Method by terminal in wireless communication system and terminal

Abstract

The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and security services. The present disclosure relates to a method and apparatus for quickly recovering a connection to a network when a connection to the network fails in a next generation mobile communication system.

Description

[0001] This application is a divisional application of an invention patent application with an application date of March 23, 2020, application number 202080023173.9, and invention name “Method and device for recovering network connection failure in the next generation mobile communication system”. Technical Field

[0002] The present disclosure relates to a method and apparatus for quickly recovering a network connection failure that has occurred in a next generation mobile communication system. Background Art

[0003] In order to meet the demand for wireless data services that has grown since the deployment of the fourth generation (4G) communication system, efforts have been made to develop improved fifth generation (5G) or pre-5G communication systems. Therefore, 5G or pre-5G communication systems are also referred to as "super 4G networks" or "post-long term evolution (LTE) systems". 5G communication systems are considered to be implemented in higher frequency (millimeter wave) bands, such as the 60 GHz band, in order to achieve higher data rates. In order to reduce the propagation loss of radio waves and increase the transmission distance, beamforming, massive multiple input multiple output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive antenna technology are discussed in 5G communication systems. In addition, in 5G communication systems, system network improvements are being developed based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communications, wireless backhaul, mobile networks, cooperative communications, coordinated multipoint (CoMP), receiving-end interference cancellation, etc. In 5G systems, hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC) have also been developed as advanced coded modulation (ACM), as well as filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0004] The Internet, which is a human-centered connected network in which humans generate and consume information, is now developing toward the Internet of Things (IoT) in which distributed entities (such as things) exchange and process information without human intervention. The Internet of Everything (IoE) has emerged, which is a combination of IoT technology and big data processing technology through connection with cloud servers. As technology elements such as "sensing technology", "wired / wireless communication and network infrastructure", "service interface technology" and "security technology" have been implemented for IoT, sensor networks, machine-to-machine (M2M) communication, machine type communication, etc. have been studied recently. This IoT environment can provide smart Internet technology services that create new value for human life by collecting and analyzing data generated in connected things. Through the convergence and combination between existing information technology (IT) and various industrial applications, IoT can be applied to various fields, including smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, healthcare, smart appliances, and advanced medical services.

[0005] In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine type communications (MTC), and machine-to-machine (M2M) communications can be implemented through beamforming, MIMO, and array antennas. Cloud radio access networks (RANs) as an application of the above-mentioned big data processing technologies can also be considered as an example of the fusion of 5G technology and IoT technology. Summary of the invention

[0006] Technical issues

[0007] In order to support services with high data transmission rate and low transmission delay in the next generation mobile communication system, base stations need to quickly configure carrier aggregation (CA) or dual connectivity (DC) for terminals.

[0008] The above information is provided as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with respect to the present disclosure.

[0009] Technical Solution

[0010] According to one aspect of the present disclosure, a method performed by a terminal in a wireless communication system includes: detecting an MCG radio link failure from a primary cell group (MCG); sending an MCG radio link failure report to a secondary cell group (SCG) via a separate signaling radio bearer (SRB) 1 or SRB3 when an MCG radio link failure is detected; and starting a timer when the MCG radio link failure report is sent to the SCG.

[0011] In an embodiment, wherein sending the MCG radio link failure report comprises sending the MCG radio link failure report via the split SRB1 if both split SRB1 and SRB3 are configured.

[0012] In an embodiment, the method further comprises: stopping the timer if a response is received from the MCG.

[0013] In an embodiment, the method further comprises: triggering a radio resource control (RRC) connection reestablishment procedure when the timer expires.

[0014] In an embodiment, the method further comprises: triggering a radio resource control (RRC) connection reestablishment procedure in a case where a SCG radio link failure (SCG RLF) occurs while the timer is operating.

[0015] According to another aspect of the present disclosure, a method performed by a secondary cell group (SCG) in a wireless communication system includes: upon detecting a primary cell group (MCG) radio link failure, receiving an MCG radio link failure report from a terminal via a separate signaling radio bearer (SRB) 1 or SRB3, wherein upon receiving the MCG radio link failure report from the terminal, a timer is started by the terminal.

[0016] According to another aspect of the present disclosure, a terminal includes: a transceiver for sending and receiving at least one signal; and at least one processor, coupled to the transceiver and configured to: detect an MCG radio link failure from a primary cell group (MCG), and when the MCG radio link failure is detected, control the transceiver to send an MCG radio link failure report to a secondary cell group (SCG) via a separate signaling radio bearer (SRB) 1 or SRB3, and when the MCG radio link failure report is sent to the SCG, control a timer to start.

[0017] According to another aspect of the present disclosure, a secondary cell group (SCG) includes: a transceiver for sending and receiving at least one signal; and at least one processor coupled to the transceiver and configured to: upon detecting a primary cell group (MCG) radio link failure, receive an MCG radio link failure report from a terminal via a separate signaling radio bearer (SRB) 1 or SRB3; and upon receiving the MCG radio link failure report from the terminal, control a timer to be started by the terminal.

[0018] According to another aspect of the present disclosure, a method performed by a terminal in a wireless communication system includes: detecting a radio link failure of a primary cell group (MCG) associated with a primary base station; and sending a message about the radio link failure of the MCG to the primary base station via a secondary cell group (SCG) associated with the secondary base station, using an SRB or SRB3 configured as a separate signaling radio bearer (SRB) 1, wherein, when SRB1 is configured as a separate SRB and packet data convergence protocol (PDCP) replication is not configured, the configuration for uplink transmission is changed from a primary radio link control (RLC) entity associated with the MCG to a secondary radio link control (RLC) entity associated with the SCG.

[0019] According to another aspect of the present disclosure, a terminal in a wireless communication system includes: a transceiver; and a controller connected to the transceiver, wherein the controller is configured to: detect a radio link failure of a primary cell group (MCG) associated with a primary base station; and send a message about the radio link failure of the MCG to the primary base station via a secondary cell group (SCG) associated with the secondary base station using an SRB or SRB3 configured as a separate signaling radio bearer (SRB) 1, wherein, when SRB1 is configured as a separate SRB and packet data convergence protocol (PDCP) replication is not configured, the configuration for uplink transmission is changed from a primary radio link control (RLC) entity associated with the MCG to a secondary radio link control (RLC) entity associated with the SCG.

[0020] Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the presented embodiments.

[0021] Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses various embodiments of the disclosure.

[0022] Advantageous Effects of the Invention

[0023] In the case where carrier aggregation or dual connectivity is configured for the terminal, when a connection failure occurs in a Pcell or Pscell (Spcell), an Scell, a primary cell group (MCG) in dual connectivity, or a secondary cell group (SCG) in dual connectivity, data loss and data transmission delays may occur even in the cell or cell group that remains connected, as long as the terminal and the network are completely disconnected.

[0024] In order to support services with high data transmission rate and low transmission delay in the next generation mobile communication system, the base station needs to quickly configure carrier aggregation (CA) or dual connectivity (DC) for the terminal. In the case of configuring carrier aggregation or dual connectivity for the terminal, connection failure may occur in Pcell or Pscell (Spcell), Scell, primary cell group (MCG) in dual connectivity, or secondary cell group (SCG) in dual connectivity.

[0025] An aspect of the present disclosure is to solve at least the above problems and / or disadvantages, and to provide at least the advantages described below. Therefore, an aspect of the present disclosure is to provide a method for restoring a connection to a cell or cell group in which a connection is maintained or adding a novel connection without completely disconnecting a terminal from a network. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent from the following description in conjunction with the accompanying drawings, in which:

[0027] Figure 1A The structure of a Long Term Evolution (LTE) system to which the present disclosure may be applied according to an embodiment of the present disclosure is shown;

[0028] Figure 1B The wireless protocol architecture in the LTE system to which the present disclosure can be applied according to an embodiment of the present disclosure is shown;

[0029] Figure 1C The structure of a next generation mobile communication system to which the present disclosure can be applied according to an embodiment of the present disclosure is shown;

[0030] Figure 1D The wireless protocol architecture in the next generation mobile communication system to which the present disclosure can be applied according to the embodiments of the present disclosure is shown;

[0031] Figure 1E A process according to an embodiment of the present disclosure is shown, wherein in the next generation mobile communication system of the present disclosure, a terminal switches from a radio resource control (RRC) idle mode or an RRC inactive mode to an RRC connected mode, and a base station configures carrier aggregation or dual connectivity for the terminal;

[0032] Figure 1F The structure of a protocol layer device of a terminal configured with dual connectivity in the present disclosure according to an embodiment of the present disclosure is shown;

[0033] Figure 1G The architecture of a protocol layer device of a terminal configured with carrier aggregation in the present disclosure according to an embodiment of the present disclosure is shown;

[0034] Figure 1HThe operation of the terminal in the embodiment according to the present disclosure is shown;

[0035] Fig. 1I shows the structure of a terminal to which the embodiment can be applied according to the embodiment of the present disclosure; and

[0036] Figure 1J A block configuration of a TRP in a wireless communication system to which an embodiment of the present disclosure can be applied is shown.

[0037] Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. DETAILED DESCRIPTION

[0038] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of the various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details that assist in that understanding but these are considered to be exemplary only. Therefore, one of ordinary skill in the art will recognize that various changes and modifications may be made to the various example embodiments described herein without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and structures may be omitted for clarity and conciseness.

[0039] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Therefore, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustrative purposes only and is not intended to limit the present disclosure as defined by the appended claims and their equivalents.

[0040] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

[0041] In the following description, for the sake of convenience, 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 used below, and other terms referring to subjects with equivalent technical meanings may be used.

[0042] In the following description, for ease of description, the present disclosure uses terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard. 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, 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".

[0043] The present disclosure considers a terminal in which carrier aggregation (CA) or dual connectivity (DC) is configured, and specifies methods presented by using the following terms.

[0044] -Primary Cell (Pcell): The Pcell is a serving cell in which the terminal configures the initial connection to the base station. The Pcell is used to send and receive important radio resource control (RRC) messages, thereby configuring the connection. In addition, the Pcell always has physical uplink control channel (PUCCH) transmission resources, so it can indicate a hybrid automatic repeat request (HARQ) acknowledgement (ACK) or negative acknowledgement (NACK), has uplink and downlink that are always configured, and can be used as a reference cell for timing advance (primary timing advance group (pTAG)). For example, when a Pcell is configured and then a Scell ​​is added by configuring carrier aggregation, the Scell ​​can refer to the timing advance value of the Pcell to perform uplink data transmission. In addition, when dual connectivity is configured, the Pcell is the Pcell of the primary cell group (MCG).

[0045] -Master Cell Group (MCG): MCG is a group of cells supported by a base station or serving cells used when a terminal configures an initial connection to a base station. When dual connectivity is configured, the primary RRC message is sent or received through the MCG.

[0046] -Secondary Cell Group (SCG): The terminal configures a connection to a base station and can add a cell of another base station in addition to the MCG. The SCG is a group of cells supported by another base station. When dual connectivity is configured, the SCG can be added in order to increase additional data transmission rate or efficiently support the mobility of the terminal.

[0047] - Primary Secondary Cell (Pscell): When a terminal configures a connection to a base station, a group of cells of another base station other than the MCG is added, and dual connectivity is configured, the cell corresponding to the Pcell in the SCG is called a Pscell.

[0048] -Secondary cell (Scell): Scell ​​is a cell additionally configured by the base station so that the terminal configures the initial connection to the base station and then configures carrier aggregation. The Scell ​​may have PUCCH transmission resources configured according to the base station, and may have uplink and downlink configured according to the base station configuration. In addition, according to the base station configuration, the Scell ​​may be used as a reference cell for a timing advance auxiliary timing advance group (sTAG). For example, when a Pcell is configured, a Scell ​​is added by configuring carrier aggregation, and an sTAG is configured, and other Scells of the sTAG may refer to the timing advance value of the specified Scell ​​to perform uplink data transmission. In addition, when dual connectivity is configured for the terminal, the Scell ​​may be a Scell ​​of a Pcell different from the MCG or a Scell ​​of a Pscell different from the SCG.

[0049] When a terminal configured with carrier aggregation or dual connectivity cannot establish a wireless connection with a base station (or cell) in a Pcell, MCG, SCG, or Scell ​​(for example, radio link failure), there may be a cell (Pcell, Pscell, or Scell) or a cell group (MCG or SCG) in the Pcell, MCG, SCG, or Scell ​​that maintains a wireless connection with the base station (or cell). Regarding this situation, the present disclosure proposes a method that is not used to completely release the connection and re-establish the connection, but to restore the disconnected cell or cell group or configure a novel connection while continuing to send / receive data to / from the cell or cell group that maintains the wireless connection. The present disclosure also proposes a method for replacing an existing cell or cell group that maintains a connection with a Pcell or MCG.

[0050] The present disclosure proposes an efficient process in consideration of the following embodiments.

[0051] The first embodiment considers a case where a terminal configured with dual connectivity maintains a connection with a base station (or cell) in an MCG and fails to make a wireless connection with a base station (or cell) in an SCG.

[0052] The second embodiment considers a case where a terminal configured with dual connectivity maintains a connection with a base station (or cell) in an SCG and fails to make a wireless connection with a base station (or cell) in an MCG.

[0053] The third embodiment considers a case where a terminal configured with carrier aggregation maintains connection with a base station (or cell) in a Pcell or Pscell (when dual connectivity is also configured) and fails to establish a wireless connection with a base station (or cell) in a Scell.

[0054] In the fourth embodiment, it is considered that the terminal in which carrier aggregation is configured maintains connection with the base station (or cell) in the Scell ​​and fails to establish a wireless connection with the base station (or cell) in the Pcell or Pscell (in which dual connectivity is also configured).

[0055] The above embodiment can also be extended and applied to the case where both carrier aggregation and dual connectivity are configured.

[0056] Hereinafter, specific methods regarding the above-mentioned embodiments of the present disclosure, efficient operations of a base station, or efficient operations of a terminal are proposed.

[0057] Figure 1A The structure of a Long Term Evolution (LTE) system to which the present disclosure may be applied according to an embodiment of the present disclosure is shown.

[0058] refer to Figure 1A , a radio access network of the LTE system includes an evolved Node B (hereinafter, "ENB", "Node B" or "base station") (1a-05, 1a-10, 1a-15 or 1a-20) and a mobility management entity (MME) 1a-25, and a serving gateway (S-GW) 1a-30. A user equipment (hereinafter, "UE" or "terminal") 1a-35 is connected to an external network through the ENB 1a-05, 1a-10, 1a-15 or 1a-20 and the S-GW 1a-30.

[0059] exist Figure 1A In the LTE system, ENB 1a-05, 1a-10, 1a-15 or 1a-20 corresponds to an existing Node B of a Universal Mobile Telecommunications System (UMTS) system. The ENB is connected to the UE 1a-35 through a wireless channel and can play a more complex role than the existing Node B. In the LTE system, all user services including real-time services, such as IP voice over the Internet Protocol, are provided through a shared channel. Therefore, a device for collecting and scheduling state information of the UE (such as buffer status, available transmission power status, channel status, etc.) is required, and ENB 1a-05, 1a-10, 1a-15 or 1a-20 is used as such a device. One ENB can generally control multiple cells. For example, in order to achieve a transmission speed of 100 Mbps, the LTE system uses orthogonal frequency division multiplexing (hereinafter referred to as "OFDM") as a radio access technology in a 20 MHz bandwidth. In addition, 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 terminal is applied. S-GW 1a-30 is a device for providing a data bearer, and generates or removes a data bearer according to the control of MME 1a-25. MME is a device for various types of control functions in addition to a mobility management function for a terminal, and is connected to a plurality of base stations.

[0060] Figure 1B A wireless protocol architecture in an LTE system to which the present disclosure may be applied according to an embodiment of the present disclosure is shown.

[0061] refer to Figure 1B , the wireless protocols of the LTE system include Packet Data Convergence Protocol (PDCP) 1b-05 and 1b-40, Radio Link Control (RLC) 1b-10 and 1b-35, and Medium Access Control (MAC) 1b-15 and 1b-30 in the terminal and ENB respectively. PDCP 1b-05 and 1b-40 perform operations such as IP header compression / recovery. The main functions of PDCP can be summarized as follows:

[0062] -Header compression and decompression: ROHC only

[0063] -Transfer of user data

[0064] - For RLC AM, in-sequence delivery of upper layer PDUs during PDCP reestablishment

[0065] - For split bearer in DC (supports RLC AM only): PDCP PDU routing for transmission and PDCP PDU reordering for reception

[0066] - For RLC AM, duplicate detection of lower layer SDUs during PDCP re-establishment

[0067] - For RLC AM, retransmission of PDCP SDUs at handover and retransmission of PDCP PDUs during PDCP data recovery for split bearers in DC

[0068] -Encryption and decryption

[0069] - Timer-based SDU discard in uplink

[0070] The radio link controller (hereinafter referred to as "RLC") 1b-10 and 1b-35 reconstructs the PDCP packet data unit (PDCP PDU) into an appropriate size and performs ARQ operations, etc. The main functions of the RLC can be summarized as follows:

[0071] - Delivery of upper layer PDU

[0072] - Error correction via ARQ (applicable only for AM data transfer)

[0073] - RLC SDU splicing, segmentation and reassembly (only for UM and AM data delivery)

[0074] - Re-segmentation of RLC data PDU (only for AM data delivery)

[0075] - Reordering of RLC data PDUs (only for UM and AM data delivery)

[0076] - Duplicate detection (for UM and AM data delivery only)

[0077] -Protocol error detection (for AM data transfer only)

[0078] -RLC SDU discard (only for UM and AM data delivery)

[0079] -RLC reconstruction

[0080] MAC 1b-15 and 1b-30 are connected to a plurality of RLC layer devices included in one terminal, and multiplex RLC PDUs into MAC PDUs and demultiplex RLC PDUs from MAC PDUs. The main functions of MAC can be summarized as follows:

[0081] - Mapping between logical channels and transport channels

[0082] - Multiplex / demultiplex MAC SDUs belonging to one or more different logical channels into / from transport blocks (TBs) delivered to / from the physical layer on transport channels

[0083] -Dispatch information report

[0084] - Error correction through HARQ

[0085] - Priority handling between logical channels of a UE

[0086] - Prioritization between UEs through dynamic scheduling

[0087] -MBMS service identification

[0088] -Transmission format selection

[0089] -filling

[0090] The physical layers 1b-20 and 1b-25 channel-code and modulate the upper layer data into OFDM symbols and transmit the symbols through the wireless channel, or demodulate and channel-code the OFDM received through the wireless channel and transmit it to the upper layer.

