70). While triggering each random access operation, the terminal (1d-05) can start the T304 timer for each operation (1d-55, 1d-65). In the present embodiment, the T304 timer for CHO is referred to as the MN T304 timer, and the T304 timer for CPC is referred to as the SN T304 timer. Each T304 timer can be stopped when the corresponding CHO or CPC execution operation completes successfully.Since the CHO and CPC execution operations are triggered only when both the CHO execution condition and the CPC execution condition are satisfied, a single T304 timer may be applied. The single T304 timer starts to run when both the CHO execution condition and the CPC execution condition are satisfied, and the T304 timer is stopped only when both the CHO and CPC execution operations are successfully completed. If the random access process is successfully completed before the corresponding T304 expires, the terminal (1d-05) can consider the corresponding CHO or CPC to have been successfully completed. Since the target MN (1d-25) must recognize the source SN (1d-15) selected in the CPC operation, after the random access to the CHO is successfully completed, the terminal (1d-05) can report the target PSCell information selected in the CPC operation to the target PCell (1d-25) via a predetermined RRC message (e.g., an RRCReconfigurationComplete message) (1d-70). The target PCell (1d-25) that has received the target PSCell information can transmit an SN Reconfiguration Complete message to the target PSCell (1d-20) (1d-75). Through the above process, the target MN (1d-25) and the target SN (1d-20) recognize each other as the final Dual Connectivity combination according to the simultaneous configuration of CHO and CPC.

[0053] In an operation where the CHO and CPC are set up and performed simultaneously, if both the CHO execution condition and the CPC execution condition are satisfied, the terminal (1d-05) performs both the CHO execution operation and the CPC execution operation. At this time, the CHO or CPC execution operation may fail. That is, the corresponding random access process may not be successfully completed until T304 expires. At this time, the terminal (1d-05) may consider the CHO and CPC simultaneous setup to have failed and perform a re-establishment operation. However, since a number of MNs and SNs exchange necessary information and pre-allocate necessary radio resources to trigger the CHO and CPC simultaneous setup, performing the re-establishment operation renders the previous process meaningless. In this embodiment, a method is proposed in which the CHO and CPC simultaneous setup can be successfully completed by applying CHO failure recovery or CPC failure recovery.

[0054] FIG. 1e is a flowchart of a process for releasing a condition-based PSCell change operation when a condition-based handover fails according to an embodiment of the present invention.

[0055] In an operation where the above CHO and CPC are set and performed simultaneously, if only the CHO fails but the random access corresponding to the CPC succeeds, the terminal can release the successfully completed CPC while triggering a re-establishment operation. The above process can be applied when the CHO Failure Recovery operation is not set.

[0056] In order to set up an operation in which CHO and CPC are performed simultaneously for a terminal (1e-05), a source MN (1e-10), a source SN (1e-15), a target SN (1e-20), and a target MN (1e-25) may exchange related information with each other and configure setting information for the operation. At this time, if the CHO execution fails, an instruction instructing the terminal (1e-05) to perform CHO Failure Recovery may not be included. The source MN (1e-15) may transmit the configured setting information to the terminal (1e-05) (1e-30). The terminal (1e-05) that receives the setting information may evaluate whether CHO and CPC execution conditions are satisfied (1e-35). CHO and CPC can be executed only when both the CHO execution conditions and the CPC execution conditions are satisfied (1e-40). If both the above CHO execution conditions and CPC execution conditions are satisfied, the terminal (1e-05) can trigger a random access operation to each target PCell and PSCell of the CHO and CPC (1e-50, 1e-65). While triggering each of the above random access operations, the terminal (1e-05) can start a T304 timer (or a single T304 timer) for each operation (1e-45, 1e-60). If the random access process is successfully completed before the SN T304 expires, the terminal can consider the corresponding CPC to have been successfully completed (1e-75).However, if the random access process is not successfully completed before the MN T304 expires (1e-80), the terminal (1e-05) cannot transmit an RRCReconfigurationComplete message to the target PCell (1e-25) (1e-55), and thus, the target PCell (1e-25) cannot transmit an SN Reconfiguration Complete message to the target PSCell (1e-20) (1e-70). Therefore, the PSCell (1e-20) cannot immediately recognize whether the CHO operation is successfully completed. The terminal (1e-05) may consider that the corresponding CHO has not been successfully completed, and may report the CHO failure to the target PSCell (1e-20) corresponding to the previously successful CPC using a predetermined signaling (1e-85). For example, the predetermined signaling may be an MCGFailureInformation message or a new RRC message. The target PSCell (1e-20) that received the above report recognizes that the CHO has failed (1e-90) and releases the previously successful CPC (1e-95). The CPC release means releasing (or suspending) the configuration information and radio resources allocated to the terminal (1e-05). Another method for releasing the previously successful CPC is that if the target PSCell does not receive an SN Reconfiguration Complete message from a predetermined target PCell (1e-25) for a predetermined period of time (1e-70), the target PSCell (1e-20) can release the previously successful CPC. At this time, the terminal (1e-05) considers the previously successful CPC to have also been released after the MN T304 timer corresponding to the CHO has expired. The predetermined period of time may be determined through a preset configuration between nodes or may be predefined.However, the above-mentioned specified time must be at least equal to or longer than the T304 timer value. The above-mentioned operations can also be applied when a single T304 is applied. When the single T304 timer expires, if only the CHO fails but the random access corresponding to the CPC succeeds, the above-mentioned operations can be performed.

[0057] FIG. 1f is a diagram for explaining a condition-based PSCell change operation during a CHO Failure Recovery operation according to an embodiment of the present invention.

