Method and apparatus for reporting fast MCG recovery information in next generation mobile communication system

Abstract

The present invention relates to a method for a terminal, comprising the steps of: detecting radio link failure (RLF) for a master cell group (MCG) among the MCG and a secondary cell group (SCG), in which dual connectivity (DC) is set for the terminal; transmitting a first radio resource control (RRC) message to the SCG if at least one condition for transmitting the first RRC message including information indicating the RLF for the MCG to the SCG is satisfied; if a second RRC message including information related to a target cell is received from the SCG, performing a procedure for establishing a connection with the target cell on the basis of the information related to the target cell; and identifying connection failure with the target cell, wherein first information about the RLF for the MCG is stored in an RLF report, and second information about the connection failure is additionally stored in the RLF report in which the first information is stored.

Description

Method and device for reporting FAST MCG LINK RECOVERY information in a next-generation mobile communication system

[0001] The present disclosure relates to a technique for reporting information related to fast MCG link recovery operations.

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

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

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

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

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

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

[0008] Meanwhile, when a terminal is connected to base stations via dual connectivity, if a connection issue with the SN occurs, it is reported to the MN, triggering an SCG reset operation. However, if a connection issue with the MN occurs, an RLF declaration and connection re-establishment operation may be performed. To address the time required for connection recovery, the fast MCG link recovery operation was introduced.

[0009] One purpose of the present disclosure is to provide a method for reporting information related to a fast MCG link recovery operation to a network through an existing reporting mechanism.

[0010] In order to solve the above problems, the present invention provides a method performed by a terminal in a wireless communication system, the method comprising: detecting a radio link failure (RLF) for a master cell group (MCG) and a secondary cell group (SCG) for which dual connectivity (DC) is set for the terminal; transmitting a first radio resource control (RRC) message including information indicating the RLF for the MCG to the SCG when at least one condition for transmitting the first RRC message including the information indicating the RLF for the MCG is satisfied; performing a procedure for establishing a connection with a target cell based on the information related to the target cell when a second RRC message including information related to a target cell is received from the SCG; and confirming a connection failure with the target cell, wherein the first information about the RLF for the MCG is stored in an RLF report, and the second information about the connection failure is additionally stored in the RLF report in which the first information is stored.

[0011] According to an example of the present disclosure, when a fast MCG link recovery operation is triggered, information related thereto can be reported to the network using an existing reporting mechanism, and even if a handover failure occurs during the fast MCG link recovery operation, there is an effect of being able to appropriately report information related to fast MCG link recovery and information related to handover failure to the network.

[0012] FIG. 1 is a diagram illustrating the structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0013] FIG. 2 is a diagram for explaining a Radio Link Monitoring (RLM) operation according to one embodiment of the present disclosure.

[0014] FIG. 3 is a diagram for explaining a Radio Link Failure (RLF) operation according to one embodiment of the present disclosure.

[0015] FIG. 4 is a diagram for explaining a fast MCG link recovery operation according to an embodiment of the present disclosure.

[0016] FIG. 5 is a flowchart of a procedure for setting up a fast MCG link recovery operation according to an embodiment of the present disclosure.

[0017] FIG. 6 is a flowchart of an operation for reporting fast MCG link recovery-related information according to an embodiment of the present disclosure.

[0018] FIG. 7 is a flowchart of a terminal operation for reporting fast MCG link recovery-related information according to an embodiment of the present disclosure.

[0019] FIG. 8 is a diagram illustrating a problem in which previous RLF Report information is lost due to a handover failure according to an embodiment of the present disclosure.

[0020] FIG. 9 is a flowchart of a terminal operation for reporting fast MCG link recovery-related information after a handover failure according to an embodiment of the present disclosure.

[0021] FIG. 10 is a flowchart of a terminal operation for reporting fast MCG link recovery-related information after a handover failure according to an embodiment of the present disclosure.

[0022] Figure 11 is a block diagram showing the internal structure of a terminal according to the present disclosure.

[0023] Fig. 12 is a block diagram showing the configuration of a base station according to the present disclosure.

[0024] In the following description of the present invention, detailed descriptions of related known functions or configurations will be omitted if they are deemed to unnecessarily obscure the gist of the present invention. Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. The terms described below are defined based on their functions in the present invention and may vary depending on the intent or custom of the user or operator. Therefore, their definitions should be based on the contents throughout this specification.

[0025] FIG. 1 is a diagram illustrating the structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0026] Referring to FIG. 1, as illustrated, a wireless access network of a next-generation mobile communication system (New Radio, NR) is composed of a next-generation base station (New Radio Node B, hereinafter referred to as gNB) (1a-10) and an access and mobility management function (AMF) (1a-05, New Radio Core Network). A user terminal (New Radio User Equipment, hereinafter referred to as NR UE or terminal) (1a-15) accesses an external network through the gNB (1a-10) and the AMF (1a-05).

