Method and apparatus for handling link failure of a chain in a wireless communication system

Abstract

The disclosure relates to a 5th-Generation (5G) or pre-5G communication system to be implemented to support higher data transmission rates beyond a 4th-Generation (4G) communication system such as a Long Term Evolution (LTE). According to various embodiments of the disclosure, a method of a base station for which a master cell group (MCG) is configured in a wireless communication system can include detecting a failure of a primary cell (PCell) (PScell) of a secondary cell group (SCG), based on the detecting, transmitting, to a terminal, inter radio access technology (RAT) measurement configuration information, and transmitting, to a base station for which the SCG is configured, information about a cell identified based on the measurement configuration information.

Description

TECHNICAL FIELD

[0001] The disclosure relates generally to a wireless communication system, and in particular, to an apparatus and method for handling a link failure in a wireless communication system. BACKGROUND

[0002] To meet the demand for wireless data traffic having increased since the commercialization of 4th generation (4G) communication systems, efforts are being made to develop an improved 5th generation (5G) communication system or a pre-5G communication system. Therefore, the 5G communication system or the pre-5G communication system is also called a beyond 4G network communication system or a post long term evolution (LTE) system.

[0003] To achieve a high data transmission rate, the 5G communication system is considered to be implemented in a mmWave band (e.g., 60 GHz band). To reduce a propagation path loss and increase a propagation transmission distance in the mmWave band, technologies such as beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beam forming, and large scale antenna in the 5G communication system are discussed.

[0004] In addition, to improve the network of the system, in the 5G communication system, technologies such as evolved small cell, advanced small cell, cloud radio access network (RAN), ultra-dense network, device to device (D2D) communication, wireless backhaul, mobile network, cooperative communication, coordinated multi-point (CoMP), and reception interference cancellation are being developed.

[0005] In addition, in the 5G system, hybrid frequency shift keying and quadrature amplitude modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) technique, and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology are being developed.

[0006] An efficient communication service can be provided in a multiple-connection system in which a base station and a terminal are coupled by independent radio access technologies. With the introduction of the multiple-connection system, when a link failure occurs in one cell group, a method of handling a link failure (e.g., radio link failure (RLF)) is required. SUMMARY

[0007] TECHNICAL PROBLEM

[0008] Based on the above discussion, the disclosure provides an apparatus and method for handling a link failure when a link failure occurs in a wireless communication system.

[0009] Further, the disclosure provides an apparatus and method for handling a failure when failure information about a cell group is received in a wireless communication system.

[0010] Further, the disclosure provides an apparatus and method for managing a link failure by handling a cell and a bearer of a base station in an environment in which a plurality of cell groups are configured in a wireless communication system.

[0011] Technical solutions

[0012] According to various embodiments of the disclosure, a method of a base station to which a master cell group (MCG) is configured in a wireless communication system can include detecting a failure of a primary cell (PCell) (PScell) of a secondary cell group (SCG), based on the detection, transmitting inter-radio access technology (RAT) measurement configuration information to a terminal, and transmitting information about a cell identified based on the measurement configuration information to a base station to which the SCG is configured.

[0013] According to various embodiments of the disclosure, a base station to which a master cell group (MCG) is configured in a wireless communication system can include at least one transceiver, and at least one processor. The at least one processor can be configured to detect a failure of a primary cell (PCell) (PScell) of a secondary cell group (SCG), based on the detection, transmit inter-radio access technology (RAT) measurement configuration information to a terminal, and transmit information about a cell identified based on the measurement configuration information to a base station to which the SCG is configured.

[0014] According to various embodiments of the disclosure, a method of a base station to which an SCG is configured in a wireless communication system can include detecting a failure of a PScell, identifying a cell based on the detection, and performing a connection procedure with a terminal by transmitting information about the cell to a base station to which an MCG is configured.

[0015] Advantageous effects

[0016] The apparatuses and methods according to various embodiments of the disclosure can detect a link failure and control the failure, thereby providing efficient communication performance when operating multiple-connectivity.

[0017] The advantages obtained by the present disclosure are not limited to the above-mentioned advantages, and other advantages which are not mentioned herein can be clearly understood by a person skilled in the art from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 A wireless communication system according to various embodiments of the disclosure is illustrated;

[0019] Figure 2AAn example of a cell group in a wireless communication system according to various embodiments of the disclosure is illustrated;

[0020] Figure 2B Another example of a cell group in a wireless communication system according to various embodiments of the disclosure is illustrated;

[0021] Figure 3 An example of signaling for controlling link failure in a master node (MN) in a wireless communication system according to various embodiments of the disclosure is illustrated;

[0022] Figure 4 An example of signaling for managing blacklisted cells in the MN in a wireless communication system according to various embodiments of the disclosure is illustrated;

[0023] Figure 5 Another example of signaling for managing blacklisted cells in the MN in a wireless communication system according to various embodiments of the disclosure is illustrated;

[0024] Figure 6 An example of signaling for controlling link failure in a secondary node (SN) in a wireless communication system according to various embodiments of the disclosure is illustrated;

[0025] Figure 7 A functional structure of a base station in a wireless communication system according to various embodiments of the disclosure is illustrated; and

[0026] Figure 8 A functional structure of a terminal in a wireless communication system according to various embodiments of the disclosure is illustrated. DETAILED DESCRIPTION

[0027] The terms used in the present disclosure are merely for the purpose of describing particular embodiments and are not intended to limit other embodiments. Singular expressions can include plural expressions, unless there is a clear contextual difference. All terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure is disclosed. It should also be understood that terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology and should not be interpreted in an idealized or overly formal sense. Unless defined herein, terms defined in the present disclosure should not be interpreted to exclude embodiments of the present disclosure.

[0028] Hardware-based methods are described, for example, in various embodiments of the disclosure described below. However, since various embodiments of the disclosure include technologies used by both hardware and software, embodiments of the disclosure do not exclude software-based methods.

[0029] Hereinafter, the disclosure relates to an apparatus and a method for managing a link failure in a wireless communication system. Specifically, the disclosure describes a technique for controlling and handling a link failure of a cell group in a wireless communication system in a multi-connection environment of the wireless communication system.

[0030] The terms related to multi-connection (e.g., dual connectivity (DC), multi-radio access technology (RAT) (MR)-DC, cell group, master cell group (MCG), secondary cell group (SCG)), terms referring to a signal (e.g., reference signal, system information, control signal, message, data), and terms referring to a network entity (e.g., communication node, radio node, radio unit, network node, master node (MN), secondary node (SN), transmission / reception point (TRP), digital unit (DU), radio unit (RU), massive MIMO unit (MMU)) used hereinafter are exemplified for convenience. Thus, the disclosure is not limited to the terms described below, and thus other terms having the same technical meaning can also be used.

[0031] Further, although the disclosure describes various embodiments by using terms used in some communication standards (e.g., the third generation partnership project (3GPP)), this is for exemplary purposes only. The various embodiments of the disclosure can be easily modified and applied to other communication systems.

[0032] In the embodiments of the disclosure, a measurement of a channel quality of a signal with respect to whether a condition (e.g., a measurement reporting condition) is satisfied and with respect to a measurement parameter can use at least one of various parameters. As the channel quality, a reference signal received power (RSRP), a beam reference signal received power (BRSRP), a reference signal received quality (RSRQ), a received signal strength indicator (RSSI), a signal to interference and noise ratio (SINR), a carrier to interference and noise ratio (CINR), an SNR, an error vector magnitude (EVM), a bit error rate (BER), a block error rate (BLER), other terms having equivalent technical meanings, or other metrics indicating a channel quality can be used.

[0033] Figure 1 A wireless communication system 100 according to various embodiments of the disclosure is illustrated. In Figure 1 In the disclosure, base stations 110-1, 110-2, …, 110-n and a terminal 120 are exemplified as some nodes using a radio channel in a wireless communication system. The base stations 110-1, 110-2, …, 110-n can be coupled to the terminal 120 through multi-connection (e.g., dual connectivity (DC)). Hereinafter, for convenience of description, it can be described by referring to each of the base stations 110-1, 110-2, …, 110-n as a base station 110 through common description.

