METHOD AND APPARATUS FOR PROCESSING LBT FAILURE INDICATOR DURING DAPS HANDOVER CONFIGURATION IN WIRELESS COMMUNICATION SYSTEM - Patent application

Abstract

The present disclosure relates to a communication method and system for integrating a fifth generation (5G) communication system, which supports a higher data transmission rate than a fourth generation (4G) system, with Internet of Things (IoT) technology. The present disclosure is applicable to intelligent 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, security and safety services. A method performed by a terminal in the communication system is provided. The method may include the steps of receiving a first message from a first base station, the first message including first information used for detecting a failure of a consistent uplink pre-talk (LBT) to the first base station, receiving a second message for handover from the first base station; when third information configuring at least one Dual Active Protocol Stack (DAPS) bearer is included in the second message and the indication of the consistent uplink LBT failure, the second message is identified based on the first information to the first base station while performing a procedure related to handover to a second base station including second information for reconfiguration by synchronization, and suspending data communication of all Data Radio Bearers (DRBs) associated with the first base station.

Description

[Technical field]

[0001] In a wireless communication system, more specifically, when 3GPP (registered trademark) 5G NR (new radio) technology is used in an unlicensed band, the present invention relates to a method for detecting and recovering from an uplink LBT (listen-before-talk) failure during handover while simultaneously communicating with a source base station and a target base station in a dual active protocol stack (DAPS) handover (HO) setting. [Background technology]

[0002] Since the commercialization of the 4G communication system, efforts have been made to develop improved 5G or pre-5G communication systems to meet the ever-increasing demand for wireless data traffic. For this reason, the 5G or pre-5G communication systems are called Beyond 4G Network or Post LTE systems. To achieve high data transmission rates, the 5G communication system is being considered for implementation in ultra-high frequency (mmWave) bands (such as the 60 GHz band). In order to mitigate the path loss of radio waves in ultra-high frequency bands and increase the transmission distance of radio waves, beamforming, massive MIMO, full dimensional MIMO (FD-MIMO), array antenna, analog beam-forming, and large scale antenna technologies are being discussed in the 5G communication system. In addition, to improve the system network, technologies being developed for the 5G communication system include advanced small cells, improved small cells, cloud radio access networks (cloud RAN), ultra-dense networks, device to device communication (D2D), wireless backhaul, moving networks, cooperative communication, CoMP (Coordinated Multi-Points), and interference cancellation.In addition, the 5G system includes advanced coding modulation (ACM) methods such as FQAM (Hybrid FSK and QAM Modulation) and SWSC (Sliding Window Superposition Coding), as well as advanced connection technologies such as FBMC (Filter Bank Multi Carrier), NOMA (non-orthogonal multiple access), and SCMA (sparse code multiple access).

[0003] Meanwhile, the Internet is evolving from a human-centered connected network where humans generate and consume information to an IoT (Internet of Things) network where information is exchanged and processed between distributed components such as things. IoE (Internet of Everything) technology is also emerging, which combines big data processing technology using connections with cloud servers with IoT technology. In order to realize IoT, technological elements such as sensing technology, wired and wireless communication and network infrastructure, service interface technology, and security technology are required, and recently, technologies such as sensor networks for connecting things, communication between things (Machine to Machine, M2M), and machine type communication (MTC) are being researched. In the IoT environment, it is possible to provide intelligent IT (Internet Technology) services that create new value in human life by collecting and analyzing data generated between connected things. IoT can be applied to fields such as smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, healthcare, smart home appliances, and advanced medical services by integrating and combining existing IT (information technology) technology with various industries.

[0004] Therefore, various attempts are being made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine-to-machine (M2M) and machine-type communication (MTC) are being embodied by 5G communication technologies such as beamforming, MIMO and array antennas. The application of cloud radio access network (cloud RAN) as the big data processing technology mentioned above is also one example of the fusion of 5G and IoT technologies.

[0005] The above information is provided solely as background information to aid in the understanding of the present disclosure. No determination or assertion has been made that any of the above is applicable as prior art in connection with the present disclosure. Summary of the Invention [Problem to be solved by the invention]

[0006] We propose a method to handle the problem of uplink transmission failure due to interference from other devices in unlicensed bands during DAPS handover. [Means for solving the problem]

[0007] One aspect of the present disclosure addresses at least the problems and / or shortcomings mentioned above and provides at least the advantages described below. Accordingly, one aspect of the present disclosure provides a method for handling the problem of uplink transmission failure due to interference of other devices in an unlicensed spectrum during a DAPS handover.

[0008] According to the present disclosure, a method performed by a terminal in a communication system may include a step of receiving, from a first base station, a first message including first information used to detect a consistent uplink listen before talk (LBT) failure to the first base station; a step of receiving, from the first base station, a second message for handover to a second base station including second information for reconfiguration with sync; and a step of suspending data communication of all data radio bearers (DRBs) associated with the first base station when third information configuring at least one dual active protocol stack (DAPS) bearer is included in the second message and an indication of the consistent uplink LBT failure to the first base station is identified based on the first information during a procedure related to the handover.

[0009] According to the present disclosure, a method performed by a first base station in a communication system includes a step of transmitting, to a terminal, a first message including first information used for detecting a consistent uplink LBT (listen before talk) failure to the first base station; and a step of transmitting, to the terminal, a second message for handover to a second base station including second information for reconfiguration with sync, wherein third information configuring at least one DAPS (dual active protocol stack) bearer is included in the second message, and data communication of all DRBs (data radio bearers) associated with the first base station may be interrupted if an indication of the consistent uplink LBT failure to the first base station is identified based on the first information during a procedure related to the handover.

[0010] According to the present disclosure, a terminal of a communication system includes a transceiver unit; and a control unit connected to the transceiver unit, wherein the control unit receives from a first base station a first message including first information used to detect a consistent uplink listen before talk (LBT) failure to the first base station; receives from the first base station a second message for handover to a second base station including second information for reconfiguration with sync; and, third information configuring at least one dual active protocol stack (DAPS) bearer is included in the second message, and based on the first information, may be configured to suspend data communication of all data radio bearers (DRBs) associated with the first base station when an indication of the consistent uplink LBT failure to the first base station is identified during a procedure related to the handover.

[0011] According to the present disclosure, a first base station of a communication system includes a transceiver unit; and a controller connected to the transceiver unit, wherein the controller may be configured to: transmit, to a terminal, a first message including first information used for detecting a consistent uplink listen before talk (LBT) failure for the first base station; and transmit, to the terminal, a second message for handover to a second base station including second information for reconfiguration with sync, wherein third information configuring at least one dual active protocol stack (DAPS) bearer is included in the second message, and when an indication of the consistent uplink LBT failure for the first base station is identified based on the first information during a procedure related to the handover, data communication of all data radio bearers (DRBs) associated with the first base station is interrupted. Effect of the Invention

[0012] According to the present disclosure, it is possible to reduce delays caused by LBT failures during DAPS handover in unlicensed bands.