[0027] In Fig. 1, the gNB corresponds to the eNB (Evolved Node B) of the existing LTE (long term evolution) system. The gNB is connected to the NR UE via a wireless channel and can provide a service superior to the existing Node B (1a-20). In the next-generation mobile communication system, all user traffic is serviced through a shared channel, so a device that collects status information such as the buffer status of UEs, available transmission power status, and channel status and performs scheduling is required, and this is handled by the gNB (1a-10). A single gNB typically controls multiple cells. In order to implement ultra-high-speed data transmission compared to the existing LTE, it can have a bandwidth higher than the existing maximum, and beamforming technology can be additionally incorporated using the orthogonal frequency division multiplexing (OFDM) as a wireless access technology. In addition, an adaptive modulation and coding (AMC) method is applied, which determines the modulation scheme and channel coding rate according to the channel status of the terminal.

[0028] The AMF (1a-05) performs functions such as mobility support, bearer setup, and QoS (quality of service) setup. The AMF is a device that handles various control functions as well as mobility management for terminals and is connected to multiple base stations. Furthermore, the next-generation mobile communication system can be interoperable with the existing LTE system, and the AMF is connected to the mobility management entity (MME) (1a-25) via a network interface. The MME is connected to the existing base station, the eNB (1a-30). Terminals that support LTE-NR Dual Connectivity can transmit and receive data while maintaining connections to both the gNB and the eNB (1a-35).

[0029] FIG. 2 is a diagram for explaining the Radio Link Monitoring (RLM) operation in the present disclosure.

[0030] Referring to Figure 2, the physical (PHY) layer of the terminal measures the quality of the downlink signal from the cell-specific reference signal (CRS) of the serving cell (1b-05). Then, in the physical layer of the terminal, the measured signal quality is determined to be greater than a specific threshold value Q. out Determine whether the threshold value is lower than (1b-10). Here, the threshold value is a signal quality value corresponding to a specific BLER (block error rate) measured on a PDCCH (physical downlink control channel). If the signal quality is lower than a specific threshold value Q out If it is lower, the physical layer transmits an 'out-of-sync' indication to the higher layer. This operation is called RLM in LTE technology. If the indication is transmitted to the higher layer more than a certain number of times, the higher layer starts a specific timer, and when the timer expires, declares an RLF (1b-15).

[0031] FIG. 3 is a diagram for explaining the Radio Link Failure (RLF) operation in the present disclosure.

[0032] As explained above, RLF can be declared based on the result of RLM operation. More specifically, referring to Fig. 3, the terminal physical layer can be declared at a specific period, Q out At each evaluation period, the downlink signal quality measured from the CRS of the serving cell is reduced to a certain threshold Q. out Determine whether the measured signal quality is lower than a certain threshold value Q. out If the physical layer is lower than the threshold Q, the physical layer transmits an 'out-of-sync' indicator to the upper layer. After the initial indicator is transmitted to the upper layer (1c-05), if the out-of-sync indicator is transmitted to the upper layer a specific number of times N310, a specific timer T310 is started in the upper layer (1c-10). In addition, the physical layer is configured to detect if the downlink signal quality measured from the CRS of the serving cell is below a specific threshold Q. in It is also determined whether the measured signal quality is higher than a certain threshold Q. inIf higher, the physical layer transmits an 'in-sync' indicator to the upper layer. When the in-sync indicator is transmitted to the upper layer a certain number of times, the T310 timer running in the upper layer is stopped. If the T310 timer expires without being stopped, the upper layer declares an RLF (1c-15). After the RLF is declared, the terminal starts another timer T311. Then, the terminal searches for a new suitable cell. If a new suitable cell is not found before the T311 expires, the terminal switches to idle mode (1c-25). On the other hand, if a new suitable cell is found before the timer T311 expires, the terminal starts the T301 timer based on this and performs a re-establishment process with the cell (1c-20). At this time, if the re-establishment is not successfully completed before the T301 timer expires, the terminal switches to idle mode (1c-30). If the above re-establishment is successful, the terminal continues in connected mode in the cell.

[0033] Meanwhile, RLF can be declared by the above RLM operation, and can also be declared by other conditions. For example, as shown in (2) of Fig. 3, RLF can be declared even when random access fails (1c-35). As another example, as shown in (3) of Fig. 3, RLF is declared even when the maximum number of retransmissions is reached in the RLC (radio link control) layer, for example, when a packet is not successfully transmitted (1c-40). The description of the operations related to the above-described T301 and T311 operations is as follows [Table 1].

[0034]

[0035] As in (4) of Fig. 3, an RLF can be declared even when a handover fails. When the terminal receives an RRCConnectionReconfiguration message containing handover configuration information, for example, a mobilityControlInfo IE (1c-45), it starts a T304 timer. The timer value of T304 is provided in the mobilityControlInfo. If a random access with the target cell is not successfully completed before the T304 timer expires, it is considered a handover failure and an RLF is declared (1c-50).

[0036] When an RLF occurs at a terminal, certain information collected is useful for optimizing cell coverage. Therefore, the terminal stores this information when an RLF occurs, and when the terminal successfully transitions to connected mode, the stored information is reported to the base station. This report is referred to as an RLF Report, and the information reported is as follows.