[0058] In this embodiment, we consider a case where, in an operation where the CHO and CPC are set and performed simultaneously, only the CHO fails, but the random access corresponding to the CPC succeeds. In this case, the terminal triggers a CHO Failure Recovery operation, and if a predetermined condition is met, the successfully completed CPC can be applied as is.

[0059] To enable simultaneous CHO and CPC operations, the base station can provide the UE with configuration information for a single candidate PCell combined with configuration information for a single candidate PSCell. Furthermore, multiple combinations can be provided to a single UE. For a single candidate PCell, different candidate PSCells may be considered, and in this case, different combinations of configuration information may be provided to the UE. As another example, if configuration information for the same candidate PCell is provided for multiple candidate PSCells, a configuration information combination comprising multiple candidate PSCells may be provided for a single candidate PCell.

[0060] The base station can provide the terminal with a combination of configuration information consisting of one CHO configuration information (1f-05) and one CPC configuration information (1f-10). At this time, the CHO configuration information can include an indicator for configuring CHO Failure Recovery. The base station can provide the terminal with combinations of multiple configuration information as described above. The terminal can evaluate whether the CHO and CPC execution conditions contained in each configuration information are satisfied. If both the CHO execution conditions and the CPC execution conditions are satisfied for one target PCell 1 and one target PSCell 1, the terminal can perform CHO and CPC execution operations for the target cells. At this time, if the random access operation for the target PCell 1 is not successfully completed before the T304 timer expires, the terminal searches for one suitable cell through a Cell Selection operation. If the suitable cell is another candidate target cell PCell 2, the terminal can perform a handover to the PCell 2 again according to the CHO Failure Recovery operation. The terminal can successfully complete the handover by applying the CHO configuration information (1f-15) of the target PCell 2. On the other hand, the CPC execution operation can be successfully completed. That is, the random access operation for the target PSCell 1 can be successfully completed before the T304 timer expires.

[0061] In the present embodiment, if the target PSCell 1 of the previously successful CPC is set among the candidate target PSCells corresponding to the PCell 2 selected in the CHO Failure Recovery operation, the previously successful CPC is not released. At this time, the configuration information (1f-20) of the PSCell 1 corresponding to the PCell 2 may be applied, and the CPC may not be released only if the CPC execution condition of the PSCell 1 indicated by the configuration information is still satisfied.

[0062] FIG. 1g is a flowchart of a first process for performing a condition-based PSCell change operation during a CHO Failure Recovery operation according to an embodiment of the present invention.

[0063] In the first process, in an operation in which the CHO and CPC are set and performed simultaneously, if only the CHO fails and the random access corresponding to the CPC succeeds, the terminal is characterized in that it can maintain the successfully completed CPC while triggering a CHO Failure Recovery operation when a predetermined condition is satisfied.

[0064] In order to set up an operation in which CHO and CPC are performed simultaneously for a terminal (1g-05), a source MN (1g-10), a source SN (1g-15), a target SN (1g-20), a target MN (1g-25), and another target MN (1g-30) can exchange related information with each other and configure setting information for the operation. At this time, if the CHO execution fails, an instruction for instructing the terminal (1g-05) to perform CHO Failure Recovery may be included. The source MN (1g-10) can transmit the configured setting information to the terminal (1g-05) (1g-35). The terminal (1g-05) that receives the setting information can evaluate whether CHO and CPC execution conditions are satisfied (1g-40). CHO and CPC can be executed only when both the CHO execution conditions and the CPC execution conditions are satisfied (1g-45). If both the CHO execution condition and the CPC execution condition are satisfied, the terminal (1g-05) can trigger a random access operation to each target PCell and PSCell of the CHO and CPC (1g-55, 1g-70). While triggering each random access operation, the terminal can start a T304 timer (or a single T304 timer) for each operation (1g-50, 1g-65). If the random access process is successfully completed before the SN T304 expires, the terminal (1g-05) can consider the corresponding CPC to be successfully completed (1g-80). However, if the random access process is not successfully completed before the MN T304 expires (1g-85), the terminal (1g-05) can consider the corresponding CHO to not be successfully completed.In addition, the terminal (1g-05) cannot transmit an RRCReconfigurationComplete message to the target PCell (1g-25) (1g-60), and as a result, the target PCell (1g-25) cannot transmit an SN Reconfiguration Complete message to the target PSCell (1g-20) (1g-75). Therefore, the PSCell cannot immediately recognize whether the CHO operation has been successfully completed.

[0065] If CHO Failure Recovery is set, the terminal (1g-05) can determine whether the suitable cell found through the Cell Selection operation is one of the candidate target cells for CHO (1g-90). If the suitable cell is a candidate target cell for CHO, the terminal (1g-05) can perform a handover to the candidate target cell (1g-30) (1g-100). The terminal (1g-05) can also notify the target PSCell (1g-20) of the previously successful CPC that it is performing the CHO Failure Recovery operation (1g-95). This is to prevent the target PSCell (1g-20) from prematurely considering that the entire CHO + CPC operation has failed due to not receiving an SN Reconfiguration Complete message from any target PCell. If the suitable cell is not a candidate target cell for CHO, the terminal (1g-05) can perform a re-establishment operation to the suitable cell and also release the previously successful CPC.

[0066] If the random access process to the CHO candidate target cell is successfully completed, the terminal (1g-05) considers the corresponding CHO to have also been successfully completed. If the combination of the CHO candidate target cell and the candidate target cell of the previously successful CPC is also included in the CHO + CPC configuration information, since the candidate target cell must recognize the source SN selected in the CPC operation, after the random access to the CHO is successfully completed, the terminal (1g-05) can report the target PSCell information selected in the CPC operation to the target PCell (1g-30) via a predetermined RRC message (e.g., an RRCReconfigurationComplete message) (1g-105). The target PCell, which has received the target PSCell information, can transmit an SN Reconfiguration Complete message to the target PSCell (1g-20) (1g-110). Through the above process, the target MN and target SN become aware of each other as the final Dual Connectivity combination based on the simultaneous setting of CHO and CPC.

