Method and apparatus for handling lbt failure indicator when configuring daps handover in a wireless communication system

Abstract

The disclosure relates to a communication method and system for supporting a 5th-Generation (5G) communication system with higher data rates than a 4th-Generation (4G) system and convergence of the Internet of Things (IoT) technology. The disclosure can be applied to intelligent services based on 5G communication technology and IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method performed by a terminal in a communication system is provided. The method includes receiving a first message including first information for detecting persistent uplink Listen-Before-Talk (LBT) failure for a first base station from the first base station, receiving a second message including second information for synchronization reconfiguration for switching to a second base station from the first base station, and suspending data communication of all data radio bearers (DRBs) associated with the first base station when performing a procedure associated with the switching, in case that third information configuring at least one dual active protocol stack (DAPS) bearer is included in the second message and an indication of the persistent uplink LBT failure for the first base station is identified based on the first information.

Description

Technical Field

[0001] This disclosure relates to a method in which, when using the 3rd Generation Partnership Project (3GPP) 5th Generation (5G) New Radio (NR) technology in an unlicensed frequency band of a wireless communication system, a Dual Active Protocol Stack (DAPS) handover (HO) is configured such that concurrent communication occurs between the source and target base stations while the handover is being performed, and uplink Listen-Before-Talk (LBT) failures are detected and recovered. Background Technology

[0002] To meet the increased demand for wireless data services since the deployment of fourth-generation (4G) communication systems, efforts have been focused on developing improved 5G or near-5G communication systems. Therefore, 5G or near-5G communication systems are also referred to as "super-4G networks" or "post-LTE systems." 5G communication systems are considered to be implemented in higher frequency (mmWave) bands (e.g., the 60GHz band) to achieve higher data rates. To reduce radio wave propagation loss and increase transmission distance, beamforming, massive MIMO, full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive MIMO technologies have been discussed in 5G communication systems. Furthermore, system network improvements are being developed in 5G communication systems based on advanced small cells, cloud radio access networks (RAN), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, mobile networks, cooperative communication, coordinated multipoint multi-point (CoMP), and receiver interference cancellation. In 5G systems, hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) (FQAM) and sliding window superposition coding (SWSC) have been developed as advanced coding and modulation (ACM), as well as filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0003] The Internet is a human-centric, interconnected network in which humans generate and consume information. The Internet is now evolving into the Internet of Things (IoT), in which distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), a combination of IoT and big data processing technologies, has emerged through connections to cloud servers. As technological elements, technologies such as sensing, wired / wireless communication and network infrastructure, service interface technologies, and security technologies have been required for IoT implementation. Recently, sensor networks, machine-to-machine (M2M) communication, and machine-type communication have been studied. This IoT environment can provide intelligent Internet technology services that create new value for human life by collecting and analyzing data generated between connected things. Through the integration and combination of existing information technologies 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] Correspondingly, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine-type communication (MTC), and machine-to-machine (M2M) communication can be implemented using beamforming, MIMO, and array antennas. The application of cloud wireless access networks, as a big data processing technology, can also be seen as an example of the convergence between 5G and IoT technologies.

[0005] The above information is provided for background information purposes only to aid in understanding this disclosure. There is no determination or assertion as to whether any of the foregoing content applies to the prior art relating to this disclosure. Summary of the Invention

[0006] [Technical Issues]

[0007] One aspect of this disclosure is to provide a method for handling uplink transmission failures caused by interference from other devices in the unlicensed band during DAPS handover.

[0008] [Technical Solution]

[0009] The aspects of this disclosure at least address the aforementioned problems and / or disadvantages, and at least provide the following advantages. Therefore, one aspect of this disclosure is to provide a method for handling uplink transmission failures caused by interference from other devices in the unlicensed band during DAPS handover.

[0010] According to one aspect of this disclosure, a method performed by a terminal in a communication system is provided. The method includes: receiving a first message from a first base station, the first message including first information for detecting a persistent uplink listen-before-talk (LBT) failure of the first base station; receiving a second message from the first base station for handover to a second base station, the second message including second information for reconfiguration with sync; and, while performing a handover-related procedure, suspending data communication of all data radio bearers (DRBs) associated with the first base station if third information configuring at least one dual active protocol stack (DAPS) bearer is included in the second message and an indication of a persistent uplink LBT failure of the first base station is identified based on the first information.

[0011] According to another aspect of this disclosure, a method performed by a first base station in a communication system is provided. The method includes: sending a first message to a terminal, the first message including first information for detecting a persistent uplink (LBT) failure of the first base station; and sending a second message to the terminal for handover to a second base station, the second message including second information for synchronous reconfiguration, wherein, when performing a handover-related procedure, if the second message includes third information configuring at least one dual-activity protocol stack (DAPS) bearer, and an indication of a persistent uplink (LBT) failure of the first base station is identified based on the first information, data communication of all data radio bearers (DRBs) associated with the first base station is suspended.

[0012] According to another aspect of this disclosure, a terminal in a communication system is provided. The terminal includes a transceiver and a controller, the controller being coupled to the transceiver and configured to: receive a first message from a first base station, the first message including first information for detecting a persistent uplink (LBT) failure of the first base station; receive a second message from the first base station for handover to a second base station, the second message including second information for synchronization reconfiguration; and, when performing a handover-related procedure, if third information configuring at least one dual-active protocol stack (DAPS) bearer is included in the second message and an indication of a persistent uplink (LBT) failure of the first base station is identified based on the first information, suspend data communication of all data radio bearers (DRBs) associated with the first base station.

[0013] According to another aspect of this disclosure, a first base station in a communication system is provided. The first base station includes a transceiver and a controller, the controller being coupled to the transceiver and configured to: send a first message to a terminal, the first message including first information for detecting a persistent uplink LBT failure of the first base station; and send a second message to the terminal for handover to a second base station, the second message including second information for synchronization reconfiguration, wherein, when performing a handover-related process, if the second message includes third information configuring at least one dual active protocol stack (DAPS) bearer and identifies an indication of a persistent uplink LBT failure of the first base station based on the first information, data communication of all data radio bearers (DRBs) associated with the first base station is suspended.

[0014] [Beneficial Effects]

[0015] According to this disclosure, delays caused by LBT failures during DAPS handover in unlicensed bands can be reduced.