[0091] Figure 1C A structure of a next-generation mobile communication system to which the present disclosure can be applied according to an embodiment of the present disclosure is shown.

[0092] refer to Figure 1C, as shown in the figure, the radio access network of the next generation mobile communication system (hereinafter referred to as "NR" or "5G") includes a new radio node B (hereinafter, "NR gNB" or "NR base station") 1c-10 and a new radio core network (NRCN) 1c-05. The user terminal (new radio user equipment, hereinafter, "NR UE" or "terminal") 1c-15 is connected to an external network through the NR gNB 1c-10 and the NR CN 1c-05.

[0093] exist Figure 1C , NR gNB 1c-10 corresponds to the evolved Node B (ENB) of the existing LTE system. NR gNB is connected to UE 1c-15 through a wireless channel and can provide better services than the existing Node B. In the next generation mobile communication system, all user services are provided through a shared channel. Therefore, a device for collecting and scheduling status information of UE (such as buffer status, available transmission power status, channel status, etc.) is required, and NR gNB 1c-10 is used as such a device. One NR gNB can generally control multiple cells. In order to achieve ultra-high-speed data transmission compared with the existing LTE, NR gNB can have an existing maximum bandwidth or more, and in addition, beamforming technology can be applied by using orthogonal frequency division multiplexing (OFDM) as a radio access technology. In addition, 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 terminal is applied. NR CN 1c-05 performs functions such as mobility support, bearer configuration, and quality of service (QoS) configuration. NR NC is a device for performing various types of control functions in addition to the mobility management function for the terminal, and is connected to multiple base stations. In addition, the next generation mobile communication system can interwork with the existing LTE system, and the NR CN is connected to the MME 1c-25 through a network interface. The MME is connected to the existing base station ENB1c-30.

[0094] Figure 1D A wireless protocol architecture in a next generation mobile communication system to which the present disclosure can be applied according to an embodiment of the present disclosure is shown.

[0095] refer to Figure 1D The wireless protocols of the next generation mobile communication system include NRSDAP 1d-01 and 1d-45, NR PDCP 1d-05 and 1d-40, NR RLC 1d-10 and 1d-35, and NR MAC 1d-15 and 1d-30 in the terminal and NR base station respectively.

[0096] The main functions of NR SDAP 1d-01 and 1d-45 may include some of the following functions:

[0097] - User plane data delivery

[0098] - Mapping between QoS flows and Data Radio Bearers (DRBs) for DL ​​and UL

[0099] -Mark QoS flow ID in DL and UL packets

[0100] - Reflected QoS flow to DRB mapping for UL SDAP PDU.

[0101] Regarding the SDAP layer device, the configuration of whether to use the header of the SDAP layer device for each PDCP layer device, each bearer or each logical channel or whether to use the function of the SDAP layer device is given to the terminal through the RRC message. When the SDAP header is configured, the AS QoS reflection configuration 1-bit indicator (AS reflection QoS) and NAS QoS reflection configuration 1-bit indicator (NAS reflection QoS) of the SDAP header can be used to indicate that the terminal updates or reconfigures the mapping information of the data bearer and QoS flow for each of the downlink and uplink. The SDAP header may include QoS flow ID information indicating QoS. QoS information can be used as data processing priority, scheduling information, etc. for supporting smooth services.

[0102] The main functions of NR PDCP 1d-05 and 1d-40 may include some of the following functions:

[0103] -Header compression and decompression: ROHC only

[0104] -Transfer of user data

[0105] - In-sequence delivery of upper layer PDUs

[0106] - Out-of-order delivery of upper layer PDUs

[0107] - Reordering of received PDCP PDUs

[0108] - Duplicate detection of lower layer SDU

[0109] -Retransmission of PDCP SDU

[0110] -Encryption and decryption

[0111] - Timer-based SDU discard in uplink

[0112] The reordering function of the NR PDCP device in the above functions refers to the function of rearranging the PDCP PDUs received at the lower layer in sequence based on the PDCP sequence number (PDCP SN), and may include the function of transmitting data to the upper layer in the order of arrangement, or may include the function of transmitting immediately regardless of the order, may include the function of recording the lost PDCP PDU by reordering, may include the function of sending a status report of the lost PDCP PDU to the sender, and may include the function of requesting retransmission of the lost PDCP PDU.

[0113] The main functions of NR RLC 1d-10 and 1d-35 may include some of the following functions:

[0114] - Delivery of upper layer PDU

[0115] - In-sequence delivery of upper layer PDUs

[0116] - Out-of-order delivery of upper layer PDUs

[0117] - Error correction via ARQ

[0118] - RLC SDU splicing, segmentation and reassembly

[0119] - Re-segmentation of RLC data PDU

[0120] - Reordering of RLC data PDUs

[0121] - Duplicate detection

[0122] -Protocol error detection

[0123] -RLC SDU discarded

[0124] -RLC reconstruction

[0125] The in-sequence delivery function of the NR RLC device refers to a function of delivering the RLC SDU received from the lower layer to the upper layer in sequence. When the original RLC SDU is divided into multiple RLC SDUs and the RLC SDUs are received, the in-sequence delivery function may include reassembling and delivering the received RLC PDU; a function of rearranging the received RLC PDUs based on the RLC SN (sequence number) or the PDCP SN (sequence number), a function of recording the lost RLC PDUs by reordering, a function of sending a status report of the lost RLC PDUs to the sender, a function of requesting retransmission of the lost RLC PDUs, a function of delivering only the RLC SDUs before the lost RLC SDUs to the upper layer in sequence if there are lost RLC SDUs; or a function that when the timer expires, all RLC SDUs received before the start of the timer or until that time are delivered to the upper layer in sequence even if there are lost RLC SDUs. In addition, the RLC PDUs may be processed in the order in which the RLC PDUs are received (in the order of arrival, regardless of the sequence number order), and the processed RLC PDUs may be delivered to the PDCP device regardless of the order (out-of-order delivery). In the case of segmentation, the segments stored or to be received later may be received, reconfigured into one integrated RLC PDU, processed, and delivered to the PDCP device. The NR RLC layer may not include a splicing function. The splicing function may be performed in the NR MAC layer, or may be replaced by a multiplexing function of the NR MAC layer.

[0126] The out-of-order delivery function of the NR RLC device refers to a function of directly delivering the RLC SDU received from the lower layer to the upper layer without considering the order. When the original one RLC SDU is divided into multiple RLC SDUs and the RLC SDUs are received, the out-of-order delivery function may include a function of reassembling and transmitting the RLC SDUs, and may include a function of storing the RLC SN or PDCP SN of the received RLC PDU and recording the lost RLC PDU by reordering.

[0127] NR MAC 1d-15 and 1d-30 can be connected to various NR RLC layer devices included in one terminal, and the main functions of NR MAC can include some of the following functions.

[0128] - Mapping between logical channels and transport channels

[0129] -Multiplexing / demultiplexing of MAC SDU

[0130] -Dispatch information report

[0131] - Error correction through HARQ

[0132] - Priority handling between logical channels of a UE

[0133] - Priority handling between UEs through dynamic scheduling

[0134] -MBMS service identification

[0135] -Transmission format selection

[0136] -filling

[0137] NR PHY layers 1d-20 and 1d-25 may encode and modulate an upper layer data channel into an OFDM symbol and send the symbol through a wireless channel, or may demodulate and channel-decode an OFDM symbol received through a wireless channel and transmit it to an upper layer.

[0138] The bearers in the present disclosure may include SRBs and DRBs, SRBs are signaling radio bearers, and DRBs are data radio bearers. UM DRBs are DRBs using an RLC layer device operating in unacknowledged mode (UM), and AM DRBs are DRBs using an RLC layer device operating in acknowledged mode (AM). SRB0 is an SRB that has not yet been encrypted, and is a bearer configured in the MCG of the terminal, through which the terminal exchanges RRC messages with the base station. SRB1 is an encrypted SRB, and is a bearer configured in the MCG of the terminal, through which the terminal and the base station configure the connection therebetween and exchange RRC messages related to NAS. SRB2 is an encrypted SRB, and is a bearer configured in the MCG of the terminal, through which the terminal exchanges RRC messages for primary connection configuration with the base station. SRB3 is an encrypted SRB, and is a bearer configured in the SCG of the terminal, through which the terminal can send RRC messages directly to the MCG via the SCGMAC layer device. A split SRB is an SRB through which one PDCP layer device is located in an MCG or SCG, two RLC layer devices are connected to the one PDCP layer device and perform data transmission / reception, one RLC layer device is connected to the MCG MAC layer device, and the other RLC layer device is connected to the SCG MAC layer device.

[0139] Figure 1E A process according to an embodiment of the present disclosure is shown, wherein in the next generation mobile communication system of the present disclosure, the terminal switches from RRC idle mode or RRC inactive mode to RRC connected mode, and the base station configures carrier aggregation or dual connectivity for the terminal.

[0140] refer to Figure 1E, due to a predetermined reason, the base station may switch a terminal that is in RRC connected mode and has configured a connection to the network to RRC idle mode or RRC inactive mode. The predetermined reason may include lack of scheduling resources, stopping sending / receiving data to / from the terminal for a predetermined time, etc.

[0141] The base station may send an RRCRelease message to the terminal to instruct the terminal to switch to the RRC idle mode or the RRC inactive mode. By including an indicator (suspend-config) in the RRCRelease message, the base station may instruct the terminal to switch to the RRC inactive mode. When the indicator (suspend-config) is not included in the RRCRelease message, the base station may switch the terminal to the RRC idle mode (operation 1e-05).

[0142] When connection to the network is required due to a predetermined reason, the terminal that has switched to RRC idle mode or RRC inactive mode can send a random access preamble to perform a random access procedure, can receive a random access response, can request RRC connection configuration, and can receive an RRC message, and perform RRC connection configuration (operations 1e-10, 1e-15, 1e-20, 1e-25, 1e-30, 1e-35 and 1e-40).

[0143] The terminal may establish reverse transmission synchronization with the base station through a random access procedure, and may send an RRCSetupRequest message or an RRCResumeRequest message (when the terminal is in the RRC inactive mode) to the base station (operation 1e-25). The RRCSetupRequest message or the RRCResumeRequest message (when the terminal is in the RRC inactive mode) may include a cause for establishing a connection (establishmentCause) with an identifier of the terminal.

[0144] The base station may send an RRCSetup message or an RRCResume message (when the terminal is in the RRC inactive mode) to enable the terminal to configure the RRC connection (operation 1e-30). The RRCSetup message or the RRCResume message (when the terminal is in the RRC inactive mode) may include at least one of configuration information of each logical channel, configuration information of each bearer, configuration information of the PDCP layer device, configuration information of the RLC layer device, and configuration information of the MAC layer device.

[0145] The RRCSetup message or the RRCResume message (when the terminal is in the RRC inactive mode) can allocate a bearer identifier (e.g., an SRB identifier or a DRB identifier) ​​to each bearer, and can indicate the configuration of the PDCP layer device, the RLC layer device, the MAC device, and the PHY layer device for each bearer.

[0146] The terminal that has configured the RRC connection may send an RRCSetupComplete message or an RRCResumeComplete message (when the terminal is in RRC inactive mode) to the base station (operation 1e-40). The RRCSetupComplete message or the RRCResumeComplete message (when the terminal is in RRC inactive mode) may include a control message called SERVICE REQUEST, in which the terminal requests the bearer configuration of a predetermined service from the AMF or MME. The base station may send a SERVICE REQUEST message included in the RRCSetupComplete message or the RRCResumeComplete message (when the terminal is in RRC inactive mode) to the AMF or MME. The AMF or MME may determine whether to provide the service requested by the terminal.

[0147] When the AMF or MME has determined to provide the service requested by the terminal, the AMF or MME may send an INITIALCONTEXT SETUP REQUEST message to the base station. The INITIALCONTEXT SETUP REQUEST message may include quality of service (QoS) information to be applied to the data radio bearer (DRB) configuration and security-related information (e.g., security keys and security algorithms) to be applied to the DBR.

[0148] In order to configure security with the terminal, the base station may send and receive a SecurityModeCommand message and a SecurityModeComplete message to complete the security configuration. When the security configuration is completed, the base station may send an RRCConnectionReconfiguration message to the terminal (operation 1e-45).

[0149] The RRCConnectionReconfiguration message may allocate a bearer identifier (eg, an SRB identifier or a DRB identifier) ​​to each bearer, and may indicate configurations of a PDCP layer device, an RLC layer device, a MAC layer device, and a PHY layer device with respect to each bearer.

[0150] In addition, the RRCConnectionReconfiguration message may configure an additional Scell ​​in order to configure carrier aggregation for the terminal, or may configure additional SCG configuration information in order to configure dual connectivity.

[0151] In addition, the RRCConnectionReconfiguration message may include configuration information of the DRB through which the user data is to be processed. The terminal may configure the DBR by applying the information, and may send an RRCConnectionReconfigurationComplete message to the base station (operation 1e-50). The base station that has completed the DRB configuration with the terminal sends an INITIAL CONTEXT SETUP COMPLETE message to the AMF or MME, and may complete the connection (operation 1e-50).

[0152] When all the above processes are completed, the terminal can send data to and receive data from the base station through the core network. According to some embodiments, the data transmission process may include three steps: RRC connection configuration; security configuration; and DRB configuration. In addition, the base station may send an RRC Connection Reconfiguration message to the terminal to update, add or change the configuration for a predetermined reason. For example, the base station may perform a configuration for adding, releasing or changing a Scell ​​in carrier aggregation, and may change or add an SCG configuration in a dual connection.

[0153] The process of configuring carrier aggregation or dual connection for the terminal by the base station as described above can be summarized as follows. First, when the terminal configures the connection to the base station and the base station configures the frequency measurement configuration information with respect to the terminal in the RRC connection mode, the terminal can measure the frequency based on the frequency measurement configuration information, and can report the measurement result to the base station. In order to configure carrier aggregation for the terminal, the base station can configure the configuration information about the additional Scell ​​as an RRC message based on the frequency measurement result reported from the terminal, and can send a MAC CE to make the Scell ​​active, idle or inactive. In addition, the base station can configure the additional cell group (secondary cell group) configuration information based on the frequency measurement result reported from the terminal to configure dual connection for the terminal.

[0154] Figure 1F The architecture of a protocol layer device of a terminal configured with dual connectivity according to an embodiment of the present disclosure is shown.

[0155] refer to Figure 1FWhen the base station configures the SCG configuration information for the dual connectivity of the terminal, the terminal may consider the bearer identifier and the logical identifier corresponding to the SCG, such as Figure 1F The SCG is shown to establish a PDCP layer device or an RLC layer device. Therefore, in the terminal, a MAC layer device 1f-15 for the MCG and a MAC layer device 1f-20 for the SCG can be configured respectively, and an RLC layer device and a PDCP layer device corresponding to each of the MCG and the SCG can be configured. In addition, a separate SRB or a separate DRB can have an architecture in which one PDCP layer device, such as reference numeral 1f-30, belongs to the MCG or the SCG, and two different RLC layer devices are connected to the MCG MAC layer device and the SCG MAC layer device.

[0156] In the case of a base station, a base station corresponding to an MCG may be configured to have the same layer architecture as the protocol layer device architecture of an MCG for a terminal, and a base station corresponding to an SCG may be configured to have the same layer architecture as the protocol layer device architecture of an SCG for a terminal.

[0157] In the first embodiment, as shown in FIG. 1 , it is considered that a terminal for which dual connectivity has been configured maintains a connection with a base station (or cell) in an MCG and fails to establish a wireless connection with a base station (or cell) in an SCG.

[0158] It can be determined that the radio link failure in the SCG can be determined to be due to one of the following reasons.

[0159] 1. When a timer (e.g., T310) is started in the Pscell by indicating a signal synchronization mismatch in the RRC layer device SCG physical (PHY) layer device, and the timer has expired,

[0160] 2. When integrity verification fails in SRB3,

[0161] 3. When the RRC layer device is indicated that a random access problem has occurred in the SCG MAC layer device and a predetermined timer (e.g., T300, T301, T304, T311, or T319) is not operating, and

[0162] 4. When the number of retransmissions in the AM RLC layer device connected to the SCG MAC layer device has reached the maximum number of retransmissions, the packet replication technology has not been configured in the RLC layer device (configured as carrier aggregation or dual connectivity), and only the mapping (allowedServingCell) for sending / receiving to / from the logical channel corresponding to the RLC layer device is configured in the Scell.