[0037] - plmn-IdentityList

[0038] - measResultLastServCell

[0039] - measResultNeighCells

[0040] - locationInfo

[0041] - failedPCellId

[0042] - previousPCellId

[0043] - timeConnFailure

[0044] - C-RNTI used in the source PCell

[0045] - connectionFailureType

[0046] After an RLF occurs, the terminal performs cell selection and RRC reestablishment operations. The information collected during this process can be useful for optimizing cell coverage.

[0047] FIG. 4 is a diagram for explaining a fast MCG link recovery operation according to an embodiment of the present disclosure.

[0048] A terminal (1d-15) configured with Dual Connectivity can transmit and receive data by connecting to two base stations, a Master Node (MN, 1d-05) and a Secondary Node (SN, 1d-10). If a problem occurs in the connection with the SN, the terminal can report the problem to the MN. The MN, upon receiving this report, can reset the Secondary Cell Group (SCG). On the other hand, if a problem occurs in the connection with the MN, the terminal declares an RLF and performs a re-establishment process. However, restoring the connection state through the re-establishment process takes a rather long time and has the disadvantage of having to reapply most of the settings.

[0049] To overcome the above-mentioned shortcomings, the Rel-16 NR standard introduced fast MCG (master cell group) link recovery technology. In this technology, when a terminal configured with Dual Connectivity (DC) experiences a problem in connecting to an MN, the terminal declares an RLF and then transmits a predetermined radio resource control (RRC) message, MCGFailureInformation, indicating the MCG failure (1d-20), to the SN. If the SN and a Split SRB (signaling radio bearer) (1d-25) are configured, the terminal transmits the RRC message to the MN via the Split SRB, i.e., via the SN. Conversely, if the SN and SRB 3 (1d-30) are configured, the terminal transmits the RRC message to the MN via the SN via the SRB 3. When the SRB 3 is used, a ULInformationTransferMRDC message is transmitted to the SN as an RRC message containing the MCGFailureInformation message. Along with the transmission of the MCGFailureInformation, a predetermined timer, T316, is started, and the re-establishment operation is postponed until the started T316 timer expires. If an RRCRelease or RRCReconfiguration message configuring a handover is received from the SN before the T316 timer expires, the terminal stops the T316 timer. Specifically, the T316 timer is started when the MCGFailureInformation message is transmitted, and is stopped when at least one of the following conditions is satisfied.

[0050] - When receiving the RRCRelease message

[0051] - When receiving an RRCReconfiguration message including a reconfigurationWithSync IE for PCell (primary cell)

[0052] - When receiving a MobilityFromNRCommand message (for inter-RAT (radio access technology) handover purposes)

[0053] - When the re-establishment action is triggered

[0054] When SRB 3 is used to transmit the MCGFailureInformation message, the SN transmits a DLInformationTransferMRDC message containing an RRCRelease or RRCReconfiguration message that sets up a handover to the UE. If the SN and Split SRB or SRB3 are not configured, the UE cannot perform the fast MCG link recovery operation.

[0055] In the present invention, a case in which a terminal fails to receive the RRCRelease or RRCReconfiguration message configuring a handover until the T316 timer expires despite transmitting the MCGFailureInformation is referred to as a fast MCG link recovery failure. When such a fast MCG link recovery failure occurs, the terminal triggers a re-establishment operation.

[0056] FIG. 5 is a flowchart of a procedure for setting up a fast MCG link recovery operation according to an embodiment of the present disclosure.

[0057] The terminal (1e-05) receives an RRCReconfiguration message containing T316 configuration information from the base station (1e-10) (1e-15). If an RLF occurs during the connection with the MN, the terminal (1e-05) transmits an MCGFailureInformation message to the network (1e-10, e.g., SN) (1e-20). Here, the MCGFailureInformation message includes information as shown in [Table 2] below.

[0058]

[0059] Referring to [Table 2], failureType is used to indicate the cause of connection failure with the MCG. In addition, measResultFreqList, measResultFreqListEUTRA, and measResultFreqListUTRA-FDD included in the MCGFailureInformation message contain the measurement values ​​of the NR frequency, evolved-universal terrestrial radio access (E-UTRA) frequency, or UTRA frequency configured in measConfig. In addition, measResultSCG and measResultSCG-EUTRA contain the measurement values ​​of the NR frequency or E-UTRA frequency configured in measConfig of the SCG.

[0060] When a connection failure with an MCG occurs and an RLF is declared, the terminal stores the information valid at that time. That is, the RLF contents are stored in the terminal, and when the terminal switches to connected mode in the future, it reports an RLF Report containing the RLF contents stored in the base station. The present invention is characterized in that the terminal reports information related to fast MCG link recovery to the network using a predetermined reporting mechanism (e.g., an RLF Report). The present embodiments can be applied not only to NR-DC but also to EN-DC or NE-DC scenarios.

[0061] FIG. 6 is a flowchart of an operation for reporting fast MCG link recovery-related information according to an embodiment of the present disclosure.

[0062] Referring to FIG. 6, the MN base station (1f-10) configures a fast MCG link recovery operation for a terminal (1f-05) configured with Dual Connectivity using a predetermined RRC message, RRCReconfiguration (1f-20). The above configuration includes the T316 timer value.

