Apparatus and terminal operations in next generation mobile communication systems

Abstract

Disclosed is a communication technology and a system thereof that combine a 5G communication system for supporting a higher data transmission rate than a 4G system with an IoT technology, and the like. Based on the 5G communication technology and the IoT-related technology, the disclosure can be applied to intelligent services (e.g., smart home, smart building, smart city, smart car or connected car, health care, digital education, retail, security and safety-related services, etc.). The disclosure relates to an operation method of a terminal in a wireless communication system, and in particular, to a method and apparatus for performing the same, the method including generating master cell group (MCG) failure information, transmitting the MCG failure information to a base station of a secondary cell group (SCG), receiving a radio resource control (RRC) reconfiguration message from the base station, and transmitting an RRC reconfiguration complete message based on the RRC reconfiguration message, wherein if the RRC reconfiguration message is included in a downlink information transfer message so as to be received via a signaling radio bearer (SRB) 3 of the SCG, the RRC reconfiguration complete message is transmitted via an SRB 1 configured based on the RRC reconfiguration message.

Description

TECHNICAL FIELD

[0001] The disclosure relates to operations of a user equipment (UE) and a base station in a mobile communication system. Further, the disclosure relates to a device receiving an RRC message and a UE operation in a next-generation mobile communication system. BACKGROUND

[0002] To meet increasing demand with respect to wireless data traffic since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a 'Beyond 4G Network' or a 'Post LTE System'. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (massive MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed for use in the 5G communication system. In addition, in the 5G communication system, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a technology for coordination between cells, a cooperative multi-cell transmission, an interference mitigation, a network slicing, a vehicle-to-everything (V2X), a device-to-device (D2D) communication, and the like. In the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), a non-orthogonal multiple access (NOMA), and a sparse code multiple access (SCMA) as an advanced access technology have been developed.

[0003] The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged as a new paradigm for the IoT. As technology elements, such as "sensing technology", "wired / wireless communication and network infrastructure", "service interface technology", and "security technology" have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and the like have been researched. Such an IoT environment can provide intelligent Internet technology (IT) services that create a new value through collection and analysis of data generated from connected things. The IoT can be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances, and advanced medical services through the combination and interworking of existing information technology (IT) and various industrial applications.

[0004] In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, techniques such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication can be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (cloud RAN) as the above-described big data processing technology can also be considered as an example of convergence between the 5G technology and the IoT technology. SUMMARY

[0005] TECHNICAL PROBLEM

[0006] The disclosure provides an operation of a user equipment (UE) in a next-generation mobile communication system and an operation of a base station communicating with the UE.

[0007] Further, the disclosure provides an operation of a UE in a case where an RRC reconfiguration message in response to MCG failure is received and an apparatus in a next-generation mobile communication system.

[0008] Further, the disclosure relates to a method of applying a secondary cell group recovery operation in a case where a secondary cell group failure occurs even in a case where a master cell group failure occurs, and is adopted in a next-generation mobile communication system, and particularly, a UE operation is implemented in a case where an RRC reconfiguration message in response to a master cell group failure is received.

[0009] TECHNICAL SOLUTION

[0010] To overcome the above-described drawbacks, the disclosure provides an operation method of a user equipment (UE) in a wireless communication system, the method including generating master cell group (MCG) failure information, transmitting the MCG failure information to a base station of a secondary cell group (SCG), receiving a radio resource control (RRC) reconfiguration message from the base station, and transmitting an RRC reconfiguration complete message based on the RRC reconfiguration message, wherein, in a case where the RRC reconfiguration message is included in a downlink information transfer message and is received via a signaling radio bearer (SRB) 3 of the SCG, the RRC reconfiguration complete message is transmitted via an SRB 1 configured based on the RRC reconfiguration message.

[0011] The disclosure provides a UE in a wireless communication system, the UE including a transceiver and a controller configured to perform control to generate master cell group (MCG) failure information, transmit the MCG failure information to a base station of a secondary cell group (SCG), receive a radio resource control (RRC) reconfiguration message from the base station, and transmit an RRC reconfiguration complete message based on the RRC reconfiguration message, wherein, in case that the RRC reconfiguration message is included in a downlink information transfer message and is received via a signaling radio bearer (SRB) 3 of the SCG, the RRC reconfiguration complete message is transmitted via an SRB1 configured based on the RRC reconfiguration message.

[0012] The technical subject pursued by the disclosure can not be limited to the above technical subject, and other technical subjects not mentioned can be clearly understood by those skilled in the art to which the disclosure pertains through the following description.

[0013] Advantageous effects

[0014] According to various embodiments of the disclosure, it can be possible to provide an operation of a user equipment (UE) in a next-generation mobile communication system and an operation of a base station communicating with the UE.

[0015] Further, according to various embodiments of the disclosure, it can be possible to provide a UE operation and a device in case that an RRC reconfiguration message in response to MCG failure is received in a next-generation mobile communication system.

[0016] Further, according to various embodiments of the disclosure, in case that an RRC reconfiguration message in response to master cell group failure is received by a UE via a predetermined signaling radio bearer (SRB), it can be possible to clearly define a master cell group recovery operation by clearly determining an SRB to be used to transmit an RRC reconfiguration complete message and operations related thereto. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a diagram illustrating a structure of an LTE system, with reference to which the disclosure is described.

[0018] Figure 2 is a diagram illustrating a structure of a radio protocol in an LTE system, with reference to which the disclosure is described.

[0019] Figure 3 is a diagram illustrating a structure of a next-generation mobile communication system to which the disclosure is applied.

[0020] Figure 4 is a diagram illustrating a structure of a radio protocol of a next-generation mobile communication system to which the disclosure is applicable.

[0021] Figure 5is a diagram illustrating the entire operation of transmitting the SCGFailurelnformation message in the case where the SCG failure occurs, with reference to which the present disclosure is described.

[0022] Figure 6 is a diagram illustrating the entire procedure of a user equipment (UE) reporting an MCG failure and receiving and applying a response message thereto in the case where a split SRB1 is configured in an SRB as Embodiment 1 of the present disclosure.

[0023] Figure 7 is a diagram illustrating the structure of a split bearer applied to EUTRA NR-dual connectivity (EN-DC), NR EUTRA-dual connectivity (NE-DC), and NR-DC.

[0024] Figure 8 is a diagram illustrating the structure of a split bearer applied to EN-DC, NE-DC, and NR-DC.

[0025] Figure 9 is a diagram illustrating the entire procedure of a UE reporting an MCG failure and receiving and applying a response message thereto in the case where a split SRB1 is not configured and an SRB3 is configured in an SRB as Embodiment 2 of the present disclosure.

[0026] Figure 10 is a diagram illustrating a UE operation of transmitting an MCGFailurelnformation message according to a configured SRB type as a first UE operation applied to embodiments of the present disclosure.

[0027] Figure 11 is a diagram illustrating a UE operation performed depending on an SRB via which an RRCReconfiguration message in response to MCGFailurelnformation is received as a second UE operation applied to embodiments of the present disclosure.

[0028] Figure 12 is a diagram illustrating a subsequent UE operation performed depending on an SRB via which an RRCReconfiguration message in response to MCGFailurelnformation is received and depending on a type of the transmitted RRCReconfiguration message as a third UE operation applied to embodiments of the present disclosure.

[0029] Figure 13 is a diagram illustrating a base station operation applied to all embodiments of the present disclosure.

[0030] Figure 14 is a diagram illustrating a configuration of a UE according to embodiments of the present disclosure.

[0031] Figure 15 is a diagram illustrating a configuration of a base station according to an embodiment of the disclosure. DETAILED DESCRIPTION

[0032] Hereinafter, the operation principle of the disclosure will be described in detail with reference to the accompanying drawings. In the following description of the disclosure, a detailed description of known functions or configurations incorporated herein will be omitted when it is determined that the disclosure can be unnecessarily unclear. The terms to be described below are terms defined in consideration of the functions in the disclosure, and can differ according to users, user's intention, or habits. Therefore, the definition of the terms should be based on the contents throughout the specification. In the following description, for convenience, terms for identifying access nodes, terms for referring to network entities, terms for referring to messages, terms for referring to interfaces between network entities, terms for referring to various identification information, and the like are used illustratively. Therefore, the disclosure is not limited to the terms used below, and other terms referring to the subject matter having equivalent technical meanings can be used.

