Method for handling node failure in an integrated access and backhaul system and method for transmitting redirection information therein

Abstract

The present disclosure relates to a communication method and system for integrating a fifth generation (5G) communication system supporting a higher data rate than a fourth generation (4G) system with Internet of Things (IoT) technology. The present disclosure can be applied to smart services based on 5G communication technology and IoT-related technologies, such as smart homes, smart buildings, smart cities, smart cars, connected cars, healthcare, digital education, smart retail, safety and security services.

Description

Technical Field

[0001] The present disclosure provides a method for processing a base station in which an operation failure has occurred in a radio integrated access and backhaul system. In addition, the present disclosure provides a method for managing redirection information required for a terminal part to re-access a network in a radio integrated access and backhaul system. Background Art

[0002] In order to meet the demand for wireless data services that have increased since the deployment of 4G communication systems, efforts have been made to develop improved 5G or quasi-5G communication systems. Therefore, 5G or quasi-5G communication systems are also called "super 4G networks" or "post-LTE systems". 5G communication systems are considered to be implemented in higher frequency (mmWave) bands (e.g., 60GHz bands) to achieve higher data rates. In order to reduce the propagation loss of radio waves and increase the transmission distance, beamforming, massive multiple input multiple output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming and massive antenna technology are discussed in 5G communication systems. In addition, in 5G communication systems, based on advanced small cells, cloud radio access networks (RAN), ultra-dense networks, device-to-device (D2D) communications, wireless backhaul, mobile networks, collaborative communications, coordinated multi-point (CoMP) and receiving-end interference elimination, system network improvements are being developed. In 5G systems, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) have been developed as advanced coding modulation (ACM), and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0003] The Internet, which is a human-centered connected network in which people can generate and consume information, is now evolving into the Internet of Things (IoT), in which distributed entities (such as objects) exchange and process information without human intervention. The Internet of Everything (IoE) has emerged, which combines IoT technology and big data processing technology through connection with cloud servers. The implementation of IoT requires technical elements such as "sensing technology", "wired / wireless communication and network infrastructure", "service interface technology" and "security technology", and recently sensor networks, machine-to-machine (M2M) communication, machine type communication (MTC), etc. have also been studied. By collecting and analyzing data generated between connected objects, such an IoT environment can provide smart Internet technology services that create new value for human life. Through the integration and combination between existing information technology (IT) and various industrial applications, IoT can be applied to various fields, including smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, healthcare, smart appliances, and advanced medical services.

[0004] In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine type communications (MTC), and machine-to-machine (M2M) communications can be implemented through beamforming, MIMO, and array antennas. The application of cloud radio access networks (RANs) as the above-mentioned big data processing technology can also be regarded as an example of the fusion between 5G technology and IoT technology.

[0005] The above information is presented as background information only to assist with understanding the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with respect to the present disclosure. Summary of the invention

[0006] Technical issues

[0007] If communication occurs between a core network and a terminal in a case where the topology includes multiple hops of IAB nodes, a radio link failure may occur depending on the channel conditions of each IAB node. If an IAB node of an intermediate hop fails, its subsequent nodes and terminals connected thereto have no direct connection between themselves and the failed node, and therefore cannot identify the failure. If the failure condition persists, the downstream connected IAB nodes and terminals continue to be disconnected. This may cause serious problems. Therefore, the present disclosure is characterized in that a method and apparatus for solving the above-mentioned problems are provided.

[0008] In addition, if communication occurs between the core network and the terminal in the case of a topology including multiple hops of IAB nodes, the core-side access point is the IAB donor node. The donor node includes a centralized unit (CU), controls a distributed unit (DU), and controls operations related to sending data to / receiving data from the terminal through the DU. In the event of a connection failure in the mobile terminal (MT) part of the intermediate IAB node or the terminal receiving services from the IAB node, or even in the case of a normal RRC release, for the purpose of network re-access, accessing the same IAB donor that has been accessed is a method of re-access that does not burden the terminal and the network as an internal HO. This is because, in the case of the architecture option 1 group, there are PDCP and RRC entities in the CU, and for this reason, there is no packet loss due to PDCP reconstruction, so no security update is required, and lossless HO is possible. For this reason, it is necessary to give redirection information so that the MT part of the terminal and the IAB node becomes advantageous during re-access. Therefore, the present disclosure is characterized in that a method and apparatus for providing redirection information are provided.

[0009] Technical Solution

[0010] According to one aspect of the present disclosure, a method for a first node in an integrated access and backhaul (IAB) system is provided, the method comprising: detecting the occurrence of a fault related to an upstream node; if the fault is detected, performing a first recovery process regarding the fault; and based on the result of the first recovery process, sending a first message including information about the result of the first recovery process to a second node, the second node being a downstream node relative to the first node.

[0011] In an exemplary embodiment, the failure includes at least one of a radio link failure (RLF), a handover failure, a reconfiguration failure, and an integrity check failure.

[0012] In an exemplary embodiment, the method further includes operating a timer while performing a first recovery procedure with respect to the fault if the fault is detected.

[0013] In an exemplary embodiment, the method further includes: if the fault is detected, sending a second message including at least one of information indicating the fault and information indicating execution of the first recovery procedure for the fault to the second node while executing the first recovery procedure for the fault.

[0014] In an exemplary embodiment, at least one of the first message and the second message is transmitted via at least one of a backhaul adaptation protocol (BAP) layer signal, a master information block (MIB), a system information block (SIB), and a backhaul adaptation protocol (BAP) layer signal.

[0015] According to another aspect of the present disclosure, a first node in an integrated access and backhaul (IAB) system is provided, the first node comprising: a first entity configured to send / receive signals with an upstream node; and a second entity configured to send / receive signals with a second node, the second node being a downstream node relative to the first node, wherein: the first entity is configured to detect the occurrence of a fault associated with the upstream node, and if the fault is detected, perform a first recovery process regarding the fault, and based on a result of the first recovery process, the second entity is configured to send a first message including information regarding a result of the first recovery process to the second node.

[0016] According to another aspect of the present disclosure, a method of a second node is provided, wherein the second node is a downstream node relative to a first node in an integrated access and backhaul (IAB) system, the method comprising: receiving a first message from the first node, the first message including information about a result of a first recovery process related to a fault associated with an upstream node; and in response to receiving the first message, performing a second recovery process by the second node.

[0017] According to another aspect of the present disclosure, a second node is provided, which is a downstream node relative to a first node in an integrated access and backhaul (IAB) system, and the second node is configured to: receive a first message from the first node, the first message including information about a result of a first recovery process related to a fault associated with an upstream node; and perform a second recovery process in response to receipt of the first message.

[0018] Beneficial technical effects

[0019] According to the above disclosure, the base station on which the failure occurs refers to the timer to determine whether to release the downstream terminal and IAB node so that they reside on the new cell or remain unchanged. If the timer expires, and if the downstream IAB node and the terminal are notified of the failure of the base station, the terminal can perform an operation of searching for a new IAB node, so that a connection can be established with the new base station more quickly. In addition, the terminal is prohibited from requesting an additional connection to the base station on which the failure occurs or performing cell selection or reselection for reasons such as paging, thereby reducing the possibility of unnecessary data transmission / reception delays of the terminal.

[0020] In addition, according to the present disclosure, if information of a cell connected to an existing IAB donor is provided when a failure occurs, after releasing the RRC or when a reconstruction is performed, the terminal that subsequently re-accesses the network will re-access the cell connected to the existing IAB donor, if possible, with no additional overhead for the terminal and the base station due to PDCP lossless transmission and security refresh. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, wherein like reference numerals represent like parts:

[0022] Figure 1A is a diagram showing the structure of an existing LTE system;

[0023] Figure 1B is a diagram showing a radio protocol structure of an existing LTE system;

[0024] Figure 1C is a diagram showing the structure of a new wireless mobile communication system to which the present disclosure can be applied;

[0025] Figure 1D is a diagram showing a wireless protocol structure of a new radio mobile communication system to which the present disclosure can be applied;

[0026] Figure 1E is a block diagram showing the internal structure of a terminal to which the present disclosure is applied;

[0027] Figure 1F is a block diagram showing a configuration of an NR base station according to the present disclosure;

[0028] Figure 1G is a diagram showing a configuration of an IAB system to which the present disclosure is applied;

[0029] Figure 1H An exemplary topology for describing the present disclosure is shown;

[0030] Fig. 1I An operation in the case where RRC re-establishment succeeds before a given timer expires in an embodiment to which the present disclosure is applied is shown;

[0031] Figure 1J 1. The operation when a failure of an IAB node occurs, a timer is started, an MT part of the failed node performs a reestablishment operation, and an RRC setting is received before the timer expires according to another embodiment;

[0032] Figure 1K shows a situation where a timer starts and then expires before a re-establishment operation successfully completes;

[0033] Figure 1L is a diagram showing the operation of a terminal, in particular the MT part of a failed IAB node;

[0034] Figure 1M is a diagram showing the operation of a terminal or a downstream IAB node connected to a failed IAB node or a DU portion of a failed IAB node, or residing thereon;

[0035] Figure 2A is a diagram showing the structure of an existing LTE system;

[0036] Figure 2B is a diagram showing a radio protocol structure of an existing LTE system;

[0037] Figure 2C is a diagram showing the structure of a new wireless mobile communication system to which the present disclosure can be applied;

[0038] Figure 2D is a diagram showing a wireless protocol structure of a new radio mobile communication system to which the present disclosure can be applied;

[0039] Figure 2E is a block diagram showing the internal structure of a terminal to which the present disclosure is applied;

[0040] Figure 2F is a block diagram showing a configuration of an NR base station according to the present disclosure;

[0041] Figure 2G is a diagram showing a configuration of an IAB system to which the present disclosure is applied;

[0042] Figure 2H An exemplary topology for describing the present disclosure is shown;

[0043] Fig.2I is a diagram illustrating possible signaling by which redirection information is delivered;

[0044] Figure 2J is a diagram illustrating a case where, if redirection information is delivered to a DU of an upstream IAB node through F1-AP or F1-C signaling, the information is bypassed between the MT and the DU of the IAB node;

[0045] Figure 2K is a diagram showing a redirection operation in the event of a terminal failure;

[0046] Figure 2L is a diagram showing an operation flow of a terminal; and

[0047] Figure 2M is a diagram showing a case in which redirection information is delivered to an RRC release message. DETAILED DESCRIPTION

[0048] Hereinafter, the operating principle of the present disclosure will be described in detail with reference to the accompanying drawings. When describing the present disclosure below, when it is determined that the detailed description therein may unnecessarily obscure the subject matter of the present disclosure, the detailed description of the related known configurations or functions incorporated herein will be omitted. The terms to be described below are defined in consideration of the functions in the present disclosure, and may be different depending on the user, the user's intention or habit. Therefore, the definition of the terms should be based on the content of the entire specification.

[0049] In the following description, the terms used to identify access nodes, the terms referring to network entities, the terms referring to messages, the terms referring to interfaces between network entities, and the terms referring to various identification information are for the convenience of description. Therefore, the present disclosure may not be limited by the terms provided below, and other terms indicating the subject matter having equivalent technical meanings may be used.

[0050] For ease of description, the present disclosure uses terms and names defined in 3GPP LTE (3rd Generation Partnership Project Long Term Evolution). However, the present disclosure is not limited to the above terms and names, and is also applicable to systems complying with other standards.

[0051] Integrated access and backhaul (IAB) is a concept representing a relay node that is configured so that a single node performs operations on a mobile terminal (MT) of an upstream IAB node and functions as a base station for a downstream IAB node. The relay node collects uplink traffic from downstream IAB nodes and uplink traffic from ordinary nodes that have accessed the relay node, and then delivers the traffic to the upstream IAB node. The relay node forwards the traffic delivered downstream from the core network to the downstream IAB node as downlink traffic, or forwards it to an ordinary node that has accessed the relay node as downlink traffic. In this process, a single node performs operations of communicating with an upstream IAB node and operations of communicating with a downstream IAB node and a terminal. Therefore, IAB refers to a system of nodes that combine access and backhaul communication operations and a topology including the node. A node directly connected to the core network is called an IAB donor. The IAB donor has no upstream IAB node and is connected to the core network by using an IP address system.