[0163] If, due to one of the above reasons, the terminal in which dual connectivity has been configured maintains connection with the base station (or cell) in the MCG but fails to establish a wireless connection with the base station (or cell) in the SCG, the following operations of the terminal are proposed, so that the terminal can continuously send / receive data in the MCG, and can restore the SCG, replace the SCG with another SCG, or release the SCG in which the radio link failure has occurred. In addition, when data transmission / reception through the SCG is not stopped, if a radio link failure is detected, the terminal may be allowed to perform the following operations.

[0164] -When the RRC layer device is indicated that the signal synchronization in the SCG physical (PHY) layer device is mismatched, a timer (e.g., T310) is started in the Pscell, and when the timer expires,

[0165] -When the RRC layer device is indicated that a random access problem has occurred in the SCG MAC layer device and a predetermined timer (e.g., T300, T301, T304, T311, or T319) is not operating,

[0166] -When integrity verification fails in SRB3,

[0167] -When the number of retransmissions in the AM RLC layer device connected to the SCG MAC layer device has reached the maximum number of retransmissions,

[0168] ■If the send / receive mapping of the logical channels corresponding to / from the RLC layer device is configured only in the Scell ​​(allowedServingCell),

[0169] ◆The terminal is not sure that an SCG radio link failure has occurred, and can send failure information to the base station to report that the RLC layer device has failed. Specifically, the failure information may include an indicator indicating the cell group (MCG or SCG) to which the failed RLC layer device belongs, a logical channel identifier, and a failure type (for example, the maximum number of retransmissions has been reached). When the failure occurs in an RLC layer device connected to an SCG MAC layer device, if dual connectivity to an LTE base station and an NR base station or to an NR base station and an NR base station is configured in the terminal, and SRB3 (or separate SRB) is configured, the terminal can report the failure of the SCG RLC layer device to the MCG base station through SRB3 (or separate SRB). If dual connectivity is not configured or SRB3 (or separate SRB) is not configured, the terminal can include the failure information in an RRC message in the MCG MAC layer device, and can send the RRC message to the base station. In addition, measurement results of other frequencies can be included in the failure information and sent, so that the base station can use the measurement results to quickly configure a novel Scell ​​or a novel SCG.

[0170] ■When the mapping of transmission / reception to / from the logical channel corresponding to the RLC layer device (allowedServingCell) is not configured only in the Scell, or in other cases,

[0171] ◆Consider that a radio link failure (Radio Link Failure (RLF)) occurs in the SCG.

[0172] ◆In addition, the terminal can report the SCG radio link failure to the base station. Specifically, since the terminal has detected the SCG radio link failure, the terminal can stop transmission to the SCG base station with respect to all configured SRBs or DRBs. The SCG MAC layer device is initialized. When timer 304 (a timer operating in the case of switching) is operating, timer 304 can be stopped (because, during switching, for example, in the case of SCG change, SCG radio link failure can be detected). The terminal can indicate the type of SCG radio link failure (for example, exceeding the maximum number of RLC retransmissions, integrity verification failure, or synchronization mismatch, or timer expiration), form an SCG radio link failure message, and can report the SCG radio link failure to the MCG base station via the SRB connected to the MCG MAC layer device. In addition, measurement results of other frequencies can be included in the failure information and sent so that they are available when the base station quickly configures a novel Scell ​​or a novel SCG.

[0173] As described above, when a terminal that has been configured with dual connectivity maintains a connection with a base station (or cell) in the MCG but fails to establish a wireless connection with a base station (or cell) in the SCG, the terminal is configured to: continuously send / receive data in the MCG; and report the SCG radio link failure to the MCG base station so that the base station can restore the SCG or replace the SCG with another SCG, or release the SCG in which the radio link failure has occurred, thereby enabling continuous data transmission.

[0174] When an SCG radio link failure is reported, the MCG base station may restore the SCG of the terminal, may replace the SCG with another SCG, or may send configuration information through an RRC message via an SRB (e.g., SRB1 or SRB2) of an MCG MAC layer device connected to the terminal, so that the terminal releases the SCG in which the radio link failure has occurred. Specifically, the MCG base station may instruct the terminal to release the existing SCG configuration information, may send novel SCG configuration information to notify the random access information to be used in the random access process, so that the terminal is configured to connect to the novel SCG, or may notify the random access information to be used in the random access process, so that the terminal attempts to reconnect to the existing SCG.

[0175] In the second embodiment, if Figure 1F As shown, it is considered that the terminal that has been configured with dual connectivity maintains a connection with a base station (or cell) in the SCG and fails to establish a connection with a base station (or cell) in the MCG.

[0176] It can be determined that the radio link failure in the MCG can be determined to be due to one of the following reasons.

[0177] 1. When a timer (e.g., T310) is started in the Pcell by indicating a signal synchronization mismatch in the RRC layer device MCG physical (PHY) layer device, and the timer has expired,

[0178] 2. When integrity verification fails in SRB1 or SRB2,

[0179] 3. When the RRC layer device is indicated that a random access problem has occurred in the MCG MAC layer device and a predetermined timer (e.g., T300, T301, T304, T311, or T319) has not operated, and

[0180] 4. When the number of retransmissions in the AM RLC layer device connected to the MCG MAC layer device has reached the maximum number of retransmissions, the packet replication technology has not been configured in the RLC layer device (configured as carrier aggregation or dual connectivity), and only the mapping (allowedServingCell) for sending / receiving to / from the logical channel corresponding to the RLC layer device is configured in the Scell.

[0181] If, due to one of the above reasons, the terminal in which dual connectivity has been configured maintains connection with the base station (or cell) in the SCG but fails to establish connection with the base station (or cell) in the MCG, the following operations of the terminal are proposed so that the terminal can continuously send / receive data in the SCG, and can restore the MCG, replace the MCG with another MCG, release the MCG in which the radio link failure occurs, or switch the SCG currently maintaining connection to the MCG. In addition, when data transmission / reception through the MCG is not stopped, if a radio link failure is detected, the terminal can be allowed to perform the following operations.

[0182] -When the RRC layer device is indicated that the signal synchronization in the MCG physical (PHY) layer device does not match, a timer (e.g., T310) is started in the Pcell, and when the timer expires,

[0183] - When the RRC layer device is indicated that a random access problem has occurred in the MCG MAC layer device and a predetermined timer (e.g., T300, T301, T304, T311, or T319) is not operating,

[0184] -When integrity verification fails in SRB1 or SRB2,

[0185] -When the number of retransmissions in the AM RLC layer device connected to the MCG MAC layer device has reached the maximum number of retransmissions,

[0186] ■If the send / receive mapping of the logical channels corresponding to / from the RLC layer device is configured only in the Scell ​​(allowedServingCell),

[0187] ◆The terminal is not sure that an MCG radio link failure has occurred, and can send failure information to the base station to report that the RLC layer device has failed. Specifically, the failure information may include an indicator indicating the cell group (MCG or SCG) to which the failed RLC layer device belongs, a logical channel identifier, and a failure type (for example, the maximum number of retransmissions has been reached). When a failure occurs in the RLC layer device connected to the MCG MAC layer device, the terminal may include the failure information in the RRC message in the MCG MAC layer device, and may send the RRC message to the base station via SRB1. In addition, measurement results of other frequencies may be included in the failure information and sent so that they are available when the base station quickly configures a novel Scell ​​or a novel SCG.

[0188] ■When the mapping of transmission / reception to / from the logical channel corresponding to the RLC layer device (allowedServingCell) is not configured only in the Scell, or in other cases,

[0189] ◆Consider that a radio link failure (Radio Link Failure (RLF)) occurs in the MCG.

[0190] ◆If the AS security configuration is not activated (when a connection failure occurs during RRC connection configuration), or if the AS security configuration is activated but SRB2 and at least one DRB are not configured (when a full RRC connection is not configured), the terminal can switch to RRC idle mode.

[0191] Otherwise,

[0192] ●If the terminal is configured with dual connectivity, the SCG does not stop transmission and data sending / reception is possible, and if the terminal is configured with: separate SRBs (for example, separate SRB1) of an MCG MAC layer device (wherein the PDCP layer device is in the MCG) and an SCG MAC layer device connected to the MCG base station and connected to the terminal; and SRBs (for example, SRB3) connected to the SCG base station and connected to the SCG MAC layer device (wherein the PDCP layer device is in the SCG), the terminal may perform one of the following methods.

[0193] ■Method 1: The terminal may report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station may notify the MCG base station of the MCG radio link failure of the terminal). Specifically, since the terminal has detected the MCG radio link failure, the terminal may stop sending all SRBs or DRBs configured in the configured MCG to the MCG base station. The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized, and data transmission / reception may continue to be performed. If timer T304 (a timer operating in a handover situation) is operating, timer T304 may be stopped (because during handover, a radio link failure may be detected). The terminal can indicate the type of MCG radio link failure (for example, exceeding the maximum number of RLC retransmissions, integrity verification failure, or synchronization mismatch, or timer expiration), form an MCG radio link failure message, and can report the MCG radio link failure to the MCG base station or SCG base station through a separate SRB connected to the SCG MAC layer device (for example, separate SRB1) or through an SRB connected to the SCG MAC layer device (for example, SRB3). In addition, measurement results of other frequencies can be included in the failure information and sent so that they are available when the base station quickly configures a novel cell (for example, Pcell) or a novel cell group (for example, MCG). In addition, the radio link failure information can indicate the cause of the failure. Method 1 is a method in which the terminal indicates MCG failure information so that the base station can restore or change the MCG indicated by the radio link failure. Method 1 enables the terminal to solve the radio link failure problem based on the MCG base station or SCG base station.

[0194] ■Method 2: Since the terminal has detected the MCG radio link failure, the terminal can stop the transmission of all SRBs or DRBs to the MCG base station except the configured SRB0 (SRB0 must send an RRC re-establishment message, and the transmission of SRB0 cannot be stopped). The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized, and data transmission / reception can continue to be performed. If timer T304 (a timer operating in a handover situation) is operating, timer T304 can be stopped (because during the handover, a radio link failure can be detected). The terminal can trigger the RRC connection re-establishment process for the MCG base station. When an RRC connection re-establishment request message is sent during this process, the terminal can indicate that a radio link failure has occurred. In addition, the radio link failure information can indicate the cause of the failure. Method 2 enables the terminal to identify the MCG failure information and resolve the MCG failure problem by itself.

[0195] ■Method 3: Since the terminal has detected the MCG radio link failure, the terminal can stop transmitting all configured SRBs or DRBs to the MCG base station. The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized, and data transmission / reception can continue to be performed. If timer T304 (a timer operating in a switching case) is operating, timer T304 can be stopped (because during the switching, a radio link failure can be detected). The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, the terminal can trigger an RRC connection reestablishment process for the MCG base station or the SCG base station. When an RRC connection reestablishment request message is sent in this process, the terminal can indicate to the MCG base station or the SCG base station that an MCG radio link failure has occurred. When the MCG connection reestablishment request message is sent in this process, the terminal may indicate that an MCG radio link failure has occurred by connecting to a separate SRB (e.g., separate SRB1) connected to the SCG MAC layer device or by connecting to an SRB (e.g., SRB3 or SRB0) connected to the SCG MAC layer device. In addition, the radio link failure information may indicate the cause of the failure. Method 3 is a method in which the terminal indicates MCG failure information by separating SRB1 or SRB3 so that the base station can restore or change the MCG indicated for the radio link failure. Method 3 enables the terminal to resolve the radio link failure problem based on the MCG base station or the SCG base station.

[0196] ■Method 4: Since the terminal has detected the MCG radio link failure, the terminal can stop the transmission of all SRBs or DRBs except the configured SRB0 to the MCG base station (SRB0 must send an RRC re-establishment message and the transmission of SRB0 cannot be stopped). The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized and data transmission / reception can continue to be performed. If timer T304 (a timer operating in a handover situation) is operating, timer T304 can be stopped (because during the handover, a radio link failure can be detected). The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, the terminal can trigger the RRC connection re-establishment process for the MCG base station or the SCG base station. That is, the terminal can reside on a cell in which a good signal can be obtained through a cell reselection process, and then send an RRC connection reestablishment request message through SRB0, and an indicator can be used to indicate to the MCG base station or SCG base station that an MCG radio link failure has occurred. In addition, the radio link failure information can indicate the cause of the failure. Method 4 is a method in which the terminal indicates MCG failure information through SRB0 so that the base station can restore or change the MCG indicated by the radio link failure. Method 4 enables the terminal to solve the radio link failure problem based on the MCG base station or SCG base station.

[0197] ● If the terminal is not configured with dual connectivity, the SCG stops transmission and data transmission / reception is not possible, and if the terminal is not configured with an SRB connected to the SCG base station or a detached SRB (e.g., detached SRB1), or in other cases,

[0198] ■Since the terminal has detected the MCG radio link failure, the terminal can stop the transmission of all SRBs or DRBs except the configured SRB0 to the MCG base station (SRB0 must send an RRC re-establishment message, and the transmission of SRB0 cannot be stopped). The MCG MAC layer device is initialized. In addition, all bearers (SRBs or DRBs) configured in the SCG are stopped, and the SCG MAC layer device is also initialized. The SCG bearer and SCG configuration information are released. If timer T304 (a timer operating in a handover situation) is operating, timer T304 can be stopped (because during the handover, a radio link failure can be detected). The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, the terminal can trigger the RRC connection re-establishment process for the MCG base station or the SCG base station. That is, the terminal can reside on a cell where a good signal can be obtained through a cell reselection process, and then send an RRC connection reestablishment request message through SRB0, and an indicator can be used to indicate to the MCG base station or SCG base station that an MCG radio link failure has occurred. In addition, the radio link failure information can indicate the cause of the failure.

[0199] As described above, when a terminal that has been configured with dual connectivity maintains a connection with a base station (or cell) in an SCG but fails to establish a wireless connection with a base station (or cell) in an MCG, the terminal is configured to: continuously send / receive data in the MCG; and report the MCG radio link failure to the MCG base station or the SCG base station, so that the base station can restore the MCG, can release the MCG in which the radio link failure has occurred, and add a novel cell group to use it as an MCG, or can use the SCG in which the wireless connection is currently maintained as the MCG, thereby enabling continuous data transmission.

[0200] When an MCG radio link failure is reported, the MCG base station, the SCG base station, or the novel base station (in the case where the RRC connection reestablishment process has been performed using the novel base station after cell reselection) can restore the MCG of the terminal, can release the MCG in which the radio link failure has occurred, and add a novel cell group to be used as the MCG, or can send configuration information through a detached SRB (e.g., detached SRB1 or detached SRB2) connected to the SCG MAC layer device of the terminal or an SRB (e.g., SRB3) connected to the SCG MAC layer device, or through SRB0 connected to the MCG MAC layer device, by means of an RRC message, so that the terminal can use the SCG that currently maintains the wireless connection as the MCG. Specifically, the base station can instruct the terminal to release the existing MCG configuration information, can send novel cell group configuration information and notify the random access information to be used in the random access process, so as to instruct the terminal to configure the connection to the novel cell group and use the novel cell group as the MCG, or can notify the random access information to be used in the random access process, so that the terminal attempts to reconnect to the existing MCG. In another method, the base station may include information indicating that the terminal regards the SCG configuration information previously configured for the terminal as the MCG in the RRC message, and the RRC message may be sent through a separate SRB (e.g., separate SRB1 or separate SRB2) connected to the MCG MAC layer device of the terminal or an SRB (e.g., SRB3) connected to the SCG MAC layer device or through SRB0 connected to the MCG MAC layer device. Therefore, a cell that is already a Pscell may be regarded as a Pcell, and when the role of an existing SCG is changed to that of an MCG in its role, the base station may perform configuration so that another cell group is added as an SCG, thereby reconfiguring dual connectivity.

[0201] Figure 1G The architecture of a protocol layer device of a terminal configured with carrier aggregation in the present disclosure according to an embodiment of the present disclosure is shown.

[0202] refer to Figure 1G , when the base station configures Scell ​​configuration information, bearer configuration information and protocol layer device configuration information so as to refer to Figure 1EWhen carrier aggregation is configured for the terminal as described above, the terminal can establish a PDCP layer device, an RLC layer device, or a MAC layer device. Therefore, the terminal can configure a MAC layer device 1g-15 for a Pcell 1g-01 and multiple Scells 1g-02 and 1g-03. The MAC layer device can divide multiple RLC layer devices connected to the MAC layer device by a logical channel identifier, can multiplex various types of data received from multiple RLC layer devices, and form the multiplexed data into one type of data, and can send the one type of data to the Pcell or Scell. For the base station, the same architecture as the protocol architecture of the terminal can be configured.

[0203] The third embodiment considers a case in which a terminal for which carrier aggregation has been configured maintains connection to a base station (or cell) and fails to make a wireless connection with a base station (or cell) in a Pcell.

[0204] It can be determined that the radio link failure in the Pcell is caused by one of the following reasons.