[0016] Other aspects, advantages and distinctive features of this disclosure will become apparent to those skilled in the art from the following detailed description of various embodiments of the present disclosure in conjunction with the accompanying drawings. Attached Figure Description

[0017] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent from the following description taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a diagram illustrating the structure of a novel radio NR system according to an embodiment of the present disclosure; Figure 2 This is a diagram illustrating the radio protocol structure in a Long Term Evolution (LTE) system and an NR system according to embodiments of the present disclosure; Figure 3 This is a diagram of the downlink and uplink channel frame structure when performing beam-based communication in an NR system according to an embodiment of the present disclosure; Figure 4 This is a diagram illustrating a contention-based four-step random access process to a base station performed by a terminal according to an embodiment of the present disclosure; Figure 5 This is a diagram illustrating a Listen-Before-Speak (LBT) type 1 according to an embodiment of the present disclosure; Figure 6 This is a diagram illustrating LBT type 2 according to an embodiment of the present disclosure; Figure 7 This is a diagram illustrating the process between the terminal and the base station when the terminal detects an uplink LBT failure according to an embodiment of the present disclosure; Figure 8AThis is a diagram illustrating the process of using a Dual Active Protocol Stack (DAPS) during handover according to an embodiment of this disclosure; Figure 8B This is a diagram illustrating the process of using a dual-active protocol stack during a handover according to an embodiment of the present disclosure; Figure 9 This is a diagram illustrating the terminal operation sequence when an LBT failure is detected during DAPS handover according to an embodiment of the present disclosure; Figure 10 A block diagram of a terminal in a wireless communication system according to an embodiment of the present disclosure is shown; and Figure 11 A block diagram of a base station in a wireless communication system according to an embodiment of the present disclosure is shown.

[0018] Throughout the accompanying drawings, it should be noted that the same reference numerals are used to describe the same or similar elements, features, and structures. Detailed Implementation

[0019] The following description, with reference to the accompanying drawings, is provided to aid in a comprehensive understanding of the various embodiments of this disclosure as defined by the claims and their equivalents. It includes various specific details to aid understanding, but these details are to be considered exemplary only. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the various embodiments described herein without departing from the scope and spirit of this disclosure. Additionally, for clarity and brevity, descriptions of well-known functions and structures may be omitted.

[0020] The terms and words used in the following description and claims are not limited to their literal meaning, but are used by the inventors only to enable a clear and consistent understanding of this disclosure. Therefore, it will be apparent to those skilled in the art that the following description, which provides various embodiments of this disclosure, is for illustrative purposes only and is not intended to limit the disclosure as defined by the appended claims and their equivalents.

[0021] It should be understood that the singular forms “a,” “an,” and “the” include plural indicators unless the context clearly specifies otherwise. Thus, for example, referring to “the surface of a component” includes referring to one or more such surfaces.

[0022] In the following description, for convenience, terms for identifying access nodes, terms relating to network entities, terms relating to messages, terms relating to interfaces between network entities, terms relating to various identification information, etc., are used illustratively. Therefore, this disclosure is not limited to the terminology used below, and other terms relating to subjects with equivalent technical meaning may be used.

[0023] In the following description, for ease of description, the terms and names defined in the Long Term Evolution (LTE) and New Radio (NR) standards will be used to describe this disclosure, which are the most recent standards specified by the 3rd Generation Partnership Project (3GPP) among existing communication standards. However, this disclosure is not limited to these terms and names and can be applied in the same manner to systems conforming to other standards. In particular, this disclosure can be applied to 3GPP NR (the fifth-generation mobile communication standard).

[0024] Figure 1 This is a diagram illustrating the structure of an NR system according to an embodiment of the present disclosure.

[0025] refer to Figure 1 The wireless communication system includes multiple base stations 1-05, 1-10, 1-15, and 1-20, an Access and Mobility Management Function (AMF) 1-25, and a User Plane Function (UPF) 1-30. User terminals (user equipment, hereinafter referred to as UEs or terminals) 1-35 access external networks via base stations 1-05, 1-10, 1-15, and 1-20 and UPF 1-30.

[0026] Base stations 1-05, 1-10, 1-15, and 1-20 are access nodes of the cellular network and provide radio access to terminals accessing the network. That is, base stations 1-05, 1-10, 1-15, and 1-20 collect status information such as the buffer status, available transmission power status, and channel status of terminals, and perform scheduling to serve user services, supporting the connection between terminals and the core network (CN; specifically, the CN in NR is referred to as 5GC). In communication, the user plane (UP) related to actual user data transmission and the control plane (CP) such as connection management can be partitioned and configured. In the attached diagram, next-generation NodeBs (gNBs) 1-05 and 1-20 use the UP and CP technologies defined in NR technology, while ng-eNBs 1-10 and 1-15, although connected to 5GC, use the UP and CP technologies defined in LTE technology.

[0027] AMF / Session Management Function (SMF) 1-25 is a device responsible for various control functions and mobility management functions of the terminal and is connected to multiple base stations, and UPF 1-30 is a gateway device that provides data transmission.

[0028] Figure 2 This is a diagram illustrating the radio protocol structure in an LTE system and an NR system according to embodiments of the present disclosure.

[0029] The radio protocols of the LTE system include the Packet Data Convergence Protocol (PDCP) 2-05 and 2-40 for the UE and evolved NodeB (eNB), the Radio Link Control (RLC) 2-10 and 2-35, and the Media Access Control (MAC) 2-15 and 2-30. The Packet Data Convergence Protocol (PDCP) 2-05 and 2-40 are responsible for operations such as IP header compression / reconstruction, and the Radio Link Control (RLC) 2-10 and 2-35 reconfigures PDCP Packet Data Units (PDUs) to appropriate sizes. The MAC 2-15 and 2-30 connect to multiple RLC layer devices included in a single terminal, multiplexing RLC PDUs to MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. Physical (PHY) layers 2-20 and 2-25 perform channel coding and modulation on upper-layer data, converting the channel-coded and modulated upper-layer data into Orthogonal Frequency Division Multiplexing (OFDM) symbols and transmitting these OFDM symbols via radio channels; or demodulating and channel decoding the OFDM symbols received via radio channels and transmitting them to the upper layer. The physical layer uses Hybrid Automatic Repeat Request (HARQ) for additional error correction, and the receiver sends a 1-bit indication of whether it has received a packet sent by the transmitter. This is called HARQ ACK / NACK information. In LTE, downlink HARQ ACK / NACK information for uplink data transmission is transmitted via the Physical Hybrid ARQ Indicator Channel (PHICH), which is the physical channel. In NR, the need for retransmission or new transmission can be determined based on the scheduling information of the corresponding terminal on the Physical Dedicated Control Channel (PDCCH), which transmits downlink / uplink resource allocation, etc. This is due to the application of asynchronous HARQ in NR. Uplink HARQ ACK / NACK information used for downlink data transmission can be transmitted via physical channels such as the Physical Uplink Control Channel (PUCCH) or the Physical Uplink Shared Channel (PUSCH). The PUCCH is typically transmitted in the uplink of a PCell, which will be described later. However, if the terminal supports it, the base station can also transmit the PUCCH to the terminal in a subcell (SCell), which will be described later; this is referred to as the PUCCH SCell.

[0030] Although not shown in the figure, the Radio Resource Control (RRC) layer exists above the PDCP layer in each of the terminals and base stations, and configuration control messages related to measurement and access can be exchanged in the RRC layer for radio resource control.