[0063] Thereafter, the terminal (1f-05) declares an RLF based on the occurrence of a connection failure between MNs and stores (logs) the RLF content (1f-25). In addition, the terminal (1f-05) transmits an MCGFailureInformation message to the SN base station (1f-15) via Split SRB (1f-30) or SRB 3 (1f-35) if certain conditions are satisfied. For example, as described above, the MCGFailureInformation message may be transmitted to the SN (1f-15) via Split SRB (1f-30), or the MCGFailureInformation message may be included in ULInformationTransferMRDC and transmitted to the SN (1f-15) via SRB 3 (1f-35). Here, the certain conditions are as follows.

[0064] - if T316 is configured

[0065] -if SCG transmission is not suspended

[0066] -if the SCG is not deactivated

[0067] - if neither PSCell change nor PSCell addition is ongoing (ie timer T304 for the NR PSCell is not running in case of NR-DC or timer T307 of the E-UTRA PSCell is not running in NE-DC)

[0068] If the MCGFailureInformation message is not triggered, the terminal (1f-05) may store the reason for not triggering the fast MCG link recovery operation and then report this to the network. At this time, the information stored as the reason for not triggering the fast MCG link recovery operation may include the following indicator information.

[0069] - An indicator to indicate if T316 is (not) configured (ie if fast MCG Recovery has been configured)

[0070] - An indicator to indicate if SCG transmission is (not) suspended

[0071] - An indicator to indicate if neither PSCell change nor PSCell addition is ongoing (ie timer T304 for the NR PSCell is not running in case of NR-DC or timer T307 of the E-UTRA PSCell is not running in NE-DC)

[0072] - time information to indicate between MCG failure (or transmitting MCGFailureInformation) and suspending SCG transmission

[0073] - time information to indicate between MCG failure (or transmitting MCGFailureInformation) and the initiation of PSCell change (or PSCell addition)

[0074] The proposed new information can be stored as RLF Report content by the terminal only when AS security is activated. Furthermore, the terminal can configure the new indicators in bitmap form and report them to the base station.

[0075] When SN (1f-15) receives MCGFailureInformation message transmitted by terminal (1f-05), it forwards it to MN (1f-10). At this time, terminal (1f-05) starts T316 timer (1f-40). At this time, if RRCRelease message or RRCReconfiguration message including handover configuration information is received from SN (1f-15) before the running timer 316 expires (1f-45), terminal (1f-05) considers that the fast MCG link recovery operation is successful and stops the running T316 timer (1f-47). In addition, after terminal (1f-05) transmits MCGFailureInformation message, it can store information about RRC message received in response thereto and then report the stored information to the network. At this time, the stored information can include the following indicator information.

[0076] - An indicator to indicate if RRCRelease (Redirection) or RRCReconfiguration (HO command) is received

[0077] - If RRCRelease is received, Redirection-related information included in the RRCRelease, eg information included in ReedirectedCarrierInfo IE

[0078] - Serving cell / neighboring cells measurement results at the reception of RRCRelease

[0079] - If RRCReconfiguration is received, Handover-related information included in RRCReconfiguration, eg target cell-related info (PCI, CGI of target cell)

[0080] - Serving cell / neighboring cells measurement results at the reception of RRCReconfiguration

[0081] The proposed new information can be stored as RLF Report content by the terminal only when AS security is activated. Furthermore, the terminal can configure the new indicators in bitmap form and report them to the base station.

[0082] The terminal (1f-05) according to the example of the present disclosure can store the information proposed above as RLF Report content.

[0083] In contrast, if the terminal (1f-05) does not receive the RRCRelease message or the RRCReconfiguration message including the handover configuration information from the SN (1f-15) until the timer T316 expires, the fast MCG link recovery operation is considered to have failed. For example, the terminal (1f-05) may not have a good wireless link with the SN (1f-15), so that the MCGFailureInformation may not be transmitted to the SN (1f-15), or the RRCRelease or the RRCReconfiguration message configuring the handover from the SN (1f-15) may not be received by the terminal. Alternatively, the information provided by the terminal (1f-05) may not be transmitted from the SN (1f-15) to the MN (1f-10), or the MN (1f-10) may not make any decision even if it receives the information provided by the terminal (1f-05) from the SN (1f-15). In this case, the terminal (1f-05) may store information indicating a problem with the SCG link and then report the stored information to the network. The information stored in the terminal may include the following indicator information.

[0084] - An indicator if SCG transmission is (not) suspended

[0085] - An indicator if SCG is deactivated (eg SCG may deactivate while not identifying MCG RLF and MCGFailureInformation)

[0086] - time information to indicate between the transmission of MCGFailureInformation and suspending SCG transmission

[0087] - time information to indicate between the transmission of and the initiation of PSCell change (or PSCell addition)

[0088] The proposed new information can be stored as RLF Report content by the terminal only when AS security is activated. Furthermore, the terminal can configure the new indicators in bitmap form and report them to the base station.