[0052] The present disclosure provides a method, wherein, in a multi-hop system including an IAB node, if a failure (including a wireless connection failure) that can be recognized by the RRC layer occurs in an intermediate node, the intermediate node notifies subsequent IAB nodes and terminals of the fact that it (the failed IAB node) has failed, and performs IAB operation suspension and disabling operations.

[0053] Figure 1A It is a diagram showing the structure of an existing LTE system.

[0054] refer to Figure 1A As shown, the wireless access network of the LTE system may include evolved Node Bs (hereinafter, referred to as eNBs, Node Bs or base stations) 1a-05, 1a-10, 1a-15 and 1a-20, a mobility management entity (MME) 1a-25 and a serving gateway (S-GW) 1a-30. User equipment (hereinafter, referred to as UE or terminal) 1a-35 may access an external network through eNBs 1a-05 to 1a-20 and S-GW 1a-30.

[0055] exist Figure 1AIn the LTE system, eNB 1a-05 to 1a-20 may correspond to an existing Node B of a UMTS system. The eNB may be connected to a UE 1a-35 via a wireless channel and may perform functions more complex than an existing Node B. In an LTE system, all user services, including real-time services such as Voice over IP (VoIP) over Internet Protocol, may be provided via a shared channel. Therefore, a device is required for collecting status information (such as UE buffer status, available transmission power status, and channel status) and then scheduling it, and eNB 1a-05 to 1a-20 may be responsible for it. A single eNB may typically control multiple cells. For example, in order to achieve a transmission rate of 100 Mbps, an LTE system may use orthogonal frequency division multiplexing (OFDM) as a radio access technology, for example, in a bandwidth of 20 MHz. An adaptive modulation and coding (AMC) scheme may also be applied, which determines a modulation scheme and a channel coding rate according to the channel status of a terminal. S-GW 1a-30 is a device configured to provide a data bearer, and may generate or remove a data bearer under the control of MME 1a-25. The MME is a device that processes not only a mobility management function related to a terminal but also various control functions, and can be connected to a plurality of base stations.

[0056] Figure 1B This is a diagram showing a radio protocol structure of a conventional LTE system.

[0057] refer to Figure 1B , the radio protocols of the LTE system may include Packet Data Convergence Protocol (PDCP) 1b-05 and 1b-40, Radio Link Control (RLC) 1b-10 and 1b-35, and Medium Access Control (MAC) 1b-15 and 1b-30 located at the terminal side and the eNB side, respectively. PDCP may be responsible for operations such as IP header compression / recovery. The main functions of PDCP can be summarized as follows:

[0058] -Header compression and decompression: ROHC only

[0059] -Transmission of user data

[0060] - In-sequence delivery of upper layer PDUs during PDCP re-establishment of RLC AM

[0061] - For split bearers in DC (supports RLC AM only): PDCP PDU routing for transmission and PDCP PDU reordering for reception

[0062] - Repeated detection of lower layer SDUs during PDCP re-establishment of RLC AM

[0063] - For split bearers in DC, retransmit PDCP SDUs at handover, and for RLC AM, retransmit PDCP PDUs during PDCP data recovery

[0064] -Encryption and decryption

[0065] - Timer based SDU discard in uplink.

[0066] Radio Link Control (RLC) 1b-10 and 1b-35 can perform operations such as reconfiguring PDCP packet data units (PDUs) to an appropriate size and performing ARQ operations. The main functions of RLC can be summarized as follows:

[0067] -Transmission of upper layer PDU

[0068] - Error correction via ARQ (for AM data transmission only)

[0069] -RLC SDU concatenation, segmentation and reassembly (only for UM and AM data transmission)

[0070] - Re-segmentation of RLC data PDU (only for AM data transmission)

[0071] - Reordering of RLC data PDUs (only for UM and AM data transmission)

[0072] - Duplicate detection (for UM and AM data transmission only)

[0073] -Protocol error detection (for AM data transmission only)

[0074] -RLC SDU discard (only for UM and AM data transmission)

[0075] -RLC reconstruction.

[0076] MAC 1b-15 and 1b-30 can be connected to multiple RLC layer devices configured in a single terminal, and can perform operations of multiplexing RLC PDUs into MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The main functions of MAC can be summarized as follows:

[0077] - Mapping between logical channels and transport channels

[0078] - Multiplexing MAC SDUs belonging to one or different logical channels into a transport block (TB) delivered to the physical layer on a transport channel, or demultiplexing MAC SDUs belonging to one or different logical channels from a transport block (TB) delivered from the physical layer on a transport channel

[0079] -Dispatch information report

[0080] - Error correction through HARQ

[0081] - Priority handling between logical channels of a UE

[0082] - Priority handling between UEs through dynamic scheduling

[0083] -MBMS service identification

[0084] -Transmission format selection

[0085] -filling.

[0086] The physical layers 1b-20 and 1b-25 may perform the following operations: channel-code and modulate the upper layer data, generate OFDM symbols therefrom and transmit them through a wireless channel, or demodulate OFDM symbols received through a wireless channel, channel-decode them and then transmit them to an upper layer.

[0087] Figure 1C is a diagram showing the structure of a new radio mobile communication system.

[0088] refer to Figure 1C , the radio access network of the new radio (hereinafter referred to as NR or 2g) mobile communication system may include a new radio node B (hereinafter referred to as NR gNB or NR base station) 1c-10 and a new radio core network (NR CN) 1c-05. The new radio user equipment (NR UE or terminal) can access the external network through the NR gNB1c-10 and NR CN 1c-05.

[0089] exist Figure 1CIn the NR mobile communication system, the NR gNB 1c-10 can correspond to the evolved Node B (eNB) of the existing LTE system. The NR gNB can be connected to the NR UE 1c-15 through a wireless channel and can provide better services than the existing Node B. In the NR mobile communication system, all user services can be provided through a shared channel. Therefore, equipment is required for collecting status information (for example, UE buffer status, available transmission power status, and channel status) and then scheduling it, and the NR NB1c-10 can be responsible for it. A single NR gNB can control multiple cells. In the NR mobile communication system, in order to achieve ultra-high-speed data transmission compared with the current LTE, a bandwidth equal to or greater than the current maximum bandwidth can be applied. In addition, orthogonal frequency division multiplexing (OFDM) can be used as a wireless access technology, and beamforming technology can be combined with it in addition. It is also possible to apply an adaptive modulation and coding (AMC) scheme, which determines the modulation scheme and channel coding rate according to the channel state of the terminal. The NRCN 1c-05 can perform functions such as mobility support, bearer configuration, and QoS configuration. NR CN is a device that not only handles mobility management functions related to the terminal but also handles various control functions, and can be connected to multiple base stations. In addition, the NR mobile communication system can interoperate with the existing LTE system, and the NR CN can be connected to the MME 1c-25 through the network interface. The MME can be connected to the eNB1c-30 (existing base station).

[0090] Figure 1D 2 is a diagram showing a wireless protocol structure of an NR mobile communication system to which the present disclosure can be applied.

[0091] refer to Figure 1D The wireless protocols of the NR mobile communication system include NR Service Data Adaptation Protocol (SDAP) 1d-01 and 1d-45, NR PDCP 1d-05 and 1d-40, NR RLC 1d-10 and 1d-35, and MAC 1d-15 and 1d-30, which are located on the terminal side and the NR base station side respectively.

[0092] The main functions of NR SDAP 1d-01 and 1d-45 may include some of the following functions:

[0093] -Transmission of user plane data

[0094] - Mapping between QoS flows and DRBs for both DL and UL

[0095] - Marking of QoS Flow ID in both DL and UL packets

[0096] - Mapping of Reflective QoS Flow to DRB for UL SDAP PDU.

[0097] Regarding the SDAP layer device, the terminal can use a radio resource control (RRC) message to receive configuration about whether to use the header of the SDAP layer device or the function of the SDAP layer device for each PDCP layer device, for each bearer or for each logical channel. If the SDAP header is configured, the terminal can indicate by using a one-bit indicator (NAS reflects QoS) of the non-access stratum (NAS) quality of service (QoS) reflecting the SDAP header and a one-bit indicator (AS reflects QoS) reflecting the access stratum (AS) QoS, so that the terminal can update or reconfigure the mapping information related to the data bearer and the QoS flow of the uplink and downlink. The SDAP header may include information of the QoS flow ID indicating the QoS. The QoS information can be used as data processing priority, scheduling information, etc. for supporting effective services.

[0098] The main functions of NR PDCP 1d-05 and 1d-40 may include some of the following functions:

[0099] -Header compression and decompression: ROHC only

[0100] -Transmission of user data

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

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

[0103] -PDCP PDU reordering for reception

[0104] - Duplicate detection of lower layer SDU

[0105] -Retransmission of PDCP SDU

[0106] -Encryption and decryption

[0107] - Timer based SDU discard in uplink.

[0108] In the above description, the reordering function of the NR PDCP device may refer to a function of reordering the PDCP PDU received from the lower layer based on the PDCP sequence number (SN). The reordering function of the NR PDCP device may include a function of delivering data to the upper layer in a reordered order, or may include a function of directly delivering data without considering the order. The reordering function of the NR PDCP device may include: a function of recording the lost PDCP PDU as a result of the reordering, a function of reporting the status of the lost PDCP PDU to the transmitting side, and a function of requesting retransmission of the lost PDCP PDU.

[0109] The main functions of NR RLC 1d-10 and 1d-35 may include some of the following functions:

[0110] -Transmission of upper layer PDU

[0111] - In-sequence delivery of upper layer PDUs

[0112] - Out-of-order delivery of upper layer PDUs

[0113] - Error correction via ARQ

[0114] - Concatenation, segmentation and reassembly of RLC SDU

[0115] - Re-segmentation of RLC data PDUs

[0116] - Reordering of RLC data PDUs

[0117] - Duplicate detection

[0118] -Protocol error detection

[0119] -RLC SDU discarded

[0120] -RLC reconstruction.

[0121] In the above description, the in-sequence delivery function of the NR RLC device may refer to a function of delivering the RLC SDU received from the lower layer to the upper layer in sequence. If a single RLC SDU has been segmented into multiple RLC SDUs and then received, the in-sequence delivery function of the NR RLC device may refer to a function of reassembling and delivering them.

[0122] The in-sequence delivery function of the NR RLC device may refer to: a function of reordering the received RLC PDU with reference to the RLC sequence number (SN) or the PDCP SN, a function of recording the lost RLC PDU as a result of the reordering, a function of reporting the status of the lost PDCP PDU to the transmitting side, and a function of requesting retransmission of the lost PDCP PDU.

[0123] The in-sequence delivery function of the NR RLC device may include: if there is a lost RLC SDU, only the RLC SDU before the lost RLC SDU is delivered to the upper layer in sequence.

[0124] The in-sequence delivery function of the NR RLC device may include: if there is a lost RLC SDU, but if a predetermined timer expires, the function of delivering all RLC SDUs received before the timer starts to the upper layer in sequence.

[0125] The in-sequence delivery function of the NR RLC device may include the function of delivering all currently received RLC SDUs to the upper layer in sequence if there are lost RLC SDUs but if a predetermined timer expires.

[0126] The NR RLC device may process the RLC PDUs in the order received, regardless of the order of the sequence numbers (out-of-order delivery), and may deliver them to the NR PDCP device.

[0127] If segments are received, the NR RLC device may receive the segments stored in the buffer or the segments to be received later, may reconfigure them into a single complete RLC PDU, and may then deliver it to the NR PDCP device.

[0128] The NR RLC layer may not include the cascading function, which may be performed by the NR MAC layer or may be replaced by the multiplexing function of the NR MAC layer.

[0129] In the above description, the out-of-order delivery function of the NR RLC device may refer to a function of directly delivering the RLC SDU received from the lower layer to the upper layer without considering the order. The out-of-order delivery function of the NR RLC device may refer to a function of reassembling and delivering a single RLC SDU if it has been segmented into multiple RLC SDUs and then received. The out-of-order delivery function of the NR RLC device may include a function of storing the RLC SN or PDCP SN of the received RLC PDU and recording the lost PDCP PDU as a result of reordering.