[0033] In the following description, for convenience of description, terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard or terms and names modified based thereon will be used to describe the disclosure. However, the disclosure is not limited to these terms and names, and can be applied in the same manner to systems conforming to other standards. That is, the disclosure can be applied to the entire mobile communication system, particularly, all LTE and NR systems.

[0034] Figure 1 is a diagram illustrating a structure of an LTE system, with reference to which the disclosure is described.

[0035] Reference Figure 1 As illustrated, a radio access network of the LTE system includes next generation base stations (evolved Node Bs (eNBs), Node Bs, or base stations) 105, 110, 115, and 120, a mobility management entity (MME) 125, and a serving gateway (S-GW) 130. A user equipment (UE) (or terminal) 135 accesses an external network via the eNBs 105 to 120 and the S-GW 130.

[0036] In Figure 1In the middle, the eNBs 105, 110, 115, and 120 correspond to existing Node Bs in a UMTS system. The eNB 105 is connected to the UE 135 via a wireless channel, and performs more complex functions than the existing Node B. In an LTE system, real-time services (such as Voice over Internet Protocol (VoIP)) as well as all user traffic are provided via a shared channel. Therefore, a device that performs scheduling by collecting state information (such as a buffer state, an available transmission power state, a channel state, etc.) associated with a UE is required, and the eNBs 105, 110, 115, and 120 can be responsible for the device. One eNB generally controls multiple cells. For example, to achieve a transmission rate of 100 Mbps, an LTE system uses Orthogonal Frequency Division Multiplexing (OFDM) as a wireless access technique in a 20 MHz bandwidth. In addition, an Adaptive Modulation and Coding (AMC) scheme that determines a modulation scheme and a channel coding rate can be applied based on a channel state of a UE. The S-GW 130 is a device for providing a data bearer, and generates or removes a data bearer according to control performed by the MME 125. The MME 125 is a device responsible for various control functions other than a mobility management function associated with a UE, and can be connected to multiple eNBs.

[0037] Figure 2 is a diagram illustrating a structure of a wireless protocol in an LTE system, with reference to which the present disclosure is described.

[0038] Referring to Figure 2 , a wireless protocol of an LTE system can include Packet Data Convergence Protocols (PDCPs) 205 and 240, Radio Link Controls (RLCs) 210 and 235, and Medium Access Controls (MACs) 215 and 230 for UEs and eNBs, respectively. The PDCPs 205 and 240 are responsible for IP header compression / decompression, etc. Main functions of the PDCPs 205 and 240 are summarized as follows.

[0039] - header compression and decompression (header compression and decompression: ROHC only)

[0040] - transfer of user data

[0041] - in-sequence delivery (in-sequence delivery of upper layer PDUs at PDCP re-establishment for RLC AM)

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

[0043] - duplicate detection (duplicate detection of lower SDU at PDCP re-establishment for RLC AM) - header compression and decompression (header compression and decompression: ROHC only)

[0040] - transfer of user data

[0041] - in-sequence delivery (in-sequence delivery of upper layer PDUs at PDCP re-establishment for RLC AM)

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

[0043] - duplicate detection (duplicate detection of lower SDU at PDCP re-establishment for RLC AM)

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

[0045] - ciphering and deciphering

[0046] - timer-based SDU discard (timer-based SDU discard in uplink)

[0047] - Radio Link Control (RLC) 210 and 235 reestablish PDCP packet data units (PDUs) with appropriate sizes and perform ARQ, etc. The main functions of RLC 210 and 235 are summarized as follows.

[0048] - data transfer (transfer of upper layer PDUs)

[0049] - ARQ (error correction through ARQ (only for AM data transfer))

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

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

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

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

[0054] - error detection (protocol error detection (only for AM data transfer))

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

[0056] - RLC re-establishment

[0057] - MAC 215 and 230 are connected with multiple RLC layer devices configured for a single UE and multiplex RLC PDUs into a MAC PDU and demultiplex RLC PDUs from a MAC PDU. The main functions of MAC 215 and 230 are summarized as follows.

[0058] - mapping (mapping between logical channels and transport channels)

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

[0060] - Scheduling information reporting

[0061] - HARQ (hybrid automatic repeat request (HARQ) error correction)

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

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

[0064] - MBMS service identification

[0065] - Transport format selection

[0066] - Padding

[0067] The PHY layers 220 and 225 perform operations of channel-coding and modulating higher layer data to generate OFDM symbols and transmitting the OFDM symbols via a wireless channel or demodulating and channel-decoding OFDM symbols received via a wireless channel and transmitting the demodulated and channel-decoded OFDM symbols to a higher layer.

[0068] Although not shown in the drawings, there is a radio resource control (RRC) layer above the PDCP layer of each UE and eNB. In the RRC layer, a configuration control message related to access and measurement can be transmitted or received for radio resource control.

[0069] Figure 3 is a diagram showing a structure of a next-generation mobile communication system to which the disclosure is applied.

[0070] Reference Figure 3 As illustrated, a radio access network of a next-generation mobile communication system includes a next-generation base station (new radio node-B (NR NB) or NR gNB) 310 and a new radio core network (NR CN) 305. A user equipment (new radio user equipment (NR UE) or UE) 315 accesses an external network via the NR gNB 310 and the NR CN 305.

[0071] In Figure 3In the middle, the NR gNB 310 corresponds to an evolved Node B (eNB) of a conventional LTE system. The NR gNB is connected to the NR UE 315 via a wireless channel and can provide a better service than a service from a conventional Node B. In the next-generation mobile communication system, all user traffic is serviced via a shared channel. Therefore, a device that performs scheduling by collecting state information (such as a buffer state, an available transmission power state, a channel condition, etc.) associated with a UE, and the NR gNB 310 in charge thereof are required. A single NR gNB generally controls multiple cells. In order to implement ultra-high-speed data transmission compared to the conventional LTE, a bandwidth greater than or equal to the current maximum bandwidth can be used, and an orthogonal frequency division multiplexing (OFDM) is used as a wireless access technology, and additionally, a beamforming technique is used. Furthermore, an adaptive modulation and coding (AMC) scheme that determines a modulation scheme and a channel coding rate can be applied based on a channel state of the UE. The NR CN 305 performs functions of supporting mobility, configuring a bearer, configuring QoS, etc. The NR CN 305 is a device that is in charge of various control functions other than a mobility management function associated with a UE, and can be connected to multiple base stations. Furthermore, the next-generation mobile communication system can interoperate with the conventional LTE system, and the NR CN 305 can be connected to the MME 325 via a network interface. The MME 325 is connected to the eNB 330 which is a conventional eNB.

[0072] Figure 4 is a diagram illustrating a structure of a wireless protocol of a next-generation mobile communication system to which the disclosure is applicable.

[0073] Referring to Figure 4 , the wireless protocol of the network generation mobile communication system can include NR SDAPs 401 and 445, NR PDCPs 405 and 440, NR RLCs 410 and 435, and NR MACs 415 and 430 for the UE and the NR gNB, respectively.

[0074] The main functions of the NR SDAPs 401 and 445 can include some of the following functions.

[0075] - Transfer of user data (transfer of user plane data)

[0076] - Mapping between QoS flows and data bearers for both uplink and downlink (mapping between QoS flows and DRBs for both DL and UL)

[0077] - Marking of QoS flow ID in uplink and downlink (marking of QoS flow ID in DL and UL packets)

[0078] - mapping of reflective QoS flow to data bearers for uplink SDAP PDU (DRB mapping of reflective QoS flow to UL SDAP PDU)

[0079] In association with the SDAP layer device, whether to use a header of the SDAP layer device or a function of the SDAP layer device can be configured for the UE via an RRC message for each PDCP layer device, for each bearer, or for each logical channel. If the SDAP header is configured, an NAS reflective QoS configuration one-bit indicator and an AS reflective QoS configuration one-bit indicator of the SDAP header can provide an indication so that the UE updates or reconfigures mapping information between a QoS flow and a data bearer in uplink and downlink. The SDAP header can include QoS flow ID information indicating QoS. The QoS information can be used as data processing priority information, scheduling information, etc. for supporting a smooth service.

[0080] The main functions of the NR PDCP 405 and 440 can include some of the following functions.