[0013] Other aspects, advantages and special features of the present disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the accompanying drawings, illustrates various embodiments of the present disclosure.

[0014] The above and other aspects, features, and advantages of an embodiment of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 illustrates the structure of an NR system that is referenced for the purposes of explaining this disclosure. [Diagram 2] FIG. 1 illustrates a radio protocol structure in LTE and NR systems referenced for the purposes of the present disclosure. [Diagram 3] FIG. 1 is an illustrative diagram of downlink and uplink channel frame structures during beam-based communication in an NR system. [Figure 4] A diagram showing a procedure in which a terminal performs contention-based four-step random access to a base station. [Diagram 5] FIG. 1 is a diagram explaining LBT Type 1. [Figure 6] FIG. 1 is a diagram explaining LBT Type 2. [Figure 7] A diagram showing the procedure between a terminal and a base station when the terminal detects an uplink LBT failure problem. [Figure 8A] FIG. 1 is a diagram illustrating the process of using DAPS (dual active protocol stack) during handover. [Figure 8B] FIG. 1 is a diagram illustrating the process of using DAPS (dual active protocol stack) during handover. [Figure 9]13 is a diagram showing the operation sequence of a terminal when an LBT failure is detected during a DAPS handover. [Figure 10] FIG. 2 is a diagram illustrating a block configuration of a terminal in a wireless communication system according to an embodiment of the present disclosure. [Figure 11] FIG. 2 is a diagram showing a block configuration of a base station in a wireless communication system according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In the drawings, the same reference numbers may be used to denote the same or similar elements, features and structures.

[0017] The following description with reference to the accompanying drawings is provided to aid in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. Although various specific details are included herein to aid in understanding, they should be considered merely as examples. Therefore, those skilled in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and configurations may be omitted for clarity and conciseness.

[0018] The terms and words used in the following description and claims are not limited to their dictionary meanings, but are merely used by the inventor to enable a clear and consistent understanding of the present invention. Therefore, it will be apparent to those skilled in the art that the following description of various embodiments of the present invention is provided for illustrative purposes only, and is not intended to limit the present invention as defined by the appended claims and their equivalents.

[0019] Singular terms should be understood to include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a "component surface" includes reference to one or more of that surface.

[0020] In the following description, terms for identifying connection nodes, terms representing network entities, terms representing messages, terms representing interfaces between network objects, terms representing various identification information, etc. are provided as examples for the convenience of description. Therefore, the present disclosure is not limited to the terms described below, and other terms representing objects having equivalent technical meanings may be used.

[0021] For the sake of convenience, the present disclosure uses terms and names defined in the LTE and NR standards, which are the latest standards defined by the 3GPP (3rd Generation Partnership Project) among the existing communication standards. However, the present disclosure is not limited to these terms and names and may be equally applied to systems conforming to other standards. In particular, the present disclosure is applicable to 3GPP / NR (5th generation mobile communication standard).

[0022] FIG. 1 is a diagram illustrating the structure of an NR system to which reference is made for the purposes of explaining this disclosure.

[0023] Referring to Fig. 1, the wireless communication system includes a number of base stations (1-05), (1-10), (1-15), (1-20), an access and mobility management function (AMF) (1-25), and a user plane function (UPF) (1-30). A user equipment (UE or terminal) (1-35) connects to an external network via the base stations (1-05), (1-10), (1-15), (1-20) and the UPF (1-30).

[0024] The base stations (1-05), (1-10), (1-15), and (1-20) are access nodes of the cellular network and provide wireless connection to terminals connecting to the network. That is, the base stations (1-05), (1-10), (1-15), and (1-20) collectively schedule state information such as terminal buffer state, available transmission power state, and channel state to service user traffic, and support connection between the terminal and a core network (CN, core network; in particular, the CN of NR is called 5GC). Meanwhile, in communication, a user plane (UP) related to the transmission of actual user data and a control plane (CP) such as connection management can be configured separately. In the figure, the gNB (1-05) (1-20) uses UP and CP technologies defined in the NR technology, and the ng-eNB (1-10) (1-15) uses UP and CP technologies defined in the LTE technology, even though it is connected to 5GC.

[0025] The AMF / SMF (1-25) is a device that handles various control functions in addition to mobility management functions for terminals and is connected to multiple base stations, and the UPF (1-30) is a type of gateway device that provides data transmission.

[0026] FIG. 2 is a diagram illustrating a radio protocol structure in LTE and NR systems that is referenced for the purposes of explaining this disclosure.

[0027] Referring to FIG. 2, the radio protocol of the LTE system consists of packet data convergence protocol (PDCP) (2-05) (2-40), radio link control (RLC) (2-10) (2-35), and medium access control (MAC) (2-15) (2-30) in the terminal and ENB, respectively. Packet data convergence protocol (PDCP) (2-05) (2-40) is responsible for operations such as IP header compression / decompression, and radio link control (hereinafter referred to as RLC) (2-10) (2-35) reconstructs PDCP PDUs (packet data units) to an appropriate size. MAC (2-15) (2-30) is connected to multiple RLC layer devices configured in one terminal, and performs operations of multiplexing RLC PDUs into MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The physical layer (2-20) (2-25) performs channel coding and modulation of higher layer data and transmits it as OFDM symbols on a radio channel, or demodulates and channel-decodes the OFDM symbols received through the radio channel and transmits them to a higher layer. The physical layer also uses HARQ (Hybrid ARQ) for additional error correction, and the receiving end transmits the reception or non-reception of the packet sent from the transmitting end in one bit. This is called HARQ ACK / NACK information. In LTE, downlink HARQ ACK / NACK information for uplink data transmission is transmitted through a physical channel such as PHICH (physical hybrid-ARQ indicator channel), and in NR, it can be determined whether a retransmission is necessary or a new transmission should be performed using the scheduling information of the terminal in the PDCCH (physical dedicated control channel), which is a channel that transmits downlink / uplink resource allocations, etc. This is why asynchronous HARQ is applied in NR.Uplink HARQ ACK / NACK information for downlink data transmission may be transmitted via a physical channel such as a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH). The PUCCH is generally transmitted on an uplink PCell, which will be described later, but the base station may also transmit the PUCCH to a terminal on an SCell, which will be described later, if the terminal supports it, and this is called a PUCCH SCell.

[0028] Although not shown in the figure, there is a radio resource control (RRC) layer above the PDCP layer of each of the terminal and the base station, and the RRC layer can exchange connection and measurement related configuration control messages for radio resource control.

[0029] Meanwhile, the PHY layer may be composed of one or more frequencies / carriers, and a technology for simultaneously setting and using multiple frequencies is called carrier aggregation (hereinafter, referred to as CA). The CA technology uses only one carrier for communication between a terminal (or user equipment, UE) and a base station (E-UTRAN NodeB, eNB), but by further using a primary carrier and one or more secondary carriers, the transmission amount can be drastically increased by the number of secondary carriers. Meanwhile, in LTE, a cell in a base station using a primary carrier is called a primary cell or PCell (primary cell), and a cell in a base station using a secondary carrier is called a secondary cell or SCell (secondary cell).