[0205] 1. When a timer (e.g., T310) is started in the Pcell by indicating a signal synchronization mismatch in the RRC layer device MCG physical (PHY) layer device, and the timer has expired,

[0206] 2. When integrity verification fails in SRB1 or SRB2,

[0207] 3. When the RRC layer device is indicated that a random access problem has occurred in the MCG MAC layer device and a predetermined timer (e.g., T300, T301, T304, T311, or T319) is not operating, and

[0208] 4. When the number of retransmissions in the AM RLC layer device connected to the MCG MAC layer device has reached the maximum number of retransmissions, the packet replication technology has not been configured in the RLC layer device (configured as carrier aggregation or dual connectivity), and only the mapping (allowedServingCell) for sending / receiving to / from the logical channel corresponding to the RLC layer device is configured in the Scell.

[0209] If, due to one of the above reasons, a terminal in which carrier aggregation has been configured maintains a connection with a base station (or cell) in the Scell ​​but fails to establish a wireless connection with a base station (or cell) in the Pcell, the following specific operations of the terminal are proposed so that the terminal can continuously send / receive data in the Scell, and can restore the Pcell, replace the Pcell with another Pcell, release the Pcell in which a radio link failure occurs, or switch the currently connected Scell ​​to the Pcell. In addition, when data transmission / reception through the SCG is not stopped, if a radio link failure is detected, the terminal may be allowed to perform the following operations. In order to report or indicate a radio link failure in a Pcell through a Scell ​​as proposed in the present disclosure, a Scell ​​that satisfies multiple of the following conditions must be configured in the terminal. That is, reporting of a radio link failure in a Pcell is allowed only for a Scell ​​that satisfies multiple of the following conditions.

[0210] - First condition: Scell ​​must be configured as a separate timing advance group (sTAG) different from Pcell. The reason is that when Scell ​​is configured as a Pcell timing advance group (pTAG), since Pcell radio link failure has occurred, radio link failure may also occur in Scell ​​referring to Pcell.

[0211] - Second condition: In the Scell, both uplink and downlink must be configured. The reason is that in order to report a Pcell radio link failure, the uplink must be configured and additional configuration information must be received via the downlink.

[0212] - Third condition: In Scell, PUCCH must be configured. PUCCH must be configured to report Pcell radio link failure, receive additional configuration information message, and then indicate HARQ ACK / NACK information, or report PHR.

[0213] - Fourth condition: Scell ​​must be activated. The reason is that only when the Scell ​​is activated, data transmission / reception can be performed through uplink and downlink.

[0214] - Fifth condition: An activated bandwidth part (BWP) must be configured in the Scell. In addition, in order to match signal synchronization, there may be a SSB in the activated BWP.

[0215] - Sixth condition: As disclosed in the present invention Figure 1EIn the present invention, when the base station configures the cell configuration information through the RRC message, the base station can use the indicator to indicate a specific Scell. In the specific Scell, when a connection failure occurs in the MCG (or Pcell) or SCG (or Pscell), the MCG (or Pcell) or SCG (or Pscell) connection failure can be reported.

[0216] The third embodiment proposes a specific terminal operation, in which, when a terminal in which carrier aggregation has been configured maintains a wireless connection with a base station (or cell) in a Scell ​​but fails to establish a connection with a base station (or cell) in a Pcell, the terminal continues to send / receive data in the Scell ​​and reports a Pcell radio link failure to a specific Scell, so that the Pcell can be restored or replaced by another Pcell, the Pcell in which the radio link failure occurs can be released, or the Scell ​​that currently maintains the connection can be switched to the Pcell.

[0217] -When a timer (e.g., T310) is started in the Pcell by indicating a signal synchronization mismatch in the RRC layer device MCG physical (PHY) layer device, and the timer has expired,

[0218] - When the RRC layer device is indicated that a random access problem has occurred in the MCG MAC layer device and a predetermined timer (e.g., T300, T301, T304, T311, or T319) is not operating,

[0219] - When an integrity verification failure occurs in SRB1 or SRB2, and

[0220] -When the number of retransmissions in the AM RLC layer device connected to the MCG MAC layer device has reached the maximum number of retransmissions,

[0221] ■If the mapping of transmission / reception to / from the logical channel corresponding to the RLC layer device is configured only in the Scell ​​(allowedServingCell),

[0222] ◆The terminal is not sure that an MCG radio link failure has occurred, and can send failure information to the base station to report that the RLC layer device has failed. Specifically, the failure information may include an indicator indicating the cell group (MCG or SCG) to which the failed RLC layer device belongs, a logical channel identifier, and a failure type (for example, the maximum number of retransmissions has been reached). When a failure occurs in the RLC layer device connected to the MCGMAC layer device, the terminal may include the failure information in the RRC message in the MCG MAC layer device, and may send the RRC message to the base station via SRB1. In addition, measurement results of other frequencies may be included in the failure information and sent so that they are available when the base station quickly configures a novel Scell ​​or a novel SCG.

[0223] ■When the mapping of transmission / reception to / from the logical channel corresponding to the RLC layer device (allowedServingCell) is not configured only in the Scell, or in other cases,

[0224] ◆Consider that a radio link failure (Radio Link Failure (RLF)) occurs in the MCG.

[0225] ◆If the AS security configuration is not activated (when a connection failure occurs during RRC connection configuration), or if the AS security configuration is activated but SRB2 and at least one DRB are not configured (when a full RRC connection is not configured), the terminal can switch to RRC idle mode.

[0226] Otherwise,

[0227] ● If carrier aggregation is configured in the terminal, and there is an Scell ​​configured to satisfy the first condition, the second condition, the third condition, the fourth condition, the fifth condition or the sixth condition among the configured Scells,

[0228] ■The terminal can report the Pcell radio link failure through the Scell. Specifically, the terminal can form an RRC message for the Pcell radio link failure information, and can configure the information as data in the MCG MAC layer device by carrying SRB1 or SRB2, that is, by a logical channel identifier corresponding to SRB1 or SRB2, and can send the Pcell radio link failure information to the base station through the Scell ​​that meets multiple conditions.

[0229] ● If carrier aggregation is not configured in the terminal, and there is no Scell ​​configured to meet the first condition, the second condition, the third condition, the fourth condition, the fifth condition or the sixth condition among the configured Scells,

[0230] ■If the terminal is configured with dual connectivity, the SCG will not stop transmission and data sending / reception is possible, and if the terminal is configured with: a separate SRB (e.g., separate SRB1) connected to the MCG base station and connected to the MCG MAC layer device of the terminal (where the PDCP layer device is the MCG) and the SCG MAC layer device; or an SRB (e.g., SRB3) connected to the SCG base station and connected to the SCG MAC layer device (where the PDCP layer device is in the SCG), the terminal can perform one of the following methods.

[0231] ◆Method one: The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, since the terminal has detected the MCG radio link failure, the terminal can stop sending all SRBs or DRBs configured in the configured MCG to the MCG base station. The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized, and data transmission / reception can continue. If timer T304 (a timer operating in a switching situation) is operating, timer T304 can be stopped (because during switching, a radio link failure can be detected). The terminal can indicate the type of MCG radio link failure (for example, exceeding the maximum number of RLC retransmissions, integrity verification failure, or synchronization mismatch, or timer expiration), form an MCG radio link failure message, and can report the MCG radio link failure to the MCG base station or SCG base station through a separate SRB connected to the SCG MAC layer device (for example, separate SRB1) or through an SRB connected to the SCG MAC layer device (for example, SRB3). In addition, measurement results of other frequencies can be included in the failure information and sent so that they are available when the base station quickly configures a novel cell (for example, Pcell) or a novel cell group (for example, MCG). In addition, the radio link failure information can indicate the cause of the failure. Method 1 is a method in which the terminal indicates MCG failure information so that the base station can restore or change the MCG indicated by the radio link failure. Method 1 enables the terminal to solve the radio link failure problem based on the MCG base station or SCG base station.

[0232] ◆Method 2: Since the terminal has detected the MCG radio link failure, the terminal can stop the transmission of all SRBs or DRBs to the MCG base station except the configured SRB0 (SRB0 must send an RRC re-establishment message and the transmission of SRB0 cannot be stopped). The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized and data transmission / reception can continue to be performed. If timer T304 (a timer operating in a handover situation) is operating, timer T304 can be stopped (because during the handover, a radio link failure can be detected). The terminal can trigger the RRC connection re-establishment process for the MCG base station. When an RRC connection re-establishment request message is sent during this process, the terminal can indicate that a radio link failure has occurred. In addition, the radio link failure information can indicate the cause of the failure. Method 2 enables the terminal to identify the MCG failure information and resolve the MCG failure problem by itself.

[0233] ◆Method three: Since the terminal has detected the MCG radio link failure, the terminal can stop transmitting all configured SRBs or DRBs to the MCG base station. The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized, and data transmission / reception can continue. If timer T304 (a timer operating in a switching situation) is operating, timer T304 can be stopped (because during the switching, a radio link failure can be detected). The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, the terminal can trigger an RRC connection reestablishment process for the MCG base station or the SCG base station. When an RRC connection reestablishment request message is sent in this process, the terminal can indicate to the MCG base station or the SCG base station that an MCG radio link failure has occurred. When sending the RRC connection reestablishment request message in this process, the terminal may indicate that an MCG radio link failure has occurred by connecting to a detached SRB (e.g., detached SRB1) connected to the SCG MAC layer device or by connecting to an SRB (e.g., SRB3 or SRB0) connected to the SCG MAC layer device. In addition, the radio link failure information may indicate the cause of the failure. Method 3 is a method in which the terminal indicates MCG failure information by detaching SRB1 or SRB3 so that the base station can restore or change the MCG indicated for the radio link failure. Method 3 enables the terminal to resolve the radio link failure problem based on the MCG base station or the SCG base station.

[0234] ◆Method 4: Since the terminal has detected the MCG radio link failure, the terminal can stop the transmission of all SRBs or DRBs except the configured SRB0 to the MCG base station (SRB0 must send an RRC re-establishment message and the transmission of SRB0 cannot be stopped). The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized and data transmission / reception can continue to be performed. If timer T304 (a timer operating in a handover situation) is operating, timer T304 can be stopped (because during the handover, a radio link failure can be detected). The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, the terminal can trigger the RRC connection re-establishment process for the MCG base station or the SCG base station. That is, the terminal can reside on a cell in which a good signal can be obtained through a cell reselection process, and then send an RRC connection reestablishment request message through SRB0, and an indicator can be used to indicate to the MCG base station or SCG base station that an MCG radio link failure has occurred. In addition, the radio link failure information can indicate the cause of the failure. Method 4 is a method in which the terminal indicates MCG failure information through SRB0 so that the base station can restore or change the MCG indicated by the radio link failure. Method 4 enables the terminal to solve the radio link failure problem based on the MCG base station or SCG base station.

[0235] ■ If the terminal is not configured with dual connectivity, the SCG stops transmission and data transmission / reception is not possible, and if the terminal is not configured with an SRB connected to the SCG base station or a separate SRB (e.g., separate SRB1), or in other cases,

[0236] ◆Since the terminal has detected the MCG radio link failure, the terminal can stop the transmission of all SRBs or DRBs except the configured SRB0 to the MCG base station (SRB0 must send an RRC re-establishment message, and the transmission of SRB0 cannot be stopped). The MCG MAC layer device is initialized. In addition, all bearers (SRBs or DRBs) configured in the SCG are stopped, and the SCG MAC layer device is also initialized. The SCG bearer and SCG configuration information are released. If timer T304 (a timer operating in a handover situation) is operating, timer T304 can be stopped (because during the handover, a radio link failure can be detected). The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, the terminal can trigger the RRC connection re-establishment process for the MCG base station or the SCG base station. That is, the terminal can reside on a cell where a good signal can be obtained through the cell reselection process, and then an RRC connection reconstruction request message can be sent through SRB0, and an indicator can be used to indicate to the MCG base station or SCG base station that an MCG radio link failure has occurred. In addition, the radio link failure information can indicate the cause of the failure.

[0237] As described above, when a terminal in which carrier aggregation has been configured maintains a connection with a base station (or cell) in a Scell ​​but fails to establish a wireless connection with a base station (or cell) in a Pcell, the terminal is configured to: continuously send / receive data in the Scell; and report the Pcell radio link failure to the MCG base station through a Scell ​​in the Scell ​​that satisfies multiple conditions, so that the base station can recover the Pcell, release the Pcell in which the radio link failure has occurred and add a novel cell to use it as a Pcell, or use a Scell ​​in the Scell ​​in which a wireless connection is currently maintained that satisfies multiple conditions as a Pcell, thereby achieving continuous data transmission.

[0238] When a Pcell radio link failure is reported, the MCG base station may restore the Pcell of the terminal, may release the Pcell in which the radio link failure has occurred, and add a novel cell to be used as the Pcell, or may send configuration information to the base station through an Scell ​​that satisfies multiple conditions by means of an RRC message, so that the terminal can use the Scell ​​that satisfies multiple conditions in the Scell ​​that currently maintains the wireless connection as the Pcell. Specifically, the base station may instruct the terminal to release the existing Pcell configuration information, may send new cell configuration information and notify the random access information to be used in the random access process, so as to instruct the terminal to configure a connection to the new cell and use the new cell as the Pcell, or may notify the random access information to be used in the random access process, so that the terminal attempts to reconnect to the existing Pcell. In another method, the base station may include information in the RRC message indicating that the terminal regards the Scell ​​configuration information previously configured for the terminal as the Pcell, and may send the RRC message through the Scell ​​that satisfies multiple conditions and is connected to the MCG MAC layer device of the terminal. Therefore, a cell that has been an Scell ​​may be considered as a Pcell, and when the role of an existing Scell ​​is changed to that of a Pcell, the base station may perform configuration such that another cell is added as an Scell, thereby reconfiguring carrier aggregation.

[0239] The above embodiment can also be extended and applied to the case where both carrier aggregation and dual connectivity are configured.

[0240] In the present disclosure, when reporting MCG radio link failure (or Pcell radio link failure), if both a separate SRB (e.g., SRB1) and an SRB (e.g., SRB3) connected to the SCG base station are configured, the terminal can report the MCG radio link failure through the separate SRB. The reason is that when reporting the radio link failure through the SRB connected to the SCG base station, the SCG base station must re-encapsulate the received data and transmit it to the MCG, so a processing delay may occur.

[0241] The fourth embodiment proposes a specific terminal operation, in which, when a terminal in which carrier aggregation has been configured maintains a connection with a base station (or cell) in an Scell ​​or SCG, but fails to connect with a base station (or cell) in a Pcell (or MCG), the terminal continues to send / receive data in the Scell ​​or SCG, and reports a Pcell radio link failure to a specific Scell, so that the Pcell can be restored or replaced by another Pcell, the Pcell in which the radio link failure has occurred can be released, or the Scell ​​currently maintaining the connection can be switched to the Pcell. In addition, the fourth embodiment proposes a terminal operation, which can be considered in the case where the MCG radio link failure (or Pcell connection failure) reporting process fails at the time of the MCG radio link failure (or Pcell connection failure) report. Specifically, when the MCG radio link failure (or Pcell connection failure) has occurred, if the MCG radio link failure is reported by the Scell ​​of the MCG that satisfies the first condition, the second condition, the third condition, the fourth condition, the fifth condition, or the sixth condition of the present disclosure, the terminal can define and trigger a first timer. The first timer can be configured using an RRC message, and the timer value can also be configured in the RRC message. When the MCG radio link failure report is triggered or sent, the terminal may start a first timer. If the terminal does not receive an RRC message until the first timer expires, such as an RRC message for indicating a handover to recover the MCG radio link failure, an RRC message for reestablishing the RRC connection, or an RRC message for disconnecting the MCG, the terminal may determine that the MCG radio link failure reporting process has failed, and may trigger the RRC connection reestablishment process to reestablish the MCG wireless connection (in this case, the connection configuration information about the Scell ​​or SCG may be released). During the RRC connection reestablishment process, the terminal may attempt to establish a wireless connection with a suitable Scell ​​selected through the cell reselection process, but may directly perform the RRC connection reestablishment process for a cell supported by the SCG base station configured with an effective connection. In another method, when the MCG radio link failure reporting process to the Scell ​​fails, if dual connectivity is configured and the SCG wireless connection is valid, the terminal may also trigger the MCG radio link failure reporting process to the SCG again. When the SCG radio link failure is detected during the operation of the first timer, the terminal may perform the SCG radio link failure reporting process without directly triggering the RRC connection reestablishment process.

[0242] In addition, when an MCG radio link failure (or a Pcell connection failure) has occurred, if dual connectivity is configured and the SCG wireless connection is valid (for example, when there is no MCG Scell ​​that meets the conditions or an MCG radio link failure report to the Scell ​​has been performed but failed, or when dual connectivity is configured when there is no MCG Scell ​​and the SCG is valid), the terminal may report the MCG radio link failure through the SCG, and a second timer may be defined and triggered. The second timer may be configured using an RRC message, and the timer value may also be configured in the RRC message. When the MCG radio link failure report is triggered or sent, the terminal may start the first timer. If the terminal does not receive an RRC message until the first timer expires, such as an RRC message indicating a handover to recover the MCG radio link failure, an RRC message for reestablishing the RRC connection, or an RRC message for disconnecting the MCG, the terminal may determine that the MCG radio link failure reporting process has failed, and may trigger the RRC connection reestablishment process to reestablish the MCG wireless connection (in this case, the connection configuration information about the Scell ​​or SCG may be released). When the SCG radio link failure is detected during the operation of the second timer, the terminal can directly trigger the RRC connection reestablishment process to reestablish the MCG wireless connection. During the RRC connection reestablishment process, the terminal can attempt to establish a wireless connection with a suitable Scell ​​selected through the cell reselection process, but can directly perform the RRC connection reestablishment process on the cell supported by the SCG base station configured with an effective connection to prevent connection delays caused by cell reselection.

