Method and device for reporting PDCP layer sequence number interval for handover in wireless communication system

Abstract

Disclosed is that a first base station transmits, to a second base station, a first message including information about discarding of an uplink PDCP, wherein information about discarding of an uplink PDCP SDU includes first information for indicating a PDCP SDU discarded by a terminal.

Description

Method and device for reporting PDCP layer sequence number interval for handover in wireless communication system

[0001] The present disclosure relates generally to wireless communication systems, and more particularly, to methods and devices for reporting a sequence number interval of a PDCP layer in a wireless communication system.

[0002] 5G mobile communication technology defines a wide frequency band to enable fast transmission speeds and new services, and can be implemented not only in the sub-6GHz frequency band such as 3.5 gigahertz (3.5GHz), but also in the ultra-high frequency band called millimeter wave (mmWave) such as 28GHz and 39GHz ('Above 6GHz'). In addition, for 6G mobile communication technology, which is called the system after 5G communication (Beyond 5G), implementation in the terahertz band (for example, the 3 terahertz (3THz) band at 95GHz) is being considered to achieve a transmission speed that is 50 times faster than 5G mobile communication technology and an ultra-low latency time that is reduced to one-tenth.

[0003] In the early stages of 5G mobile communication technology, the goal is to support services and satisfy performance requirements for enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (URLLC), and massive Machine-Type Communications (mMTC). These include beamforming and massive MIMO to mitigate path loss of radio waves in ultra-high frequency bands and increase the transmission distance of radio waves, support for various numerologies (such as operation of multiple subcarrier intervals) and dynamic operation of slot formats for efficient use of ultra-high frequency resources, initial access technology to support multi-beam transmission and wideband, definition and operation of BWP (Bidth Part), new channel coding methods such as LDPC (Low Density Parity Check) codes for large-capacity data transmission and Polar Code for reliable transmission of control information, and L2 pre-processing (L2). Standardization has been made for network slicing, which provides dedicated networks specialized for specific services, and pre-processing.

[0004] Currently, discussions are underway to improve and enhance the initial 5G mobile communication technology in consideration of the services that 5G mobile communication technology was intended to support, and physical layer standardization is in progress for technologies such as V2X (Vehicle-to-Everything) to help autonomous vehicles make driving decisions and increase user convenience based on their own location and status information transmitted by vehicles, NR-U (New Radio Unlicensed) for the purpose of system operation that complies with various regulatory requirements in unlicensed bands, NR terminal low power consumption technology (UE Power Saving), Non-Terrestrial Network (NTN), which is direct terminal-satellite communication to secure coverage in areas where communication with terrestrial networks is impossible, and Positioning.

[0005] In addition, standardization of wireless interface architecture / protocols is in progress for technologies such as intelligent factories (Industrial Internet of Things, IIoT) to support new services through linkage and convergence with other industries, Integrated Access and Backhaul (IAB) that provides nodes for expanding network service areas by integrating wireless backhaul links and access links, Mobility Enhancement technology including Conditional Handover and Dual Active Protocol Stack (DAPS) handover, and 2-step random access (2-step RACH for NR) that simplifies random access procedures. Standardization is also in progress for system architecture / services such as 5G baseline architecture (e.g., Service-based Architecture, Service-based Interface) for grafting Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) that provides services based on the location of the terminal.

[0006] Once these 5G mobile communication systems are commercialized, an explosive increase in connected devices will be connected to the communication network, necessitating enhanced functionality and performance of 5G mobile communication systems and integrated operation of these connected devices. To this end, new research will be conducted on improving 5G performance and reducing complexity, supporting AI services, supporting metaverse services, and drone communications by utilizing eXtended Reality (XR), Artificial Intelligence (AI), and Machine Learning (ML) to efficiently support Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR).

[0007] In addition, the development of these 5G mobile communication systems includes new waveforms to ensure coverage in the terahertz band of 6G mobile communication technology, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), Array Antenna, and Large Scale Antenna, metamaterial-based lenses and antennas to improve the coverage of terahertz band signals, high-dimensional spatial multiplexing technology using Orbital Angular Momentum (OAM), Reconfigurable Intelligent Surface (RIS) technology, as well as full duplex technology to improve the frequency efficiency and system network of 6G mobile communication technology, satellite, AI (Artificial Intelligence) from the design stage and AI-based communication technology that realizes system optimization by internalizing end-to-end AI support functions, and ultra-high-performance communication and computing resources to provide services with complexity that exceeds the limits of terminal computing capabilities. It can serve as a basis for the development of next-generation distributed computing technologies that can be realized by utilizing them.

[0008] Based on the discussion as described above, the present disclosure aims to provide a method and apparatus for reporting a sequence number interval of a PDCP layer in a wireless communication system.

[0009] The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0010] The present invention proposes a method and device for reporting a sequence number interval of a PDCP layer.

[0011] More specifically, a method according to one embodiment of the present disclosure includes the steps of receiving a first control signal transmitted from a base station, processing the received first control signal, and transmitting a second control signal generated based on the processing to the base station.

[0012] One embodiment of the present invention provides a device and method capable of effectively providing a service in a wireless communication system.

[0013] The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present disclosure pertains from the description below.

[0014] FIG. 1 illustrates the structure of a wireless communication system according to one embodiment of the present disclosure.

[0015] FIG. 2 illustrates a wireless protocol structure in a wireless communication system according to one embodiment of the present disclosure.

[0016] FIG. 3 illustrates a procedure for a user equipment (UE) to establish a connection with a network in a wireless communication system according to one embodiment of the present disclosure.

[0017] FIG. 4 illustrates an operation of a terminal and a base station transmitting and / or receiving a PDCP (Packet Data Convergence Protocol) SN (Sequence Number) Gap Report in a wireless communication system according to one embodiment of the present disclosure.