[0030] FIG. 3 is an exemplary diagram of downlink and uplink channel frame structures during beam-based communication in an NR system.

[0031] In Figure 3, a base station (3-01) transmits signals in the form of beams (3-11), (3-13), (3-15), and (3-17) to provide wider coverage or transmit a stronger signal. Therefore, a terminal (3-03) in a cell must transmit and receive data using a specific beam (beam #1 (3-13) in this example drawing) transmitted by the base station.

[0032] Meanwhile, the state of the terminal is divided into a dormant mode (RRC_IDLE) and a connected mode (RRC_CONNECTED) depending on whether the terminal is connected to the base station. Therefore, the location of the terminal in the dormant mode is unknown to the base station.

[0033] If a terminal in the dormant mode state is to transition to the connected mode state, the terminal receives synchronization signal blocks (SSBs) (3-21), (3-23), (3-25), and (3-27) transmitted by the base station. These SSBs are SSB signals transmitted periodically according to a period set by the base station, and each SSB is divided into a primary synchronization signal (PSS) (3-41), a secondary synchronization signal (SSS) (3-43), and a physical broadcast channel (PBCH).

[0034] In this example, a scenario is assumed in which SSBs are transmitted for each beam. For example, it is assumed that SSB#0 (3-21) is transmitted using beam#0 (3-11), SSB#1 (3-23) is transmitted using beam#1 (3-13), SSB#2 (3-25) is transmitted using beam#2 (3-15), and SSB#3 (3-27) is transmitted using beam#3 (3-17). In this example, it is assumed that a dormant mode terminal is located in beam#1, but even when a connected mode terminal performs random access, the terminal selects the SSB that is received at the time of random access.

[0035] Thus, in the figure, SSB #1 transmitted by beam #1 is received. Upon receiving SSB #1, the terminal obtains the physical cell identifier (PCI) of the base station by the PSS and SSS, and by receiving the PBCH, the terminal can ascertain the identifier (i.e., #1) of the currently received SSB, the position where the currently received SSB is located within a 10 ms frame, and in addition, the SFN (system frame number) having a period of 10.24 seconds. In addition, the PBCH includes a master information block (MIB), which indicates the position where SIB1 (system information block type 1), which broadcasts more detailed cell configuration information, can be received. Upon receiving SIB1, the terminal knows the total number of SSBs transmitted by the base station and can know the location of a PRACH occasion (physical random access channel occasion) (in this example drawing, a scenario in which allocation is performed every 1 ms is assumed: (3-30) to (3-39)) for which random access can be performed to transition to a connected mode state (more precisely, a preamble, which is a physical signal specially designed for uplink synchronization, can be transmitted). In addition, based on the information, it can know which PRACH occasion is mapped to which SSB index among the PRACH occasions. For example, in this example drawing, a scenario in which allocation is performed every 1 ms is assumed, and a scenario in which 1 / 2 SSBs are allocated per PRACH occasion (i.e., there are two PRACH occasions per SSB) is assumed. Therefore, a scenario in which two PRACH occasions are allocated for each SSB from the start of the PRACH occasion starting from the SFN value is shown. That is, (3-30)(3-31) is assigned for SSB#0, (3-32)(3-33) is assigned for SSB#1, etc. After configuration for all SSBs, PRACH occasions are again assigned for the first SSB (3-38)(3-39).

[0036] Therefore, the terminal checks the position of the PRACH occasion (3-32)(3-33) for SSB#1, and transmits the random access preamble on the currently earliest PRACH occasion (e.g. (3-32)) among the PRACH occasions (3-32)(3-33) corresponding to SSB#1. Since the base station received the preamble on the PRACH occasion (3-32), it knows that the terminal selected SSB#1 to transmit the preamble, and thus it can transmit and receive data through that beam during the subsequent random access.

[0037] Meanwhile, when a connected terminal moves from a current (source) base station to a destination (target) base station for reasons such as handover, the terminal also performs random access to the target base station and selects an SSB as described above to transmit a random access preamble. In addition, when handover is performed, a handover command is sent to the terminal to move from the source base station to the target base station, and the message may include a dedicated random access preamble identifier for the terminal for each SSB of the target base station so that the target base station can use the dedicated random access preamble identifier for random access. In this case, the base station does not assign a dedicated random access preamble identifier to all beams (depending on the current location of the terminal, etc.), and therefore, some SSBs may not be assigned a dedicated random access preamble (for example, only beams #2 and #3 are assigned a dedicated random access preamble). If a dedicated random access preamble is not assigned to the SSB selected by the terminal for preamble transmission, the terminal may arbitrarily select a contention-based random access preamble to perform random access. For example, in the figure, a scenario is possible in which the terminal initially performs random access in beam #1 to which a dedicated random access preamble is not assigned, but after failure, transmits the dedicated preamble again in beam #3 to which a dedicated random access preamble is assigned. Even in a random access, i.e., in a single random access procedure, when a preamble retransmission occurs, a contention-based random access procedure or a non-contention-based random access procedure may be performed for each preamble transmission depending on whether a dedicated random access preamble is assigned to the selected SSB.

[0038] FIG. 4 is a diagram showing a procedure in which a terminal performs contention-based four-step random access to a base station.

[0039] FIG. 4 is a diagram showing a contention-based four-stage random access procedure that a terminal performs when a terminal needs to access a base station for initial connection, reconnection, handover, or other various occasions.

[0040] The terminal (4-01) selects a PRACH according to FIG. 3 in order to connect to the base station (4-03), and transmits a random access preamble on the PRACH (4-11). A case may occur in which one or more terminals transmit random access preambles simultaneously on the PRACH resource. The PRACH resource may span one subframe, or only some symbols in one subframe may be used. Information on the PRACH resource may be included in system information broadcast by the base station, so that the terminal knows which time-frequency resource it should transmit the preamble on. In addition, the random access preamble corresponds to a specific sequence that can be received by the base station even if it is transmitted before being completely synchronized with the base station, and there may be multiple preamble identifiers (indexes) according to the standard. If there are multiple preamble identifiers, the preamble transmitted by the terminal may be a preamble selected randomly by the terminal, or a specific preamble designated by the base station.

[0041] When the base station receives the preamble, it transmits a random access response (RAR) message to the terminal (4-21). The RAR message may include at least one of preamble identifier information and uplink transmission timing correction information used in step (4-11), uplink resource allocation information used in the following step (i.e., step (4-31)), and temporary terminal identifier information. The preamble identifier information is transmitted to indicate which preamble the RAR message is a response message to when multiple terminals transmit different preambles in step (4-11) to attempt random access. The uplink resource allocation information is detailed information of resources used by the terminal in step (4-31), and may include at least one of physical location and size of resources, a modulation and coding scheme (MCS) used during transmission, and power adjustment information during transmission. The temporary terminal identifier information is a value that is transmitted to the terminal to be used for communication with the base station when the terminal that transmitted the preamble makes an initial connection and the terminal does not have an identifier assigned by the base station for communication with the base station.