[0081] - header compression and decompression: (header compression and decompression: ROHC only)

[0082] - transfer of user data

[0083] - in-sequence delivery (in-sequence delivery of upper layer PDUs)

[0084] - out-of-sequence delivery (out-of-sequence delivery of upper layer PDUs)

[0085] - reordering (reordering of received PDCP PDUs)

[0086] - duplicate detection (duplicate detection of lower layer SDUs)

[0087] - retransmission (retransmission of PDCP SDUs)

[0088] - ciphering and deciphering

[0089] - timer-based SDU discard (timer-based SDU discard in uplink)

[0090] The reordering function of the NR PDCP device can refer to a function of sequentially reordering PDCP PDUs received from a lower layer according to a PDCP sequence number (SN), and can include a function of transferring sequentially reordered data to an upper layer, a function of immediately transferring data regardless of order, a function of recording a missing PDCP PDU after sequential reordering, a function of reporting a status of the missing PDCP PDU to a sender, and a function of requesting retransmission of the missing PDCP PDU.

[0091] The main functions of the NR RLC 410 and 435 can include some of the following functions.

[0092] - Transfer of data (transfer of upper layer PDUs)

[0093] - In-sequence delivery (in-sequence delivery of upper layer PDUs)

[0094] - Out-of-sequence delivery (out-of-sequence delivery of upper layer PDUs)

[0095] - ARQ (error correction through ARQ)

[0096] - Concatenation, segmentation, and reassembly (concatenation, segmentation, and reassembly of RLC SDUs)

[0097] - Re-segmentation (re-segmentation of RLC data PDUs)

[0098] - Reordering (reordering of RLC data PDUs)

[0099] - Duplicate detection

[0100] - Error detection (protocol error detection)

[0101] - RLC SDU discard

[0102] - RLC re-establishment

[0103] The in-sequence delivery function (in-sequence delivery) of the NR RLC device referred to is a function of delivering the RLC SDU received from a lower layer to an upper layer in sequence. If a single original RLC SDU is divided into a plurality of RLC SDUs, and a plurality of RLC SDUs are received, the in-sequence delivery function can include a function of reassembling and delivering the same. The in-sequence delivery function can include a function of reordering the received RLC PDUs according to an RLC sequence number (SN) or a PDCP SN, a function of recording a missing RLC PDU after the in-sequence reordering, a function of reporting a status of the missing RLC PDU to a transmitter, a function of requesting retransmission of the missing RLC PDU, a function of delivering the RLC SDU to a higher layer in sequence only before a missing RLC SDU if there is the missing RLC SDU, a function of delivering all RLC SDUs received before a predetermined timer starts to the higher layer even if there is a missing RLC SDU if the predetermined timer expires, or a function of delivering all RLC SDUs received so far to the higher layer even if there is a missing RLC SDU if the predetermined timer expires. In addition, the RLC PDUs are processed in the order of reception (in the order of arrival, regardless of the sequence number or the order number), and are transmitted to the PDCP device regardless of the order (out-of-sequence delivery). In the case of segmentation, the segments stored in the buffer or to be received in the future are received and reconfigured into a single complete RLC PDU, and the reconfigured one is processed and transmitted to the PDCP device. The NR RLC layer can not include a concatenation function. In addition, the concatenation function can be performed in the NR MAC layer, or can be replaced with a multiplexing function in the NR MAC layer.

[0104] The out-of-sequence delivery function (out-of-sequence delivery) of the NR RLC device is a function of immediately delivering the RLC SDU received from a lower layer to an upper layer regardless of the order. If a single original RLC SDU is divided into a plurality of RLC SDUs, and a plurality of RLC SDUs are received, the out-of-sequence delivery function can include a function of reassembling and transmitting the same, and a function of storing the RLC SN or the PDCP SN of the received RLC PDU, performing in-sequence ordering, and recording a missing RLC PDU.

[0105] The NR MACs 415 and 430 can be connected to a plurality of NR RLC layer devices configured for a single UE, and the main functions of the NR MAC can include some of the following functions.

[0106] - Mapping (mapping between logical channels and transport channels)

[0107] - Multiplexing and demultiplexing (multiplexing / demultiplexing of MAC SDUs)

[0108] - Scheduling information reporting

[0109] - HARQ (through HARQ error correction)

[0110] - Priority handling between logical channels (priority handling between logical channels of one UE)

[0111] - Priority handling between UEs (priority handling between UEs through means of dynamic scheduling)

[0112] - MBMS service identity

[0113] - Transport format selection

[0114] - Padding

[0115] The NR PHY layers 420 and 425 perform channel coding and modulation of higher layer data to generate OFDM symbols, and transmit the OFDM symbols via a wireless channel, or perform demodulation and channel decoding of OFDM symbols received via a wireless channel, and transmit the demodulated and channel decoded OFDM symbols to a higher layer.

[0116] Although not shown in the drawings, there is a radio resource control (RRC) layer above the PDCP layer in each of the UE and the gNB. In the RRC layer, a configuration control message related to access and measurement can be transmitted or received for radio resource control.

[0117] Figure 5 is a diagram illustrating the entire operation of transmitting the SCGFailureInformation message in the case where the SCG failure occurs, with reference to which in the present disclosure. In Figure 5 In an embodiment of FIG. 1, the MCG can be used interchangeably with a base station of the MCG and a serving base station of the MCG, and the SCG can be used interchangeably with a base station of the SCG and a serving base station of the SCG.

[0118] In operation 505, the UE 501 in a state connected to an MCG of the serving base station 502 which is the MCG can receive a request for reporting UE capability from the base station 502 via a UECapabilityEnquiry message, and in operation 510, can transmit a UECapabilityInformation message including UE capability information of the UE itself in response thereto to the base station 502. The corresponding UECapabilityInformation message can include UE capability associated with whether to support SCG failure reporting and recovery. This can be transmitted in one bit per UE, or can indicate capability associated with a predetermined radio access technology (RAT) type. The base station 502 identifying the UE information can determine that the corresponding UE 501 is capable of transmitting an SCG failure message to the base station 502 in the case of occurrence of SCG failure, and later, in the case of indicating SCG recovery and release based on the corresponding information, the base station 502 can know that the corresponding operation can be applied.

[0119] In operation 515, the base station 502 can transmit an RRC reconfiguration message including overall configuration information for data transmission or reception and control in an RRC connected state to the UE 501. The message can include radio bearer configuration, SCell addition and change, dual connectivity configuration, measurement configuration, etc. In operation 520, the UE 501 can transmit an RRC reconfiguration complete message to the base station 502 in order to confirm completion of reception of the RRC reconfiguration message and to apply the corresponding configuration. In the drawing, it is assumed that the base station 502 configures dual connectivity (hereinafter, DC) for the UE 501 in the corresponding operation. Subsequently, in operation 525, the UE 501 performs data transmission or reception with the base station 502 by applying the configured information, and can identify a problem in a connection state associated with a secondary cell group (SCG) in a predetermined case, and can declare SCG failure. The predetermined case can be a case where a T310 timer expires, random access fails, the number of RLC retransmissions exceeds the maximum number of RLC retransmissions, SCG synchronization fails, SCG reconfiguration fails, integrity associated with SRB3 fails, etc. For reference, operations related to T310 are as shown in Table 1 below.

[0120] [Table 1]

[0121]

[0122] For the above reasons, in the case where the UE 501 identifies a problem in the connection state of the SCG, in operation 530, the UE 501 can generate an SCGFailureInformation message and can transmit the same to the base station 502. The SCGFailureInformation message can include a cause of failure, measurement frequency information measured by the UE, measurement frequency information configured for the UE 501 via the SCG, and a measurement value of the corresponding frequency. For reference, the configuration of the SCGFailureInformation is shown in Table 2 below.