[0067] FIG. 1h is a flowchart of a second process for performing a condition-based PSCell change operation during a CHO Failure Recovery operation according to an embodiment of the present invention.

[0068] In the second process, in an operation in which the CHO and CPC are set and performed simultaneously, if only the CHO fails and the random access corresponding to the CPC succeeds, the terminal is characterized in that it releases the successfully completed CPC while triggering a CHO Failure Recovery operation if a predetermined condition is satisfied. For example, if the target PSCell of the previously successful CPC is not set among the candidate target PSCells corresponding to the target PCell selected in the CHO Failure Recovery, it is preferable to release the CPC.

[0069] In order to set up an operation in which CHO and CPC are performed simultaneously for a terminal (1h-05), a source MN (1h-10), a source SN (1h-15), a target SN (1h-20), a target MN (1h-25), and another target MN (1h-30) can exchange related information with each other and configure setting information for the operation. At this time, if the CHO execution fails, an instruction instructing the terminal (1h-05) to perform CHO Failure Recovery may be included. The source MN (1h-10) can transmit the configured setting information to the terminal (1h-05) (1h-35). The terminal (1h-05) that receives the setting information can evaluate whether CHO and CPC execution conditions are satisfied (1h-40). CHO and CPC can be executed only when both the CHO execution conditions and the CPC execution conditions are satisfied (1h-45). If both the CHO execution condition and the CPC execution condition are satisfied, the terminal (1h-05) triggers a random access operation to each target PCell and PSCell of the CHO and CPC (1h-55, 1h-70). While triggering each random access operation, the terminal may start a T304 timer (or a single T304 timer) for each operation (1h-50, 1h-65). If the random access process is successfully completed before the SN T304 expires, the terminal (1h-05) may consider the corresponding CPC to be successfully completed (1h-80). However, if the random access process is not successfully completed before the MN T304 expires (1h-85), the terminal (1h-05) may consider the corresponding CHO to not be successfully completed.In addition, the terminal (1h-05) cannot transmit an RRCReconfigurationComplete message to the target PCell (1h-25) (1h-60), and as a result, the target PCell (1h-25) cannot transmit an SN Reconfiguration Complete message to the target PSCell (1h-20) (1h-75). Therefore, the PSCell (1h-20) cannot immediately recognize whether the CHO operation has been successfully completed. If CHO Failure Recovery is set, the terminal (1h-05) can determine whether a suitable cell found through a Cell Selection operation is one of the candidate target cells of CHO (1h-90). If the suitable cell is a candidate target cell of CHO, a handover can be performed to the candidate target cell (1h-30) (1h-100). If the random access process to the CHO candidate target cell is successfully completed, the terminal (1h-05) can consider that the corresponding CHO has also been successfully completed. If the target PSCell of the previously successful CPC is not set among the candidate target PSCells corresponding to the target PCell selected in CHO Failure Recovery, the terminal (1h-05) can request the dismantling of the previously successful CPC using the following options.

[0070] Option 1: The terminal may request the target PSCell (1h-20) of the previously successful CPC to release the CPC (1h-95).

[0071] Second Option: Since the candidate target cell must recognize the source SN (1h-15) selected in the CPC operation, after the random access to the CHO is successfully completed, the terminal (1h-05) reports CPC release request information together with the target PSCell information selected in the CPC operation to the target PCell (1h-30) via a predetermined RRC message (e.g., RRCReconfigurationComplete message) (1h-105). The target PCell, which has received the target PSCell information, can transmit an SN Reconfiguration Complete message to the target PSCell (1h-20) (1h-110). The message can include an indicator requesting to release the already successful CPC.

[0072] FIG. 1i is a flowchart of a third process for performing a condition-based PSCell change operation during a CHO Failure Recovery operation according to an embodiment of the present invention.

[0073] In the third process, in an operation in which the CHO and CPC are set and performed simultaneously, if only the CHO fails and the random access corresponding to the CPC succeeds, the terminal is characterized in that, if a predetermined condition is satisfied, the terminal triggers a CHO Failure Recovery operation, reevaluates the CPC execution condition, and, if necessary, re-performs the CPC execution operation.