[0042] The RAR message must be transmitted within a predetermined period of time starting from a predetermined time after the transmission of the preamble, and this period is called the "RAR window." The RAR window begins when a predetermined time has elapsed since the transmission of the first preamble. The predetermined time may be in units of subframes (1 ms) or a smaller value. Also, the length of the RAR window may be a predetermined value set by the base station for each PRACH resource or for one or more PRACH resource sets in a system information message broadcast by the base station.

[0043] Meanwhile, when the RAR message is transmitted, the base station schedules the RAR message via a PDCCH, and the scheduling information is scrambled by a random access-radio network temporary identifier (RA-RNTI). The RA-RNTI is mapped to a PRACH resource used to transmit the (4-11) message, and a terminal that transmits a preamble on a specific PRACH resource attempts to receive a PDCCH based on the RA-RNTI and determines whether there is a corresponding RAR message. That is, if the RAR message is a response to a preamble transmitted by a terminal in step (4-11) as in this example drawing, the RA-RNTI used in the RAR message scheduling information includes information on the (4-11) transmission. To this end, the RA-RNTI may be determined based on time resource or frequency resource information on which a preamble is transmitted, and may be calculated, for example, by the following formula:

[0044] [Number 1] RA-RNTI = 1 + s_id + 14 × t_id + 14 × 80 × f_id + 14 × 80 × 8 × ul_carrier_id

[0045] Here, s_id is an index corresponding to the first OFDM symbol where the preamble transmission transmitted in step (4-11) starts, and has a value of 0≦s_id<14 (i.e., the maximum number of OFDMs in one slot). Also, t_id is an index corresponding to the first slot where the preamble transmission transmitted in step (4-11) starts, and has a value of 0≦t_id<80 (i.e., the maximum number of slots in one system frame (10 ms)). Also, f_id indicates which PRACH resource in frequency the preamble transmitted in step (4-11) is transmitted from, and has a value of 0≦f_id<8 (i.e., the maximum number of PRACHs in frequency within the same time). In addition, the ul_carrier_id is a factor used to distinguish whether the preamble is transmitted in a normal uplink (NUL) (in this case, 0) or in a supplementary uplink (SUL) (in this case, 1) when two carriers are used in the uplink for one cell.

[0046] The terminal that has received the RAR message transmits different messages to the resources allocated to the RAR message according to the various purposes described above (4-31). In this exemplary drawing, the third message to be transmitted is also called Msg3 (i.e., the preamble in step (4-11) or (4-13) is also called Msg1, and the RAR in step (4-21) is also called Msg2). Examples of the Msg3 transmitted by the terminal include an RRCConnectionRequest message, which is a message of the RRC layer, in the case of initial connection, an RRCConnectionReestablishmentRequest message in the case of reconnection, and an RRCConnectionReconfigurationComplete message in the case of handover. Alternatively, a Buffer Status Report (BSR) message for resource request, etc. may be transmitted.

[0047] Then, if it is an initial transmission (i.e., Msg3 does not include base station identifier information already assigned to the terminal), the terminal receives a contention resolution message from the base station (4-41). The contention resolution message includes the content transmitted by the terminal in Msg3 as is, and even if there are multiple terminals that selected the same preamble in step (4-11) or (4-13), it can indicate which terminal the response is for.

[0048] Meanwhile, a contention resolution timer (ra-ContentionResolutionTimer) is started or restarted at the time when the uplink allocated for transmitting Msg3 via the RAR or PDCCH ends (e.g., the first OFDM symbol after the uplink). Thus, the terminal attempts to receive Msg4 from the base station until the timer expires, and if Msg4 is not received until the timer expires, the terminal determines that contention resolution has failed and retransmits the preamble.

[0049] On the other hand, the above-mentioned 5G system can be considered to operate in an unlicensed band. An unlicensed band can mean a frequency band that can be freely used by anyone without a separate license within the regulatory limits. For example, there is the 2.4 GHz or 5 GHz band, and wireless LAN and Bluetooth (registered trademark) use the frequency to communicate.

[0050] In order to communicate in the unlicensed band, data must be transmitted and received in accordance with regulations set by each country. Furthermore, in accordance with the regulations, before a communication device transmits in an unlicensed band, the communication device must "listen" to determine whether the unlicensed band is occupied by another communication device, and "transmit" if it is determined to be free. This method of listening and transmitting when it is free is called LBT (Listen-Before-Talk). Regulations on when to perform the LBT are set by country and by unlicensed band, and communication devices must perform LBT in accordance with such regulations when communicating in an unlicensed band.

[0051] The LBT is roughly divided into Type 1 and Type 2.

[0052] FIG. 5 is a diagram illustrating LBT Type 1.

[0053] LBT Type 1 is a method in which a device randomly determines the time to listen for other peripheral devices to transmit before transmitting, and transmits when the channel is free during that random time. d ), and if the channel is free, it will listen again at a random time (N) to see if the channel is free.

[0054] At this time, the T d The value of N can be determined differentially, and in this embodiment, a total of four differential classes are given as an example. The classes are called channel access priority classes (CAPC).

[0055] In addition, the CAPC d =16+m p *9(μs) time length, N=random(0,CW p )*9(μs), and the CW value is CW min,p It starts at 0, but increases with each failed transmission, up to CWmax,p For example, when performing LBT using a method with a CAPC of 3, T d has a length of 16+3*9=43 μs, and for the initial transmission, a random value between 0 and 15 is selected for N. If, for example, 7 is selected, N becomes 7*9=63 μs, and the communication device transmits data when the channel is free for 106 μs.

[0056] [Table 1]

[0057] In the above example (when 7 is selected for N), if the terminal determines that the channel is occupied by another device (i.e., the received signal strength (RSSI) is greater than or equal to a predetermined threshold) during the process of determining whether the channel is free (e.g., when only 3 of the 7 have passed and only 4 remains), the terminal waits until the channel occupation ends and then performs another T d After waiting for 4 seconds, the channel is judged to be free during the remaining 4 seconds and then transmission is performed. As can be seen from the table, the LBT method with a low CAPC may be used when transmitting high priority traffic.

[0058] FIG. 6 is a diagram illustrating LBT Type 2.

[0059] Referring to FIG. 6, LBT Type 2 is a method in which the time for listening to whether other peripheral devices are transmitting before transmitting is fixed, and therefore, when the channel is free during the fixed time, the communication device immediately transmits. That is, in this example, when a communication device needs to transmit, short (=T f +T s ) and if it is determined that the channel is free, it immediately transmits data. This is an LBT method that can be used when transmitting signals with very high priority. Therefore, the random access preamble ((4-11) in FIG. 4) and the PUCCH described above are signals of high importance, and therefore can be transmitted using this LBT method.

[0060] FIG. 7 is a diagram showing a procedure between a terminal and a base station when the terminal detects an uplink LBT failure problem.