[0089] If the fast MCG link recovery operation fails, the terminal (1f-05) triggers an RRC re-establishment operation (1f-55). The terminal (1f-05) then performs an RRC (re)establishment operation to switch to a connected mode at a predetermined base station (1f-60). In this drawing, the terminal illustrates an SN as a base station performing an RRC connection (re)establishment, but is not limited thereto, and the terminal may perform a connection (re)establishment operation with other base stations. At this time, the terminal (1f-05) includes an availability indicator indicating that it stores the RLF Report in an RRCSetupComplete or RRCReetablishmentComplete message, and transmits it to the base station that triggered the RRC connection re-establishment. The base station requests a report of the RLF Report using a UEInformationRequest message (1f-65). The terminal (1f-05) that received the above request reports the stored RLF Report to the corresponding base station using the UEInformationResponse message (1f-70).

[0090] FIG. 7 is a flowchart of a terminal operation for reporting fast MCG link recovery related information according to an embodiment of the present disclosure.

[0091] At step 1g-05, the terminal recognizes an MCG failure.

[0092] In step 1g-10, the terminal stores valid information related to MCG failure as RLF content.

[0093] In step 1g-15, the terminal determines whether the conditions for performing the fast MCG link recovery operation are satisfied and the transmission operation of the MCGFailureInformation message is triggered.

[0094] In step 1g-20, if Split SRB or SRB 3 is set and the conditions for performing the fast MCG link recovery operation are satisfied, the terminal transmits MCGFailureInformation to the SN base station and starts the T316 timer.

[0095] At step 1g-25, the terminal determines whether the T316 timer has stopped operating or expired.

[0096] In step 1g-30, if the T316 timer has stopped running, the terminal additionally stores information related to the RRCReconfiguration or RRCRelease message received in response to the previously transmitted MCGFailureInformation message in the RLF Report content. At this time, the following indicator information may be stored in the RLF Report content.

[0097] - An indicator to indicate if RRCRelease (Redirection) or RRCReconfiguration (HO command) is received

[0098] - If RRCRelease is received, Redirection-related information included in the RRCRelease, eg information included in ReedirectedCarrierInfo IE

[0099] - Serving cell / neighboring cells measurement results at the reception of RRCRelease

[0100] - If RRCReconfiguration is received, Handover-related information included in RRCReconfiguration, eg target cell-related info (PCI, CGI of target cell)

[0101] - Serving cell / neighboring cells measurement results at the reception of RRCReconfiguration

[0102] In step 1g-35, if the T316 timer has expired, the terminal additionally stores information on the cause of the failure of the fast MCG link recovery operation in the RLF Report content. At this time, the following indicator information may be stored in the RLF Report content.

[0103] - An indicator to indicate if SCG transmission is (not) suspended

[0104] - An indicator to indicate if SCG is deactivated (eg SCG may deactivate while not identifying MCG RLF and MCGFailureInformation)

[0105] - time information to indicate between the transmission of MCGFailureInformation and suspending SCG transmission

[0106] - time information to indicate between the transmission of and the initiation of PSCell change (or PSCell addition)

[0107] In step 1g-40, if the transmission operation of the MCGFailureInformation message was not triggered, the terminal additionally stores information indicating which condition was not satisfied in the RLF Report content. At this time, the following indicator information may be stored in the RLF Report content.

[0108] - An indicator to indicate if T316 is configured

[0109] - An indicator to indicate if SCG transmission is not suspended

[0110] - An indicator to indicate if the SCG is not deactivated

[0111] - An indicator to indicate if neither PSCell change nor PSCell addition is ongoing (ie timer T304 for the NR PSCell is not running in case of NR-DC or timer T307 of the E-UTRA PSCell is not running in NE-DC)

[0112] - time information to indicate between MCG failure (or transmitting MCGFailureInformation) and suspending SCG transmission

[0113] - time information to indicate between MCG failure (or transmitting MCGFailureInformation) and the initiation of PSCell change (or PSCell addition)

[0114] FIG. 8 is a diagram illustrating a problem in which previous RLF Report information is lost due to a handover failure according to an embodiment of the present disclosure.

[0115] Referring to Figure 8, when an RLF occurs in MCG, the terminal stores information related to the RLF as RLF Report content (1h-05). If certain conditions are met, the terminal transmits an MCGFailureInformation message to SCG (1h-10). At this time, information related to the fast MCG link recovery operation may also be additionally stored in the RLF Report content.

[0116] After transmitting the MCGFailureInformation message, the terminal receives an RRCReconfiguration message including handover configuration information from the SCG (1h-15). Then, the terminal performs a handover operation according to the handover configuration information received from the SCG (1h-20). If a handover failure (HOF) for the handover operation is recognized, the terminal stores information related to the handover failure as RLF Report content (1h-25). At this time, since the previously stored RLF Report content is deleted due to the storage of the HOF-related information, the network cannot obtain information related to the fast MCG link recovery operation.

[0117] FIG. 9 is a flowchart of a terminal operation for reporting fast MCG link recovery-related information after a handover failure according to an embodiment of the present disclosure.

[0118] The MN base station (1i-10) configures a fast MCG link recovery operation for a terminal (1i-05) configured with Dual Connectivity using a predetermined RRC message, RRCReconfiguration (1i-20). The above configuration includes a T316 timer value. Afterwards, when an RLF occurs in the connection with the MN, the terminal (1i-05) declares an RLF and stores information related to it as the RLF content (1i-25). Then, if predetermined conditions are satisfied, the terminal (1i-05) transmits an MCGFailureInformation message to the SN base station (1i-15) via Split SRB (1i-30) or SRB 3 (1i-35). Here, the predetermined conditions are as follows.