[0123] [Table 2]

[0124]

[0125] Figure 6 FIG. 1 is a diagram illustrating an entire procedure in which the UE reports MCG failure and receives and applies a response message thereto in the case where SRB1 is configured in a split SRB as Embodiment 1 of the disclosure. In the embodiment of FIG. 1, the MCG can be used interchangeably with the base station of the MCG and the serving base station of the MCG, and the SCG can be used interchangeably with the base station of the SCG and the serving base station of the SCG. Figure 6

[0126] ​In operation 605, the UE 601 can camp on the predetermined base station, can receive system information from the corresponding serving cell, and can prepare for a connected state. Subsequently, due to a predetermined reason, in operation 610, the UE 601 can perform an RRC connection procedure with the corresponding serving cell (MCG) 602. In operation 615, the UE 601 can receive a request for reporting UE capability from the base station 602 via a UECapabilityEnquiry message, and can transmit a UECapabilityInformation message including UE capability information of the UE itself to the base station 602 in response thereto. The corresponding UECapabilityInformation message can include UE capability associated with whether MCG failure reporting and recovery is supported. This can be transmitted in one bit per UE, or can indicate capability associated with a predetermined RAT type. For example, one bit of supporting MCG failure reporting and recovery in EN-DC and one bit of supporting MCG failure reporting and recovery in NR-DC and NE-DC can be indicated, respectively, or one bit of supporting MCG failure reporting and recovery in EN-DC can include UE capability in NR-DC and NE-DC and can be indicated. The base station 602 identifying the UE information can determine that the corresponding UE 601 is capable of transmitting a MCG failure report message to the base station 602 in the event of MCG failure (the message can be transmitted to the MCG base station via the SCG due to the occurrence of MCG failure), and later, in the event of handover and connection release based on the corresponding information indication, the base station 602 can know that the corresponding operation can be applied.

[0127] Based on the UE capability report in operation, in operation 620, the base station 602 can transmit an RRC reconfiguration message to the UE 601, and the corresponding message can include radio bearer configuration, SCell addition and change, dual connectivity configuration, measurement configuration, etc. Specifically, in the drawing, DC configuration (SCG configuration), radio bearer configuration (DRB configuration, SRB configuration, in particular, SRB3 configuration, etc.), and MCG failure related configuration information (T316, including an indicator of a measurement result associated with a configured MO in the SCG) for fast MCG recovery can be provided in the corresponding operation. The T316 timer is a guard timer until an RRC reestablishment operation is performed after declaring MCG failure, and is triggered in the case where the UE 601 transmits MCGFailureInformation, and in the case where the corresponding timer expires, the UE 601 can perform an RRC reestablishment operation. This can be interpreted as a time for the UE to wait for a response from the base station 602 in response to MCGFailureInformation during a predetermined period of time. As a reference, a description related to the T316 timer is shown in Table 3 below.

[0128] [Table 3]

[0129]

[0130] In operation 625, the UE 601 can transmit an RRC reconfiguration complete message to the base station 602 for confirming completion of reception of the RRC reconfiguration message and application of the corresponding configuration. Subsequently, in operation 630, the UE 601 can perform data transmission or reception with the base station 602 by applying the configured information, and in operation 635, can perform channel measurement on a serving cell and a neighboring cell according to a measurement configuration configured during RRC reconfiguration. In this case, the measurement configuration can correspond to measurement objects (MOs) 636 and 637 of a serving frequency and a neighboring frequency configured by a master node (MN), and measurement objects (MOs) 638 and 639 of a serving frequency and a neighboring frequency configured by a secondary node (SN), and the UE 601 can perform measurement on the configured MOs, can apply the measurement values, and can report the measurement values in a predetermined case.

[0131] In operation 640, the UE 601 supporting MCG recovery and failure reporting in a predetermined case can identify a problem in a connection state associated with the MCG, and can declare MCG failure. The predetermined case can be a case where a T310 timer expires, random access fails, the number of RLC retransmissions exceeds the maximum number of RLC retransmissions, etc. For operations associated with T310, refer to Table 4 below.

[0132] [Table 4]

[0133]

[0134]

[0135] The UE 601 that triggers the MCG failure can declare the MCG failure in this operation, and can generate the MCGFailureInformation in operation 645, and the corresponding message can include at least one among the measurement values of the MCG frequency (e.g., NR), the cause of the MCG failure, the measurement values of the SCG frequency (e.g., LTE), the measurement values of the non-serving cell, etc. Further, the measurement values of the MCG and SCG frequencies can be reported separately according to which of the MCG and SCG performs the configuration, or the MCG frequency measurement value and the SCG frequency measurement value can be reported regardless of the cell group performing the configuration. That is, the measurement results of the MO configured by the MCG and the SCG can be included in separate lists or a single list. Further, in this operation, the UE 601 can suspend the data transmission or reception performed with the MCG, and maintain the data transmission or reception performed with the SCG. Table 5 shown below is an example of the structure of the MCGFailureInformation, and Table 6 is a field description of the information elements included in Table 5. In the following example, the measurement results of the MCG and SCG configurations are included in separate lists.

[0136] - Measurement list configured by MCG: measResultFreqList-r16, measResultFreqListEUTRA-r16

[0137] - Measurement list configured by SCG: measResultSCG-r16, measResultSCG-EUTRA-r16 (the corresponding field can be included in the measurement list configured by the MCG, and can be transmitted, and in this case, the corresponding field is not required).

[0138] [Table 5]

[0139]

[0140] [Table 6]

[0141]

[0142] In the present embodiment, the following relates to the case where the base station 602 configures the DC for the UE 601 and configures the split bearer for the SRB1 (i.e., split SRB1) in operation 620, and the case can include the case where the split SRB1 and SRB3 are configured at the same time. As a reference, the split bearer can be applied to the SRB1 and SRB2, but the embodiment of the present disclosure assumes the application to the SRB1 only. Further, for the PDCP of the split bearer, entities belonging to a single cell group are used, and the transmission and reception of data from the PDCP (common PDCP) are enabled via separate RLC per cell group (MCG and SCG). The structure of the split bearer of the EN-DC is described in 3GPP TS 38.300 v16.5.0.Figure 7 and the structure applied to the separate bearer of NE-DC and NR-DC is referred to Figure 8 .

[0143] In operation 650, the UE 601 can transmit the MCGFailureInformation message generated in operation 645 to the base station (SCG) 603 via the separate SRB1 configured for the SCG. Since the failure occurs in the link to the MCG, it is necessary to transmit the MCGFailureInformation to the base station 603 of the SCG, and only in the case where the separate SRB1 is configured, the MCG and the SCG can process the RRC message via the same SRB. In other words, in the case where the separate SRB1 is not configured and in the case where the SRB3 is not configured, the UE can not transmit the MCGFailureInformation message to the base station 603 of the SCG. As described above, Embodiment 1 describes only the case where the separate SRB1 is configured. The detailed description of the MCGFailureInformation has been described above.

[0144] The base station 603 of the SCG receiving the MCGFailureInformation message can transmit a corresponding message to the MCG via an inter-node message (RRC or Xn message), and the MCG can determine a subsequent operation based on this. In the case where the UE 601 is instructed about handover and PSCell change, etc., in operation 655, the base station 602 of the MCG can generate an RRCReconfiguration message including a reconfigurationWithSync configuration, and can transmit the same to the base station 603 of the SCG, and the base station 603 of the SCG can transmit the RRCReconfiguration message received from the MCG to the UE 601 via the SRB1. Alternatively, an RRCRelease message releasing the corresponding UE 601 can be transmitted, and any message can not be transmitted, so that the UE automatically performs an RRC reestablishment operation. Operation 655 is an operation in which the SCG transmits the RRCReconfiguration message received from the MCG to the UE via the SRB1 among the described base station operations, and the corresponding message can include a reconfigurationWithSync configuration. In operation 660, the UE 601 receiving the RRC reconfiguration message can apply the received RRC reconfiguration, and in the case where an operation such as handover and PSCell change is instructed, the UE 601 can also apply. In the case of handover, an RRCReconfigurationComplete message can be transmitted via the SRB1 of the target cell 604.

[0145] Figure 9 is a diagram illustrating an entire procedure in which the UE reports MCG failure and receives and applies a response message thereto in a case where the unconfigured split SRB1 and the configured SRB3 are in the SRB, as Embodiment 2 of the disclosure. In Figure 9 In the embodiment of FIG. 10, the MCG can be interchangeably used with a base station of the MCG and a serving base station of the MCG, and the SCG can be interchangeably used with a base station of the SCG and a serving base station of the SCG.

[0146] In operation 901, the UE 905 can camp on a predetermined base station, can receive system information from a corresponding serving cell, and can prepare for a connected state. Subsequently, for a predetermined reason, in operation 910, an RRC connection procedure with the corresponding serving cell (MCG) 902 can be performed. In operation 915, a request for reporting UE capability is received from the base station 902 via a UECapabilityEnquiry message, and in response thereto, a UECapabilityInformation message including UE capability information of the UE itself is transmitted to the base station 902. The corresponding UECapabilityInformation message can include UE capability associated with whether MCG failure reporting and recovery are supported. This can be transmitted in one bit per UE, or can indicate capability associated with a predetermined RAT type. For example, one bit indicating support for MCG failure reporting and recovery in EN-DC and one bit indicating support for MCG failure reporting and recovery in NR-DC and NE-DC can be indicated, respectively, or one bit indicating support for MCG failure reporting and recovery in EN-DC can include UE capability in NR-DC and NE-DC, and can be indicated. The base station 902 identifying the UE information can determine that the corresponding UE 901 is capable of transmitting an MCG failure report message to the base station 902 in a case where MCG failure occurs (the message can be transmitted to the MCG base station via the SCG due to the occurrence of MCG failure), and subsequently, in a case where handover and connection release are indicated based on the corresponding information, the base station 902 can know that the corresponding operation can be applied.

