Apparatus and method for failure recovery of master cell group in integrated access and backhaul system

Abstract

The disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting ultra-high data rates with IoT technology. The disclosure can be applied to intelligent services based on the 5G communication technology and IoT-related technology, such as smart home, smart building, smart city, smart car, smart grid, health care, digital education, smart retail, security and safety services. According to an embodiment of the present disclosure, there is provided a method of a third integrated access and backhaul (IAB) node in a wireless communication system, the method comprising: receiving, from a first IAB node related to a first cell group of the third IAB node, a backhaul radio link failure (RLF) indicator related to a recovery failure of an RLF of a backhaul of the first IAB node; determining that an RLF of the first cell group is detected based on the backhaul RLF indicator; and transmitting, to an IAB donor through a second IAB node related to a second cell group of the third IAB node, a message including backhaul RLF information indicating that the RLF of the first cell group is associated with the RLF of the backhaul of the first IAB node.

Description

TECHNICAL FIELD

[0001] The present invention provides a method for operating necessary forwarding information when a terminal part re-accesses a network in a wireless integrated access and backhaul system. BACKGROUND

[0002] To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a "beyond 4G network" or a "post LTE system." The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed for use with the 5G communication system. In addition, in the 5G communication system, development for improvement of a network structure, development of a coordination between nodes, and development of a cooperative communication scheme for the network have been conducted. Further, in the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

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

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

[0005] Integrated Access and Backhaul (IAB) is a kind of relay node in which one node operates as a mobile terminal (MT) (or terminal or user equipment (UE)) with respect to an upper IAB node and operates as a base station with respect to a lower IAB node. For example, the node can converge the uplink traffic from the lower IAB node and the uplink traffic of normal terminals that have accessed the node together and transmit it as uplink traffic to the upper IAB node, and transmit the traffic transmitted from the core network as downlink traffic to the lower IAB node or transmit it as downlink traffic to the normal terminals that have accessed the node. IAB can refer to a single node and a topology system including the node, which performs the operations of communication with the upper IAB node and communication with the lower IAB node and the terminal in the above-described process, thereby combining access and backhaul communication operations. A node directly connected to a core network is defined as an IAB donor, and the IAB donor can be connected to the core network by using an IP address system without having an upper IAB node. SUMMARY

[0006] Technical problem

[0007] The present disclosure proposes a method for more efficient re-accessing the network in a wireless communication system comprising multi-hop of IAB nodes, wherein an intermediate node with a failure, such as a radio link failure, that can be identified by the RRC layer, informs the donor base station about the failure fact and receives a corresponding command from the network.

[0008] Technical solution

[0009] To solve the above problems, a method of a third integrated access and backhaul (IAB) node in a wireless communication system according to an embodiment of the present application can include receiving, from a first IAB node related to a first cell group of the third IAB node, a backhaul radio link failure (RLF) indicator related to a recovery failure of an RLF of a backhaul of the first IAB node, determining that the RLF of the first cell group is detected based on the backhaul RLF indicator, and transmitting, to an IAB donor through a second IAB node related to a second cell group of the third IAB node, a message including backhaul RLF information indicating that the RLF of the first cell group is associated with the RLF of the backhaul of the first IAB node.

[0010] Further, according to another embodiment of the present disclosure, a method of a first integrated access and backhaul (IAB) node in a wireless communication system can include detecting a recovery failure of a radio link failure (RLF) of a backhaul of the first IAB node, transmitting, to a third IAB node, a backhaul RLF indicator related to the recovery failure of the RLF of the backhaul of the first IAB node, wherein the first IAB node is related to a first cell group of the third IAB node, wherein the RLF of the first cell group is determined to be detected based on the backhaul RLF indicator, and wherein a message including backhaul RLF information indicating that the RLF of the first cell group is associated with the RLF of the backhaul of the first IAB node is transmitted, to an IAB donor node through a second IAB node related to a second cell group of the third IAB node.

[0011] Also, according to another embodiment of the disclosure, a third integrated access and backhaul (IAB) node in a wireless communication system can include a transceiver; and a controller configured to control the transceiver to receive, from a first IAB node related to a first cell group of the third IAB node, a backhaul radio link failure (RLF) indicator related to a failure of recovery of an RLF of a backhaul of the first IAB node, determine that the RLF of the first cell group is detected based on the backhaul RLF indicator, and control the transceiver to transmit, to an IAB donor, a message including backhaul RLF information through a second IAB node related to a second cell group of the third IAB node, the backhaul RLF information indicating that the RLF of the first cell group is associated with the RLF of the backhaul of the first IAB node.

[0012] Also, according to another embodiment of the disclosure, a first integrated access and backhaul (IAB) node in a wireless communication system can include a transceiver; and a controller configured to detect a failure of recovery of a radio link failure (RLF) of a backhaul of the first IAB node; and control the transceiver to transmit, to a third IAB node, a backhaul RLF indicator related to the failure of recovery of the RLF of the backhaul of the first IAB node, wherein the first IAB node is related to a first cell group of the third IAB node, wherein it is determined that the RLF of the first cell group is detected based on the backhaul RLF indicator, and wherein a message including backhaul RLF information is transmitted, to an IAB donor node, through a second IAB node related to a second cell group of the third IAB node, the backhaul RLF information indicating that the RLF of the first cell group is associated with the RLF of the backhaul of the first IAB node.

[0013] Technical effects

[0014] According to one embodiment of the disclosure, in a wireless communication system including multi-hop of IAB nodes, an intermediate node having a failure such as a radio link failure that can be recognized by an RRC layer informs a donor base station of the failure fact and receives a corresponding command from the network, thereby more efficiently re-accessing the network.

[0015] According to another embodiment of the disclosure, when a radio link fails, or after an RRC release, or when a re-establishment is performed, if information of a cell connected to an old IAB donor is provided, the terminal re-accesses the cell connected to the old IAB donor when re-accessing the network again later if possible, and can more efficiently re-access the network due to no additional terminal and base station overhead caused by PDCP lossless transmission and security refresh. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a structure diagram of an existing LTE system.

[0017] Figure 2 is a radio protocol structure diagram of the existing LTE system.

[0018] Figure 3 is a structure diagram illustrating a next-generation mobile communication system to which the present disclosure can be applied.

[0019] Figure 4 is a radio protocol structure diagram illustrating a next-generation mobile communication system to which the present disclosure can be applied.

[0020] Figure 5 is a diagram illustrating a UE device according to an embodiment of the present disclosure.

[0021] Figure 6 is a diagram illustrating a base station device according to an embodiment of the present disclosure.

[0022] Figure 7 is a diagram illustrating a case of MCG failure through RLF detection in an SA case.

[0023] Figure 8 is a diagram illustrating a case of MCG failure through RLF notification in an SA case.

[0024] Figure 9 is a diagram illustrating a case of SCG failure through RLF detection in an SA case.

[0025] Figure 10 is a diagram illustrating a case of SCG failure through RLF notification in an SA case.

[0026] Figure 11 is a diagram illustrating a case of SCG failure through RLF detection in an NSA case.

[0027] Figure 12A is a diagram illustrating a case of SCG failure through RLF notification in an NSA case.

[0028] Figure 12B is a diagram illustrating a case in which an RLF recovery failure notification due to SCG release is transmitted.

[0029] Figure 13A is a flowchart illustrating a cell selection operation of a mobile termination (MT) accessing an IAB node included in the same donor gNB during connection reestablishment.

[0030] Figure 13B is a diagram illustrating a case in which an MT receives an indicator related to a current donor gNB / CU through an RRC message when combining an IAB network.

[0031] Figure 13Cis a diagram illustrating a case where an MT receives information about cell IDs currently accessible under a donor gNB / CU through an RRC message when combining an IAB network.

[0032] Figure 14 is a flowchart illustrating a cell selection operation for an MT not accessing a cell under an underlying IAB node during connection reestablishment. DETAILED DESCRIPTION

[0033] In describing embodiments in the present specification, a description of well-known technologies to which the embodiments pertain will be omitted. Such an unnecessary description will be omitted in order to prevent obscuring the main idea of the present disclosure and to more clearly convey the main idea.

[0034] For the same reason, in the drawings, some elements can be exaggerated, omitted, or schematically illustrated. Also, the size of each element does not completely reflect the actual size. In the drawings, the same or corresponding elements are denoted by the same reference numerals.

[0035] The advantages and features of the present disclosure and implementations thereof will be apparent from the embodiments described below in detail with reference to the accompanying drawings. However, the present disclosure is not limited to the embodiments set forth below, but can be implemented in various forms. The embodiments are provided only to completely disclose the present disclosure and to inform those skilled in the art to the scope of the present disclosure, and the present disclosure is defined only by the scope of the appended claims. Throughout the specification, the same or similar reference numerals denote the same or similar elements.

[0036] In this document, each block denoted by a dashed line in the flowchart can represent a module, segment, or code section which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks can occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or the blocks can sometimes be executed in the reverse order, depending upon the implementation. Each block and each combination of blocks can be implemented by a dedicated processor, a processor that is shared among the blocks, a processor dedicated to an individual block or blocks, or a combination of dedicated and shared processors.