[0031] Meanwhile, the PHY layer can include one or more frequencies / carriers, and the technique of concurrently configuring and using multiple frequencies is called carrier aggregation (hereinafter referred to as CA). In CA, communication between a terminal (or user equipment (UE)) and a base station (evolved Universal Mobile Telecommunications Service (UMTS) Terrestrial Radio Access Network (E-UTRAN) nodeB (eNB)) using only one carrier is changed to further using a primary carrier and one or more subcarriers, allowing the transmission capacity to increase significantly with the number of subcarriers. In LTE, the cell of a base station using the primary carrier is called the primary cell (PCell), and the cell of a base station using a secondary carrier is called the secondary cell (SCell).

[0032] Figure 3 This is a diagram of the downlink and uplink channel frame structure when performing beam-based communication in an NR system according to an embodiment of the present disclosure.

[0033] refer to Figure 3 Base station 3-01 transmits signals in the form of beams to send strong signals or signals with wider coverage, such as 3-11, 3-13, 3-15, and 3-17. Therefore, terminal 3-03 within the cell needs to use the specific beams transmitted by the base station (…). Figure 3 The beam #1 (3-13) is used to send or receive data.

[0034] Depending on whether the terminal is connected to the base station, the terminal's state is divided into idle mode (RRC_IDLE) and connected mode (RRC_CONNECTED). The base station cannot identify the location of a terminal in idle mode.

[0035] If a terminal in idle mode needs to switch to connected mode, the terminal receives synchronization signal blocks (SSBs) 3-21, 3-23, 3-25, and 3-27 sent by the base station. SSBs are periodically transmitted according to the period configured 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) 3-45.

[0036] In this diagram, it is assumed that SSBs are transmitted per 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 diagram, it is assumed that the terminal in idle mode is located in beam #1. However, even when a terminal in connected mode performs random access, the terminal selects the SSB received at the time of performing random access.

[0037] Therefore, in this diagram, SSB#1 is received via beam #1. Upon receiving SSB#1, the terminal can obtain the physical cell identifier (PCI) of the base station via the PSS and SSS, and the terminal can determine the identifier of the currently received SSB (i.e., #1), the position of receiving the current SSB within a 10 ms frame, and the position within a system frame number (SFN) with a period of 10.24 seconds by receiving the PBCH. The main information block is included in the PBCH, and the main information block indicates the position of the system information block type SIB1, which is to receive broadcasts of more detailed cell configuration information. Upon receiving SIB1, the terminal can identify the total number of SSBs sent by the base station and can determine the position of the physical random access channel (PRACH) timing (in this diagram, a scenario of allocation every 1 ms has been assumed: from 3-30 to 3-39), which enables random access to the connection mode (more precisely, enables the transmission of a preamble, a physical signal specifically designed for uplink synchronization). Furthermore, based on this information, it is possible to identify which PRACH timing is mapped to which SSB index. For example, in this diagram, a scenario where allocation occurs every 1 ms is assumed, and a scenario where each PRACH timing is allocated 1 / 2 of an SSB (i.e., each SSB has two PRACHs) is also assumed. Therefore, the following scenario is shown: starting with the PRACH timing based on the SFN value, two PRACH timings are allocated to each SSB. That is, in this scenario, 3-30 and 3-31 are assigned to SSB#0, and 3-32 and 3-33 are assigned to SSB#1. Similarly, 3-34 and 3-35 are assigned to SSB#2, and 3-36 and 3-37 are assigned to SSB#3. After all SSBs are configured, PRACH timings 3-38 and 3-39 are reassigned to the first SSB.

[0038] Therefore, the terminal identifies the positions of PRACH timings 3-32 and 3-33 for SSB#1, and thus sends a random access preamble at the current time via the fastest PRACH timing (e.g., 3-32) among the PRACH timings 3-32 and 3-33 corresponding to SSB#1. Since the base station has already received the preamble in PRACH timing 3-32, it can know that the terminal has selected SSB#1 and sent the preamble, and therefore can send or receive data via the corresponding beam when performing subsequent random access.

[0039] As described above, even when a connected terminal moves from the current (source) base station to the target base station due to handover or other reasons, the terminal performs random access to the target base station and selects an SSB to transmit a random access preamble. Furthermore, during handover, a handover command is sent to the terminal, causing it to move from the source base station to the target base station. This message may include a dedicated random access preamble identifier for each SSB of the target base station, allowing the use of this dedicated random access preamble identifier when performing random access in the target base station. At this time, the base station may not assign dedicated random access preamble identifiers to all beams (depending on the terminal's current location, etc.), and therefore may not assign dedicated random access preambles to some SSBs (e.g., dedicated random access preambles are only assigned to beams #2 and #3). If a dedicated random access preamble is not assigned to an SSB selected for preamble transmission, the terminal may randomly select a contention-based random access preamble to perform random access. For example, in this figure, the terminal is initially located in beam #1, which has not been assigned a dedicated random access preamble, and the terminal performs random access. However, after a failure, when the random access preamble is retransmitted, it might be in a scenario where the terminal is located in beam #3, which has been assigned a dedicated random access preamble, to transmit the dedicated preamble. In other words, if preamble retransmission occurs even within a single random access procedure, a contention-based or non-contention-based random access procedure can be performed depending on whether the dedicated random access preamble is assigned to the selected SSB in each preamble transmission.

[0040] Figure 4 This is a diagram illustrating a contention-based four-step random access process to a base station performed by a terminal according to an embodiment of the present disclosure.

[0041] Figure 4 This diagram illustrates a contention-based four-step random access process performed by a terminal in various situations requiring initial access to a base station, reconnection, handover, and other random access.

[0042] refer to Figure 4 In order to access base station (Node B) 4-03, terminal 4-01 performs the following steps as described above. Figure 3PRACH is selected, and a random access preamble is sent to PRACH in operation 4-11. One or more terminals can concurrently send random access preambles via PRACH resources. PRACH resources can span a subframe, or they can use only some symbols in a subframe. Information about PRACH resources can be included in system information broadcast by the base station, so that the terminal can identify the time-frequency resources for which the preamble should be sent. In addition, the random access preamble corresponds to a specific sequence that can be received even if transmission is performed before full synchronization with the base station, and multiple preamble identifiers (indices) can exist according to the standard. If multiple preamble identifiers exist, the preamble sent by the terminal can be randomly selected by the terminal, or it can be a specific preamble specified by the base station.

[0043] If the base station receives the preamble, it sends a Random Access Response (RAR) message to the terminal in operation 4-21. The RAR message may include at least one of the following: preamble identifier information used in operation 4-11, uplink transmission timing check information, uplink resource allocation information to be used in subsequent operations (i.e., 4-31), and temporary terminal identifier information. For example, if multiple terminals attempt random access in operation 4-11 by sending different preambles, the preamble identifier information is sent to indicate the preamble, and the RAR message is a response message to that preamble. The uplink resource allocation information is detailed information about the resources to be used by the terminal in operation 4-31, including at least one of the following: the physical location and size of the resource, the modulation and coding scheme (MCS) used during transmission, and power adjustment information during transmission. If the terminal that sent the preamble performs initial access, the terminal does not have an identifier assigned by the base station for communicating with the base station; therefore, the temporary terminal identifier information is a value sent to the terminal for communicating with the base station.