[0061] In the figure, it is assumed that a terminal (7-01) is connected to a base station (7-03) operating in an unlicensed band and is in an RRC connected state (RRC_CONNECTED). In the RRC connected state, the terminal can transmit and receive data with the base station. In addition, the terminal can receive parameter settings related to uplink LBT problem detection (described later) from the base station via an RRCReconfiguration message or a SIB (system information) message.

[0062] Thus, the terminal can receive uplink resource scheduling from the base station via the PDCCH (7-13), or perform uplink transmission to perform random access, transmit a PUCCH, transmit data on the configured uplink resource (configured uplink grant), etc.

[0063] As described above, when transmitting data in an unlicensed band, the terminal must perform an LBT operation. The type of LBT to be performed is set for each uplink resource allocation in the PDCCH or for each logical channel in the RRC message, and the LBT can be performed according to the highest (or lowest) priority setting among the logical channels to which the data to be actually transmitted belongs.

[0064] Therefore, when the UE is unable to transmit due to an LBT failure during uplink transmission, the UE starts a timer (lbt-FailureDetectionTimer) for detecting an LBT failure. The length of the timer may be set by the RRCReconfiguration message or SIB message. Furthermore, every time an LBT fails (7-19) (7-21), a predetermined counter is incremented and the timer is restarted (7-17). This is so that if the counter reaches a value (lbt-FailureInstanceMaxCount) set by the base station by the RRCReconfiguration or SIB message while the timer is running, the UE recognizes that the UL LBT problem is serious and performs additional operations.

[0065] Thereafter, if no failures occur for the number of times set by the base station (e.g., four times) until the timer expires, the terminal determines that no further uplink LBT problems will occur and sets the counter to 0 (7-23).

[0066] As another example, when the terminal is unable to transmit due to an LBT failure during uplink transmission (7-37), the timer is started (7-31). After that, when the terminal attempts further uplink transmission, but the transmission continues to fail due to a UL LBT problem, and the number of failures occurs a number of times set by the base station (e.g., four times), the terminal recognizes that an uplink LBT problem has occurred to the extent that there is a problem with the uplink transmission, and performs an additional procedure to recover from the problem (7-45). The additional procedure may include a procedure of transmitting an LBT failure MAC CE, and, in the case of an SpCell, switching to another bandwidth part (BWP) in another SpCell where no LBT failure has occurred, or, if an LBT failure has occurred in all BWPs, the MAC layer of the terminal may inform the upper layer (RRC) of the fact, and have the upper layer of the terminal declare a radio link failure (RLF). When a wireless connection failure is declared, the terminal selects a cell with the strongest signal among the surrounding cells and attempts to re-establish the connection (connection re-establishment).

[0067] 8A and 8B are diagrams illustrating a process of using a dual active protocol stack (DAPS) in a handover process.

[0068] When performing a general handover, the terminal stops data transmission and reception with the source cell when receiving the handover configuration information, and starts data transmission and reception with the target cell after the handover process is successful. Therefore, an interruption time occurs, which is a time period during which data transmission and reception is not possible. On the other hand, if the terminal has a dual active protocol stack, data transmission and reception with the source cell can be maintained during the time period. In the present disclosure, the handover that takes into account the terminal capabilities as described above is called a DAPS handover. When a DAPS handover is set, the terminal can simultaneously receive downlink data from the source cell and the target cell only for data belonging to a data bearer for which a DAPS operation is set. The bearer is a logical data path, and a base station can set multiple bearers that differ depending on the type of data, and when there are multiple data bearers, the base station can set DAPS for each bearer. However, simultaneous uplink data transmission to the source cell and the target cell may be possible only when certain conditions are met due to a lack of terminal transmission power, signal interference, etc. For example, in order to minimize terminal complexity, uplink data transmission is possible only on one link during DAPS handover, and the uplink on which data transmission is performed may be switched from the source cell to the target cell at a specific time.

[0069] At each key point in time, the activation states and terminal operations of the dual protocol stacks corresponding to the source cell and the target cell are different.

[0070] Referring to FIG. 8A, before handover is performed (8-05), the terminal uses only the protocol stack corresponding to the source cell.

[0071] When the DAPS handover configuration information is provided to the terminal and before RACH is performed to the target cell (8-10), the terminal configures a protocol stack corresponding to the target cell when the DAPS handover configuration information is provided in an RRCReconfiguration message. However, the terminal still uses only the protocol stack corresponding to the source cell. Meanwhile, the protocol stack corresponding to the target cell may be in an inactive state.

[0072] In the RACH execution period (8-15), when the RACH operation starts, at least the PHY layer and the MAC layer in the protocol stack corresponding to the target cell are activated to perform the RACH operation. At this time, the terminal still maintains data transmission and reception with the source cell.

[0073] Steps from 8-20 onwards are illustrated in FIG. 8B.

[0074] When the terminal transmits an HO success completion message (i.e., an RRCReconfigurationComplete message of the RRC layer) to the target cell (8-20), at least some functions of the PHY layer, MAC layer, RLC layer, and PDCP layer in the protocol stack corresponding to the target cell must be activated and the terminal must be able to process the HO success completion message transmitted via a signaling radio bearer. The terminal can transmit uplink data to the source cell at least until it transmits the HO success completion message to the target cell.

[0075] After receiving the RAR from the target cell (8-25), the terminal activates all of the dual active protocol stacks. The terminal maintains data transmission and reception with the source cell until a specific time point arrives after receiving the RAR. Meanwhile, the time at which the terminal can maintain downlink data reception with the source cell and the time at which the terminal can maintain uplink data transmission may be different. The terminal can transmit uplink data to the source cell until it transmits an HO success completion message to the target cell, but can still receive downlink data thereafter.

[0076] After the terminal releases the source cell (8-30), it also releases the protocol stack corresponding to the source cell, after which the terminal uses only the protocol stack corresponding to the target cell.

[0077] FIG. 9 is a diagram illustrating an operation sequence of a terminal when an LBT failure is detected during a DAPS handover.

[0078] In the figure, it is assumed that the terminal is connected to a base station operating in an unlicensed band and is in an RRC connected state. In the RRC connected state, the terminal can transmit and receive data with the base station. The terminal can receive parameter settings related to uplink LBT problem detection (described later) from the base station via an RRCReconfiguration message or a SIB (system information) message (9-03).

[0079] Then, the terminal may be commanded to perform handover from the base station to another base station (9-05). The handover command may mean that a reconfigurationWithSync field is included in an RRCReconfiguration message of the RRC layer. The reconfigurationWithSync field may include terminal identifier information used in the target base station, and timer (T304) length information used to detect handover failure. In addition, when connecting to the target base station for the handover procedure, information regarding dedicated resources (the above-mentioned dedicated random access preamble) that can be used during the random access procedure may be selectively included.

[0080] Meanwhile, in order to reduce delay during handover, the base station can instruct the terminal to perform the above-mentioned DAPS HO. The DAPS HO is executed only if there is a bearer with the daps-Config field set to true among the data bearers configured in the terminal (9-07). If the terminal operates in an unlicensed band, or if the LBT failure detection and recovery related setting is configured in the terminal, the base station may not set the DAPS HO in the terminal. This is to prevent the use of a function such as the DAPS HO used to reduce handover delay in an unlicensed band, since operation in an unlicensed band can cause delays for various reasons. However, in this embodiment, it can be assumed that the DAPS handover is configured to reduce handover delay.