[0018] FIG. 5 illustrates a PDCP SN Gap Report format in a wireless communication system according to one embodiment of the present disclosure.

[0019] FIG. 6 illustrates a terminal handover operation in a wireless communication system according to one embodiment of the present disclosure.

[0020] FIG. 7 illustrates a terminal handover operation in a wireless communication system according to one embodiment of the present disclosure.

[0021] FIG. 8 illustrates a configuration of a terminal in a wireless communication system according to one embodiment of the present disclosure.

[0022] FIG. 9 illustrates a configuration of a base station in a wireless communication system according to one embodiment of the present disclosure.

[0023] The operating principles of the present disclosure are described in detail below with reference to the attached drawings. In the following description of the present disclosure, detailed descriptions of related known functions or configurations will be omitted if they are deemed to unnecessarily obscure the gist of the present disclosure. Furthermore, the terms described below are defined based on the functions of the present disclosure and may vary depending on the intent or custom of the user or operator. Therefore, their definitions should be based on the overall content of this specification.

[0024] In describing the embodiments of this disclosure, descriptions of technical details that are well known in the technical field to which this disclosure pertains and are not directly related to this disclosure will be omitted. This is to more clearly convey the gist of this disclosure without obscuring it by omitting unnecessary explanations.

[0025] For the same reason, some components in the attached drawings are exaggerated, omitted, or schematically depicted. Furthermore, the dimensions of each component do not entirely reflect its actual size. Identical or corresponding components in each drawing are assigned the same reference numbers.

[0026] The advantages and features of the present disclosure, and methods for achieving them, will become clearer with reference to the embodiments described below in detail together with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various different forms. These embodiments are provided solely to ensure that the present disclosure is complete and to fully inform those skilled in the art of the scope of the disclosure, and the present disclosure is defined only by the scope of the claims. Like reference numerals designate like elements throughout the specification.

[0027] At this time, it will be understood that each block of the processing flow diagrams and combinations of the flow diagrams can be performed by computer program instructions. These computer program instructions can be installed in a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing equipment, so that the instructions executed by the processor of the computer or other programmable data processing equipment create a means for performing the functions described in the flow diagram block(s). These computer program instructions can also be stored in a computer-available or computer-readable memory that can direct a computer or other programmable data processing equipment to implement the functions in a specific manner, so that the instructions stored in the computer-available or computer-readable memory can also produce a manufactured item that includes an instruction means for performing the functions described in the flow diagram block(s). Since the computer program instructions may be installed on a computer or other programmable data processing device, a series of operational steps may be performed on the computer or other programmable data processing device to create a computer-executable process, and the instructions that cause the computer or other programmable data processing device to perform the steps for performing the functions described in the flowchart block(s) may also provide steps for performing the functions described in the flowchart block(s).

[0028] Additionally, each block may represent a module, segment, or portion of code that contains one or more executable instructions for performing a specific logical function(s). It should also be noted that in some alternative implementation examples, the functions described in the blocks may occur out of order. For example, two blocks depicted in succession may actually be executed substantially concurrently, or the blocks may sometimes be executed in reverse order, depending on their respective functions.

[0029] Here, the term '~ part' used in the present embodiment means software or hardware components such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit), and the '~ part' performs certain roles. However, the '~ part' is not limited to software or hardware. The '~ part' may be configured to be on an addressable storage medium and may be configured to play one or more processors. Therefore, as an example, the '~ part' includes components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and '~ parts' may be combined into a smaller number of components and '~ parts' or further separated into additional components and '~ parts'. Additionally, components and '~parts' may be implemented to regenerate one or more CPUs within a device or secure multimedia card.

[0030] Hereinafter, the base station is an entity that performs resource allocation of the terminal, and may be at least one of a Node B, a BS (Base Station), an eNB (eNode B), a gNB (gNode B), a wireless access unit, a base station controller, or a node on a network. The terminal may include a UE (User Equipment), an MS (Mobile Station), a cellular phone, a smartphone, a computer, or a multimedia system capable of performing a communication function. In addition, the embodiments of the present disclosure may be applied to other communication systems having a similar technical background or channel type to the embodiments of the present disclosure described below. In addition, the embodiments of the present disclosure may be applied to other communication systems with some modifications without significantly departing from the scope of the present disclosure at the discretion of a person having skilled technical knowledge. For example, the 5th generation mobile communication technology (5G, new radio, NR) developed after LTE-A may be included here, and the 5G below may also be a concept that includes existing LTE, LTE-A, and other similar services. In addition, the present disclosure may be applied to other communication systems with some modifications within a scope that does not significantly deviate from the scope of the present disclosure, as judged by a person having skilled technical knowledge.

[0031] In the following description, terms used to identify connection nodes, terms referring to network entities or network functions (NFs), terms referring to messages, terms referring to interfaces between network objects, terms referring to various identification information, etc. are provided as examples for convenience of explanation. Therefore, the present disclosure is not limited to the terms described below, and other terms referring to objects having equivalent technical meanings may be used.

[0032] For convenience of explanation below, some terms and names defined in the 3rd generation partnership project (3GPP) LTE (long term evolution) standard and / or 3GPP NR (new radio) standard may be used. However, the present disclosure is not limited by these terms and names, and can be equally applied to systems conforming to other standards.

[0033] FIG. 1 illustrates the structure of a wireless communication system according to one embodiment of the present disclosure. More specifically, referring to FIG. 1, the structure of an NR system is illustrated.

[0034] Referring to FIG. 1, the wireless communication system may include a plurality of base stations (e.g., gNB (100), ng-eNB (110), ng-eNB (120), gNB (130)), an Access and Mobility Management Function (AMF) (140), and a User Plane Function (UPF) (150). Of course, the wireless communication system is not limited to the configuration illustrated in FIG. 1, and may include more or fewer components.