[0034] The base stations 110-1, 110-2, …, 110-n are network infrastructure that provides radio access to the terminals 120. The base station 110 has a coverage area defined as a specific geographic area according to a distance at which a signal can be transmitted. The term "coverage" used below can refer to a service coverage area in the base station 110. The base station 110 can cover one cell, or can cover a plurality of cells. Here, the plurality of cells can be divided by a supported frequency and an area of a covered sector.

[0035] In addition to the term "base station", the base station 110 can be referred to as an "access point (AP)", an "eNodeB (eNB)", a "fifth generation (5G) node", a "5G NodeB (NB)", a "next generation NodeB (gNB)", a "wireless point", a "transmission / reception point (TRP)", a "distributed unit (DU)", a "radio unit (RU)", a remote radio head (RRH), or other terms having equivalent technical meanings. According to various embodiments, the base station 110 can be coupled to at least one TRP. The base station 110 can transmit a downlink signal or receive an uplink signal to / from the terminal 120 through the at least one TRP.

[0036] The terminal 120 communicates with the base station 110 through a radio channel as a device used by a user. Alternatively, the terminal 120 can be operated without the involvement of a user. That is, as a device for performing machine type communication (MTC), the terminal 120 can not be carried by a user. In addition to the term "terminal", the terminal 120 can be referred to as a "user equipment (UE)", a "mobile station", a "subscriber station", a "customer premises equipment (CPE)", a "remote terminal", a "wireless terminal", an "electronic device", a "vehicle-mounted terminal", a "user device", or other terms having equivalent technical meanings.

[0037] A dual connectivity (DC) technique is a multi-connectivity technique introduced from a third generation partnership project (3GPP) standard version 12. In the DC technique, a terminal is simultaneously coupled to two independent heterogeneous or homogeneous wireless communication cell groups, has a separate radio resource control entity, and frequency resources on component carriers of cells located in different frequency bands in each cell group are used for signal transmission / reception to improve frequency use efficiency of the terminal and the base station. The DC consists of a master cell group directly coupled to a core network on a control plane to manage a radio resource control state of the terminal and a secondary cell group associated with the master cell group.

[0038] A carrier aggregation (CA) technology is a technology introduced in Release 10 of the 3GPP standard. In the CA technology, a terminal is coupled to a homogeneous set of radio communication cells having a common radio resource control entity, and frequency resources on component carriers of each cell located in different frequency bands are used for signal transmission / reception to improve frequency use efficiency of the terminal and a base station.

[0039] The DC technology and the CA technology have been actively researched in the academic world due to their technical advantages in improving efficiency in utilizing limited radio communication resources of terminals and base stations. In particular, the 5G mobile communication system uses a non-standalone type that implements operations in association with a 4G core network as a basic operation scheme, and is used as a core technology in supporting commercial services of the 5G mobile communication system.

[0040] In various embodiments of the disclosure, a case in which the base stations 110-1, 110-2, …, 110-n are coupled to the terminal 120 through multi-connection is described. As described above, the multi-connection refers to a communication technology in which the terminal 210 is coupled to each of the base stations 110-1, 110-2, …, 110-n through independent radio access technologies (RATs). For example, the terminal 120 can be coupled to each of two base stations through dual connectivity (DC) that is one type of multi-connection. For example, the terminal 120 can be coupled to an eNB base station through long term evolution (LTE) and can be coupled to a gNB base station through new radio (NR). Each base station can be referred to as a communication node. One or more cells provided in one base station can be referred to as a cell group. That is, the base station can support one or more cell groups. The base station providing a master cell group (MCG) can provide a master node (MN), and the base station providing a secondary cell group (SCG) can provide a secondary node (SN). In various embodiments, the relationship between the base station and the cell group can be defined differently. According to an embodiment, one base station can provide one cell group. Further, according to another embodiment, one base station can provide one or more cell groups. Specific relationships will be described below with reference to Figure 2A and Figure 2B Further, according to an embodiment, each base station can perform carrier aggregation (CA). In this case, the terminal can perform CA with respect to the base station through cells of each cell group.

[0041] In various embodiments of the disclosure, a multi-connection can be configured individually, or a CA can be configured together with the multi-connection. The disclosure provides a base station apparatus and a method for performing an operation of controlling transmission power of a terminal in a distributed manner on a real-time basis and an operation of controlling transmission power of a terminal in a distributed manner on a non-real-time basis. Cell groups constituting a multi-connection can be referred to as a first cell group, a second cell group, …, an Mth cell group, respectively. In the disclosure, the first cell group can be replaced with a master cell group or a primary cell group constituting a multi-connection, and the second cell group, …, the Mth cell group can be replaced with a secondary cell group.

[0042] Figure 2A An example of a cell group in a wireless communication system according to various embodiments of the disclosure is illustrated. Figure 2A The wireless communication system of FIG. 1 illustrates a case where one base station manages all cell groups.

[0043] Referring to Figure 2A , the base station 110 can provide a terminal with a plurality of cell groups 211-1, 211-2, 211-3, …, 211-M. Each of the plurality of cell groups can include one or more cells. Although one base station manages all cell groups in Figure 2A , the disclosure is not limited thereto. In some embodiments, a separate network entity coupled to a base station can perform the link failure management procedure described below.

[0044] Figure 2B Another example of a cell group in a wireless communication system according to various embodiments of the disclosure is illustrated. Figure 2B The wireless communication system of FIG. 2 illustrates a case where at least two base stations manage all cell groups. The at least two base stations can include base stations 110-1, 110-2, …, 110-n.

[0045] Referring to Figure 2B , the base stations 110-1, 110-2, …, 110-n can provide a terminal with a plurality of cell groups 211-1, 211-2, 211-3, …, 211-M. In this case, the number of cell groups coupled to a base station can be configured differently for each base station. For example, the first base station 110-1 can provide a terminal with three cell groups (e.g., CG#1 261a, CG#2 261b, and CG#3 261c). The second base station 110-2 can provide a terminal with three cell groups (e.g., CG#4 262a, CG#5 262b, and CG#6 262c). The third base station 110-3 can provide a terminal with two cell groups (e.g., CG#7 263a and CG#8 263b). The Nth base station 110-n can provide a terminal with one cell group (e.g., CG#M 264). Each of the plurality of cell groups can include one or more cells.

[0046] Although a plurality of base stations manages all cell groups in Figure 2B The present application is not limited to this. In some embodiments, a separate network entity coupled to a plurality of base stations can perform the link failure management procedure described below.

[0047] In the case of multi-connectivity (e.g., dual connectivity (DC)) providing homogeneous or heterogeneous RATs, problems can occur in the wireless case with MCG or SCG. When a radio link failure (RLF) occurs in the wireless link in the cells of the MCG or SCG, optimized recovery can be required under the control of the base station.

[0048] When a failure occurs in the MCG or SCG, a node managing a cell group can receive failure information from a node in which a failure occurs. In this case, the receiving node needs to manage recovery and other processing operations based on the failure information. That is, a method for handling a link failure in the MN of the MCG or the SN of the SCG is required. Hereinafter, although an entity managing the MCG is described as an MN and an entity managing the SCG is described as an SN, embodiments implemented in a CU-DU structure (or including a DU-RU structure) having a distributed deployment are not excluded, in addition to the base station as a single entity. According to embodiments, the MN managing the MCG can include a central unit (CU)-control plane (CP), a CU-user plane (UP), and a distributed unit (DU). The SN managing the SCG can include a CU-CP, a CU-UP, and a DU. Hereinafter, a multi-connectivity case in which a terminal is coupled to the MCG / SCG at the same time is described. The terminal can be coupled to one or more SCGs.

[0049] According to the object in which a link failure occurs and the subject that handles the failure, the operation type can be divided into the following four cases.