[0147] Based on the UE capability report in the operation, the base station 902 can transmit an RRC reconfiguration message to the UE in operation 920, and the corresponding message can include radio bearer configuration, SCell addition and change, dual connectivity configuration, measurement configuration, etc. Specifically, in the figure, the DC configuration (SCG configuration), radio bearer configuration (DRB configuration, SRB configuration, in particular, SRB3 configuration, etc.), and MCG failure related configuration information (T316, including an indicator of a measurement result associated with a configured MO in the SCG) for fast MCG recovery can be provided in the corresponding operation. The T316 timer is a guard timer until the RRC reestablishment operation is performed after declaring MCG failure, and is triggered in the case where the UE transmits MCGFailureInformation, and in the case where the corresponding timer expires, the UE can perform the RRC reestablishment operation. This can be interpreted as a time during which the UE waits for a response from the base station in response to the MCGFailureInformation during a predetermined period of time. For reference, a description associated with the T316 timer is shown in Table 3. In operation 925, the UE 901 can transmit an RRC reconfiguration complete message to the base station 902 in order to confirm completion of reception of the RRC reconfiguration message and to apply the corresponding configuration. Subsequently, in operation 930, the UE 901 can perform data transmission or reception with the base station 902 by applying the configured information, and in operation 935, can perform channel measurement on serving cells and neighboring cells according to the measurement configuration configured during the RRC reconfiguration. In this case, the measurement configuration can correspond to measurement objects (MOs) 936 and 937 of serving frequencies and neighboring frequencies configured by the MN, and measurement objects (MOs) 938 and 939 of serving frequencies and neighboring frequencies configured by the SN, and the UE 901 can perform measurement on the configured MOs, can apply the measurement values, and can report the measurement values in a predetermined case.

[0148] In operation 940, the UE 901 supporting the MCG recovery and the failure report in the predetermined case can identify a problem in a connection state associated with the MCG, and can declare MCG failure. The predetermined case can be a case where the T310 timer expires, random access fails, the number of RLC retransmissions exceeds the maximum number of RLC retransmissions, etc. For reference, a description related to the T310 timer is shown in Table 4. The UE 901 triggering the MCG failure can declare the MCG failure in this operation, and can generate the MCGFailureInformation in operation 945, and the corresponding message can include at least one among the measurement value of the MCG frequency (e.g., NR), the cause of the MCG failure, the measurement value of the SCG frequency (e.g., LTE), the measurement value of the non-serving cell, etc. Further, the measurement values of the MCG and SCG frequencies can be reported separately according to which of the MCG and SCG performs the configuration, or the MCG frequency measurement value and the SCG frequency measurement value can be reported regardless of the cell group performing the configuration. That is, the measurement results of the MO configured by the MCG and the SCG can be included in separate lists or a single list. Further, in this operation, the UE 901 can suspend data transmission or reception performed with the MCG, and can maintain data transmission or reception performed with the SCG. The structure of the MCGFailureInformation and its related description are referred to Table 5 and Table 6. In the following example, the measurement results of the MCG and SCG configurations are contained in separate lists.

[0149] - Measurement list configured by MCG: measResultFreqList-r16, measResultFreqListEUTRA-r16

[0150] - Measurement list configured by SCG: measResultSCG-r16, measResultSCG-EUTRA-r16 (The corresponding field can be included in the measurement list configured by the MCG, and can be transmitted, and in this case, the corresponding field is not required)

[0151] In this embodiment, the following describes a case where the base station 902 configures the DC for the UE 901 and configures only the SRB3, as opposed to configuring the separate bearer of the SRB1 (i.e., separate SRB1) in operation 920. In operation 950, the UE 901 can encapsulate the MCGFailureInformation message generated in the previous operation in the ULInformationTransferMRDC message and can transmit it to the base station (SCG) 903 via the SRB3 configured for the SCG. Since the failure occurs in the link to the MCG, it is necessary to transmit the MCGFailureInformation to the SCG. Since the separate SRB1 is not configured, the transmission can be performed via the SRB3, and the ULInformationTransferMRDC can be used for the transmission, which is a new RRC message that is the RRC message of the SCG, as opposed to the RRC message of the MCG. The MCGFailureInformation actually required to be transmitted to the MCG can be included in the ULInformationTransferMRDC message, and the SCG base station 903 receiving the ULInformationTransferMRDC message from the UE 901 can extract the MCGFailureInformation message from the corresponding message and can transmit it to the MCG. As described above, Embodiment 2 describes a case where the separate SRB1 is not configured and only the SRB3 is configured. The MCG can receive the MCGFailureInformation through the inter-node RRC or Xn message and can interpret it to determine the subsequent operation.

[0152] In case of indicating handover and PSCell change, etc. to the UE 901, the base station 902 of the MCG can generate an RRCReconfiguration message including a reconfigurationWithSync configuration, and can transmit it to the base station 903 of the SCG, and the base station 903 of the SCG can transmit the RRCReconfiguration message received from the MCG to the UE 901 via SRB3. Alternatively, an RRCRelease message releasing the corresponding UE 901 can be transmitted, and any message can not be transmitted, so that the UE 901 automatically performs an RRC reestablishment operation. Among the above operations, operation 955 is an operation in which the base station 903 of the SCG generates a DLInformationTransferMRDC message including the RRCReconfiguration message received from the MCG, and transmits it to the UE 901 via SRB3, and the corresponding RRCReconfiguration message can include a reconfigurationWithSync configuration. In operation 960, the UE 901 receiving the RRC reconfiguration message can apply the received RRC reconfiguration, and in case of indicating an operation such as handover and PSCell change, the UE 901 can also apply. In case of handover, an RRCReconfigurationComplete message can be transmitted via SRB1 of the target cell. However, in case that the RRC reconfiguration message does not indicate handover, the UE 901 can transmit the RRCReconfigurationComplete message via SRB3 via which the RRC reconfiguration message is received.

[0153] Table 7 shows the structure of ULInformationTransferMRDC, and Table 8 is a field description of the information elements of Table 7. Table 9 shows the structure of DLInformationTransferMRDC, and Table 10 is a field description of the information elements of Table 9.

[0154] [Table 7]

[0155]

[0156] [Table 8]

[0157]

[0158]

[0159] [Table 9]

[0160]

[0161] [Table 10]

[0162]

[0163] Figure 10 FIG. 10 is a diagram illustrating a UE operation of transmitting an MCGFailureInformation message according to a configured SRB type as a first UE operation applied to the embodiments of the disclosure.

[0164] In operation 1005, the UE can receive a request for reporting UE capability from the base station via a UECapabilityEnquiry message, and can transmit a UECapabilityInformation message including UE capability information of the UE itself in response thereto. The corresponding UECapabilityInformation message can include UE capability associated with whether MCG failure reporting and recovery is supported. This can be transmitted in one bit per UE, or can indicate capability associated with a predetermined RAT type. For example, one bit of supporting MCG failure reporting and recovery in EN-DC and one bit of supporting MCG failure reporting and recovery in NR-DC and NE-DC can be indicated respectively, or one bit of supporting MCG failure reporting and recovery in EN-DC can include UE capability in NR-DC and NE-DC and can be indicated. The base station identifying the UE information can determine that the corresponding UE is capable of transmitting an MCG failure report message to the base station in the event of MCG failure, and later, in the event of handover and connection release indicated based on the corresponding information, the base station can know that the corresponding operation can be applied.