[0081] Therefore, if LBT failure detection is set and DAPS HO related setting information is included in the RRCReconfiguration message, the UE performs additional operations due to LBT failure detection in the source base station and the target base station (9-11).

[0082] For example, if consecutive LBT failures are detected in the source base station according to the procedure described in FIG. 7 during DAPS handover, the terminal can suspend transmissions for data bearers established with the source base station and release the connection with the source base station.

[0083] If this is expressed in terms of the 3GPP RRC standard procedures, it is as follows (the underlined parts are changes from the existing 3GPP RRC standard procedures):

[0084] [Table 2]

[0085] Meanwhile, LBT failure may occur in the target base station during DAPS handover. Therefore, if the target base station detects consecutive LBT failures according to the procedure described in FIG 7, the following methods can be used by the terminal.

[0086] The first method is to ignore an LBT failure detected in the target base station during DAPS HO and wait for expiration of T304 used for detecting a general handover failure.

[0087] In the second method, when an LBT failure at the target base station is detected during DAPS HO, the terminal considers the handover to have failed and performs an operation to be performed when a handover failure occurs (i.e., an operation to be performed when the handover is not completed until T304 expires) in advance. The operation to be performed when the handover fails includes releasing a dedicated random access resource configured for the handover, restoring the terminal's configuration to the configuration previously configured by the source base station, and performing an RRC connection re-establishment procedure. In the RRC connection re-establishment procedure, a cell selection procedure that can be connected to a neighboring cell is performed, and an RRC connection re-establishment procedure is performed by random access to the selected cell (including transmitting an RRCReestablishmentRequest message). When performing the RRC connection re-establishment procedure, the terminal may notify the base station that there is connection failure information to report by including a connEstFailInfoAvailable field in the RRCReestablishmentComplete message. Therefore, when the base station requests the terminal to obtain the information by setting rlf-ReportReq to true in a UEInformationRequest message, the terminal reports the details of the previously generated RLF to the base station using the rlf-Report field in a UEInformationResponse message. At this time, since a problem occurred during handover, the terminal can report the connection failure cause (connectionFailureType) as the occurrence of handover failure (hof) in the rlf-Report field. In addition, the terminal can report that the handover failed due to LBT failure as the detailed handover failure cause (hof-Cause) (lbt-Failure).Alternatively, in the case of an LBT failure, even though the connection failure occurred due to a handover failure, it can be notified that it occurred due to an RLF and not due to a handover failure (i.e., the connectionFailureType field is set to rlf).In this case, the RLF cause (rlf-Cause) can be notified that the RLF occurred due to an LBT failure (lbt-Failure).

[0088] If this is expressed in terms of the 3GPP RRC standard procedure, it is as follows (the underlined parts are changes from the existing 3GPP RRC standard procedure specifications):

[0089] [Table 3]

[0090] [Table 4A] [Table 4B] [Table 4C]

[0091] If an LBT failure occurs in the target base station as described above, the UE can prevent the same problem from reoccurring by selecting another cell other than the target base station when performing cell selection for connection reconfiguration. Meanwhile, if LBT failure detection is set and DAPS HO related setting information is not included in the RRCReconfiguration message, the UE performs only an additional operation due to the detection of the LBT failure in the target base station (9-13). Therefore, if the target base station detects consecutive LBT failures according to the procedure described in FIG. 7, the UE can ignore the detection of the LBT failure in the target base station and wait for the expiration of T304 used for general handover failure detection. That is, even if consecutive LBT failures are detected during the operation of T304, they can be ignored and no additional operation can be taken.

[0092] If this is expressed in terms of the 3GPP RRC standard procedures, it is as follows (the underlined parts are changes from the existing 3GPP RRC standard procedures):

[0093] [Table 5]

[0094] Meanwhile, in the procedure of the RRC standard, when daps is not set (i.e., 1>else:), it includes both a case where a general handover is being performed (i.e., LBT failure occurs during handover) and a case where a handover is not being performed (i.e., LBT failure occurs during communication with a base station). Therefore, the operations in both cases can be differentiated. For example, when a handover is not being performed (i.e., when T304 starts after receiving a handover command from the base station), the terminal assumes that the handover has failed after detecting the LBT failure and performs an operation to be performed when a handover failure occurs (i.e., an operation to be performed when the handover is not completed until T304 expires) in advance without waiting until T304 expires. The operation to be performed when the handover fails includes releasing the dedicated random access resource set for the handover, restoring the terminal's configuration to the configuration previously set by the source base station, and performing an RRC connection re-establishment procedure. In the RRC connection re-establishment procedure, a procedure for selecting a neighboring cell that can be connected to is performed, and the RRC connection re-establishment procedure is performed by random access to the selected cell (including transmission of an RRCReestablishmentRequest message). This can be expressed in terms of the 3GPP RRC standard procedure as follows (the underlined parts are changes from the existing 3GPP RRC standard procedure):

[0095] [Table 6A] [Table 6B] [Table 6C] [Table 6D] [Table 6E]

[0096] On the other hand, in both of the above-mentioned procedures (9-11) and (9-13), if the terminal wishes to ignore an LBT failure that occurs at the target base station during handover, the LBT failure detection procedure method described in FIG. 7 may be changed so that the RRC layer does not need to be notified.

[0097] The first method for this is that the MAC layer of the terminal does not trigger any additional procedures for consecutive LBT failures during handover (i.e., during T304 operation; or during a random access procedure for reconfiguration with sync) even if the number of LBT failures in the SpCell reaches a critical value.

[0098] This can be expressed in terms of the 3GPP MAC standard procedures as follows (the underlined parts are changes from the existing 3GPP MAC standard procedures):

[0099] [Table 7]

[0100] The second method is that during handover (i.e., while T304 is running; or during a random access procedure for reconfiguration with sync), if the number of LBT failures in the SpCell reaches a critical value, the MAC layer of the terminal triggers a procedure for consecutive LBT failures, but does not inform the RRC layer (higher layer) of this, thereby avoiding additional procedures.

[0101] This can be expressed in terms of the 3GPP MAC standard procedures as follows (the underlined parts are changes from the existing 3GPP MAC standard procedures):

[0102] [Table 8]

[0103] Although not shown in the figure, another method may be considered in which the physical layer does not transmit an LBT failure indication to the MAC layer during handover. That is, the procedure "1>if LBT failure indication has been received from lower layers:" may not be executed in the example procedure of the MAC standard.

[0104] According to the above procedure, the UE may perform a handover procedure when the LBT failure is detected and the DAPS is set. Also, any one of the above-described embodiments may be used, or a plurality of the embodiments may be simultaneously applied and used.

[0105] FIG. 10 illustrates a block configuration of a terminal in a wireless communication system according to an embodiment of the present disclosure.

