Method and apparatus for mobility robustness optimization for voice fallback in next generation mobile communication system

Abstract

The present invention relates to a method and an apparatus for mobility robustness optimization of voice fallback in a next generation mobile communication system, and in particular, to an operation and an apparatus in which a terminal includes an ID of a cell to which the terminal is reconnected and information on time elapsed since RLF when making an RF report.

Description

Technical Field

[0001] The present disclosure relates to a method and apparatus for optimizing mobility robustness for voice fallback in a next generation mobile communication system, and in particular, to an operation and apparatus for including an ID of a cell to which a terminal is reconnected and information associated with a time elapsed from the RLF when making an RLF report. Background Art

[0002] 5G mobile communication technology defines a wide frequency band so that high transmission rates and new services are possible, and can be realized not only in "below 6 GHz" frequency bands such as 3.5 GHz, but also in "above 6 GHz" frequency bands called mmWave including 28 GHz and 39 GHz. In addition, implementation of 6G mobile communication technology (called super 5G system) in terahertz frequency bands (e.g., 95 GHz to 3 THz frequency bands) has been considered in order to achieve a transmission rate fifty times faster than 5G mobile communication technology and an ultra-low latency one-tenth of 5G mobile communication technology.

[0003] At the beginning of the development of 5G mobile communication technology, in order to support services and meet the performance requirements related to enhanced mobile broadband (eMBB), ultra-reliable low latency communications (URLLC), and massive machine type communications (mMTC), there has been ongoing standardization on beamforming and massive MIMO for mitigating radio wave path loss and increasing radio wave transmission distance in mmWave, parameter sets to support dynamic operation for efficient utilization of mmWave resources and time slot formats (e.g., operating multiple subcarrier spacings), initial access technology for supporting multi-beam transmission and broadband, definition and operation of BWP (bandwidth part), new channel coding methods (such as LDPC (low-density parity check) codes for large data transmission and polar codes for highly reliable transmission of control information), L2 pre-processing, and network slicing for providing dedicated networks dedicated to specific services.

[0004] Currently, there are ongoing discussions on improvements and performance enhancements of initial 5G mobile communication technologies in view of the services that 5G mobile communication technologies are to support, and there has been physical layer standardization on technologies such as V2X (Vehicle-to-Everything) for assisting autonomous vehicles in making driving decisions based on information about the location and status of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) for system operations that are intended to comply with various regulatory-related requirements in unlicensed bands, NR UE power saving, a non-terrestrial network (NTN) as UE-satellite direct communication for providing coverage in areas where communication with terrestrial networks is unavailable, and positioning.

[0005] In addition, there is ongoing standardization of air interface architecture / protocols for technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing nodes for network service area extension by supporting wireless backhaul links and access links in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access (NR's two-step RACH) for simplifying the random access procedure. There is also ongoing standardization of system architecture / services for 5G baseline architecture (e.g., service-based architecture or service-based interface) for combining network function virtualization (NFV) and software-defined networking (SDN) technologies, and mobile edge computing (MEC) for receiving services based on UE location.

[0006] As 5G mobile communication systems are commercialized, the number of connected devices, which has been growing exponentially, will be connected to the communication network, and it is expected that enhanced functions and performance of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research related to extended reality (XR) is arranged to effectively support AR (augmented reality), VR (virtual reality), MR (mixed reality), etc., by utilizing artificial intelligence (AI) and machine learning (ML), AI service support, metaverse service support, and drone communication, with improved 5G performance and reduced complexity.

[0007] Furthermore, such development of 5G mobile communication systems will serve as the basis for developing not only new waveforms for providing terahertz band coverage for 6G mobile communication technology, multi-antenna transmission technologies such as full-dimensional MIMO (FD-MIMO), array antennas, and massive antennas, metamaterial-based lenses and antennas for improving terahertz band signal coverage, high-dimensional spatial multiplexing technologies using OAM (orbital angular momentum), and RIS (reconfigurable smart surfaces), but also full-duplex technologies for improving frequency efficiency and improving system networks for 6G mobile communication technology, AI-based communication technologies for achieving system optimization by utilizing satellites and AI (artificial intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technologies for achieving services with a complexity level that exceeds the operating limits of UEs by utilizing ultra-high-performance communication and computing resources. Summary of the invention

[0008] Technical issues

[0009] In case of performing voice fallback, since its detailed information is not included in the RLF report information, it may be difficult for an operator managing a base station to optimize the network, so the present disclosure will overcome this problem.

[0010] Technical Solution

[0011] The operation method of a terminal in a wireless communication system according to an embodiment may include: an operation of receiving a handover command message from NR including information that a target radio access technology (RAT) is configured as LTE from an NR base station, an operation of selecting a suitable LTE cell when there is an available suitable LTE cell and selecting an acceptable LTE cell when there is no available suitable LTE cell in the case of detecting a failure in handover from NR, an operation of entering an RRC idle mode, an operation of performing an RRC connection establishment procedure for the selected LTE cell, an operation of storing a time value from handover failure to reconnection and an ID of the LTE cell to which the RRC connection is performed in a VarRLF-Report associated with the NR when the LTE cell to which the RRC connection is performed is a suitable LTE cell, and an operation of storing the time value from handover failure to reconnection in a VarRLF-Report associated with the NR when the LTE cell to which the RRC connection is performed is an acceptable LTE cell.

[0012] When the LTE cell to which the RRC connection is performed is an acceptable LTE cell, the ID of the LTE cell to which the RRC connection is performed may not be stored in the VarRLF-Report associated with the NR.

[0013] The SWITCH FROM NR COMMAND message may include an indicator for voice fallback.

[0014] The method of the terminal may further include an operation of storing information indicating that the switching is for voice fallback in a VarRLF-Report associated with the NR.

[0015] When the ID of the LTE cell is not stored in the VarRLF-Report associated with the NR, an operation of storing a time value from handover failure to reconnection or an ID of the LTE cell to which the RRC connection is performed in the VarRLF-Report associated with the NR may be performed.

[0016] The terminal may be a terminal supporting inter-RAT RLF reporting.

[0017] The method of the terminal may also include an operation of establishing an RRC connection with an NR base station after updating the VarRLF-Report associated with the NR with respect to the selected LTE cell, an operation of receiving a terminal information request message from the NR base station, and an operation of sending a terminal information response message including the VarRLF-Report associated with the NR to the NR base station.

[0018] A terminal in a wireless communication system according to another embodiment of the present disclosure may include a transceiver and a controller, and the controller may be configured to receive a handover command message from an NR base station, the handover command message from the NR including information that a target radio access technology (RAT) is configured as LTE, and in the case of detecting a handover failure from the NR, when there is an available suitable LTE cell, select a suitable LTE cell, and when there is no available suitable LTE cell, select an acceptable LTE cell, enter an RRC idle mode, perform an RRC connection establishment procedure for the selected LTE cell, when the LTE cell to which the RRC connection is performed is a suitable LTE cell, store a time value from handover failure to reconnection and an ID of the LTE cell to which the RRC connection is performed in a VarRLF-Report associated with the NR, and when the LTE cell to which the RRC connection is performed is an acceptable LTE cell, store the time value from handover failure to reconnection in the VarRLF-Report associated with the NR.

[0019] Beneficial Effects

[0020] According to various embodiments of the present disclosure, regarding voice fallback, the terminal includes the ID of the cell to which the terminal reconnects and information associated with the time elapsed from RLF when making an RLF report, so that an operator managing a base station can effectively operate a network based on the information. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The structure of an LTE system according to an embodiment of the present disclosure is shown.

[0022] Figure 2 A radio protocol structure of an LTE system according to an embodiment of the present disclosure is shown.

[0023] Figure 3 A structure of a next generation mobile communication system according to an embodiment of the present disclosure is shown.

[0024] Figure 4 A radio protocol structure of a next generation mobile communication system according to an embodiment of the present disclosure is shown.

[0025] Figure 5 is a flowchart of a process of updating radio link failure or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a terminal in a next generation mobile communication system fails according to an embodiment of the present disclosure;

[0026] Figure 6is a flowchart of a process of updating radio link failure or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a terminal in a next generation mobile communication system fails according to an embodiment of the present disclosure;

[0027] Figure 7 is a flowchart of a process of updating radio link failure or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a terminal in a next generation mobile communication system fails according to an embodiment of the present disclosure;

[0028] Figure 8 is a flowchart of a process of updating radio link failure or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a terminal in a next generation mobile communication system fails according to an embodiment of the present disclosure;

[0029] Fig. 9 is a flowchart of a process in which a terminal transmits radio link failure information or handover failure information to a base station in a next generation mobile communication system according to an embodiment of the present disclosure;

[0030] Fig.10 is a flowchart of a process in which a terminal transmits radio link failure information or handover failure information to a base station in a next generation mobile communication system according to an embodiment of the present disclosure;

[0031] Fig.11 is a flowchart of a process of updating radio link failure or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a terminal in a next generation mobile communication system fails according to an embodiment of the present disclosure;

[0032] Fig.12 is a flowchart of a process of updating radio link failure or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a terminal in a next generation mobile communication system fails according to an embodiment of the present disclosure;

[0033] Fig.13 is a block diagram of an internal structure of a terminal according to an embodiment of the present disclosure; and

[0034] Fig.14 is a block diagram illustrating the configuration of an NR base station according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0035] Hereinafter, the operating principle of the present disclosure will be described in detail in conjunction with the accompanying drawings. When describing the present disclosure below, when it is determined that the description may make the subject matter of the present disclosure unnecessarily unclear, the detailed description of the known functions or configurations incorporated herein will be omitted. The terms to be described below are terms defined in consideration of the functions in the present disclosure, and may differ depending on the user, the user's intention or custom. Therefore, the definition of the terms should be based on the content in the entire specification.

[0036] In describing the present disclosure below, a detailed description of known functions or configurations incorporated herein will be omitted when it is determined that the description may make the subject matter of the present disclosure unnecessarily unclear. Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0037] In the following description, for the convenience of description, terms for identifying access nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, terms referring to various identification information, etc. are illustratively used. Therefore, the present disclosure is not limited to the terms described below, and other terms referring to subjects with equivalent technical meanings may also be used.

[0038] In the following description, for the convenience of description, the terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard will be used. However, the present disclosure is not limited to these terms and names, and can be applied to systems conforming to other standards in the same manner. In the present disclosure, for the convenience of description, the term "eNB" can be used interchangeably with the term "gNB". That is, a base station described as an "eNB" can refer to a "gNB".

[0039] Figure 1 The structure of an LTE system according to an embodiment of the present disclosure is shown.

[0040] refer to Figure 1 As shown therein, the radio access network of the LTE system includes next generation base stations (evolved Node Bs, hereinafter referred to as eNBs, Node Bs or base stations) 1-05, 1-10, 1-15 and 1-20, a mobility management entity (MME) 1-25 and a serving gateway (S-GW) 1-30. User equipment (hereinafter referred to as UE or terminal) 1-35 accesses an external network through the ENBs 1-05 to 1-20 and the S-GW 1-30.

[0041] exist Figure 1In the LTE system, each of the ENBs 1-05 to 1-20 corresponds to a conventional Node B in the UMTS system. The ENB is connected to the UE 1-35 through a radio channel and performs a more complex role than the conventional Node B. In the LTE system, since all user services including real-time services such as Voice over IP (VoIP) via Internet Protocol are served through a shared channel, a device that collects state information such as the buffer state of the UE, the available transmission power state, and the channel state and performs scheduling accordingly is required, and the eNBs 1-05 to 1-20 serve as the device. Generally, one ENB controls a plurality of cells. For example, in order to achieve a transmission rate of 100 Mbps, the LTE system uses orthogonal frequency division multiplexing (hereinafter referred to as OFDM) as a radio access technology in a bandwidth of, for example, 20 MHz. In addition, the next generation mobile communication system adopts an adaptive modulation and coding (hereinafter referred to as AMC) scheme for determining a modulation scheme and a channel coding rate according to the channel state of the UE. The S-GW 1-30 is a device that provides data bearers, and generates or removes data bearers under the control of the MME 1-25. The MME is a device responsible for various control functions and a mobility management function for UE, and is connected to a plurality of base stations.