[0165] In operation 1010, the UE can receive an RRC reconfiguration message from the base station, and the corresponding message can include radio bearer configuration, SCell addition and change, dual connectivity configuration (SCG configuration), measurement configuration, etc. Specifically, DC configuration (SCG configuration), radio bearer configuration (DRB configuration, SRB configuration, in particular, SRB3 configuration, etc.), and MCG failure related configuration information (T316, including an indicator of a measurement result associated with a configured MO in the SCG) for fast MCG recovery can be provided in the corresponding operation according to the embodiments of the disclosure. The T316 timer is a guard timer until an RRC reestablishment operation is performed after declaring MCG failure, and is triggered in the case where the UE transmits MCGFailureInformation, and in the case where the corresponding timer expires, the UE can perform an RRC reestablishment operation. This can be interpreted as a time during which the UE waits for a response from the base station in response to MCGFailureInformation during a predetermined period of time.

[0166] In operation 1015, the UE can perform a DC operation, a channel measurement, and data transmission or reception based on the configuration in operation 1010.

[0167] In operation 1020, the UE can identify a problem in a connection state for a predetermined reason, and can declare MCG failure. The predetermined situation can be a case where a T310 timer expires, a random access fails, the number of RLC retransmissions exceeds the maximum number of RLC retransmissions, etc. In particular, after declaring MCG failure, an MCG failure procedure can be performed. That is, MCGFailureInformation can be generated, and a corresponding message can include a measurement value of an MCG frequency (e.g., NR), a reason for MCG failure, a measurement value of an SCG frequency (e.g., LTE), a measurement value of a non-serving cell, etc. Further, the measurement values of the MCG and SCG frequencies can be reported separately according to which of the MCG and SCG the configuration is performed, or the MCG frequency measurement value and the SCG frequency measurement value can be reported regardless of the cell group for which the configuration is performed. That is, the measurement results of MOs configured by the MCG and the SCG can be included in separate lists or a single list. Further, in this operation, the UE can suspend data transmission or reception performed with the MCG, and can maintain data transmission or reception performed with the SCG. In the following example, the measurement results configured by the MCG and the SCG are included in separate lists.

[0168] - Measurement list configured by MCG: measResultFreqList-r16, measResultFreqListEUTRA-r16

[0169] - Measurement list configured by SCG: measResultSCG-r16, measResultSCG-EUTRA-r16 (corresponding fields can be included in the measurement list configured by the MCG, and can be transmitted, and in this case, the corresponding fields are not needed)

[0170] In operation 1025, the UE can identify whether a split SRB1 is configured in the SCG, and can perform different operations.

[0171] In case that the separate SRB1 of the SCG is configured in the RRCReconfiguration message configured in operation 1010, the UE can transmit the MCGFailureInformation message generated in the previous operation to the SCG via the configured SRB1 in operation 1030. Meanwhile, the configured T316 timer is running. Subsequently, in case that the RRCReconfiguration message or the RRCRelease message is received from the SCG, the operation of applying the same can be performed. If the T316 timer expires, the UE can proceed to the RRC re-establishment operation in operation 1035.

[0172] In case that the separate SRB1 of the SCG is not configured in the RRCReconfiguration message configured in operation 1010, the UE can identify whether the SRB3 is configured in operation 1040. In case that the SRB3 is configured, the UE can include the MCGFailureInformation message generated in the previous operation in the ULInformationTransferMRDC message in operation 1045, and can transmit the same to the SCG via the configured SRB3. Meanwhile, the configured T316 timer is running. Subsequently, in case that the RRCReconfiguration message or the RRCRelease message is received from the SCG, the operation of applying the same message can be performed. If the T316 timer expires, the UE can proceed to the RRC re-establishment operation in operation 1050. In case that it is identified that the separate SRB1 is not configured and the SRB3 is not configured in operation 1040, the UE can perform the RRC re-establishment operation with respect to the MCG. In this case, although it is expressed as operation 1055 in the drawing, the corresponding condition is discriminated after operation 1010, and thus, in case that the problem in the connection with the MCG is detected in operation 1020, the subsequent operations can all be omitted, and the MCG RRC re-establishment operation can be immediately performed.

[0173] Figure 11 is a diagram illustrating the UE operation performed depending on the SRB via which the RRCReconfiguration message in response to the MCGFailureInformation is received, as the second UE operation applied to the embodiment of the disclosure. The corresponding drawing illustrates the operation related to Figure 10 , and only predetermined operations are illustrated. That is, the operation performed after the UE transmits the MCGFailureInformation in operation Figure 10 is illustrated.

[0174] In operation 1105, the UE can receive an RRCReconfiguration message in response to the MCGFailureInformation message transmitted by the UE to the SCG, and the corresponding message can include a reconfigurationWithSync configuration. The reconfigurationWithSync can include at least one piece of information among information indicating handover or PSCell change. In operation 1110, the UE can identify an SRB via which the RRCReconfiguration message in response to the MCGFailureInformation message is received. In the case of performing reception via SRB1 (i.e., via reception of a separate SRB1), in operation 1115, the UE can directly receive the corresponding RRCReconfiguration message. However, in operation 1120, reception is performed via SRB3 instead of SRB1, the RRCReconfiguration message can be directly received, or the RRCReconfiguration message can be encapsulated in a DLInformationTransferMRDC message.

[0175] Reference will be made to Figure 12 Subsequent UE operations will be described in detail.

[0176] Figure 12 is a diagram illustrating subsequent UE operations performed depending on an SRB via which an RRCReconfiguration message in response to MCGFailureInformation is received and depending on a type of a transmitted RRCReconfiguration message as a third UE operation applied to embodiments of the disclosure.

[0177] In operation 1205, the UE can receive an RRCReconfiguration message via a predetermined SRB, and in operation 1210, can determine an operation depending on an SRB via which reception is performed. In the case of receiving an RRCReconfiguration message via SRB1, in operation 1215, the UE can determine to transmit an RRCReconfigurationComplete message via SRB1 through which reception is performed, can generate the message, and can transmit the corresponding RRCReconfigurationComplete message to the base station via SRB1 in operation 1220. This can be a normal UE operation regardless of the MCG and the SCG.

[0178] In operation 1210, in case the UE receives the RRCReconfiguration message or the DLInformationTransferMRDC message including RRCReconfiguration via SRB3, the UE can perform operations differently by distinguishing the cases. This can be determined in operation 1225, and in case the RRCReconfiguration is included in the DLInformationTransferMRDC and is transmitted, operation 1230 can be performed. The UE can apply the configuration of the received RRCReconfiguration message, can apply the handover and PSCell change included in the corresponding message, and then, can determine to transmit the RRCReconfigurationComplete message via the target cell through which the handover is performed. In operation 1235, the UE can generate the RRCReconfigurationComplete message, and can transmit the corresponding RRCReconfigurationComplete message to the target base station via SRB1. In operation 1225, in contrast to receiving the DLInformationTransferMRDC, in case it is identified that the UE receives the RRCReconfiguration message directly via SRB3, the UE can proceed to operation 1240. In operation 1240, the UE can determine to transmit the RRCReconfigurationComplete message via SRB3 through which the RRCReconfiguration message is received. In operation 1245, the UE can generate the RRCReconfigurationComplete message, and can transmit the corresponding RRCReconfigurationComplete message to the SCG via SRB3. This can be a normal UE operation regardless of the MCG and the SCG.

[0179] Figure 13 FIG. 1 is a diagram illustrating base station operations applied to all embodiments of the disclosure.

[0180] In operation 1305, the base station requests a UE in a connected state to report UE capability via a UECapabilityEnquiry message, and receives UE capability information in response thereto via a UECapabilityInformation message. The corresponding UE capability information can include UE capability associated with whether MCG failure reporting and recovery is supported. This can be transmitted in one bit per UE, or can indicate capability associated with a predetermined RAT type. For example, one bit indicating support of MCG failure reporting and recovery in EN-DC and one bit indicating support of MCG failure reporting and recovery in NR-DC and NE-DC can be indicated respectively, or one bit indicating support of MCG failure reporting and recovery in EN-DC can include UE capability in NR-DC and NE-DC, and can be indicated. The base station identifying the UE information can determine that the corresponding UE is capable of transmitting a MCG failure report message to the base station in the event of MCG failure, and later, in the event of handover and connection release indicated based on the corresponding information, the base station can know that the corresponding operation can be applied.