[0050] (1) Method for MN to handle SCG failure

[0051] (2) Method for SN to handle SCG failure

[0052] (3) Method for SN to handle MCG failure

[0053] (4) Method for MN to handle MCG failure

[0054] The SCG failure refers to a case where an RLF occurs in a cell of the SCG. When the SCG failure occurs, the PCell of the SCG, i.e., the PSCell, is not suitable for performing communication, which can be a case requiring recovery through other nodes (e.g., the MN). Hereinafter, operations are described based on scenarios (1) and (2), but the same or similar processing methods can be applied to scenarios (3) and (4) unless otherwise specified. That is, operations for handling scenarios (1) and (3) where a failure occurs in the counterpart CG differ only in the name of a network entity (NE), and the basic operation specification is the same (when some parts are different, specified separately). Operations for handling scenarios (2) and (4) where a failure occurs in their own CG differ only in the name of the NE, and the basic operation specification is the same (when some parts are different, specified separately).

[0055] Figure 3 An example of signaling for controlling a link failure in a master node (MN) in a wireless communication system according to various embodiments of the disclosure is illustrated. Referring to Figure 3 , operations between an MN, an SN, and a UE for handling an SCG failure when the SCG failure occurs, performed by the MN, are described.

[0056] As Figure 3 indicated, a case where a multi-connection is implemented in a UE is illustrated. The UE can be coupled to an MN and an SN. The UE can be coupled to data radio bearers (DRBs) activated in the MN and the SN. The UE can be coupled to the SN at a radio resource control (RRC) / packet data convergence protocol (PDCP) level.

[0057] <1. SCG failure detection and suspension>

[0058] The MN can detect an SCG failure and inform the SN of information about the detected SCG failure. In this case, the SN can suspend transmission of the SCG. The detailed procedure is as follows.

[0059] In step S301, the MN can detect an SCG failure. The MN can receive information about the SCG failure (hereinafter, referred to as SCG failure information) from the UE or can receive the SCG failure information from the SN. The MN can detect the SCG failure by obtaining the SCG failure information. The MN can detect that an RLF has occurred in a cell of the SCG. The MN can receive the SCG failure information from the counterpart node or receive the SCG failure information from the UE.

[0060] In step S303, the MN can send information about SCG failure to the SN. The information can be sent in the form of a modification request message. The MN can send a modification request message to the SN. The modification request message can include cell group configuration information (CG-ConfigInfo) or an X2 cause. The CG-ConfigInfo can include information about the SCG failure cause and measurement results (e.g., NR measurement results). The X2 cause can indicate that the UE connection cannot be found (e.g., the wireless connection with the UE is lost).

[0061] In step S305, the SN can suspend SCG transmission. The SN can identify a failure in the SCG by receiving information about SCG failure from the MN. Alternatively, the SN can autonomously detect a failure in the SCG. Upon detecting the SCG failure, the SN suspends transmission of the SCG. Thereafter, in step S307, the SN can send a modification request response to the MN. It can be selectively sent to the MCG by including an NR RRC to change the UL path.

[0062] <2. Inter-RAT measurement configuration for SCG recovery>

[0063] The MN can send a measurement configuration to the UE to recover the SCG connection.

[0064] The specific procedure is as follows. In step S311, the MN can configure the measurement. To configure the measurement, the MN can send an RRC connection reconfiguration message to the UE. To recover the SCG, the MN can send an inter-RAT measurement configuration to the UE. To configure the SN-requested UL path change configuration, NR RRC information can be optionally sent to the UE together. In step S313, the UE can send an RRC connection reconfiguration complete message to the MN. In step S315, the MN can send a reconfiguration complete message to the SN.

[0065] <3. Inter-RAT measurement reporting>

[0066] The MN can configure the SN based on the measurement report received from the UE. When the UE meets the criteria for configuring the RAT measurement (e.g., when the reporting criteria is met (e.g., the channel quality is greater than or equal to the threshold value)), the UE can send the measurement results (e.g., the measured cell information) to the MN base station. The MN can specify the target SN and the SCG based on the corresponding report and send the measured cell information to the new target SN through the SN modification or SN addition procedure for the existing target SN. The specific procedure is as follows.

[0067] In step S321, the UE can transmit a measurement report to the MN. In this case, the measurement report can include measurement results. The measurement results can include inter-RAT measurement results. The measurement results can include measurement results depending on the measurement configuration configured through step S311. In step S323, the MN can transmit an SN modification request message to the SN based on the measurement report. According to an embodiment, the SN modification request message can include information on at least one cell (e.g., a candidate cell list), information on measurement results (e.g., NR cell measurement results), and X2 cause information. The X2 cause information can indicate SCG mobility. In step S325, the MN can receive a response to the SN modification request from the SN.

[0068] <4. SCG recovery operation and inter-RAT measurement removal>

[0069] The SN can recover the SCG connection based on the obtained measurement information (e.g., step S321). The SN performs an access procedure with the UE through a target PSCell (PCell of the SCG) based on the measured cell information. The MN, upon receiving the SN modification request, can release the inter-RAT measurement configuration if there is a specific cause. The UE performs an access procedure including a random access procedure through the received reconfiguration message and recovers data transmission / reception. The specific procedure is as follows.

[0070] In step S331, the SN can perform a recovery procedure. As a typical cell access procedure, the SN can initiate a radio connection recovery procedure through a random access procedure. In step S333, the SN can transmit information related to the recovery procedure to the MN. For example, the SN can transmit an SN modification required message of the UE to the MN. The information related to the recovery procedure can include a cell (e.g., an ID of a PSCell) used when the SN is coupled to the UE. Further, the information related to the recovery procedure can include an X2 cause (SCG mobility) as a cause of information transmission. Optionally, the SN can transmit an NR RRC including UL path information to the MN to recover the UL path. In step S335, the MN can remove a measurement configuration according to the request of the SN. The MN can identify the cause indication "SCG mobility" transmitted from the SN. Upon identifying the cause indication "SCG mobility", the MN can remove a preset measurement configuration (e.g., a B1 configuration). In step S337, the MN can transmit an RRC connection reconfiguration message to the UE. For the RRC connection reconfiguration message, a message including configuration removal (e.g., B1 removal) can be transmitted to the UE. In this case, in an embodiment, the RRC connection reconfiguration message can include an NR RRC configuration (information for UE configuration transmitted by the SN as an NR base station to the MN) together. In step S339, the UE can transmit an RRC connection reconfiguration complete message to the MN. In step S341, the MN can transmit an SN modification confirm message to the SN. Thereafter, in step S343, the UE can be coupled to a target cell of the SCG through a physical random access channel (PRACH) procedure (e.g., an NR PRACH in an E-UTRA-NR-dual connectivity (EN-DC) case).

[0071] Although the operation of each node is described in detail in Figure 3 to describe the operation between the MN, the SN, and the UE, each procedure for recovering the SCG failure can be operated individually. That is, the inter-node operation of the procedure can be applied as a separate embodiment, and unnecessary operations can be omitted in some embodiments.

[0072] When the SN experiences SCG failure, a more reliable recovery procedure can be performed through signaling with the MN and signaling of the MN and the UE, rather than autonomously performing a recovery procedure by the SN through RRE. For example, even in the case of RLF in a gNB in EN-DC, the UE can be coupled to the PSCell of the gNB through signaling between the eNB and the UE. The PSCell of the gNB can be reliably coupled to the UE through a more reliable RRC reconfiguration procedure with the eNB. As another example, a case where one gNB and another gNB are coupled through DC can be considered. The MN can be a gNB that provides a serving cell of frequency range #1 (FR1), and the SN can be a gNB that provides a serving cell of frequency range #2 (FR2). In the case of FR2, RLF can frequently occur due to a high frequency band. In this case, since operations are performed in a relatively low frequency domain, the SCG recovery procedure can be performed for the gNB of FR2 through signaling between the UE and the gNB to provide a reliable connection.

[0073] Meanwhile, it is obvious that, not only when the SCG of the SN fails, but also when the MCG of the MN fails, the signaling is performed in the same or similar manner Figure 3 According to an embodiment, when RLF occurs in a gNB that is the MN in the case of NR-E-UTRA-dual connectivity (NE-DC), the eNB that is the SN can perform a recovery procedure with the UE. Further, according to an embodiment, when RLF occurs in a cell of an eNB that is the MN in the case of EN-DC, the gNB that is the SN can perform a recovery procedure with the UE. Since RLF occurrence can not be caused by simple channel quality deterioration, but by factors (e.g., configuration failure, change in the environment around the corresponding base station, base station failure, etc.) caused by a specific node, the failure of the SCG or the MCG can be effectively corrected by performing a recovery procedure by another node.