[0042] Figure 2 A radio protocol structure of an LTE system according to an embodiment of the present disclosure is shown.

[0043] refer to Figure 2 , the radio protocol of the LTE system includes a packet data convergence protocol (PDCP) 2-05 or 2-40, a radio link control (RLC) 2-10 or 2-35, and a medium access control (MAC) 2-15 or 2-30 on each of the UE side and the ENB side. The packet data convergence protocol (PDCP) 2-05 or 2-40 is responsible for operations such as IP header compression / reconstruction. The main functions of PDCP are summarized as follows.

[0044] Header compression and decompression: ROHC only

[0045] Transmission of user data

[0046] In-sequence delivery of upper layer PDUs during PDCP re-establishment of RLC AM

[0047] For split bearers in DC (supported only for RLC AM): PDCP PDU routing for transmission and PDCP PDU reordering for reception

[0048] Repeated detection of lower layer SDUs during PDCP re-establishment of RLC AM

[0049] For RLC AM, PDCP SDUs are retransmitted at handover, and for split bearers in DC, PDCP PDUs are retransmitted during PDCP data recovery

[0050] Encryption and Decryption

[0051] Timer-based SDU discard in uplink

[0052] Radio Link Control (hereinafter referred to as RLC) 2-10 or 2-35 reconfigures a PDCP protocol data unit (PDU) into an appropriate size to perform an ARQ operation, etc. The main functions of the RLC are summarized as follows.

[0053] Transmission of upper layer PDU

[0054] Error correction via ARQ (for AM data transmission only)

[0055] Concatenation, segmentation and reassembly of RLC SDUs (for UM and AM data transport only)

[0056] Re-segmentation of RLC data PDU (for AM data transmission only)

[0057] Reordering of RLC data PDUs (only for UM and AM data transmission)

[0058] Duplicate Detection (for UM and AM data transmission only)

[0059] Protocol error detection (AM data transmission only)

[0060] RLC SDU discard (only for UM and AM data transmission)

[0061] RLC Reconstruction

[0062] MAC 2-15 or 2-30 is connected to several RLC layer devices configured in a single terminal, and multiplexes RLC PDU into MAC PDU and demultiplexes MAC PDU into RLC PDU. The main functions of MAC are summarized as follows.

[0063] Mapping between logical channels and transport channels

[0064] Multiplexes / demultiplexes MAC SDUs belonging to one or different logical channels into / from transport blocks (TBs) delivered to / from the physical layer on a transport channel

[0065] Dispatch Information Report

[0066] Error correction through HARQ

[0067] Priority handling between logical channels of a UE

[0068] Priority handling between UEs with dynamic scheduling

[0069] MBMS Service Identifier

[0070] Transmission format selection

[0071] filling

[0072] The physical layer 2-20 or 2-25 performs operations of channel coding and modulating upper layer data to obtain OFDM symbols, and delivers the OFDM symbols through a wireless channel, or demodulates OFDM symbols received through a wireless channel, channel-decodes the OFDM symbols, and delivers the OFDM symbols to an upper layer.

[0073] Figure 3 A structure of a next generation mobile communication system according to an embodiment of the present disclosure is shown.

[0074] refer to Figure 3 As illustrated therein, the radio access network of the next generation mobile communication system (hereinafter referred to as NR or 5G) includes a next generation base station (new radio node B, hereinafter referred to as NR gNB or NR base station) 3-10, and a new radio core network (NR CN) 3-05. The user terminal (new radio user equipment, hereinafter referred to as NR UE or NR terminal) 3-15 accesses the external network via the NR gNB 3-10 and the NR CN 3-05.

[0075] NR gNB 3-10 can be connected to NR UE 3-15 through a radio channel and provide excellent services compared to conventional Node B. In the next generation mobile communication system, since all user traffic is served through a shared channel, a device that collects status information (such as the buffer status of the UE, the available transmission power status, and the channel status) and performs scheduling accordingly is required, and NR gNB 3-10 serves as the device. Generally, one NR gNB controls multiple cells. In order to achieve ultra-high-speed data transmission beyond the current LTE, the next generation mobile communication system may have a wider bandwidth than the existing maximum bandwidth, may adopt orthogonal frequency division multiplexing (hereinafter referred to as OFDM) as a radio access technology, and may additionally integrate beamforming technology therewith. In addition, the next generation mobile communication system adopts an adaptive modulation and coding (hereinafter referred to as AMC) scheme for determining a modulation scheme and a channel coding rate according to the channel status of the UE. NR CN 3-05 performs functions such as mobility support, bearer configuration, and QoS configuration. NR CN 3-05 is a device responsible for various control functions as well as the mobility management function of the UE, and may be connected to multiple base stations. In addition, the next generation mobile communication system can interoperate with the existing LTE system, and the NR CN is connected to the MME 3-25 via a network interface. The MME is connected to the eNB 3-30 which is an existing base station.

[0076] Figure 4 A radio protocol structure of a next generation mobile communication system according to an embodiment of the present disclosure is shown.

[0077] Figure 4 A radio protocol structure of a next-generation mobile communication system to which the present disclosure is applicable is shown.

[0078] refer to Figure 4 , the radio protocol of the next generation mobile communication system includes NR SDAP 4-01 or 4-45, NR PDCP 4-05 or 4-40, NR RLC 4-10 or 4-35 and NR MAC 4-15 or 4-30 on each of the UE and NR base station sides.

[0079] The main functions of NR SDAP 4-01 or 4-45 may include some of the following functions.

[0080] User plane data transmission

[0081] Mapping between QoS flows and DRBs for both DL and UL

[0082] Marking QoS Flow ID in both DL and UL packets

[0083] Reflective QoS flow to DRB mapping for UL SDAP PDU

[0084] Regarding the SDAP layer device, whether the UE uses the header of the SDAP layer device or whether to use the function of the SDAP layer device for each PDCP layer device or each bearer or each logical channel can be configured through an RRC message, and if the SDAP header is configured, the non-access layer (NAS) QoS reflection configuration 1-bit indicator (NAS reflection QoS) and AS QoS reflection configuration 1-bit indicator (AS reflection QoS) of the SDAP header can be indicated, so that the UE can update or reconfigure the mapping information of the QoS flow and data bearer for the uplink and downlink. The SDAP header may include QoS flow ID information indicating QoS. QoS information can be used as data processing priority, scheduling information, etc. for smoothly supporting services.

[0085] The main functions of NR PDCP 4-05 or 4-40 may include some of the following functions.

[0086] Header compression and decompression: ROHC only

[0087] Transmission of user data

[0088] In-order delivery of upper layer PDUs

[0089] Out-of-order delivery of upper layer PDUs

[0090] Reordering of received PDCP PDUs

[0091] Duplicate detection of lower layer SDUs

[0092] Retransmission of PDCP SDU

[0093] Encryption and Decryption

[0094] Timer-based SDU discard in uplink

[0095] The reordering of the NR PDCP device refers to a function of reordering the PDCP PDUs received from the lower layer in an order based on the PDCP sequence number (SN), and may include a function of transmitting data to the upper layer according to the rearranged order, may include a function of directly transmitting data without considering the order, may include a function of rearranging the order to record the lost PDCP PDU, may include a function of reporting the status of the lost PDCP PDU to the transmitting side, or may include a function of requesting retransmission of the lost PDCP PDU.

[0096] The main functions of NR RLC 4-10 or 4-35 may include some of the following functions.

[0097] Transmission of upper layer PDU

[0098] In-order delivery of upper layer PDUs

[0099] Out-of-order delivery of upper layer PDUs

[0100] Error correction via ARQ

[0101] Concatenation, segmentation, and reassembly of RLC SDUs

[0102] Re-segmentation of RLC data PDUs

[0103] Reordering of RLC data PDUs

[0104] Duplicate Detection

[0105] Protocol error detection

[0106] RLC SDU discarded

[0107] RLC Reconstruction

[0108] The in-sequence delivery of the NR RLC device refers to the function of continuously delivering the RLC SDU received from the lower layer to the upper layer, which may include the function of reassembling and delivering the received multiple RLC SDUs into which one of the original RLC SDUs has been segmented, may include the function of reordering the received RLC PDU with reference to the RLC sequence number (SN) or the PDCP sequence number (SN), may include the function of recording the RLC PDU lost as a result of the reordering, may include the function of reporting the status of the lost RLC PDU to the transmitting side, may include the function of requesting retransmission of the lost RLC PDU, may include the function of continuously delivering to the upper layer only the RLC SDU before the lost RLC SDU if there is a lost RLC SDU, may include the function of continuously delivering to the upper layer all RLC SDUs received before the timer is started despite the existence of the lost RLC SDU if a predetermined timer has expired, and may include the following function: if the predetermined timer has expired, all RLC SDUs received so far are continuously delivered to the upper layer despite the existence of the lost RLC SDU. In addition, the NR RLC device may process the RLC PDUs in the order received (in the order of arrival regardless of the sequence number order) and deliver them to the PDCP device regardless of the order (out-of-order delivery), and in case of segmentation, receiving segments stored in a buffer or received later, it may be reconfigured into one complete RLC PDU, processed and delivered to the PDCP device. The NR RLC layer may not include the cascading function, which may be performed in the NR MAC layer or replaced by the multiplexing function of the NR MAC layer.

[0109] Out-of-order delivery of the NR RLC device refers to the function of delivering the RLC SDU received from the lower layer to the upper layer immediately regardless of the order, which may include the function of reassembling and delivering multiple RLC SDUs into which an original RLC SDU is segmented if they are received, and may include the function of storing the RLC SN or PDCP SN of the received RLC PDU and recording the RLC PDU lost due to reordering.

[0110] NR MAC 14-15 or 4-30 can be connected to multiple NR RLC layer devices configured in one UE, and the main functions of NR MAC may include some of the following functions.

[0111] Mapping between logical channels and transport channels

[0112] MAC SDU multiplexing / demultiplexing

[0113] Dispatch Information Report

[0114] Error correction through HARQ

[0115] Priority handling between logical channels of a UE

[0116] Priority handling between UEs with dynamic scheduling

[0117] MBMS Service Identifier

[0118] Transmission format selection

[0119] filling

[0120] The NR PHY layer 4-20 or 4-25 can perform operations of channel coding and modulating upper layer data to obtain OFDM symbols and deliver the OFDM symbols through a radio channel, or demodulate OFDM symbols received through a radio channel, channel-decode the OFDM symbols, and deliver the OFDM symbols to an upper layer.

[0121] Figure 5 The present invention is a flowchart of a process of updating radio link failure information or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a UE in a next generation mobile communication system fails according to an embodiment of the present disclosure.

[0122] refer to Figure 5 , in operation 5-05, UE 5-01 can be in RRC connected mode (RRC_CONNECTED) by configuring an RRC connection with the NR base station 5-02.

[0123] In operation 5-10, UE 5-01 may send a UE capability information message (UECapabilityInformation) to base station 5-02. An indicator associated with an acceptable cell may be included in the message, and this may be an indicator associated with a cell different from the suitable cell of the VarRLF-Report. In addition, the message may include UE capability information associated with the ability to store information different from the suitable cell of the VarRLF-Report.

[0124] In operation 5-15, the UE 5-01 may detect a radio link failure (RLF), or a handover failure (handover failure or reconfiguration with synchronization failure) may occur due to a predetermined reason. For example, when the timer T310 for the currently connected primary cell (PCell) 5-02 expires, the UE may detect the RLF, or when the timer T304 expires, although the UE receives an RRC message indicating that a handover is required (e.g., RRCReconfiguration or MobilityFromNRCommand) from the currently connected primary cell, a handover failure may occur.

[0125] In operation 5-20, UE 5-01 may store radio link failure information (when RLF is detected) or handover failure information (when handover failure occurs) in VarRLF-Report. Specifically, the UE may store radio link failure information or handover failure information in VarRLF-Report according to the following process.