[0074] In order to set up an operation in which CHO and CPC are performed simultaneously for a terminal (1i-05), a source MN (1i-10), a source SN (1i-15), a target SN (1i-20), a target MN (1i-25), another target MN (1i-30), and another target SN (1i-35) can exchange related information with each other and configure setting information for the operation. At this time, if the CHO execution fails, an instruction instructing the terminal (1i-05) to perform CHO Failure Recovery may be included. The source MN (1i-10) can transmit the configured setting information to the terminal (1i-05) (1i-40). The terminal (1i-05) that receives the setting information can evaluate whether the CHO and CPC execution conditions are satisfied (1i-45). CHO and CPC can be executed only when both CHO execution conditions and CPC execution conditions are satisfied (1i-50). If both the CHO execution conditions and the CPC execution conditions are satisfied, the terminal (1i-05) can trigger a random access operation to each target PCell and PSCell of the CHO and CPC (1i-60, 1i-75). While triggering each random access operation, the terminal can start a T304 timer (or a single T304 timer) for each operation (1i-55, 1i-70). If the random access process is successfully completed before the SN T304 expires, the terminal (1i-05) can consider the corresponding CPC to have been successfully completed (1i-85). However, if the random access process is not successfully completed before the MN T304 expires (1i-90), the terminal (1i-05) can consider the corresponding CHO to have not been successfully completed.At this time, the terminal (1i-05) cannot transmit an RRCReconfigurationComplete message to the target PCell (1i-25) (1i-65), and as a result, the target PCell (1i-25) cannot transmit an SN Reconfiguration Complete message to the target PSCell (1i-20) (1e-80). Therefore, the PSCell (1i-20) cannot immediately recognize whether the CHO operation has been successfully completed. If CHO Failure Recovery is set, the terminal (1i-05) can determine whether a suitable cell found through a Cell Selection operation is one of the candidate target cells for CHO (1i-95). If the suitable cell is a candidate target cell for CHO, a handover can be performed to the candidate target cell (1i-30) (1i-100). The terminal (1i-05) may also notify the target PSCell (1g-20) of the previously successful CPC that it is performing a CHO Failure Recovery operation. This is to prevent the target PSCell from considering the entire CHO + CPC operation as failed due to not receiving an SN Reconfiguration Complete message from any target PCell. If the suitable cell is not a candidate target cell for CHO, the terminal (1i-05) performs a re-establishment operation with the suitable cell. It may be evaluated whether the CPC performing conditions are satisfied for the CPC candidate target cells combined with the CHO candidate target cell (1i-105). If a specific CPC candidate target cell satisfies the CPC performing conditions (1i-110), the terminal may perform a random access procedure with the corresponding cell (1i-115).If the PSCell of the previously successful CPC is a cell that satisfies the CPC execution conditions, the terminal (1i-05) does not need to perform the random access process again with the cell. If a CPC candidate target cell that satisfies the CPC execution conditions does not appear within a predetermined period of time, the terminal considers the CPC operation to have failed. Even if the CPC operation fails, the terminal can still perform the CHO operation.

[0075] If the random access process to the CHO candidate target cell is successfully completed, the terminal (1i-05) can consider that the corresponding CHO has also been successfully completed. Since the candidate target cell must recognize the source SN selected in the CPC operation, after the random access to the CHO is successfully completed, the terminal (1i-05) reports the target PSCell information selected in the CPC operation to the target PCell (1i-30) via a predetermined RRC message (e.g., an RRCReconfigurationComplete message) (1i-120). The target PCell, which has received the target PSCell information, can transmit an SN Reconfiguration Complete message to the target PSCell (1i-35) (1i-125). Through the above process, the target MN and the target SN recognize each other as the final Dual Connectivity combination according to the simultaneous configuration of CHO and CPC.

[0076] FIG. 1j is an example of a process for performing a condition-based PSCell change operation during a CHO Failure Recovery operation according to an embodiment of the present invention.

[0077] The above-mentioned proposed processes 1, 2 and 3 are not mutually exclusive and can be applied simultaneously as terminal operations.

[0078] In step 1j-05 of FIG. 1, the terminal may receive configuration information related to the simultaneous execution of CHO and CPC from the base station. The configuration information may include combinations of CHO and CPC candidate cells and CHO and CPC execution condition information corresponding to each combination.

[0079] In step 1j-10 of FIG. 1, the terminal can evaluate whether both the CHO execution condition and the CPC execution condition are satisfied for the CHO and CPC candidate cells indicated in the configuration information.

[0080] In step 1j-15 of FIG. 1, the terminal can perform CHO and CPC operations if both the CHO performance conditions and the CPC performance conditions are satisfied for the given CHO and CPC candidate cells. That is, the terminal can perform a random access process with the CHO candidate PCell and CPC candidate PSCell that satisfy the conditions.

[0081] In step 1j-20 of FIG. 1, the terminal may successfully complete the CPC operation even though the CHO operation has failed.

[0082] In step 1j-25 of FIG. 1, the terminal can determine whether CHO Failure Recovery is configured. If CHO Failure Recovery is not configured, CHO failure is confirmed. Since the base station has configured operations in which CHO and CPC are performed simultaneously, maintaining only CPC in the event of CHO failure is meaningless. Therefore, if CHO fails and CHO Failure Recovery is not configured, the terminal can release a previously successful CPC or delete previously received CPC-related configuration information.

[0083] In step 1j-30 of FIG. 1, if CHO Failure Recovery is set, the terminal can find a suitable cell through a cell selection operation. At this time, the suitable cell may mean a CHO candidate target cell indicated by the CHO configuration information.

[0084] In step 1j-35 of FIG. 1, the terminal can determine whether it already has corresponding CHO + CPC configuration information for the newly selected CHO candidate target cell and the PSCell of the previously successful CPC through CHO Failure Recovery. Furthermore, the terminal can determine whether the candidate PSCell corresponding to the newly selected candidate PCell through CHO Failure Recovery is the same as the candidate PSCell corresponding to the existing target PCell associated with the CHO failure. Furthermore, it can additionally determine whether the CPC execution conditions are still satisfied for the previously successful CPC.

[0085] In step 1j-40, if the terminal already has the corresponding CHO + CPC setting information, it can maintain the previously successful CPC. This corresponds to the first step.

[0086] In step 1j-45 of FIG. 1, if the terminal does not have the corresponding CHO + CPC configuration information, it can re-evaluate whether there is a cell that satisfies the CPC execution conditions among the CPC candidate cells related to the newly selected CHO candidate target cell.

[0087] In step 1j-50, the terminal can determine whether there is a cell that satisfies the CPC execution conditions among the CPC candidate cells associated with the newly selected CHO candidate target cell. This corresponds to the third step.