[0037] Furthermore, each block in the flow diagram can represent a code module, code segment, or code portion for implementing one or more specified logical functions. It should also be noted that in some alternative implementations, the function noted in the blocks can occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.

[0038] As used herein, "unit" refers to a software or hardware element, such as a field programmable gate array (FPGA) or application specific integrated circuit (ASIC), that performs one or more specified functions. However, a "unit" need not be limited to a software or hardware element, and can refer to a combination of software and hardware elements, or be embodied in hardware alone, software alone, or a combination of hardware and software. Moreover, "unit" can be embodied as one or more processing units that are located in one or more devices or security multimedia cards.

[0039] Hereinafter, the operational principle of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description of the present disclosure, when it is determined that detailed description of known functions or configurations incorporated in the present disclosure can unnecessarily obscure the subject matter of the present disclosure, such detailed description will be omitted. The terms to be described hereinafter are terms defined in consideration of functions in the present disclosure, and can vary according to users, user intentions, or customs. Therefore, the definition of the terms should be based on the contents throughout the specification.

[0040] In the following description of the present disclosure, for convenience of description, terms for identifying access nodes, terms for referring to network entities, terms for referring to messages, terms for referring to interfaces between network entities, terms for referring to various identification information, and the like are illustratively used. Therefore, the present disclosure is not limited to the terms used below, and other terms referring to the subject matter having equivalent technical meanings can be used.

[0041] In the following description of the present disclosure, for convenience of description, terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard will be used. However, the present disclosure is not limited to these terms and names, and can be applied in the same manner to systems conforming to other standards.

[0042] According to one embodiment of the disclosure, in the case where communication between the core network and the UE is made in a topology consisting of multiple hops of IAB nodes, the connection point on the core network side can be an IAB donor node. The donor node includes a central unit (CU) and controls the operation related to the control of a distributed unit (DU) and the transmission / reception of data to / from a terminal through the DU. When the connection fails, the terminal part (mobile terminal MT, terminal, or user equipment UE) of the intermediate IAB node or the terminal receiving service from the IAB node informs the network of the reason why the MCG or SCG link is problematic. In this case, not only the reason for detecting the existing radio link failure (RLF) is informed, but also information indicating that the parent IAB node is disconnected from the network. Accordingly, the network can know that the parent IAB node of the IAB node that has reported the failure is also problematic, and can indicate the movement (mobility) to the IAB node other than the corresponding parent IAB node at the time of cell selection. In addition, in the cell selection process of the IAB node after the failure, a whitelist allowing only the reselection of the IAB node under the same donor gNB and a cell selection blacklist for avoiding the selection of one's own descendant IAB node can be introduced.

[0043] Figure 1 is a structural diagram of the existing LTE system.

[0044] Referring to Figure 1 As illustrated, the radio access network of the LTE system can be composed of next-generation base stations (Evolved Node Bs (ENBs), hereinafter referred to as ENBs, Node Bs, or base stations) 1-05, 1-10, 1-15, 1-20, a mobility management entity (MME) 1-25, and a serving gateway (S-GW) 1-30. A user equipment (hereinafter referred to as UE or terminal) 1-35 can access an external network through the ENBs 1-05 to 1-20 and the S-GW 1-30.

[0045] In Figure 1In the middle, ENBs 1-05 to 1-20 can correspond to existing Node Bs of the UMTS system. The ENB can be connected to the UE 1-35 through a radio channel, and can perform a more complex role than the existing Node B. In the LTE system, all user traffic including real-time services such as Voice over Internet Protocol (VoIP) through an Internet protocol can be serviced through a shared channel. Accordingly, a device that performs scheduling by collecting state information such as a buffer state of the UE, an available transmission power state, a channel state, etc. is necessary, and the ENB 1-05 to 1-20 can be in charge of the device. One NB generally controls multiple cells. For example, to achieve a transmission rate of 100 Mbps, the LTE system can use, for example, Orthogonal Frequency Division Multiplexing (OFDM) in a 20 MHz bandwidth as a radio access technology. In addition, an Adaptive Modulation and Coding (AMC) scheme that determines a modulation scheme and a channel coding rate based on a channel state of the UE can be applied. The S-GW 1-30 is a device that provides a data bearer, and can generate or remove a data bearer under the control of the MME 1-25. The MME is a device that is in charge of various control functions of the UE as well as a mobility management function, and can be connected to multiple base stations.

[0046] Figure 2 is a radio protocol structure diagram of the existing LTE system.

[0047] Referring to Figure 2 , the radio protocol of the LTE system can be composed of a Packet Data Convergence Protocol (PDCP) 2-05 and 2-40, a Radio Link Control (RLC) 2-10 and 2-35, and a Medium Access Control (MAC) 2-15 and 2-30 in the UE and the ENB, respectively. The PDCP is responsible for IP header compression / decompression and the like. The main functions of the PDCP can be summarized as follows.

[0048] - Header compression and decompression (only ROHC)

[0049] - User data transfer

[0050] - In-sequence delivery of upper layer PDUs at PDCP re-establishment procedure for RLC AM

[0051] - PDCP PDU routing for split bearers in DC (only RLC AM is supported): for transmission and PDCP PDU reordering for reception

[0052] - Duplicate detection of lower SDU at PDCP re-establishment procedure for RLC AM

[0053] - For RLC AM, retransmission of PDCP SDUs at handover and (for split bearers in DC) at PDCP data recovery procedure,

[0054] - Encryption and deciphering

[0055] - Timer-based SDU discard in uplink

[0056] Radio link control (RLC) 2-10 and 2-35 can perform an ARQ operation by reconfiguring a PDCP packet data unit (PDU) to an appropriate size. The main functions of the RLC are summarized as follows.

[0057] - Transfer of upper layer PDUs

[0058] - Error correction through ARQ (only for AM data transfer)

[0059] - Concatenation, segmentation, and reassembly of RLC SDUs (only for UM and AM data transfer)

[0060] - Re-segmentation of RLC data PDUs (only for AM data transfer)

[0061] - Reordering of RLC data PDUs (only for UM and AM data transfer)

[0062] - Duplicate detection (only for UM and AM data transfer)

[0063] - Protocol error detection (only for AM data transfer)

[0064] - RLC SDU discard (only for UM and AM data transfer)

[0065] - RLC re-establishment

[0066] MAC 2-15 and 2-30 can be connected to several RLC layers configured in one UE, and can perform the operation of multiplexing and demultiplexing a RLC PDU to and from a MAC PDU. The main functions of the MAC can be summarized as follows.

[0067] - Mapping between logical channels and transport channels

[0068] - Multiplexing of MAC SDUs belonging to one or different logical channels into transport blocks (TB) delivered to the physical layer on transport channels, or demultiplexing of MAC SDUs belonging to one or different logical channels from transport blocks (TB) delivered by the physical layer on transport channels

[0069] - Reporting of scheduling information

[0070] - Error correction through HARQ

[0071] - Prioritization between logical channels of one UE

[0072] - Priority handling between UEs in a dynamic scheduling manner

[0073] - MBMS service identification

[0074] - Transport format selection

[0075] - Padding

[0076] The physical layer 2-20 and 2-25 can channel-encode and modulate upper layer data, make OFDM symbols, and transmit the OFDM symbols through a radio channel, or can demodulate and channel-decode the OFDM symbols received through the radio channel and deliver them to the upper layer.

[0077] Figure 3 is a structural diagram illustrating a next-generation mobile communication system to which the present disclosure can be applied.

[0078] Referring to Figure 3 , a radio access network of a next-generation mobile communication system (hereinafter, NR or 5G) can be composed of a next-generation base station (New Radio Node-B, hereinafter, NR gNB or NR base station) 3-10 and a new radio core network (NR CN) 3-05. A new radio user equipment (NR UE or UE) 3-15 can access an external network through the NR gNB 3-10 and the NR CN 3-05.

[0079] In Figure 3In the middle, the NR gNB 3-10 can correspond to an evolved Node B (eNB) of the existing LTE system. The NR gNB can be connected to the NR UE 3-15 through a radio channel, and can provide services superior to the existing Node B. In the next generation mobile communication system, all user traffic can be serviced through a shared channel. Accordingly, a device that schedules by collecting state information such as a buffer state of the UE, an available transmission power state, a channel state, etc. is necessary, and the NR NB 3-10 can be responsible for the device. One NR gNB can control multiple cells. In the next generation mobile communication system, a bandwidth greater than or equal to the existing maximum bandwidth can be applied to implement ultra-high speed data transmission compared to the current LTE. In addition, an additional beamforming technique can be incorporated by using Orthogonal Frequency Division Multiplexing (OFDM) as a radio access technology. In addition, an Adaptive Modulation and Coding (hereinafter referred to as AMC) scheme for determining a modulation scheme and a channel coding rate according to the channel state of the UE can be applied. The NR CN 3-05 can perform functions such as mobility support, bearer configuration, QoS configuration, etc. The NR CN is a device responsible for various control functions of the UE as well as mobility management functions, and can be connected to multiple base stations. In addition, the next generation mobile communication system can be linked with the existing LTE system, and the NR CN can be connected to the MME 3-25 through a network interface. The MME can be connected to the existing base station eNB 3-30.

[0080] Figure 4 is a diagram showing a radio protocol structure of a next generation mobile communication system to which the disclosure can be applied.