[0126] The UE shall determine the content of the VarRLF-Report as follows:

[0127] 1> Clear the information included in VarRLF-Report, if any;

[0128] 1> Set plmn-IdentityList to include the EPLMN list stored by the UE (i.e. including RPLMN);

[0129] 1> measResultLastServCell is set to include the cell-level RSRP, RSRQ and available SINR of the source PCell (in case of HO failure) or PCell (in case of RLF) based on the available SSB and CSI-RS measurements collected until the UE detects the failure;

[0130] 1> If SS / PBCH block based measurements are available:

[0131] 2> Based on the available SS / PBCH block based measurements collected until the UE detects the failure, set rsIndexResults in measResultLastServCell to include all available measurements of the source PCell (in case of HO failure) or PCell (in case of RLF), which are ordered such that if SS / PBCH block RSRP measurement results are available, the highest SS / PBCH block RSRP is listed first, otherwise if SS / PBCH block RSRQ measurement results are available, the highest SS / PBCH block SINR is listed first;

[0132] 1> If CSI-RS based measurements are available:

[0133] 2> Based on the available CSI-RS based measurements collected until the UE detects the failure, set rsIndexResults in measResultLastServCell to include all available measurements of the source PCell (in case of HO failure) or PCell (in case of RLF), which are ordered so that if CSI-RS RSRP measurement results are available, the highest CSI-RS RSRP is listed first, otherwise if CSI-RS RSRQ measurement results are available, the highest CSI-RS RSRQ is listed first, otherwise the highest CSI-RS SINR is listed first;

[0134] 1> Set ssbRLMConfigBitmap and / or csi-rsRLMConfigBitmap in measResultLastServCell to include the radio link monitoring configuration of the source PCell (in case of HO failure) or PCell (in case of RLF), if available;

[0135] 1>For each configuration of measObjectNR where measurement is available:

[0136] 2> If SS / PBCH block-based measurements are available:

[0137] 3> Based on the available SS / PBCH block based measurements collected until the UE detects the failure, set measResultListNR in measResultNeighCells to include all available measurements of the best measured cells except the source PCell (in the case of HO failure) or PCell (in the case of RLF), which are sorted so that if SS / PBCH block RSRP measurement results are available, the cell with the highest SS / PBCH block RSRP is listed first, otherwise the cell with the highest SS / PBCH block RSRQ is listed first, otherwise the cell with the highest SS / PBCH block SINR is listed first;

[0138] 4> For each neighboring cell included, include the available optional fields;

[0139] NOTE 0a: For neighbor cells included in measResultListNR in measResultNeighCells ordered based on SS / PBCH block measurement quantities, the UE also includes CSI-RS based measurement quantities, if available.

[0140] 2> If CSI-RS based measurements are available:

[0141] 3> Based on the available CSI-RS based measurements collected until the UE detects the radio link failure, measResultListNR in measResultNeighCells is set to include all available measurements of the best measured cells except the source PCell (in the case of HO failure) or PCell (in the case of RLF), which are sorted so that if the CSI-RS RSRP measurement result is available, the cell with the highest CSI-RS RSRP is listed first, otherwise if the CSI-RS RSRQ measurement result is available, the cell with the highest CSI-RS RSRQ is listed first, otherwise the cell with the highest CSI-RS SINR is listed first;

[0142] 4> For each neighboring cell included, include the available optional fields;

[0143] NOTE 0b: To rank neighbor cells based on CSI-RS measurement quantities, the UE includes measurements only for cells that are not already included in measResultListNR in measResultNeighCells to avoid overwriting SS / PBCH block based ordered measurements.

[0144] 2> For each neighboring cell included in measResultListNR in measResultNeighCells (if any):

[0145] 3> If the UE supports RLF reporting for conditional handover and if the neighbor cell is one of the candidate cells that included reconfigurationWithSync in the masterCellGroup in MCG VarConditionalReconfig when a failure was detected:

[0146] 4> Set choConflg in MeasResult2NR to the execution condition of each measID in CondTriggerConfig associated with the neighboring cell in MCG varConditionalReconfig;

[0147] 4> if the first entry of choConflg corresponds to an execution condition that is satisfied upon handover failure or radio link failure; or

[0148] 4> If the second entry of choConflg (if applicable) corresponds to an execution condition that is satisfied upon handover failure or radio link failure:

[0149] 5> Set firstTriggerEvent to the execution condition condFirstEvent corresponding to the first entry of choConflg or the execution condition condSecondEvent corresponding to the second entry of choConflg, whichever execution condition is satisfied first in time;

[0150] 5> If both the first execution condition corresponding to the first entry and the second execution condition corresponding to the second entry in choConflg are satisfied, timeBetweenEvents is set to the elapsed time between the time point at which the condition in choConflg is satisfied first and the time point at which the condition in choConflg is satisfied second in time;

[0151] 1> For each configured EUTRA frequency available for measurement;

[0152] 2> based on the measurements collected until the UE detects the failure, measResultListUTRA in measResultNeighCells is set to include the best measured cells, the best measured cells are ordered so that if RSRP measurement results are available, the cell with the highest RSRP is listed first, otherwise the cell with the highest RSRQ is listed first;

[0153] 3> For each neighboring cell included, include the available optional fields;

[0154] NOTE 1: The measured quantities are filtered by L3 filters as configured in the mobility measurement configuration. The measurements are based on time domain measurement resource restrictions (if configured). Cells listed for exclusion do not need to be reported.

[0155] 1> Set the C-RNTI to the C-RNTI used in the source PCell (in case of HO failure) or PCell (in case of RLF);

[0156] 1> If a failure is detected due to a reconfiguration with synchronization failure as described in 5.3.5.8.3, the fields in VarRLF-report are set as follows:

[0157] 2>Set connectionFailureType to Hof;

[0158] 2> If the UE supports RLF reporting for DAPS handover and if any DAPS bearers are configured when T304 is running:

[0159] 3> Set lastHO-Type to daps;

[0160] 3> According to Section 5.3.10.3, if a radio link failure is detected in the source PCell, then:

[0161] 4> set timeConnSourceDAPS-Failure to the time between the initiation of DAPS handover execution and the radio link failure detected in the source PCell when T304 is running;

[0162] 4> set rlf-Cause to the trigger for detecting source radio link failure according to Section 5.3.10.4;

[0163] 2> If the UE supports RLF reporting for conditional handover and if the configuration for conditional handover is available in MCG VarConditionalReconfig at the time of handover failure:

[0164] 3> If the UE performs a conditional handover towards the target PCell according to the condRRCReconfig of the target PCell:

[0165] 4> timeSinceCHO-Reconfig is set to the time that has passed between executing the last RRCReconfiguration message including reconfigurationWithSync of the target PCell for the failed conditional handover and receiving the last CondReconfiguration including condRRCReconfig of the target PCell for the failed conditional handover in the source PCell;

[0166] 3> Otherwise:

[0167] 4> timeSinceCHO-Reconfig is set to the time that has passed between executing the last RRCReconfiguration message including reconfigurationWithSync of the target PCell for failed handover and receiving the last conditionalReconfiguration including condRRCReconfig in the source PCell;

[0168] 3> Set choCandidateCellList to include the global cell identity (if available), otherwise set it to the physical cell identity and carrier frequency of each of the candidate target cells for conditional handover included in condRRCReconfig in MCG VarConditionalReconfig when the handover fails, excluding the candidate target cells included in measResulNeighCells;

[0169] 2> If the UE supports RLF reporting for conditional handover, and if the last executed RRCReconfiguration message including reconfigurationWithSync involves conditional handover:

[0170] 3> Set lastHO-Type to cho;

[0171] 2> Set nrFailedPCellID in FailedPCellID to the global cell ID and tracking area code (if available), otherwise set it to the physical cell ID and carrier frequency of the target PCell of the failed handover;

[0172] 2> Include nrPreviousCell in PreviousPCellID and set it to the global cell identity and tracking area code of the PCell that received the last RRCReconfiguration message including reconfigurationWithSync;

[0173] 2> timeConnFailure is set to the time that has passed since the last RRCReconfiguration message including reconfigurationWithSync was executed;

[0174] 1> Otherwise, if the failure is detected due to mobility failure from NR as described in 5.4.3.5, the fields in varRLF-Report are set as follows:

[0175] 2>Set the correlationFailureType to hof;

[0176] 2> If last_mobilityFromNRCommand refers to a failed Inter-RAT handover from NR to E-UTRA and if the UE supports Radio Link Failure Reporting for Inter-RAT MRO EUTRA (NR to EUTRA):

[0177] 3> Set the EUTRAFailedPCellID in FailedPCellID to the global cell identity and tracking area code (if available), otherwise set it to the physical cell identity and carrier frequency of the target PCell of the failed handover;

[0178] 2> Include nrPreviousCell in PreviousPCellID and set it to the global cell identifier and tracking area code of the PCell that received the last MobilityFromNRCommand message;

[0179] 2> timeConnFailure is set to the time that has passed since the initiation of the handover associated with the last MobilityFromNRCommand message;

[0180] 1> Otherwise, if a failure is detected due to a radio link failure as described in 5.3.10.3, the fields in the VarRLF-report are set as follows:

[0181] 2>Set cormectionFailureType to rlf;

[0182] 2> set rlf-Cause to the trigger for detecting radio link failure according to Section 5.3.10.4;

[0183] 2> Set nrFailedPCellID in FailedPCellID to the global cell identity and tracking area code (if available), otherwise set it to the physical cell identity and carrier frequency of the PCell where the radio link failure was detected;

[0184] 2> If an RRCReconfiguration message including reconfigurationWithSync is received before the connection fails:

[0185] 3> if the last executed RRCReconfiguration message including reconfigurationWithSync relates to an intra-NR handover and it was received while connected to a previous PCell to which the UE was connected before connecting to the PCell in which the radio link failure was detected; and

[0186] 3> If the PCell in which the radio link failure is detected is the result of cell selection, and T311 is not running at the time of PCell selection:

[0187] 4> Include nrPreviousCell in PreviousPCellID and set it to the global cell identity and tracking area code of the PCell that received the last executed RRCReconfiguration message including reconfigurationWithSync;

[0188] 4> If the last executed RRCReconfiguration message including reconfigurationWithSync involves DAPS switching:

[0189] 5> Set lastHO-Type to daps;

[0190] 4> Otherwise, if the last executed RRCReconfiguration message including reconfiguration WithSync involves conditional switching:

[0191] 5>Set lastHO-Type to cho;

[0192] 4> Set timeConnFailure to the time that has passed since the last RRCReconfiguration message including reconflgarationWithSync was executed;

[0193] 3> Otherwise, if the last RRCReconfiguration message including reconfigurationWithSync concerned a handover from E-UTRA to NR and if the UE supports radio link failure reporting for inter-RAT MRO EUTRA:

[0194] 4> include eutraPreviousCell in PreviousPCellID and set it to the global cell identity and tracking area code of the E-UTRA PCell where the last RRCReconfiguration message including reconfigurationWithSync was received embedded in the E-UTRA RRC message MobilityFromEUTRACommandmessage as specified in TS 36,331

[10] section 5.43.3;

[0195] 4> timeConnFailure is set to the time that has elapsed since the receipt of the last RRCReconfiguration message including reconfigurationWithSync embedded in the E-UTRA RRC message MobilityFromEUTRACommand message as specified in TS 36.331

[10] section 5.4.3.3;

[0196] 2> If configuration for conditional switching is available in MCG VarConditionalReconfig when radio link failure is declared:

[0197] 3> timeSinceCHO-Reconfig is set to the time that has passed between the detection of the radio link failure and the receipt of the last conditionalReconfiguration including the CondRRCeconfig message in the source PCell;

[0198] 3> Set choCandidateCellList to include the global cell identity (if available), otherwise set it to the physical cell identity and carrier frequency of each of all candidate target cells for conditional handover included in condRRCReconfig within MCG VarConditionalReconfig on radio link failure (excluding candidate target cells included in measResulNeighCells);

[0199] 1> if connectionFailureType is rlf and rlf-Cause is set to randomAccessProblem or beamFailureRecoveryFailure; or

[0200] 1> If connectionFailureType is hof and if the failed handover is an intra-RAT handover:

[0201] 2> RA-InformationCommon is set to include random access related information as described in Section 5.7.10.5;

[0202] 1> If available, set LocationInfo as in 5,3.3.7.