[0044] RAR messages should be sent within a predetermined period starting from a predetermined time after the transmission of the preamble, and this period is referred to as the "RAR window" 4-23. The RAR window begins at a predetermined time after the transmission of the first preamble. The predetermined time may be in subframes (1 ms) or may be a smaller value. The length of the RAR window may be a predetermined value configured by the base station, specific to each PRACH resource or specific to one or more PRACH resource sets, within the system information message broadcast by the base station.

[0045] When a RAR message is sent, the base station schedules the RAR message via the PDCCH and scrambles the scheduling information using a Random Access Radio Network Temporary Identifier (RA-RNTI). In operation 4-11, the RA-RNTI is mapped to the PRACH resource used to send the message, and a terminal that has sent a preamble to a specific PRACH resource attempts to receive the PDCCH based on the RA-RNTI and determines whether a corresponding RAR message exists. That is, as shown in the figure, if the RAR message is a response to a preamble sent by the terminal in operation 4-11, the RA-RNTI used in the RAR message of the scheduling information includes information about what was transmitted in operation 4-11. For this purpose, the RA-RNTI can be determined based on information such as the time or frequency resources for which the preamble has been sent, and can be calculated, for example, by the following equation: [Equation 1] RA-RNTI=1 + s_id + 14×t_id + 14×80×f_id + 14×80×8×ul_carrier_id Here, s_id is the index corresponding to the first OFDM symbol in which preamble transmission begins in operation 4-11, and its value is 0 ≤ s_id ≤ 14 (i.e., the maximum number of OFDM symbols in a time slot). Furthermore, t_id is the index corresponding to the first time slot in which preamble transmission begins in operation 4-11, and its value is 0 ≤ t_id ≤ 80 (i.e., the maximum number of time slots in a system frame (10 ms)). Additionally, f_id indicates the order of PRACH resources on the frequency in which the preamble is transmitted in operation 4-11, and its value is 0 ≤ f_id ≤ 8 (i.e., the maximum number of PRACH symbols on the frequency at the same time). If two carriers are used in the uplink for a cell, ul_carrier_id is a factor used to distinguish whether the preamble is transmitted in the normal uplink (UL) (NUL) (0 in this case) or in the supplementary uplink (SUL) (1 in this case).

[0046] For the purposes described above, in 4-31, the terminal that has received the RAR message sends different messages to the resources allocated to the RAR message. In this diagram, the third message is also referred to as Msg3 (i.e., the preamble in operation 4-11 is referred to as Msg1, and the RAR in operation 4-21 is referred to as Msg2). As an example of Msg3 sent by the terminal, an RRCConnectionRequest message, which is an RRC layer message, is sent in the case of initial connection, an RRCConnectionReestablishmentRequest message is sent in the case of reconnection, and an RRCConnectionReconfigurationComplete message is sent during handover. Alternatively, a Buffer Status Report (BSR) message for resource requests, etc., may be sent.

[0047] Subsequently, in operation 4-41, the terminal receives a contention resolution message from the base station for initial transmission (i.e., when Msg3 does not include information about the base station identifier previously assigned to the terminal, etc.). The contention resolution message also includes the content sent by the terminal in Msg3, so that even if multiple terminals have selected the same preamble in operation 4-11, the responding terminal can be notified.

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

[0049] The aforementioned 5G system can be considered for scenarios where it operates in unlicensed frequency bands. Unlicensed frequency bands refer to frequency bands that, within the scope of regulatory approval, can be freely used by anyone on the corresponding frequencies without a license. Examples include the 2.4GHz band and the 5GHz band, and communication is performed using these frequencies via Wi-Fi, Bluetooth, etc.

[0050] In order to conduct communications in unlicensed frequency bands, data must be sent or received according to rules established for each country. More specifically, regulations stipulate that before a communication device can transmit in an unlicensed frequency band, it must "listen" to determine whether the unlicensed frequency band is occupied by another communication device. If the unlicensed frequency band is determined to be free, then a "transmission" is performed. This scheme of listening and transmitting when the unlicensed frequency band is free is called Listen Before Talk (LBT). Regulations requiring LBT to be performed for each country and each unlicensed frequency band have been established, and according to these regulations, communication devices are required to perform LBT when conducting communications in unlicensed frequency bands.

[0051] According to embodiments of this disclosure, there can be two types of LBTs: Type 1 and Type 2. However, this disclosure is not limited thereto.

[0052] Figure 5 This is a diagram illustrating LBT type 1 according to an embodiment of the present disclosure.

[0053] refer to Figure 5 LBT type 1 uses the following method: Before transmission, it randomly determines whether other peripheral devices will perform transmission, and it performs transmission when the channel is idle (unoccupied) for a random period of time. The communication device first listens to see if the channel has been idle for a fixed time (T). d When the channel is idle, determine again whether the channel has been idle for a random period of time (N).

[0054] Here, T is determined. d The method for determining the value of N can vary depending on the priority and importance of the service, and in this embodiment, a total of four different categories are illustrated. These categories can be referred to as Channel Access Priority Classes (CAPC).

[0055] According to CAPC, the time length T is obtained. d =16 + mp 9μs, and obtained N = random (0, CW) p ) 9μs, where the CW value changes from CW min，p Initially, the CW value increases with each transmission failure, reaching a maximum value of CW. max，p For example, if LBT is performed using a scheme with CAPC of 3, then T d The length is 16 + 3 9 = 43 μs, and N is chosen as a random value between 0 and 15 for the initial transmission, where, for example, if 7 is chosen, then N is 7. 9 = 63 μs, and the communication device can send data when the channel is idle for 106 μs.

[0056] [Table 1]

[0057] In this example (when N is selected as 7), if it is determined that the channel is occupied by another device (i.e., the Received Signal Strength Indicator (RSSI) is equal to or greater than a predetermined threshold) during the determination of whether the channel is idle (e.g., in the case of 4 after 3 in 7), the terminal waits until the channel occupancy ends and then waits for T again. d The system determines whether the channel is idle for the remaining time period of 4, and then performs transmission. As shown in the table above, a low-CAPC LBT scheme can be used when sending high-priority services.

[0058] Figure 6 This is a diagram illustrating LBT type 2 according to an embodiment of the present disclosure.

[0059] refer to Figure 6 LBT type 2 is a method that uses a fixed time to listen for whether other peripheral devices are performing transmissions before executing a transmission itself. Therefore, it executes a transmission immediately when the channel is idle for a fixed period of time. That is, in this diagram, LBT type 2 is the following scheme: when the communication device needs to perform a transmission, the communication device listens for a fixed period of time T... short (=T) f + T s The system listens to (senses) the channel and, if the channel is determined to be idle, immediately transmits data. This is the LBT scheme available when transmitting extremely high-priority signals. Therefore, the aforementioned random access preamble (e.g., Figure 4 Operations 4-11) The PUCCH and other signals are highly important signals, therefore the LBT scheme should be used to send them.

[0060] Figure 7 This is a diagram illustrating the process between the terminal and the base station when the terminal detects an uplink LBT failure according to an embodiment of the present disclosure.