[0130] NR MAC 1d-15 and 1d-30 can be connected to multiple NR RLC layer devices configured in a single terminal, and the main functions of NR MAC can include some of the following functions:

[0131] - Mapping between logical channels and transport channels

[0132] -Multiplexing / demultiplexing of MAC SDU

[0133] -Dispatch information report

[0134] - Error correction through HARQ

[0135] - Priority handling between logical channels of a UE

[0136] - Priority handling between UEs through dynamic scheduling

[0137] -MBMS service identification

[0138] -Transmission format selection

[0139] -filling.

[0140] NR PHY layers 1d-20 and 1d-25 can perform the following operations: channel coding and modulating upper layer data, generating OFDM symbols therefrom and sending them through a wireless channel, or demodulating OFDM symbols received through a wireless channel, channel decoding them and then passing them to an upper layer.

[0141] Figure 1E is a block diagram showing an internal structure of a terminal to which the present disclosure is applied.

[0142] Referring to the figure, the terminal includes a radio frequency (RF) processing unit 1e-10, a baseband processing unit 1e-20, a storage unit 1e-30, and a control unit 1e-40.

[0143] The RF processing unit 1e-10 performs functions for sending / receiving signals through a wireless channel, such as frequency band conversion of signals and amplification thereof. That is, the RF processing unit 1e-10 up-converts the baseband signal provided by the baseband processing unit 1e-20 into an RF band signal, transmits it through an antenna, and down-converts the RF band signal received by the antenna into a baseband signal. For example, the RF processing unit 1e-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Although only one antenna is shown in the figure, the terminal may include multiple antennas. In addition, the RF processing unit 1e-10 may include multiple RF chains. In addition, the RF processing unit 1e-10 may perform beamforming. In order to perform beamforming, the RF processing unit 1e-10 may adjust the phase and amplitude of the corresponding signal sent / received by multiple antennas or antenna elements. In addition, the RF processing unit may perform MIMO, and may receive multiple layers when performing MIMO operations.

[0144] The baseband processing unit 1e-20 performs the function of converting between the baseband signal and the bit string according to the physical layer specification of the system. For example, during data transmission, the baseband processing unit 1e-20 encodes and modulates the transmission bit string to generate complex symbols. In addition, during data reception, the baseband processing unit 1e-20 demodulates and decodes the baseband signal provided from the RF processing unit 1e-10 to restore the received bit string. For example, when following the orthogonal frequency division multiplexing (OFDM) scheme, the baseband processing unit 1e-20 encodes and modulates the transmission bit string during data transmission to generate complex symbols and maps the complex symbols to subcarriers, and configures OFDM symbols through inverse fast Fourier transform (IFFT) and cyclic prefix (CP) insertion. In addition, during data reception, the baseband processing unit 1e-20 divides the baseband signal received from the RF processing unit 1e-10 for each OFDM symbol, restores the signal mapped to the subcarrier through fast Fourier transform (FFT), and restores the received bit string through demodulation and decoding.

[0145] As described above, the baseband processing unit 1e-20 and the RF processing unit 1e-10 send and receive signals. Therefore, the baseband processing unit 1e-20 and the RF processing unit 1e-10 can be referred to as a sending unit, a receiving unit, a sending or receiving unit, or a communication unit. In addition, at least one of the baseband processing unit 1e-20 and the RF processing unit 1e-10 may include a plurality of communication modules to support different multiple wireless access technologies. In addition, at least one of the baseband processing unit 1e-20 and the RF processing unit 1e-10 may include different communication modules to process signals in different frequency bands. For example, different wireless access technologies may include wireless LAN (e.g., IEEE 802.11), cellular networks (e.g., LTE), etc. In addition, different frequency bands may include ultra-high frequency (SHF) (e.g., 2.NRHz, NRHz) bands and millimeter wave (e.g., 60GHz) bands.

[0146] The storage unit 1e-30 stores data for the operation of the terminal, such as basic programs, applications, and configuration information. In particular, the storage unit 1e-30 can store information about a second access node that performs wireless communication by using a second wireless access technology. In addition, the storage unit 1e-30 provides the stored data at the request of the control unit 1e-40.

[0147] The control unit 1e-40 controls the overall operation of the terminal. For example, the control unit 1e-40 sends / receives signals through the baseband processing unit 1e-20 and the RF processing unit 1e-10. In addition, the control unit 1e-40 records and reads data in the storage unit 1e-40. To this end, the control unit 1e-40 may include at least one processor. For example, the control unit 1e-40 may include a communication processor (CP) configured to perform control communication and an application processor (AP) configured to control an upper layer (such as an application).

[0148] Figure 1F is a block diagram showing the configuration of an NR base station according to the present disclosure.

[0149] As shown in the figure, the base station includes an RF processing unit 1f-10, a baseband processing unit 1f-20, a backhaul communication unit 1f-30, a storage unit 1f-40 and a control unit 1f-50.

[0150] The RF processing unit 1f-10 performs functions for sending / receiving signals through a wireless channel, such as frequency band conversion of the signal and amplification thereof. That is, the RF processing unit 1f-10 up-converts the baseband signal provided by the baseband processing unit 1f-20 into an RF band signal, transmits it through an antenna, and down-converts the RF band signal received by the antenna into a baseband signal. For example, the RF processing unit 1f-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is shown in the figure, the first access node may include multiple antennas. In addition, the RF processing unit 1f-10 may include multiple RF chains. In addition, the RF processing unit 1f-10 may perform beamforming. In order to perform beamforming, the RF processing unit 1f-10 may adjust the phase and amplitude of the corresponding signals sent / received through multiple antennas or antenna elements. The RF processing unit may perform downlink MIMO operations by sending at least one layer.

[0151] The baseband processing unit 1f-20 performs the function of converting between the baseband signal and the bit string according to the physical layer specification of the first wireless access technology. For example, during data transmission, the baseband processing unit 1f-20 encodes and modulates the transmission bit string to generate a complex symbol. In addition, during data reception, the baseband processing unit 1f-20 demodulates and decodes the baseband signal provided from the RF processing unit 1f-10 to recover the received bit string. For example, when following the OFDM scheme, the baseband processing unit 1f-20 encodes and modulates the transmission bit string during data transmission to generate a complex symbol and maps the complex symbol to a subcarrier, and configures the OFDM symbol through IFFT operation and CP insertion. In addition, during data reception, the baseband processing unit 1f-20 divides the baseband signal received from the RF processing unit 1f-10 for each OFDM symbol, recovers the signal mapped to the subcarrier through FFT operation, and recovers the received bit string through demodulation and decoding. As described above, the baseband processing unit 1f-20 and the RF processing unit 1f-10 transmit and receive signals. Therefore, the baseband processing unit 1f-20 and the RF processing unit 1f-10 can be referred to as a transmitting unit, a receiving unit, a transmitting / receiving unit, a communication unit, or a wireless communication unit.

[0152] The backhaul communication unit 1f-30 provides an interface for communicating with other nodes within the network. That is, the backhaul communication unit 1f-30 converts a bit string sent from the main base station to other nodes (e.g., an auxiliary base station or a core network) into a physical signal, and converts a physical signal received from other nodes into a bit string.

[0153] The storage unit 1f-40 stores data used for the operation of the main base station, such as basic programs, applications, and configuration information. In particular, the storage unit 1f-40 can store information about the bearer assigned to the accessed terminal, the measurement results reported from the accessed terminal, etc. In addition, the storage unit 1f-40 can store information used as a reference for determining whether to provide multiple connections to the terminal or to terminate them. In addition, the storage unit 1f-40 provides the stored data at the request of the control unit 1f-50.

[0154] The control unit 1f-50 controls the overall operation of the main base station. For example, the control unit 1f-50 sends / receives signals through the baseband processing unit 1f-20 and the RF processing unit 1f-10, or through the backhaul communication unit 1f-30. In addition, the control unit 1f-50 records and reads data in the storage unit 1f-40. To this end, the control unit 1f-50 may include at least one processor.

[0155] Figure 1G1 is a diagram showing the configuration of an IAB system to which the present disclosure is applied. Reference numeral 1g-1 denotes an IAB donor node that performs wired communication with a core network 1g-5. The IAB donor node includes a centralized unit (CU) 1g-10 and a plurality of distributed units (DU) 1g-15. Among them, the CU includes a control plane (CP) and a user plane (UP). The CP exchanges control signals required for data transmission / reception and connection between the IAB donor node and the DU of the downstream IAB node. The DU receives the control signal from the CU and performs data transmission / reception with the terminal. Other IAB nodes other than the IAB donor node have at least one wireless connection established with the CN, and each IAB node 1g-20 may have a terminal 1g-25 from which it receives services and a downstream IAB node 1g-30 from which it receives services. There is a wireless backhaul link 1g-35 between the IAB nodes, and a wireless access link 1g-40 between the IAB node and the terminal. The wireless backhaul and the wireless access link may use the same frequency resources or separate frequency resources.

[0156] Figure 1H An exemplary topology for describing the present disclosure is shown. It is assumed that the terminal user UE11h-1 can send / receive data through a single data path. Alternatively, even if data can be sent / received by using multiple paths, the method according to the present disclosure is applicable to the case where a path switching accompanied by RRC information is required between multiple paths. It is assumed that the data path has been configured by IAB 2 in this example, and a radio link failure has occurred between the mobile terminal (MT) of IAB node 2 and the mobile terminal of IAB node 1. Under normal circumstances, if RLF occurs, the terminal performs an RRC reconstruction operation. When performing this operation, the terminal performs cell selection, re-accesses the selected cell, receives a connection reconstruction message from the core network, and sends "Complete" in response to the message. In this case, it is impossible to know how long the cell selection will take, and if a new cell is accessed and if the corresponding cell does not have a terminal context, the cell may become idle.

[0157] Fig. 1I 1 shows an operation in which RRC reestablishment succeeds before a given timer expires according to an embodiment of the present disclosure. A terminal receiving service from a faulty IAB node, or an MT portion 1i-1 of a downstream IAB node receiving service from a faulty IAB node, may maintain connection to the faulty IAB node 1i-5, or may reside while remaining idle or inactive (1i-3). The MT portion 1i-10 of the IAB node maintains connection to the serving cell (1i-30). The serving cell may be Figure 1HThe cell served by the IAB node 2 in the IAB node. The MT part of the IAB node can configure the timer value through dedicated signaling in the connected state (1i-35), or can receive the configuration through system information (1i-25). The MT part in the connected state may fail (1i-40). Although the radio link failure is taken as an example in this specification, all examples of failures in the normal RRC process, such as switching failures, reconfiguration failures, and integrity check failures, can be applied. If a failure occurs, the MT operates a predetermined timer (1i-45). In this process, fault indication signaling may exist between the MT part and the base station part of the IAB node where the failure occurs (1i-90). If a failure occurs, the MT operates the timer and performs the RRC connection reconstruction operation at the same time. If the reconstruction operation ends successfully before the timer expires, the MT stops the timer (1i-75). In this process, the MT can send a recovery indication to the DU part or the base station part of the IAB node (1i-95). The RRC re-establishment operation may include cell selection (1i-50), a process (1i-55) of randomly accessing the selected cell (1i-20), sending an RRC re-establishment request message (1i-60) to the target cell 1i-20 of the MT, receiving an RRC re-establishment message (1i-65), and sending an RRC re-establishment completion message (1i-70). As a condition for stopping the timer, the reception of the RRC re-establishment message by the MT (1i-65) may be considered. In addition, after receiving the message, the sending of the RRC re-establishment completion message (1i-70) may also be regarded as a stop condition. When the timer operates in this manner, the DU part of the faulty IAB node connected to the MT, or the faulty IAB node may not allow other connections from the terminal, or may perform operations to prevent the terminal in inactive / idle mode from residing through cell (re)selection. If the timer starts (1i-45), an indication may be sent to a master information block (MIB), which is sent to the SSB to indicate that the cell is prohibited (1i-80). Alternatively or / and the prohibition factors may be configured with respect to the access categories of all terminals, the access prohibition factor values ​​among these factors may become zero with respect to all access categories and access identifications, and the changed system information may be sent. The failed IAB node continues to operate 1i-80 and 1i-85 until the re-establishment is successful and the timer is therefore stopped. If the timer stops after successful re-establishment (1i-75), the SSB and MIB transmissions may be rolled back so that the content is sent before the timer operation (1i-100). Similarly, instead of sending system information after configuring the prohibition factor to zero, the system information may be sent after configuring the prohibition factor to the value before the timer is started (1i-105). The SSB / MIB and broadcast cell prohibition indication after selecting the access prohibition factor in the SIB to be zero may be referred to as an IAB suspension.