[0081] Referring to Figure 4 , the radio protocol of the next generation mobile communication system is composed of NR Service Data Adaptation Protocol (SDAP) 4-01 and 4-45, NR PDCP 4-05 and 4-40, NR RLC 4-10 and 4-35, and NR MAC 4-15 and 4-30 in the UE and the NR base station, respectively.

[0082] The main functions of the NR SDAP 4-01 and 4-45 can include some of the following functions.

[0083] - Transfer of user plane data

[0084] - Mapping of QoS flows to DRBs for both DL and UL

[0085] - Marking QoS flow ID in both DL and UL data packets

[0086] - Reflective QoS flow to DRB mapping for UL SDAP PDU

[0087] With respect to the SDAP layer, the UE can be configured with a radio resource control (RRC) message indicating whether to use an SDAP layer header or the function of the SDAP layer for each PDCP layer, each bearer, or each logical channel. In the case of being configured with the SDAP header, the UE can indicate that the UE updates or reconfigures mapping information of uplink and downlink QoS flows and data bearers with a non-access stratum (NAS) quality of service (QoS) reflective configuration 1-bit indicator (NAS reflective QoS) and an access stratum (AS) QoS reflective configuration 1-bit indicator (AS reflective QoS) of the SDAP header. The SDAP header can include QoS flow ID information indicating QoS. The SDAP header can include QoS flow ID information indicating QoS. The QoS information can be used as data processing priority, scheduling information, etc., to support a smooth service.

[0088] The main functions of the NR PDCP 4-05 and 4-40 can include some of the following functions.

[0089] - header compression and decompression (only ROHC)

[0090] - user data transfer

[0091] - in-sequence delivery of upper layer PDUs

[0092] - out-of-sequence delivery of upper layer PDUs

[0093] - PDCP PDU reordering for reception

[0094] - duplicate detection of lower layer SDUs

[0095] - retransmission of PDCP SDUs

[0096] - ciphering and deciphering

[0097] - timer-based SDU discard in uplink

[0098] In the above description, the reordering function of the NR PDCP can refer to a function of reordering PDCP PDUs received from a lower layer based on a PDCP sequence number (SN). The reordering function of the NR PDCP can include a function of transmitting data to an upper layer in a reordered order or a function of directly transmitting data without considering the order, a function of recording a missing PDCP PDU by reordering the order, a function of reporting a status of the missing PDCP PDU to a transmission side, and a function of requesting retransmission of the missing PDCP PDU.

[0099] The main functions of the NR RLC 4-10 and 4-35 can include some of the following functions.

[0100] - Transfer of upper layer PDUs

[0101] - In-sequence delivery of upper layer PDUs

[0102] - Out-of-sequence delivery of upper layer PDUs

[0103] - Error correction by ARQ

[0104] - Concatenation, segmentation, and reassembly of RLC SDUs

[0105] - Re-segmentation of RLC data PDUs

[0106] - Reordering of RLC data PDUs

[0107] - Duplicate detection

[0108] - Protocol error detection

[0109] - RLC SDU discard

[0110] - RLC re-establishment

[0111] In the above description, the in-sequence delivery of the NR RLC can refer to a function of delivering RLC SDUs received from a lower layer to an upper layer in sequence. In a case in which one RLC SDU is initially divided into several RLC SDUs and is received, the in-sequence delivery of the NR RLC can include a function of reassembling and delivering the divided RLC SDUs.

[0112] The in-sequence delivery of the NR RLC can include a function of rearranging received RLC PDUs based on an RLC sequence number (SN) or a PDCP sequence number (SN), a function of reordering and recording missing RLC PDUs, a function of reporting a status of the missing RLC PDUs to a transmitting side, and a function of requesting retransmission of the missing RLC PDUs.

[0113] The in-sequence delivery of the NR RLC can include a function of delivering only RLC SDUs before a missing RLC SDU to an upper layer when the missing RLC SDU exists.

[0114] The in-sequence delivery of the NR RLC can include a function of delivering all RLC SDUs received before a timer is started to an upper layer even if a missing RLC SDU exists if a predetermined timer has expired.

[0115] The in-sequence delivery of the NR RLC can include a function of delivering all RLC SDUs received up to now to an upper layer even if a missing RLC SDU exists if a predetermined timer has expired.

[0116] The NR RLC can process the RLC PDU in the order of reception and the sequence number of the out-of-order, and deliver the processed RLC PDU to the NR PDCP.

[0117] In the case of the reception of segments by the NR RLC, segments stored in the buffer or to be received later can be received, reconfigured into one complete RLC PDU, and delivered to the NR PDCP.

[0118] The NR RLC layer can not include a concatenation function, and the function can be performed by the NR MAC layer or replaced by a multiplexing function of the NR MAC layer.

[0119] In the above description, the out-of-order delivery of the NR RLC device can refer to a function of directly delivering an RLC SDU received from a lower layer to an upper layer without considering the order. The out-of-order delivery of the NR RLC device can include a function of reassembling and delivering in the case where one RLC SDU is initially divided into several RLC SDUs and received. The out-of-order delivery of the NR RLC device can include a function of storing the RLC SN or the PDCP SN of the received RLC PDU, arranging the order, and recording a missing RLC PDU.

[0120] The NR MACs 4-15 and 4-30 can be connected to several NR RLC layers configured in one UE, and the main functions of the NR MAC can include some of the following functions.

[0121] - Mapping between a logical channel and a transport channel

[0122] - Multiplexing / demultiplexing of MAC SDUs

[0123] - Scheduling information reporting

[0124] - Error correction through HARQ

[0125] - Priority handling between logical channels of one UE

[0126] - Priority handling between UEs in a manner of dynamic scheduling

[0127] - MBMS service identification

[0128] - Transport format selection

[0129] - Padding

[0130] The NR PHY layers 4-20 and 4-25 can channel-encode and modulate upper layer data, make OFDM symbols, and transmit the OFDM symbols through a radio channel, or can demodulate and channel-decode OFDM symbols received through a radio channel and transmit the same to an upper layer.

[0131] Figure 5 FIG. 1 is a diagram illustrating a UE device according to an embodiment of the disclosure.

[0132] Referring to the diagram, the UE can include a radio frequency (RF) processor 5-10, a baseband processor 5-20, a storage 5-30, and a controller 5-40.

[0133] The RF processor 5-10 can perform a function for transmitting and receiving a signal through a radio channel, such as band conversion and amplification of a signal. For example, the RF processor 5-10 can up-convert a baseband signal provided from the baseband processor 5-20 to an RF band signal, transmit the RF band signal through an antenna, and down-convert an RF band signal received through the antenna to a baseband signal. For example, the RF processor 5-10 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. Only one antenna is illustrated in the diagram, but the UE can include a plurality of antennas. Also, the RF processor 5-10 can include a plurality of RF chains. Also, the RF processor 5-10 can perform beamforming. For beamforming, the RF processor 5-10 can adjust a phase and a magnitude of each signal transmitted and received through a plurality of antennas or antenna elements. Also, the RF processor can perform MIMO, and can receive a plurality of layers when performing a MIMO operation.

[0134] The baseband processor 5-20 can perform a function of converting between a baseband signal and a bit stream according to a physical layer standard of a system. For example, when transmitting data, the baseband processor 5-20 can generate a complex symbol by encoding and modulating a transmitted bit stream. Also, when receiving data, the baseband processor 5-20 can recover a received bit stream by demodulating and decoding a baseband signal provided from the RF processor 5-10. For example, in the case of following an orthogonal frequency division multiplexing (OFDM) scheme, when transmitting data, the baseband processor 5-20 can generate a complex symbol by encoding and modulating a transmitted bit stream, map the complex symbol to a subcarrier, and then configure an OFDM symbol through an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion. Also, when receiving data, the baseband processor 5-20 can divide a baseband signal provided from the RF processor 5-10 into an OFDM symbol unit, recover a signal mapped to a subcarrier through a fast Fourier transform (FFT) operation, and then recover a received bit stream through demodulation and decoding.

[0135] The baseband processor 5-20 and the RF processor 5-10 transmit and receive signals as described above. Accordingly, the baseband processor 5-20 and the RF processor 5-10 can be referred to as a transmitter, a receiver, a transceiver, or a communicator. Also, at least one of the baseband processor 5-20 and the RF processor 5-10 can include a plurality of communication modules to support a plurality of different radio access technologies. Also, at least one of the baseband processor 5-20 and the RF processor 5-10 can include different communication modules to process signals of different frequency bands. For example, the different radio access technologies can include wireless LAN (e.g., IEEE 802.11), cellular network (e.g., LTE), etc. Also, the different frequency bands can include super high frequency (SHF) (e.g., 2.5 GHz, 5 GHz) bands and millimeter wave (e.g., 60 GHz) bands.

[0136] The storage 5-30 can store data. Such as a basic program, an application program, and configuration information for UE operation. In particular, the storage 5-30 can store information related to a second access node that performs wireless communication by using a second radio access technology. Also, the storage 5-30 can provide the stored data according to a request of the controller 5-40.