[0061] refer to Figure 7 It is assumed that terminal 7-01 is connected to base station 7-03 operating in the unlicensed frequency band and is therefore in RRC connected state (RRC_CONNECTED). In RRC connected state, the terminal can send data to or receive data from the base station. In operation 7-11, the terminal can receive configuration of parameters related to uplink LBT problem detection from the base station via RRCReconfiguration messages or SIB messages, which will be described later.

[0062] Therefore, the terminal can receive 7-13 scheduled uplink resources from the base station via PDCCH, or it can perform uplink transmissions for random access, PUCCH transmissions, data transmissions for configured uplink authorizations, etc.

[0063] As described above, if data is transmitted in an unlicensed frequency band, the terminal needs to perform an LBT operation, and can configure the type of LBT to be performed for each logical channel in the RRC message or for each corresponding uplink resource allocation in the PDCCH. The terminal can perform the LBT according to the configuration of the highest (or lowest) priority in the logical channel to which the actual transmitted data belongs.

[0064] Therefore, if the terminal is unable to perform an uplink transmission in operation 7-19 due to an LBT failure, the terminal starts (drives) a timer (e.g., lbt-FailureDetectionTimer) for LBT failure detection in operation 7-15. The timer length can be configured according to the RRCReconfiguration or SIB message. A predetermined counter is incremented whenever an LBT failure occurs in operations 7-19 and 7-21, and the timer is restarted in operation 7-17. This is to allow the terminal to identify the severity of the UL LBT problem while the timer is running, and to perform additional operations when the counter reaches the value configured by the base station according to the RRCReconfiguration or SIB message.

[0065] Subsequently, if the number of failures that occur before the timer expires does not reach the value configured by the base station (e.g., 4 times), the terminal determines that the uplink LBT problem no longer occurs and sets the counter to 0 in operation 7-23.

[0066] As another example, if the terminal is unable to perform a transmission in operation 7-37 due to an uplink LBT failure, the terminal starts a timer in operation 7-31. Subsequently, if the terminal has further attempted to perform uplink transmissions, such as in operations 7-39, 7-41, and 7-43, and is continuously unable to perform transmissions due to a UL LBT problem, with the timer restarting in operations 7-33 and 7-35, and the number of failures occurring is as many as configured by the base station (e.g., four), the terminal identifies an uplink LBT problem sufficient to cause problems in uplink transmissions and performs additional procedures in operation 7-45 to resolve the problem. These additional procedures may include: sending an LBT failure MAC CE; in the case of a specific cell (SpCell), switching to another bandwidth portion in another SpCell where an LBT failure has not yet occurred; or, if LBT failures have occurred in all BWPs, the terminal's MAC layer notifying the upper layer (RRC) of the LBT failure, thereby causing the upper layer to declare a radio link failure (RLF). If a radio link failure is declared, the terminal selects the cell with the strongest signal from the neighboring cells and attempts to re-establish the connection (connection re-establishment).

[0067] Figure 8A and Figure 8B This is a diagram illustrating the process of using a Dual Active Protocol Stack (DAPS) during handover according to various embodiments of this disclosure.

[0068] During a normal handover, the terminal stops sending or receiving data from the source cell upon receiving handover configuration information, and begins sending or receiving data from the target cell after a successful handover. This results in an interruption period, a time during which data transmission / reception is not possible. If the terminal has a dual-active protocol stack, it can continue sending or receiving data from the source cell during this period. In this disclosure, this handover, performed considering the terminal's capabilities, can be referred to as a dual-active protocol stack (DAPS) handover. When DAPS handover is configured, the terminal can concurrently receive downlink data from both the source and target cells, only for data belonging to data bearers configured with DAPS operation. A bearer is a logical data path; the base station can configure multiple different bearers based on data type. When multiple data bearers exist, the base station can configure DAPS for each bearer. However, uplink data can only be transmitted concurrently to the source and target cells when predetermined conditions are met due to insufficient terminal transmission power, signal interference, or other reasons. For example, in order to minimize terminal complexity, uplink data transmission during DAPS handover can be performed on only one link, and the uplink performing the data transmission can be switched from the source cell to the target cell at a specific time.

[0069] At each major specific point in time, the terminal operation and activity status of the dual protocol stack corresponding to the source cell and the target cell are different.

[0070] refer to Figure 8A Before the handover is performed in Operation 8-05, the terminal only uses the protocol stack corresponding to the source cell.

[0071] In operations 8-10, before the DAPS handover configuration information is provided to the terminal and RACH is performed on the target cell, if the DAPS handover configuration information is received via the RRCReconfiguration message, the terminal configures the protocol stack corresponding to the target cell. However, the terminal still only uses the protocol stack corresponding to the source cell. It is irrelevant even if the protocol stack corresponding to the target cell is inactive.

[0072] During the RACH execution time of operations 8-15, when the RACH operation begins, at least the PHY layer and MAC layer are activated in the protocol stack corresponding to the target cell to execute the RACH operation. At this time, the terminal continues to send data to or receive data from the source cell.

[0073] Reference Figure 8B Describe the actions following operation 8-20.

[0074] When the time point 8-20 arrives when the terminal sends a successful handover completion message (i.e., an RRCReconfigurationComplete message from the RRC layer) to the target cell, the terminal should be able to process the handover success message transmitted via the signaling radio bearer by activating at least some functions of the PHY, MAC, RLC, and PDCP layers in the protocol stack corresponding to the target cell. The terminal can send uplink data to the source cell at least before sending the successful handover completion message to the target cell.

[0075] After receiving the RAR from the target cell in operation 8-25, the terminal activates the entire dual-activity protocol stack. The terminal continues to send data to or receive data from the source cell until a specific time point after RAR reception arrives. The time point at which the terminal can maintain downlink data reception from the source cell may differ from the time point at which the terminal can maintain uplink data transmission. The terminal can send uplink data to the source cell until the HO successful completion message is sent to the target cell, but downlink data reception can continue even after this point.

[0076] After the terminal releases the source cell in operation 8-30, the protocol stack corresponding to the source cell is also released. From then on, the terminal only uses the protocol stack corresponding to the target cell.

[0077] Figure 9 This is a diagram illustrating the terminal operation sequence when an LBT failure is detected during DAPS handover according to an embodiment of the present disclosure.

[0078] refer to Figure 9 It is assumed that at start point 9-01, the terminal accesses a base station operating in an unlicensed frequency band and is in RRC connection state. In RRC connection state, the terminal can send data to or receive data from the base station. In operation 9-03, the terminal can receive configuration parameters related to uplink LBT problem detection from the base station via RRCReconfiguration messages or System Information Block (SIB) messages, which will be described later.

[0079] Subsequently, the terminal can receive a handover command for moving from one base station to another in operation 9-05. The handover command may refer to a case where the `RRCReconfiguration` message at the RRC layer includes the `reconfigurationWithSync` field. The `reconfigurationWithSync` field may include the terminal's identifier information to be used at the target base station, the length information of timer T304 used to detect handover failure, etc. Optionally, the `reconfigurationWithSync` field may also include information about dedicated resources (the aforementioned dedicated random access preamble), which can be used during the random access procedure when accessing the target base station used for the handover process.