[0158] According to another embodiment, without applying a timer, the IAB suspension of the DU may be directly started or stopped according to the reestablishment state of the terminal. If the above-mentioned fault (e.g., RLF) occurs in the MT, the MT performs an RRC reestablishment process, and the IAB node or DU part of the MT simultaneously performs an IAB suspension operation. In this case, a fault indication may be delivered from the MT to the DU part or the IAB node. Delivering a fault indication may mean that an IAB suspension operation is performed.

[0159] If, while performing an IAB suspension operation initiated by the DU part or the IAB node, the MT successfully completes the RRC reestablishment process caused by the failure, the performed IAB suspension operation is stopped. That is, roll back to the time before the IAB suspension (delete cellBarred from the SSB and MIB, delete the barring factor that has been configured as zero for all access categories), new system information and SSB information can be received from the donor CU and then transmitted. If a failure occurs in the MT, if T311 that has been running in the MT expires after the failure occurs, if the cell selection is successful and then the RACH operation in the corresponding cell fails, or if the cell selection is successful and then the RACH in the corresponding cell is successful and T301 expires, the IAB node or the DU part of the MT can stop the IAB suspension operation that was originally in progress, or can return to its previous state, and can perform steps 1k-100, steps 1k-105, or steps 1k-110.

[0160] As an IAB suspension operation among the above operations, specifically, the DU part of the faulty IAB node connected to the MT, or the faulty IAB node may not allow additional connections from the terminal, or may perform an operation to prevent the terminal in the inactive / idle mode from camping through cell (re)selection. An indication may be transmitted to a master information block (MIB), which is transmitted to the SSB to indicate that the cell is prohibited (1i-80). Or / and the prohibition factor may be configured with respect to the access category of all terminals, the access prohibition factor value among the factors may be changed to zero for all access categories and access identifications, and the changed system information may be transmitted.

[0161] The above steps 1k-100, 1k-105 and 1k-110 will now be described in detail. The DU part of the faulty node or the faulty IAB node performs at least one of the following three operations:

[0162] As RRC dedicated signaling, the DU part or the faulty IAB node may send a message to RRC to release each terminal and downstream IAB node in a connected state. This may be referred to as option 1 (1k-100). The message may be transmitted via an RRC dedicated message, may be transmitted to a MAC CE, or may be transmitted via a control channel of a PHY. Unlike an RRC release message, a message containing an indicator indicating a node failure indication may be transmitted. Alternatively, the indicator may be transmitted via RRC dedicated signaling, a MAC CE, or a PHY signal. If a node failure indication is received, the downstream IAB node receiving it may perform RRC reconstruction.

[0163] Alternatively, the DU part or the faulty IAB node may insert a flag indicating RRC release, reconnection, or reestablishment failure into a system information block, MIB, or synchronization signal block (SSB) and then send it. This may be referred to as option 2 (1k-105). This may be a one-bit indicator using a Boolean value.

[0164] As another method, the transmission of the reference signal for radio link monitoring (RLM) may be stopped. This may be referred to as option 3 (1k-110). This method prevents the terminal from searching for a cell, so that the terminal cannot sense the presence of the cell, and is therefore referred to as IAB disabling. The reference signal may be an SSB for RLM-RS and / or an SSB or CSI-RS for cell quality measurement, and has nothing to do with CIS-RS or RLM-RS.

[0165] In addition, the transmission of system information may be stopped, or the transmission of DMRS may be stopped. Alternatively, the service may be stopped, or shutdown or power off may be performed.

[0166] If the method of Option 1 or 2 is performed, the terminal connected to or residing on the faulty IAB node and the MT part of the downstream IAB node may be turned into an idle mode.

[0167] In the case of option 3, the terminal connected to the failed IAB node or residing on the failed IAB node and the MT part of the downstream IAB node can perform the RRC re-establishment process in the connected state. If a failure occurs during the re-establishment process of the MT part of the failed IAB node before the timer expires, the methods of options 1, 2 and 3 can also be initiated.

[0168] Failures that may occur during the re-establishment process may include the following: a predefined timer expires during a cell selection operation (e.g., T311 expires); cell selection is successful, a random access preamble is transmitted to the target cell, and then a RACH failure occurs without receiving an RAR within a predefined time window; and an RRC re-establishment request is issued, and then no re-establishment message or setup message is received from the target cell until a predefined timer expires, or the target cell becomes unsuitable before a defined timer expires (e.g., T301 expires).

[0169] As another example, if the MT begins to fail, the methods of 1k-100, 1k-105, and 1k-110 may be performed immediately without the IAB suspension process.

[0170] As another embodiment, if a failure (e.g., RLF) occurs in the MT, the methods of 1k-100, 1k-105, and 1k-110 may deliver different information depending on the state of the recovery process. The failure may refer to the RLF of the backhaul link between the MT and the parent IAB node, or the RLF notification is received from the parent IAB node of the MT. If a failure occurs in the MT, or a recovery related to the failure (or a reconstruction operation, a search for different cells, or the initiation of re-access (including random access) to the same or different cells), the IAB node of the MT that has failed, or the DU, may deliver an indication of the occurrence of the failure to the downstream IAB node and the access UE accessing it. The indication may include an indication that recovery is in progress. As a method for transmitting an indication of the occurrence of a failure, it may be transmitted via a system information block including SIB1, or one of the methods of 1k-100, 1k-105, and 1k-110 may be used.

[0171] In addition, if the MT succeeds in performing recovery, an indication of recovery success may be similarly delivered to the downstream IAB node and the access UE. As used herein, recovery may mean a successful reestablishment operation, or may refer to re-access (including random access) or switching to a different or the same cell. As a method for delivering an indication of recovery success in this case, it may be transmitted through a system information block including SIB1, or one of 1k-100, 1k-105, and 1k-110 may be used.

[0172] In addition, if the MT fails while performing recovery, a failure indicator may be delivered to a downstream IAB node and an access UE. As a method for delivering the failure indicator, it may be transmitted through a system information block including SIB1, or one of 1k-100, 1k-105, and 1k-110 may be used.

[0173] After receiving the above multiple pieces of information, the IAB node may stop the operation of sending data to / receiving data from the faulty IAB node, or may perform an operation of storing it in its buffer. Alternatively, the IAB node may send / receive data while maintaining the connection. In addition, the IAB node may perform an operation of searching for and selecting another IAB node. The IAB node may perform an operation of evaluating whether the cell found as a result of the cell search is a cell in which the IAB node capability exists or a suitable cell in the existing operation. In addition, in the previous embodiment, the DU of the corresponding IAB node may perform an IAB suspension operation. If the MT of the fault indicates a recovery failure, and if the downstream IAB node receives the indication, the MT of the downstream IAB node may be disconnected from the IAB node of the faulty MT, and may be connected to a newly selected cell, or an RRC reconstruction operation may be performed.

[0174] Figure 1J The operation according to another embodiment is shown when an IAB node fails, a timer is started, the MT part of the failed node performs a reestablishment operation, and receives an RRC setting before the timer expires. If there is no UE context of the MT part in the target cell, and if it falls back to the RRC setting, it is also regarded as a successful recovery, and the timer is stopped. When the timer is operating, the following is performed Fig. 1I The IAB shown in FIG. 10A suspends operation. The MT portion 1j-1 of a terminal receiving service from the failed IAB node or a downstream IAB node receiving service from the failed IAB node may remain connected to the failed IAB node 1j-5 or may be in a camping state (1j-3) while remaining idle or inactive. The MT portion 1j-10 of the IAB node remains connected to the serving cell (1j-30). The serving cell may be Figure 1HThe cell served by the IAB node 2 in the IAB node. The MT part of the IAB node can configure the timer value through dedicated signaling in the connected state (1j-35), or can receive the configuration through system information (1j-25). The MT component in the connected state may fail (1j-40). Although the radio link failure is taken as an example in this specification, all examples of failures in the normal RRC process, such as switching failures, reconfiguration failures and integrity check failures, can be applied. If a failure occurs, the MT operates a predetermined timer (1j-45). During this process, fault indication signaling may exist between the MT part and the base station part of the faulty IAB node (1j-90). If a failure occurs, the MT operates the timer and performs the RRF connection reconstruction operation at the same time. If the reconstruction operation ends successfully before the timer expires, the MT stops the timer (1j-75). During this process, the MT can send a recovery indication to the DU part or the base station part of the IAB node (1j-95). The RRC re-establishment operation may include cell selection (1j-50), a process of random access to the selected cell (1j-20) (1j-55), sending an RRC re-establishment request message (1j-60) to the target cell 1j-20 of the MT, receiving an RRC setup message (1j-65), and sending an RRC setup completion message (1j-70). As a condition for stopping the timer, the reception of the RRC setup message by the MT (1j-65) may be considered. In addition, after receiving the message, the sending of the RRC setup completion message (1j-70) may also be regarded as a condition for stopping the timer. When the timer operates in this manner, the DU part of the faulty IAB node or the faulty IAB node connected to the MT may not allow other connections from the terminal, or may perform operations to prevent a terminal in an inactive or idle mode from residing through cell (re)selection. If the timer is started (1j-45), an indication may be sent to a master information block (MIB), which is sent to the SSB to indicate that the cell is prohibited (1j-80). Alternatively or / and the prohibition factors may be configured with respect to the access categories of all terminals, the access prohibition factor values ​​among these factors may become zero with respect to all access categories and access identifications, and the changed system information may be sent. The failed IAB node continues to operate 1j-80 and 1j-85 until the re-establishment is successful and the timer is therefore stopped. If the timer stops after successful re-establishment (1j-75), the SSB and MIB transmissions may be rolled back so that the content is transmitted before the timer operation (1j-100). Similarly, instead of sending the system information after configuring the prohibition factor to zero, the system information may be sent after the prohibition factor is configured to the value before the timer is started (1j-105).

[0175] Figure 1KA situation is shown in which a timer is started and then expires before the reestablishment operation is successfully completed. A terminal receiving service from a failed IAB node, or an MT portion 1k-1 of a downstream IAB node receiving service from a failed IAB node, may remain connected to the failed IAB node 1k-5, or reside while remaining in an idle or inactive state (1k-3). The MT portion 1k-10 of the IAB node remains connected to the serving cell (1k-30). The serving cell may be Figure 1HThe cell served by the IAB node 2 in the IAB node. The MT part of the IAB node can receive the configuration of the timer value from the serving cell through dedicated signaling in the connected state (1k-35), or can receive the configuration through system information (1k-25). The MT component in the connected state may fail (1k-40). Although the radio link failure is taken as an example in this specification, all examples of failures in the normal RRC process, such as switching failures, reconfiguration failures and integrity check failures, can be applied. If a failure occurs, the MT operates a predetermined timer (1k-45). In this process, fault indication signaling can exist between the MT part and the base station part of the faulty IAB node (1k-90). If a failure occurs, the MT operates the timer and performs an RRF connection reconstruction operation at the same time. The RRC reconstruction operation may include, in sequence, cell selection (1k-50), a random access process (1k-55) to the selected cell (1k-20), sending an RRC reconstruction request message to the target cell 1k-20 of the MT, receiving an RRC setup / reconstruction message, and sending an RRC setup or reconstruction completion message. If the timer expires (1k-75) when the MT part of the faulty node and the target cell perform a reconstruction operation, the DU part of the faulty node or the faulty IAB node 1k-5 performs at least one of the following three operations. As RRC dedicated signaling, a message (1k-100) that the RRC releases the downstream IAB nodes of each terminal in a connected state can be transmitted. Alternatively, the RRC release mark can be inserted into a system information block, a MIB, or a synchronization signal block (SSB) and then sent (1k-105). This can be a one-bit indicator using a Boolean value. As another method, the transmission of a reference signal for radio link monitoring (RLM) can be stopped (1k-110). This method eliminates the basic existence of the cell and is therefore referred to as IAB disabling. The reference signal can be an SSB for RLM-RS and / or an SSB or CSI-RS for cell quality measurement, regardless of CIS-RS or RLM-RS. In addition, the transmission of system information can be stopped, or the transmission of DMRS can be stopped. If the method of option 1 or 2 is performed, the terminal connected to the faulty IAB node or residing on the faulty IAB node and the MT part of the downstream IAB node can be transformed into an idle mode. In the case of option 3, the terminal connected to the faulty IAB node or residing on the faulty IAB node and the MT part of the downstream IAB node can perform the RRC reestablishment process in the connected state. If a failure occurs during the reestablishment process of the MT part of the faulty IAB node before the timer expires, the methods of options 1, 2 and 3 can also be initiated.Failures that may occur during the re-establishment process may include the following: a predefined timer expires during a cell selection operation (e.g., T311 expires); cell selection is successful, a random access preamble is transmitted to the target cell, a RACH failure occurs without receiving an RAR within a predefined time window; and an RRC re-establishment request is issued, and then no re-establishment message or setup message is received from the target cell until a predefined timer expires, or the target cell becomes unsuitable before a defined timer expires (e.g., T301 expires).