[0181] Subsequently, in operation 1310, the base station can generate and transmit an RRCReconfiguration message in consideration of the UE capability, and the corresponding message can include radio bearer configuration, SCell addition and change, dual connectivity configuration (SCG configuration), measurement configuration, etc. Specifically, DC configuration (SCG configuration), radio bearer configuration (DRB configuration, SRB configuration, in particular, SRB3 configuration, etc.), and MCG failure related configuration information (T316, including an indicator of measurement result associated with MO configured in the SCG) for fast MCG recovery can be provided in the corresponding operation in the embodiments of the disclosure. The T316 timer is a guard timer until an RRC reestablishment operation is performed after declaring MCG failure, and is triggered in the event that the UE transmits MCGFailureInformation, and in the event that the corresponding timer expires, the UE can perform an RRC reestablishment operation. This can be interpreted as a time during which the UE waits for a response from the base station in response to MCGFailureInformation during a predetermined period of time.

[0182] In operation 1315, the base station can receive the MCGFailureinformation message from the SCG. The SCG can receive the corresponding message from the UE via a predetermined SRB, and there are cases of reception via SRB1 and cases of reception via SRB3. In the case of reception via SRB1, the MCGFailureinformation information can be directly transferred. In the case of reception via SRB3, the MCGFailureinformation message can be included in the ULInformationTrnasferMRDC and can be transferred.

[0183] In operation 1320, based on the received MCGFailureinformation information, the base station can determine whether to apply the information and can determine a subsequent operation. Based on the determination, the base station of the MCG can transfer an RRC reconfiguration with respect to the UE. That is, in the case of indicating handover and PSCell change to the UE based on the MCGFailureinformation information, the MCG base station can generate and transfer an RRCReconfiguration message, and can transfer an RRC release message in order to indicate RRCRelease to the corresponding UE. The message generated by the MCG can be transferred to the UE via the SCG. Alternatively, any operation can not be performed, so that the UE automatically performs an RRC reestablishment operation. This is because the UE performs an RRC reestablishment operation in the case where the T316 timer expires.

[0184] Figure 14 FIG. 1 is a diagram illustrating a configuration of a UE according to an embodiment of the disclosure.

[0185] Referring to the drawings, the UE includes a radio frequency (RF) processor 1410, a baseband processor 1420, a memory 1430, and a controller 1440. The controller 1440 can further include a multiplexing / demultiplexing processor 1442.

[0186] The RF processor 1410 performs functions of transmitting or receiving a signal via a wireless channel, such as band conversion and amplification of a signal. That is, the RF processor 1410 up-converts a baseband signal provided from the baseband processor 1420 into an RF band signal, transmits the RF band signal via an antenna, and down-converts an RF band signal received via the antenna into a baseband signal. For example, the RF processor 1410 can 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 drawing, the UE can include a plurality of antennas. Also, the RF processor 1410 can include a plurality of RF chains. Also, the RF processor 1410 can perform beamforming. For beamforming, the RF processor 1410 can control a phase and a size of each signal transmitted or received via a plurality of antennas or antenna elements. Also, the RF processor can perform MIMO, and can receive a plurality of layers in case of performing the MIMO operation.

[0187] The baseband processor 1420 operates a conversion function between a baseband signal and a bit string according to a physical layer standard of a system. For example, in case of data transmission, the baseband processor 1420 encodes and modulates a transmission bit string in order to generate a complex symbol. Also, in case of data reception, the baseband processor 1420 recovers a reception bit string by demodulating and decoding a baseband signal provided from the RF processor 1410. For example, according to an orthogonal frequency division multiplexing (OFDM) scheme, in case of data transmission, the baseband processor 1420 generates a complex symbol by encoding and modulating a transmission bit string, maps the complex symbol to a subcarrier, and then configures an OFDM symbol via an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion. Also, in case of data reception, the baseband processor 1420 divides a baseband signal provided from the RF processor 1410 in units of OFDM symbols, reconstructs a signal mapped to a subcarrier via a fast Fourier transform (FFT) operation, and then reconstructs a reception bit string via demodulation and decoding.

[0188] The baseband processor 1420 and the RF processor 1410 transmit and receive signals as described above. Accordingly, the baseband processor 1420 and the RF processor 1410 can be referred to as a transmitter, a receiver, a transceiver, or a communication unit. Also, at least one of the baseband processor 1420 and the RF processor 1410 can include a plurality of communication modules in order to support different multiple radio access technologies. Also, at least one of the baseband processor 1420 and the RF processor 1410 can include different communication modules in order to process signals of different frequency bands. For example, the different radio access technologies can include a wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. Also, the different frequency bands can include a super high frequency (SHF) (e.g., 2.NRHz, NRhz) band and a millimeter (mm) wave (e.g., 60GHz) band.

[0189] The memory 1430 stores data for UE operations, such as a basic program, an application program, configuration information, etc. In particular, the memory 1430 can store information related to a second access node that performs wireless communication using a second radio access technology. Also, the memory 1430 provides data stored therein at the request of the controller 1440.

[0190] The controller 1440 controls overall operations of the UE. For example, the controller 1440 transmits or receives a signal via the baseband processor 1420 and the RF processor 1410. Also, the controller 1440 can record or read data in or from the memory 1430. To this end, the controller 1440 can include at least one processor. For example, the controller 1440 can include a communication processor (CP) that performs control for communication, and an application processor (AP) that controls a higher layer such as an application program. According to various embodiments of the present disclosure, the controller 1440 can control operations of the UE. For example, the controller 1440 can perform control in order to generate master cell group (MCG) failure information, transmit the MCG failure information to a base station of a secondary cell group (SCG), receive a radio resource control (RRC) reconfiguration message from the base station, and transmit an RRC reconfiguration complete message based on the RRC reconfiguration message. In the case where the RRC reconfiguration message is included in a downlink information transfer message and is received via a signaling radio bearer (SRB) 3 of the SCG, the RRC reconfiguration complete message can be transmitted via an SRB1 configured based on the RRC reconfiguration message. The downlink information transfer message can correspond to a downlink (DL) information transfer multiple radio (MR) dual connectivity (DC) message.

[0191] Further, in a case where the RRC reconfiguration message is not included in the downlink information transfer message and is received via the SRB3, the controller 1440 can perform control so that the RRC reconfiguration complete message is transmitted via the SRB3. In a case where the RRC reconfiguration message is received via the split SRB1, the controller 1440 can perform control so that the RRC reconfiguration complete message is transmitted via the SRB1 configured based on the RRC reconfiguration message.

[0192] The RRC reconfiguration message can include handover information, and the SRB1 can be an SRB1 of a target cell configured based on the handover information. Further, in a case where the split SRB1 is configured, the controller 1440 can perform control so as to transmit the MCG failure information to the base station via the split SRB1. Further, in a case where the SRB3 is configured, the controller 1440 can perform control so as to include the MCG failure information in the uplink information transfer message and transmit the same via the SRB3. Further, the controller 1440 can perform control so that information indicating whether support of the MCG failure recovery is reported via the UE capability information.

[0193] Figure 15 FIG. 1 is a diagram illustrating a configuration of a base station according to an embodiment of the disclosure.

[0194] As illustrated, the base station can include an RF processor 1510, a baseband processor 1520, a backhaul communication unit 1530, a memory 1540, and a controller 1550. The controller 1550 can further include a multiple access processor 1552.

[0195] The RF processor 1510 performs a function of transmitting or receiving a signal via a wireless channel, such as band conversion and amplification of a signal. That is, the RF processor 1510 up-converts a baseband signal provided by the baseband processor 1520 into an RF band signal, transmits the RF band signal via an antenna, and down-converts an RF band signal received via the antenna into a baseband signal. For example, the RF processor 1510 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only a single antenna is illustrated in the drawing, the first access node can include a plurality of antennas. Further, the RF processor 1510 can include a plurality of RF chains. In addition, the RF processor 1510 can perform beamforming. For beamforming, the RF processor 1510 can control a phase and a size of each signal transmitted or received via a plurality of antennas or antenna elements. The RF processor can perform a downlink MIMO operation by transmitting one or more layers.

[0196] The baseband processor 1520 performs a conversion function between a baseband signal and a bit string according to a physical layer standard of the first radio access technology. For example, in the case of data transmission, the baseband processor 1520 encodes and modulates a transmission bit string to generate complex symbols. Also, in the case of data reception, the baseband processor 1520 recovers a reception bit string by demodulating and decoding a baseband signal provided from the RF processor 1510. For example, according to an OFDM scheme, in the case of data transmission, the baseband processor 1520 can generate complex symbols by encoding and modulating a transmission bit string, can map the complex symbols to subcarriers, and then can configure OFDM symbols via an IFFT operation and CP insertion. Also, in the case of data reception, the baseband processor 1520 divides a baseband signal provided from the RF processor 1510 in units of OFDM symbols, recovers signals mapped to subcarriers via an FFT operation, and recovers a reception bit string via demodulation and decoding. The baseband processor 1520 and the RF processor 1510 transmit and receive signals as described above. Accordingly, the baseband processor 1520 and the RF processor 1510 can be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0197] The backhaul communication unit 1530 can provide an interface for performing communication with other nodes in a network. That is, the backhaul communication unit 1530 can convert a bit string transmitted from the master base station to another node (e.g., a secondary base station, a core network, etc.) into a physical signal, and can convert a physical signal received from another node into a bit string.