[0088] In step 1j-55 of FIG. 1, if there is no cell that satisfies the CPC execution conditions among the CPC candidate cells related to the newly selected CHO candidate target cell, the terminal may release the previously successful CPC and delete the previously set CPC-related configuration information. This corresponds to the second step.

[0089] In step 1j-60 of FIG. 1, if there is a cell that satisfies the CPC execution condition among the CPC candidate cells related to the newly selected CHO candidate target cell, the terminal can perform random access to the cell.

[0090] FIG. 1k is a diagram for explaining a CPC Failure Recovery operation according to one embodiment of the present invention.

[0091] In this embodiment, in an operation where the CHO and CPC are set and performed simultaneously, a case is considered where the CPC fails but the random access corresponding to the CHO succeeds. At this time, if a predetermined condition is satisfied, the terminal can apply the previously successfully completed CHO as it is while triggering the CPC Failure Recovery operation. The CPC Failure Recovery operation means a technology in which, if a Conditional PSCell Change operation is performed but the operation is considered failed due to the expiration of T304, the terminal performs a PSCell change by applying the previously received CPC configuration information to a CPC candidate cell that satisfies a predetermined condition (e.g., a suitable cell condition or a cell that provides a better reception signal strength than a predetermined threshold value) if there is one.

[0092] To enable simultaneous CHO and CPC operations, the base station can provide the UE with configuration information for a single candidate PCell combined with configuration information for a single candidate PSCell. Furthermore, multiple combinations can be provided to a single UE. For a single candidate PCell, different candidate PSCells may be considered, and in this case, each combination of configuration information will be provided to the UE. As another example, if configuration information for the same candidate PCell is provided for multiple candidate PSCells, a configuration information combination comprising multiple candidate PSCells can be provided for a single candidate PCell.

[0093] The base station can provide a combination of configuration information consisting of one CHO configuration information (1k-05) and one CPC configuration information (1k-10) to the terminal. At this time, the CPC configuration information includes an indicator for setting CPC Failure Recovery. The base station can provide a combination of multiple configuration information as described above to the terminal. The terminal can evaluate whether the CHO and CPC execution conditions contained in each configuration information are satisfied. If both the CHO execution conditions and the CPC execution conditions are satisfied for one target PCell 1 and one target PSCell 1, the CHO and CPC execution operations can be performed for the target cells. At this time, if the random access operation for the target PSCell 1 is not successfully completed before the T304 timer expires, the terminal can find one candidate target PSCell that satisfies a predetermined condition. The PSCell may mean one of the candidate target cells of the preset CPC. For example, through the Cell Selection operation, the terminal can find one candidate target PSCell that satisfies a suitable cell condition. Alternatively, the terminal can select one candidate target PSCell that can provide a better reception signal strength than a predetermined threshold. If the suitable cell is another candidate target cell PSCell 2, the terminal can perform a PSCell Change operation again for the PSCell 2 according to the CPC Failure Recovery operation. The terminal can successfully complete the PSCell Change by applying the CPC configuration information (1k-15) of the target PSCell 2. On the other hand, the CHO execution operation can be successfully completed. That is, the random access operation for the target PCell 1 can be successfully completed before the T304 timer expires.

[0094] In this embodiment, if the target PCell 1 of the previously successful CHO is set among the candidate target PCells corresponding to the PSCell 2 selected in CPC Failure Recovery, the CHO is not released.

[0095] FIG. 11 is a flowchart of a process for performing a CHO Failure Recovery operation according to an embodiment of the present invention.

[0096] In an operation in which the above CHO and CPC are set and performed simultaneously, if only the CPC fails and the random access corresponding to the CHO succeeds, the terminal is characterized in that it reevaluates the CPC execution condition while triggering the CPC Failure Recovery operation if a predetermined condition is satisfied, and re-performs the CPC execution operation if necessary.

[0097] In order to set up an operation in which CHO and CPC are performed simultaneously for a terminal (1l-05), a source MN (1l-10), a source SN (1l-15), a target SN (1l-20), a target MN (1l-25), and another target SN (1l-30) may exchange related information with each other and configure setting information for the operation. At this time, an instruction instructing the terminal (1l-05) to perform CPC Failure Recovery when the CPC execution fails may be included. The source MN (1l-10) may transmit the configured setting information to the terminal (1l-05) (1l-35). The terminal (1l-05) that receives the setting information may evaluate whether CHO and CPC execution conditions are satisfied (1l-40). CHO and CPC can be executed only when both the CHO execution conditions and the CPC execution conditions are satisfied (1l-45). If both the CHO execution condition and the CPC execution condition are satisfied, the terminal (11-05) can trigger a random access operation to each target PCell and PSCell of the CHO and CPC (11-55, 11-70). While triggering each random access operation, the terminal can start a T304 timer (or a single T304 timer) for each operation (11-50, 11-65). If the random access process is successfully completed before the MN T304 expires, the terminal can consider the corresponding CHO to be successfully completed. The terminal (11-05) can transmit an RRCReconfigurationComplete message to the target PCell, and the message can include target PSCell information selected in the CPC operation (11-60).Using the above information, the target PCell can transmit an SN Reconfiguration Complete message to the target PSCell (11-75). However, the target PSCell may recognize that the random access from the terminal was not successfully completed even though it received the message (11-90). If the random access process is not successfully completed before the SN T304 expires (11-80), the terminal (11-05) may perform a CPC Failure Recovery operation (11-95). If CPC Failure Recovery is configured, the terminal (11-05) may determine whether a PSCell found according to a predetermined rule (e.g., Cell Selection operation) is one of the candidate target cells of the CPC. If the cell is a candidate target cell of the CPC, a PSCell change operation may be performed to the candidate target cell (11-30) (11-95). If the above PSCell change operation is successfully completed, the terminal must make the target MN and the target SN recognize that the target MN and the target SN are the final Dual Connectivity combination according to the simultaneous configuration of CHO and CPC. To this end, the terminal (1l-05) can transmit the target PSCell cell information to the PCell (1l-25) of the CHO or the target PSCell (1l-30) when the PSCell Change is successfully completed through the CPC Failure Recovery operation using a predetermined RRC message (1l-100, 1l-115).When the PCell of the CHO receives the above information, the PCell may transmit an SN Reconfiguration Complete message to the target PSCell (11-105) and, if necessary, report information indicating that the previous CPC operation has failed to the PSCell associated with the previously failed CPC (11-110). When the target PSCell receives the above information, the PSCell may report to the PCell of the successfully completed CHO that it is the final target SN through the CPC Failure Recovery operation (11-20).