[0203] For reference, the UE may determine the rlf-Cause according to the following procedure.

[0204] The UE shall set the rlf-Cause in the VarRLF-Report as follows:

[0205] 1> If the UE declares radio link failure due to expiration of T310:

[0206] 2> Set rlf-Cause to t310-Expiry;

[0207] 1> Else if the UE declares a radio link failure due to a Random Access Problem indication from the MCG MAC:

[0208] 2> If a random access procedure is initiated for beam failure recovery:

[0209] 3> Set rlf-Cause to beamFailureRecoveryFailure;

[0210] 2> Otherwise:

[0211] 3> Set rlf-Cause to randomAccessProblem;

[0212] 1> Else if UE declares radio link failure due to reaching maximum number of retransmissions from MCG RLC:

[0213] 2> Set rlf reason to rlc-MaxNvmRetx;

[0214] 1> else if the UE declares radio link failure due to consistent uplink LBT failure:

[0215] 2> Set rlf-Cause to IbtFailure;

[0216] 1> Else if the IAB-MT declares a radio link failure due to receipt of a BH RLF indication at the BAP entity:

[0217] 2> Set rlf-Cause to bh-rlfRecoveryFailure.

[0218] 1> Else if the UE declares radio link failure due to expiry of T312:

[0219] 2> Set the rlf reason to t312-expiry;

[0220] In operation 5-25, UE 5-01 may initiate an RRC connection reestablishment procedure. However, UE 5-01 may not successfully perform the procedure, but fail due to a predetermined reason. For example, the UE may operate timer T311 when initiating the RRC connection reestablishment procedure, but when the UE fails to select a suitable NR cell before timer T311 expires, the procedure may fail.

[0221] In operation 5-30, UE 5-01 may transition to RRC idle (RRC_IDLE) mode.

[0222] In operation 5-35, UE 5-01 may camp on an acceptable NR cell 5-03.

[0223] In operation 5-40, UE 5-01 may perform an RRC connection establishment procedure to establish an RRC connection with an acceptable NR cell 5-03. That is, UE 5-01 may send an RRC connection establishment request message (RRCSetupRequest) to cell 5-03. In response, the cell may send an RRC connection establishment message (RRCSetup) to the UE in operation 5-45. In operation 5-46, the UE may switch to RRC connection mode (RRC_CONNECTED) by applying RRCSetup. The UE may regard or determine the cell as the current PCell. In operation 5-48, the UE according to the present disclosure may propose to perform at least one of the proposed methods (i.e., one of the following methods or a combination of some or all of the methods) according to the following conditions.

[0224] - If the radio link failure information or the handover failure information is included in the VarRLF-Report and the public land mobile network (registered PLMN) with which the UE is registered is included in the plmn-IdentityList stored in the VarRLF-Report (if the UE has the radio link failure or handover failure information available in the VarRLF-Report and if the RPLMN is included in the plmn-IdentityList stored in the VarRLF-Report), or if the UE has the radio link failure information or the handover failure information included in the VarRLF-Report and the acceptable cell is the current PCell.

[0225] ■ If reconnectCellId is not set in VarRLF-Report after failure of the RRC connection re-establishment procedure (If reconnectCellId is not set in VarRLF-Report after failure to perform re-establishment).

[0226] ◆If the UE supports RLF-Report for conditional handover and choCellId is set in VarRLF-Report (if the UE supports RLF-Report for conditional handover and if choCellId is set in VarRLF-Report).

[0227] ●Method 1: Information associated with the time elapsed from the radio link failure or handover failure in FailedPCelld stored in VarRLF-Report can be set in timeUntilReconnection in VarRLF-Report (timeUntilReconnection in VarRLF-Report is set to the time elapsed from the experienced radio link failure or handover failure in FailedPCelld stored in VarRLF-Report).

[0228] ● Method 2: The setting in timeUntilReconnection in VarRLF-Report may not be performed. Since this value is not set, when a suitable cell retrieves VarRLF-Report from the UE in the future, network optimization may be performed by recognizing that the UE has established an RRC connection with an acceptable cell.

[0229] ● Method 3: The information associated with the time elapsed from the radio link failure or handover failure stored in the failedPCellId in the VarRLF-Report may be set in a new timeUntilReconnection of the acceptable cell in the VarRLF-Report. Through the above, when the appropriate cell retrieves the VarRLF-Report from the UE in the future, network optimization may be performed by recognizing that the UE has established an RRC connection with the acceptable cell.

[0230] Otherwise (in other cases),

[0231] ● Method 5: The UE may set the time until Reconnection in the VarRLF-Report to the time since the last radio link failure or handover failure.

[0232] ● Method 6: The setting of timeUntilReconnection in VarRLF-Report may not be performed. In the case where this value is not set, when a suitable cell retrieves VarRLF-Report from the UE in the future, network optimization may be performed by recognizing that the UE has established an RRC connection with an acceptable cell.

[0233] ● Method 7: The UE may set the time elapsed since the last radio link failure or handover failure in a new timeUntilReconnection for an acceptable cell in the VarRLF-Report. Through the above, when the appropriate cell retrieves the VarRLF-Report from the UE in the future, network optimization may be performed by recognizing that the UE has established an RRC connection with an acceptable cell.

[0234] ◆The UE may set the global cell identifier and tracking area code of the current PCell to the nrReconnectCellId in the reconnectCellId of the VarRLF-Report (set the nrReconnectCellId in the reconnectCellId in the VarRLF-Report to the global cell identifier and tracking area code of the PCell). The UE may include an indicator in the VarRLF-Report indicating that the corresponding cell is an acceptable cell. Alternatively, the UE may not set any information in the reconnectCellId of the VarRLF-Report. Through the above, when the appropriate cell retrieves the VarRLF-Report from the UE in the future, network optimization can be performed by identifying that the UE has established an RRC connection with an acceptable cell.

[0235] Regarding the above-mentioned content, the base station can control which method the UE is to apply according to the configuration. The UE can send an RRC connection setup complete (RRCSetupComplete) message to the cell in operation 5-50. The UE can later send the VarRLF-Report to the appropriate cell 5-02 via the UE information process, and the operator managing the appropriate cell can optimize the network based on the corresponding information. For example, based on the timeUntilReconnection information, the operator can identify how much time has passed since the RRC connection reestablishment failed until the UE with the radio link failure information or the handover failure information in the VarRLF-Report configures the RRC connection with the predetermined cell again. Therefore, if the corresponding time is too long, the operator can operate the network by additionally providing a new cell or optimizing an existing cell. Similarly, based on the reconnectCellId, the operator can identify the cell to which the UE is subsequently connected, and this information can be used to determine whether to provide an additional cell or to appropriately manage the existing cell. In addition, if the reconnectCellId for an acceptable cell is set in the VarRLF-Report, the UE may not report the corresponding information to the appropriate cell. The acceptable cell does not belong to the operator subscribed by the UE, so if the UE sends reconnectCellId to the subscribed operator, the network operation information of another operator is provided.

[0236] Figure 6 Detailed description is a flowchart of a process of updating radio link failure information or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a UE in a next generation mobile communication system fails according to an embodiment of the present disclosure.

[0237] refer to Figure 6, in operation 6-05, UE 6-01 can be in RRC connected mode (RRC_CONNECTED) by configuring an RRC connection with the NR base station 6-02.

[0238] In operation 6-10, UE 6-01 may send a UE capability information message (UECapabilityInformation) to base station 6-02. This may be the same as the above embodiment.

[0239] In operation 6-15, the UE 6-01 may detect a radio link failure (RLF), or a handover failure (handover failure or reconfiguration with synchronization failure) may occur due to a predetermined reason. For example, when the timer T310 for the currently connected primary cell (PCell) 6-02 expires, the UE may detect the RLF, or when the timer T304 expires, although the UE receives an RRC message indicating that a handover is required (e.g., RRCReconfiguration or MobilityFromNRCommand) from the currently connected primary cell, a handover failure may occur.

[0240] In operation 6-20, the UE 6-01 may store radio link failure information (when RLF is detected) or handover failure information (when handover failure occurs) in VarRLF-Report. This may be the same as the above embodiment.

[0241] In operation 6-25, UE 6-01 may initiate an RRC connection reestablishment procedure. However, UE 6-01 may not successfully perform the procedure, but fail due to a predetermined reason. For example, the UE may operate timer T311 when initiating the RRC connection reestablishment procedure, but when the UE fails to select a suitable NR cell before timer T311 expires, the procedure may fail.

[0242] In operation 6-30, UE 6-01 may transition to an RRC idle mode (RRC_IDLE).

[0243] In operation 6-35, UE 6-01 may camp on an acceptable LTE cell 6-03.

[0244] In operation 6-40, UE 6-01 may perform an RRC connection establishment procedure to establish an RRC connection with an acceptable cell 6-03. That is, UE 6-01 may send an RRC connection establishment request message (RRCSetupRequest) to cell 6-03. In response thereto, the cell may send an RRC connection establishment message (RRCSetup) to the UE in operation 6-45. In operation 6-46, the UE may switch to RRC connection mode (RRC_CONNECTED) by applying RRCSetup. The UE may regard or determine the cell as the current PCell. In operation 6-48, the UE according to the present disclosure may propose to perform at least one of the proposed methods (i.e., one of the following methods or a combination of some or all of the methods) according to the following conditions.

[0245] - If the UE supports RLF reporting for inter-RAT MRO EUTRA defined in TS 38.306 standard, the radio link failure information or handover failure information is included in the VarRLF-Report of TS 38.331 standard, and the public land mobile network (registered PLMN) registered by the UE is included in the plmn-IdentityList stored in the VarRLF-Report of TS 38.331 standard (if the UE supports RLF reporting for inter-RAT MRO EUTRA defined in TS 38.306), and if the UE has radio link failure or handover failure information available in the VarRLF-Report of TS 38.331, and if the RPLMN is included in the plmn-IdentityList stored in the VarRLF-Report of TS 38.331), or if the handover failure information is included in the VarRLF-Report and the acceptable cell is the current PCell.

[0246] If reconnectCellId is not set in the VarRLF-Report of TS 38.331 standard after the RRC connection reestablishment procedure fails (if reconnectCellId in the VarRLF-Report of TS 38.331 is not set after the reestablishment fails to be performed).

[0247] Method 1: The UE may set the time that has passed since the last radio link failure or handover failure in timeUntilReconnection in VarRLF-Report of the TS 38.331 standard (set timeUntilReconnection in VarRLF-Report of TS 38.331 to the time that has passed since the last radio link failure or handover failure).

[0248] Method 2: The setting of timeUntilReconnection in VarRLF-Report of TS 38.331 standard may not be performed. Since this value is not set, when the appropriate cell retrieves VarRLF-Report from the UE in the future, network optimization can be performed by recognizing that the UE has established an RRC connection with an acceptable cell.

[0249] Method 3: The UE can set the time elapsed since the last radio link failure or handover failure in the new timeUntilReconnection for the acceptable cell in the VarRLF-Report of the TS 38.331 standard. Through the above, when the appropriate cell retrieves the VarRLF-Report from the UE in the future, network optimization can be performed by recognizing that the UE has established an RRC connection with the acceptable cell.

[0250] The UE may set the global cell identifier and tracking area code of the current PCell to the eutraReconnectCellId in the reconnectCellId of the VarRLF-Report of the TS 38.331 standard (set the eutraReconnectCellId in the reconnectCellId in the VarRLF-Report of TS 38.331 to the global cell identifier and tracking area code of the PCell). The UE may include an indicator in the VarRLF-Report indicating that the corresponding cell is an acceptable cell. Alternatively, the UE may not set any information in the reconnectCellId of the VarRLF-Report. Through the above, when the appropriate cell retrieves the VarRLF-Report from the UE in the future, network optimization may be performed by recognizing that the UE has established an RRC connection with an acceptable cell.