[0198] The memory 1540 stores data for master base station operations such as a basic program, an application program, configuration information, etc. In particular, the memory 1540 can store information associated with bearers allocated to connected UEs, measurement results reported from the connected UEs, etc. Also, the memory 1540 can provide a plurality of accesses to the UEs, or can store information as a criterion for determining whether to suspend a connection. Also, the memory 1540 provides data stored therein at the request of the controller 1550.

[0199] The controller 1550 can control the overall operation of the master base station. For example, the controller 1550 can transmit or receive a signal via the baseband processor 1520 and the RF processor 1510 or via the backhaul communication unit 1530. Also, the controller 1550 can record data in or read data from the memory 1540. To this end, the controller 1550 can include at least one processor. The controller 1550 can control the operation of the base station according to various embodiments of the disclosure.

[0200] In the above detailed embodiments of the disclosure, according to the presented detailed embodiments, the elements included in the disclosure are expressed in singular or plural. However, for the convenience of description, the singular form or the plural form is appropriately selected as the presented situation, and the disclosure is not limited to the elements expressed in singular or plural. Therefore, the elements expressed in plural can also include a single element, or the elements expressed in singular can also include a plurality of elements.

[0201] Although specific embodiments have been described in the detailed description of the disclosure, various modifications and changes can be made thereto without departing from the scope of the disclosure. Accordingly, the scope of the disclosure should not be defined by the embodiments, but by the appended claims and their equivalents.

Claims

1. A method performed by a user equipment (UE) in a wireless communication system, the method comprising: transmitting, to a base station of a secondary cell group (SCG), master cell group (MCG) failure information including a failure type, MCG measurement information, and SCG measurement information; receiving, from the base station, a radio resource control (RRC) reconfiguration message associated with the MCG failure information; in case that the RRC reconfiguration message is received via a signaling radio bearer (SRB) 3 of the SCG: in case that the RRC reconfiguration message is included in a downlink (DL) information transfer message, transmitting an RRC reconfiguration complete message via an SRB1 configured based on the RRC reconfiguration message, and in case that the RRC reconfiguration message is not included in the DL information transfer message, transmitting the RRC reconfiguration complete message via the SRB3, and in case that the RRC reconfiguration message is received via a split SRB1, transmitting the RRC reconfiguration complete message via the SRB1 configured based on the RRC reconfiguration message. the DL information transfer message corresponds to a DL information transfer multi radio (MR) dual connectivity (DC) message.

2. The method of claim 1, wherein, the RRC reconfiguration message includes handover information, and the SRB1 is an SRB1 of a target cell configured based on the handover information.

3. The method of claim 1, wherein, in case that the split SRB1 is configured, the MCG failure information is transmitted to the base station via the split SRB1, and 4. The method of claim 1, wherein, wherein, in case that the SRB3 is configured, the MCG failure information is included in an uplink information transfer message and transmitted via the SRB3. reporting information indicating whether MCG failure recovery is supported via UE capability information.

5. The method of claim 1, wherein, 6.A user equipment (UE) in a wireless communication system, the UE comprising: a transceiver; and a controller configured to: transmit, to a base station of a secondary cell group (SCG), master cell group (MCG) failure information including a failure type, MCG measurement information, and SCG measurement information, receive, from the base station, a radio resource control (RRC) reconfiguration message associated with the MCG failure information, and in case that the RRC reconfiguration message is received via a signaling radio bearer (SRB) 3 of the SCG: in case that the RRC reconfiguration message is included in a downlink (DL) information transfer message, transmit an RRC reconfiguration complete message via an SRB1 configured based on the RRC reconfiguration message, and in case that the RRC reconfiguration message is not included in the DL information transfer message, transmit the RRC reconfiguration complete message via the SRB3, and in case that the RRC reconfiguration message is received via a split SRB1, the controller is further configured to transmit the RRC reconfiguration complete message via the SRB1 configured based on the RRC reconfiguration message. the DL information transfer message corresponds to a DL information transfer multi radio (MR) dual connectivity (DC) message. ​ 7. The UE of claim 6, wherein, ​ 8. The UE of claim 6, wherein, The RRC reconfiguration message includes handover information, and the SRB1 is an SRB1 of a target cell configured based on the handover information.

9. The UE of claim 6, wherein, In a case where the split SRB1 is configured, the MCG failure information is transmitted to the base station via the split SRB1, and wherein, in a case where the SRB3 is configured, the MCG failure information is included in an uplink information transfer message and is transmitted via the SRB3.

10. The UE of claim 6, wherein, Information indicating whether MCG failure recovery is supported is reported via UE capability information. 11.A method performed by a base station of a secondary cell group (SCG) in a wireless communication system, the method comprising: receiving, from a user equipment (UE), master cell group (MCG) failure information including a failure type, MCG measurement information, and SCG measurement information; and transmitting, to the UE, a radio resource control (RRC) reconfiguration message associated with the MCG failure information, wherein, in a case where the RRC reconfiguration message is transmitted via a signaling radio bearer (SRB) 3 of the SCG and the RRC reconfiguration message is not included in a downlink (DL) information transfer message, an RRC reconfiguration complete message is received by the base station via the SRB 3, wherein, in a case where the RRC reconfiguration message is transmitted via the SRB 3 and the RRC reconfiguration message is included in the DL information transfer message, an RRC reconfiguration complete message is transferred by the UE via an SRB1 configured based on the RRC reconfiguration message, and wherein, in a case where the RRC reconfiguration message is transferred via a split SRB1, an RRC reconfiguration complete message is transmitted by the UE via the SRB1 configured based on the RRC reconfiguration message.

12. The method of claim 11, wherein, The DL information transfer message corresponds to a DL information transfer multi-radio (MR) dual connectivity (DC) message, and wherein information indicating whether MCG failure recovery is supported is reported via UE capability information.

13. The method of claim 11, wherein, The RRC reconfiguration message includes handover information, and the SRB1 is an SRB1 of a target cell configured based on the handover information, wherein, in a case where the split SRB1 is configured, the MCG failure information is transmitted to the base station via the split SRB1, and wherein, in a case where the SRB3 is configured, the MCG failure information is included in an uplink information transfer message and is transmitted via the SRB3. 14.A base station in a wireless communication system, the base station comprising: a transceiver; and a controller configured to: receive, from a user equipment (UE), master cell group (MCG) failure information including a failure type, MCG measurement information, and SCG measurement information, and transmit, to the UE, a radio resource control (RRC) reconfiguration message associated with the MCG failure information, wherein, in a case where the RRC reconfiguration message is transmitted via a signaling radio bearer (SRB) 3 of the SCG and the RRC reconfiguration message is not included in a downlink (DL) information transfer message, an RRC reconfiguration complete message is received by the base station via the SRB 3, wherein, in case that the RRC reconfiguration message is transmitted via the SRB3 and the RRC reconfiguration message is included in the DL information transfer message, an RRC reconfiguration complete message is transmitted by the UE via an SRB1 configured based on the RRC reconfiguration message, and wherein, in case that the RRC reconfiguration message is transmitted via a split SRB1, an RRC reconfiguration complete message is transmitted by the UE via an SRB1 configured based on the RRC reconfiguration message.

15. The base station of claim 14, wherein, The DL information transfer message corresponds to a DL information transfer multi-radio (MR) dual connectivity (DC) message, and wherein, information indicating whether MCG failure recovery is supported is indicated via UE capability information report.

16. The base station of claim 14, wherein, The RRC reconfiguration message includes handover information, and the SRB1 is an SRB1 of a target cell configured based on the handover information, wherein, in case that the split SRB1 is configured, the MCG failure information is transmitted to the base station via the split SRB1, and wherein, in case that the SRB3 is configured, the MCG failure information is included in an uplink information transfer message and transmitted via the SRB3.

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