[0098] In another embodiment, although the base station provides CHO + CPC configuration information to set up an operation in which CHO and CPC are performed simultaneously, the CHO execution condition may be satisfied through evaluation for a predetermined period of time, but the CPC execution condition may not be satisfied. In such a case, the base station may set a predetermined indicator to cause the terminal to perform only the CHO execution. In this case, only the CHO-related information is utilized in the CHO + CPC configuration information. Alternatively, in the above case, the base station may set up a PSCell Change to be performed to a pre-configured PSCell regardless of whether the CPC execution condition is satisfied if the CPC execution condition is not satisfied. To this end, the base station may provide the PSCell information in advance through the CHO + CPC configuration information.

[0099] In another embodiment, if the base station sets an operation in which CHO and CPC are performed simultaneously, both the CHO execution condition and the CPC execution condition must be satisfied in order to execute CHO and CPC. For example, if only the CPC condition is satisfied, the terminal may maintain the evaluation operation and delay the CHO and CPC execution operations until the CHO condition is satisfied. Conversely, if only the CHO condition is satisfied, the CHO and CPC execution operations may be delayed until the CPC condition is satisfied. However, the CHO or CPC condition that was satisfied may no longer be satisfied. In the present embodiment, the terminal considers the above case by applying one of the following options.

[0100] - Option 1: If the CHO or CPC condition for one target PCell or target PSCell is satisfied, the terminal stops evaluating the corresponding CHO or CPC condition and continues to consider the condition as satisfied.

[0101] - Option 2: Even if the CHO or CPC conditions for one target PCell or target PSCell are met, the terminal continues to evaluate the CHO and CPC conditions. If the conditions are not met again, the terminal applies them as is. If another target PCell or target PSCell that satisfies the conditions is found, it is considered instead.

[0102] - Option 3: Even if the CHO or CPC conditions for one target PCell or target PSCell are satisfied, the terminal continues to evaluate the CHO and CPC conditions, and if the conditions are not satisfied again, the corresponding CHO or CPC is considered to have failed.

[0103] The terminal performs the above CHO and CPC operations simultaneously, but may experience multiple scenarios as described above. The terminal may include indicator information indicating each scenario in the RLF Report. The network that receives this information can utilize it to optimize the network. For example, the terminal may consider the following indicators:

[0104] - An indicator that indicates that in an operation where the above CHO and CPC are set and performed simultaneously, only the CHO fails (T304 expiry) and the random access corresponding to the CPC succeeds.

[0105] - In an operation where the above CHO and CPC are set and performed simultaneously, if only the CHO fails and the random access corresponding to the CPC succeeds, the terminal indicates that a certain condition is satisfied and the CHO Failure Recovery operation has been triggered.

[0106] - In an operation where the above CHO and CPC are set and performed simultaneously, if only the CHO fails and the random access corresponding to the CPC succeeds, the terminal indicates that it has maintained the previously successful CPC while triggering the CHO Failure Recovery operation by satisfying a predetermined condition.

[0107] - In an operation where the above CHO and CPC are set and performed simultaneously, if only the CHO fails and the random access corresponding to the CPC succeeds, the terminal triggers the CHO Failure Recovery operation when a predetermined condition is satisfied and indicates that the successfully completed CPC has been released.

[0108] - In an operation where the above CHO and CPC are set and performed simultaneously, if only the CHO fails and the random access corresponding to the CPC succeeds, the terminal reevaluates the CPC execution conditions while triggering the CHO Failure Recovery operation when a certain condition is satisfied, and, if necessary, an indicator indicating that the CPC execution operation has been re-performed.

[0109] - An indicator indicating that a CPC Failure Recovery operation has been triggered.

[0110] Figure 1m is a block diagram showing the internal structure of a terminal to which the present invention is applied.

[0111] Referring to the above drawing, the terminal includes an RF (Radio Frequency) processing unit (1m-10), a baseband processing unit (1m-20), a storage unit (1m-30), and a control unit (1m-40).

[0112] The RF processing unit (1m-10) may perform functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1m-10) may up-convert a baseband signal provided from the baseband processing unit (1m-20) 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 (1m-10) 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 (1m-10) may include multiple RF chains. Furthermore, the RF processing unit (1m-10) may perform beamforming. For the above beamforming, the RF processing unit (1m-10) 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 receive multiple layers when performing the MIMO operation.

[0113] The baseband processing unit (1m-20) 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 (1m-20) can generate complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (1m-20) can restore a reception bit stream by demodulating and decoding a baseband signal provided from the RF processing unit (1m-10). For example, in the case of following the OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processing unit (1m-20) 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 (1m-20) divides the baseband signal provided from the RF processing unit (1m-10) into OFDM symbol units, restores signals mapped to subcarriers through FFT (fast Fourier transform) operation, and then restores the received bit string through demodulation and decoding.