[0176] If the timer 1k-45 starts and then expires (1k-75), or if a failure occurs during the reestablishment process before the timer expires, the MT part of the failed IAB node transitions to idle mode (1k-115)).

[0177] If the timer has been started and has not expired, the DU part of the faulty IAB node connected to the MT or the faulty IAB node may not allow other connections from the terminal, or may perform operations to prevent terminals in inactive or idle mode from residing through cell (re)selection. If the timer is started (1k-45), an indication may be sent to the master information block (MIB), which is sent to the SSB to indicate that the cell is prohibited (1k-80). Or / and the prohibition factor may be configured with respect to the access categories of all terminals, the access prohibition factor value among these factors may become zero with respect to all access categories and access identifications, and the changed system information may be sent. The faulty IAB node continues to operate 1k-80 and 1k-85 until the timer expires before the reestablishment is successful.

[0178] Figure 1L 11-15 is a diagram showing the operation of a terminal (particularly the MT part of a faulty IAB node). The terminal performs data transmission / reception with an upstream IAB node in a normal connection state (11-5). In this case, the terminal can receive a value related to a timer for operating IAB disabling from a serving cell (11-10). At a time point after the configuration value D1, a terminal fails (11-15). If a failure occurs, the timer is first started, the terminal performs an RRC connection reconstruction operation, and notifies the IABDU part or IAB node therein of an IAB suspension operation (11-20). If a failure occurs during the reconstruction operation, or the timer expires (11-25), the terminal causes the DU part or IAB node to perform an IAB disabling operation (11-30). If no failure occurs during the reconstruction operation, and if recovery is successful before the timer expires, a normal data transmission / reception operation is performed with the new target cell (11-5).

[0179] Figure 1MIt is a diagram showing the operation of a terminal or downstream IAB node connected to a faulty IAB node or a DU part of a faulty IAB node or resident thereon. The term "terminal" will be used in a broad manner in this article. A terminal in connection mode performs normal data transmission / reception with a serving cell (i.e., the DU part of an IAB node), or a terminal in idle / inactive mode resides on a corresponding serving cell (1m-5). If the MT part of the serving cell (i.e., the MT part of an IAB node) fails, the MT causes IAB to suspend. As a result, a terminal in a previous connection mode cannot establish an additional RRC connection, and a terminal in idle / inactive mode cannot perform cell selection / reselection to reside on the corresponding cell (1m-10). Thereafter, if the disable timer expires in the MT part, or if the RRC reconstruction performed on the MT part fails in the middle, the RRC release information is inserted into a dedicated message or system information through the cell performed by the DU part of the corresponding faulty IAB node, and is delivered to the terminal or downstream IAB node within the coverage of the cell performed by the corresponding DU part. Alternatively, the DU part of the failed IAB node stops transmitting the RS of the RLM of the cell performed by it. After receiving the IAB node disable operation, in the case of option 1 or 2, the connected terminal and the MT part of the IAB node transition to idle mode, or perform an RRC re-establishment operation in the case of option 3 (1m-30).

[0180] In addition to the MAC and RRC layer messages, the Backhaul Adaptation Protocol (BAP) layer may play a similar role.

[0181] If the MT claims RLF in the link with the parent IAB node, the MT may send a signal about the RLF that occurred to the DU. After receiving the signal, the DU may send an RLF occurrence indication to its child IAB node through BAP layer signaling. After receiving the RLF occurrence indication, the child IAB node may buffer the UL data for the parent IAB node that sent the RLF occurrence indication, and may suspend data transmission / reception with the parent IAB node.

[0182] Similarly, if the MT performs a recovery operation after RLF occurs in the link with the parent IAB node and successfully completes the operation, the MT can notify the DU of the recovery success. The DU can deliver the RLF recovery success indication to the node previously notified of the occurrence of RLF among its child IAB nodes, or to all child nodes through BAP layer signaling. If data transmission / reception with the parent IAB node to which the indication was previously sent has been suspended, the child IAB node that receives the RLF recovery indication can resume data transmission / reception.

[0183] If the MT performs a recovery operation and fails after RLF occurs in the link with the parent IAB node, the MT can notify the DU of the recovery failure. The DU can deliver the recovery failure indication to the node previously notified of the occurrence of RLF among its child IAB nodes, or to all child nodes through BAP layer signaling. If the child IAB node receiving the indication has a link connected to another parent IAB node, it can perform a path switch to the corresponding link. If there is no other link, the recovery failure indication can be delivered to its child IAP node again through BAP layer signaling.

[0184] The content of the BAP layer control packet used for BAP layer signaling (or control information delivered to the BAP layer) may include at least one of the following: RLF occurrence, RLF recovery success, (sending or DL) BPA identifier or (sending, egress or DL) BPA address of the MT or IAB node where RLF recovery has failed, and (or) the (receiving, ingress or UL) BAP identifier or BAP address of the receiving child IAB node. In addition, the content may include indications corresponding to RLF, recovery success, and recovery failure.

[0185] If the MT fails in RLF recovery, the MT may deliver an indication to the child node through BAP layer signaling, and the DU of the IAB node to which the MT belongs may be powered off, a message may be sent to the terminal accessing it to perform RRC connection reconstruction, or a message requesting RRC release may be sent. The message may be an RRC dedicated message or SIB, or may be a NAC CE. After receiving the message, the terminal may perform an RRC reconstruction operation or enter an idle mode.

[0186] If the child node has received the above three indications from the parent node in the existing MAC layer, the child node can notify its BAP layer of RLF occurrence, recovery success or failure. If the BAP has received a recovery failure indication, the BAP can delete the entry passing through the faulty IAB node from the routing table of the BAP layer for processing the UL business maintained by the BAP.

[0187] Hereinafter, the operating principle of the present disclosure will be described in detail with reference to the accompanying drawings. When describing the present disclosure below, when it is determined that the detailed description of the relevant known configuration or function incorporated herein may unnecessarily obscure the subject matter of the present disclosure, its detailed description will be omitted. The terms to be described below are defined in consideration of the functions in the present disclosure, and may be different depending on the user, the user's intention or habit. Therefore, the definition of the terms should be based on the content of the entire specification.

[0188] In the following description, the terms used to identify access nodes, the terms referring to network entities, the terms referring to messages, the terms referring to interfaces between network entities, and the terms referring to various identification information are for the convenience of description. Therefore, the present disclosure is not limited to the terms described below, and other terms may also be used to refer to objects with the same technical meaning.

[0189] Hereinafter, for ease of description, the present disclosure will use terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard. However, the present disclosure is not limited to the above terms and names, and is also applicable to systems complying with other standards.

[0190] refer to Figure 2A As shown, the wireless access network of the LTE system may include evolved Node Bs (hereinafter, referred to as eNBs, Node Bs or base stations) 2a-05, 2a-10, 2a-15 and 2a-20, a mobility management entity (MME) 2a-25 and a serving gateway (S-GW) 2a-30. User equipment (hereinafter, referred to as UE or terminal) 2a-35 may access an external network through eNBs 2a-05 to 2a-20 and S-GW 2a-30.

[0191] exist Figure 2A In the LTE system, eNB 2a-05 to 2a-20 can correspond to the existing Node B of the UMTS system. The eNB can be connected to the UE 2a-35 through a wireless channel and can perform more complex functions than the existing Node B. In the LTE system, all user services, including real-time services such as voice over IP (VoIP) over the Internet Protocol, can be provided through a shared channel. Therefore, equipment is required for collecting status information (such as UE buffer status, available transmission power status, and channel status) and then scheduling it, and eNB 2a-05 to 2a-20 can be responsible for it. A single eNB can usually control multiple cells. For example, in order to achieve a transmission rate of 100Mbps, the LTE system can use orthogonal frequency division multiplexing (OFDM) as a wireless access technology, for example, in a bandwidth of 20MHz. An adaptive modulation and coding (AMC) scheme can also be applied, which determines the modulation scheme and channel coding rate according to the channel state of the terminal. S-GW 2a-30 is a device configured to provide data bearers, and can generate or remove data bearers under the control of MME 2a-25. The MME is a device that processes not only a mobility management function related to a terminal but also various control functions, and can be connected to a plurality of base stations.

[0192] Figure 2B This is a diagram showing a radio protocol structure of a conventional LTE system.

[0193] refer to Figure 2B , the radio protocols of the LTE system may include Packet Data Convergence Protocol (PDCP) 2b-05 and 2b-40, Radio Link Control (RLC) 2b-10 and 2b-35, and Medium Access Control (MAC) 2b-15 and 2b-30 located at the terminal side and the eNB side, respectively. PDCP may be responsible for operations such as IP header compression / recovery. The main functions of PDCP can be summarized as follows:

[0194] -Header compression and decompression: ROHC only

[0195] -Transmission of user data

[0196] - In-sequence delivery of upper layer PDUs during PDCP re-establishment of RLC AM

[0197] - For split bearers in DC (supports RLC AM only): PDCP PDU routing for transmission and PDCP PDU reordering for reception

[0198] - Repeated detection of lower layer SDUs during PDCP re-establishment of RLC AM

[0199] - For split bearers in DC, retransmit PDCP SDUs at handover, and for RLC AM, retransmit PDCP PDUs during PDCP data recovery

[0200] -Encryption and decryption

[0201] - Timer based SDU discard in uplink.

[0202] Radio Link Control (RLC) 2b-10 and 2b-35 can perform operations such as reconfiguring PDCP packet data units (PDUs) to an appropriate size and performing ARQ operations. The main functions of RLC can be summarized as follows:

[0203] -Transmission of upper layer PDU

[0204] - Error correction via ARQ (for AM data transmission only)

[0205] -RLC SDU concatenation, segmentation and reassembly (only for UM and AM data transmission)

[0206] - Re-segmentation of RLC data PDU (only for AM data transmission)

[0207] - Reordering of RLC data PDUs (only for UM and AM data transmission)

[0208] - Duplicate detection (for UM and AM data transmission only)

[0209] -Protocol error detection (for AM data transmission only)

[0210] -RLC SDU discard (only for UM and AM data transmission)

[0211] -RLC reconstruction.

[0212] MAC 2b-15 and 2b-30 can be connected to multiple RLC layer devices configured in a single terminal, and can perform operations of multiplexing RLC PDU into MAC PDU and demultiplexing RLC PDU from MAC PDU. The main functions of MAC can be summarized as follows:

[0213] - Mapping between logical channels and delivery channels

[0214] - Multiplexing MAC SDUs belonging to one or different logical channels into a transport block (TB) delivered to the physical layer on a transport channel, or demultiplexing MAC SDUs belonging to one or different logical channels from a transport block (TB) delivered from the physical layer on a transport channel

[0215] -Dispatch information report

[0216] - Error correction through HARQ

[0217] - Priority handling between logical channels of a UE

[0218] - Priority handling between UEs through dynamic scheduling

[0219] -MBMS service identification

[0220] -Transmission format selection

[0221] -filling.

[0222] The physical layers 2b-20 and 2b-25 may perform the following operations: channel-encode and modulate the upper layer data, generate OFDM symbols therefrom and transmit them through a wireless channel, or demodulate OFDM symbols received through a wireless channel, channel-decode them and then transmit them to an upper layer.