[0137] The controller 5-40 can control the overall operation of the UE. For example, the controller 5-40 can transmit and receive signals through the baseband processor 5-20 and the RF processor 5-10. Also, the control unit 5-40 can write data in the storage 5-30 and read data. To this end, the controller 5-40 can include at least one processor. For example, the controller 5-40 can include a communication processor (CP) that controls communication and an application processor (AP) that controls an upper layer such as an application program.

[0138] Figure 6 FIG. 6 is a diagram illustrating a base station apparatus according to an embodiment of the disclosure.

[0139] As illustrated, the base station can be configured to include an RF processor 6-10, a baseband processor 6-20, a backhaul communicator 6-30, a storage 6-40, and a controller 6-50.

[0140] The RF processor 6-10 can perform functions for transmitting and receiving signals through a radio channel, for example, band conversion and amplification of a signal. For example, the RF processor 6-10 can up-convert a baseband signal provided from the baseband processor 6-20 into an RF band signal, transmit the RF band signal through an antenna, and down-convert an RF band signal received through the antenna into a baseband signal. For example, the RF processor 6-10 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is illustrated in the drawing, the first access node can include a plurality of antennas. Also, the RF processor 6-10 can include a plurality of RF chains. Also, the RF processor 6-10 can perform beamforming. For beamforming, the RF processor 6-10 can adjust a phase and a magnitude of each signal transmitted and received through a plurality of antennas or antenna elements. The RF processor can perform a downlink MIMO operation by transmitting one or more layers.

[0141] The baseband processor 6-20 can perform a function of converting between a baseband signal and a bit stream according to a physical layer standard of a first radio access technology. For example, when transmitting data, the baseband processor 6-20 can generate complex symbols by encoding and modulating a transmitted bit stream. Also, when receiving data, the baseband processor 6-20 can recover a received bit stream by demodulating and decoding a baseband signal provided from the RF processor 6-10. For example, in the case of following an OFDM scheme, when transmitting data, the baseband processor 6-20 can generate complex symbols by encoding and modulating a transmitted bit stream, map the complex symbols to subcarriers, and then configure OFDM symbols through an IFFT operation and CP insertion. Also, when receiving data, the baseband processor 6-20 can divide a baseband signal provided from the RF processor 6-10 into OFDM symbol units, recover signals mapped to subcarriers through an FFT operation, and then recover a received bit stream through demodulation and decoding. The baseband processor 6-20 and the RF processor 6-10 transmit and receive signals as described above. Accordingly, the baseband processor 6-20 and the RF processor unit 6-10 can be referred to as a transmitter, a receiver, a transceiver, a communicator, or a wireless communicator.

[0142] The backhaul communicator 6-30 can provide an interface for communicating with other nodes in a network. For example, the backhaul communicator 6-30 can convert a bit stream transmitted from a master base station to another node, for example, an auxiliary base station, a core network, etc., into a physical signal, and can convert a physical signal received from another node into a bit stream.

[0143] The storage 6-40 can store data such as a basic program, an application program, and configuration information for the main base station operation. In particular, the storage 6-40 can store information on a bearer allocated to an access UE, a measurement result reported from the access UE, and the like. Further, the storage 6-40 can store information serving as a criterion for determining whether to provide or stop a plurality of connections with the UE. Further, the storage 6-40 can provide the stored data according to a request of the controller 6-50.

[0144] The controller 6-50 can control the overall operation of the main base station. For example, the controller 6-50 can transmit and receive a signal through the baseband processor 6-20 and the RF processor 6-10 or through the backhaul communicator 6-30. Further, the control unit 6-50 can write data in the storage 6-40 and read the data. To this end, the controller 6-50 can include at least one processor.

[0145] Figure 7 is a diagram illustrating a case of a master cell group failure (MCG failure) detected through RLF in a standalone (SA) case.

[0146] In Figure 7 , it can be assumed that the IAB nodes 1 and 2 are connected to a CU of a donor node through a relay link. Hereinafter, "IAB node" or "node" will be used interchangeably.

[0147] The IAB node 3 can have the node 1 as a parent node of an MCG link and the node 2 as a parent node of a secondary cell group (SCG) link. The figure illustrates an operation of handling RLF in a case where a mobile termination (MT) of the node 3 detects RLF of the MCG link. The RLF case of the MCG link can include at least one of a case where a T310 timer expires in the MT, a case where maximum retransmission performed by an RLC layer is indicated, and a case where a random access problem is indicated in a MAC. When the MT detects RLF in the MCG link, the MT of the IAB node 3 can perform at least one of the following operations.

[0148] - suspending transmission to a master cell group (MCG). In this case, the object of the suspended transmission can be all signaling radio bearers (SRBs), data radio bearers (DRBs), and backhaul RLC channels / egress backhaul RLC channels.

[0149] - resetting the MCG MAC. If there is an RLC SDU or PDU that has failed to be transmitted, it can be retransmitted to the SCG RLC stack without MAC reset.

[0150] - update routing entries of the IAB node. In this case, a specific operation can remove a routing entry with a failed MCG link as an egress link in a backhaul adaptation protocol (BAP) entity and replace the failed MCG with an SCG link when the SCG is configured.

[0151] - The MCGFailureInformation message can be transmitted to the donor CU by the parent node using SRB 3 or split SRB1. In this case, one of a T310 timer expiration, an RLC maximum retransmission arrival, and a random access channel (RACH) problem occurrence can be set as a cause value. In addition, the corresponding message can include a measurement result value of a serving cell and a measurement result of a neighbor cell existing at a frequency corresponding to a measurement object configured in the MCG. Also, a measurement result of a serving cell and a measurement result of a neighbor cell existing at a frequency corresponding to a measurement object configured in the SCG can also be included. In addition, routing information used by the BAP layer at the time of failure can also be included. The routing information can include an egress link and a next hop ID mapped to each routing ID, and can also include BH RLC channel mapping information used in this case.

[0152] - When transmitting the message, if PDCP duplication is configured, the MT does not change the primary path, and transmits the message through split SRB1. If not, the primary path is changed. If the MT transmits the message through SRB3, the MT can directly transmit the message through SRB3 without encapsulating the message in an ULInformationTransfer-MRDC message. In this regard, a master node (MN) can deliver an RRCReconfiguration or RRCrelease message through the received SRB. Similarly, when received through SRB3, the RRC message can be directly transmitted without separately using a message such as a DLInformationTransfer-MRDC message that encapsulates a message for MRDC. Upon receiving this message, the MT applies the corresponding RRC message.

[0153] - In another embodiment, after the MT delivers the message to the network, in addition to the RRC message (e.g., RRCReconfiguration / RRCrelease) to be applied to the MT, the network can include a message that sends a message to the MT part of the parent node corresponding to the failed MCG link. This message can also be an RRC reconfiguration or RRC release message. Upon receiving this message (e.g., a set of RRC messages to be applied to the MT and an RRC message to be applied to the parent node of the MCG) from the network, the MT can separate the message to be applied to the parent node corresponding to the MCG link and deliver the message before applying the RRC message required for the MT. In this case, a control packet of the BAP layer can be used, or an uplink dedicated control channel (UL-DCCH) can be used. After delivering the message, the MT can apply the RRC message to be applied to itself. The MCG parent node can receive the message necessary for itself from the MT of the child node, and then apply the MT of the node.

[0154] - Send the message described above and start a timer. If the MT receives an RRC message until the timer expires, the MT can perform RRC reestablishment.

[0155] According to one embodiment, the IAB node 3 700 can perform RLF detection of the IAB node 1 710 (S700). The IAB node 3 700 can perform a MCGFailureInformation procedure (S705). The MCGFailureInformation procedure can include at least one of the following operations.

[0156] - TX suspension on MCG (egress BH RLC channels, SRBs and DRBs)

[0157] - Reset MCG MAC

[0158] - Routing entry update

[0159] - Transmission of MCGFailureInformation (Cause: Legacy RLF)

[0160] - Start T316 if configured and not running before

[0161] The IAB node 3 700 can transmit the MCGFailureInformation message to the IAB node 2 720 over split SRB1 or SRB3 (without encapsulation) (S710). The IAB node 2 720 can transmit the MCGFailureInformation message to the donor CU 730 over BH traffic (S715). The donor CU 730 can identify that the node 3 700 cannot reach the node 1 710 (S720). For example, the donor CU 730 can identify that the radio link between the node 3 700 and the node 1 710 is disconnected. The donor CU 730 can transmit an RRC message corresponding to the MCGFailureInformation to the IAB node 2 720 over BH traffic (S725). The IAB node 2 720 can transmit the RRCReconfiguration / RRCRelease to the IAB node 3 700 over split SRB1 or SRB3 (without encapsulation) (S730).

[0162] The RRCReconfiguration message transmitted in step S730 can include information for recovery in case of IAB link failure. For example, the RRCReconfiguration message can include an IP address to be used in the DU part of the corresponding IAB node after connection recovery. Further, the RRCRelease message can include a PCI (Physical Cell ID) to be used for cell measurement and cell selection in IDLE mode included in the IAB node. In case that the IAB node 3 700 receives the IP address in the RRCReconfiguration message, the received IAB node 3 700 can use the corresponding IP address as an IP layer destination address of the DU without an additional IP address request operation after connection. By this, the IAB node 3 700 can exchange control signals and user plane signals of F1 in the IP layer with the CU and the DU of the donor node. In case that the IAB node 3 700 receives the PCI to be used for cell selection in the RRCRelease message, the received IAB node 3 700 can consider only the corresponding cell as a selectable cell or an appropriate cell as a condition when selecting a cell in IDLE mode.