[0243] The same timer or an existing defined timer may be the first timer and the second timer. Separate timers may be defined and used, respectively.

[0244] The specific operations proposed in the fourth embodiment are as follows.

[0245] -When a timer (e.g., T310) is started in the Pcell by indicating a signal synchronization mismatch in the RRC layer device MCG physical (PHY) layer device and the timer has expired,

[0246] - When the RRC layer device is indicated that a random access problem has occurred in the MCG MAC layer device and a predetermined timer (e.g., T300, T301, T304, T311, or T319) is not operating,

[0247] - When an integrity verification failure occurs in SRB1 or SRB2, and

[0248] -When the number of retransmissions in the AM RLC layer device connected to the MCG MAC layer device has reached the maximum number of retransmissions,

[0249] ■If the mapping of sending / receiving logical channels to / from the corresponding RLC layer device is configured only in Scell ​​(allowedServingCell),

[0250] ◆The terminal is not sure that an MCG radio link failure has occurred, and can send failure information to the base station to report that the RLC layer device has failed. Specifically, the failure information may include an indicator indicating the cell group (MCG or SCG) to which the failed RLC layer device belongs, a logical channel identifier, and a failure type (for example, the maximum number of retransmissions has been reached). When a failure occurs in the RLC layer device connected to the MCG MAC layer device, the terminal may include the failure information in the RRC message in the MCG MAC layer device, and may send an RRC message to the base station via SRB1. In addition, measurement results of other frequencies may be included in the failure information and sent so that they are available when the base station quickly configures a new Scell ​​or a new SCG.

[0251] ■When the mapping of transmission / reception to / from the logical channel corresponding to the RLC layer device (allowedServingCell) is not configured only in the Scell, or in other cases,

[0252] ◆Consider that a radio link failure (Radio Link Failure (RLF)) occurs in the MCG.

[0253] ◆If the AS security configuration is not activated (when a connection failure occurs during RRC connection configuration), or if the AS security configuration is activated but SRB2 and at least one DRB are not configured (when a full RRC connection is not configured), the terminal can switch to RRC idle mode.

[0254] Otherwise,

[0255] If carrier aggregation is configured in the terminal, and there is an Scell ​​configured to satisfy the first condition, the second condition, the third condition, the fourth condition, the fifth condition, or the sixth condition among the configured Scells, and if the MCG radio link failure report is first triggered in the Scell,

[0256] ■The terminal can report the Pcell radio link failure through the Scell. Specifically, the terminal can form an RRC message for the Pcell radio link failure information, and can configure the information as data in the MCG MAC layer device by carrying SRB1 or SRB2, that is, by a logical channel identifier corresponding to SRB1 or SRB2, and can send the Pcell radio link failure information to the base station through the Scell ​​that meets multiple conditions.

[0257] ■In addition, a first timer may be started. (As described above, in the process for responding to the MCG radio link failure report message, when an RRC message indicating that a handover enables the base station to recover the MCG radio link failure, an RRC message for reestablishing an RRC connection, or an RRC message for disconnecting the MCG is received as a response, the terminal may stop or initialize the first timer.)

[0258] If carrier aggregation is not configured in the terminal, and there is no Scell ​​configured to satisfy the first condition, the second condition, the third condition, the fourth condition, the fifth condition or the sixth condition in the configured Scell, or / and if an MCG radio link failure report has been triggered in the Scell, and the MCG radio link failure reporting procedure has failed in the Scell ​​or the first timer has expired,

[0259] ■If the terminal is configured with dual connectivity, the SCG does not stop transmission and data sending / reception is possible, and if the terminal is configured with: a separate SRB (e.g., separate SRB1) connected to the MCG base station and connected to the MCG MAC layer device of the terminal (where the PDCP layer device is the MCG); or an SRB (e.g., SRB3) connected to the SCG base station and connected to the SCG MAC layer device (where the PDCP layer device is in the SCG), the terminal may perform one of the following methods.

[0260] ◆Method one: The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, since the terminal has detected the MCG radio link failure, the terminal can stop sending all SRBs or DRBs configured in the configured MCG to the MCG base station. The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized, and data transmission / reception can continue. If timer T304 (a timer operating in a switching situation) is operating, timer T304 can be stopped (because during switching, a radio link failure can be detected). The terminal can indicate the type of MCG radio link failure (for example, exceeding the maximum number of RLC retransmissions, integrity verification failure, or synchronization mismatch, or timer expiration), form an MCG radio link failure message, and can report the MCG radio link failure to the MCG base station or SCG base station through a separate SRB connected to the SCG MAC layer device (for example, separate SRB1) or through an SRB connected to the SCG MAC layer device (for example, SRB3). In addition, measurement results of other frequencies can be included in the failure information and sent so that they are available when the base station quickly configures a new cell (for example, Pcell) or a new cell group (for example, MCG). In addition, the radio link failure information can indicate the cause of the failure. Method 1 is a method in which the terminal indicates MCG failure information so that the base station can restore or change the MCG indicated by the radio link failure. Method 1 enables the terminal to solve the radio link failure problem based on the MCG base station or SCG base station. In addition, a second timer can be started. (As described above, in the process for responding to the MCG radio link failure report message, when an RRC message indicating that a handover enables the base station to recover the MCG radio link failure, an RRC message for reestablishing an RRC connection, or an RRC message for disconnecting the MCG is received as a response, the terminal may stop or initialize the second timer.)

[0261] ◆Method 2: Since the terminal has detected the MCG radio link failure, the terminal can stop the transmission of all SRBs or DRBs to the MCG base station except the configured SRB0 (SRB0 must send an RRC re-establishment message, and the transmission of SRB0 cannot be stopped). The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized, and data transmission / reception can continue to be performed. If timer T304 (a timer operating in a handover situation) is operating, timer T304 can be stopped (because during the handover, a radio link failure can be detected). The terminal can trigger the RRC connection re-establishment process for the MCG base station, the appropriate Scell ​​selected through the cell reselection process, or the cell supported by the SCG base station configured with an effective connection. When sending an RRC connection re-establishment request message during this process, the terminal can indicate that a radio link failure has occurred. In addition, the radio link failure information can indicate the cause of the failure. Method 2 enables the terminal to identify the MCG failure information and solve the MCG failure problem by itself.

[0262] ◆Method three: Since the terminal has detected the MCG radio link failure, the terminal can stop transmitting all configured SRBs or DRBs to the MCG base station. The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized, and data transmission / reception can continue. If timer T304 (a timer operating in a switching situation) is operating, timer T304 can be stopped (because during the switching, a radio link failure can be detected). The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, the terminal can trigger an RRC connection reestablishment process for the MCG base station or the SCG base station. When an RRC connection reestablishment request message is sent in this process, the terminal can indicate to the MCG base station or the SCG base station that an MCG radio link failure has occurred. When the MCG connection reestablishment request message is sent in this process, the terminal may indicate that an MCG radio link failure has occurred by connecting to a detached SRB (e.g., detaching SRB1) connected to the SCG MAC layer device or by connecting to an SRB (e.g., SRB3 or SRB0) connected to the SCG MAC layer device. In addition, the radio link failure information may indicate the cause of the failure. Method 3 is a method in which the terminal indicates MCG failure information by detaching SRB1 or SRB3 so that the base station can recover or change the MCG indicated by the radio link failure. Method 3 enables the terminal to solve the radio link failure problem based on the MCG base station or the SCG base station. In addition, a second timer may be started. (As described above, in the process for responding to the MCG radio link failure report message, when an RRC message indicating that a handover enables the base station to recover the MCG radio link failure, an RRC message for reestablishing the RRC connection, or an RRC message for disconnecting the MCG is received in response, the terminal may stop or initialize the second timer.)

[0263] ◆Method 4: Since the terminal has detected the MCG radio link failure, the terminal can stop the transmission of all SRBs or DRBs except the configured SRB0 to the MCG base station (SRB0 must send an RRC re-establishment message, and the transmission of SRB0 cannot be stopped). The MCG MAC layer device is initialized. However, the bearer or layer device configured in the SCG is maintained without being initialized, and data transmission / reception can continue to be performed. If the timer T304 (a timer operating in the case of handover) is operating, the timer T304 can be stopped (because during the handover, a radio link failure can be detected). The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, the terminal can trigger the RRC connection re-establishment process for the MCG base station or the SCG base station. That is, after camping on a cell selected by the cell reselection process where a good signal can be obtained or camping on a cell supported by a SCG with a valid connection, the terminal can send an RRC connection re-establishment request message through SRB0. In addition, the terminal may use an indicator to indicate to the MCG base station or SCG base station that an MCG radio link failure has occurred. In addition, the radio link failure information may indicate the cause of the failure. Method 4 is a method in which the terminal indicates the MCG failure information through SRB0 so that the base station can restore or change the MCG indicated with the radio link failure. Method 4 enables the terminal to solve the radio link failure problem based on the MCG base station or SCG base station.

[0264] ■ If the terminal does not configure dual connectivity, the SCG stops transmission and data transmission / reception is impossible, and if the terminal does not configure an SRB connected to the SCG base station or a detached SRB (e.g., detached SRB1), if the first timer or the second timer has expired, or in other cases,

[0265] ◆Since the terminal has detected the MCG radio link failure, the terminal can stop the transmission of all SRBs or DRBs except the configured SRB0 to the MCG base station (SRB0 must send an RRC re-establishment message, and the transmission of SRB0 cannot be stopped). The MCG MAC layer device is initialized. In addition, all bearers (SRBs or DRBs) configured in the SCG are stopped, and the SCG MAC layer device is also initialized. The SCG bearer and SCG configuration information are released. If timer T304 (a timer operating in a handover situation) is operating, timer T304 can be stopped (because during the handover, a radio link failure can be detected). The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, the terminal can trigger the RRC connection re-establishment process for the MCG base station or the SCG base station. That is, after camping on the MCG base station, the cell selected through the cell reselection process that can obtain a good signal, or the cell supported by the SCG base station configured with an effective connection, the terminal can send an RRC connection reestablishment request message through SRB0. In addition, the terminal can use an indicator to indicate to the MCG base station or SCG base station that an MCG radio link failure has occurred. In addition, the radio link failure information can indicate the cause of the failure.

[0266] As described above, when a terminal in which carrier aggregation has been configured maintains a connection with a base station (or cell) in a Scell ​​but fails to establish a wireless connection with a base station (or cell) in a Pcell, the terminal is configured to: continuously send / receive data in the Scell; and report the Pcell radio link failure to the MCG base station through a Scell ​​in the Scell ​​that satisfies multiple conditions, so that the base station can restore the Pcell, release the Pcell in which the radio link failure has occurred and add a new cell to use it as a Pcell, or use a Scell ​​in the Scell ​​in which a wireless connection is currently maintained that satisfies multiple conditions as the Pcell, thereby achieving continuous data transmission.

[0267] When a Pcell radio link failure is reported, the MCG base station may restore the Pcell of the terminal, may release the Pcell in which the radio link failure has occurred and add a new cell as the Pcell, or may send configuration information to the base station through an Scell ​​that satisfies multiple conditions by means of an RRC message, so that the terminal can use the Scell ​​that satisfies multiple conditions in the Scell ​​that currently maintains the wireless connection as the Pcell. Specifically, the base station may instruct the terminal to release the existing Pcell configuration information, may send new cell configuration information and notify the random access information to be used in the random access process, so as to instruct the terminal to configure the connection to the new cell and use the new cell as the Pcell, or may notify the random access information to be used in the random access process, so that the terminal attempts to reconnect to the existing Pcell. In another method, the base station may include information in the RRC message indicating that the terminal regards the Scell ​​configuration information previously configured for the terminal as the Pcell, and may send the RRC message through the Scell ​​that satisfies multiple conditions and is connected to the MCG MAC layer device of the terminal. Therefore, a cell that is already a Scell ​​may be regarded as a Pcell (for example, it may be configured to be regarded as a Pcell by configuring the cell identifier of the existing configured Scell ​​to zero). When the role of an existing Scell ​​is changed to the role of a Pcell, the base station may perform configuration so that another cell is added as an Scell, thereby reconfiguring carrier aggregation.

[0268] When a Pcell radio link failure is reported, the MCG base station can restore the MCG of the terminal, can release the MCG in which the radio link failure has occurred and add a new cell to be used as the MCG, or can send configuration information to the base station through the SCG by means of an RRC message so that the terminal can use the SCG that currently maintains the wireless connection as the MCG. Specifically, the base station can instruct the terminal to release the existing MCG configuration information, can send new cell configuration information and notify the random access information to be used in the random access process, so as to instruct the terminal to configure the connection to the new cell and use the new cell as the MCG, or can notify the random access information to be used in the random access process so that the terminal attempts to reconnect to the existing MCG. In another method, the base station can include information in the RRC message indicating that the terminal regards the SCG configuration information previously configured for the terminal as the MCG, and can send the RRC message through the SRB connected to the MCG or SCG MAC layer device of the terminal. Therefore, a cell that is already an SCG can be regarded as a Pcell (for example, it can be configured to be regarded as an MCG by configuring the cell identifier of the existing configured SCG to zero). When the role of an existing SCG is changed to the role of an MCG, the base station may perform configuration such that another cell is added as an SCG, thereby reconfiguring carrier aggregation.

[0269] In another method, the SCG base station may send an RRC connection reestablishment message to the terminal to instruct the terminal to restore the wireless connection in the SCG. Therefore, the wireless connection is not restored in such a way that the terminal triggers the RRC reestablishment process, sends an RRC reestablishment request message to the base station, receives an RRC reestablishment message from the base station, and sends an RRC reestablishment completion message to the base station. However, the wireless connection may be restored in such a way that when the base station (e.g., SCG) recognizes that the MCG radio link has failed, the base station (e.g., SCG) triggers the RRC reestablishment process and sends an RRC reestablishment message to the terminal, and the terminal recognizes the message and sends an RRC reestablishment completion message to the base station. The base station (e.g., SCG) notifies the base station (e.g., MCG) with which the terminal failed to establish a wireless connection that the terminal has reestablished a connection with the base station (e.g., SCG), thereby allowing the base station (e.g., MCG) to release the context of the terminal.

[0270] In addition, in the MCG radio link failure reporting method of the present disclosure, if the terminal reports the MCG radio link failure through the separate SRB1 configured in the MCG MAC layer device and the SCG MAC layer device, when the packet copy function is not configured, by changing the configuration from the first RLC layer device (primary RLC entity) to the second RLC layer device (secondary RLC entity) and from the second RLC layer device (secondary RLC entity) to the first RLC layer device (primary RLC entity), the MCG radio link failure report message sent by the terminal can be sent, and the PDCP control data (PDCP control PDU) generated or triggered in the PDCP layer device can be sent through the separate SRB1 connected to the SCG MAC layer device to allow the base station to successfully receive the MCG radio link failure report message or the PDCP control data. The reason why the configuration change is required is that when the packet copy is configured in the separate SRB1, the terminal can send data to the second RLC layer device, but when the packet copy is not configured, the terminal may not send data (MCG radio link failure report or PDCP control data) to the second RLC layer device. In another method, the radio link failure report or PDCP control data is allowed to be sent to the second RLC layer device only when the MCG radio link failure reporting procedure is triggered. If the configuration is changed from the first RLC layer device to the second RLC layer device with respect to the separation SRB1, when a response to the MCG failure report recovery is received, the changed configuration may be allowed to return to the original configuration, or may be maintained until an RRC message indicating a return to the original configuration is received.

[0271] The above embodiment can also be extended and applied to the case where both carrier aggregation and dual connectivity are configured.

[0272] The separated SRB (e.g., separated SRB1) described in the present disclosure is characterized by having: a PDCP layer device for MCG in terminal implementation; a structure in which a PDCP layer device is connected to a RLC layer device for MCG and a RLC layer device for SCG; and a structure in which a RLC layer device for MCG is connected to a MAC layer device and a PHY layer device for MCG, and a RLC layer device for SCG is connected to a MAC layer device and a PHY layer device for SCG. A base station is characterized by having: a PDCP layer device in an MCG base station; a structure in which a RLC layer device for SCG is connected to a PDCP layer device in an SCG base station, and a PDCP layer device in the SCG base station is connected to a RLC layer device for MCG via an X interface (e.g., X2, Xn, etc.) or an S interface (e.g., S1, Sn, etc.); and a structure in which a RLC layer device for MCG is connected to a MAC layer device and a PHY layer device of the MCG base station, and a RLC layer device for SCG is connected to a MAC layer device and a PHY layer device of the SCG base station.

[0273] In addition, the SRB3 described in the present disclosure is characterized by having: a PDCP layer device for SCG in terminal implementation; a structure in which one PDCP layer device is connected to one RLC layer device for SCG; and a structure in which one RLC layer device for SCG is connected to a MAC layer device and a PHY layer device for SCG. In addition, a base station is characterized by having: a PDCP layer device in an SCG base station; a structure in which one RLC layer device for SCG is connected to one PDCP layer device; and a structure in which one RLC layer device for MCG is connected to a MAC layer device and a PHY layer device of an MCG base station; and a structure in which one RLC layer device for SCG is connected to a MAC layer device and a PHY layer device of an SCG base station.