[0106] Referring to FIG. 10, the terminal includes an RF (Radio Frequency) processing unit (10-10), a baseband processing unit (10-20), a storage unit (10-30), and a control unit (10-40).

[0107] The RF processing unit (10-10) performs functions such as band conversion and amplification of signals to transmit and receive signals through a wireless channel. That is, the RF processing unit (10-10) up-converts a baseband signal provided from the baseband processing unit (10-20) to an RF band signal, transmits the RF band signal through an antenna, and down-converts an RF band signal received through the antenna to a baseband signal. For example, the RF processing unit (10-10) 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), and the like. Although one antenna is shown in FIG. 10, the terminal may include multiple antennas. Also, the RF processing unit (10-10) may include multiple RF chains. Also, the RF processing unit (10-10) may perform beamforming. For the beamforming, the RF processor (10-10) can adjust the phase and magnitude of each of the signals transmitted and received via a plurality of antennas or antenna elements.

[0108] The baseband processor (10-20) performs a conversion function between a baseband signal and a bit stream according to a system physical layer standard. For example, when transmitting data, the baseband processor (10-20) generates complex symbols by encoding and modulating a transmission bit stream. When receiving data, the baseband processor (10-20) restores a reception bit stream by demodulating and decoding a baseband signal provided from the RF processor (10-10). For example, in the case of an OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processor (10-20) generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and then configures OFDM symbols by performing an inverse fast Fourier transform (IFFT) operation and inserting a cyclic prefix (CP). In addition, when receiving data, the baseband processing unit (10-20) divides the baseband signal provided from the RF processing unit (10-10) into OFDM symbol units, restores the signal mapped to the subcarrier by FFT (fast Fourier transform) operation, and then restores the received bit string by demodulation and decoding.

[0109] The baseband processing unit (10-20) and the RF processing unit (10-10) transmit and receive signals as described above. Therefore, the baseband processing unit (10-20) and the RF processing unit (10-10) can be called a transmitting unit, a receiving unit, a transceiver unit, or a communication unit. Furthermore, at least one of the baseband processing unit (10-20) and the RF processing unit (10-10) can include a plurality of communication modules to support a plurality of different wireless connection technologies. Furthermore, at least one of the baseband processing unit (10-20) and the RF processing unit (10-10) can include different communication modules to process signals of different frequency bands. For example, the different wireless connection technologies can include a wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. In addition, the different frequency bands may include a super high frequency (SHF) band (eg, 2.5 GHz, 5 GHz) and a millimeter wave (mm wave) band (eg, 60 GHz).

[0110] The memory unit (10-30) stores data such as basic programs, application programs, and setting information for the operation of the terminal. In particular, the memory unit (10-30) can store information related to wireless LAN nodes that perform wireless communication using wireless LAN connection technology. The memory unit (10-30) provides the stored data in response to a request from the control unit (10-40).

[0111] The control unit (10-40) controls the overall operation of the terminal. For example, the control unit (10-40) transmits and receives signals via the baseband processing unit (10-20) and the RF processing unit (10-10). The control unit (10-40) also records and reads data in the memory unit (10-40). To this end, the control unit (10-40) may include at least one processor. For example, the control unit (10-40) may include a CP (communication processor) that controls communication and an AP (application processor) that controls higher layers such as application programs. According to an embodiment of the present disclosure, the control unit (10-40) includes a multiple connection processing unit (10-42) that performs processing for operating in a multiple connection mode. For example, the control unit (10-40) may control the terminal to perform the procedure shown in the terminal operation of FIG. 5.

[0112] The control unit (10-40) according to the embodiment of the present disclosure controls how to operate when a UL LBT problem is detected during DAPS HO in the above-described manner.

[0113] FIG. 11 illustrates a block configuration of a base station in a wireless communication system according to an embodiment of the present disclosure.

[0114] As shown in the figure, the base station includes an RF processing unit (11-10), a baseband processing unit (11-20), a backhaul communication unit (11-30), a storage unit (11-40), and a control unit (11-50).

[0115] The RF processing unit (11-10) performs functions for transmitting and receiving signals through a wireless channel, such as band conversion and amplification of signals. That is, the RF processing unit (11-10) up-converts a baseband signal provided from the baseband processing unit (11-20) to an RF band signal, transmits the RF band signal through an antenna, and down-converts an RF band signal received through the antenna to a baseband signal. For example, the RF processing unit (11-10) may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, and the like. Although one antenna is shown in the figure, the first connection node may include multiple antennas. Also, the RF processing unit (11-10) may include multiple RF chains. In addition, the RF processing unit (11-10) may perform beamforming. For the beamforming, the RF processing unit (11-10) may adjust the phase and magnitude of each of the signals transmitted and received through multiple antennas or antenna elements. The RF processing unit may perform a downlink MIMO operation by transmitting one or more layers.

[0116] The baseband processor (11-20) performs a conversion function between a baseband signal and a bit string in accordance with the physical layer standard of the first wireless access technology. For example, when transmitting data, the baseband processor (11-20) generates complex symbols by encoding and modulating a transmission bit string. When receiving data, the baseband processor (11-20) restores a reception bit string by demodulating and decoding a baseband signal provided from the RF processor (11-10). For example, in the case of OFDM, when transmitting data, the baseband processor (11-20) generates complex symbols by encoding and modulating a transmission bit string, maps the complex symbols to subcarriers, and then configures OFDM symbols by performing IFFT and inserting CPs. During data reception, the baseband processing unit (11-20) divides the baseband signal provided from the RF processing unit (11-10) into OFDM symbol units, restores the signal mapped to the subcarrier by FFT operation, and restores the received bit string by demodulation and decoding. The baseband processing unit (11-20) and the RF processing unit (11-10) transmit and receive signals as described above. For this reason, the baseband processing unit (11-20) and the RF processing unit (11-10) can be called a transmitting unit, a receiving unit, a transmitting / receiving unit, a communication unit, or a wireless communication unit.

[0117] The backhaul communication unit (11-30) provides an interface for communicating with other nodes in the network, i.e., converts a bit string transmitted from the main base station to other nodes, such as a secondary base station or a core network, into a physical signal, and converts a physical signal received from the other nodes into a bit string.

[0118] The memory unit (11-40) stores data such as basic programs, application programs, and setting information for the operation of the main base station. In particular, the memory unit (11-40) can store information on bearers assigned to connected terminals, measurement results reported from connected terminals, and the like. The memory unit (11-40) can also store information that is a criterion for determining whether to provide or interrupt multiple connections to a terminal. The memory unit (11-40) provides the stored data in response to a request from the control unit (11-50).

[0119] The control unit (11-50) controls the overall operation of the main base station. For example, the control unit (11-50) transmits and receives signals via the baseband processing unit (11-20) and the RF processing unit (11-10) or via the backhaul communication unit (11-30). The control unit (11-50) also records and reads data in the memory unit (11-40). To this end, the control unit (11-50) may include at least one processor.

[0120] The methods according to the embodiments described in the claims or specification of the present disclosure may be implemented in the form of hardware, software, or a combination of hardware and software.