[0035] According to one embodiment of the present disclosure, a user equipment (hereinafter referred to as UE or terminal) (160) can access an external network through base stations (100, 110, 120, 130) and UPF (150).

[0036] In Fig. 1, base stations (100, 110, 120, 130) can serve as access nodes of a cellular network and provide wireless access to terminals accessing the network. For example, base stations (100, 110, 120, 130) can collect status information such as buffer status, available transmission power status, and channel status of terminals to schedule the status information and support connections between terminals and a core network (CN, particularly, the CN of NR is referred to as 5GC) in order to service user traffic.

[0037] In Fig. 1, gNB (100, 130) can control multiple ro cells and apply an adaptive modulation and coding (AMC) method that determines a modulation scheme and a channel coding rate according to the channel status of the terminal.

[0038] The core network, a device responsible for terminal mobility management and various control functions, can be connected to multiple base stations. 5GC can also be integrated with existing LTE systems.

[0039] Meanwhile, in a wireless communication system, a user plane (UP) related to transmission of actual user data and a control plane (CP) such as connection management may be configured separately. The gNB (100) and gNB (130) of FIG. 1 may use the UP and CP technologies defined in NR technology, and the ng-eNB (110) and ng-eNB (120), although connected to 5GC, may use the UP and CP technologies defined in LTE (Long Term Evolution) technology.

[0040] AMF (140) is a device that is responsible for various control functions as well as mobility management functions for terminals and can be connected to multiple base stations.

[0041] UPF (150) may refer to a type of gateway device that provides data transmission. Although not illustrated in FIG. 1, the NR wireless communication system may also include a Session Management Function (SMF). The SMF can manage packet data network connections, such as PDU (protocol data unit) sessions provided to terminals.

[0042] FIG. 2 illustrates a wireless protocol structure in a wireless communication system according to one embodiment of the present disclosure. More specifically, referring to FIG. 2, a wireless protocol structure in an NR system is illustrated.

[0043] Referring to FIG. 2, the wireless protocol of the NR system may be composed of SDAP (Service Data Adaptation Protocol) (200) (290), PDCP (Packet Data Convergence Protocol) (210) (280), RLC (Radio Link Control) (220) (270), MAC (Medium Access Control) (230) (260), and PHY (Physical) (240) (250) in the terminal and the base station, respectively.

[0044] The SDAP (Service Data Adaptation Protocol) layer (200, 290) can transmit user data, perform operations for mapping QoS (quality of service) flows to specific DRBs (data radio bearers) for uplink and downlink, mark QoS flow IDs for uplink and downlink, and map reflective QoS flows to data bearers for uplink SDAP PDUs (protocol data units). SDAP settings corresponding to each DRB can be provided from a higher RRC layer. Of course, the present invention is not limited to the above examples.

[0045] The PDCP (Packet Data Convergence Protocol) (210, 280) layer can handle operations such as IP header compression / decompression. Furthermore, PDCP (210, 280) can provide sequential and out-of-order delivery functions, reordering, duplicate detection, retransmission, and encryption and decryption functions. Of course, the examples are not limited to these.

[0046] Radio Link Control (RLC) (220, 270) can reconfigure PDCP PDUs to an appropriate size. Furthermore, the RLC (220, 270) layer provides in-order and out-of-order transmission functions, and can provide automatic repeat request (ARQ) functions, concatenation, segmentation, reassembly, re-segmentation, reordering, duplicate detection, and error detection functions. Of course, the examples are not limited thereto.

[0047] The MAC (medium access control) (230, 260) is connected to multiple RLC layer devices configured in a single terminal, and can perform operations of multiplexing RLC PDUs into MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. In addition, the MAC (230)(260) can provide a mapping function, a scheduling information reporting function, a HARQ (hybrid ARQ) function, a priority control function between logical channels, a priority control function between terminals, an MBMS (multimedia broadcast multicast service) service confirmation function, a transmission format selection function, and a padding function. Of course, the present invention is not limited to the examples.

[0048] The PHY (physical) layer (240, 250) performs the operation of channel coding and modulating upper layer data, converting it into OFDM (orthogonal frequency division multiplexing) symbols and transmitting it through a wireless channel, or demodulating and channel decoding OFDM symbols received through a wireless channel and transmitting them to the upper layer. In addition, the physical layer also uses HARQ for additional error correction, and the receiver transmits 1 bit whether or not it has received a packet transmitted from the transmitter. The 1 bit information is called HARQ ACK (acknowledgement) / NACK (negative ACK) information.

[0049] Downlink HARQ ACK / NACK information for uplink data transmission is transmitted through the PHICH (Physical Hybrid-ARQ Indicator Channel) physical channel in the case of LTE, and in the case of NR, it can determine whether retransmission is necessary or new transmission can be performed through the scheduling information of the terminal through the PDCCH (Physical Downlink Control Channel), which is a channel through which downlink / uplink resource allocation, etc. are transmitted. This is because NR applies asynchronous HARQ. Uplink HARQ ACK / NACK information for downlink data transmission can be transmitted through the PUCCH (Physical Uplink Control Channel) or PUSCH (Physical Uplink Shared Channel) channel. PUCCH is generally transmitted in the uplink on the PCell, which will be described later, but if the terminal supports it, the base station may additionally transmit it to the terminal on the SCell, which will be described later, and this may be referred to as PUCCH SCell.

[0050] Although not shown in Figure 2, an RRC (Radio Resource Control) layer exists above the PDCP layer of each terminal and base station, and the RRC layer can transmit and receive connection and measurement-related setting control messages for radio resource control.