[0074] In some embodiments, when a failure occurs in the SCG, the UE can not store measurement configuration information set in the SCG. In various cases of MR-DC, such as the EN-DC case or the DC case between FR1-FR2, when RLF occurs in the SN, the UE can be configured not to store any settings of the corresponding cell any more. That is, since the UE does not consider the settings related to the SN, it can not be easy to find a new cell (NR). Accordingly, the UE can receive measurement configuration information for the RAT of the SN (inter-RAT measurement configuration information of the eNB) through a reconfiguration procedure with another node (eNB). The UE can perform measurement on the PSCell of the SN based on the control of the MN. According to various embodiments, when RLF occurs in a specific node, measurement configuration information is provided under the control of another node, and on this basis, connection is re-established with the specific node, thereby reducing the case where the connection recovery procedure is delayed due to the limitation of the UE.

[0075] Figure 4 An example of signaling for management of blacklisted cells in the MN in a wireless communication system according to various embodiments of the disclosure is shown. Based on the blacklist (measurement barring), operations performed by the MN between the MN, the SN, and the UE for handling SCG failure when it occurs are described.

[0076] As Figure 4 shown, a case where multi-connection is implemented in the UE. The UE can be coupled to the MN and the SN. The MN is an LTE base station (or LTE MN), and the SN is an NR base station (or NR SN). The UE can be coupled to multiple base stations through EN-DC.

[0077] <1. Tracking current PSCell information>

[0078] The MN can manage the cell information of the SN, i.e., the SCG cell information. The MN can identify the PScell information of the SCG by tracking information about the cell of the SCG. The detailed procedure is as follows.

[0079] In step S401, the SN can identify the cell information of the SN. The cell information of the SN can be the SCG cell information of the SN. In step S403, the SN can transmit the SCG cell information to the MN. The cell information can include information about the PSCell that is the Pcell of the SCG. In some embodiments, the SN can identify the information of the PScell coupled to the current UE in initial access, and can transmit it to the MN. Further, in some embodiments, the SN can identify the information of the PScell coupled to the current UE whenever the PScell changes, and can transmit it to the MN. Further, in some embodiments, the SN can identify the information of the PScell coupled to the current UE when a predetermined event is satisfied, and can transmit it to the MN. In addition, in some embodiments, the SN can periodically identify the information of the PScell coupled to the current UE, and can transmit it to the MN. In step S405, the MN can identify the information of the cell (PSCell) of the SCG. In some embodiments, the MN can detect the SCG failure by tracking the cell information of the SCG.

[0080] <2. SN release, register the failed cell to the blacklist>

[0081] After detecting the SCG failure, the MN can release the SCG. In this case, the MN can manage the corresponding connection by registering the cell of the detected SCG to the blacklist and by operating a timer. The detailed procedure is as follows.

[0082] In step 411, RLF of the SCG can occur in the SN. The SN release is performed due to the SCG failure. In some embodiments, the MN can detect the SCG failure. In some other embodiments, the SN can detect the SCG failure. When the SCG failure is detected, if the SN release is SN initiated, a specific cause is sent to the MN informing that this is a release case due to SCG failure.

[0083] In step 413, the MN can identify the SCG failure. The MN can configure a measurement reporting event (e.g., B1 event). The configuration of the measurement reporting event can mean that when the UE satisfies a predetermined condition, the parameters configuring the predetermined condition are configured into a measurement report in which a measurement result is transmitted to a base station. The MN according to various embodiments can register the cell in which the failure is detected into a blacklist. Even if a measurement report of the cell registered into the blacklist is received, the MN can be configured to ignore the measurement report.

[0084] In step S415, the MN can perform the SN release. The MN can perform the SN release due to the SCG failure. The MN can transmit a message for the SN release, i.e., an RRC connection reconfiguration message, to the UE. The RRC connection reconfiguration message can include the SN release command. The RRC connection reconfiguration message can include the inter-RAT measurement configuration (e.g., B1 event configuration).

[0085] In step 417, the MN can detect the SCG failure and can start a timer when performing the MN or SN initiated SN release. Here, the timer can be a timer configured for a cell in which the SCG failure occurs. The MN can register the PSCell of the SCG in which the failure occurs into a blacklist until the timer expires. Although it is shown that step 417 is performed after step 415, the two steps can be independently / parallelly performed.

[0086] In step S419, the UE can receive the RRC connection reconfiguration message from the MN. The UE can identify the SN release command. The UE can perform the SN release. The UE can identify the B1 event configuration. The UE can perform the measurement on the SCG based on the inter-RAT measurement configuration (e.g., B1 event configuration).

[0087] <3. B1 Skipping of a failure cell

[0088] In step S421, the UE performs a measurement, and when a configured condition (e.g., measurement report: B1 event) is satisfied, the UE can transmit the measurement result to the MN. When the channel quality (e.g., RSRP, RSRQ) satisfies the condition (e.g., entry condition - above threshold, exit condition - below threshold) configured for the inter-RAT B1 measurement, the UE can transmit the measured cell information to the MN base station. Even if the measurement report corresponding to the blacklist is received, the MN can ignore this while the timer is running. That is, since it is before the timer expires, when the measurement result includes the measurement result of the cell registered to the blacklist (i.e., the PSCell where the RLF occurred), the UE can ignore the measurement result of the PSCell.

[0089] <4. B1 acceptance after expiration of the timer>

[0090] In step S431, the timer can expire. When the timer expires, the MN can remove the PCell of the SCG included in the blacklist, i.e., the PSCell. Thereafter, in step S433, the MN can receive a measurement report of a corresponding cell of the UE. In step S440, the MN can perform an SN addition procedure based on the measurement report.

[0091] Although the operation of each node is described in detail in Figure 4 to describe the operation between the MN, the SN, and the UE, each process for recovering the SCG failure can be operated individually. That is, the operation between the nodes of the procedure can be applied as a separate embodiment, and unnecessary operations can be omitted in some embodiments. For example, depending on when the measurement report is received, the MN can perform step S440 after step S421.

[0092] In addition, although step S440 is described in Figure 4 as a procedure performed by the MN to establish a connection with the UE, the signaling between the MN and the SN can be defined as specific operations of the MN and the SN. For example, the signaling can be exemplified by the operations of steps S323 and S325 of Figure 3 .

[0093] When SCG failure occurs in the SN, a more reliable recovery procedure can be performed through signaling with the MN as well as signaling of the MN and the UE, rather than the recovery procedure being autonomously performed by the SN through RRE. For example, even if RLF occurs in a gNB in an EN-DC case, an eNB can configure a B1 event and perform measurement reporting with the UE based thereon. In addition, the eNB can operate a timer and a blacklist so that the UE is coupled to a PSCell of the gNB. The gNB can be reliably coupled to the UE through a more reliable RRC reconfiguration procedure with the eNB. As another example, a case in which one gNB and another gNB are coupled through DC can be considered. The MN can be a gNB that provides a serving cell of frequency range #1 (FR1), and the SN can be a gNB that provides a serving cell of frequency range #2 (FR2). In the case of FR2, RLF can frequently occur due to a high frequency band. In this case, since operations are performed in a relatively low frequency domain, a gNB of FR2 can be configured with cell measurement information through signaling between the UE and the gNB to provide a reliable connection. According to a measurement result based on the measurement configuration information, the gNB of FR1 can perform an SCG recovery procedure for FR2.

[0094] Meanwhile, it is obvious that, not only when SCG failure of the SN, but also when MCG failure of the MN, signaling is performed in the same or similar manner Figure 4 . According to an embodiment, when RLF occurs in a gNB as the MN in an NE-DC case, an eNB as the SN can perform a recovery procedure with the UE. In addition, according to an embodiment, when RLF occurs in a cell of an eNB as the MN in an EN-DC case, a gNB as the SN can perform a recovery procedure with the UE through timer operation and blacklist operation. Since RLF occurrence can not be caused by simple channel quality deterioration, but by factors (e.g., configuration failure, change in the environment around the corresponding base station, base station failure, etc.) caused by a specific node, failure of the SCG or the MCG can be effectively corrected by another node performing a recovery procedure.