[0080] To reduce handover latency, the base station can indicate the aforementioned DAPS HO to the terminal. DAPS HO is executed at operation 9-07 only if a DAPS-Config field is configured as true in the data bearer configured for the terminal. If the terminal is operating in an unlicensed band, or if LBT failure detection and recovery-related configurations are configured for the terminal, the base station may not configure DAPS HO for the terminal. This is essentially to prevent the use of features such as DAPS HO, designed to reduce handover latency, in unlicensed bands, as latency can occur for various reasons during operation. However, in this embodiment, it can be assumed that DAPS handover is configured to reduce handover latency.

[0081] Therefore, if the RRCReconfiguration message includes configuration information related to DAPS HO when LBT failure detection is configured, the terminal will perform additional operations in operations 9-11 based on the LBT failure detection in the source and target base stations.

[0082] For example, if according to Figure 7 If the source also detects continuous LBT failures in the base station during the DAPS handover process, the terminal can suspend the transmission of the data bearer (data radio bearer) configured for it by the DAPS at the source base station, and can terminate the connection with the source base station.

[0083] This is represented by the following 3GPP RRC standard process. (The underlined part represents a change to the existing 3GPP RRC standard process.)

[0084] [Table 2]

[0085] LBT failure may also occur at the target base station during DAPS handover. Therefore, when according to Figure 7When persistent LBT failures are also detected in the target base station during the process, the following methods can be exemplified as methods that can be used in the terminal.

[0086] The first approach is to ignore the detection even if an LBT failure is detected in the target base station during DAPS HO, and wait for the T304 period, which is used to detect general handover failures, to expire.

[0087] In the second method, when an LBT failure is detected in the target base station during DAPS HO, the terminal considers the handover to have failed and pre-executes the operations to be performed upon handover failure (i.e., the operations to be performed when the handover is not completed until the T304 period expires). The operations to be performed upon handover failure may include releasing the dedicated random access resources configured for handover, returning the terminal configuration to the configuration previously configured by the source base station, and performing RRC connection reconstruction. RRC connection reconstruction is performed by selecting a neighboring accessible cell and performing random access to the selected cell (including the transmission of an RRCReestablishmentRequest message). When performing RRC connection reconstruction, the terminal can notify the base station of the existence of connection failure information to be reported by including the connEstFailInfoAvailable field in the RRCReestablishmentComplete message. Therefore, in order for the base station to obtain information, if the base station requests information from the terminal by configuring rlf-ReportTM to true in the UEInformationRequest message, the terminal reports the details of the previously occurred RLF to the base station using the rlf-ReportTM field in the UEInformationResponse message. Since a problem occurred during handover, the terminal can report a connection failure (connectionFailureType) as the cause of the handover failure (hof). The detailed cause of the handover failure (hof-Cause) can indicate that the handover failure was due to an LBT failure (lbt-Failure). Alternatively, in the case of an LBT failure, even if the connection failure occurred due to a handover failure, it can be reported that the connection failure occurred due to an RLF (i.e., the connectionFailureType field is configured as rlf), and in this case, the cause of the RLF (rlf-Cause) can be reported as an RLF failure due to an LBT failure (lbt-Failure).

[0088] This is represented by the following 3GPP RRC standard process. (The underlined part represents a change to the existing 3GPP RRC standard process.)

[0089] [Table 3]

[0090] [Table 4]

[0091] If an LBT failure occurs at the target base station as described above, the terminal can prevent the same problem from recurring by selecting a cell other than the target base station when performing cell selection for reconfiguration. If the RRCReconfiguration message does not include configuration information related to DAPS HO when LBT failure detection is configured, the terminal only performs the additional operations 9-13 based on the LBT failure detection at the target base station. Therefore, when based on Figure 7 When consecutive LBT failures are detected in the target base station, the terminal can ignore the detection and wait for the T304 period (used for detecting general handover failures) to expire. In other words, even if consecutive LBT failures are detected while T304 is running, the terminal can ignore the detection and perform no additional operations.

[0092] This is represented by the following 3GPP RRC standard process. (The underlined part represents a change to the existing 3GPP RRC standard process.)

[0093] [Table 5]

[0094] In the RRC standard process, if DAPS is not configured (i.e., 1>otherwise: hereinafter), it includes the case of performing a normal handover (i.e., LBT failure occurs during handover) and the case of not performing a handover (i.e., LBT failure occurs during communication with a base station). Therefore, the operations for these two cases can be distinguished. For example, in the case of not performing a handover (i.e., when T304 is initiated by receiving a handover command from a base station), the terminal considers the handover to have failed after detecting a T304 failure, and the terminal does not wait for T304 to expire, but performs the operations that would be performed in the event of a handover failure (i.e., the operations performed when the handover is not completed until T304 expires). The operations performed in the event of a handover failure may include releasing the dedicated random access resources configured for handover, returning the terminal configuration to the configuration previously configured by the source base station, and performing RRC connection reconstruction. RRC connection reconstruction is performed by selecting a neighboring accessible cell and performing random access to the selected cell (including the transmission of RRCReestablishmentRequest messages). (The underlined part is a change to the process in the existing 3GPP RRC standard.)

[0095] [Table 6]

[0096] In the aforementioned processes 9-11 and 9-13, when an LBT failure occurs at the target base station during handover, if the terminal wants to ignore the LBT failure, it can change... Figure 7 The LBT failure detection process described herein does not notify the RRC layer of the occurrence of an LBT failure. The process then terminates in operation 9-21.

[0097] In the first method used here, even if the number of LBT failures in SpCell reaches a threshold during handover (i.e., when T304 is running; or during the random access procedure for reconfiguration synchronization), the terminal's MAC layer will not trigger consecutive LBT failures or perform additional procedures.

[0098] This is represented by the following 3GPP MAC standard process. (The underlined part represents a change to the existing 3GPP MAC standard process.)

[0099] [Table 7]

[0100] In the second approach, if the number of LBT failures in SpCell reaches a threshold during handover (i.e., when T304 is running; or during the random access procedure for reconfiguration synchronization), the terminal's MAC layer triggers a continuous LBT failure, but does not notify the RRC layer (upper layer) of the event to avoid additional procedures.

[0101] This is represented by the following 3GPP MAC standard process. (The underlined part represents a change to the existing 3GPP MAC standard process.)

[0102] [Table 8]

[0103] Although not depicted in the accompanying figures, an alternative approach can be considered in which the physical layer does not send an LBT failure indication to the MAC layer during the handover. That is, the process of "1> if an LBT failure indication has already been received from the lower layer" can be prevented during the MAC standard procedure.

[0104] According to this process, the terminal can perform the handover procedure under DAPS configuration and LBT failure detection. Only one of the foregoing embodiments can be used, or multiple embodiments can be applied and used simultaneously.