[0051] Meanwhile, the physical layer can be composed of one or more frequencies / carriers, and the technology that sets and uses multiple frequencies simultaneously can be referred to as carrier aggregation (CA). CA technology can dramatically increase the transmission capacity by the number of secondary carriers by additionally using a primary carrier and one or more secondary carriers, rather than the general use of only one carrier for communication between a terminal and a base station (e.g., eNB or gNB). Meanwhile, in LTE / NR, a cell within a base station that uses a primary carrier is called a primary cell or PCell (Primary Cell), and a cell within a base station that uses a secondary carrier is called a secondary cell or SCell (Secondary Cell).

[0052] - MCG (Master Cell Group): This can refer to the serving cell where the terminal initially establishes a connection with the base station, or a group of cells supported by the base station. When dual access technology is configured, key RRC messages can be transmitted or received through the MCG.

[0053] - SCG (Secondary Cell Group): A terminal establishes a connection with a base station and can add cells from other base stations in addition to the MCG. This can refer to a group of cells supported by other base stations. When dual access technology is enabled, this can be added to increase additional data rates or efficiently support terminal mobility.

[0054] - PScell ​​(Primary Secondary Cell): When a terminal establishes a connection with a base station and a group of cells from other base stations is added in addition to the MCG and dual access technology is set, the cell corresponding to the Pcell in the SCG can be called a PScell.

[0055] - Scell ​​(Secondary Cell): Cells additionally configured by a base station to set up carrier aggregation technology after a terminal establishes an initial connection with a base station can be called Scells. SCells may have PUCCH transmission resources depending on the base station settings. Additionally, SCells may be configured for uplink or downlink depending on the base station settings. Additionally, SCells may be used as reference cells for timing adjustment (e.g., sTAG (Secondary Timing Advance Group)) depending on the base station settings. For example, if frequency aggregation technology is configured after a Pcell is configured, Scells are added and an sTAG is configured, other Scells in the sTAG can perform uplink data transmission by referencing the timing adjustment value of the designated Scell. In addition, if dual access technology is configured for a terminal, an Scell ​​may represent Scells excluding the PCell of an MCG or Scells excluding the PScell ​​of an SCG.

[0056] In the embodiments of the present disclosure, an entity may be referred to as a hierarchical device and may be used with the same meaning.

[0057] FIG. 3 illustrates a procedure for a terminal to establish a connection with a network in a wireless communication system according to one embodiment of the present disclosure.

[0058] FIG. 3 illustrates a procedure in which a terminal establishes a connection with a network by switching from RRC idle mode (RRC_IDLE) to RRC connected mode (RRC_CONNECTED) in the present disclosure. In FIG. 3, the terminal can establish uplink and / or downlink transmission synchronization with a base station through a random access process, and can transmit an RRCSetupRequest message to the base station (300). The RRCSetupRequest message can include an identifier of the terminal and a reason for establishing a connection (e.g., EstablishmentCause). The base station can transmit an RRCSetup message to the terminal so that the terminal establishes an RRC connection (305).

[0059] In one embodiment, the RRCSetup message may include configuration information (e.g., RadioBearerConfig) for each Radio Bearer (e.g., DRB or SRB). The Radio Bearer configuration information may include at least one of an ID of each Radio Bearer and configuration information (PDCP-Config) for the PDCP layer device of the Radio Bearer, or an indicator indicating whether the Radio Bearer is a Dual Active Protocol Stack (DAPS) Bearer. Of course, the present invention is not limited to the above examples.

[0060] A terminal that has established an RRC connection can enter RRC_CONNECTED mode and transmit an RRCSetupComplete message to the base station (310). If the base station does not know the terminal capabilities of the terminal currently establishing the connection or wants to determine the terminal capabilities, the base station can transmit a message inquiring about the terminal's capabilities (e.g., UE capability enquiry) to the terminal (315). In addition, the terminal can transmit a message reporting its capabilities (e.g., UE capability information) to the base station (320).

[0061] The base station may send a SecurityModeCommand message to the terminal to establish security with the terminal (325). The terminal may then send a SecurityModeComplete message to the base station (330). Once the security setting is complete, the base station may send an RRCReconfiguration message to the terminal (335).

[0062] In one embodiment, the RRCReconfiguration message may include configuration information (e.g., RadioBearerConfig) for each Radio Bearer (e.g., DRB or SRB). The Radio Bearer configuration information may include at least one of an ID of each Radio Bearer, configuration information (PDCP-Config) for the PDCP layer device of the Radio Bearer, or an indicator indicating whether the Radio Bearer is a DAPS Bearer. Of course, the present invention is not limited to the above examples.

[0063] In one embodiment of the present disclosure, PDCP-Config may include at least one of the following configuration information, but is not limited to the following examples.

[0064] - discardTimer: Value in ms of discardTimer specified in TS 38.323. Value ms10 corresponds to 10 ms, value ms20 corresponds to 20 ms, and so on. The value for this field cannot be changed in case of reconfiguration with sync, if the bearer is configured as a DAPS bearer.

[0065] - pdcp-SN-SizeUL: PDCP sequence number size for uplink, 12 or 18 bits, as specified in TS 38.323. For SRBs, only the value len12bits is applicable. The value for this field cannot be changed in case of reconfiguration with sync, if the bearer is configured as a DAPS bearer.

[0066] - pdcp-SN-SizeDL: PDCP sequence number size for downlink, 12 or 18 bits, as specified in TS 38.323. For SRBs, only the value len12bits is applicable. The value for this field cannot be changed in case of reconfiguration with sync, if the bearer is configured as a DAPS bearer.

[0067] - outOfOrderDelivery: Indicates whether or not outOfOrderDelivery specified in TS 38.323 is configured. This field should be either always present or always absent after the radio bearer is established.

[0068] - statusReportRequired: For AM DRBs, AM MRBs and DAPS UM DRBs, indicates whether the DRB or the multicast MRB is configured to send a PDCP status report in the uplink, as specified in TS 38.323. For DAPS AM DRBs, it also indicates whether the DRB is configured to send a second PDCP status report in the uplink, as specified in TS 38.323.