[0251] Regarding the above-mentioned content, the base station can control which method the UE is to apply according to the configuration. The UE can send an RRC connection setup complete message (RRCConnectionSetupComplete) to the cell in operation 6-50. The UE can send the VarRLF-Report to the appropriate cell 6-02 via the UE information process, and the operator managing the appropriate cell can optimize the network based on the corresponding information. For example, based on the timeUntilReconnection information, the operator can identify how much time has passed since the RRC connection reestablishment failed until the UE with the radio link failure information or the handover failure information in the VarRLF-Report reconfigures the RRC connection with the predetermined cell. Therefore, if the corresponding time is too long, the operator can operate the network by additionally providing a new cell or optimizing an existing cell. Similarly, based on the reconnectCellId, the operator can identify the cell to which the UE is subsequently connected, and this information can be used to determine whether to provide an additional cell or to appropriately manage the existing cell. In addition, if the reconnectCellId for an acceptable cell is set in the VarRLF-Report, the UE may not report the corresponding information to the appropriate cell. The acceptable cell does not belong to the operator subscribed by the UE, so if the UE sends reconnectCellId to the subscribed operator, the network operation information of another operator is provided.

[0252] Figure 7 The present invention is a flowchart of a process of updating radio link failure information or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a UE in a next generation mobile communication system fails according to an embodiment of the present disclosure.

[0253] Reference Figure 7 , UE 7-01 may be in RRC connected mode (RRC_CONNECTED) by configuring an RRC connection with LTE base station 7-02. In operation 7-05, the LTE base station may be connected to EPC or 5GC.

[0254] In operation 7-10, UE 7-01 may send a UE capability information message (UECapabilityInformation) to base station 7-02. An indicator associated with an acceptable cell may be included in the message, and this may be an indicator associated with a cell different from the suitable cell of the VarRLF-Report. In addition, the message may include UE capability information associated with the ability to store information different from the suitable cell of the VarRLF-Report.

[0255] In operation 7-15, the UE 7-01 may detect a radio link failure (RLF), or a handover failure may occur due to a predetermined reason (handover failure). For example, when the timer T310 for the currently connected primary cell (PCell) 7-02 expires, the UE may detect the RLF, or although the UE receives an RRC message indicating that a handover from the currently connected primary cell is required (e.g., RRCConnectionReconfiguration or MobilityFromEUTRACommand, so that targetRAT-Type is set to nr), a handover failure may occur when the timer T304 expires.

[0256] In operation 7-20, UE 7-01 may store radio link failure information (when RLF is detected) or handover failure information (when handover failure occurs) in VarRLF-Report. Specifically, the UE may store radio link failure information in VarRLF-Report according to the following process.

[0257] 2> Store the following radio link failure information in VarRLF-Report (VarRLF-Report-NB in ​​NB-IoT) by setting its fields as follows:

[0258] 3> Clear the information included in VarRLF-Report (VarRLF-Report-NB in ​​NB-IoT), if any;

[0259] 3> Set PLMNs-IdentityList to include the list of EPLMNs stored by the UE (i.e. including RPLMN);

[0260] 3> Based on the measurements collected until the UE detects the radio link failure, measResultLastServCell is set to include the RSRP and RSRQ of the PCell (if available);

[0261] 3> In addition to NB-IoT, measResultNeighCells is set to include the best measured cells other than PCell, which are ordered so that the best cell is listed first and are based on measurements collected until the UE detects a radio link failure, and its fields are set as follows;

[0262] 4> If the UE is configured to perform measurements on one or more EUTRA frequencies, MeasResultListUTRA is included;

[0263] 4> if the UE is configured to perform measurement reporting for one or more adjacent UTRA frequencies, measResultListUTRA is included;

[0264] 4> if the UE is configured to perform measurement reporting for one or more neighboring GERAN frequencies, measResultListGERAN is included;

[0265] 4> if the UE is configured to perform measurement reporting for one or more adjacent CDMA2000 frequencies, measResultsCDMA2000 is included;

[0266] 4> if the UE is configured to perform measurement reporting not related to NR sidelink communications for one or more adjacent NR frequencies, including measResultListNR;

[0267] 4> For each neighboring cell included, include the available optional fields;

[0268] NOTE 1: The measured quantities are filtered by L3 filters as configured in mobility measurements. Measurements are based on time domain measurement resource restrictions (if configured). Cells listed for exclusion do not need to be reported.

[0269] 3> In addition to NB-IoT, if available, logMeasResultListWLAN is set to include WLAN measurement results in descending order of RSSI of WLAN APs;

[0270] 3> In addition to NB-IoT, if available, logMeasResultListBT is set to include Bluetooth measurement results in order of decreasing RSSI of Bluetooth beacons;

[0271] 3> If detailed location information is available, set the content of LocationInfo as follows:

[0272] 4> include locationCoordinates;

[0273] 4> Include horizontalVelocity, if available;

[0274] 3> Set FailedPCellID to the global cell identity, if available, otherwise, except for NB-IoT, set FailedPCellID to the physical cell identity and carrier frequency of the PCell where the radio link failure was detected;

[0275] 3> Except for NB-IoT, set tac-FailedPCell to the tracking area code of the PCell where the radio link failure was detected (if available);

[0276] 3>Except for NB-IoT, if an RRCConnectionReconfiguration message including mobilityControlInfo is received before the connection fails:

[0277] 4> If the last RRCConnectionReconfiguration message including mobilityControlInfo involves intra-E-UTRA handover:

[0278] 5> Include perviousPCellID and set it to the global cell identity of the PCell in which the last RRCConnectionReconfiguration message including mobilityControlInfo was received;

[0279] 5> timeConnFailure is set to the time that has passed since the last RRCConnectionReconfiguration message including mobilityControlInfo was received;

[0280] 4> if the last RRCConnectionReconfiguration message including mobilityControlInfo involved a handover from UTRA to E-UTRA and if the UE supports radio link failure reporting for inter-RAT MRO;

[0281] 5> include previousTRA-CellID and set it to the physical cell identity, carrier frequency and global cell identity (if applicable) of the UTRA cell in which the last RRCConnectionReconfiguration message including mobilityControlInfo was received;

[0282] 5> timeConnFailure is set to the time that has passed since the last RRCConnectionReconfiguration message including mobilityControlInfo was received;

[0283] 4> If the last RRCConnectionReconfiguration message including mobilityControlInfo involved a handover from NR to E-UTRA and if the UE supports radio link failure reporting for inter-RAT MRO NR:

[0284] 5> include previousNRPCellID and set it to the global cell identity of the PCell in which the last RRCConnectionReconfiguration message including mobilityControlInfo was received embedded in the NR RRC message MohilityFromNRCommand message as specified in TS 38.331

[82] section 5.4.3.3;

[0285] 5> timeConnFailure is set to the time that has elapsed since the last reception of an RRCConnectionReconfiguration message including MobilityControlInfo embedded in an NR RRC message MobilityFromNRCommand message, as specified in section 5.4.3.3 of TS 38.331

[82] .

[0286] 3>Except for NB IoT, if the UE supports QCI1 indication in the radio link failure report and has a DRB for which QCI is 1 indication:

[0287] 4>include drb-EstablishedWithQCI-1;

[0288] 3> Except for NB-IoT, set connectionFailureType to rlf;

[0289] 3> In addition to NB-IoT, set C-RNTI to the C-RNTI used in PCell;

[0290] 3> In addition to NB-IoT, set rlf-Cause as the trigger for detecting radio link failure;

[0291] The UE may store the handover failure information in the VarRLF-Report according to the following procedure.

[0292] 3> Clear the information included in VarRLF-Report, if any;

[0293] 3> Set PLMNs-IdentityList to include the list of EPLMNs stored by the UE (i.e. including RPLMN);

[0294] 3> Set measResultLastServCell to include the RSRP and RSRQ of the source PCell (if available), based on the measurements collected until the UE detects a handover failure and according to the following;

[0295] 4> If the UE includes rsrqResult, it includes IastServCellRSRQ-Type;

[0296] 3> set measResultNeighCells to include the best measured cells other than the source PCell, which is ordered so that the best cell is listed first and is based on the measurements collected until the UE detects a handover failure, and set its fields as follows;

[0297] 4> if the UE is configured to perform measurements on one or more EUTRA frequencies, measResultListUTRA is included;

[0298] 4> If the UE includes rsrqResult, it includes rsrq-Type;

[0299] 4> If the UE is configured to perform measurement reporting for one or more neighboring UTRA frequencies, measResidListUTRA is included.

[0300] 4> if the UE is configured to perform measurement reporting for one or more neighboring GERAN frequencies, measResultListGERAN is included;

[0301] 4> if the UE is configured to perform measurement reporting for one or more adjacent CDMA2000 frequencies, measResultsCDMA2000 is included;

[0302] 4> if the UE is configured to perform measurement reporting not related to NR sidelink communications for one or more adjacent NR frequencies, measResultListNR is included;

[0303] 4> For each neighboring cell included, include the available optional fields;

[0304] NOTE 2: The measured quantities are filtered by L3 filters as configured in mobility measurements. Measurements are based on time domain measurement resource restrictions (if configured). Cells listed for exclusion do not need to be reported.

[0305] 3> If available, set logMeasResultListWLAN to include WLAN measurement results in descending order of RSSI of WLAN APs;

[0306] 3> If available, set logMeasResultListBT to include Bluetooth measurement results in order of decreasing RSSI of Bluetooth beacons;

[0307] 3> If detailed location information is available, set the content of LocationInfo as follows:

[0308] 4> include locationCoordinates;

[0309] 4> Include horizontalVelocity, if available;

[0310] 3> If the last RRCConnectionReconfiguration message including mobilityControlInfo involved a failed intra-RAT handover (E-UTRA to E-UTRA):

[0311] 4> Set FailedPCelUID to the global cell ID (if available), otherwise set it to the physical cell ID and carrier frequency of the target PCell of the failed handover;

[0312] 4> Include previousPCellID and set it to the global cell identity of the PCell that received the last RRCConnectionReconfiguration message including mobilityControlInfo;

[0313] 4> Set timeConnFailure to the time that has passed since the last RRCConnectionReconfiguration message including mobilityControlInfo was received

[0314] 3> Otherwise, if the last mobilityFromEUTRACommand involved a failed inter-RAT handover from E-UTRA to NR:

[0315] 4> Set xlyq_failedNR-PCellID to the global cell identity and tracking area code (if available), otherwise set it to the physical cell identity and carrier frequency of the target PCell of the failed handover;

[0316] 4> Include PreviousPCellID and set it to the global cell identity of the PCell that received the last MobilityFromEUTRACommand message;

[0317] 4> Set timeConnFailure to the time that has passed since the last MobilityFromEUTRACommand message was received;

[0318] 3>Set connectionFailureType to 'hof';

[0319] 3> Set the C-RNTI to the C-RNTI used in the source PCell;

[0320] In operation 7-25, UE 7-01 may initiate an RRC connection reestablishment procedure. However, UE 7-01 may not successfully perform the procedure, but fail due to a predetermined reason. For example, the UE may operate timer T311 when initiating the RRC connection reestablishment procedure, but when the UE fails to select a suitable LTE cell before timer T311 expires, the procedure may fail.

[0321] In operation 7-30, UE 7-01 may transition to an RRC idle mode (RRC_IDLE).

[0322] In operation 7-35, UE 7-01 may camp on an acceptable LTE cell 7-03.

[0323] In operation 7-40, UE 7-01 may perform an RRC connection establishment procedure to establish an RRC connection with an acceptable LTE cell 7-03. That is, UE 7-01 may send an RRC connection establishment request message (RRCConnectionRequest) to cell 7-03. In response to this, the cell may send an RRC connection establishment message (RRCConnectionSetup) to the UE in operation 7-45. In operation 7-46, the UE may switch to RRC connection mode (RRC_CONNECTED) by applying RRCConnectionSetup. The UE may regard or determine the cell as the current PCell. In operation 7-48, the UE according to the present disclosure may propose to perform at least one of the proposed methods (i.e., one of the following methods or a combination of some or all of the methods) according to the following conditions.