[0223] Figure 2C is a diagram showing the structure of a new radio mobile communication system.

[0224] refer to Figure 2C, the radio access network of the new radio (hereinafter referred to as NR or 2g) mobile communication system may include a new radio node B (hereinafter referred to as NR gNB or NR base station) 2c-10 and a new radio core network (NR CN) 2c-05. The new radio user equipment (NR UE or terminal) can access the external network through the NR gNB2c-10 and the NR CN 2c-05.

[0225] exist Figure 2C In the NR mobile communication system, the NR gNB 2c-10 can correspond to the evolved Node B (eNB) of the existing LTE system. The NR gNB can be connected to the NR UE 2c-15 through a wireless channel and can provide better services than the existing Node B. In the NR mobile communication system, all user services can be provided through a shared channel. Therefore, equipment is required for collecting status information (for example, UE buffer status, available transmission power status, and channel status) and then scheduling it, and the NR NB 2c-10 can be responsible for it. A single NR gNB can control multiple cells. In the NR mobile communication system, in order to achieve ultra-high-speed data transmission compared with the current LTE, a bandwidth equal to or greater than the current maximum bandwidth can be applied. In addition, orthogonal frequency division multiplexing (OFDM) can be used as a wireless access technology, and beamforming technology can be combined with it in addition. It is also possible to apply an adaptive modulation and coding (AMC) scheme, which determines the modulation scheme and channel coding rate according to the channel state of the terminal. NR CN2c-05 can perform functions such as mobility support, bearer configuration, and QoS configuration. NR CN is a device that not only handles the mobility management function related to the terminal but also handles various control functions, and can be connected to multiple base stations. In addition, the NR mobile communication system can interoperate with the existing LTE system, and the NR CN can be connected to the MME 2c-25 through the network interface. The MME can be connected to the eNB 2c-30 (existing base station).

[0226] Figure 2D 2 is a diagram showing a wireless protocol structure of an NR mobile communication system to which the present disclosure can be applied.

[0227] refer to Figure 2D The wireless protocols of the NR mobile communication system include NR Service Data Adaptation Protocol (SDAP) 2d-01 and 2d-45, NR PDCP 2d-05 and 2d-40, NR RLC 2d-10 and 2d-35, and NRMAC 2d-15 and 2d-30, which are located on the terminal side and the NR base station side respectively.

[0228] The main functions of NR SDAP 2d-01 and 2d-45 may include some of the following functions:

[0229] -Transmission of user plane data

[0230] - Mapping between QoS flows and DRBs for both DL and UL

[0231] - Marking of QoS Flow ID in both DL and UL packets

[0232] - Mapping of Reflective QoS Flow to DRB for UL SDAP PDU.

[0233] Regarding the SDAP layer device, the terminal can use a radio resource control (RRC) message to receive configuration about whether to use the header of the SDAP layer device or the function of the SDAP layer device for each PDCP layer device, for each bearer or for each logical channel. If the SDAP header is configured, the terminal can indicate by using a one-bit indicator (NAS reflects QoS) of the non-access stratum (NAS) quality of service (QoS) reflecting the SDAP header and a one-bit indicator (AS reflects QoS) reflecting the access stratum (AS) QoS, so that the terminal can update or reconfigure the mapping information related to the data bearer and the QoS flow of the uplink and downlink. The SDAP header may include information of the QoS flow ID indicating the QoS. The QoS information can be used as data processing priority, scheduling information, etc. for supporting effective services.

[0234] The main functions of NR PDCP 2d-05 and 2d-40 may include some of the following functions:

[0235] -Header compression and decompression: ROHC only

[0236] -Transmission of user data

[0237] - In-sequence delivery of upper layer PDUs

[0238] - Out-of-order delivery of upper layer PDUs

[0239] -PDCP PDU reordering for reception

[0240] - Duplicate detection of lower layer SDU

[0241] -Retransmission of PDCP SDU

[0242] -Encryption and decryption

[0243] - Timer based SDU discard in uplink.

[0244] In the above description, the reordering function of the NR PDCP device may refer to a function of reordering the PDCP PDU received from the lower layer based on the PDCP sequence number (SN). The reordering function of the NR PDCP device may include a function of delivering data to the upper layer in a reordered order, or may include a function of directly delivering data without considering the order. The reordering function of the NR PDCP device may include: a function of recording the lost PDCP PDU as a result of the reordering, a function of reporting the status of the lost PDCP PDU to the transmitting side, and a function of requesting retransmission of the lost PDCP PDU.

[0245] The main functions of NR RLC 2d-10 and 2d-35 may include some of the following functions:

[0246] -Transmission of upper layer PDU

[0247] - In-sequence delivery of upper layer PDUs

[0248] - Out-of-order delivery of upper layer PDUs

[0249] - Error correction via ARQ

[0250] - Concatenation, segmentation and reassembly of RLC SDU

[0251] - Re-segmentation of RLC data PDUs

[0252] - Reordering of RLC data PDUs

[0253] - Duplicate detection

[0254] -Protocol error detection

[0255] -RLC SDU discarded

[0256] -RLC reconstruction.

[0257] In the above description, the in-sequence delivery function of the NR RLC device may refer to a function of delivering the RLC SDU received from the lower layer to the upper layer in sequence. If a single RLC SDU has been segmented into multiple RLC SDUs and then received, the in-sequence delivery function of the NR RLC device may refer to a function of reassembling and delivering them.

[0258] The in-sequence delivery function of the NR RLC device may refer to: a function of reordering the received RLC PDU with reference to the RLC sequence number (SN) or the PDCP SN, a function of recording the lost RLC PDU as a result of the reordering, a function of reporting the status of the lost PDCP PDU to the transmitting side, and a function of requesting retransmission of the lost PDCP PDU.

[0259] The in-sequence delivery function of the NR RLC device may include: if there is a lost RLC SDU, only the RLC SDU before the lost RLC SDU is delivered to the upper layer in sequence.

[0260] The in-sequence delivery function of the NR RLC device may include: if there is a lost RLC SDU, but if a predetermined timer expires, the function of delivering all RLC SDUs received before the timer starts to the upper layer in sequence.

[0261] The in-sequence delivery function of the NR RLC device may include the function of delivering all currently received RLC SDUs to the upper layer in sequence if there are lost RLC SDUs but if a predetermined timer expires.

[0262] The NR RLC device may process the RLC PDUs in the order received, regardless of the order of the sequence numbers (out-of-order delivery), and may deliver them to the NR PDCP device.

[0263] If segments are received, the NR RLC device may receive the segments stored in the buffer or the segments to be received later, may reconfigure them into a single complete RLC PDU, and may then deliver it to the NR PDCP device.

[0264] The NR RLC layer may not include the cascading function, which may be performed by the NR MAC layer or may be replaced by the multiplexing function of the NR MAC layer.

[0265] In the above description, the out-of-order delivery function of the NR RLC device may refer to a function of directly delivering the RLC SDU received from the lower layer to the upper layer without considering the order. The out-of-order delivery function of the NR RLC device may refer to a function of reassembling and delivering a single RLC SDU if it has been segmented into multiple RLC SDUs and then received. The out-of-order delivery function of the NR RLC device may include a function of storing the RLC SN or PDCP SN of the received RLC PDU and recording the lost PDCP PDU as a result of reordering.

[0266] NR MAC 2d-15 and 2d-30 can be connected to multiple NR RLC layer devices configured in a single terminal, and the main functions of NR MAC can include some of the following functions:

[0267] - Mapping between logical channels and transport channels

[0268] -Multiplexing / demultiplexing of MAC SDU

[0269] -Dispatch information report

[0270] - Error correction through HARQ

[0271] - Priority handling between logical channels of a UE

[0272] - Priority handling between UEs through dynamic scheduling

[0273] -MBMS service identification

[0274] -Transmission format selection

[0275] -filling.

[0276] The NR PHY layers 2d-20 and 2d-25 may perform the following operations: channel coding and modulating the upper layer data, generating OFDM symbols therefrom and transmitting them through a wireless channel, or demodulating the OFDM symbols received through a wireless channel, channel decoding them and then passing them to the upper layer.

[0277] Figure 2E is a block diagram showing an internal structure of a terminal to which the present disclosure is applied.

[0278] Referring to the figure, the terminal includes a radio frequency (RF) processing unit 2e-10, a baseband processing unit 2e-20, a storage unit 2e-30 and a control unit 2e-40.

[0279] The RF processing unit 2e-10 performs functions for sending / receiving signals through wireless channels, such as frequency band conversion of signals and amplification thereof. That is, the RF processing unit 2e-10 up-converts the baseband signal provided by the baseband processing unit 2e-20 into an RF band signal, transmits it through an antenna, and down-converts the RF band signal received by the antenna into a baseband signal. For example, the RF processing unit 2e-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Although only one antenna is shown in the figure, the terminal may include multiple antennas. In addition, the RF processing unit 2e-10 may include multiple RF chains. In addition, the RF processing unit 2e-10 may perform beamforming. In order to perform beamforming, the RF processing unit 2e-10 may adjust the phase and amplitude of the corresponding signal sent / received by multiple antennas or antenna elements. In addition, the RF processing unit may perform MIMO, and may receive multiple layers when performing MIMO operations.

[0280] The baseband processing unit 2e-20 performs the function of converting between the baseband signal and the bit string according to the physical layer specification of the system. For example, during data transmission, the baseband processing unit 2e-20 encodes and modulates the transmission bit string to generate complex symbols. In addition, during data reception, the baseband processing unit 2e-20 demodulates and decodes the baseband signal provided from the RF processing unit 2e-10 to restore the received bit string. For example, when following the orthogonal frequency division multiplexing (OFDM) scheme, the baseband processing unit 2e-20 encodes and modulates the transmission bit string during data transmission to generate complex symbols and maps the complex symbols to subcarriers, and configures OFDM symbols through inverse fast Fourier transform (IFFT) and cyclic prefix (CP) insertion. In addition, during data reception, the baseband processing unit 2e-20 divides the baseband signal received from the RF processing unit 2e-10 for each OFDM symbol, recovers the signal mapped to the subcarrier through fast Fourier transform (FFT), and recovers the received bit string through demodulation and decoding.

[0281] As described above, the baseband processing unit 2e-20 and the RF processing unit 2e-10 send and receive signals. Therefore, the baseband processing unit 2e-20 and the RF processing unit 2e-10 can be referred to as a sending unit, a receiving unit, a sending or receiving unit or a communication unit. In addition, at least one of the baseband processing unit 2e-20 and the RF processing unit 2e-10 may include a plurality of communication modules to support different multiple wireless access technologies. In addition, at least one of the baseband processing unit 2e-20 and the RF processing unit 2e-10 may include different communication modules to process signals in different frequency bands. For example, different wireless access technologies may include wireless LAN (e.g., IEEE 802.11), cellular networks (e.g., LTE), etc. In addition, different frequency bands may include ultra-high frequency (SHF) (e.g., 2.NRHz, NRHz) bands and millimeter wave (e.g., 60GHz) bands.

[0282] The storage unit 2e-30 stores data for the operation of the terminal, such as basic programs, applications, and configuration information. In particular, the storage unit 2e-30 can store information about a second access node that performs wireless communication by using a second wireless access technology. In addition, the storage unit 2e-30 provides the stored data at the request of the control unit 2e-40.

[0283] The control unit 2e-40 controls the overall operation of the terminal. For example, the control unit 2e-40 sends / receives signals through the baseband processing unit 2e-20 and the RF processing unit 2e-10. In addition, the control unit 2e-40 records and reads data in the storage unit 2e-40. To this end, the control unit 2e-40 may include at least one processor. For example, the control unit 2e-40 may include a communication processor (CP) configured to perform control communication and an application processor (AP) configured to control an upper layer (such as an application).

[0284] Figure 2F is a block diagram showing the configuration of an NR base station according to the present disclosure.

[0285] As shown in the figure, the base station includes an RF processing unit 2f-10, a baseband processing unit 2f-20, a backhaul communication unit 2f-30, a storage unit 2f-40 and a control unit 2f-50.