[0163] Figure 8 is a diagram illustrating a case of MCG failure through RLF notification in the SA case.

[0164] In Figure 8 , it can be assumed that the IAB nodes 1 and 2 are connected to the CU of the donor node through a relay link.

[0165] The IAB node 3 has node 1 as a parent node of MCG link and node 2 as a parent node of SCG link. Node 3 has node 5 as a child node and can serve the MCG link. Node 4 can serve the SCG link of node 5. In case the mobile termination (MT) of node 3 detects RLF of the MCG link, node 3 can perform RRC connection reestablishment operation. When this reestablishment fails, node 3 can deliver RLF recovery failure notification to the child node. The MT of the child node that has received the notification can consider that RLF has occurred in the received link. In Figure 8 case the node 3 is the MN in node 5 as a child node, the MT of node 5 can consider that RLF has occurred in the MCG link.

[0166] For example, when the IAB node receives the RLF recovery failure notification of its parent node, it can consider that RLF has occurred in the corresponding link. Thus, when the notification is received from the MCG, the MCG failure information operation can be performed, and when the notification is received from the SCG, the SCG failure information operation can be performed. The MCG failure information can perform at least one of the following operations.

[0167] - suspending transmission to the MCG. In this case, the object of suspending transmission can be all SRBs, DRBs, and backhaul RLC channels / egress backhaul RLC channels.

[0168] - resetting the MCG MAC. If there is an RLC SDU or PDU that has been transmitted with failure, it can be transmitted again to the SCG RLC stack without MAC reset.

[0169] - updating the routing entry of the IAB node. In this case, a specific operation can remove the routing entry with the failed MCG link as an egress link in the BAP entity and replace the failed MCG with the SCG link when the SCG is configured.

[0170] - The MCGFailurelnformation message can be transmitted to the parent node on the SCG side through SRB 3 or split SRB1. In this case, the cause value can be set to a value indicating a state in which the parent node that has transmitted the notification, for example, the MN has lost its connection with its parent node or network. Unlike the general RLF report, the corresponding message can not include the measurement result values of the serving cells and the neighboring cells present at the frequencies corresponding to the measurement objects configured in the MCG. In addition, the measurement results of the serving cells and the neighboring cells present at the frequencies corresponding to the measurement objects configured in the SCG can not be included. The routing information used by the BAP layer at the time of failure can also be included. In this case, the routing information can include the egress link and the next hop ID mapped to each routing ID, and can also include the BH RLC channel mapping information used in this case.

[0171] - When transmitting the message, if PDCP duplication is configured, the MT does not change the primary path, and transmits the message through split SRB1. If not, the primary path is changed. If the MT transmits the message through SRB3, the MT can directly transmit the message through SRB3 without encapsulating the message in the ULInformationTransfer-MRDC message. In this regard, the master node (MN) can deliver the RRCReconfiguration or RRCrelease message through the received SRB. Similarly, when received through SRB3, the RRC message can be directly transmitted without separately using a message encapsulating the message for MRDC, such as DLInformationTransfer-MRDC. Upon receiving this message, the MT applies the corresponding RRC message

[0172] - In another embodiment, after the MT delivers the message to the network, in addition to the RRC message to be applied to the MT (e.g., RRCReconfiguration / RRCrelease), the network can include a message that sends a message to the MT part of the parent node corresponding to the failed MCG link. This message can also be an RRC reconfiguration or RRC release message. Upon receiving this message (e.g., a set of RRC messages to be applied to the MT and an RRC message to be applied to the parent node of the MCG) from the network, the MT can separate the message to be applied to the parent node corresponding to the MCG link and deliver it before applying the RRC message required for the MT. In this case, a control packet of the BAP layer can be used, or an uplink dedicated control channel (UL-DCCH) can be used. After delivering this message, the MT can apply the RRC message to be applied to itself. The MCG parent node can receive the message necessary for itself from the MT of the child node and then apply the MT of the node.

[0173] - Send the message described above and start a timer. If the MT receives an RRC message until the timer expires, the MT can perform RRC reestablishment.

[0174] According to one embodiment, if the IAB node 3 810 RRC reestablishment fails, the IAB node 5 800 can receive an RLF recovery failure indication from the IAB node 3 810 (S800). The IAB node 5 800 can perform a MCGFailureInformation procedure (S805). The MCGFailureInformation procedure can include at least one of the following operations.

[0175] - TX suspension on MCG (egress BH RLC channels, SRBs and DRBs)

[0176] - Reset MCG MAC

[0177] - Routing entry update

[0178] - Transmission of MCGFailureInformation (cause: failure_on_parent)

[0179] - Start T316 if configured and not running before

[0180] In case of RRC reestablishment failure, after transmitting the RLF recovery failure indication, the IAB node 3 810 can be turned off in case of DU and can be switched to IDLE mode in case of MT (S810). The turning off can mean stopping all signal transmission and stopping UL / DL transmission and reception. The IAB node 5 800 can transmit the MCGFailureInformation message to the IAB node 4 820 through split SRB1 or SRB3 (without encapsulation) (S815). The IAB node 4 820 can transmit the BH traffic including the MCGFailureInformation message to the donor CU 830 (S820). The donor CU 830 can identify that the node 3 810 cannot reach the node 1 and the node 2, and can identify that the link between the node 3 and the CU is disconnected (S825). The donor CU 830 can transmit the BH traffic to the IAB node 4 820 (S830). The IAB node 4 820 can transmit the RRCReconfiguration / RRCRelease message to the IAB node 5 800 through split SRB1 or SRB3 (without encapsulation) (S835).

[0181] The RRCReconfiguration message transmitted in step S835 can include information for recovery in case of IAB link failure. For example, the RRCReconfiguration message can include an IP address to be used in the DU part of the corresponding IAB node after connection recovery. In addition, the RRCRelease message can include a PCI (Physical Cell ID) to be used for cell measurement and cell selection in IDLE mode included in the IAB node. In case that the IAB node 5 800 receives the IP address in the RRCReconfiguration message, the received IAB node 5 800 can use the corresponding IP address as an IP layer destination address of the DU without an additional IP address request operation after recovery of the connection. Through this, the IAB node 5 800 can exchange control signals and user plane signals of F1 in the IP layer with the CU and the DU of the donor node. In case that the IAB node 5 800 receives the PCI to be used for cell selection in the RRCRelease message, the received IAB node 5 800 can consider only the corresponding cell as a selectable cell or an appropriate cell as a condition when selecting a cell in IDLE mode.

[0182] Figure 9 is a diagram illustrating a case of SCG failure through RLF detection in the SA case.

[0183] In Figure 9 , it can be assumed that the IAB nodes 1 and 2 are connected to the CU of the donor node through a relay link.

[0184] IAB node 3 has node 1 as a parent node of MCG link and node 2 as a parent node of SCG link. Node 3 has node 5 as a child node and can serve MCG link. Node 4 can serve SCG link of node 5. In case that a mobile termination (MT) of node 3 detects RLF of SCG link, node 3 can perform SCG failure information operation. The SCG failure information can perform at least one of the following operations.

[0185] - suspending transmission to SCG. In this case, the object of suspending transmission can be all SRB, DRB, and backhaul RLC channel / egress backhaul RLC channel.

[0186] - resetting SCG MAC. If there is an RLC SDU or PDU that has been transmitted with failure, it can be retransmitted to MCG RLC stack without MAC reset.

[0187] - updating routing entry of IAB node. In this case, a specific operation can remove a routing entry with failed SCG link as an egress link in BAP entity and replace the failed SCG with MCG link.

[0188] - SCGFailureInformation message can be transmitted to donor CU through parent node through SRB1. In this case, the cause value can be a cause value of general RLF such as T310 timer expiration, RLC maximum retransmission number reaching, RACH problem occurring, etc. The corresponding message can include measurement result values of serving cells and measurement results of neighboring cells existing at frequencies corresponding to measurement objects configured in SCG, and measurement results of serving cells and measurement results of neighboring cells existing at frequencies corresponding to measurement objects configured in MCG. Routing information used by BAP layer at the time of failure can also be included. In this case, the routing information can include egress link and next hop ID mapped to each routing ID, and can also include BH RLC channel mapping information used in this case.

[0189] According to one embodiment, IAB node 3 900 can perform RLF detection of IAB node 2 910 (S900). IAB node 3 900 can perform SCGFailureInformation procedure (S905). The SCGFailureInformation procedure can include at least one of the following operations.

[0190] - TX suspension on SCG (egress BH RLC channel, SRB, and DRB)

[0191] - Resetting SCG MAC

[0192] - Routing entry update

[0193] - Transmission of SCGFailureInformation (Cause: Legacy RLF)

[0194] The IAB node 3 900 can transmit the SCGFailureInformation message to the IAB node 1 915 through SRB1 (S910). The IAB node 1 915 can transmit BH traffic to the donor CU 920 (S915). The donor CU 920 can transmit BH traffic to the IAB node 1 915 (S920). The IAB node 1 915 can transmit the RRCReconfiguration message to the IAB node 3 900 through SRB1 (S925).