[0119] - if T316 is configured

[0120] -if SCG transmission is not suspended

[0121] -if the SCG is not deactivated

[0122] - if neither PSCell change nor PSCell addition is ongoing (ie timer T304 for the NR PSCell is not running in case of NR-DC or timer T307 of the E-UTRA PSCell is not running in NE-DC)

[0123] Although not shown in the drawing, the SN (1i-15) that received the MCGFailureInformation message transmitted by the terminal (1i-05) forwards the MCGFailureInformation message to the MN (1i-10). Meanwhile, the terminal (1i-05) that transmitted the MCGFailureInformation message starts the T316 timer (1i-40). At this time, if the terminal (1i-05) receives an RRCReconfiguration message including handover configuration information from the SN (1i-15) before the T316 timer expires (1i-45), the fast MCG link recovery is considered successful and the terminal stops the T316 timer that was running (1i-50).

[0124] In addition, the terminal (1i-05) triggers a handover operation according to the received handover configuration information (1i-55). At this time, the terminal (1i-05) that initiated the handover operation starts the T304 timer (1i-60). If the handover is not successfully completed by the time the T304 timer expires (1i-65), the terminal (1i-05) considers the handover to have failed (1i-70). According to the existing technology, the previously stored RLF Report content is deleted, and information related to the handover failure is stored as the RLF Report content. In contrast, in the present embodiment, if the triggered handover is triggered according to the fast MCG link recovery operation, the previously stored RLF Report content is not deleted, and certain information is additionally stored in the RLF Report content (1i-75). That is, the following information may be additionally stored in the RLF Report content.

[0125] - An indication to indicate if the failed HO was resulted from Fast MCG Recovery

[0126] - An indication to indicate if there was Fast MCG Recovery procedure before the failed HO

[0127] - Handover-related information, eg target cell-related info (PCI, CGI of target cell)

[0128] - Serving cell / neighboring cells measurement results at the handover failure

[0129] - time information to indicate between the MCG RLF (ie RLF happening at MCG) and the handover failure

[0130] - time information to indicate between the transmission of MCGFailureInformation (or initiation of MCG failure information procedure) and the handover failure

[0131] - time information to indicate between the reception of RRCReconfiguration (HO Command) in response of MCGFailureInformation, and the handover failure

[0132] In another embodiment, the RLF Report content may be newly saved with information related to the handover failure, but additional information related to the Fast MCG Link Recovery may be stored. For example, the following information may be additionally saved as information related to the Fast MCG Link Recovery.

[0133] - An indication to indicate if the failed HO was resulted from Fast MCG Recovery

[0134] - An indication to indicate if there was Fast MCG Recovery procedure before the failed HO

[0135] - Serving cell / neighboring cells measurement results at the reception of RRCReconfiguration (HO Command) in response of MCGFailureInformation

[0136] - time information to indicate between the MCG RLF (ie RLF happening at MCG) and the handover failure

[0137] - time information to indicate between the transmission of MCGFailureInformation (or initiation of MCG failure information procedure) and the handover failure

[0138] - time information to indicate between the reception of RRCReconfiguration (HO Command) in response of MCGFailureInformation, and the handover failure

[0139] In another embodiment, the terminal may store both existing RLF Report content containing information related to Fast MCG link recovery and RLF Report content containing information related to the handover failure. In this case, the RLF Report content containing information related to the handover failure may additionally include the following information.

[0140] - An indication to indicate if the failed HO was resulted from Fast MCG Recovery

[0141] - An indication to indicate if there was Fast MCG Recovery procedure before the failed HO

[0142] - time information to indicate between the MCG RLF (i.e. RLF happening at MCG) and the handover failure

[0143] - time information to indicate between the transmission of MCGFailureInformation (or initiation of MCG failure information procedure) and the handover failure

[0144] - time information to indicate between the reception of RRCReconfiguration (HO Command) in response of MCGFailureInformation, and the handover failure

[0145] Afterwards, the terminal (1i-05) triggers an RRC re-establishment operation (1i-80). The terminal (1i-05) then performs an RRC (re)establishment operation to switch to a connected mode at a predetermined base station (1i-85). In this drawing, the terminal illustrates an SN as a base station performing an RRC connection (re)establishment, but is not limited thereto, and the terminal may perform a connection (re)establishment operation with other base stations. At this time, the terminal (1i-05) receives an availability indicator indicating that it stores the RLF Report in the RRCSetupComplete or RRCReetablishmentComplete message and transmits it to the base station. The base station requests a report of the RLF Report using a UEInformationRequest message (1i-90). The terminal (1i-05) that received the above request reports the RLF Report stored in the terminal (1i-05) to the base station using the UEInformationResponse message (1i-95).

[0146] FIG. 10 is a flowchart of a terminal operation for reporting fast MCG link recovery-related information after a handover failure according to an embodiment of the present disclosure.

[0147] At step 1j-05, the terminal recognizes an MCG failure.