[0286] The RF processing unit 2f-10 performs functions for sending / receiving signals through a wireless channel, such as frequency band conversion of signals and amplification thereof. That is, the RF processing unit 2f-10 up-converts the baseband signal provided by the baseband processing unit 2f-20 into an RF band signal, transmits it through an antenna, and down-converts the RF band signal received by the antenna into a baseband signal. For example, the RF processing unit 2f-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is shown in the figure, the first access node may include multiple antennas. In addition, the RF processing unit 2f-10 may include multiple RF chains. In addition, the RF processing unit 2f-10 may perform beamforming. In order to perform beamforming, the RF processing unit 2f-10 may adjust the phase and amplitude of the corresponding signals sent / received through multiple antennas or antenna elements. The RF processing unit may perform downlink MIMO operations by sending at least one layer.

[0287] The baseband processing unit 2f-20 performs the function of converting between the baseband signal and the bit string according to the physical layer specification of the first wireless access technology. For example, during data transmission, the baseband processing unit 2f-20 encodes and modulates the transmission bit string to generate a complex symbol. In addition, during data reception, the baseband processing unit 2f-20 demodulates and decodes the baseband signal provided from the RF processing unit 2f-10 to recover the received bit string. For example, when following the OFDM scheme, the baseband processing unit 2f-20 encodes and modulates the transmission bit string during data transmission to generate a complex symbol and maps the complex symbol to a subcarrier, and configures the OFDM symbol through IFFT operation and CP insertion. In addition, during data reception, the baseband processing unit 2f-20 divides the baseband signal received from the RF processing unit 2f-10 for each OFDM symbol, recovers the signal mapped to the subcarrier through FFT operation, and recovers the received bit string through demodulation and decoding. As described above, the baseband processing unit 2f-20 and the RF processing unit 2f-10 transmit and receive signals. Therefore, the baseband processing unit 2f-20 and the RF processing unit 2f-10 can be referred to as a transmitting unit, a receiving unit, a transmitting / receiving unit, a communication unit, or a wireless communication unit.

[0288] The backhaul communication unit 2f-30 provides an interface for communicating with other nodes within the network. That is, the backhaul communication unit 2f-30 converts a bit string sent from the main base station to other nodes (e.g., an auxiliary base station or a core network) into a physical signal, and converts a physical signal received from other nodes into a bit string.

[0289] The storage unit 2f-40 stores data used for the operation of the main base station, such as basic programs, applications, and configuration information. In particular, the storage unit 2f-40 can store information about the bearer assigned to the accessed terminal, the measurement results reported from the accessed terminal, etc. In addition, the storage unit 2f-40 can store information used as a reference for determining whether to provide multiple connections to the terminal or to terminate them. In addition, the storage unit 2f-40 provides the stored data at the request of the control unit 2f-50.

[0290] The control unit 2f-50 controls the overall operation of the main base station. For example, the control unit 2f-50 sends / receives signals through the baseband processing unit 2f-20 and the RF processing unit 2f-10, or through the backhaul communication unit 2f-30. In addition, the control unit 2f-50 records and reads data in the storage unit 2f-40. To this end, the control unit 2f-50 may include at least one processor.

[0291] Figure 2G2g-1 represents an IAB donor node that performs wired communication with a core network 2g-5. The IAB donor node includes a centralized unit (CU) 2g-10 and a plurality of distributed units (DU) 2g-15. Among them, the CU includes a control plane (CP) and a user plane (UP). The CP exchanges control signals required for data transmission / reception and connection between the IAB donor node and the DU of the downstream IAB node. The DU receives the control signal from the CU and performs data transmission / reception with the terminal. Other IAB nodes other than the IAB donor node have at least one wireless connection established with the CN, and each IAB node 2g-20 may have a terminal 2g-25 from which it receives services and a downstream IAB node 2g-30 from which it receives services. There is a wireless backhaul link 2g-35 between the IAB nodes, and a wireless access link 2g-40 between the IAB node and the terminal. The wireless backhaul and the wireless access link may use the same frequency resources or separate frequency resources.

[0292] Figure 2H An exemplary topology for describing the present disclosure is shown. It is assumed that the terminal user UE12h-1 can send / receive data through a single data path. Alternatively, even if data can be sent / received by using multiple paths, the method according to the present disclosure is applicable to the case where a path switching accompanied by RRC information is required between multiple paths. It is assumed that the data path has been configured by IAB 2 in this example, and a radio link failure has occurred between the mobile terminal (MT) of IAB node 2 and the mobile terminal of IAB node 1. Under normal circumstances, if RLF occurs, the terminal performs an RRC reconstruction operation. When performing this operation, the terminal performs cell selection, re-accesses the selected cell, receives a connection reconstruction message from the core network, and transmits "Complete" in response to the message. In this case, it is impossible to know how long the cell selection will take, and if a new cell is accessed and if the corresponding cell has no terminal context, the cell may become idle.

[0293] <delivered redirect information>

[0294] The redirection information delivered to the terminal can be as follows:

[0295] A physical cell ID (PCI) of a cell provided by a downstream IAB node connected to the same IAB donor node as the currently connected or before connection failure, or by the DU part of the downstream IAB node; NR-specific cell global identity (NCGI); gNB ID; DU ID; or a combination thereof. As lower layer information of NCGI, the following items may be considered: PLMN ID information that the corresponding cell can support, ARFCN information related to the transmission synchronization signal and PBCH block (SSB) used for measurement purposes of the corresponding cell as frequency information, subcarrier spacing used when SSB is transmitted, SSB measurement time configuration (SMTC) information, or GSCN value.

[0296] As another embodiment, not only the information related to the cells provided by the downstream IAB node connected to the same IAB donor node or by the DU part of the downstream IAB node as mentioned above, but also the information related to the limited cells among them can be delivered. For example, it is possible to selectively deliver only the information related to the cells of the IAB node belonging to the serving DU geographically close to the terminal, where the redirection information is delivered to the terminal or the serving IAB node. In this case, the above-mentioned cell-related information can also be delivered.

[0297] In another embodiment, if each IAB node experiences a node failure including a backhaul failure, and the downstream IAB node performs a recovery operation (or performs the following operations: performs reconstruction, searches for another cell, or performs re-access (including random access) to the same or different cell), each IAB node may deliver information related to the IAB node information that needs to be preferentially selected or information related to the cell managed by the DU of the IAB node to the downstream IAB node. The IAB node information or the information related to the cell managed by the DU may include an IAB node ID, an ID of the cell managed by the DU, or a combination of the two. The time point for delivering the information may be the time point when the connection between the IAB node and the downstream IAB node is established, or any time point thereafter. Alternatively, after the IAB node experiences a failure, the cell information may be delivered when it is included in the failure indicator.

[0298] The preferentially selected cell may not only refer to a cell of a downstream IAB node connected to the same IAB donor node, but may also refer to a cell of an IAB node that can replace a parent IAB node of an IAB node that has currently experienced a failure in terms of topology.

[0299] Alternatively, in contrast, if each IAB node experiences a node failure including a backhaul failure, and if the downstream IAB node performs a recovery operation, the IAB node may deliver information about non-selected IAB nodes or information about cells managed by the DU of the IAB node to the downstream IAB node. The information may be delivered by the IAB node to each DU through the F1 interface. Alternatively, each IAB node may deliver it to the downstream IAB node through a relay.

[0300] If the IAB node receives the information, and if a node failure including RLF occurs in the upstream IAB node, the IAB node selects one from among already given cells, or preferentially selects a given cell, and then accesses the cell. There may be no separate operation for cell selection.

[0301] In addition to the delivered cell ID information, offset information related to the signal strength to be used when the terminal selects the corresponding cell may be delivered. The terminal can verify the suitability of the cell by applying the offset value. For reference, the verification suitability meets the cell selection criteria in the latter part of this document and includes the operation of verifying the cell status (including cell barring and cell retention). In the case of cell selection, the existing criteria are as follows:

[0302] Srxlev>0 and Squal>0

[0303] in

[0304] Srxlev=Q rxlevmeas -(Q rxlevmin +Q rxlevminoffset )-P compensation -Qoffset temp

[0305] Squal=Q qualmeas -(Q qualmin +Q qualminoffset )-Qoffset temp

[0306] The definitions of each factor are as follows:

[0307] [Table 1] Cell selection factors

[0308]

[0309] The main objectives are as follows:

[0310] Srxlev>0 and Squal>0

[0311] Alternatively, in the present disclosure, the IAB offset term is added as follows:

[0312] Srxlev=Q rxlevmeas -(Q rxlevmin +Q rxlevminoffset )-P compensation -Qoffset temp +Q rxlevIABcell

[0313] Squal=Q qualmeas -(Q qualmin +Q qualminoffset )-Qoffset temp +Q qualIABcell

[0314] Among them, Q rxlevIABcell It is a cell-specific factor provided by the IAB node and is the value used when evaluating the RSRP value among the cell signal strength measurement values ​​during the cell selection operation. In addition, QqualIABcell is a cell-specific factor provided by the IAB node and is the value used when evaluating the RSRQ value among the cell signal strength measurement values ​​during the cell selection operation. These two values ​​can be given in dB or dBm and can be delivered through system information sent by the corresponding cell or through dedicated signaling. If the terminal accesses a specific IAB node, operates, performs a reconstruction operation, performs cell selection, and preferentially selects a cell belonging to the redirection information previously received by the terminal, and if the cell broadcasts an offset value as system information, the terminal applies the value and performs a suitability check. Taking into account the fact that the above-mentioned various factors are used for cell selection in specific cases, the following various suitability checks can be performed.

[0315] Regarding the objective function,

[0316] If Srxlev>0 and Squal>0 are still required, the following element formula can be applied:

[0317] Srxlev=Q rxlevmeas -Q rxlevIABcell

[0318] Squal=Q qualmeas -Q qualIABcell (Formula 1)

[0319] or

[0320] Srxlev=Q rxlevmeas -(Q rxlevmin )+Q rxlevIABcell

[0321] Squal=Q qualmeas -(Q qualmin )+Q qualIABcell (Formula 2)

[0322] or

[0323] Srxlev=Q rxlevmeas -(Q rxlevmin +Q rxlevminoffset )+Q rxlevIABcell

[0324] Squal=Q qualmeas -(Q qualmin +Q qualminoffset )+Q qualIABcell (Formula 3)

[0325] or

[0326] Srxlev=Q rxlevmeas -(Q rxlevmin +Q rxlevminoffset )-P compensation +Q rxlevIABcell

[0327] Squal=Q qualmeas -(Q qualmin +Q qualminoffset )+Q qualIABcell (Formula 4)

[0328] or

[0329] Srxlev=Q rxlevmeas -(Q rxlevmin +Q rxlevminoffset )-Q offsettemp +Q rxlevIABcell

[0330] Squal=Q qualmeas -(Q qualmin +Q qualminoffset )-Q offsettemp +Q qualIABcell (Formula 5)

[0331] or

[0332] Srxlev=Q rxlevmeas -(Q rxlevmin +Q rxlevminoffset )-P compensation -Qoffset temp +Q rxlevIABcell

[0333] Squal=Q qualmeas -(Q qualmin +Q qualminoffset )-Qoffset temp +Q qualIABcell (Formula 6)

[0334] The above formula can be the element formula for suitability testing.

[0335] Fig.2I is a diagram showing possible signaling through which redirection information is delivered. The redirection information may be delivered from the DU of the upstream IAB node to the terminal via system information or dedicated signaling. The redirection information may become an RRC release message (option 1) via dedicated signaling, or conversely may become an RRC reconfiguration message (option 2). To this end, in the CU-CP, the redirection information may be delivered to the DU of the corresponding upstream IAB node via F1-AP or F1-C signaling. For example, part or all of the redirection information may be delivered via a UE context modification request message.

[0336] Figure 2J The following situation is shown: if the redirection information is delivered to the DU of the upstream IAB node through F1-AP or F1-C signaling, the information is bypassed between the MT and the DU of the IAB node.

[0337] The operation in the case where redirection information is given will now be described.

[0338] Figure 2K The redirection operation in the case of terminal failure is shown.