[0324] - If the radio link failure information or the handover failure information is included in the VarRLF-Report and the public land mobile network (registered PLMN) with which the UE is registered is included in the plmn-IdentityList stored in the VarRLF-Report (if the UE has the radio link failure or handover failure information available in the VarRLF-Report and if the RPLMN is included in the plmn-IdentityList stored in the VarRLF-Report), or if the UE has the radio link failure information or the handover failure information in the VarRLF-Report and the acceptable cell is the current PCell.

[0325] ■ If reconnectCellId is not set in VarRLF-Report after failure of the RRC connection re-establishment procedure (If reconnectCellId is not set in VarRLF-Report after failure to perform re-establishment).

[0326] ◆Method 1: The UE may set the time that has passed since the last radio link failure or handover failure in timeUntilReconnection in VarRLF-Report (set timeUntilReconnection in VarRLF-Report to the time that has passed since the last radio link failure or handover failure).

[0327] ◆Method 2: The setting of timeUntilReconnection in VarRLF-Report may not be performed. Since this value is not set, when a suitable cell retrieves VarRLF-Report from the UE in the future, network optimization may be performed by recognizing that the UE has established an RRC connection with an acceptable cell.

[0328] ◆Method 3: The UE may set the time elapsed since the last radio link failure or handover failure in a new timeUntilReconnection for acceptable cells in the VarRLF-Report. Through the above, when the appropriate cell retrieves the VarRLF-Report from the UE in the future, network optimization can be performed by recognizing that the UE has established an RRC connection with an acceptable cell.

[0329] ■The UE may set the global cell identifier and tracking area code of the current PCell to the eutraReconnectCellId in the reconnectCellId of the VarRLF-Report (set the eutraReconnectCellId in the reconnectCellId in the VarRLF-Report to the global cell identifier and tracking area code of the PCell). The UE may include an indicator in the VarRLF-Report indicating that the corresponding cell is an acceptable cell. Alternatively, the UE may not set any information in the reconnectCellId of the VarRLF-Report. Through the above, when the appropriate cell retrieves the VarRLF-Report from the UE in the future, network optimization can be performed by identifying that the UE has established an RRC connection with an acceptable cell.

[0330] Regarding the above-mentioned content, the base station can control which method the UE is to apply according to the configuration. The UE can send an RRC connection setup complete message (RRCConnectionSetupComplete) to the cell in operation 7-50. The UE can send VarRLF-Report to the appropriate cell 7-02 via the UE information process, and the operator managing the appropriate cell can optimize the network based on the corresponding information. For example, based on the timeUntilReconnection information, the operator can identify how much time has passed since the RRC connection reestablishment failed until the UE with the radio link failure information or the handover failure information in the VarRLF-Report configures the RRC connection with the predetermined cell again. Therefore, if the corresponding time is too long, the operator can operate the network by additionally providing a new cell or optimizing an existing cell. Similarly, based on the reconnectCellId, the operator can identify the cell to which the UE is subsequently connected, and this information can be used to determine whether to provide an additional cell or to appropriately manage the existing cell. In addition, if the reconnectCellId for an acceptable cell is set in the VarRLF-Report, the UE may not report the corresponding information to the appropriate cell. The acceptable cell does not belong to the operator subscribed by the UE, so if the UE sends reconnectCellId to the subscribed operator, the network operation information of another operator is provided.

[0331] Figure 8 Detailed description is a flowchart of a process of updating radio link failure information or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a UE in a next generation mobile communication system fails according to an embodiment of the present disclosure.

[0332] refer to Figure 8, UE 8-01 may be in RRC connected mode (RRC_CONNECTED) by configuring an RRC connection with LTE base station 8-02. In operation 8-05, the LTE base station may be connected to EPC or 5GC.

[0333] In operation 8-10, UE 8-01 may send a UE capability information message (UECapabilityInformation) to base station 8-02. An indicator associated with an acceptable cell may be included in the message, and may be an indicator associated with a cell different from a suitable cell of VarRLF-Report. In addition, the message may include UE capability information associated with a capability to store information different from a suitable cell of VarRLF-Report.

[0334] In operation 8-15, the UE 8-01 may detect a radio link failure (RLF), or a handover failure may occur due to a predetermined reason (handover failure). For example, when the timer T310 for the currently connected primary cell (PCell) 8-02 expires, the UE may detect the RLF, or although the UE receives an RRC message indicating that a handover from the currently connected primary cell is required (e.g., RRCConnectionReconfiguration or MobilityFromEUTRACommand, so that targetRAT-Type is set to nr), a handover failure may occur when the timer T304 expires.

[0335] In operation 8-20, UE 8-01 may store radio link failure information (when RLF is detected) or handover failure information (when handover failure occurs) in VarRLF-Report. This may be the same as the above embodiment.

[0336] In operation 8-25, UE 8-01 may initiate an RRC connection reestablishment procedure. However, UE 8-01 may not successfully perform the procedure, but fail due to a predetermined reason. For example, the UE may operate timer T311 when initiating the RRC connection reestablishment procedure, but when the UE fails to select a suitable LTE cell before timer T311 expires, the procedure may fail.

[0337] In operation 8-30, UE 8-01 may transition to an RRC idle mode (RRC_IDLE).

[0338] In operation 8-35, UE 8-01 may camp on an acceptable NR cell 8-03.

[0339] In operation 8-40, UE 8-01 may perform an RRC connection establishment procedure to establish an RRC connection with an acceptable NR cell 8-03. That is, UE 8-01 may send an RRC connection establishment request message (RRCSetupRequest) to cell 8-03. In response to this, the cell may send an RRC connection establishment message (RRCSetup) to the UE in operation 8-45. In operation 8-46, the UE may switch to RRC connection mode (RRC_CONNECTED) by applying RRCSetup. The UE may regard or determine the cell as the current PCell. In operation 8-48, the UE according to the present disclosure may propose to perform at least one of the proposed methods (i.e., one of the following methods or a combination of some or all of the methods) according to the following conditions.

[0340] - If the UE supports RLF reporting for inter-RAT MRO NR as defined in TS 36.306 standard, the radio link failure information or handover failure information is included in the VarRLF-Report of TS 36.331 standard, and the public land mobile network (registered PLMN) with which the UE is registered is included in the plmn-IdentityList stored in the VarRLF-Report of TS 36.331 (if the UE supports RLF reporting for inter-RAT MRO NR as defined in TS 36.306), and if the UE has the radio link failure or handover failure information available in the VarRLF-Report of TS 36.331, and if the RPLMN is included in the plmn-IdentityList stored in the VarRLF-Report of TS 36.331), or if the UE supports RLF reporting for inter-RAT MRO NR as defined in TS 36.306 standard, the radio link failure information or handover failure information is included in the VarRLF-Report of TS 36.331. 36.331 standard VarRLF-Report, and the acceptable cell is the current PCell.

[0341] ■ If reconnectCellId is not set in the VarRLF-Report of the TS 36.331 standard after the RRC connection reestablishment procedure fails (if reconnectCellId in the VarRLF-Report is not set after a failure to perform reestablishment).

[0342] ◆Method 1: The UE can set the time that has passed since the radio link failure or handover failure in the timeUntilReconnection in the VarRLF-Report of the TS 36.331 standard (set the timeUntilReconnection in the VarRLF-Report of TS 36.331 to the time that has passed since the last radio link failure or handover failure).

[0343] ◆Method 2: The setting of timeUntilReconnection in VarRLF-Report of TS 36.331 standard may not be performed. Since this value is not set, when the appropriate cell retrieves VarRLF-Report from the UE in the future, network optimization can be performed by recognizing that the UE has established an RRC connection with an acceptable cell.

[0344] ◆Method 3: The UE can set the time elapsed since the last radio link failure or handover failure in the new timeUntilReconnection for acceptable cells in the VarRLF-Report of the TS36.331 standard. Through the above, when the appropriate cell retrieves the VarRLF-Report from the UE in the future, network optimization can be performed by recognizing that the UE has established an RRC connection with the acceptable cell.

[0345] ■The UE may set the global cell identity and tracking area code of the current PCell to the nrReconnectCellId in the reconnectCellId of the VarRLF-Report of the TS 36.331 standard (set the nrReconnectCellId in the reconnectCellId in the VarRLF-Report of TS 36.331 to the global cell identity and tracking area code of the PCell). The UE may include an indicator in the VarRLF-Report indicating that the corresponding cell is an acceptable cell. Alternatively, the UE may not set any information in the reconnectCellId of the VarRLF-Report. Through the above, when the appropriate cell retrieves the VarRLF-Report from the UE in the future, network optimization can be performed by recognizing that the UE has established an RRC connection with an acceptable cell.

[0346] Regarding the above-mentioned content, the base station can control which method the UE is to apply according to the configuration. The UE can send an RRC connection setup complete message (RRCSetupComplete) to the cell in operation 8-50. The UE can send the VarRLF-Report to the appropriate cell 8-02 via the UE information process, and the operator managing the appropriate cell can optimize the network based on the corresponding information. For example, based on the timeUntilReconnection information, the operator can identify how much time has passed since the RRC connection reestablishment failed until the UE with the radio link failure information or the handover failure information in the VarRLF-Report configures the RRC connection with the predetermined cell again. Therefore, if the corresponding time is too long, the operator can operate the network by additionally providing a new cell or optimizing an existing cell. Similarly, based on the reconnectCellId, the operator can identify the cell to which the UE is subsequently connected, and this information can be used to determine whether to provide an additional cell or to appropriately manage the existing cell. In addition, if the reconnectCellId for an acceptable cell is set in the VarRLF-Report, the UE may not report the corresponding information to the appropriate cell. The acceptable cell does not belong to the operator subscribed by the UE, so if the UE sends reconnectCellId to the subscribed operator, the network operation information of another operator is provided.

[0347] Fig. 9 is a flowchart of a process in which a UE transmits radio link failure information or handover failure information to a base station in a next generation mobile communication system according to an embodiment of the present disclosure.

[0348] Reference Fig. 9 , in operation 9-05, UE 9-01 can be in RRC connected mode (RRC_CONNECTED) by configuring an RRC connection with the NR base station 9-02.

[0349] In operation 9-10, the base station 9-02 may send a UE information request message (UEInformationRequest) to the UE 9-01 for which security is successfully activated. The message may include rlf-ReportReq configured as true.

[0350] In operation 9-15, when rlf-ReportReq is configured as true in the UE information request message received in operation 9-10, the UE 9-01 may perform the following process and may send a UE information response message (UEInformationResponse) to the base station 9-02.

[0351] 2> If the UE has radio link failure information or handover failure information available in the VarRLF-Report, and if the RPLMN is included in the PFMN-IdentityList stored in the VarRLF-Report:

[0352] 3> Set timeSinceFailure in VarRLF-Report to the time since the last radio link failure or handover failure in NR;

[0353] 3> Set the rlf-Report in the UEInformationResponse message to the value of rlf-Report in VarRLF-Report;

[0354] 3> Upon successful delivery of the UEInformationResponse message confirmed by the lower layer, the rlf-Report from the VarRLF-Report is discarded;

[0355] 2> Otherwise, if the UE is capable of inter-RAT RLF reporting as defined in TS 38.306 and has radio link failure information or handover failure information available in the VarRLF-Report of TS 36.331, and if the RPLMN is included in the plmn-IdentityList stored in the VarRLF-Report of TS 36.331:

[0356] 3> Set timeSinceFailure in VarRLF-Report of TS 36.331

[10] to the time since the last radio link failure or handover failure in EUTRA;

[0357] 3> Set the FailedPCellID-EUTRA in the rlf-Report in the UEInformationResponse message to indicate the PCell where the RLF is detected or the source PCell of the failed handover in the VarRLF-Report of TS 36.331

[10] ;

[0358] 3> Set measResult-RLF-Report-EUTRA in the RLF-Report in the UEInformationResponse message to the value of rlf-Report in the VarRLF-Report of TS 36.331;

[0359] 3> Upon successful delivery of the UEInformationResponse message confirmed by the lower layer, the rlf-Report from the VarRLF-Report of TS 36.331 is discarded;

[0360] The RLF-Report included in the UE Information Response message may have an ASN.1 structure as shown below: In this case, the UE may configure the RLF-Report by applying the above-mentioned embodiment, and may include the RLF-Report in the UE Information Response message.