[0274] In the second embodiment or the fourth embodiment, after an MCG radio link failure occurs and is reported to the base station through the Scell ​​or SCG, if a radio link failure occurs in the Scell ​​or SCG through which the radio link failure report has been performed before the first timer or the second timer expires or a response to the MCG radio link failure report is received, the terminal can determine that all wireless connections have failed and can trigger the RRC connection reestablishment process.

[0275] In the second embodiment, when the MCG radio link failure is determined, the terminal may perform bearer stop (e.g., data transmission / reception stop or data processing stop in the SDAP, PDCP, RLC or MAC layer device of each bearer) for the bearers other than SRB0 among the bearers configured for the MCG. Since the connection to the MCG is configured again, the terminal may not perform MAC initialization. However, with respect to the bearers for the SCG, the terminal may continuously perform data transmission / reception and data processing.

[0276] In the second embodiment and the fourth embodiment, when it is determined that the MCG radio link fails, the terminal can perform the MCG radio link failure reporting process through the Scell ​​of the MCG that meets the predetermined conditions. Specifically, the terminal can perform a bearer stop (for example, data transmission / reception stop or data processing stop in the SDAP, PDCP, RLC or MAC layer device of each bearer) for the bearers configured for the MCG except SRB0 or ​​SRB1. Since the connection to the MCG is configured again, the terminal may not perform MAC initialization. However, when dual connection is configured, the terminal can continuously perform data transmission / reception and data processing for the bearer used for the SCG. With respect to the MAC layer device, initialization is not performed, but a partial initialization (partial MAC reset) process can be performed. That is, in the fourth embodiment, if the terminal is configured with carrier aggregation and a Scell ​​that meets the predetermined conditions is configured, when a radio link failure is detected, the RRC layer device of the terminal can indicate a partial MAC reset, so that the terminal can send an MCG radio link failure report message from the MCG MAC layer device to the Scell. A partial MAC reset can initialize the processing information of the data sent / received while maintaining the existing configuration of the MAC layer device, and can be triggered by the MAC layer device preparing for a new transmission or MCG radio link failure report. A partial MAC reset allows the MCG radio link failure report message to be sent to the MCG MAC layer device even when a radio link failure is detected.

[0277] A partial MAC reset may include one or more of the following processes.

[0278] - If the upper layer device (eg, RRC layer device) instructs the MAC layer device to reset the partial MAC, the MAC layer device may perform one or more of the following processes. In another method, for a Scell ​​that meets a predetermined condition, the MAC layer device may perform one or more of the following processes.

[0279] ■ A process of configuring the NDI value of all uplink transmission HARQ processes to zero in order to initialize the information about previously transmitted / received data.

[0280] ■ The process of flushing all uplink transmission HARQ buffers to initialize the information about the previously sent / received data.

[0281] ■ The process of stopping all operating DRX uplink retransmission timers.

[0282] ■The process of stopping all operating uplink HARQ RTT timers.

[0283] ■The process of stopping the random access procedure being executed.

[0284] ■ A process of discarding information on a random access preamble indicated in detail or random access transmission resource information.

[0285] ■The process of initializing the message 3 buffer.

[0286] ■Release the temporarily configured temporary C-RNTI.

[0287] In a fourth embodiment, when the terminal detects an MCG radio link failure, is configured with an Scell ​​that meets a predetermined condition, is configured with dual connectivity, and maintains a valid connection to the SCG, and when the terminal is configured with a detached SRB (e.g., detached SRB1), the terminal may report the MCG radio link failure using the detached SRB. Specifically, the terminal may generate an MCG radio link failure report message, and may send the MCG radio link failure report message from the MCGMAC layer device to the Scell ​​that meets the predetermined condition through an RLC layer device that processes data in the PDCP layer device of the MCG corresponding to the detached SRB1 and is connected to the MCG MAC layer device. In addition, the terminal may generate an MCG radio link failure report message, and may send the MCG radio link failure report message from the SCG MAC layer device to the Pcell or Scell ​​through an RLC layer device that processes data in the PDCP layer device of the MCG corresponding to the detached SRB1 and is connected to the SCGMAC layer device. In another method, the terminal may generate an MCG radio link failure report message, and may send the MCG radio link failure report message from the MCG MAC layer device to the Scell ​​that meets the predetermined condition through an RLC layer device, which processes data in the PDCP layer device of the MCG corresponding to the separated SRB1 and is connected to the MCG MAC layer device, so that the data replicates the MCG radio link failure report message and sends the message in a replicated manner. In addition, the terminal may send the MCG radio link failure report message from the SCG MAC layer device to the Pscell or Scell ​​through the RLC layer device connected to the SCG MAC layer device. That is, if the terminal is configured with carrier aggregation, configured with an Scell ​​that meets the predetermined condition, and configured with dual connectivity, and a wireless connection to the SCG Pscell or SCG Scell ​​is established with a predetermined signal strength or greater, the terminal may generate an MCG radio link failure report message, apply packet replication thereto to packet replicate the MCG radio link failure report message in the MCG PDCP layer device, and send the replicated message from the MCG MAC layer device to the Scell ​​in a replicated manner by using the separated SRB through the MCG RLC layer device. In addition, the terminal can copy and send the MCG radio link failure report message from the SCG MAC layer device to the Pscell or Scell ​​through the SCG RLC layer device. Therefore, the MCG radio link failure report message can be sent with low transmission delay and high reliability.

[0288] Figure 1H The operation of the terminal in the embodiment according to the embodiment of the present disclosure is shown.

[0289] refer to Figure 1H Specifically, in an embodiment, when a terminal that has been configured with carrier aggregation or dual connectivity fails to connect to a base station (or cell) in a Pcell, the terminal continues to send / receive data in the Scell ​​or SCG, and reports a Pcell radio link failure (MCG radio link failure) to a specific Scell ​​or SCG, so that the Pcell or MCG can be restored or replaced by another Pcell or MCG, the Pcell or MCG in which a radio link failure has occurred can be released, or the Scell ​​or SCG that is currently connected can be switched to the Pcell or MCG.

[0290] In the terminal, a radio link failure (MCG radio link failure) with a base station (or cell) may occur or be detected in a Pcell (operation 1h-05).

[0291] If the terminal is configured with carrier aggregation and is configured with a Scell ​​that satisfies the first condition, the second condition, the third condition, the fourth condition, the fifth condition, or the sixth condition in the configured Scell ​​(operation 1h-10), the terminal may report the Pcell radio link failure through the Scell. Specifically, the terminal may generate an RRC message for the Pcell radio link failure information, may configure the information as data by carrying SRB1 or SRB2, that is, by a logical channel identifier corresponding to SRB1 or SRB2, and may send the Pcell radio link failure information to the base station through the Scell ​​that satisfies multiple conditions (operation 1h-15).

[0292] If the terminal is not configured with carrier aggregation or is not configured with an Scell ​​that satisfies the first, second, third, fourth, fifth or sixth condition in the configured Scell, if the terminal is configured with dual connectivity, the SCG does not stop transmission and data sending / reception is possible, and if the terminal is configured with: a MCG MAC layer device (wherein the PDCP layer device is in the MCG) connected to the MCG base station and the terminal and a separate SRB (for example, separate SRB1) of the SCG MAC layer device; or an SRB (for example, SRB3) connected to the SCG base station and connected to the SCG MAC layer device (wherein the PDCP layer device is in the SCG) (operation 1h-20), the terminal may report an MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station may notify the MCG base station of the MCG radio link failure of the terminal.) (operation 1h-25).

[0293] If the terminal does not configure dual connectivity, the SCG stops transmission and data transmission / reception is impossible, and if the terminal does not configure an SRB connected to the SCG base station or a detached SRB (e.g., detached SRB1), or in other cases (operations 1h-30), since the terminal has detected an MCG radio link failure, the terminal can stop transmission of all SRBs or DRBs to the MCG base station except the configured SRB0 (SRB0 must send an RRC reestablishment message, and transmission of SRB0 cannot be stopped). The MCG MAC layer device is initialized. In addition, all bearers (SRBs or DRBs) configured in the SCG are stopped, and the SCG MAC layer device is also initialized. The SCG bearer and SCG configuration information are released. If timer T304 (a timer operating in a handover situation) is operating, timer T304 can be stopped (because during handover, a radio link failure can be detected). The terminal can report the MCG radio link failure to the MCG base station or the SCG base station (when the MCG radio link failure is reported to the SCG base station, the SCG base station can notify the MCG base station of the MCG radio link failure of the terminal). Specifically, the terminal can trigger the RRC connection reconstruction process for the MCG base station or the SCG base station. That is, after residing on a cell selected by the cell reselection process that can obtain a good signal, the terminal can send an RRC connection reconstruction request message through SRB0. In addition, the terminal can use an indicator to indicate to the MCG base station or the SCG base station that an MCG radio link failure has occurred. In addition, the radio link failure information can indicate the cause of the failure.

[0294] In a terminal that has been configured with dual connectivity and carrier aggregation, when a connection failure occurs in a Pscell of an SCG, the above embodiment can be extended to a process of reporting the Pscell connection failure to an SCG base station. That is, the above embodiment considers the Pscell connection failure in the SCG, instead of the Pscell connection failure in the MCG, and can be extended to reporting the Pscell connection failure in the SCG through the Scell ​​of the SCG, instead of reporting the Pscell connection failure in the MCG through the Scell ​​of the MCG.

[0295] The above embodiment proposes a method for reporting MCG radio link failure to a base station when MCG radio link failure is detected. If the base station receives the MCG radio link failure report message, the base station may instruct the terminal to use one of the following methods to recover the MCG radio link failure.

[0296] -Method 1: If a terminal in which carrier aggregation has been configured maintains a connection with a base station (or cell) in the Scell, but fails to establish a wireless connection with a base station (or cell) in the Pcell, the terminal can continuously send / receive data in the Scell, and the base station can restore the Pcell, release the Pcell in which a radio link failure has occurred and add a new cell as the Pcell, or give a configuration to the terminal through an RRC message so that the terminal can use a Scell ​​that satisfies multiple conditions in the Scell ​​currently maintaining a wireless connection as the Pcell. That is, when an MCG (Pcell) radio link failure is reported, the MCG base station can restore the Pcell of the terminal, release the Pcell in which a radio link failure has occurred, and add a new cell as the Pcell, or send configuration information to the base station through an RRC message through a Scell ​​that satisfies multiple conditions so that the terminal can use a Scell ​​that satisfies multiple conditions in the Scell ​​currently maintaining a wireless connection as the Pcell. Specifically, the base station may instruct the terminal to release the existing Pcell configuration information, may send new cell configuration information and notify the random access information to be used in the random access process so as to instruct the terminal to configure a connection to the new cell and use the new cell as the Pcell, or may notify the random access information to be used in the random access process so that the terminal attempts to reconnect to the existing Pcell. In another method, the base station may include information in an RRC message indicating that the terminal regards the Scell ​​configuration information previously configured for the terminal as a Pcell, and send the RRC message through a Scell ​​that satisfies multiple conditions and is connected to the MCG MAC layer device of the terminal. Therefore, a cell that is already a Scell ​​may be regarded as a Pcell (for example, it may be configured to be regarded as a Pcell by configuring the cell identifier of the existing configured Scell ​​to zero). When the role of the existing Scell ​​is changed to the role of the Pcell, the base station may perform configuration so that another cell is added as a Scell, thereby reconfiguring carrier aggregation.

[0297] -Method 2: When a Pcell radio link failure is reported, the MCG base station may restore the MCG of the terminal, may release the MCG in which the radio link failure has occurred and add a new cell to be used as the MCG, or may send configuration information to the base station through the SCG by means of an RRC message so that the terminal can use the SCG that currently maintains the wireless connection as the MCG. Specifically, the base station may instruct the terminal to release the existing MCG configuration information, may send new cell configuration information and notify the random access information to be used in the random access process so as to instruct the terminal to configure the connection to the new cell and use the new cell as the MCG, or may notify the random access information to be used in the random access process so that the terminal attempts to reconnect to the existing MCG. In another method, the base station may include information in the RRC message indicating that the terminal regards the SCG configuration information previously configured for the terminal as the MCG, and may send the RRC message through the SRB connected to the MCG or SCG MAC layer device of the terminal. Therefore, a cell that is already an SCG may be regarded as a Pcell (for example, it may be configured to be regarded as an MCG by configuring the cell identifier of the existing configured SCG to zero). When the role of an existing SCG is changed to the role of an MCG, the base station may perform configuration such that another cell is added as an SCG, thereby reconfiguring carrier aggregation.

[0298] -Method 3: In another method, the SCG base station may send an RRC connection reestablishment message to the terminal to instruct the terminal to restore the wireless connection in the SCG. Therefore, the wireless connection is not restored in such a way that the terminal triggers the RRC reestablishment process, sends an RRC reestablishment request message to the base station, receives the RRC reestablishment message, and sends an RRC reestablishment completion message to the base station. However, the wireless connection may be restored in such a way that when the base station (e.g., SCG) recognizes that the MCG radio link has failed, the base station (e.g., SCG) triggers the RRC reestablishment process and sends an RRC reestablishment message to the terminal, and the terminal recognizes the message and sends an RRC reestablishment completion message to the base station. The base station (e.g., SCG) notifies the base station (e.g., MCG) with which the terminal failed to establish a wireless connection that the terminal has reestablished a connection with the base station (e.g., SCG), thereby allowing the base station (e.g., MCG) to release the context of the terminal.

[0299] When the method proposed above is applied, the terminal can initialize the configuration information about the SCG base station, can receive a new configuration from the base station, and can receive dual connectivity. In another method, when the method proposed above is applied, the terminal maintains the configuration information about the SCG base station, but can initialize the MAC layer device and rebuild the RLC layer device and the PDCP layer device. In another method, the terminal can apply the method proposed above to continuously maintain data transmission / reception to / from the SCG base station.

[0300] In order to prevent data transmission / reception failure when applying the above-mentioned method 1, method 2 or method 3, when dual connectivity is configured for the terminal, the terminal can continuously maintain data transmission / reception with the SCG base station, or the terminal can receive a switching instruction from the base station and perform switching to the MCG base station while maintaining data transmission / reception with the SCG base station. Hereinafter, the present disclosure proposes problems that may occur in this case and suggests methods for solving these problems.

[0301] First, when the base station instructs the terminal to switch to a new cell or base station in order to recover the failure of the MCG radio link, or instructs the terminal that has been configured with dual connectivity to continuously perform data transmission / reception to / from the SCG and switch the MCG, the terminal must receive a new security key about the MCG base station, and must introduce and apply the new security key in order to perform encoding and decoding or integrity protection and integrity verification processes in the PDCP layer device. In addition, when the security key value of the MCG base station changes, the security key value of the SCG base station corresponding thereto must be newly introduced and updated. Therefore, when the MCG security key value changes due to the switching or recovery of the MCG while maintaining data transmission / reception to / from the SCG, the security key value is changed while the SCG and the terminal send / receive data. Therefore, the terminal and the base station may not distinguish between data encoded and integrity protected using the old security key and data encoded and integrity protected using the new security key.

[0302] Therefore, the present disclosure proposes a method in which a terminal and a base station can distinguish whether an old security key is applied to each type of data in a PDCP layer device, or whether a new security key is applied to each type of data in a PDCP layer device.

[0303] -Method 1: When the security key is changed while performing data transmission / reception as described above, the base station can instruct the initialization of the MAC layer device (MAC reset), the reconstruction of the RLC layer device, or the reconstruction of the PDCP layer device, so that the PDCP layer device can distinguish between data (e.g., PDCP PDU or PDCP SDU) to which the old security key is applied and data to which the new security key is applied.

[0304] -Method 2: When the security key changes while performing data transmission / reception as described above, a new PDCP control PDU may be defined and used to indicate it. The new PDCP control PDU may be used as an end indicator (end marker) and may be configured to indicate the data (PDCP PDU or PDCP SDU) to which the old security key value has been applied, including the last PDCP sequence number or COUNT value to which the old security key value has been applied, and the data from which the new security key value has begun to be applied. In another method, the new PDCP control PDU may be used as a first indicator (first marker) and may be configured to indicate the data (PDCP PDU or PDCP SDU) from which the new security key value has begun to be applied, including the first PDCP sequence number or COUNT value to which the new security key value has been applied, and the data to which the old security key value has been applied. When the security key value changes, the PDCP control PDU proposed above may be sent for each bearer.

[0305] -Method 3: When the security key changes while performing data transmission / reception as described above, a 1-bit indicator is defined in the PDCP header of the PDCP layer device to indicate it, and can be used to indicate which of the old security value or the new security key value has been applied to the data corresponding to the PDCP header. When the PDCP control PDU proposed in method 2 is sent to each bearer through the change of the security key value, the PDCP control PDU may not be lost in the RLC AM mode, but may be lost in the RLC UM mode. In addition, since the NR RLC layer device transmits data to the PDCP layer device through the out-of-order transmission method, when the PDCP control PDU arrives late, decoding failure may occur in the receiving PDCP layer device. On the other hand, the 1-bit indicator of the PDCP header proposed in method 3 can indicate which of the older security key value or the new security key value has been applied to each type of data. Therefore, even when the NR RLC layer device performs out-of-order transmission and data is lost, the receiving PDCP layer device can more efficiently process the non-lost data. When the 1-bit indicator of the PDCP header determines from the lower layer (RLC ACK) or from the received PDCP status report that the first data to which the new security key is applied and the last data to which the old security key is applied are successfully transmitted, the 1-bit indicator of the PDCP header may no longer be configured. In another method, when the handover of the MCG is completed, the 1-bit indicator may not be configured. In another method, the 1-bit indicator may be configured or released according to the instruction of the RRC message or the handover command message. In another method, a 1-bit indicator using a toggle method may be used. That is, whenever the security key value changes, the 1-bit indicator may be indicated by toggling from 0 to 1 or from 1 to 0. In another method, the receiving PDCP layer device (base station or terminal) identifies the 1-bit indicator of the PDCP header and may use the 1-bit indicator until the receiving PDCP layer device sends feedback to the sending PDCP layer device (terminal or base station) indicating that the new security key and the old security key can be distinguished normally. A new PDCP control PDU may be defined and used for feedback.