[0195] The RRCReconfiguration message transmitted in step S925 can include information for recovery in the case of IAB link failure. For example, the RRCReconfiguration message can include an IP address to be used in the DU part of the corresponding IAB node after connection recovery. In the case where the IAB node 3 900 receives the IP address in the RRCReconfiguration message, the received IAB node 3 900 can use the corresponding IP address as an IP layer destination address of the DU without an additional IP address request operation after recovery of the connection. Through this, the IAB node 3 900 can exchange control signals and user plane signals of F1 in the IP layer with the CU and the DU of the donor node.

[0196] Figure 10 is a diagram illustrating a case of SCG failure notification through RLF in the SA case.

[0197] In Figure 10 , it can be assumed that the IAB nodes 1 and 2 are connected to the CU of the donor node through a relay link.

[0198] The IAB node 4 has the node 1 as a parent node of an MCG link and the node 2 as a parent node of an SCG link. The node 4 has the node 5 as a child node and can serve the SCG link. The node 3 can serve the MCG link of the node 5. When the node 4 fails in reestablishment, an RLF recovery failure notification can be delivered to the child node. The MT of the child node that has received the notification can consider that RLF has occurred in the received link. When the node 5 receives the RLF recovery failure notification from the node 4 of the SCG link, the node 5 can perform an SCG failure information operation. The SCG failure information can perform at least one of the following operations.

[0199] - suspending transmission to SCG. In this case, the object of suspending transmission can be all SRBs, DRBs and backhaul RLC channels / egress backhaul RLC channels.

[0200] - resetting SCG MAC. If there are RLC SDUs or PDUs that have failed to be transmitted, they can be retransmitted to MCG RLC stack without MAC reset.

[0201] - updating routing entries of IAB node. In this case, a specific operation can remove the routing entry with failed SCG link as egress link in BAP entity and replace the failed SCG with MCG link.

[0202] - SCGFailureInformation message can be sent to the parent node of MCG link through SRB1. In this case, the cause value can be set to a value indicating the state in which the parent node that has sent the notification, e.g., SN, has lost its connection with its parent node or network. The corresponding message can not include measurement result values of serving cells and neighboring cells existing at frequencies corresponding to measurement objects configured in the SCG, as well as measurement results of serving cells and neighboring cells existing at frequencies corresponding to measurement objects configured in the MCG. Instead, routing information used by the BAP layer at the time of failure can be included. In this case, the routing information can include egress links and next hop IDs mapped to each routing ID, and can further include BH RLC channel mapping information used in this case.

[0203] According to one embodiment, the IAB node 5 1000 can receive an RLF recovery failure indication from the IAB node 4 1010 (S1000). The IAB node 5 1000 can perform an SCGFailureInformation procedure (S1005). The SCGFailureInformation procedure can include at least one of the following operations.

[0204] - TX suspension on SCG (egress BH RLC channels, SRBs and DRBs)

[0205] - resetting SCG MAC

[0206] - routing entry update

[0207] - transmission of SCGFailureInformation (cause: failure_on_parent)

[0208] The IAB node 5 1000 can transmit the SCGFailurelnformation message to the IAB node 3 1020 through SRB1 (S1010). The IAB node 3 1020 can transmit BH traffic to the donor CU 1030 (S1015). The donor CU 1030 can transmit BH traffic to the IAB node 3 1020 (S1020). The IAB node 3 1020 can transmit the RRCReconfiguration message to the IAB node 5 1000 through SRB1 (S1025).

[0209] The RRCReconfiguration message transmitted in step S1025 can include information for recovery in the case of IAB link failure. For example, the RRCReconfiguration message can include an IP address to be used in the DU part of the corresponding IAB node after connection recovery. In the case where the IAB node 5 1000 receives the IP address in the RRCReconfiguration message, the received IAB node 5 1000 can use the corresponding IP address as an IP layer destination address of the DU without an additional IP address request operation after connection recovery. Through this, the IAB node 5 1000 can exchange control signals and user plane signals of F1 in the IP layer with the CU and the DU of the donor node.

[0210] Figure 11 is a diagram illustrating a case where SCG failure is put by RLF detection in a non-standalone (NSA) case.

[0211] In Figure 11 , the IAB nodes 1 and 2 are an ENDC case in which the MN is connected to the MCG link as an eNB using LTE RAT and the SN is connected to the SCG link as a donor gNB using NR RAT. In this case, when RLF is detected in the SCG link, the MT of the IAB node can perform the SCG failure information operation.

[0212] The SCG failure information can perform at least one of the following operations.

[0213] - suspending transmission to the SCG. In this case, the object of the suspended transmission can be all SRBs, DRBs, and backhaul RLC channels / egress backhaul RLC channels.

[0214] - resetting the SCG MAC. If there is an RLC SDU or PDU that has been transmitted with failure, it can be transmitted again to the MCG RLC stack without performing MAC reset.

[0215] - update routing entries of the IAB node. In this case, the specific operation can remove the routing entry with the failed SCG link as an egress link in the BAP entity and replace the failed SCG with the MCG link.

[0216] - The SCGFailureInformation message can be sent to the parent node of the MCG link through SRB1. In this case, the cause value can be a general RLF detection occurrence factor such as expiration of the T310 timer, reaching of the RLC maximum retransmission number, occurrence of the RACH problem, etc. The corresponding message can include measurement result values of serving cells and adjacent cells existing at frequencies corresponding to measurement objects configured in the SCG and measurement results of serving cells and adjacent cells existing at frequencies corresponding to measurement objects configured in the MCG. Routing information used by the BAP layer at the time of failure can be included. In this case, the routing information can include an egress link and a next hop ID mapped to each routing ID, and can further include BH RLC channel mapping information used in this case.

[0217] According to one embodiment, the IAB node 1 1100 can perform RLF detection of the donor CU 1110 (S1100). The IAB node 1 1100 can perform an SCGFailureInformation procedure (S1105). The SCGFailureInformation procedure can include at least one of the following operations.

[0218] - TX suspension on SCG (egress BH RLC channel, SRB, and DRB)

[0219] - Reset SCG MAC

[0220] - Routing entry update

[0221] - Transmission of SCGFailureInformation (cause: legacy RLF)

[0222] The IAB node 1 1100 can transmit an SCGFailureInformation message to the eNB 1120 through SRB1 (S1110). The eNB 1120 can transmit BH traffic to the donor gNB CU 1130 (S1115). The donor gNB CU 1130 can transmit BH traffic to the eNB 1120 (S1120). The eNB 1120 can transmit an RRCReconfiguration message to the IAB node 1 1100 through SRB1 (S1125).

[0223] The RRCReconfiguration message transmitted in step S1125 can include information for recovery in case of IAB link failure. For example, the RRCReconfiguration message can include an IP address to be used in the DU part of the corresponding IAB node after connection recovery. In case the IAB node 1 1100 receives the IP address in the RRCReconfiguration message, the received IAB node 1 1100 can use the corresponding IP address as an IP layer destination address of the DU without an additional IP address request operation after recovery of the connection. Through this, the IAB node 1 1100 can exchange control signals and user plane signals of F1 in the IP layer with the CU and the DU of the donor node.

[0224] Figure 12A is a diagram illustrating a case of SCG failure notification by RLF in an NSA case.

[0225] In Figure 12A , the IAB nodes 1 and 2 are an ENDC case in which the MN is connected to the MCG link as an eNB using LTE RAT and the SN is connected to the SCG link as a donor gNB using NR RAT. In this case, when the MCG link detects RLF or MCG failure recovery fails, RRC connection reestablishment can be performed, and if this reestablishment fails, the IAB node can deliver RLF recovery failure notification to the child node. The child node receiving this notification can perform an SCG failure information operation in the MT.

[0226] The SCG failure information can perform at least one of the following operations.

[0227] - suspending transmission to the SCG. In this case, the object of the suspended transmission can be all SRBs, DRBs, and backhaul RLC channels / egress backhaul RLC channels.

[0228] - resetting the SCG MAC. If there are RLC SDUs or PDUs that have been transmitted with failure, they can be transmitted again to the MCG RLC stack without MAC reset.

[0229] - updating the routing entry of the IAB node. In this case, a specific operation can remove the routing entry with the failed SCG link as an egress link in the BAP entity and replace the failed SCG with the MCG link.

[0230] - The SCGFailurelnformation message can be transmitted to the parent node of the MCG link over SRB1. In this case, the cause value can be set to a value indicating a state in which the notifying parent node, e.g., SN, has lost its connection with its parent node or network. The corresponding message can not include measurement result values of serving cells and neighboring cells existing at frequencies corresponding to measurement objects configured in the SCG, as well as measurement results of serving cells and neighboring cells existing at frequencies corresponding to measurement objects configured in the MCG. Routing information used by the BAP layer at the time of failure can be included. In this case, the routing information can include an egress link and a next hop ID mapped to each routing ID, and can further include BH RLC channel mapping information used in this case.

[0231] According to one embodiment, an RRE failure can occur in the node1 1210 (S1200). The node1 1210 can transmit an RLF recovery failure indication to the IAB node2 1200 (S1205). The IAB node2 1200 can perform an SCGFailurelnformation procedure (S1210). The SCGFailurelnformation procedure can include at least one of the following operations.