[0361]

[0362]

[0363] Fig.10 is a flowchart of a process in which a UE transmits radio link failure information or handover failure information to a base station in a next generation mobile communication system according to an embodiment of the present disclosure.

[0364] refer to Fig.10 In operation 10-05, UE 10-01 may be in RRC connected mode (RRC_CONNECTED) by configuring an RRC connection with LTE base station 10-02. An LTE base station connected to EPC may be referred to as an eNB, and an LTE base station connected to 5GC may be referred to as an ng-eNB.

[0365] In operation 10-10, the base station 10-02 may send a UE information request message (UEInformationRequest) to the UE 10-01 for which security is successfully activated. The message may include rlf-ReportReq configured as true.

[0366] In operation 10-15, when rlf-ReportReq is configured as true in the UE Information Request message received in operation 10-10, the UE 10-01 may perform the following process and may send a UE Information Response message (UEInformationResponse) to the base station 10-02.

[0367] 1> If rlf-ReportReq is set to true and the UE has Radio Link Failure Information or Handover Failure Information available in the VarRLF-Report (VarRLF-Report-NB in ​​NB-IoT) and if the RPLMN is included in the PLMN-IdentityList stored in the VarRLF-Report:

[0368] 2> For NB-IoT, if the global cell identity of the selected cell is the same as the reestablishmentCellID in VarRLF-Report-NB:

[0369] 3> Remove reestablishmentCellID from VarRLF-Report-NB.

[0370] 2> Set timeSinceFailure in VarRLF-Report (VarRLF-Report-NB in ​​NB-IoT) to the time elapsed since the last radio link or handover failure in E-UTRA;

[0371] 2> Set the rlf-Report in the UEInformationResponse message to the value of rlf-Report in VarRLF-Report (VarRLF-Report-NB in ​​NB-IoT);

[0372] 2> upon successful delivery of the UEInformationResponse message confirmed by the lower layer, the rlf report from VarRLF-Report (VarRLF-Report-NB in ​​NB-IoT) is discarded;

[0373] The RLF-Report included in the UE Information Response message may have an ASN.1 structure as shown below: In this case, the UE may configure the RLF-Report by applying the above-mentioned embodiment, and may include the RLF-Report in the UE Information Response message.

[0374]

[0375]

[0376]

[0377]

[0378] Fig.11 Detailed description is a flowchart of a process of updating radio link failure or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a UE in a next generation mobile communication system fails according to an embodiment of the present disclosure.

[0379] refer to Fig.11 , UE 11-01 can be in RRC connected mode (RRC_CONNECTED) by configuring an RRC connection with NR base station 1-02.

[0380] In operation 11-10, UE 11-01 may send a UE capability information message (UECapabilityInformation) to base station 11-02. An indicator associated with an acceptable cell may be included in the message, and this may be an indicator associated with a cell different from the suitable cell of the VarRLF-Report. In addition, the message may include UE capability information associated with the ability to store information different from the suitable cell of the VarRLF-Report. In the message, capability information associated with whether it has the ability to store information associated with voice fallback and / or emergency service fallback in the NR RLF report.

[0381] In operation 11-15, UE 11-01 may receive a MobilityFromNRCommand message from base station 11-02. The message may include a targetRAT-Type configured as eutra. The message may include a voiceFallbackIndication.

[0382] In operation 11-20, UE 11-01 may determine that mobility failure from NR occurs due to a predetermined reason. For example, if a connection to the target radio access technology is not successfully performed (if the UE does not successfully establish a connection to the target radio access technology), it is determined that mobility failure from NR occurs.

[0383] In operation 11-25, if the targetRAT-Type in the MobilityFromNRCommand received in operation 11-15 is configured as eutra and the UE 11-01 supports radio link failure reporting of inter-RAT MRO EUTRA (if the targetRAT-Type in the received MobilityFromNRCommand is set to eutra and the UE supports radio link failure reporting of inter-RAT MRO EUTRA), the UE 11-01 may store the handover failure information in VarRLF-Report. This may be performed according to at least one of the above-mentioned embodiments. In addition, if voiceFallbackIndication is included in MobilityFormNRCommand, or if the mobility procedure from NR is for emergency service fallback, the UE may store an indicator indicating it in VarRLF-Report.

[0384] In operation 11-30, UE 11-01 may attempt to select an E-UTRA cell. For reference, if voiceFallbackIndication is included in MobilityFormNRCommand, or if the mobility procedure from NR is for emergency service fallback, the UE may attempt to select an E-UTRA cell.

[0385] In operation 11-35, when a suitable LTE cell 11-03 is selected, the UE 11-01 may transition to an RRC idle mode (RRC_IDLE).

[0386] In operation 11-40, UE 11-01 may perform an RRC connection establishment procedure with a suitable LTE cell 11-03. That is, the UE may send an RRC connection establishment request message (RRCConnectionRequest) to the cell in operation 11-40. In response thereto, the cell may send an RRC connection configuration message (RRCConnectionSetup) to the UE in operation 11-45. The UE may switch to RRC connection mode in operation 11-46 and may regard the cell as a primary cell. When condition 1 is met and condition 2 is met accordingly, the UE may perform operation 1 in operation 11-50.

[0387] Condition 1:

[0388] - If the UE supports RLF reporting for inter-RAT MRO EUTRA as defined in TS 38.306 standard, the radio link failure information or handover failure information is included in the VarRLF-Report of TS 38.331 standard, and the public land mobile network (registered PLMN) registered by the UE is included in the plmn-IdentityList stored in the VarRLF-Report of TS 38.331 standard (if the UE supports RLF reporting for inter-RAT MRO EUTRA as defined in TS 38.306, and if the UE has the radio link failure or handover failure information available in the VarRLF-Report of TS 38.331, and if the RPLMN is included in the plmn-IdentityList stored in the VarRLF-Report of TS38.331).

[0389] Condition 2:

[0390] -If reconnectCellId is not set in the VarRLF-Report of the TS 38.331 standard, and EPS fallback for IMS voice is triggered via MobilityFromNRCommand or emergency service fallback is triggered via MobilityFromNRCommand (if reconnectCellId in the VarRLF-Report of TS 38.331 is not set, and EPS fallback for IMS voice or emergency service fallback is triggered in NR via MobilityFromNRCommand, that is, if the operation is performed by performing operations 11-30 and 11-35).

[0391] Operation 1:

[0392] - The UE may set the time that has passed since the radio link failure or handover failure in timeUntilReconnection in VarRLF-Report of the TS 38.331 standard (set timeUntilReconnection in VarRLF-Report of TS 38.331 to the time that has passed since the last radio link failure or handover failure).

[0393] -The UE may set the global cell identity and tracking area code of the current PCell to the eutraReconnectCellId in the reconnectCellId in the VarRLF-Report of the TS 38.331 standard (set the eutraReconnectCellId in the reconnectCellId in the VarRLF-Report of TS 38.331 to the global cell identity and tracking area code of the PCell).

[0394] In operation 11-55, UE 11-01 may send an RRC connection setup complete message (RRCConnectionSetupComplete) to cell 11-03.

[0395] In operation 11-60, the UE may be in RRC connected mode by configuring an RRC connection with the NR base station 11-02.

[0396] In operation 11-65, the NR base station 11-02 may send a UE information request message (UEInformationRequest) to the UE 11-01 that has successfully activated security. The message may include an rlf-ReportReq configured as true.

[0397] In operation 11-70, UE 11-01 may send a UE information response message (UEInformationResponse) including an RLF-Report to NR base station 11-02. This may be performed according to the above-described embodiment.

[0398] Fig.12 The present invention is a flowchart of a process of updating radio link failure information or handover failure information in an RRC connection establishment process after an RRC connection reestablishment process performed by a UE in a next generation mobile communication system fails according to an embodiment of the present disclosure.

[0399] refer to Fig.12 , in operation 12-05, UE 12-01 can be in RRC connected mode (RRC_CONNECTED) by configuring an RRC connection with the NR base station 12-02.

[0400] In operation 12-10, the UE 12-01 may send a UE capability information message (UECapabilityInformation) to the base station 12-02. This may be performed according to the above-mentioned embodiment.

[0401] In operation 12-15, UE 12-01 may receive a MobilityFromNRCommand message from base station 12-02. In the message, targetRAT-Type may be configured as eutra. In the message, voiceFallbackIndication may be included.

[0402] In operation 12-20, UE 12-01 may determine that mobility failure from NR occurs due to a predetermined reason. For example, if the connection to the target radio access technology is not successfully performed (if the UE does not successfully establish a connection to the target radio access technology), it is determined that mobility failure from NR occurs.

[0403] In operation 12-25, if the targetRAT-Type in the MobilityFromNRCommand received in operation 12-15 is configured as eutra and the UE 12-01 supports radio link failure reporting of inter-RAT MRO EUTRA (if the targetRAT-Type in the received MobilityFromNRCommand is set to eutra and the UE supports radio link failure reporting of inter-RAT MRO EUTRA), the UE 11-01 may store the handover failure information in VarRLF-Report. This may be performed according to at least one of the above-mentioned embodiments. In addition, if voiceFallbackIndication is included in MobilityFormNRCommand, or if the mobility procedure from NR is for emergency service fallback, the UE may store an indicator indicating it in VarRLF-Report.

[0404] In operation 12-30, UE 12-01 may attempt to select an E-UTRA cell. For reference, if voiceFallbackIndication is included in MobilityFormNRCommand, or if the mobility procedure from NR is for emergency service fallback, the UE may attempt to select an E-UTRA cell.

[0405] In operation 12-35, if there is no suitable LTE cell and an acceptable cell 12-03 that supports emergency calls is selected when there is an ongoing emergency call (if no suitable E-UTRA cell is available and an acceptable E-UTRA cell that supports emergency calls is selected when the UE has an ongoing emergency call), the UE 12-01 may transition to RRC idle mode (RRC_IDLE).

[0406] In operation 12-40, UE 12-01 may perform an RRC connection establishment process with an acceptable LTE cell 12-03. That is, the UE may send an RRC connection establishment request message (RRCConnectionRequest) to the cell in operation 12-40. In response to this, the cell may send an RRC connection configuration message (RRCConnectionSetup) to the UE in operation 12-45. The UE may switch to RRC connection mode in operation 12-46 and may regard the cell as a primary cell. In this instance, the UE may not store any information in VarRLF-Report. Through the above, when the base station retrieves the RLF report from the UE later, in the case where timeUntilReconnection and reconnectCellId do not exist and voiceFallbackIndication is included in MobilityFormNRCommand, or in the case where the RLF report includes an indicator indicating that the mobility process from NR is used for emergency service fallback, the base station can identify that the UE selects an acceptable E-UTRA cell that supports emergency calls. Alternatively, when condition 1 is satisfied and condition 2 is correspondingly satisfied, the UE may perform operation 1 in operation 12-50.

[0407] Condition 1:

[0408] - If the UE supports RLF reporting for inter-RAT MRO EUTRA as defined in the TS 38.306 standard, the radio link failure information or the handover failure information is included in the VarRLF-Report of the TS 38.331 standard, and the public land mobile network (registered PLMN) with which the UE is registered is included in the plmn-IdentityList stored in the VarRLF-Report of TS 38.331 (if the UE supports RLF reporting for inter-RAT MRO EUTRA as defined in TS 38.306, and if the UE has the radio link failure or handover failure information available in the VarRLF-Report of TS 38.331, and if the RPLMN is included in the plmn-IdentityList stored in the VarRLF-Report of TS 38.331), or if the UE supports RLF reporting for inter-RAT MRO EUTRA as defined in the TS 38.306 standard, and the radio link failure information or the handover failure information is included in the VarRLF-Report of the TS 38.331 standard.

[0409] Condition 2:

[0410] -If reconnectCellId is not set in the VarRLF-Report of the TS 38.331 standard, and EPS fallback for IMS voice is triggered via MobilityFromNRCommand or emergency service fallback is triggered via MobilityFromNRCommand (if reconnectCellId in the VarRLF-Report of TS 38.331 is not set, and EPS fallback for IMS voice or emergency service fallback is triggered in NR via MobilityFromNRCommand, that is, if operations 12-30 and 12-35 are performed), or if EPS fallback for IMS voice is triggered via MobilityFromNRCommand or emergency service fallback is triggered via MobilityFromNRCommand.