[0306] The present disclosure proposes a method for: when an MCG (or Pcell) radio link failure is detected, when carrier aggregation is configured, reporting the MCG (or Pcell) radio link failure through the Scell ​​of the MCG; and when dual connectivity is configured, reporting the MCG (or Pcell) radio link failure through the SCG (e.g., SRB3 or separated SRB1).

[0307] Hereinafter, the present disclosure proposes different conditions according to which the method proposed by the present disclosure can be performed, and a specific fifth embodiment will be described as follows.

[0308] The following describes the first (5-1) embodiment, in which the first embodiment, the second embodiment, the third embodiment or the fourth embodiment proposed in the present disclosure is performed under different conditions. The feature of the first (5-1) embodiment is that when an MCG (or Pcell) radio link failure is detected, if both dual connectivity and carrier aggregation have been configured in the terminal, the MCG (or Pcell) radio link failure is first reported using the dual connectivity. In addition, the feature of the first (5-1) embodiment is that when both SRB3 and separated SRB1 are configured in the dual connectivity, the MCG (or Pcell) radio link failure is reported through SRB3. The reason is that when the connection to the SCG base station operates normally, it can be determined that the connection to the SCG has a higher reliability than the connection to the Scell ​​of the MCG, and it can be determined that the SRB3 connected to the SCG has a higher reliability than the separated SRB1. When SRB3 has not been configured, the MCG (or Pcell) radio link failure can be reported through the separated SRB1. When a separate SRB1 or SRB3 has not been configured and there is an MCG Scell ​​that meets the predetermined conditions, the MCG (or Pcell) radio link failure can be reported through the Scell. When the radio link failure cannot be reported as described above, the terminal can trigger the RRC connection reestablishment process to reconfigure the connection.

[0309] - When dual connectivity is configured in the terminal (or carrier aggregation is configured) when MCG (or Pcell) radio link failure is detected,

[0310] ■If SRB3 connected to the SCG base station is configured in the terminal (or SRB1 is configured to be separated),

[0311] ◆ The terminal reports the MCG (or Pcell) radio link failure to the base station via SRB3. The reporting may be performed as in the method proposed in the present disclosure (eg, the second embodiment).

[0312] ■ Otherwise (or if SRB3 connected to the SCG base station is not configured in the terminal and / or a split SRB1 is configured),

[0313] ◆The terminal reports the MCG (or Pcell) radio link failure to the base station by separating SRB1. The reporting may be performed as in the method proposed in the present disclosure (e.g., the second embodiment). In another method, if carrier aggregation is configured in the terminal and a Scell ​​that satisfies a predetermined condition is configured, the MCG (or Pcell) radio link failure message may be sent to the SCG and the Scell ​​of the MCG by replicating the MCG (or Pcell) radio link failure message by using a packet replication technique.

[0314] ■ Otherwise (or if, when the MCG (or Pcell) radio link failure is detected, SRB3 is not configured in the terminal, split SRB1 is not configured, and / or carrier aggregation is configured and a Scell ​​that satisfies a predetermined condition is configured (for example, as in the fourth embodiment)),

[0315] ◆ The terminal reports the MCG (or Pcell) radio link failure to the base station through the Scell ​​that meets the predetermined condition. The reporting may be performed as in the method proposed in the present disclosure (eg, the fourth embodiment).

[0316] ■Otherwise,

[0317] ◆The terminal triggers the RRC connection reestablishment process to reconfigure the connection.

[0318] The following describes the first (5-2) embodiment, in which the first embodiment, the second embodiment, the third embodiment or the fourth embodiment proposed in the present disclosure is performed under different conditions. The feature of the first (5-2) embodiment is that when the MCG (or Pcell) radio link failure is detected, if both dual connectivity and carrier aggregation have been configured in the terminal, the MCG (or Pcell) radio link failure is first reported using the dual connectivity. In addition, the feature of the first (5-2) embodiment is that when both SRB3 and separate SRB1 are configured in the dual connectivity, the MCG (or Pcell) radio link failure is reported through the separate SRB1. The reason is that when the connection to the SCG base station operates normally, it can be determined that the connection to the SCG has higher reliability than the connection to the Scell ​​of the MCG, and it can be determined that the separate SRB1 directly connected to the MCG has a lower transmission delay than the SRB3 connected to the SCG. When SRB1 has not been configured, the MCG (or Pcell) radio link failure can be reported through SRB3. When a separate SRB1 or SRB3 has not been configured and there is an MCG Scell ​​that meets the predetermined conditions, the MCG (or Pcell) radio link failure can be reported through the Scell. When the MCG radio link failure cannot be reported as described above, the terminal can trigger the RRC connection reestablishment process to reconfigure the connection.

[0319] - When dual connectivity is configured in the terminal (or carrier aggregation is configured) when an MCG (or Pcell) radio link failure is detected,

[0320] ■If a separate SRB1 connected to an SCG base station is configured in the terminal (or SRB3 is configured),

[0321] ◆The terminal reports the MCG (or Pcell) radio link failure to the base station by separating SRB1. The reporting may be performed as in the method proposed in the present disclosure (e.g., the second embodiment). In another method, if carrier aggregation is configured in the terminal and a Scell ​​that satisfies a predetermined condition is configured, the MCG (or Pcell) radio link failure message may be sent to the SCG and the Scell ​​of the MCG by replicating the MCG (or Pcell) radio link failure message by using a packet replication technique.

[0322] ■ Otherwise (or if the split SRB1 connected to the SCG base station is not configured and / or SRB3 is configured in the terminal),

[0323] ◆ The terminal reports the MCG (or Pcell) radio link failure to the base station via SRB3. The reporting may be performed as in the method proposed in the present disclosure (eg, the second embodiment).

[0324] ■ Otherwise (or if, when the MCG (or Pcell) radio link failure is detected, SRB3 is not configured in the terminal, split SRB1 is not configured, and / or carrier aggregation is configured and a Scell ​​that satisfies a predetermined condition is configured (for example, as in the fourth embodiment)),

[0325] ◆ The terminal reports the MCG (or Pcell) radio link failure to the base station through the Scell ​​that meets the predetermined condition. The reporting may be performed as in the method proposed in the present disclosure (eg, the fourth embodiment).

[0326] ■Otherwise,

[0327] ◆The terminal triggers the RRC connection reestablishment process to reconfigure the connection.

[0328] The following describes the first (5-3) embodiment, in which the first embodiment, the second embodiment, the third embodiment or the fourth embodiment proposed in the present disclosure is performed under different conditions. The feature of the first (5-3) embodiment is that when an MCG (or Pcell) radio link failure is detected, if both dual connectivity and carrier aggregation have been configured in the terminal, the MCG (or Pcell) radio link failure is first reported using carrier aggregation. In addition, the feature of the first (5-3) embodiment is that when there is no MCG Scell ​​that meets the predetermined condition, and both SRB3 and separation SRB1 are configured in the dual connectivity, the MCG (or Pcell) radio link failure is reported through separation SRB1. The reason is that when the connection to the MCG base station operates normally, it can be determined that the Scell ​​of the MCG has a lower transmission delay, and it can be determined that the separation SRB1 directly connected to the MCG has a lower transmission delay than the SRB3 connected to the SCG. When SRB1 has not been configured, the MCG (or Pcell) radio link failure can be reported through SRB3. When a separate SRB1 or SRB3 is not configured and therefore the MCG radio link failure cannot be reported as described above, the terminal may trigger the RRC connection reestablishment procedure in order to reconfigure the connection.

[0329] - When carrier aggregation is configured in the terminal (or dual connectivity is configured) when MCG (or Pcell) radio link failure is detected,

[0330] ■ If a Scell ​​that meets a predetermined condition is configured when an MCG (or Pcell) radio link failure is detected (eg, as in the fourth embodiment),

[0331] ◆The terminal reports the MCG (or Pcell) radio link failure to the base station through the Scell ​​that meets the predetermined condition. The report can be performed as in the method proposed in the present disclosure (for example, the fourth embodiment). In another method, if dual connectivity is configured in the terminal and a separate SRB1 is configured, the MCG (or Pcell) radio link failure message can be sent to the SCG and the Scell ​​of the MCG by duplicating the MCG (or Pcell) radio link failure message through the separate SRB1 using a packet replication technology to report the MCG (or Pcell) radio link failure.

[0332] ■ Otherwise (or if there is no MCG Scell ​​satisfying the predetermined condition in the terminal, or if a separate SRB1 connected to the SCG base station is configured (or if SRB3 is configured)),

[0333] ◆ The terminal reports the MCG (or Pcell) radio link failure to the base station by detaching SRB1. The reporting may be performed as in the method proposed in the present disclosure (eg, the second embodiment).

[0334] ■ Otherwise (or if there is no MCG Scell ​​satisfying the predetermined condition in the terminal, or if a separate SRB1 connected to the SCG base station is not configured and / or SRB3 is configured),

[0335] ◆ The terminal reports the MCG (or Pcell) radio link failure to the base station via SRB3. The reporting may be performed as in the method proposed in the present disclosure (eg, the second embodiment).

[0336] ■Otherwise,

[0337] ◆The terminal triggers the RRC connection reestablishment process to reconfigure the connection.

[0338] The following describes the (5-4) embodiment, in which the first embodiment, the second embodiment, the third embodiment or the fourth embodiment proposed in the present disclosure is performed under different conditions. The (5-4) embodiment is characterized in that when an MCG (or Pcell) radio link failure is detected, if both dual connectivity and carrier aggregation have been configured in the terminal, the MCG (or Pcell) radio link failure is first reported to the Scell ​​using carrier aggregation. In addition, the (5-4) embodiment is characterized in that when there is no MCG Scell ​​that meets the predetermined condition, and both SRB3 and separate SRB1 are configured in the dual connectivity, the MCG (or Pcell) radio link failure is reported through SRB3. The reason is that when the connection to the MCG base station operates normally, it can be determined that the Scell ​​of the MCG has a lower transmission delay, and it can be determined that the SRB3 connected to the SCG has a higher reliability than the separate SRB1 directly connected to the MCG. When SRB3 has not been configured, the MCG (or Pcell) radio link failure can be reported through the separate SRB1. When a separate SRB1 or SRB3 has not been configured and therefore cannot report an MCG radio link failure as described above, the terminal may trigger an RRC connection reestablishment procedure in order to reconfigure the connection.

[0339] - When carrier aggregation is configured in the terminal (or dual connectivity is configured) when MCG (or Pcell) radio link failure is detected,

[0340] ■ If a Scell ​​that meets a predetermined condition is configured when an MCG (or Pcell) radio link failure is detected (eg, as in the fourth embodiment),

[0341] ◆The terminal reports the MCG (or Pcell) radio link failure to the base station through the Scell ​​that meets the predetermined condition. The report can be performed as in the method proposed in the present disclosure (for example, the fourth embodiment). In another method, if dual connectivity is configured in the terminal and a separate SRB1 is configured, the MCG (or Pcell) radio link failure message can be sent to the SCG and the Scell ​​of the MCG by duplicating the MCG (or Pcell) radio link failure message through the separate SRB1 using a packet replication technology to report the MCG (or Pcell) radio link failure.

[0342] ■ Otherwise (or if there is no MCG Scell ​​satisfying the predetermined condition in the terminal, or if SRB3 connected to the SCG base station is configured (or if SRB1 is configured to be separated)),

[0343] ◆ The terminal reports the MCG (or Pcell) radio link failure to the base station via SRB3. The reporting may be performed as in the method proposed in the present disclosure (eg, the second embodiment).

[0344] ■ Otherwise (or if there is no MCG Scell ​​satisfying the predetermined condition in the terminal, or if SRB3 connected to the SCG base station is not configured and / or detached SRB1 is configured),

[0345] ◆ The terminal reports the MCG (or Pcell) radio link failure to the base station by detaching SRB1. The reporting may be performed as in the method proposed in the present disclosure (eg, the second embodiment).

[0346] ■Otherwise,

[0347] ◆The terminal triggers the RRC connection reestablishment process to reconfigure the connection.

[0348] SRB3 refers to a coded bearer and is a bearer configured in the SCG of the terminal, through which the terminal can send an RRC message directly to the SCG base station via the SCG MAC layer device. The SCG base station can transmit the RRC message received through SRB3 to the MCG. Separate SRB1 refers to an SRB in which one PDCP layer device is connected to the MCG or SCG, two RLC layer devices are connected to one PDCP layer device and perform data transmission / reception, one RLC layer device is connected to the MCG MAC layer device, and the other RLC layer devices are connected to the SCG MAC layer device. The PDCP layer device can be configured for the MCG. Therefore, when the terminal sends an RRC message to the MCG RLC layer device when sending an RRC message through the separate SRB1, the RRC message is directly sent to the MCG base station through the MCG MAC layer device. When the terminal sends an RRC message to the SCG RLC layer device, the RRC message can be sent to the MCG base station through the SCG base station. The RRC message can be sent to the MCG RLC layer device or the SCG RLC layer device by using packet replication.

[0349] The following describes the first (5-5) embodiment, in which the first embodiment, the second embodiment, the third embodiment or the fourth embodiment proposed in the present disclosure is performed under different conditions. The feature of the first (5-5) embodiment is that when the MCG (or Pcell) radio link failure is detected, if both dual connectivity and carrier aggregation have been configured in the terminal, the MCG (or Pcell) radio link failure is first reported using the dual connectivity. In addition, the feature of the first (5-5) embodiment is that when both SRB3 and separate SRB1 are configured in the dual connectivity, the MCG (or Pcell) radio link failure is reported through SRB3 or separate SRB1. The reason is that when the connection to the SCG base station operates normally, it can be determined that the connection to the SCG has a higher reliability than the connection to the Scell ​​of the MCG. When separate SRB1 or SRB3 has not been configured and there is an MCG Scell ​​that meets the predetermined conditions, the MCG (or Pcell) radio link failure can be reported through the Scell. When the radio link failure cannot be reported as described above, the terminal can trigger the RRC connection reestablishment process to reconfigure the connection.

[0350] - When dual connectivity is configured in the terminal (or carrier aggregation is configured) when MCG (or Pcell) radio link failure is detected,

[0351] ■If SRB3 connected to the SCG base station is configured in the terminal (or SRB1 is configured to be separated),

[0352] ◆The terminal reports the MCG (or Pcell) radio link failure to the base station through SRB3 or separated SRB1. The reporting may be performed as in the method proposed in the present disclosure (e.g., the second embodiment). In another method, if carrier aggregation is configured in the terminal and a Scell ​​that meets a predetermined condition is configured, the MCG (or Pcell) radio link failure message may be sent to the SCG and the Scell ​​of the MCG in a replicated manner through separated SRB1 using a packet replication technique to report the MCG (or Pcell) radio link failure.

[0353] ■ Otherwise (or if, when the MCG (or Pcell) radio link failure is detected, SRB3 is not configured in the terminal, split SRB1 is not configured, and / or carrier aggregation is configured and a Scell ​​that satisfies a predetermined condition is configured (for example, as in the fourth embodiment)),

[0354] ◆ The terminal reports the MCG (or Pcell) radio link failure to the base station through the Scell ​​that meets the predetermined condition. The reporting may be performed as in the method proposed in the present disclosure (eg, the fourth embodiment).

[0355] ■Otherwise,

[0356] ◆The terminal triggers the RRC connection reestablishment process to reconfigure the connection.

[0357] In the method proposed in the present disclosure, when an MCG (or Pcell) radio link failure is detected, the terminal reports the radio link failure via SRB3 or split SRB1 by using dual connectivity, or reports the radio link failure via an MCG Scell ​​that satisfies a predetermined condition by using carrier aggregation. However, when the first timer or the second timer proposed above has expired (for example, when an RRC message corresponding to the MCG radio link failure report is not received from the base station until the timer expires), the terminal can trigger an RRC connection reestablishment process in order to reconfigure the connection.

[0358] As described above, when an MCG (or Pcell) radio link failure is detected, the terminal reports the radio link failure via SRB3 or separate SRB1 by using dual connectivity, or reports the radio link failure via the Scell ​​of the MCG that meets predetermined conditions by using carrier aggregation. At this time, when the base station indicates through an RRC message using an indicator that the base station can perform or support the MCG radio link failure recovery function, or the base station broadcasts support for the MCG radio link failure recovery function in the system information, when a radio link failure occurs, the terminal can report the MCG radio link failure based on its priority according to the method proposed in the present disclosure. In the case where the base station has determined that the terminal capability supports the MCG radio link failure recovery function through a terminal capability report message, by using an indicator through an RRC message, when the base station configures dual connectivity or carrier aggregation for the terminal, or when the base station performs bearer configuration through an RRC message, the base station can configure for the terminal whether the MCG radio link failure recovery method proposed in the present disclosure can be applied when an MCG radio link failure occurs.