[0148] In step 1j-10, the terminal stores valid information related to MCG failure as RLF content.

[0149] In step 1j-15, the terminal transmits MCGFailureInformation to the SN base station and starts the T316 timer.

[0150] In step 1j-20, the terminal receives an RRCReconfiguration message containing handover configuration information from the SN base station. At this time, the terminal stops the running T316 timer. Additionally, information related to fast MCG link recovery may be additionally stored in the RLF Report content.

[0151] In step 1j-25, the terminal performs handover according to the configuration information and starts the T304 timer.

[0152] At step 1j-30, the terminal considers the handover to have failed when the T304 timer expires.

[0153] In step 1j-35, if the triggered handover is triggered by a fast MCG link recovery operation, the terminal does not delete the previously stored RLF Report, but additionally stores certain information as RLF Report content. That is, the additional information stored in the RLF Report content may include the following indicator information.

[0154] - An indication to indicate if the failed HO was resulted from Fast MCG Recovery

[0155] Figure 11 is a block diagram showing the internal structure of a terminal to which the present invention is applied.

[0156] Referring to the above drawing, the terminal includes an RF (Radio Frequency) processing unit (1k-10), a baseband processing unit (1k-20), a storage unit (1k-30), and a control unit (1k-40).

[0157] The RF processing unit (1k-10) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1k-10) up-converts the baseband signal provided from the baseband processing unit (1k-20) into an RF band signal and transmits it through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1k-10) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital to analog convertor (DAC), an analog to digital convertor (ADC), etc. In the drawing, only one antenna is illustrated, but the terminal may be equipped with multiple antennas. In addition, the RF processing unit (1k-10) may include multiple RF chains. Furthermore, the RF processing unit (1k-10) may perform beamforming. For the above beamforming, the RF processing unit (1k-10) can adjust the phase and size of each signal transmitted and received through multiple antennas or antenna elements. In addition, the RF processing unit can perform MIMO (multiple input multiple output) and can receive multiple layers when performing MIMO operation.

[0158] The baseband processing unit (1k-20) performs a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the system. For example, when transmitting data, the baseband processing unit (1k-20) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (1k-20) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (1k-10). For example, in the case of following the OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processing unit (1k-20) generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and then configures OFDM symbols by performing an inverse fast Fourier transform (IFFT) operation and inserting a cyclic prefix (CP). In addition, when receiving data, the baseband processing unit (1k-20) divides the baseband signal provided from the RF processing unit (1k-10) into OFDM symbol units, restores signals mapped to subcarriers through FFT (fast Fourier transform) operation, and then restores the received bit string through demodulation and decoding.

[0159] The baseband processing unit (1k-20) and the RF processing unit (1k-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (1k-20) and the RF processing unit (1k-10) may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. Furthermore, at least one of the baseband processing unit (1k-20) and the RF processing unit (1k-10) may include a plurality of communication modules to support a plurality of different wireless access technologies. In addition, at least one of the baseband processing unit (1k-20) and the RF processing unit (1k-10) may include different communication modules to process signals of different frequency bands. For example, the different wireless access technologies may include a wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. Additionally, the different frequency bands may include a super high frequency (SHF) (e.g., 2.NRHz, NRhz) band and a millimeter wave (mm wave) (e.g., 60GHz) band.

[0160] The storage unit (1k-30) stores data such as basic programs, application programs, and setting information for the operation of the terminal. In particular, the storage unit (1k-30) can store information related to a second access node that performs wireless communication using a second wireless access technology. In addition, the storage unit (1k-30) provides the stored data at the request of the control unit (1k-40).

[0161] The control unit (1k-40) controls the overall operations of the terminal. For example, the control unit (1k-40) transmits and receives signals through the baseband processing unit (1k-20) and the RF processing unit (1k-10). In addition, the control unit (1k-40) records and reads data in the storage unit (1k-30). For this purpose, the control unit (1k-40) may include at least one processor. For example, the control unit (1k-40) may include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as application programs.

[0162] Figure 12 is a block diagram showing the configuration of a base station according to the present invention.

[0163] As shown in the drawing above, the base station is configured to include an RF processing unit (1l-10), a baseband processing unit (1l-20), a backhaul communication unit (1l-30), a storage unit (1l-40), and a control unit (1l-50).

[0164] The RF processing unit (11-10) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (11-10) up-converts the baseband signal provided from the baseband processing unit (11-20) into an RF band signal and transmits it through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (11-10) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. In the drawing, only one antenna is illustrated, but the first access node may have multiple antennas. In addition, the RF processing unit (11-10) may include multiple RF chains. Furthermore, the RF processing unit (11-10) may perform beamforming. For the above beamforming, the RF processing unit (11-10) can adjust the phase and magnitude of each signal transmitted and received through multiple antennas or antenna elements. The RF processing unit can perform a downlink MIMO operation by transmitting one or more layers.