[0095] In some embodiments, the UE can not store the measurement configuration information set in the SCG when a failure occurs in the SCG. In various cases of MR-DC, such as an EN-DC case or a DC case between FR1-FR2, the UE can not have the capability to store the SCG information. That is, when RLF occurs in the SN, the UE can be configured not to store any settings of the corresponding cell any more. Since the UE cannot take into account the settings related to the SN, it can not be easy to find a new cell (NR). The UE can need to obtain the measurement configuration for finding a new cell through a reconfiguration procedure with another node (eNB). The UE can receive measurement configuration information for the RAT of the SN (inter-RAT measurement configuration information of the eNB). The UE can perform measurement on the PSCell of the SN based on the control of the MN. According to various embodiments, when RLF occurs in a specific node, the UE obtains measurement configuration information from another node previously coupled, thereby solving the problem caused by the limited existing UE capability.

[0096] Figure 5 Another example of signaling for blacklisted cell management in the MN in a wireless communication system according to various embodiments of the disclosure is shown. Based on the blacklist (measurement prohibition), operations performed by the MN between the MN, the SN, and the UE for handling SCG failure when SCG failure occurs are described.

[0097] Referring to Figure 5 In the case of implementing multi-connection in the UE. The UE can be coupled to the MN and the SN. The MN is an LTE base station (or LTE MN), and the SN is an NR base station (or NR SN). The UE can be coupled to multiple base stations through EN-DC.

[0098] <Tracking current PSCell ID information>

[0099] The MN can manage the cell information of the SN, i.e., the SCG cell information. The MN can identify the PScell information of the SCG by tracking information about the cells of the SCG. The specific procedure is as follows.

[0100] In step S501, the SN can identify cell information of the SN. The cell information of the SN can be cell information of the SCG of the SN. In step S503, the SN can transmit the SCG cell information to the MN. The cell information can include information about a PSCell which is a PCell of the SCG. In some embodiments, the SN can identify information of a PScell coupled to the current UE in initial access, and can transmit the same to the MN. Further, in some embodiments, the SN can identify information of a PScell coupled to the current UE whenever the PScell is changed, and can transmit the same to the MN. Further, in some embodiments, the SN can identify information of a PScell coupled to the current UE when a predetermined event is satisfied, and can transmit the same to the MN. In addition, in some embodiments, the SN can periodically identify information of a PScell coupled to the current UE, and can transmit the same to the MN. The operations of the MN and the SN corresponding to Figure 4 may also be applied to the MN and the SN of Figure 5 in the same or similar manner.

[0101] <SN release and adding of failed cell to blacklist>

[0102] After detecting the SCG failure, the MN can release the SCG. In this case, the MN can manage the corresponding connection by registering the cell in which the SCG failure is detected to the blacklist and by operating a timer. The detailed procedure is as follows.

[0103] In step 511, RLF of the SCG can occur in the SN. Due to the SCG failure, SN release is performed. In some embodiments, the MN can detect the SCG failure. In some other embodiments, the SN can detect the SCG failure. When the SCG failure is detected, if it is SN-initiated SN release, a specific cause is transmitted to the MN, informing that the release situation is due to the SCG failure.

[0104] In step 513, the MN can identify the SCG failure, and can start a timer when performing MN- or SN-initiated SN release. Here, the timer can be a timer configured for a cell in which the SCG failure occurs. The MN can register the PSCell of the SCG in which the failure occurs to the blacklist until the timer expires. At the same time, unlike Figure 4 , the MN can not configure a measurement report event (e.g., an inter-RAT event (e.g., a B1 event)). That is, the MN can perform SN release without having to configure an event for measurement report triggering.

[0105] In step S515, the MN can perform SN release. The MN can perform SN release due to SCG failure. The MN can transmit a message for SN release, i.e., RRC connection reconfiguration message, to the UE. The RRC connection reconfiguration message can include SN release command. The UE can receive the RRC connection reconfiguration message from the MN. The UE can identify the SN release command. The UE can perform SN release.

[0106] B1 configuration after timer expiry

[0107] In step S521, the timer can expire. When the timer expires, the MN can configure inter-RAT measurement configuration. In step S523, the MN can transmit RRC connection reconfiguration including inter-RAT measurement configuration to the UE. In step S525, the UE can transmit RRC connection reconfiguration complete message to the MN. Thereafter, in step S527, the MN can perform SN addition procedure based on measurement report. Specifically, when channel quality (e.g., RSRP, RSRQ) satisfies a condition (e.g., entry condition - above threshold, exit condition - below threshold) configured for inter-RAT B1 measurement, the UE can transmit cell information measured to the MN base station. The MN can perform SN addition procedure with the SN based on the corresponding measurement report.

[0108] Although the operation of each node is described in detail in Figure 5 to describe the operation between the MN, the SN, and the UE, each procedure for recovering SCG failure can be operated individually. That is, the operation between the nodes of the procedure can be applied as a separate embodiment, and unnecessary operations can be omitted in some embodiments.

[0109] Further, although step S520 is described in Figure 5 as a procedure performed by the MN to establish a connection with the UE, signaling between the MN and the SN can be defined as specific operations of the MN and the SN. For example, the signaling can be exemplified by the operations of steps S323 and S325 of Figure 3 .

[0110] When SCG failure occurs in the SN, a more reliable recovery procedure can be performed through signaling with the MN as well as signaling of the MN and the UE, instead of the recovery procedure autonomously performed by the SN through RRE. For example, even if RLF occurs in a gNB in an EN-DC case, an eNB can operate a timer and a blacklist so that the UE is coupled to a PSCell of the gNB. Thereafter, the eNB can configure a B1 event, and based on this, can perform a measurement report with the UE. The gNB can be reliably coupled to the UE through a more reliable RRC reconfiguration procedure with the eNB. As another example, a case where one gNB and another gNB are coupled through DC can be considered. The MN can be a gNB that provides a serving cell of frequency range #1 (FR1), and the SN can be a gNB that provides a serving cell of frequency range #2 (FR2). In the case of FR2, RLF can frequently occur due to a high frequency band. In this case, since operations are performed in a relatively low frequency domain, the gNB for FR2 can be configured with cell measurement information through signaling between the UE and the gNB to provide a reliable connection. According to a measurement result based on the measurement configuration information, the gNB for FR1 can perform an SCG recovery procedure for FR2.

[0111] Meanwhile, it is obvious that, not only when SCG failure of the SN, but also when MCG failure of the MN, signaling is performed in the same or similar manner Figure 5 . According to an embodiment, when RLF occurs in a gNB as the MN in an NE-DC case, an eNB as the SN can perform a recovery procedure with the UE. Further, according to an embodiment, when RLF occurs in a cell of an eNB as the MN in an EN-DC case, a gNB as the SN can perform a recovery procedure with the UE through timer operation and blacklist operation. Since RLF occurrence can not be caused by simple channel quality deterioration, but by a factor caused by a specific node (e.g., configuration failure, change in the environment around the corresponding base station, base station failure, etc.), failure of the SCG or the MCG can be effectively corrected by another node performing a recovery procedure.

[0112] In some embodiments, when SCG failure occurs, the UE can be configured not to store measurement configuration information set in the SCG. In the case of SCG failure, since the UE cannot consider settings related to the SN, it can not be easy to find a new cell (NR). Accordingly, the UE can perform measurement on a PSCell of the SN based on control signaling of the MN including an RRC message of inter-RAT measurement configuration. According to various embodiments, when RLF occurs in a specific node, the UE obtains measurement configuration information from another node to which it was previously coupled, thereby solving a problem caused by a limitation of existing UE capability.

[0113] Figure 6An example of signaling for controlling a link failure in a secondary node (SN) in a wireless communication system according to various embodiments of the disclosure is shown. In Figure 6 In the middle, operations between an MN, an SN, and a UE for handling an SCG failure when the SCG failure occurs are described by the SN. This is in the case where multi-connectivity is implemented in the UE. The UE can be coupled to an MN and an SN. The UE can be coupled to a data radio bearer (DRB) activated in the MN and the SN. The UE can be coupled to the SN at a radio resource control (RRC) / packet data convergence protocol (PDCP) level.