[0339] The terminal 2k-5 is RRC-connected to the cell (2k-20) of the IAB node 2k-10. The terminal may receive the redirection information mentioned in the previous section through the system information 2k-25 or through the RRC dedicated message 2k-30. If a failure occurs while in the connected state, the terminal performs RRC reconstruction (2k-35) through the given redirection information. The failure condition may correspond to a failure identified at the RRC level, such as a radio link failure, an RLC failure, a reconfiguration failure, an integrity check failure, or a switching failure.

[0340] As a subordinate operation of the reconstruction operation, the terminal may initially perform cell selection (2k-40). The existing operation for cell selection is as follows: if the stored information is used, and if the cell found by using the carrier frequency information, the cell information stored due to the given measurement control, or the cell information that has been detected passes the suitability test, the cell is selected. In the present disclosure, it is assumed that the above-mentioned cell information for cell redirection has been delivered through an RRC dedicated message or an SIB and / or MIB message, and the information of the corresponding cell is stored in the terminal. Through this information, the terminal preferentially searches for the cell stored in the stored redirection information (2k-40), reads the cell selection information (2k-45) of the SIB and / or MIB of the corresponding cell 2k-15, and performs a suitability test (2k-50). If the test passes, the terminal synchronizes with the corresponding cell (2k-60) and sends an RRC connection reconstruction request (2k-60). The selected cell determines whether there is a terminal context therein. If there is a terminal context, the cell sends an RRC connection reconstruction message (2k-65). In response, the terminal sends an RRC connection reestablishment complete message (2k-70).

[0341] In step 2k-45, Q rxlevIABcell , Q qualIABcell The information may not be present in the cell selection parameters received in the system information received from the found cell 2k-15. In this case, when performing the suitability check, the terminal can perform the suitability check by evaluating the cell selection criteria using the existing factors for cell selection given in Table 1. If Q is included in the received system information in step 2k-45, rxlevIABcell , Q qualIABcell If the terminal receives the information, the terminal performs a fitness check including the information. In this case, the above formulas 1 to 6 can be used.

[0342] If the dedicated message received in step 2k-30 includes the above-mentioned cell information as redirection information and information related to the cell selection criteria of each cell, the redundant factors among the cell selection factors existing in the SIB and / or MIB 2k-45 read from the cell 2k-15 found for cell selection may be overwritten. In addition, although this information is not redundant, if the cell selection information that does not exist in the SIB and / or MIB 2k-45 exists in the dedicated message, when the terminal performs a suitability check, it is considered that the corresponding information has been given and is therefore used.

[0343] Figure 2LThe operation flow of the terminal is shown. In 21-5, the terminal receives redirection information in a connected state. Thereafter, if various RRC failure conditions occur, the terminal performs an RRC reconstruction operation. As the first subordinate operation constituting the RRC reconstruction operation, the terminal performs cell selection. In this case, one of the cells configured in the redirection information that has been received is selected. In this operation, the terminal gives priority to the cell that is always configured in the redirection information compared to the cell that is not configured. The terminal reads the SIB and / or MIB of the cell selected in this way, and performs a suitability check by using the factors required for the suitability check. If there is a Q rxlevIABcell , Q qualIABcell If the cell is determined to be suitable as a result of the suitability check, the cell is selected, and if not suitable, another cell given in the redirection information is selected and a suitability check is performed on the cell.

[0344] Figure 2M A case is shown in which redirection information is delivered via an RRC release message. The terminal that was initially in a connected state is released by a serving cell instruction, and the above-mentioned redirection information may be included in the release message. As this information, information about cells with priority during reaccess and offset information required when reselecting the corresponding cell may be given. After receiving this information, the terminal ignores the ranking information and priority information assigned to the frequency, and determines the ranking among the cells present in the redirection information according to the existing reselection scheme. That is, when performing reselection and selection operations, the terminal only considers the cells in the redirection information, and applies the following rules to inter-frequency and inter-RAT cells:

[0345] If threshServingLowQ is broadcasted in system information and more than 1 second has passed since the UE camped on the current serving cell, cell reselection shall be performed to a cell with a NR frequency or inter-RAT frequency with higher priority than the serving frequency if:

[0346] - During the time interval TreselectionRAT, the cells of the EUTRAN RAT / frequency or higher priority NR satisfy Squal>ThreshX,HighQ

[0347] Otherwise, cell reselection shall be performed for a cell on an NR frequency or inter-RAT frequency with higher priority than the serving frequency if the following conditions are met:

[0348] - During the time interval TreselectionRAT, the cell of a higher-priority NR / RAT inter-frequency satisfies Srxlev > ThreshX,HighP; and

[0349] - More than 1 second has elapsed since the UE camped on the current serving cell.

[0350] Cell reselection for cells of the same-priority NR frequencies shall be based on the ranking of intra-frequency cell reselection as defined in Subclause 5.2.4.6.

[0351] If threshServingLowQ is broadcast in the system information and more than 1 second has elapsed since the UE camped on the current serving cell, then cell reselection shall be performed on a cell of an NR frequency or an RAT inter-frequency with a lower priority than the serving frequency if the following conditions are met:

[0352] - During the time interval TreselectionRAT, the serving cell satisfies Squal < ThreshServing,LowQ, and the cell of a lower-priority NR or E-UTRAN RAT / frequency satisfies Squal > ThreshX,LowQ.

[0353] Otherwise, if the following conditions are met, cell reselection shall be performed on a cell of an NR frequency or an RAT inter-frequency with a lower priority than the serving frequency:

[0354] - During the time interval TreselectionRAT, the serving cell satisfies Srxlev < ThreshServing,LowP, and the cell of a lower-priority RAT / frequency and the cell that satisfies Srxlev > ThreshX,LowP; and

[0355] - More than 1 second has elapsed since the UE camped on the current serving cell.

[0356] If multiple cells of different priorities meet the cell reselection criteria, reselection to a cell of a higher-priority RAT / frequency shall take precedence over reselection to a cell of a lower-priority RAT / frequency.

[0357] The related parameters are defined as follows:

[0358] threshServingLowQ: The minimum RSRQ required for the serving cell

[0359] ThreshServing,lowP: The minimum RSRP required for the serving cell

[0360] Thresh_x,highQ: The expected RSRQ threshold required from the target cell due to reselection of the high priority frequency (the target cell needs to exceed this value)

[0361] Threshx,lowQ: The minimum RSRQ threshold required from the target cell due to reselection to a low priority frequency (the target cell needs to exceed this value)

[0362] TreselectionRAT: The minimum time that the target cell of the higher or lower frequency needs to maintain RSRQ / RSRP metrics during cell reselection

[0363] Thresh_x,highP: The RSRP expected threshold required from the target cell due to reselection of the high priority frequency (the target cell needs to exceed this value)

[0364] ThreshX,lowP: The minimum RSRP threshold required from the target cell due to reselection of a low priority frequency (the target cell needs to exceed this value)

[0365] Additionally, in the case of a co-frequency cell among the cells given in the redirection information, the following rules apply:

[0366] As a criterion for reselection between cells within the same frequency, the terminal needs to calculate two values.

[0367] The cell ranking criteria Rs for the serving cell and Rn for the neighboring cells are defined as:

[0368] Rs=Qmeas,s+Qhyst

[0369] Rn=Qmeas,n-Qoffset

[0370] in:

[0371] Qmeas is the RSRP measurement used in cell reselection. That is, Qmeas,s is the RSRP measurement of the serving cell, and Qmeas,n is the RSRP measurement of the neighboring cell.

[0372] For Qoffsets of the same frequency: if Qoffsets,n is valid, it is equal to Qoffsets,n, otherwise it is equal to zero.

[0373] For frequency-to-frequency: If Qoffset,n is valid, it is equal to Qoffset,n plus Qoffsetfrequency, otherwise it is equal to Qoffsetfrequency.

[0374] The UE shall perform ranking on all cells that satisfy the cell selection criterion S defined in 5.2.3.2.

[0375] The cells should be ranked according to the R criteria specified above by deriving Qmeas,n and Qmeas,s and calculating the R value using the average RSRP results.

[0376] If rangeToBestCell is not configured, the UE shall perform cell reselection on the cell ranked as the best cell. If the cell is found not suitable, the UE shall proceed according to subclause 5.2.4.4.

[0377] If rangeToBestCell is configured, the UE shall perform cell reselection on the cell with the maximum number of beams above a threshold (i.e., absThreshSS-Consolidation) among the cells whose R value is within the rangeToBestCell of the R value of the cell ranked as the best cell. If there are multiple such cells, the UE shall perform cell reselection on the highest ranked cell among them.

[0378] In all cases, the UE shall reselect a new cell only if the following conditions are met:

[0379] - During the time interval TreselectionRAT, the new cell is ranked better than the serving cell;

[0380] - More than 1 second has passed since the UE camped on the current serving cell.

[0381] If there is a cell in the redirection information with reference to the currently camped cell, the corresponding cell is searched, and a suitability check is performed by using the MIB or SIB information of the corresponding cell. If the suitability check is satisfied, the corresponding cell is reselected, and connection establishment / recovery is performed. If the suitability check is not satisfied, another cell with the next ranking given in the redirection is selected, and the above operation is repeatedly performed. If the suitability is not satisfied with respect to any cell present in the redirection, a reselection operation of an existing cell is performed.

Claims

1. A method performed by an IAB node in an integrated access and backhaul (IAB) system, the method comprising: detecting a radio link failure (RLF) on a backhaul link (BH) with a parent IAB node of the IAB node; Perform RLF recovery of the backhaul link; Identify if recovery has failed; as well as In case of RLF recovery failure, a Backhaul Adaptation Protocol (BAP) control packet data unit (PDU) including a BH RLF indication is sent to the child IAB node of the IAB node, Among them, the link that sends the BAP control PDU including the BH RLF indication is considered to be a link in which the RLF has occurred.

2. The method according to claim 1, wherein: The RLF is detected based on receipt of a BH RLF indication received from a parent IAB node.

3. The method according to claim 1, wherein: The child IAB node performs a radio resource control (RRC) reestablishment.

4. A method performed by a child IAB node in an integrated access and backhaul (IAB) system, the method comprising: In case of a radio link failure (RLF) recovery failure of a backhaul link (BH) between the IAB node and a parent IAB node of the IAB node, receiving a backhaul adaptation protocol (BAP) control packet data unit (PDU) including a BH RLF indication from the IAB node on the link; as well as Based on the BH RLF indication between the IAB node and the parent IAB node of the IAB node, it is considered that RLF has occurred on the link.

5. The method according to claim 4, wherein: The RLF between the IAB node and the parent IAB node is detected based on the receipt of a BH RLF indication from the parent IAB node to the IAB node.

6. The method according to claim 4, further comprising: Perform Radio Resource Control (RRC) re-establishment.

7. An integrated access and backhaul (IAB) node in an IAB system, the IAB node comprising: Transceiver; as well as The controller is configured as: detecting a radio link failure (RLF) on a backhaul link (BH) with a parent IAB node of the IAB node; Perform RLF recovery of the backhaul link; Identify if recovery has failed; and In case of RLF recovery failure, a Backhaul Adaptation Protocol (BAP) control packet data unit (PDU) including a BH RLF indication is sent to the child IAB node of the IAB node, Among them, the link that sends the BAP control PDU including the BH RLF indication is considered to be a link in which the RLF has occurred.

8. The IAB node according to claim 7, wherein: The RLF is detected based on receipt of a BH RLF indication received from a parent IAB node.

9. The IAB node according to claim 7, wherein: The child IAB node performs a radio resource control (RRC) reestablishment.

10. A sub-IAB node in an integrated access and backhaul (IAB) system, the sub-IAB node comprising: Transceiver; as well as The controller is configured as: In case of a radio link failure (RLF) recovery failure of a backhaul link (BH) between the IAB node and a parent IAB node of the IAB node, receiving a backhaul adaptation protocol (BAP) control packet data unit (PDU) including a BH RLF indication from the IAB node on the link; and Based on the BH RLF indication between the IAB node and the parent IAB node of the IAB node, it is considered that RLF has occurred on the link.

11. The child IAB node according to claim 10, wherein: The RLF between the IAB node and the parent IAB node is detected based on the receipt of a BH RLF indication from the parent IAB node to the IAB node.

12. The child IAB node according to claim 10, wherein: The controller is also configured to perform a radio resource control (RRC) reestablishment.

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