[0069] - t-Reordering: Value in ms of t-Reordering specified in TS 38.323. Value ms0 corresponds to 0 ms, value ms20 corresponds to 20 ms, value ms40 corresponds to 40 ms, and so on. When the field is absent, the UE applies the value infinity. The value for this field cannot be changed in case of reconfiguration with sync, if the bearer is configured as a DAPS bearer. (It may be the value in ms of t-Reordering specified in TS 38.323. ms0 corresponds to 0 ms, ms20 corresponds to 20 ms, ms40 corresponds to 40 ms, etc. When the field is absent, the UE may apply the value infinity. The value of this field cannot be changed in case of reconfiguration with sync, if the bearer is configured as a DAPS bearer.)

[0070] - pdu-SetDiscard: If set to true, the UE shall perform PDU set-based discarding for this PDCP entity, as specified in TS 38.323.

[0071] - discardTimerForLowImportance: Value in ms of discardTimerForLowImportance specified in TS 38.323. Value ms0 corresponds to 0 ms, value ms2 corresponds to 2 ms and so on. The value of this timer for a PDCP entity is always configured shorter than discardTimer, discardTimerExt or discardTimerExt2, whichever is used for the PDCP entity.

[0072] - If there are two or more RLC layer devices associated / connected with the corresponding PDCP layer device:

[0073] 1) Primary RLC layer device indicator (primaryPath): In one embodiment, the Primary RLC layer device can be configured through an indicator that indicates the Cell Group (CellGroupId) to which the RLC layer device belongs and the Logical Channel (LogicalChannelIdentity) corresponding to the RLC layer device in the Cell Group.

[0074] 2) Uplink Split Bearer Threshold (UL-DataSplitThreshold): A threshold value that can be used in Split Bearer can be set. When operating as Split Bearer, if the amount of data to be transmitted is less than the threshold value, data is transmitted only to the Primary RLC layer device. If the amount of data to be transmitted is greater than the threshold value, data can be transmitted to both the Primary RLC layer device and the Split Secondary RLC layer device.

[0075] 3) pdcp-Duplication: When the UE receives the RRC message and IE, this field may indicate whether the PDCP redundancy transmission function of the corresponding PDCP layer device is set and activated. This field may be a BOOLEAN indicating TRUE or FALSE. If this field is present, the PDCP layer device may be considered to have the redundancy transmission function set. In one embodiment, the PDCP redundancy transmission function may not be set for a CA-based LTE RLC Bearer. The setting value of this field may indicate whether the initial state of the PDCP redundancy transmission function is Activated or Deactivated when the UE receives the corresponding RRC message / IE. For example, if the setting value is TRUE, it may start in the Activated state, and if it is FALSE, it may start in the Deactivated state. In one embodiment, when the field is set for an SRB, the setting value may be specified to always be set to TRUE. If there are three or more RLC layer devices associated with the corresponding PDCP layer device (moreThanTwoRLC-DRB is present), the field may always be present. Additionally, the terminal may ignore the setting value of the field, and the initial state of the duplication transmission function activation / deactivation of the RLC layer device (other than the Primary RLC layer device) associated with the corresponding PDCP layer device may be configured through the duplicationState field. In one embodiment, the duplication transmission function in which three or more RLC layer devices (more than two associated RLC entities) are associated with the PDCP layer device may be supported only for NR RLC layer devices (NR RLC Bearer).

[0076] 4) If there are three or more RLC layer devices associated / connected with the corresponding PDCP layer device:

[0077] (1) Split Secondary RLC layer device indicator (splitSecondaryPath): An indicator indicating a Split Secondary RLC layer device may be included. In one embodiment, the base station may indicate the Split Secondary RLC layer device by indicating an LCID (Logical Channel ID) corresponding to the Split Secondary RLC layer device. In one embodiment, the Split Secondary RLC layer indicator may be used for the purpose of indicating the Split Secondary RLC layer device when the PDCP layer device falls back to the Split Bearer and operates when there are three or more RLC layer devices associated with the corresponding PDCP layer device. In one embodiment, the Split Secondary RLC layer device indicator may specify only the LCID corresponding to the corresponding RLC layer device, and may not specify the Cell Group to which the corresponding RLC layer device belongs. The Cell Group to which the corresponding RLC layer device belongs may be configured to be designated as a Cell Group other than the Cell Group to which the Primary RLC layer device belongs, among MCG and SCG. If there are two RLC layer devices associated with the PDCP layer device, the Split Secondary RLC layer device indicator may not be required. In one embodiment, since the Primary RLC layer device can be configured via the Primary RLC layer device indicator, even without the Split Secondary RLC layer device indicator, another RLC layer device other than the Primary RLC layer device can be designated as the Split Secondary RLC layer device.

[0078] (2) duplicationState: This field may be a field indicating the initial activation / deactivation state of the duplication transmission function for each RLC layer device associated with the corresponding PDCP layer device when the terminal receives the corresponding RRC message / IE. In one embodiment, the field may include three BOOLEAN setting values, and each BOOLEAN setting value may correspond to a specific RLC layer device. If the setting value of the field is set to TRUE, the activation state may be indicated for the corresponding RLC layer device, and if it is set to FALSE, the deactivation initial state may be indicated. The determination method of each RLC layer device to which the three BOOLEAN setting values ​​correspond may be such that, among the RLC layer devices associated with the corresponding PDCP layer device, in the order of MCG to SCG, excluding the Primary RLC layer device, the RLC layer devices may have a mapping relationship between the RLC layer devices and the BOOLEAN setting values ​​in the ascending order of LCID (Logical Channel ID). If there are two RLC layer devices associated with the PDCP layer device, excluding the Primary RLC layer device, the terminal may ignore the BOOLEAN setting value with the highest index value. If this field does not exist, the PDCP redundant transmission function may be considered disabled for all associated RLC layer devices.