[0114] Referring to Figure 6 In step S600, the UE can be coupled to a base station. That is, this is in the case where multi-connectivity is implemented in the UE. The UE can be coupled to an MN and an SN. The UE can be coupled to a DRB activated in the MN and the SN. The UE can be coupled to the SN at an RRC / PDCP level.

[0115] In step S610, the SN can detect an SCG failure. The SN can detect the SCG failure from information obtained from the UE, or can autonomously detect whether a specified condition or the SCG failure is satisfied by inputting to other nodes.

[0116] In step S620, the SN can initiate a reconnection procedure. The SN can identify a PSCell for reconnection. The SN can detect the SCG failure by receiving SCG failure information. In this case, when the measurement result is included in the SCG failure information, the reconnection procedure (direct re-synchronization procedure) can be performed. The SN can perform the reconnection procedure with a cell included in the measurement result. That is, a cell identifier of a candidate PSCell can be included in the SCG failure information. Here, the candidate PSCell can be a cell having the highest channel quality (e.g., a cell having the largest RSRP) among the measurement target cells and satisfying a minimum channel quality value. When the SCG failure information is not included in the measurement result, the SN can indicate a reconnection procedure with an existing PSCell. The SN can initiate the reconnection procedure with a cell having the highest channel quality among the measurement cells.

[0117] The SN having identified the PSCell for the reconnection procedure can perform a connection procedure with the UE through the MN. Specifically, the MN, the SN, and the UE can perform the following operations.

[0118] In step S631, the SN can transmit an SN modification required message to the MN. The SN modification required message can include an X2 cause and configuration information of the target PSCell. The X2 cause can be set to "SCG mobility". In step S633, the MN can transmit an RRC connection reconfiguration message to the UE. In this case, for the SN (NR base station), the RRC connection reconfiguration message can include an RRC reconfiguration message for NR in some embodiments. In step S635, the UE can transmit an RRC connection reconfiguration complete message to the MN. In this case, for the SN (NR base station), the RRC connection reconfiguration complete message can include an RRC reconfiguration complete message for NR in some embodiments.

[0119] In step S637, the MN can transmit an SN modification confirm message to the SN. Thereafter, in step S639, the UE can perform an access procedure with the SN. The UE can perform the access procedure based on the PSCell information transferred from the SN through the MN. The UE can perform data transmission and reception with the SN in the corresponding PSCell through an NR RACH procedure and an RRC resume procedure for the corresponding cell.

[0120] Although the operations of the respective nodes are described in detail in Figure 6 to describe the operations between the MN, the SN, and the UE, each procedure for recovering the SCG failure can be operated individually. That is, the inter-node operations of the procedures can be applied as a single embodiment, and unnecessary operations can be omitted in some embodiments.

[0121] Further, although step S637 is described in Figure 6 as a procedure performed by the MN to establish a connection with the UE, the signaling between the MN and the SN can be defined as specific operations of the MN and the SN. For example, the signaling can be exemplified by the operations of steps S323 and S325 of Figure 3 , steps S421 to S440, and steps S521 to S527 of Figure 4 .

[0122] The case where MN is an eNB as an LTE base station and SN is a gNB as an NR base station is described in the disclosure as an EN-DC environment. However, it is obvious that embodiments of the disclosure can also be performed in different MR-DC environments, similar to the NR-DC environment, i.e., NR-NR. In addition, as a measurement reporting event between two base stations, the B1 event for configuring inter-RAT measurement has been exemplarily described. The B1 event can be a reporting condition configured to report the measurement result of a neighboring cell having a RAT different from the RAT having a channel quality exceeding a threshold. However, this is only an exemplary described event in the EN-DC case for convenience of explanation, and embodiments of the disclosure can also be performed by other measurement reporting conditions other than the B1 event.

[0123] Figure 7 A functional structure of a base station 110 in a wireless communication system according to various embodiments of the disclosure is illustrated. Figure 7 An exemplary structure can be understood as a structure of the base station 110. Hereinafter, the term "…unit", "…device", and the like means a unit processing at least one function or operation, and can be implemented in hardware or software or in combination of hardware and software.

[0124] Referring to Figure 7 , the base station 110 includes a wireless communication unit 701, a backhaul communication unit 703, a storage unit 705, and a control unit 707.

[0125] The wireless communication unit 701 performs a function of transmitting and receiving a signal through a radio channel. For example, the wireless communication unit 701 performs a conversion function between a baseband signal and a bit stream according to a physical layer standard of a system. For example, in data transmission, the wireless communication unit 701 generates a complex symbol by encoding and modulating a transmission bit stream. Also, in data reception, the wireless communication unit 701 recovers a reception bit stream by demodulating and decoding a baseband signal. In addition, the wireless communication unit 701 up-converts a baseband signal into a radio frequency (RF) signal and then transmits it through an antenna, and down-converts an RF signal received through an antenna into a baseband signal.

[0126] To this end, the wireless communication unit 701 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Further, the wireless communication unit 701 can include a plurality of transmission / reception paths. Further, the wireless communication unit 701 can include at least one antenna array composed of a plurality of antenna elements. In terms of hardware, the wireless communication unit 701 can be composed of a digital unit and an analog unit, which can be composed of a plurality of sub-units according to operating power, operating frequency, etc. According to various embodiments, the wireless communication unit 701 can include a unit forming a beam, i.e., a beamforming unit. For example, the wireless communication unit 701 can include a massive MIMO unit (MMU).

[0127] The wireless communication unit 701 can transmit / receive a signal. To this end, the wireless communication unit 701 can include at least one transceiver. For example, the wireless communication unit 701 can transmit a synchronization signal, a reference signal, system information, a message, control information, or data. Further, the wireless communication unit 701 can perform beamforming. In order to allocate directionality according to the setting of the control unit 707 to a signal to be transmitted / received, the wireless communication unit 701 can apply beamforming weights to the signal. According to an embodiment, the wireless communication unit 701 can generate a baseband signal according to a scheduling result and a transmission power calculation result. Further, an RF unit in the wireless communication unit 701 can transmit the generated signal through an antenna.

[0128] The wireless communication unit 701 transmits and receives a signal as described above. Therefore, the wireless communication unit 701 can be referred to as a transmitter, a receiver, or a transceiver. Further, in the following description, transmission and reception performed through a radio channel are used to imply that the above-described processing is performed by the wireless communication unit 701.

[0129] The backhaul communication unit 703 provides an interface for communicating with different nodes in the network. That is, the backhaul communication unit 703 converts a bit stream transmitted from the base station 110 to different nodes (e.g., different access nodes, different base stations, upper nodes, a core network, etc.) into a physical signal and converts a physical signal received from different nodes into a bit stream. According to various embodiments, the backhaul communication unit 703 can transmit a message to another base station (e.g., any SN). In some embodiments, the message can include a SN modification request message and a response message thereto. The message can include a SN modification requirement message and a response message thereto. Further, the message can include cell information. In some embodiments, the message can include information about a currently operating cell (e.g., current PSCell information). Further, in some embodiments, the cell information can include information about a target cell for reconnection. The target cell for reconnection can be a PSCell candidate cell. The cell information can indicate a cell in the form of a cell global identifier (CGI). For example, the message can include an NR-CGI to indicate a candidate cell of a target PSCell of an NR base station.

[0130] The storage unit 705 stores data such as a basic program for operation of the base station 110, an application program, configuration information, and the like. The storage unit 705 can include a memory. The storage unit 705 can be constituted by a volatile memory, a non-volatile memory, or a combination of a volatile memory and a non-volatile memory. Further, the storage unit 705 can provide stored data according to a request of the control unit 707.