[0165] The baseband processing unit (11-20) performs a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the first wireless access technology. For example, when transmitting data, the baseband processing unit (11-20) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (11-20) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (11-10). For example, in the case of OFDM, when transmitting data, the baseband processing unit (11-20) generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and then configures OFDM symbols through IFFT operation and CP insertion. In addition, when receiving data, the baseband processing unit (11-20) divides the baseband signal provided from the RF processing unit (11-10) into OFDM symbol units, restores signals mapped to subcarriers through FFT operation, and then restores the received bit string through demodulation and decoding. The baseband processing unit (11-20) and the RF processing unit (11-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (11-20) and the RF processing unit (11-10) may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0166] The above backhaul communication unit (1l-30) provides an interface for communicating with other nodes within the network. That is, the backhaul communication unit (1l-30) converts a bit string transmitted from the main base station to another node, such as an auxiliary base station or a core network, into a physical signal, and converts a physical signal received from the other node into a bit string.

[0167] The storage unit (11-40) stores data such as basic programs, application programs, and setting information for the operation of the main base station. In particular, the storage unit (11-40) can store information on bearers assigned to connected terminals, measurement results reported from connected terminals, and the like. In addition, the storage unit (11-40) can store information that serves as a judgment criterion for whether to provide or terminate multiple connections to a terminal. In addition, the storage unit (11-40) provides the stored data at the request of the control unit (11-50).

[0168] The control unit (11-50) controls the overall operations of the base station. For example, the control unit (11-50) transmits and receives signals through the baseband processing unit (11-20) and the RF processing unit (11-10) or through the backhaul communication unit (11-30). In addition, the control unit (11-50) records and reads data in the storage unit (11-40). For this purpose, the control unit (11-50) may include at least one processor.

[0169] While the detailed description of the present invention has described specific embodiments, it is clear that various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims but also by equivalents thereof.

Claims

1. A method performed by a terminal in a wireless communication system, A step of detecting a radio link failure (RLF) for a master cell group (MCG) and a secondary cell group (SCG) among which dual connectivity (DC) is set for the terminal; A step of transmitting a first radio resource control (RRC) message to the SCG, wherein at least one condition for transmitting the first RRC message including information indicating the RLF for the MCG is satisfied; If a second RRC message including information related to a target cell is received from the SCG, a step for performing a procedure for establishing a connection with the target cell based on the information related to the target cell; and Including a step of checking a connection failure with the target cell, The first information about the RLF for the above MCG is stored in the RLF report, A method of a terminal, characterized in that the second information on the connection failure is additionally stored in the RLF report in which the first information is stored.

2. In paragraph 1, A method of a terminal, characterized in that the second information includes information indicating whether the connection failure was triggered based on transmission of the first RRC message.

3. In paragraph 1, Further comprising a step of driving a timer based on transmission of the first RRC message; The above second RRC message is received before the timer expires, A method of a terminal, characterized in that the RLF report additionally stores third information about the second RRC message.

4. In paragraph 3, The second RRC message includes an RRC message indicating redirection to the target cell or an RRC message indicating handover to the target cell, A method of a terminal, characterized in that the third information includes information related to the redirection or information related to the handover.

5. In paragraph 1, A method of a terminal, characterized in that at least one of the above conditions includes a condition in which transition of a primary secondary cell (PSCell) and addition of a PSCell are not in progress.

6. In paragraph 1, A method of a terminal, characterized in that it further comprises the step of storing, in the RLF report, an indicator indicating the unsatisfied condition if there is a condition that is not satisfied among the at least one condition.

7. In paragraph 1, A method of a terminal, characterized in that the first information and the second information are stored based on activation of Access Stratum security.

8. In a wireless communication system, at the terminal, Transmitter and receiver; and Detecting a radio link failure (RLF) for the master cell group (MCG) and secondary cell group (SCG) among the dual connectivity (DC) configured for the terminal, If at least one condition for transmitting a first radio resource control (RRC) message including information indicating the RLF for the MCG to the SCG is satisfied, transmitting the first RRC message to the SCG, If a second RRC message including information related to a target cell is received from the SCG, a procedure for establishing a connection with the target cell is performed based on the information related to the target cell, Including a control unit for checking a connection failure with the target cell, The first information about the RLF for the above MCG is stored in the RLF report, A terminal characterized in that the second information regarding the connection failure is additionally stored in the RLF report in which the first information is stored.

9. In paragraph 8, A terminal characterized in that the second information includes information indicating whether the connection failure was triggered based on transmission of the first RRC message.

10. In paragraph 8, The above control unit drives a timer based on the transmission of the first RRC message, The above second RRC message is received before the timer expires, A terminal characterized in that the RLF report additionally stores third information about the second RRC message.

11. In paragraph 10, The second RRC message includes an RRC message indicating redirection to the target cell or an RRC message indicating handover to the target cell, A terminal characterized in that the third information includes information related to the redirection or information related to the handover.

12. In paragraph 8, A terminal characterized in that at least one of the above conditions includes a condition in which conversion of a primary secondary cell (PSCell) and addition of a PSCell are not in progress.

13. In paragraph 8, A terminal characterized in that it further comprises a step of storing, in the RLF report, an indicator indicating the unsatisfied condition if there is a condition that is not satisfied among the at least one condition.

14. In paragraph 8, A terminal characterized in that the first information and the second information are stored based on activation of Access Stratum security.

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