[0359] In another method, in the case where the base station has determined through a terminal capability report message that the terminal capability supports the MCG radio link failure recovery function, the base station may notify the terminal through an RRC message and an indicator defined for each bearer or each type of cell configuration information, when the base station configures dual connectivity or carrier aggregation for the terminal, or when the base station performs bearer configuration through an RRC message, through which the MCG (or Pcell) radio link failure is reported when the MCG radio link failure occurs (e.g., separate SRB1 or SRB3), or through which the Scell ​​(e.g., one or more Scells) in the cell configured with PUCCH through which the MCG (or Pcell) radio link failure is reported when the MCG radio link failure occurs. For example, the base station configures dual connectivity for the terminal through an RRC message (e.g., an RRCReconfiguration message), and when configuring separate SRB1, the indicator may be used to indicate whether the MCG radio link failure recovery method proposed in the present disclosure can be used for the separate SRB1 to be configured. For example, the base station configures dual connectivity for the terminal through an RRC message (e.g., an RRCReconfiguration message), and when SRB3 is configured, an indicator may be used to indicate whether the MCG radio link failure recovery method proposed in the present disclosure can be used for the SRB3 to be configured. For example, the base station configures dual connectivity for the terminal through an RRC message (e.g., an RRCReconfiguration message), and when separate SRB1 and SRB3 are configured, the base station may determine whether the MCG radio link failure recovery method proposed in the present disclosure can be used for separate SRB1 or SRB3 with respect to the separate SRB1 and SRB3 to be configured, and the determination may be indicated by an indicator. When the MCG radio link failure recovery method is supported when separate SRB1 and SRB3 are configured, the base station may specify one of them and determine the terminal to report the MCG radio link failure. In another method, the base station configures dual connectivity for the terminal through an RRC message (e.g., an RRCReconfiguration message), and when configuring separate SRB1 and SRB3, the base station can indicate through an indicator whether the MCG radio link failure recovery method proposed in the present disclosure can be used for separate SRB1 or whether it can be used for SRB3, respectively, with respect to the separate SRB1 and SRB3 to be configured. When the base station indicates that the MCG radio link failure recovery method can be used in both separate SRB1 and SRB3, the terminal can select separate SRB1 or SRB3 through implementation (e.g., select a bearer connected to a MAC layer device or a cell with stronger signal strength), and when an MCG radio link failure occurs, the MCG radio link failure can be reported through the selected separate SRB1 or SRB3.

[0360] For example, the base station configures carrier aggregation for the terminal through an RRC message (e.g., an RRCReconfiguration message), and when multiple Scells are configured, it can be determined for the Scell ​​to be configured whether the MCG radio link failure recovery method proposed in the present disclosure can be used in each Scell, and the determination can be indicated by an indicator. In addition, the base station can specify a Scell ​​and determine that the terminal reports the MCG radio link failure through the specified Scell. In another method, the base station configures carrier aggregation for the terminal through an RRC message (e.g., an RRCReconfiguration message), and when multiple Scells are configured, it can be indicated for the Scell ​​to be configured by an indicator whether the MCG radio link failure recovery method proposed in the present disclosure can be used in each Scell. When the base station indicates through an indicator that the MCG radio link failure recovery method can be used in multiple Scells, the terminal can select an Scell ​​from multiple Scells in which the MCG radio link failure recovery method can be used through implementation (for example, select an Scell ​​connected to a MAC layer device or a cell with stronger signal strength, or an Scell ​​that satisfies a predetermined condition (for example, the first condition)), and when an MCG radio link failure occurs, the MCG radio link failure can be reported through the selected Scell.

[0361] For example, the base station configures carrier aggregation for the terminal through an RRC message (e.g., an RRCReconfiguration message), and when multiple Scells, separate SRB1s, or SRB3s are configured, it can be determined whether the MCG radio link failure recovery method proposed in the present disclosure can be used in each Scell, separate SRB1, or SRB3 relative to the Scell, separate SRB1, or SRB3 to be configured, and the determination can be indicated by an indicator. In addition, the base station can specify one Scell, separate SRB1, or SRB3, and can determine that the terminal reports the MCG radio link failure through the specified Scell, separate SRB1, or SRB3. In another method, the base station configures carrier aggregation for the terminal through an RRC message (e.g., an RRCReconfiguration message), and when multiple Scells, separate SRB1s, or SRB3s are configured, it can be determined whether the MCG radio link failure recovery method proposed in the present disclosure can be used in each Scell, separate SRB1, or SRB3 relative to the Scell, separate SRB1, or SRB3 to be configured, respectively. When the base station indicates that the MCG radio link failure recovery method proposed in the present disclosure can be used in each Scell, separate SRB1 or SRB3, the terminal can select an Scell ​​from multiple Scells, separate SRB1 or SRB3 that can use the MCG radio link failure recovery method (for example, select an Scell ​​or bearer (separate SRB1 or SRB3) connected to a MAC layer device or a cell with stronger signal strength, or an Scell ​​or bearer (separate SRB1 or SRB3) that satisfies a predetermined condition (for example, the first condition, the second condition, the third condition, the fourth condition, the fifth condition or the sixth condition), and when the MCG radio link failure occurs, the MCG radio link failure can be reported through the selected Scell.

[0362] When the terminal determines that an MCG radio link failure has occurred according to the method proposed in the present disclosure, the terminal may include information indicating that an MCG radio link failure has occurred in an RRC message (e.g., a ULInformationTransferMRDC message or a FailureInformation message), and send the RRC message by separating SRB1, SRB3, or Scell, so that the base station (MCG or SCG) can identify the MCG radio link failure of the terminal. When the radio link of the terminal fails, in response thereto, the base station (MCG or SCG) may generate an RRC message (e.g., an RRCReconfiguration message or an RRCRelease message) and send the RRC message to the terminal. When the SCG base station sends a response RRC message (e.g., an RRCReconfiguration message or an RRCRelease message) generated by the MCG base station, the SCG base station may transmit another RRC message (e.g., a DLInformationTranferMRDC message) including the response RRC message to the terminal. When the terminal receives an RRCReconfiguration message as a response message in response to an MCG radio link failure report (an RRC message received from an MCG base station or an SCG base station by separating SRB1 or SRB3), the terminal can complete the application of the configuration information of the received message, and then can send an RRCReconfigurationComplete message to the MCG base station or the SCG base station again by separating SRB1 or SRB3 in response to the RRCReconfiguration message. When the RRCReconfiguration message indicates switching or access to another cell, the terminal can complete random access to the cell and send an RRCReconfigurationComplete message through SRB1. However, when the terminal receives an RRCRelease message as a response message in response to an MCG radio link failure report (an RRC message received from an MCG base station or an SCG base station by separating SRB1 or SRB3), the terminal can switch to an RRC idle mode or an RRC inactive mode according to the configuration information indicated by the RRCRelease message, but may not send an additional response to the RRC message to the base station.

[0363] Fig. 1I The structure of a terminal to which the embodiment can be applied according to the embodiment of the present disclosure is shown.

[0364] refer to Fig. 1I The terminal includes a radio frequency (RF) processor 1i-10, a baseband processor 1i-20, a storage unit 1i-30 and a controller 1i-40.

[0365] The RF processor 1i-10 performs functions such as signal band conversion and signal amplification for sending / receiving signals through wireless channels. That is, the RF processor 1i-10 up-converts the baseband signal provided by the baseband processor 1i-20 into an RF band signal and transmits the RF band signal via an antenna, and down-converts the RF band signal received via the antenna into a baseband signal. For example, the RF processor 1i-10 may include a transmitting filter, a receiving filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC), etc. Fig. 1I In the figure, only one antenna is shown. However, the terminal may include multiple antennas. In addition, the RF processor 1i-10 may include multiple RF chains. The RF processor 1i-10 can perform beamforming. For beamforming, the RF processor 1i-10 can adjust the phase and size of each signal sent or received through multiple antennas or antenna elements. In addition, the RF processor can perform MIMO, and can receive multiple layers while performing MIMO. The RF processor 1i-10 can appropriately configure multiple antennas or antenna elements according to the control of the controller to perform receive beam scanning or adjust the beam direction and beam width so that the receive beam matches the transmit beam.

[0366] The baseband processor 1i-20 performs conversion between baseband signals and bit streams according to the physical layer specifications of the system. For example, when data is transmitted, the baseband processor 1i-20 encodes and modulates the transmitted bit stream to generate complex symbols. In addition, when data is received, the baseband processor 1i-20 reconstructs the received bit stream by demodulating and decoding the baseband signal provided from the RF processor 1i-10. For example, according to the orthogonal frequency division multiplexing (OFDM) scheme, when data is transmitted, the baseband processor 1i-20 encodes and modulates the transmitted bit stream to generate complex symbols, maps the complex symbols to subcarriers, and forms OFDM symbols through inverse fast Fourier transform (IFFT) operations and cyclic prefix (CP) insertion. In addition, when data is received, the baseband processor 1i-20 divides the baseband signal provided from the RF processor 1i-10 into OFDM symbol units, reconstructs the signal mapped to the subcarrier through a fast Fourier transform (FFT) operation, and reconstructs the received bit stream through demodulation and decoding.

[0367] The RF processor 1i-10 and the baseband processor 1i-20 send and receive signals as described above. Therefore, each of the RF processor 1i-10 and the baseband processor 1i-20 can be referred to as a sending unit, a receiving unit, a sending / receiving unit, or a communication unit. In addition, at least one of the RF processor 1i-10 or the baseband processor 1i-20 may include multiple communication modules to support a variety of different radio access technologies. In addition, at least one of the RF processor 1i-10 or the baseband processor 1i-20 may include different communication modules to process signals in different frequency bands. For example, different radio access technologies may include LTE networks, NR networks, and the like. In addition, different frequency bands may include ultra-high frequency (SHF) (e.g., 2.5 GHz, 5 GHz) bands and millimeter wave (mm Wave) (e.g., 60 GHz) bands.

[0368] The storage unit 1i-30 stores data used for the operation of the terminal, such as default programs, application programs, configuration information, etc. The storage unit 1i-30 provides the stored data in response to a request of the controller 1i-40.

[0369] The controller 1i-40 controls the overall operation of the terminal. For example, the controller 1i-40 can send / receive signals via the baseband processor 1i-20 and the RF processor 1i-10. In addition, the controller 1i-40 records and reads to / from the storage unit 1i-30. To this end, the controller 1i-40 may include at least one processor. For example, the controller 1i-40 may include a communication processor (CP) for controlling communication and an application processor (AP) for controlling an upper layer (such as an application).

[0370] Figure 1J A block diagram configuration of a TRP in a wireless communication system to which an embodiment of the present disclosure can be applied is shown.

[0371] refer to Figure 1J The base station includes an RF processor 1j-10, a baseband processor 1j-20, a backhaul communication unit 1j-30, a storage unit 1j-40 and a controller 1j-50.

[0372] The RF processor 1j-10 performs functions such as signal band conversion and signal amplification for sending / receiving signals through a wireless channel. That is, the RF processor 1j-10 up-converts the baseband signal provided by the baseband processor 1j-20 into an RF band signal and transmits the RF band signal via an antenna, and down-converts the RF band signal received via the antenna into a baseband signal. For example, the RF processor 1j-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Figure 1J, only one antenna is shown. However, the first access node may include multiple antennas. In addition, the RF processor 1j-10 may include multiple RF chains. In addition, the RF processor 1j-10 can perform beamforming. For beamforming, the RF processor 1j-10 can adjust the phase and size of each signal sent or received through multiple antennas or antenna elements. The RF processor can send one or more layers to perform downlink MIMO operations.

[0373] The baseband processor 1j-20 performs conversion between baseband signals and bit streams according to the physical layer specifications of the first radio access technology. For example, when data is transmitted, the baseband processor 1j-20 encodes and modulates the transmitted bit stream to generate complex symbols. In addition, when data is received, the baseband processor 1j-20 reconstructs the received bit stream by demodulating and decoding the baseband signal provided from the RF processor 1j-10. For example, according to the OFDM scheme, when data is transmitted, the baseband processor 1j-20 encodes and modulates the transmitted bit stream to generate complex symbols, maps the complex symbols to subcarriers, and forms OFDM symbols through IFFT operations and CP insertion. In addition, when data is received, the baseband processor 1j-20 divides the baseband signal provided by the RF processor 1j-10 into OFDM symbol units, reconstructs the signal mapped to the subcarriers through FFT operations, and reconstructs the received bit stream through demodulation and decoding. The RF processor 1j-10 and the baseband processor 1j-20 send and receive signals as described above. Therefore, each of the RF processor 1j-10 and the baseband processor 1j-20 can be referred to as a transmitting unit, a receiving unit, a transmitting / receiving unit, a communication unit, or a wireless communication unit.

[0374] The backhaul communication unit 1j-30 provides an interface for communicating with other nodes within the network.

[0375] The storage unit 1j-40 stores data used for the operation of the main base station, such as default programs, applications, configuration information, etc. Specifically, the storage unit 1j-40 can store information about the bearer assigned to the connection terminal, the measurement results reported from the connection terminal. In addition, the storage unit 1j-40 can provide multiple connections to the terminal, or can provide information as a reference for determining whether to stop the connection. In addition, the storage unit 1j-40 provides the stored data in response to a request from the controller 1j-50.

[0376] The controller 1j-50 controls the overall operation of the main base station. For example, the controller 1j-50 sends / receives signals via the baseband processor 1j-20 and the RF processor 1j-10 or via the backhaul communication unit 1j-30. In addition, the controller 1j-50 records data to the storage unit 1j-40 and reads data from the storage unit 1j-40. To this end, the controller 1j-50 may include at least one processor.

[0377] While the present disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the present disclosure as defined, for example, by the appended claims and their equivalents.

Claims

1. A method performed by a terminal in a wireless communication system, the method comprising: detecting a radio link failure of a master cell group (MCG) associated with a primary base station; as well as Sending a message about a radio link failure of the MCG to the primary base station via a secondary cell group (SCG) associated with the secondary base station using a split signaling radio bearer (SRB) 1 or SRB3 configured as a split signaling radio bearer (SRB) 1, Wherein, when SRB1 is configured as a split SRB and packet data convergence protocol (PDCP) duplication is not configured, the configuration for uplink transmission is changed from a primary radio link control (RLC) entity associated with the MCG to a secondary radio link control (RLC) entity associated with the SCG.

2. The method according to claim 1, wherein: In case SRB1 is configured as a detached SRB, a message about the radio link failure of the MCG is sent through SRB1.

3. The method according to claim 1, wherein: In case SRB1 is not configured as a detached SRB, the message about the radio link failure of the MCG is sent through SRB3.

4. The method according to claim 1, further comprising: starting a timer associated with the radio link failure, and Wherein, in case a response is received from the MCG, the timer is stopped.

5. The method according to claim 1, further comprising: In case the timer expires, a Radio Resource Control (RRC) connection reestablishment procedure is triggered.

6. The method according to claim 1, further comprising: In case a radio link failure to the SCG is detected while MCG transmission is suspended, a Radio Resource Control (RRC) connection re-establishment procedure is triggered.

7. The method according to claim 1, further comprising: For all SRBs except SRB0, MCG transmission is suspended; and Reset the MCG Media Access Control (MAC).

8. The method according to claim 1, in, In case the SCG is not deactivated, a message regarding the radio link failure of the MCG is sent.

9. A terminal in a wireless communication system, comprising: Transceiver; as well as A controller is connected to the transceiver, wherein the controller is configured to: detecting a radio link failure of a master cell group (MCG) associated with a primary base station; and Sending a message about a radio link failure of the MCG to the primary base station via a secondary cell group (SCG) associated with the secondary base station using a split signaling radio bearer (SRB) 1 or SRB3 configured as a split signaling radio bearer (SRB) 1, Wherein, when SRB1 is configured as a split SRB and packet data convergence protocol (PDCP) duplication is not configured, the configuration for uplink transmission is changed from a primary radio link control (RLC) entity associated with the MCG to a secondary radio link control (RLC) entity associated with the SCG.

10. The terminal according to claim 9, wherein: In case SRB1 is configured as a detached SRB, a message about the radio link failure of the MCG is sent through SRB1.

11. The terminal according to claim 9, wherein: In case SRB1 is not configured as a detached SRB, the message about the radio link failure of the MCG is sent through SRB3.

12. The terminal according to claim 9, wherein: The controller is also configured to: starting a timer associated with a radio link failure, Wherein, in case a response is received from the MCG, the timer is stopped.

13. The terminal according to claim 9, wherein: The controller is also configured to: In case the timer expires, a Radio Resource Control (RRC) connection reestablishment procedure is triggered.

14. The terminal according to claim 9, wherein: The controller is also configured to: In case a radio link failure to the SCG is detected while MCG transmission is suspended, a Radio Resource Control (RRC) connection re-establishment procedure is triggered.

15. The terminal according to claim 9, wherein: The controller is also configured to: For all SRBs except SRB0, MCG transmission is suspended; and Reset the MCG Media Access Control (MAC).

16. The terminal according to claim 9, in, In case the SCG is not deactivated, a message regarding the radio link failure of the MCG is sent.

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