[0131] The control unit 707 controls the overall operation of the base station 110. For example, the control unit 707 can transmit and receive signals via the communication unit 701 or the backhaul communication unit 703. Also, the control unit 707 writes and reads data in and from the storage unit 705. In addition, the control unit 707 can perform the functions of a protocol stack required in a communication specification. To this end, the control unit 707 can include at least one processor. In some embodiments, the control unit 707 can perform the operations of the MN or the SN. The control unit 707 can detect the occurrence of RLF in a cell. The control unit 707 can detect the failure of a cell group. The control unit 707 can configure inter-RAT measurements. The control unit 707 can control the registration / release of a blacklist. The control unit 707 can start a timer, or can detect the end of a timer. The components for each operation of the control unit 707 can be commands / codes at least temporarily residing in the control unit 707 or a storage space storing the commands / codes, or can be a part of a circuit constituting the control unit 707. Meanwhile, according to another embodiment, a scheduler and a transmission power calculation unit can be independently implemented in various devices. According to various embodiments, the control unit 707 can control the base station 110 to perform operations based on various embodiments to be described below.

[0132] Figure 7 The structure of the base station 110 shown is merely an example of a base station, and examples of a base station that performs various embodiments of the disclosure are not limited to Figure 7 the structure shown. That is, the structure can be partially added, deleted, or changed according to various embodiments.

[0133] Although the base station is described as one entity Figure 7 , the present application is not limited thereto. The base station according to various embodiments of the disclosure can be implemented to constitute an access network not only having an integrated deployment but also having a distributed deployment. According to an embodiment, the base station can be divided into a central unit (CU) and a digital unit (DU). The CU can be implemented to perform an upper layer function (e.g., a packet data convergence protocol (RRC)), and the DU can be implemented to perform a lower layer function (e.g., a medium access control (MAC) and a physical (PHY)). The DUs of the base station can constitute a beam coverage on a radio channel.

[0134] Figure 8 A functional structure of a UE in a wireless communication system according to various embodiments of the disclosure is illustrated. Figure 8 The exemplary structure of FIG. 12 can be understood as a structure of the UE 120. Hereinafter, the term "…unit", "…device", and the like indicates a unit processing at least one function or operation, and can be implemented in hardware or software or in combination of hardware and software.

[0135] Referring to Figure 8The UE 120 includes a communication unit 801, a storage unit 803, and a control unit 805.

[0136] The communication unit 801 performs a function of transmitting and receiving a signal through a radio channel. For example, the communication unit 801 performs a conversion function between a baseband signal and a bit stream according to a physical layer standard of a system. For example, in data transmission, the communication unit 801 generates a complex symbol by encoding and modulating a transmission bit stream. Also, in data reception, the communication unit 801 recovers a reception bit stream by demodulating and decoding a baseband signal. In addition, the communication unit 801 up-converts a baseband signal to an RF signal and transmits the RF signal through an antenna, and down-converts an RF signal received through an antenna to a baseband signal. For example, the communication unit 801 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, and the like.

[0137] Also, the communication unit 801 can include a plurality of transmission / reception paths. Also, the communication unit 801 can include an antenna unit. The communication unit 801 can include at least one antenna array constituted by a plurality of antenna elements. From a hardware aspect, the communication unit 801 can be constituted by a digital circuit and an analog circuit (for example, a radio frequency integrated circuit (RFIC)). Here, the digital circuit and the analog circuit can be implemented as one package. Also, the communication unit 801 can include a plurality of RF chains. Also, the communication unit 801 can perform beamforming. In order to allocate directivity according to a setting of the control unit 805 to a signal to be transmitted / received, the communication unit 801 can apply a beamforming weight to the signal. According to an embodiment, the communication unit 801 can include a radio frequency (RF) block (or an RF unit). The RF block can include a first RF circuit related to an antenna and a second RF circuit related to baseband processing. The first RF circuit can be referred to as a radio frequency antenna (RF-A). The second RF circuit can be referred to as an RF baseband (RF-B).

[0138] In addition, the communication unit 801 can transmit / receive a signal. To this end, the communication unit 801 can include at least one transceiver. The communication unit 801 can receive a downlink signal. The downlink signal can include a synchronization signal (SS), a reference signal (RS) (for example, a cell-specific reference signal (CRS), a demodulation (DM)-RS), system information (for example, an MIB, an SIB, remaining system information (RMSI), other system information (OSI), a configuration message, control information, or downlink data, and the like. In addition, the communication unit 801 can transmit an uplink signal. The uplink signal can include a random access-related signal (for example, a random access preamble (RAP) (message 1 (Msg1), message 3 (Msg3)), a reference signal (for example, a sounding reference signal (SRS), a DM-RS), or a power headroom report (PHR), and the like.

[0139] In addition, the communication unit 801 can include different communication modules to handle signals of different frequency bands. Further, the communication unit 801 can include multiple communication modules to support multiple different radio access technologies. For example, different radio access technologies can include Bluetooth Low Energy (BLE), Wireless Fidelity (WiFi), WiFi Gigabyte (WiGig), cellular networks (e.g., Long Term Evolution (LTE), New Radio (NR)), etc. Further, different frequency bands can include Super High Frequency (SHF) (e.g., 2.5 GHz, 5 GHz) bands and millimeter wave (e.g., 38 GHz, 60 GHz, etc.) bands. Further, the communication unit 801 can use the same type of radio access technology on different frequency bands (e.g., unlicensed bands for License Assisted Access (LAA), Citizens Broadband Radio Service (CBRS) (e.g., 3.5 GHz)).

[0140] The communication unit 801 transmits and receives signals as described above. Therefore, the communication unit 801 can be referred to as a transmitter, a receiver, or a transceiver. Further, in the following description, transmission and reception performed through a radio channel are used to imply that the above-described processing is performed by the communication unit 801.

[0141] The storage unit 803 stores data such as basic programs, application programs, configuration information, etc. for the operation of the UE 120. The storage unit 803 can be constituted by a volatile memory, a non-volatile memory, or a combination of a volatile memory and a non-volatile memory. Further, the storage unit 803 can provide stored data according to a request of the control unit 805. According to various embodiments, the storage unit 803 can store each beam of a beam set to be operated in the UE 120 or direction information about each beam of an auxiliary beam pair.

[0142] The control unit 805 controls the overall operation of the UE 120. For example, the control unit 805 can transmit and receive signals via the communication unit 801. Also, the control unit 805 writes and reads data in and from the storage unit 803. In addition, the control unit 805 can perform the functions of a protocol stack required in a communication specification. To this end, the control unit 805 can include at least one processor. The control unit 805 can include at least one processor or microprocessor, or can be a part of a processor. Also, a part of the communication unit 801 and the control unit 805 can be referred to as a CP. The control unit 805 can include various modules for performing communication. According to various embodiments, the control unit 805 can control the UE to perform operations based on the various embodiments described above. The control unit 805 can detect that an RLF occurs in a cell. The control unit 805 can perform measurement. The control unit 805 can detect whether a measurement reporting condition is satisfied. The control unit 805 can perform measurement reporting including a measurement result. The control unit 805 can perform an access procedure with a cell. The control unit 805 can perform measurement.

[0143] Even when an RLF occurs in a secondary node (SN) while dual connectivity between heterogeneous or homogeneous RATs in the UE is operated through a measurement reporting and signaling procedure, a timer operation, etc., a recovery and reconnection procedure can be configured for this. According to these procedures, since efficient fault management can be performed through the processing operation of an existing cell and a bearer under the control of a base station, it is possible to expect improved performance compared to conventional techniques.

[0144] Various embodiments of the disclosure can be applied to multi-radio dual connectivity (MR-DC), including: evolved universal terrestrial radio access-new radio dual connectivity (EN-DC) defined in 3GPP standards, in which a connection to a 4G core network is established between a 4G master cell group and a 5G secondary cell group; NG-RAN evolved universal terrestrial radio access-new radio dual connectivity (NGEN-DC), in which a connection to a 5G core network is established between a 4G master cell group and a 5G secondary cell group; new radio evolved universal terrestrial radio access dual connectivity (NE-DC), in which a connection to a 5G core network is established between a 4G secondary cell group and a 5G master cell group; and multi-radio dual connectivity (MR-DC), in which a connection is established between a 5G cell group and another 5G cell group.