[0232] - TX suspension on SCG (Egress BH RLC channel, SRB and DRB)

[0233] - Reset SCG MAC

[0234] - Release entry update

[0235] - Transmission of SCGFailurelnformation (Cause: failure_on_parent)

[0236] The IAB node2 1200 can transmit an SCGFailurelnformation message to the eNB 1220 over SRB1 (S1215). The eNB 1220 can transmit BH traffic to the donor CU 1230 (S1220). The donor CU 1230 can transmit BH traffic to the eNB 1220 (S1225). The eNB 1220 can transmit an RRCReconfiguration message to the IAB node2 1200 over SRB1 (S1230).

[0237] The RRCReconfiguration message transmitted in step S1230 can include information for recovery in case of IAB link failure. For example, the RRCReconfiguration message can include an IP address to be used in the DU part of the corresponding IAB node after connection recovery. In case the IAB node 2 1200 receives the IP address in the RRCReconfiguration message, the received IAB node 2 1200 can use the corresponding IP address as an IP layer destination address of the DU without an additional IP address request operation after recovery of the connection. Through this, the IAB node 2 1200 can exchange control signals and user plane signals of F1 in the IP layer with the CU and the DU of the donor node.

[0238] In another embodiment, after the IAB node transmits the SCGFailureInformation to the MN, a separate timer can be operated. If the MT does not receive the NR RRC message during the timer operation, the IAB node can perform an RRC reestablishment operation.

[0239] Figure 12B is a diagram illustrating a case in which an RLF recovery failure notification due to SCG release is transmitted.

[0240] Since the MT transmits the SCGFailureInformation to the MN and requests the SCG release from the donor gNB, when the MN requests the NR SCG release, the MT that has received the message can deliver the RLF recovery failure notification to the child node before releasing the SCG. The child node that has received the notification can perform the SCG failure information operation again. In this case, the cause value can also be a value due to the absence of network connection of the parent node corresponding to the SN. The SCG failure information can include cell measurement values of the MO configured in the SN and cell measurement values of the MO configured in the MN, which are measured by the MT. In this case, as another embodiment, upon receipt of the RLF recovery failure notification, the IAB node can perform an operation of switching to a previously defined target cell. Before performing the switching, the gNB CU can signal a specific target cell candidate group to the IAB node through RRCReconfiguration. The signal can include a condition for performing switching to the corresponding candidate target cell and configuration information to be used in the corresponding target cell.

[0241] According to one embodiment, there can be an RRE failure in the node 1 1210 (S1235). The node 1 1210 can send an RLF recovery failure indication to the IAB node 2 1200 (S1240). The IAB node 2 1200 can perform the SCGFailureInformation procedure (S1245). The SCGFailureInformation procedure can include at least one of the following operations.

[0242] - TX suspension on SCG (outgoing BH RLC channels, SRBs and DRBs)

[0243] - Resetting SCG MAC

[0244] - Releasing BAP entity

[0245] - Transmission of SCGFailureInformation (cause: failure_on_parent)

[0246] The IAB node 2 1200 can send the SCGFailureInformation message to the eNB 1220 over SRB1 (S1250). The eNB 1220 can send the BH traffic to the donor CU 1230 (S1255). It can be the no alternative way found case in the donor CU 1230 (S1260). The donor CU 1230 can send the BH traffic to the eNB 1220 (S1265). The eNB 1220 can send the SCG release message to the IAB node 2 1200 over SRB1 (S1270). The IAB node 2 1200 can send an RLF recovery failure indication to the IAB node 3 1240 (S1275). The IAB node 2 1200 can perform the RRC release (S1280). The IAB node 3 1240 can perform the SCGFailureInformation procedure (S1285). For example, it can be the SCGFailureInformation (cause: failure_on_parent).

[0247] Figure 13A is a flowchart illustrating a cell selection operation for a mobile terminal (MT) to access an IAB node included in the same donor gNB during connection reestablishment.

[0248] Once an IAB node performs a re-estimation for some reason, it can be necessary to first perform a cell selection procedure. Upon selecting a cell, cell information belonging to the corresponding IAB node is delivered to the IAB MT to select an IAB node connected to the same donor gNB or CU as the donor gNB or CU accessed in the previous connection state.

[0249] Specifically, the information delivered can be a gNB ID, a donor CU ID of a donor gNB, list information of a physical cell ID (PCI), or a cell global ID (CGI) of a cell currently connected to a corresponding gNB and CU.

[0250] The delivery method can vary depending on the information delivered. As one delivery method, when configured as an IAB MT in an IAB network, at initial access, the gNB ID of a corresponding donor gNB, CU ID, or PCI or CGI information of a cell currently connected to the CU can be transmitted from the donor CU through an RRC reconfiguration or RRC setup message. If the gNB ID / CU ID is provided to the IAB, the DU of all IAB nodes currently connected to the donor gNB can broadcast the current donor gNB ID / CU ID as SIB information. In this case, at cell selection, if the MT obtains the corresponding SIB and compares the gNB / CU ID stored therein with the ID being broadcast, cell selection can proceed. In another case, if the MT is also configured in the IAB network, a cell list can be received from the donor CU at initial access using an RRC reconfiguration or RRC setup message. In this case, the MT, at cell search or detection for reselection, can preferentially select a PCI present in the corresponding list based on the PCI value. Thereafter, a final selection can be completed by additionally determining whether it is suitable by using an existing cell selection metric.

[0251] According to one embodiment, in a case where the MT obtains the ID of a donor gNB or donor CU from the network, cell detection (S1305) can be performed at the same time as starting cell selection (S1300). The MT can measure the quality of the detected cell (S1310). For example, the cell quality can be measured through an SSB. Thereafter, SIB1 can be read to obtain factor values required for selection. At the same time, a donor gNB / CU ID present in SIB 1 additionally read therein or SIB X thereafter can be acquired. It can be determined whether the acquired information satisfies a cell selection criterion for the cell, whether the cell has an IAB-support indicator, and whether the cell is the same node as a donor gNB / CU that has been accessed before (S1320). If all are satisfied, the MT can complete selection of the corresponding cell (S1325).

[0252] Figure 13B is a diagram illustrating a case in which the MT receives an indicator related to a current donor gNB / CU through an RRC message when combining an IAB network.

[0253] In Figure 13BIn particular, the MT can receive an indicator related to the current donor gNB / CU over RRC message when combining the IAB network, can detect the cell and receive the gNB / CU ID in the SIB when performing re-establishment later, and can perform cell selection using the corresponding IAB node if the gNB / CU ID is the same as the previously accessed gNB / CU ID and if the remaining suitability criteria and IAB support are fulfilled in the cell suitability evaluation.

[0254] According to one embodiment, the child MT 1310 can send an RRC setup Request to the parent IAB node 1320 (S1330). The parent IAB node 1320 can send BH traffic including the RRC setup Request message to the donor CU 1330 (S1332). The donor CU 1330 can send BH traffic including an RRC message to the parent IAB node 1320 in response to the RRC setup Request message (S1334). The parent IAB node 1320 can send an RRC setup message including the donor gNB / CU ID to the child MT 1310 (S1336). The child MT 1310 can send an RRC setup Complete to the parent IAB node 1320 (S1338). Alternatively, the parent IAB node 1320 can include the donor gNB / CU ID in an RRC reconfiguration message to send the donor gNB / CU ID to the child MT 1310 (S1340). In response to the RRC reconfiguration message, the child MT 1310 can send an RRC reconfiguration Complete to the parent IAB node 1320 (S1342). Thereafter, the child MT 1310 can perform RRC re-establishment (S1344). The child MT 1310 can perform cell detection / measurement (S1346) and receive SIB X including the donor gNB / CU ID from the selected cell 1300 (S1348). The child MT 1310 can perform evaluation of cell selection (S1350). The evaluation of cell selection can be performed by using at least one of the following included in the received SIB X.

[0255] - evaluate S criteria using S criteria

[0256] - evaluate IAB support using IAB-support indication

[0257] - evaluate whether the selected cell corresponds to the same gNB / CU using gNB / CU ID

[0258] Figure 13Cis a diagram illustrating a case where an MT receives information about cell IDs currently accessible under a donor gNB / CU at the time of combining an IAB network through an RRC message.

[0259] In Figure 13C In this case, the MT can receive cell ID (e.g., PCI and CGI) information accessible under the current donor gNB / CU at the time of combining an IAB network through an RRC message, receive SIB1 at the time of performing reestablishment later if the detected cell corresponds to the received accessible cell, and perform cell selection using the corresponding IAB node if the remaining suitability criteria and IAB support are satisfied.

[0260] When the donor gNB / CU ID or possible cell ID is included in the RRC release message or RRC release with suspend, and the MT enters an inactive or idle state, the same operation can be performed during cell selection and reselection. For example, the suitability condition can be used at the time of selecting / reselecting a cell.