[0079] In one embodiment, the RRCReconfiguration message may include, for each Cell Group (e.g., MCG, SCG), RLC Bearer configuration information (e.g., RLC-BearerConfig) belonging to the Cell Group. The RLC Bearer configuration information may include the following information, but is not limited to the following examples.

[0080] - logicalChannelIdentity: You can indicate the LCID corresponding to the RLC Bearer / layer device.

[0081] - servedRadioBearer: Indicates the Radio Bearer ID associated with the RLC Bearer / layer device. The Radio Bearer ID can indicate a specific DRB or SRB.

[0082] - rlc-Config: You can indicate the RLC layer parameter setting information of the RLC layer device of the corresponding RLC Bearer.

[0083] As such, a typical data transmission process can largely include three steps: RRC connection setup, security setup, and DRB setup. Additionally, the base station may transmit an RRCReconfiguration message to the terminal to update, add, or change settings for a given reason (350).

[0084] In one embodiment of the present disclosure, a terminal that receives an RRC message (e.g., RRCReconfiguration) can configure each Radio Bearer by configuring the Radio Bearer of the message. In addition, the terminal can configure the corresponding PDCP layer device. In addition, the terminal can configure an RLC Bearer / layer device that has an association with each Radio Bearer / PDCP layer device, and then establish an association between the RLC layer device and the PDCP layer device.

[0085] In one embodiment of the present disclosure, one Radio Bearer corresponds to one PDCP layer device. In one embodiment, each PDCP layer device may be associated with one, two, three, four, six, or eight RLC layer devices, as follows.

[0086] - A PDCP layer device of a Split Bearer can be associated with two uplink or two downlink UM RLC layer devices, four UM RLC layer devices (e.g., two downlink and two uplink), or two AM RLC layer devices.

[0087] - An RB with PDCP redundancy transmission enabled can be associated with N UM RLC layer devices (e.g., all downlink or all uplink), 2 × N UM RLC layer devices (e.g., N uplink and N downlink), or N AM RLC layer devices, where N can be greater than or equal to 2 and less than or equal to 4.

[0088] - A PDCP layer device of a DAPS Bearer can be associated with two UM RLC layer devices (e.g., both uplink or both downlink, one for the Source cell and one for the Target cell), four UM RLC layer devices (e.g., uplink and downlink of the Source cell, uplink and downlink of the Target cell), or two AM RLC layer devices (e.g., one for the Source cell and one for the Target cell).

[0089] - In other cases, each PDCP layer device may be associated with one UM RLC layer device, two UM RLC layer devices (e.g., one each for uplink and downlink), or one AM RLC layer device.

[0090] In one embodiment of the present disclosure, a transmitter of a PDCP layer device of a terminal for which pdcp-Duplication is set may operate as follows.

[0091] - About SRB:

[0092] 1) Activate PDCP duplicate transmission function

[0093] - About DRB:

[0094] 1) If an activation instruction for the PDCP redundant transmission feature is received (via RRC or MAC CE) for the given DRB:

[0095] (1) Activate PDCP duplicate transmission function for the corresponding DRB.

[0096] 2) If PDCP redundant transmission feature is enabled for at least one associated RLC layer device (via RRC or MAC CE):

[0097] (1) Activate PDCP redundant transmission function for the indicated RLC layer device.

[0098] (2) Activate PDCP duplicate transmission function for the corresponding DRB.

[0099] 3) If a PDCP duplicate transmission feature disable instruction is received (via RRC or MAC CE) for the DRB in question:

[0100] (1) For the DRB in question, disable the PDCP duplicate transmission function.

[0101] 4) If, for at least one associated RLC layer device, a PDCP duplicate transmission feature disablement indication is received (via RRC or MAC CE):

[0102] (1) For the associated RLC layer device that received the instruction, perform PDCP duplicate transmission function deactivation.

[0103] (2) If PDCP redundant transmission feature is disabled for all associated RLC layer devices except the Primary RLC layer device:

[0104] a. Disable PDCP duplicate transmission function for the DRB in question.

[0105] In one embodiment of the present disclosure, when the PDCP redundancy transmission function is set for one or more DRBs, the base station can instruct, through MAC CE, to activate or deactivate the PDCP redundancy transmission function of all or some of the associated RLC layer devices for the DRBs for which the PDCP redundancy transmission function is set.

[0106] In one embodiment, in the following cases, the terminal may activate or deactivate the PDCP redundancy transmission function for the DRB for which the function is configured.

[0107] - When an activation / deactivation indication is received from the base station via the Duplication Activation / Deactivation MAC CE of TS 38.321 section 6.1.3.11. In one embodiment, the Duplication Activation / Deactivation MAC CE may indicate activation or deactivation of the PDCP duplicate transmission function only when the number of associated RLC layer devices is two.

[0108] - When an activation or deactivation indication is received from the base station via the Duplication RLC Activation / Deactivation MAC CE of TS 38.321 section 6.1.3.32.

[0109] - When an activation / deactivation instruction (e.g., pdcp-Duplication, duplicationState) is received from the base station via an RRC message

[0110] In one embodiment, in the following cases, the terminal may enable / disable the PDCP redundancy transmission function for all or some RLC layer devices associated with the DRB for which the function is enabled.

[0111] - When an activation / deactivation indication is received from the base station via the Duplication RLC Activation / Deactivation MAC CE of TS 38.321 section 6.1.3.32.