[0145] The method of configuring a base station of a master cell group (MCG) in a wireless communication system according to the above-described embodiments of the disclosure can include detecting a failure of a primary cell (PCell) of a secondary cell group (SCG) (PScell), based on the detection, transmitting radio access technology (RAT) measurement configuration information to a terminal, and transmitting information about a cell identified based on the measurement configuration information to a base station configured with the SCG.

[0146] In an embodiment, the information about the identified cell can include information about at least one cell, information about a measurement result according to the measurement configuration information, and X2 cause information.

[0147] In an embodiment, the detecting can include receiving information about an SCG failure from the terminal or the base station configured with the SCG.

[0148] In an embodiment, the method can further include receiving a measurement report on the measurement configuration information from the terminal, and identifying a cell based on the measurement report.

[0149] In an embodiment, the method can further include receiving information related to a recovery procedure from the base station configured with the SCG. The information related to the recovery procedure can include an identifier (ID) of the PSCell or an X2 cause.

[0150] In an embodiment, the method can further include transmitting a message including removal of the measurement configuration information to the terminal based on the information related to the recovery procedure.

[0151] In an embodiment, the method can further include receiving a response to the message including removal of the measurement configuration information from the terminal, and transmitting a modification confirmation message to the base station configured with the SCG based on the response.

[0152] A base station configured with an MCG in a wireless communication system according to the above disclosed embodiments can include at least one transceiver and at least one processor. The at least one processor can be configured to detect a failure of a PSCell, transmit inter-RAT measurement configuration information to a terminal based on the detection, and transmit information about a cell identified based on the measurement configuration information to a base station configured with an SCG.

[0153] In an embodiment, the information about the identified cell can include information about at least one cell, information about a measurement result according to the measurement configuration information, and X2 cause information.

[0154] In an embodiment, the at least one processor can be configured to receive information about an SCG failure from the terminal or the base station configured with the SCG.

[0155] In an embodiment, the at least one processor can be configured to receive a measurement report on the measurement configuration information from the terminal, and identify a cell based on the measurement report.

[0156] In an embodiment, the at least one processor can be configured to receive information related to a recovery procedure from the base station configured with the SCG. The information related to the recovery procedure can include an ID of the PSCell or an X2 cause.

[0157] In an embodiment, the at least one processor can be configured to transmit, to the terminal, a message including removal of the measurement configuration information based on information related to the recovery procedure.

[0158] In an embodiment, the at least one processor can be configured to receive, from the terminal, a response to the message including removal of the measurement configuration information, and transmit, to the base station configured with the SCG, a modification confirmation message based on the response.

[0159] A method of a base station configured with an SCG in a wireless communication system can include detecting a failure of a PScell, identifying a cell based on the detection, and performing a connection procedure with a terminal by transmitting information about the cell to a base station configured with an MCG.

[0160] A base station configured with an SCG in a wireless communication system according to the above disclosed embodiments can include at least one transceiver and at least one processor. The at least one processor can be configured to detect a failure of a PScell, identify a cell based on the detection, and perform a connection procedure with a terminal by transmitting information about the cell to a base station configured with an MCG.

[0161] Further, although the expression "greater than" or "less than" is used in the present disclosure to determine whether a certain condition is satisfied (or implemented), this is for example purposes only and does not exclude the expression "greater than or equal to" or "less than or equal to". A condition described as "greater than or equal to" can be replaced with "greater than". A condition described as "less than or equal to" can be replaced with "less than". A condition described as "greater than or equal to and less than" can be replaced with "greater than and less than or equal to".

[0162] The method based on the embodiments disclosed in the claims and / or specification of the present disclosure can be implemented in hardware, software, or a combination of both.

[0163] When implemented in software, a computer readable recording medium for storing one or more programs (i.e., software modules) can be provided. The one or more programs stored in the computer readable recording medium are configured to be executed by one or more processors in an electronic device. The one or more programs include instructions for allowing the electronic device to execute a method based on the embodiments disclosed in the claims and / or specification of the present disclosure.

[0164] The programs (i.e., software modules or software) can be stored in random access memory, non-volatile memory including a flash memory, read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), a magnetic disc storage device, a compact disc-ROM (CD-ROM), digital versatile discs (DVDs), or other form of optical storage device, and a magnetic cassette. Alternatively, the programs can be stored in a memory configured by a combination of all or some of these storage media. In addition, the number of configured memories can be plural.

[0165] Further, the programs can be stored in an attachable storage device of an electronic device that can access the electronic device through a communication network such as the Internet, an intranet, a local area network (LAN), a wide area network (WAN), or a storage area network (SAN), or a communication network configured by a combination of networks. The storage device can access the device for performing embodiments of the present disclosure through an external port. Further, the additional storage device on the communication network can access the device for performing embodiments of the present disclosure.

[0166] In the above-described specific embodiments of the present disclosure, components included in the present disclosure are expressed in singular or plural according to the specific embodiments presented herein. However, the singular or plural expression presented for the convenience of explanation is appropriately selected, and thus various embodiments of the present disclosure are not limited to a single or multiple components. Therefore, the components expressed in plural can also be expressed in singular, and vice versa.

[0167] While the present disclosure has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims. Accordingly, the scope of the present disclosure is not limited by the detailed description thereof but is defined by the appended claims, and all differences within the scope equivalent to this scope will be construed as included in the present disclosure.

Claims

1. A method performed by a first base station in which a master cell group (MCG) is configured, in a wireless communication system, the method comprising: receiving, from a user equipment (UE), secondary cell group (SCG) failure information associated with an SCG; transmitting, to a second base station in which the SCG is configured, a first secondary node modification request message; receiving, from the second base station, a secondary node modification confirm message; and transmitting, to the UE, a first radio resource control (RRC) connection reconfiguration message including configuration information for a measurement of the UE, wherein the first secondary node modification request message includes SCG failure information including an SCG failure cause; wherein the method further comprises: receiving, from the UE, a measurement report based on the configuration information for the measurement; transmitting, to the second base station, a second secondary node modification request message including information on a candidate cell list and measurement results based on the measurement report; receiving, from the second base station, a message including information on a target cell associated with SCG recovery of the UE; and transmitting, to the UE, a second RRC connection reconfiguration message including information on removal of the measurement. the secondary node modification confirm message includes information for a path.

2. The method of claim 1, wherein, 3.The method of claim 1, further comprising: receiving, from the UE, an RRC connection reconfiguration complete message; and transmitting, to the second base station, a secondary node reconfiguration complete message. 4.The method of claim 1, the first base station is an eNodeB (eNB) and the second base station is a gNodeB (gNB); or wherein the first base station is a gNB and the second base station is an eNB; or wherein wherein the first base station is a gNB and the second base station is a gNB. 5.A first base station in which a master cell group (MCG) is configured, in a wireless communication system, the first base station comprising: at least one transceiver; and at least one processor coupled to the at least one transceiver, wherein the at least one processor is configured to: receive, from a user equipment (UE), secondary cell group (SCG) failure information associated with an SCG, transmit, to a second base station in which the SCG is configured, a first secondary node modification request message, receive, from the second base station, a secondary node modification confirm message, and transmit, to the UE, a first radio resource control (RRC) connection reconfiguration message including configuration information for a measurement of the UE, wherein the secondary node modification request message includes SCG failure information including an SCG failure cause; wherein the at least one processor is further configured to: receive, from the UE, a measurement report based on the configuration information for the measurement; transmit, to the second base station, a second secondary node modification request message including information on a candidate cell list and measurement results based on the measurement report; ​ ​ ​ receiving, from the second base station, a message including information about a target cell associated with SCG recovery of the UE; and sending, to the UE, a second RRC connection reconfiguration message including information about removing the measurement.

6. The first base station of claim 5, wherein, The secondary node modification confirm message includes information for a path.

7. The first base station of claim 5, wherein, The at least one processor is further configured to: receive, from the UE, an RRC connection reconfiguration complete message, and send, to the second base station, a secondary node reconfiguration complete message.

8. The first base station of claim 5, wherein the first base station is an eNodeB (eNB) and the second base station is a gNodeB (gNB); or wherein the first base station is a gNB and the second base station is an eNB; or wherein the first base station is a gNB and the second base station is a gNB.

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