[0261] According to one embodiment, the child node MT 1310 can send an RRC setup Request to the parent IAB node 1320 (S1360). The parent IAB node 1320 can send a BH traffic including the RRC setup Request message to the donor CU 1330 (S1362). The donor CU 1330 can send an RRC message corresponding to the RRC setup Request message to the parent IAB node 1320 through the BH traffic (S1364). The parent IAB node 1320 can send an RRC setup message including a list of available cells to the child node MT 1310 (S1366). The child node MT 1310 can send an RRC setup Complete to the parent IAB node 1320 (S1368). The parent IAB node 1320 can send an RRC reconfiguration message including the list of available cells to the child node MT 1310 (S1370). The child node MT 1310 can send an RRC reconfiguration Complete to the parent IAB node 1320 (S1372). Thereafter, the child node MT 1310 can perform RRC reestablishment (S1374). The child node MT 1310 can perform cell detection / measurement (S1376) and check the PCI and if the PCI is in the list of available cells, it can further perform reception of SIB1 by receiving the SSB of the detected cell (S1378). In case the PCI is included in the list, the child node MT 1310 can receive SIB 1 from the selected cell 1300 (S1380). The child node MT 1310 can perform evaluation of cell selection (S1382). The evaluation of cell selection can be done by using at least one of the following.

[0262] - S criteria

[0263] - IAB-support

[0264] Figure 14 is a flowchart illustrating a cell selection operation for an MT not accessing its lower layer IAB node during connection reestablishment.

[0265] Figure 14is an operation for the MT not to perform cell selection on the cell of its own lower IAB node during reestablishment. In this case, the MT can receive cell information of its own lower IAB node from the donor CU. When the corresponding cell information is received through an RRC setup or RRC reconfiguration message at initial access and the MT performs cell selection (S1400), cell detection (S1405) can be performed. The MT can measure the quality of the detected cell. For example, an SSB can be measured (S1410). From the point in time at which the PCI can be identified, it can be determined whether the corresponding cell is a cell in the blacklist. For example, the blacklist can be checked at the corresponding frequency (S1415). If it is a cell present in the blacklist, the cell can be excluded from cell selection, other cells can be detected, and cell selection can be performed. If it is a cell not present in the blacklist, remaining cell suitability checks can be made. For example, the MT can receive an SIB 1 (S1420). For example, cell suitability checks can determine whether S criteria are met or whether an IAB-support indicator is present (S1425). If both conditions are met, the MT can complete selection of the corresponding cell (S1430).

[0266] The corresponding available cell list can be included in an RRC setup / reconfiguration message and an RRC release message. Accordingly, when the MT enters an idle mode or operates in an inactive mode, it can be determined whether the cell is included in the blacklist during cell selection and reselection, and can be excluded from selection.

[0267] The embodiments of the disclosure described and illustrated in this specification are presented only to facilitate an understanding of the technical content of the disclosure and to help understanding of the disclosure, and are not intended to limit the scope of the disclosure. It will be obvious to those skilled in the art that, in addition to the embodiments disclosed herein, other variations based on the technical idea of the disclosure can be implemented.

Claims

1. A method performed by an integrated access and backhaul, IAB, node operating with a first cell group and a second cell group in a wireless communication system, the method comprising: receiving, from a first parent node related to the first cell group, a backhaul radio link failure, RLF, notification indicating a recovery failure of a backhaul RLF at the first parent node; considering, based on the backhaul RLF notification, that a RLF is detected for the first cell group; suspending, based on the RLF being detected for the first cell group, transmission of all data radio bearers, DRBs, and backhaul radio link control, RLC, channels related to the first cell group; updating, based on the backhaul RLF notification, at least one routing entry in the IAB node by removing a first routing entry having an egress link associated with the first parent node and replacing the first routing entry with a second routing entry having an egress link associated with a second parent node related to the second cell group; and sending, to a second parent node related to the second cell group, a cell group failure information message including information indicating that the cell group failure information message is associated with receiving the backhaul RLF notification from the first parent node and routing information used by a backhaul adaptation protocol, BAP, layer in the IAB node upon detecting the RLF, wherein the routing information includes an egress link identifier, ID, a next hop ID mapped to each routing ID, and backhaul RLC channel mapping information used upon detecting the RLF. 2.The method of claim 1, the first cell group comprises a master cell group, MCG, wherein wherein the second cell group comprises a secondary cell group, SCG, and wherein the cell group failure information message is sent over split signaling radio bearer, SRB1 or SRB3. 3.The method of claim 1, the first cell group comprises a secondary cell group, SCG, and wherein wherein the second cell group comprises a master cell group, MCG. 4.A method performed by a first parent node related to a first cell group of an integrated access and backhaul, IAB, node in a wireless communication system, the IAB node operating with the first cell group and a second cell group, the method comprising: detecting a recovery failure of a backhaul radio link failure, RLF, at the first parent node; sending, to the IAB node, a backhaul RLF notification indicating the recovery failure of the backhaul RLF at the first parent node; and suspending reception of all data radio bearers, DRBs, and backhaul radio link control, RLC, channels related to the first cell group, wherein the RLF of the first cell group is considered to be detected according to the backhaul RLF notification, wherein the backhaul RLF notification triggers the IAB node to send, to a second parent node related to the second cell group, a cell group failure information message including information indicating that the cell group failure information message is associated with the IAB node receiving the backhaul RLF notification from the first parent node and routing information used by a backhaul adaptation protocol, BAP, layer in the IAB node upon detecting the RLF, ​ ​ wherein the routing information comprises an egress link identifier, ID, a next hop ID mapped to each routing ID, and backhaul RLC channel mapping information used upon detection of the RLF, and wherein the backhaul RLF notification triggers the IAB node to update at least one routing entry in the IAB node by removing a first routing entry having an egress link associated with a first parent node and replacing the first routing entry with a second routing entry having an egress link associated with a second parent node.

5. The method of claim 4, wherein the first cell group comprises a master cell group, MCG, wherein the second cell group comprises a secondary cell group, SCG, and wherein the cell group failure information message is transmitted over a split signaling radio bearer, SRB1 or SRB3.

6. The method of claim 4, wherein the first cell group comprises a secondary cell group, SCG, and wherein the second cell group comprises a master cell group, MCG.

7. An integrated access and backhaul, IAB, node operating with a first cell group and a second cell group in a wireless communication system, the IAB node comprising: a transceiver; and a controller configured to: receive, via the transceiver, a backhaul radio link failure, RLF, notification from a first parent node related to the first cell group indicating a recovery failure of a backhaul RLF at the first parent node, consider, based on the backhaul RLF notification, that a RLF is detected for the first cell group, suspend, based on the RLF being detected for the first cell group, transmission of all data radio bearers, DRBs, and backhaul radio link control, RLC, channels related to the first cell group, update, based on the backhaul RLF notification, at least one routing entry in the IAB node by removing a first routing entry having an egress link associated with the first parent node and replacing the first routing entry with a second routing entry having an egress link associated with a second parent node related to the second cell group, and transmit, via the transceiver, a cell group failure information message to a second parent node related to the second cell group, the cell group failure information message comprising information indicating that the cell group failure information message is associated with receiving the backhaul RLF notification from the first parent node and routing information used by a backhaul adaptation protocol, BAP, layer in the IAB node upon detection of the RLF, wherein the routing information comprises an egress link identifier, ID, a next hop ID mapped to each routing ID, and backhaul RLC channel mapping information used upon detection of the RLF.

8. The IAB node of claim 7, wherein the first cell group comprises a master cell group, MCG, wherein the second cell group comprises a secondary cell group, SCG.

9. The IAB node of claim 8, wherein the cell group failure information message is transmitted over a split signaling radio bearer, SRB1 or SRB3.

10. The IAB node of claim 7, wherein the first cell group comprises a secondary cell group, SCG, and wherein the second cell group comprises a master cell group, MCG.

11. A first parent node related to a first cell group of an integrated access and backhaul, IAB, node, the IAB node operating with the first cell group and a second cell group, the first parent node comprising: a transceiver; and a controller configured to: detect a failure of recovery of a backhaul radio link failure, RLF, at the first parent node, send, to the IAB node, a backhaul RLF notification indicating the failure of recovery of the backhaul RLF at the first parent node, suspend reception of all data radio bearers, DRBs, and backhaul radio link control, RLC, channels related to the first cell group, wherein the detection of the RLF of the first cell group is considered in accordance with the backhaul RLF notification, wherein the backhaul RLF notification triggers the IAB node to send a cell group failure information message to a second parent node related to the second cell group, the cell group failure information message including information indicating that the cell group failure information message is associated with the IAB node receiving the backhaul RLF notification from the first parent node and routing information used by a backhaul adaptation protocol, BAP, layer in the IAB node when detecting the RLF, wherein the routing information includes an egress link identifier, ID, a next hop ID mapped to each routing ID, and backhaul RLC channel mapping information used when detecting the RLF, and wherein the backhaul RLF notification triggers the IAB node to update at least one routing entry in the IAB node by removing a first routing entry having an egress link associated with the first parent node and replacing the first routing entry with a second routing entry having an egress link associated with the second parent node.

12. The first parent node of claim 11, wherein the first cell group comprising a master cell group, MCG, wherein the second cell group comprises a secondary cell group, SCG, and wherein the cell group failure information message is sent over a split signaling radio bearer, SRB1 or SRB3.

13. The first parent node of claim 11, wherein the first cell group comprising a secondary cell group, SCG, and wherein the second cell group comprises a master cell group, MCG.

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