[0121] When embodied in software, a computer-readable storage medium may be provided that stores one or more programs (software modules). The one or more programs stored in the computer-readable storage medium are configured for execution by one or more processors in an electronic device. The one or more programs include instructions that cause the electronic device to execute a method according to the embodiments described in the claims or specification of the present disclosure.

[0122] Such a program (software module, software) may be stored in a random access memory, a non-volatile memory including a flash memory, a Read Only Memory (ROM), an Electrically Erasable Programmable Read Only Memory (EEPROM), a magnetic disc storage device, a Compact Disc-ROM (CD-ROM), a Digital Versatile Disc (DVD) or other form of optical storage device, a magnetic cassette, or in a memory configured as a combination of some or all of them. Also, each of the memory components may be included in a plurality of pieces.

[0123] The program may be stored in an attachable storage device accessible through a communication network such as the Internet, an intranet, a local area network (LAN), a wide LAN (WLAN), or a storage area network (SAN), or a combination of these. Such a storage device may be connected to an apparatus that performs the embodiments of the present disclosure through an external port. Also, a separate storage device on the communication network may be connected to an apparatus that performs the embodiments of the present disclosure.

[0124] In the specific embodiments of the present disclosure described above, the components included in the present disclosure are expressed in singular or plural form according to the specific embodiments presented. However, the expressions singular or plural are appropriately selected according to the presented circumstances for the convenience of explanation, and the present disclosure is not limited to singular or plural components, and even components expressed in plural form may be composed of singular, and even components expressed in singular form may be composed of plural.

[0125] Meanwhile, in the drawings illustrating the method of the present disclosure, the order of description does not necessarily correspond to the order of execution, and the order of operations may be changed, or operations may be executed in parallel.

[0126] Alternatively, drawings illustrating the method of the present disclosure may omit some components or may include only some components, as long as the essence of the present disclosure is not compromised.

[0127] Although the present disclosure has been shown and described with reference to various embodiments thereof, it will be apparent to those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and equivalents thereof. [Explanation of symbols]

[0128] 1-05,1-10,1-15,1-20 Base station 1-25 AMF 1-30 UPF 1-35 User terminal 10-10 RF processing section 10-20 Baseband processing section 10-30 Storage section 10-40 Control section 10-42 Multiple Linkage Processing Unit 11-10 RF Processing Section 11-20 Baseband processing section 11-30 Backhaul communication section 11-40 Storage section 11-50 Control section 11-52 Multiple Linkage Processing Unit

Claims

1. A method performed by a terminal in a wireless communication system, comprising: receiving a first message from a source base station, the first message including first information used to detect a consistent uplink listen before talk (LBT) failure for the source base station; receiving a second message for handover to a target base station from the source base station, the second message including second information for reconfiguration with sync and third information for configuring at least one dual active protocol stack (DAPS) bearer; detecting the consistent uplink LBT failure for the source base station based on the first information during the handover-related procedure; suspending data communication of all data radio bearers (DRBs) associated with the source base station based on the third information and the detection.

2. The method of claim 1, further comprising a step of disconnecting from the source base station.

3. At least one DRB among all DRBs associated with the source base station is configured as the at least one DAPS bearer based on the third information; The second information for the synchronization reconfiguration includes a terminal identifier used in the target base station and length information of a timer used for the handover, The method of claim 1 , wherein the first message and the second message are received by radio resource control (RRC) signaling.

4. The method of claim 3, wherein the second information for the synchronization reconfiguration further includes a setting for contention free random access (CFRA) associated with the target base station.

5. The method described in claim 3, wherein confirmation of consistent uplink LBT failure to the target base station is omitted if the timer is running.

6. A method performed by a source base station in a wireless communication system, comprising: transmitting a first message to a terminal, the first message including first information used for detecting a consistent uplink listen before talk (LBT) failure to the source base station; transmitting a second message for handover to the target base station to the terminal, the second message including second information for reconfiguration with sync and third information for configuring at least one dual active protocol stack (DAPS) bearer; The method, wherein the consistent uplink LBT failure for the source base station is detected based on the first information while performing the handover-related procedure, and in response to the detection, data communication of all data radio bearers (DRBs) associated with the source base station is interrupted.

7. The method of claim 6, wherein the connection to the terminal is released.

8. At least one DRB among all DRBs associated with the source base station is configured as the at least one DAPS bearer based on the third information; The second information for the synchronization reconfiguration includes a terminal identifier used in the target base station and length information of a timer used for the handover, The method of claim 6 , wherein the first message and the second message are received by radio resource control (RRC) signaling.

9. The method of claim 8, wherein the second information for the synchronization reconfiguration further includes a setting for contention free random access (CFRA) associated with the target base station.

10. In a terminal of a wireless communication system, the terminal A transceiver; A control unit, the control unit comprising: receiving, from a source base station, a first message including first information used to detect a consistent uplink LBT (listen before talk) failure for the source base station; receiving a second message for handover to a target base station from the source base station, the second message including second information for reconfiguration with sync and third information for configuring at least one dual active protocol stack (DAPS) bearer; Detecting the consistent uplink LBT failure for the source base station based on the first information while performing the handover related procedure; A terminal configured to suspend data communication of all data radio bearers (DRBs) associated with the source base station based on the third information and the detection.

11. The control unit: The terminal of claim 10 , further configured to release the connection with the source base station.

12. At least one DRB among all DRBs associated with the source base station is configured as the at least one DAPS bearer based on the third information; The second information for the synchronization reconfiguration includes a terminal identifier used in the target base station and length information of a timer used for the handover, The terminal of claim 10 , wherein the first message and the second message are received by radio resource control (RRC) signaling.

13. The terminal of claim 12, wherein the second information for the synchronization reconfiguration further includes a setting for contention free random access (CFRA) associated with the target base station.

14. A terminal as described in claim 12, wherein confirmation of consistent uplink LBT failure to the target base station is omitted when the timer is running.

15. In a source base station of a wireless communication system, the source base station comprises: A transceiver; A control unit, the control unit comprising: Transmitting a first message to a terminal, the first message including first information used to detect a consistent uplink LBT (listen before talk) failure to the source base station; Transmitting a second message for handover to the target base station to the terminal, the second message including second information for reconfiguration with sync and third information for configuring at least one dual active protocol stack (DAPS) bearer; A source base station configured such that the consistent uplink LBT failure for the source base station is detected based on the first information while performing the handover-related procedure, and in response to the detection, data communication of all data radio bearers (DRBs) associated with the source base station is interrupted.

16. A source base station as described in claim 15, wherein the connection with the terminal is released.

17. At least one DRB among all DRBs associated with the source base station is configured as the at least one DAPS bearer based on the third information; The second information for the synchronization reconfiguration includes a terminal identifier used in the target base station and length information of a timer used for the handover, The source base station of claim 15 , wherein the first message and the second message are received by radio resource control (RRC) signaling.

18. The source base station of claim 17, wherein the second information for the synchronization reconfiguration further includes a setting for contention free random access (CFRA) associated with the target base station.

Images