[0114] The baseband processing unit (1m-20) and the RF processing unit (1m-10) can transmit and receive signals as described above. Accordingly, the baseband processing unit (1m-20) and the RF processing unit (1m-10) may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. Furthermore, at least one of the baseband processing unit (1m-20) and the RF processing unit (1m-10) 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 (1m-20) and the RF processing unit (1m-10) may include different communication modules to process signals of different frequency bands. For example, the different wireless access technologies may include a wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. Additionally, the different frequency bands may include a super high frequency (SHF) (e.g., 2.NRHz, NRhz) band and a millimeter wave (mm wave) (e.g., 60GHz) band.

[0115] The storage unit (1m-30) can store data such as basic programs, application programs, and setting information for the operation of the terminal. In particular, the storage unit (1m-30) can store information related to a second access node that performs wireless communication using a second wireless access technology. In addition, the storage unit (1m-30) can provide the stored data upon request from the control unit (1m-40).

[0116] The control unit (1m-40) can control the overall operations of the terminal. For example, the control unit (1m-40) can transmit and receive signals through the baseband processing unit (1m-20) and the RF processing unit (1m-10). In addition, the control unit (1m-40) records and reads data in the storage unit (1m-40). For this purpose, the control unit (1m-40) can include at least one processor. For example, the control unit (1m-40) can include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as application programs. The control unit (1m-40) can include a multi-connection processing unit (1m-42).

[0117] Figure 1n is a block diagram showing the configuration of a base station according to the present invention.

[0118] As shown in the above drawing, the base station is configured to include an RF processing unit (1n-10), a baseband processing unit (1n-20), a backhaul communication unit (1n-30), a storage unit (1n-40), and a control unit (1n-50).

[0119] The RF processing unit (1n-10) may perform functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1n-10) may up-convert a baseband signal provided from the baseband processing unit (1n-20) 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 (1n-10) 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 (1n-10) may include multiple RF chains. Furthermore, the RF processing unit (1n-10) may perform beamforming. For the above beamforming, the RF processing unit (1n-10) can adjust the phase and magnitude of each signal transmitted and received through multiple antennas or antenna elements. The RF processing unit can perform a downlink MIMO operation by transmitting one or more layers.

[0120] The baseband processing unit (1n-20) above can perform a conversion function between a baseband signal and a bit stream according to the physical layer specification of the first wireless access technology. For example, when transmitting data, the baseband processing unit (1n-20) can generate complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (1n-20) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (1n-10). For example, in the case of OFDM, when transmitting data, the baseband processing unit (1n-20) can generate complex symbols by encoding and modulating a transmission bit stream, map the complex symbols to subcarriers, and then configure OFDM symbols through IFFT operation and CP insertion. In addition, when receiving data, the baseband processing unit (1n-20) can divide the baseband signal provided from the RF processing unit (1n-10) 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 (1n-20) and the RF processing unit (1n-10) can transmit and receive signals as described above. Accordingly, the baseband processing unit (1n-20) and the RF processing unit (1n-10) may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0121] The above backhaul communication unit (1n-30) can provide an interface for performing communication with other nodes within the network. That is, the backhaul communication unit (1n-30) can 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 can convert a physical signal received from the other node into a bit string.

[0122] The above storage unit (1n-40) can store data such as basic programs, application programs, and setting information for the operation of the main base station. In particular, the storage unit (1n-40) can store information on bearers assigned to connected terminals, measurement results reported from connected terminals, and the like. In addition, the storage unit (1n-40) 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 (1n-40) can provide stored data upon request of the control unit (1n-50).

[0123] The control unit (1n-50) can control the overall operations of the base station. For example, the control unit (1n-50) can transmit and receive signals through the baseband processing unit (1n-20) and the RF processing unit (1n-10) or through the backhaul communication unit (1n-30). In addition, the control unit (1n-50) can record and read data in the storage unit (1n-40). For this purpose, the control unit (1n-50) can include at least one processor. The control unit (1n-50) can include a multi-connection processing unit (1n-52).

[0124] A device-readable storage medium may be provided in the form of a non-transitory storage medium. Here, the term "non-transitory storage medium" simply means a tangible device that does not contain signals (e.g., electromagnetic waves). This term does not distinguish between cases where data is permanently stored in the storage medium and cases where data is temporarily stored. For example, a "non-transitory storage medium" may include a buffer in which data is temporarily stored.

[0125] According to one embodiment, the method according to various embodiments disclosed in the present document may be provided as included in a computer program product. The computer program product may be traded as a product between a seller and a buyer. The computer program product may be distributed in the form of a machine-readable storage medium (e.g., compact disc read-only memory (CD-ROM)), or may be distributed online (e.g., downloaded or uploaded) through an application store or directly between two user devices (e.g., smartphones). In the case of online distribution, at least a portion of the computer program product (e.g., a downloadable app) may be temporarily stored or temporarily generated in a machine-readable storage medium, such as the memory of a manufacturer's server, an application store's server, or an intermediary server.

[0126] The methods according to the embodiments described in the claims or specification of the present disclosure may be implemented in the form of hardware, software, or a combination of hardware and software.

[0127] 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 disclosure.

[0128] These programs (software modules, software) may be stored in random access memory, non-volatile memory including flash memory, read only memory (ROM), electrically erasable programmable read only memory (EEPROM), magnetic disc storage device, compact disc ROM (CD-ROM), digital versatile discs (DVDs) or other forms of optical storage device, magnetic cassette. Or, they may be stored in a memory configured as a combination of some or all of these. In addition, each configuration memory may be included in multiple numbers.