[0105] Figure 10 A block diagram of a terminal in a wireless communication system according to an embodiment of the present disclosure is shown.

[0106] refer to Figure 10 The terminal includes a radio frequency (RF) processor 10-10, a baseband processor 10-20, a memory 10-30, and a controller 10-40.

[0107] RF processor 10-10 performs functions such as transmitting or receiving signals via a radio channel, including frequency band conversion and amplification. Specifically, RF processor 10-10 up-converts the baseband signal provided by baseband processor 10-20 into an RF band signal, transmits the converted RF band signal via an antenna, and then down-converts the RF band signal received via the antenna back into a baseband signal. For example, RF processor 10-10 may include transmit filters, receive filters, amplifiers, mixers, oscillators, digital-to-analog converters (DACs), analog-to-digital converters (ADCs), etc. Figure 10 Only one antenna is shown in the diagram, but the terminal may have multiple antennas. The RF processor 10-10 may include multiple RF chains. The RF processor 10-10 can perform beamforming. For beamforming, the RF processor 10-10 can adjust the phase and amplitude of each signal transmitted or received via multiple antennas or antenna elements.

[0108] Baseband processor 10-20 performs the conversion between baseband signals and bitstreams according to the system's physical layer specifications. For example, during data transmission, baseband processor 10-20 generates complex symbols by encoding and modulating the transmitted bitstream. When data is received, baseband processor 10-20 reconstructs the received bitstream by demodulating and decoding the baseband signal provided by RF processor 10-10. For example, in the case of an Orthogonal Frequency Division Multiplexing (OFDM) scheme, during data transmission, baseband processor 10-20 generates complex symbols by encoding and modulating the transmitted bitstream, maps the complex symbols to subcarriers, and then configures the OFDM symbols by performing an inverse Fast Fourier Transform (IFFT) operation and cyclic prefix (CP) insertion. Furthermore, during data reception, baseband processor 10-20 divides the baseband signal provided by RF processor 10-10 into units of OFDM symbols, reconstructs the signals mapped to subcarriers through a Fast Fourier Transform (FFT) operation, and then reconstructs the received bitstream through demodulation and decoding.

[0109] Baseband processor 10-20 and RF processor 10-10 transmit and receive signals as described above. Therefore, baseband processor 10-20 and RF processor 10-10 can be referred to as transmitters, receivers, transceivers, or communication units. Furthermore, at least one of baseband processor 10-20 and RF processor 10-10 may include multiple communication modules to support a variety of different wireless access technologies. At least one of baseband processor 10-20 and RF processor 10-10 may include different communication modules that process signals in different frequency bands. For example, different radio access technologies may include wireless LAN (e.g., IEEE 802.11), cellular networks (e.g., LTE), etc. Furthermore, different frequency bands may include ultra-high frequency (SHF) bands (e.g., 2.5 GHz and 5 GHz) and millimeter wave (e.g., 60 GHz) bands.

[0110] Memory 10-30 stores data used for terminal operation, such as default programs, applications, and configuration information. Specifically, memory 10-30 may store information related to wireless LAN nodes performing wireless communication using wireless LAN access technology. Memory 10-30 provides the stored data in response to requests from controller 10-40.

[0111] Controller 10-40 controls the overall operation of the terminal. For example, controller 10-40 transmits or receives signals via baseband processor 10-20 and RF processor 10-10. Controller 10-40 records and reads data in memory 10-30. For this purpose, controller 10-40 may include at least one processor. For example, controller 10-40 may include a communication processor (CP) configured to perform control over communications and an application processor (AP) configured to control upper layers (e.g., applications). According to embodiments, controller 10-40 includes a multi-connection processor 10-42 configured to perform processing for operation in a multi-connection mode. For example, controller 10-40 may control the terminal to perform the processes shown in the terminal operation illustrated in embodiments of this disclosure.

[0112] According to the embodiment, the controller 10-40 controls how to operate when a UL LBT problem is detected during DAPS HO by the method described above.

[0113] Figure 11 A block diagram of a base station in a wireless communication system according to an embodiment of the present disclosure is shown.

[0114] refer to Figure 11 The base station includes an RF processor 11-10, a baseband processor 11-20, a backhaul communication unit 11-30, a memory 11-40, and a controller 11-50.

[0115] RF processor 11-10 performs functions such as transmitting or receiving signals via a radio channel, including frequency band conversion and amplification. Specifically, RF processor 11-10 up-converts the baseband signal provided by baseband processor 11-20 into an RF band signal, transmits the converted RF band signal via an antenna, and then down-converts the RF band signal received via the antenna back into a baseband signal. For example, RF processor 11-10 may include transmit filters, receive filters, amplifiers, mixers, oscillators, DACs, ADCs, etc. Figure 11 In the diagram, only one antenna is shown, but the first access node may include multiple antennas. RF processors 11-10 may include multiple RF chains. RF processors 11-10 can perform beamforming. For beamforming, RF processors 11-10 can adjust the phase and amplitude of each signal transmitted or received via multiple antennas or antenna elements. The RF processor can perform downlink MIMO by transmitting one or more layers.

[0116] Baseband processors 11-20 perform conversion functions between baseband signals and bitstreams according to the physical layer specifications of the first radio access technology. For example, during data transmission, baseband processors 11-20 generate complex symbols by encoding and modulating the transmitted bitstream. When data is received, baseband processors 11-20 reconstruct the received bitstream by demodulating and decoding the baseband signal provided by RF processors 11-10. For example, in the case of OFDM compliance, during data transmission, baseband processors 11-20 generate complex symbols by encoding and modulating the transmitted bitstream, map the complex symbols to subcarriers, and then configure OFDM symbols by performing IFFT operations and CP insertion. Furthermore, during data reception, baseband processors 11-20 divide the baseband signal provided by RF processors 11-10 into units of OFDM symbols, reconstruct the signals mapped to subcarriers through FFT operations, and then reconstruct the received bitstream by demodulation and decoding. Baseband processors 11-20 and RF processors 11-10 transmit and receive signals as described above. Therefore, the baseband processor 11-20 and the RF processor 11-10 can be referred to as a transmitter, receiver, transceiver, communication unit, or wireless communication unit.

[0117] The backhaul communication unit 11-30 provides an interface for communication with other nodes within the network. That is, the backhaul communication unit 11-30 converts the bit stream sent from the primary base station to another node, such as a secondary base station or the core network, into physical signals, and converts the physical signals received from another node into bit streams.

[0118] Memory 11-40 stores data used for main base station operation, such as default programs, application programs, and configuration information. Specifically, memory 11-40 may store information related to bearers assigned to connected terminals, measurement results reported from connected terminals, etc. Memory 11-40 may store information used as a criterion for determining whether to provide multiple connections to a terminal or suspend multiple connections for the terminal. Memory 11-40 provides the stored data in response to requests from controller 11-50.

[0119] Controller 11-50 controls the overall operation of the base station. For example, controller 11-50 transmits or receives signals via baseband processor 11-20 and RF processor 11-10, or via backhaul communication unit 11-30. Controller 11-50 records and retrieves data in memory 11-40. For this purpose, controller 11-50 may include at least one processor. According to an embodiment, controller 11-50 may include a multi-connection processor 11-52, which is configured to perform processing for operation in multi-connection mode.