[0112] - When an activation / deactivation instruction (e.g., pdcp-Duplication, duplicationState) is received from the base station via an RRC message

[0113] In one embodiment, the terminal may enable the PDCP redundancy transmission function for all associated RLC layer devices for the DRB for which the function is configured, in the following cases:

[0114] - When receiving an Uplink Grant, which is specified by CS-RNTI and has NDI (New Data Indicator) = 1, for a Logical Channel associated with a DRB with survivalTimeStateSupport set.

[0115] In one embodiment of the present disclosure, a MAC layer device of a terminal may operate as follows for each DRB for which a PDCP redundant transmission function is set.

[0116] - When an instruction to activate the PDCP duplicate transmission function for a specific DRB is received via Duplication Activation / Deactivation MAC CE:

[0117] 1) It is possible to instruct the upper layer (PDCP) to activate the PDCP redundant transmission function for the corresponding DRB.

[0118] - When an instruction to disable PDCP duplicate transmission functionality for a specific DRB is received via Duplication Activation / Deactivation MAC CE:

[0119] 1) It is possible to instruct the upper layer (PDCP) to disable the PDCP duplicate transmission function for the corresponding DRB.

[0120] - When an indication to activate the PDCP duplicate transmission feature for a specific DRB is received via a Duplication RLC Activation / Deactivation MAC CE for one or more Secondary RLC layer devices associated with that DRB:

[0121] 1) It can instruct the upper layer (PDCP) to enable PDCP redundant transmission function for one or more Secondary RLC layer devices.

[0122] - When an instruction to disable PDCP duplicate transmission functionality for a specific DRB is received via Duplication RLC Activation / Deactivation MAC CE for one or more Secondary RLC layer devices associated with that DRB:

[0123] 1) It is possible to instruct the upper layer (PDCP) to disable the PDCP redundant transmission function for one or more Secondary RLC layer devices.

[0124] - For a Logical Channel associated with a DRB with survivalTimeStateSupport set, when receiving an Uplink Grant specified by CS-RNTI and with New Data Indicator (NDI) = 1:

[0125] 2) It can instruct the upper layer (PDCP) to enable PDCP redundant transmission function for all associated RLC layer devices of the DRB.

[0126] In one embodiment of the present disclosure, a PDCP transmitting device (Transmitting PDCP Entity) may operate as follows after receiving a PDCP SDU from an upper layer.

[0127] Upon reception of a PDCP SDU from upper layers, the transmitting PDCP entity shall:

[0128] -ifdiscardTimerForLowImportanceisconfiguredandPSIbasedSDUdiscardisactivated,andthePDCPSDUbelongstoalowimportancePDUSet:

[0129] -start thediscardTimerForLowImportanceassociated with this PDCP SDU(start the discardTimerForLowImportance associated with this PDCP SDU);

[0130] -else:

[0131] -start the discardTimer associated with this PDCP SDU (if configured).

[0132] For a PDCP SDU received from upper layers, the transmitting PDCP entity shall:

[0133] -associate the COUNT value corresponding to TX_NEXT to this PDCP SDU;

[0134] -set the PDCP SN of the PDCP Data PDU to TX_NEXT modulo 2[pdcp-SN-SizeUL];

[0135] -increment TX_NEXT by one(increment TX_NEXT by 1);

[0136] -submit the resulting PDCP Data PDU to the lower layer as specified below.

[0137] When submitting a PDCP PDU to a lower layer, the transmitting PDCP entity shall:

[0138] -if the transmitting PDCP entity is associated with one RLC entity:

[0139] -submit the PDCP PDU to the associated RLC entity;

[0140] In one embodiment of the present disclosure, the PDCP SDU discard operation of a PDCP transmitting device can be performed as follows.

[0141] When the discardTimer or discardTimerForLowImportance expires for a PDCP SDU, the transmitting PDCP entity shall:

[0142] -ifpdu-SetDiscardis configured (if pdu-SetDiscard is set):

[0143] -discard all PDCP SDUs belonging to the PDU Set to which the PDCP SDU belongs along with the corresponding PDCP Data PDUs;

[0144] -else:

[0145] -discard the PDCP SDU along with the corresponding PDCP Data PDU.

[0146] If the corresponding PDCP Data PDU has already been submitted to lower layers, the discard is indicated to the lower layers. For SRBs, when upper layers request a PDCP SDU discard, the PDCP entity shall discard all stored PDCP SDUs and PDCP PDUs (If the corresponding PDCP Data PDU has already been submitted to a lower layer, the discard may be indicated to the lower layer. For SRBs, if an upper layer requests a PDCP SDU discard, the PDCP entity may discard all stored PDCP SDUs and PDCP PDUs).

[0147] The following definitions may be utilized in this disclosure.

[0148] - HFN(State Variable): the HFN part (i.e. the number of most significant bits equal to HFN length) of the State Variable;

[0149] - SN(State Variable): the SN part (i.e. the number of least significant bits equal to PDCP SN length) of the State Variable;

[0150] - RCVD_SN: the PDCP SN of the received PDCP Data PDU, included in the PDU header;

[0151] - RCVD_HFN: the HFN of the received PDCP Data PDU, calculated by the receiving PDCP entity;

[0152] - RCVD_COUNT: the COUNT of the received PDCP Data PDU = [RCVD_HFN, RCVD_SN] (COUNT of the received PDCP Data PDU = [RCVD_HFN, RCVD_SN]).

[0153] In one embodiment of the present disclosure, when receiving a PDCP Data PDU from a lower layer, a PDCP receiving device may operate as follows.

[0154] Upon reception of a PDCP Data PDU from lower layers, the receiving PDCP entity shall determine the COUNT value of the received PDCP Data PDU, i.e., RCVD_COUNT, as follows:

[0155] - if RCVD_SN < SN(RX_DELIV) - Window_Size:

[0156] - RCVD_HFN = HFN(RX_DELIV) + 1.

[0157] - else if RCVD_SN >= SN(RX_DELIV) + Window_Size:

[0158] - RCVD_HFN = HFN(RX_DELIV) - 1.