[0411] Operation 1:

[0412] - The UE may set the time that has passed since the radio link failure or handover failure in timeUntilReconnection in VarRLF-Report of the TS 38.331 standard (set timeUntilReconnection in VarRLF-Report of TS 38.331 to the time that has passed since the last radio link failure or handover failure). For reference, timeUntilReconnection may be a new field.

[0413] For reference, whether to perform operation 1 or not to store any information in the VarRLF-Report may be determined based on the configuration of the base station.

[0414] In operation 12-55, UE 12-01 may send an RRC connection setup complete message (RRCConnectionSetupComplete) to cell 12-03.

[0415] In operation 12-60, the UE may be in RRC connected mode by configuring an RRC connection with the NR base station 12-02.

[0416] In operation 12-65, the NR base station 12-02 may send a UE information request message (UEInformationRequest) to the UE 12-01 that has successfully activated security. The message may include an rlf-ReportReq configured as true.

[0417] In operation 12-70, UE 12-01 may send a UE information response message (UEInformationResponse) including an RLF-Report to NR base station 12-02. This may be performed according to the above-described embodiment.

[0418] Fig.13 is a block diagram of the internal structure of a UE according to an embodiment of the present disclosure.

[0419] Referring to the drawing, the UE includes a Radio Frequency (RF) processor 13 - 10 , a baseband processor 13 - 20 , a storage device 13 - 30 , and a controller 13 - 40 .

[0420] The RF processor 13-10 performs functions such as signal band conversion, amplification, etc. for signal transmission or reception via a wireless channel. That is, the RF processor 13-10 converts the baseband signal provided by the baseband processor 13-20 to an RF band signal so as to transmit the RF band signal via an antenna, and converts the RF band signal received via the antenna to a baseband signal. For example, the RF processor 13-10 may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Although only a single antenna is shown in the drawings, the UE may include multiple antennas. In addition, the RF processor 13-10 may include multiple RF chains. In addition, the RF processor 13-10 may perform beamforming. For beamforming, the RF processor 13-10 may control the phase and size of each signal transmitted or received via multiple antennas or antenna elements. In addition, the RF processor may perform MIMO and may receive multiple layers when performing MIMO operations.

[0421] The baseband processor 13-20 performs a conversion function between a baseband signal and a bit stream according to the physical layer standard of the system. For example, in the case of data transmission, the baseband processor 13-20 encodes and modulates the transmission bit stream to generate complex symbols. In addition, in the case of data reception, the baseband processor 13-20 recovers the received bit stream by demodulating and decoding the baseband signal provided from the RF processor 13-10. For example, according to the orthogonal frequency division multiplexing (OFDM) scheme, in the case of data transmission, the baseband processor 13-20 generates complex symbols by encoding and modulating the transmission bit stream, maps the complex symbols to subcarriers, and then performs an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion to configure OFDM symbols. In addition, in the case of data reception, the baseband processor 13-20 divides the baseband signal provided from the RF processor 13-10 in units of OFDM symbols, reconstructs the signal mapped to the subcarrier via a fast Fourier transform (FFT), and then performs demodulation and decoding to reconstruct the received bit stream.

[0422] The baseband processor 13-20 and the RF processor 13-10 send and receive signals as described above. Therefore, the baseband processor 13-20 and the RF processor 13-10 may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. In addition, at least one of the baseband processor 13-20 and the RF processor 13-10 may include a plurality of communication modules to support different multiple radio access technologies. In addition, at least one of the baseband processor 13-20 and the RF processor 13-10 may include different communication modules to process signals of different frequency bands. For example, different radio access technologies may include wireless LAN (e.g., IEEE802.11), cellular networks (e.g., LTE), etc. In addition, different frequency bands may include ultra-high frequency (SHF) (e.g., 2.NRHz, NRHz) bands and millimeter (mm) wave (e.g., 60GHz) bands.

[0423] The storage device 13-30 may store data such as basic programs, applications, and configuration information for the operation of the UE. In particular, the storage device 13-30 may store information related to a second access node that performs wireless communication using a second radio access technology. In addition, the storage device 13-30 may provide the data stored therein according to a request from the controller 13-40.

[0424] The controller 13-40 may control the overall operation of the UE. For example, the controller 13-40 may perform signal transmission or reception via the baseband processor 13-20 and the RF processor 13-10. In addition, the controller 13-40 may record and read data in the storage 13-40. To this end, the controller 13-40 may include at least one processor. For example, the controller 13-40 may include a communication processor (CP) that performs control for communication, and an application processor (AP) that controls an upper layer such as an application program.

[0425] Fig.14 is a block diagram illustrating the configuration of an NR base station according to an embodiment.

[0426] As shown in the drawing, the base station may include an RF processor 14-10, a baseband processor 14-20, a backhaul communication unit 14-30, a storage 14-40, and a controller 14-50.

[0427] The RF processor 14-10 performs functions such as signal band conversion, amplification, etc. for signal transmission or reception via a wireless channel. That is, the RF processor 14-10 converts the baseband signal provided by the baseband processor 14-20 to an RF band signal so as to transmit the RF band signal via an antenna, and converts the RF band signal received via the antenna to a baseband signal. For example, the RF processor 14-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only a single antenna is shown in the drawings, the first access node may include multiple antennas. In addition, the RF processor 14-10 may include multiple RF chains. In addition, the RF processor 14-10 may perform beamforming. For beamforming, the RF processor 14-10 may control the phase and size of each signal transmitted or received via multiple antennas or antenna elements. The RF processor may perform downlink MIMO operations by transmitting one or more layers.

[0428] The baseband processor 14-20 performs a function for converting between a baseband signal and a bit stream according to the physical layer standard of the first radio access technology. For example, in the case of data transmission, the baseband processor 14-20 encodes and modulates the transmission bit stream to generate complex symbols. In addition, in the case of data reception, the baseband processor 14-20 recovers the received bit stream by demodulating and decoding the baseband signal provided from the RF processor 14-10. For example, according to the OFDM scheme, in the case of data transmission, the baseband processor 14-20 can generate complex symbols by encoding and modulating the transmission bit stream, mapping the complex symbols to subcarriers, and then performing IFFT operations and CP insertion to configure OFDM symbols. In addition, in the case of data reception, the baseband processor 14-20 divides the baseband signal provided from the RF processor 14-10 in units of OFDM symbols, recovers the signal mapped to the subcarrier via FFT operations, and performs demodulation and decoding to recover the received bit stream. The baseband processor 14-20 and the RF processor 14-10 send and receive signals as described above. Therefore, the baseband processor 14-20 and the RF processor 14-10 may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0429] The backhaul communication unit 14-30 may provide an interface for performing communication with other nodes in the network. That is, the backhaul communication unit 14-30 may convert a bit stream sent from the master base station to another node (e.g., a secondary base station, a core network, etc.) into a physical signal, and may convert a physical signal received from another node into a bit stream.

[0430] The storage 14-40 stores data such as basic programs, applications, and configuration information for the operation of the master base station. Specifically, the storage 14-40 may store information associated with the bearer assigned to the connected UE, measurement results reported from the connected UE, etc. In addition, the storage 14-40 may store information as a criterion for determining whether to provide multiple accesses to the UE or to stop providing multiple accesses. In addition, the memory 14-40 may provide the data stored therein according to the request of the controller 14-50.

[0431] The controller 14-50 may control the overall operation of the master base station. For example, the controller 14-50 may perform signal transmission or reception via the baseband processor 14-20 and the RF processor 14-10, or via the backhaul communication unit 14-30. In addition, the controller 14-50 may record and read data in the storage 14-40. To this end, the controller 14-50 may include at least one processor.

[0432] The embodiments of the present disclosure described and shown in the specification and the drawings are only specific examples presented to easily explain the technical content of the embodiments of the present disclosure and help understand the embodiments of the present disclosure, and are not intended to limit the scope of the embodiments of the present disclosure. It is obvious to those skilled in the art that in addition to the embodiments described herein, other variations based on the technical concept of the present disclosure can also be implemented.

Claims

1. A method for operating a terminal in a wireless communication system, the method comprising: receiving a handover command message from the NR base station, the handover command message from the NR including information that a target radio access technology (RAT) is configured as LTE; In case of detecting a handover failure from NR, selecting a suitable LTE cell if a suitable LTE cell is available, and selecting an acceptable LTE cell if no suitable LTE cell is available; Enter RRC idle mode; Perform an RRC connection establishment procedure for the selected LTE cell; If the LTE cell to which the RRC connection is performed is a suitable LTE cell, storing, in the VarRLF-Report associated with the NR, a time value from the handover failure to reconnection and an ID of the LTE cell to which the RRC connection is performed; as well as In a case where the LTE cell to which the RRC connection is performed is an acceptable LTE cell, a time value from the handover failure to reconnection is stored in the VarRLF-Report associated with the NR.

2. The method according to claim 1, wherein: In a case where the LTE cell to which the RRC connection is performed is an acceptable LTE cell, the ID of the LTE cell to which the RRC connection is performed is not stored in the VarRLF-Report associated with the NR.

3. The method according to claim 1, wherein: The NR switching command message includes a voice fallback indicator.

4. The method according to claim 3, further comprising: Information indicating that the handover is for voice fallback is stored in the VarRLF report associated with the NR.

5. The method according to claim 1, wherein: In a case where the ID of the LTE cell is not stored in the VarRLF-Report associated with the NR, storing the time value from the handover failure to the reconnection in the VarRLF-Report associated with the NR or the ID of the LTE cell to which the RRC connection is performed.

6. The method according to claim 1, wherein: The terminal is a terminal supporting inter-RAT RLF reporting.

7. The method according to claim 1, further comprising: After updating the VarRLF report associated with the NR with respect to the selected LTE cell, establishing an RRC connection with the NR base station; receiving a terminal information request message from the NR base station; and Send a terminal information response message including the VarRLF-Report associated with the NR to the NR base station.

8. A terminal operating in a wireless communication system, the terminal comprising: Transceiver; as well as Controller, Wherein, the controller is configured as: receiving a handover command message from the NR base station, the handover command message from the NR including information that a target radio access technology (RAT) is configured as LTE; In case of detecting a handover failure from NR, selecting a suitable LTE cell if a suitable LTE cell is available, and selecting an acceptable LTE cell if no suitable LTE cell is available; Enter RRC idle mode; Perform an RRC connection establishment procedure for the selected LTE cell; In a case where the LTE cell to which the RRC connection is performed is a suitable LTE cell, storing a time value from the handover failure to reconnection and an ID of the LTE cell to which the RRC connection is performed in the VarRLF-Report associated with the NR; and In a case where the LTE cell to which the RRC connection is performed is an acceptable LTE cell, a time value from handover failure to reconnection is stored in the VarRLF-Report associated with the NR.

9. The terminal according to claim 8, wherein: The controller is configured to, if the LTE cell to which the RRC connection is performed is an acceptable LTE cell, omit storing the ID of the LTE cell to which the RRC connection is performed in the VarRLF-Report associated with the NR.

10. The terminal according to claim 8, wherein: The NR switching command message includes an indicator for voice fallback. The terminal according to claim 10 , wherein: The controller is further configured to store information indicating that the switching is for voice fallback in the VarRLF-Report associated with the NR.

12. The terminal according to claim 8, wherein: The controller is also configured to, if the ID of the LTE cell is not stored in the VarRLF-Report associated with the NR, store the time value from the handover failure to the reconnection in the VarRLF-Report associated with the NR or the ID of the LTE cell to which the RRC connection is performed.

13. The terminal according to claim 8, wherein: The terminal is a terminal supporting inter-RAT RLF reporting.

14. The terminal according to claim 8, wherein: The controller is also configured to: After updating the VarRLF report associated with the NR with respect to the selected LTE cell, establishing an RRC connection to the NR base station; receiving a terminal information request message from the NR base station; and Send a terminal information response message including the VarRLF-Report associated with the NR to the NR base station.

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