[0120] The methods disclosed in the claims and / or the methods of various embodiments described in this disclosure can be implemented in hardware, software, or a combination of hardware and software.

[0121] When the method is implemented in software, a computer-readable storage medium may be provided for storing one or more programs (software modules). The one or more programs stored in the computer-readable storage medium may be configured to be executed by one or more processors within an electronic device. At least one program may include instructions to cause the electronic device to perform the method according to various embodiments of this disclosure as defined in the appended claims and / or disclosed herein.

[0122] The program (software module or software) can be stored in non-volatile memory, including random access memory and flash memory, read-only memory, electrically erasable programmable read-only memory, magnetic disk storage devices, compressed optical disc-ROM (CD-ROM), digital versatile discs (DVDs), or other types of optical storage devices or magnetic tape cassettes. Alternatively, any combination of some or all of the above-mentioned memories can form the memory storing the program. Furthermore, multiple such memories can be included in an electronic device.

[0123] Additionally, the program can be stored in an attachable storage device, which can access the electronic device via a communication network such as the Internet, intranet, local area network (LAN), wide area network (WLAN), and storage area network (SAN), or a combination thereof. This storage device can access the electronic device via an external port. Furthermore, a separate storage device on a communication network can access portable electronic devices.

[0124] In the detailed embodiments described above, elements included in this disclosure are referred to as singular or plural, depending on the presented embodiments. However, for ease of description, the singular or plural form may be appropriately chosen for the presented situation, and this disclosure is not limited to elements referred to as singular or plural. Thus, elements referred to as plural may also include a single element, or elements referred to as singular may include multiple elements.

[0125] In the accompanying drawings describing the methods of this disclosure, the order described does not always correspond to the order in which the steps of each method are performed, and the order between the steps may be changed or the steps may be performed in parallel.

[0126] Alternatively, in the accompanying drawings describing the methods of this disclosure, some elements may be omitted and only some of these elements may be included without departing from the essential spirit and scope of this disclosure.

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

Claims

1. A method performed by a terminal in a communication system, the method comprising: Receive a first message from the source base station, the first message including first information for detecting a continuous uplink listen-before-talk (LBT) failure of the source base station; The source base station receives a second message for switching to the target base station. The second message includes second information for synchronization reconfiguration and third information for configuring at least one dual active protocol stack (DAPS) bearer. When the process associated with the handover is executed, the failure of the continuous uplink LBT to the source base station is detected based on the first information; as well as Based on the third information and the detection, data communication of all data radio bearers (DRBs) associated with the source base station is suspended.

2. The method according to claim 1 further includes releasing the connection with the source base station.

3. The method according to claim 1, in, Based on the third information, at least one DRB among all the DRBs associated with the source base station is configured as the at least one DAPS bearer. The second information used for synchronous reconfiguration includes the identifier of the terminal to be used in the target base station, and length information related to the timer used for the handover. The first message and the second message are received via Radio Resource Control (RRC) signaling.

4. The method according to claim 3, wherein, The second information for synchronization reconfiguration also includes configuration for contention-free random access (CFRA) associated with the target base station.

5. The method according to claim 3, wherein, While the timer is running, the identification of continuous uplink LBT failure of the target base station is skipped.

6. A method performed by a source base station in a communication system, the method comprising: Send a first message to the terminal, the first message including first information for detecting the continuous uplink listen-before-talk (LBT) failure of the source base station; as well as A second message for switching to the target base station is sent to the terminal. The second message includes second information for synchronization reconfiguration and third information for configuring at least one Dual Active Protocol Stack (DAPS) bearer. During the handover process, if the continuous uplink LBT failure of the source base station is detected by the terminal based on the first information, in response to the detection, data communication from the terminal in all data radio bearers (DRBs) associated with the source base station is suspended by the terminal.

7. The method according to claim 6, wherein, The connection with the terminal was released.

8. The method according to claim 6, in, At least one of the DRBs associated with the source base station is configured by the terminal as the at least one DAPS bearer based on the third information. The second information used for synchronous reconfiguration includes the identifier of the terminal to be used in the target base station, and length information related to the timer used for the handover. The first message and the second message are transmitted via Radio Resource Control (RRC) signaling.

9. The method according to claim 8, wherein, The second information for synchronization reconfiguration also includes configuration for contention-free random access (CFRA) associated with the target base station.

10. A terminal in a communication system, the terminal comprising: transceiver; as well as The controller, connected to the transceiver, is configured to: A first message is received from the source base station, the first message including first information for detecting a continuous uplink listen-before-talk (LBT) failure of the source base station. The system receives a second message from the source base station for handing over to the target base station. The second message includes second information for synchronization reconfiguration and third information for configuring at least one Dual Active Protocol Stack (DAPS) bearer. When the process associated with the handover is executed, the failure of the continuous uplink LBT to the source base station is detected based on the first information, and Based on the third information and the detection, data communication of all data radio bearers (DRBs) associated with the source base station is suspended.

11. The terminal according to claim 10, wherein, The controller is also configured to release the connection with the source base station.

12. The terminal according to claim 10, in, Based on the third information, at least one DRB among all the DRBs associated with the source base station is configured as the at least one DAPS bearer. The second information used for synchronous reconfiguration includes the identifier of the terminal to be used in the target base station, and length information related to the timer used for the handover. The first message and the second message are received via Radio Resource Control (RRC) signaling.

13. The terminal according to claim 12, wherein, The second information for synchronization reconfiguration also includes configuration for contention-free random access (CFRA) associated with the target base station.

14. The terminal according to claim 12, wherein, While the timer is running, the identification of continuous uplink LBT failure of the target base station is skipped.

15. A source base station in a communication system, the source base station comprising: transceiver; as well as The controller, connected to the transceiver, is configured to: A first message is sent to the terminal, the first message including first information for detecting a continuous uplink listen-before-talk (LBT) failure of the source base station, and... A second message for switching to the target base station is sent to the terminal. The second message includes second information for synchronization reconfiguration and third information for configuring at least one Dual Active Protocol Stack (DAPS) bearer. During the handover process, if the continuous uplink LBT failure of the source base station is detected by the terminal based on the first information, in response to the detection, data communication from the terminal in all data radio bearers (DRBs) associated with the source base station is suspended by the terminal.

16. The source base station according to claim 15, wherein, The connection with the terminal was released.

17. The source base station according to claim 15, in, At least one of the DRBs associated with the source base station is configured by the terminal as the at least one DAPS bearer based on the third information. The second information used for synchronous reconfiguration includes the identifier of the terminal to be used in the target base station, and length information related to the timer used for the handover. The first message and the second message are transmitted via Radio Resource Control (RRC) signaling.

18. The source base station according to claim 17, wherein, The second information for synchronization reconfiguration also includes configuration for contention-free random access (CFRA) associated with the target base station.

Images