[0129] 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 performing an embodiment of the present disclosure via an external port. Additionally, a separate storage device on the communication network may be connected to a device performing an embodiment of the present disclosure.

[0130] In the specific embodiments of the present disclosure 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 disclosure is not limited to singular or plural components. Components expressed in the plural form may be composed of singular elements, or components expressed in the singular form may be composed of plural elements.

[0131] While the detailed description of this disclosure has described specific embodiments, it should be understood that various modifications are possible without departing from the scope of this disclosure. Therefore, the scope of this disclosure should not be limited to the described embodiments, but should be defined not only by the scope of the claims described below, but also by equivalents thereof.

[0132] A method for a terminal to perform communication in a wireless communication system according to one embodiment of the present disclosure may receive configuration information related to a conditional handover (CHO) and a conditional PSCELL change (CPC). The method may identify whether conditions for performing the CHO and CPC are met based on configuration information related to the CHO and CPC. The method may transmit a radio link failure (RLF) report including information regarding the identification result.

[0133] In one embodiment, the method may perform a CHO recovery procedure based on the identification result. The method may determine a target cell for performing CHO based on the CHO recovery procedure.

[0134] In one embodiment, the method can maintain a PSCELL based on a CPC when a condition for performing a CPC is satisfied, and can release a PSCELL based on a CPC when a condition for performing a CPC set for a target cell is not satisfied.

[0135] In one embodiment, the method may perform a CPC recovery procedure based on the identification results. Based on the CPC recovery procedure, the method may determine a new PSCELL for performing the CPC.

[0136] In one embodiment, the RLF report may include an indicator indicating whether a condition for performing a CHO is met and an indicator indicating whether a condition for performing a CPC is met.

[0137] In one embodiment, the RLF report may include an indicator that a CHO recovery procedure was triggered if the conditions for performing CHO were not met.

[0138] In one embodiment, the RLF report may include an indication as to whether to maintain PSCELL based on the CPC if the conditions for performing the CPC are met.

[0139] In one embodiment, the RLF report may include an indication as to whether a preset CPC should be re-executed.

[0140] In a wireless communication system according to one embodiment of the present disclosure, a terminal performing communication may include a transceiver and at least one processor connected to the transceiver. The at least one processor may receive configuration information related to a conditional handover (CHO) and a conditional PSCELL change (CPC). The at least one processor may identify whether conditions for performing the CHO and CPC are met based on configuration information related to the CHO and CPC. The at least one processor may transmit a radio link failure (RLF) report including information regarding the identification result.

Claims

1. In a wireless communication system, a method for a terminal to perform communication, A step of receiving configuration information related to Conditional Handover (CHO) and Conditional PSCELL Change (CPC); A step of identifying whether conditions for performing the CHO and the CPC are met based on the setting information related to the CHO and the CPC; and A method comprising: transmitting a Radio Link Failure (RLF) report including information regarding the identification result; 2. In the first paragraph, the method, Based on the above identification results, a step of performing a CHO recovery procedure; and A method further comprising: a step of determining a target cell for performing the CHO based on the CHO recovery procedure; 3. In the second paragraph, the method, If the conditions for performing the above CPC are met: A step of maintaining PSCELL based on the CPC when a condition for performing the CPC set for the target cell is satisfied; and A method comprising: a step of releasing PSCELL based on the CPC if a condition for performing the CPC set for the target cell is not satisfied; 4. In the first paragraph, the method, A step of performing a CPC recovery procedure based on the above identification results; and A method further comprising: a step of determining a new PSCELL for performing the CPC based on the CPC recovery procedure; 5. In paragraph 1, A method wherein the RLF report includes an indicator indicating whether a condition for performing the CHO is met and an indicator indicating whether a condition for performing the CPC is met.

6. In paragraph 1, A method wherein the RLF report includes an indicator that a CHO recovery procedure has been triggered if the conditions for performing the CHO are not met.

7. In paragraph 6, A method wherein the RLF report includes an indication as to whether to maintain PSCELL based on the CPC if the conditions for performing the CPC are met.

8. In paragraph 6, A method wherein the above RLF report includes an indicator as to whether the preset CPC is to be re-performed.

9. In a terminal performing communication in a wireless communication system, Transmitter and receiver; and At least one processor connected to the transceiver, wherein the at least one processor comprises: Receive configuration information related to Conditional Handover (CHO) and Conditional PSCELL Change (CPC), Based on the setup information related to the above CHO and CPC, identify whether the conditions for performing the above CHO and CPC are met; A terminal transmitting a Radio Link Failure (RLF) report including information regarding the above identification results.

10. In the 9th paragraph, at least one processor, Based on the above identification results, the CHO recovery procedure is performed, A terminal for determining a target cell for performing the CHO based on the above CHO recovery procedure.

11. In the 10th paragraph, at least one processor, If the conditions for performing the above CPC are met: If the condition for performing the CPC set for the target cell is met, the PSCELL based on the CPC is maintained, A terminal that releases PSCELL based on the CPC if the conditions for performing the CPC set for the target cell are not met.

12. In the 9th paragraph, at least one processor, Based on the above identification results, the CPC recovery procedure is performed, A terminal for determining a new PSCELL for performing the CPC based on the above CPC recovery procedure.

13. In paragraph 9, The terminal, wherein the RLF report includes an indicator indicating whether a condition for performing the CHO is met and an indicator indicating whether a condition for performing the CPC is met.

14. In paragraph 9, The above RLF report includes an indicator that the CHO recovery procedure has been triggered if the conditions for performing the CHO are not met.

15. In paragraph 14, The terminal, wherein the RLF report includes an indication as to whether to maintain PSCELL based on the CPC if the conditions for performing the CPC are met.

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