[0159] - else:

[0160] - RCVD_HFN = HFN(RX_DELIV);

[0161] - RCVD_COUNT = [RCVD_HFN, RCVD_SN].

[0162] After determining the COUNT value of the received PDCP Data PDU = RCVD_COUNT, the receiving PDCP entity shall:

[0163] - perform deciphering and integrity verification of the PDCP Data PDU using COUNT = RCVD_COUNT;

[0164] - if integrity verification fails:

[0165] - indicate the integrity verification failure to the upper layer;

[0166] - Discard the PDCP Data PDU and consider it as not received;

[0167] - if RCVD_COUNT < RX_DELIV; or

[0168] - if the PDCP Data PDU with COUNT = RCVD_COUNT has been received before:

[0169] - discard the PDCP Data PDU;

[0170] If the received PDCP Data PDU with COUNT value = RCVD_COUNT is not discarded above, the receiving PDCP entity shall:

[0171] - store the resulting PDCP SDU in the reception buffer;

[0172] - if RCVD_COUNT >= RX_NEXT:

[0173] - update RX_NEXT to RCVD_COUNT + 1.

[0174] - ifoutOfOrderDeliveryis configured:

[0175] - deliver the resulting PDCP SDU to upper layers after performing header decompression using EHC.

[0176] - if RCVD_COUNT = RX_DELIV:

[0177] - deliver to upper layers in ascending order of the associated COUNT value after performing header decompression, if not decompressed before;

[0178] - all stored PDCP SDU(s) with consecutively associated COUNT value(s) starting from COUNT = RX_DELIV(Return all stored PDCP SDU(s) with consecutively associated COUNT value(s) starting from COUNT = RX_DELIV);

[0179] - update RX_DELIV to the COUNT value of the first PDCP SDU which has not been delivered to upper layers, with COUNT value > RX_DELIV;

[0180] - ift-Reordering is running, and if RX_DELIV >= RX_REORD:

[0181] - stop and resett-Reordering(t-Reordering stop and reset).

[0182] - ift-Reordering is not running (includes the case whent-Reordering is stopped due to the actions above), and RX_DELIV < RX_NEXT):

[0183] - update RX_REORD to RX_NEXT(Update RX_REORD to RX_NEXT);

[0184] - start t-Reordering.

[0185] In one embodiment of the present disclosure, when the t-Reordering timer expires, the PDCP receiving device may operate as follows.

[0186] - deliver to upper layers in ascending order of the associated COUNT value after performing header decompression, if not decompressed before:

[0187] - all stored PDCP SDU(s) with associated COUNT value(s) < RX_REORD);

[0188] - all stored PDCP SDU(s) with consecutively associated COUNT value(s) starting from RX_REORD(Return all stored PDCP SDU(s) with consecutively associated COUNT value(s) starting from RX_REORD);

[0189] - update RX_DELIV to the COUNT value of the first PDCP SDU which has not been delivered to upper layers, with COUNT value >= RX_REORD;

[0190] - if RX_DELIV < RX_NEXT:

[0191] - update RX_REORD to RX_NEXT(Update RX_REORD to RX_NEXT);

[0192] - start t-Reordering.

[0193] In one embodiment of the present disclosure, when a PDCP transmitting device discards a PDCP SDU corresponding to a specific COUNT / SN, and the PDCP SDU is unlikely to be delivered to a receiving device, it can be expressed that an SN Gap has occurred due to the discarding of the PDCP SDU.

[0194] Therefore, a PDCP transmitter can report a PDCP receiver about a PDCP SN Gap via a specific PDCP Control PDU. In one embodiment, the PDCP Control PDU may be referred to as a PDCP SN Gap Report in the present disclosure.

[0195] FIG. 4 illustrates an operation of a terminal and a base station transmitting and receiving a PDCP SN Gap Report in a wireless communication system according to one embodiment of the present disclosure.

[0196] Referring to FIG. 4, in step 430, if the base station (410) does not know the capabilities of a terminal (400) in an RRC_CONNECTED state, or if it is necessary to determine the capabilities of the terminal, it may transmit a message (e.g., UECapabilityEnquiry) to the terminal to inquire about the capabilities of the terminal.

[0197] In step 440, the terminal may transmit a message (e.g., UECapabilityInformation) reporting its capabilities to the base station. The terminal capability report message may include an indicator (e.g., supportOfSN-GapReport) indicating whether the terminal supports PDCP SN Gap Report. In one embodiment, the terminal may support PDCP SN Gap Report only if it supports pdu-SetDiscard-r18 and / or psi-BasedDiscard-r18. In one embodiment, if the terminal supports pdu-SetDiscard-r18 and / or psi-BasedDiscard-r18, it may be considered to also support PDCP SN Gap Report.

[0198] The base station can determine whether the terminal supports PDCP SN Gap Report through a terminal capability report message (e.g., UECapabilityInformation). In step 450, if the terminal supports PDCP SN Gap Report, the base station can transmit PDCP SN Gap Report-related configuration information to the terminal through an RRC message (e.g., an RRCReconfiguration message).

[0199] The PDCP SN Gap Report-related settings set by the base station to the terminal may include the following information. However, the information is not limited to the examples below.

[0200] - The base station can be configured to transmit PDCP SN Gap Reports on a per-DRB basis. In one embodiment, this configuration can be restricted to only be configured when outOfOrderDelivery is not configured for the corresponding PDCP layer device / DRB.

[0201] At step 460, a PDCP transmitting device (Transmitting PDCP Entity) of a DRB (UM or AM DRB) configured by the upper layer to send a PDCP SN Gap Report may trigger a PDCP SN Gap Report if one or more of the following conditions are met:

[0202] - PDCP SDU(s) are discarded according to section 5.3 of TS 38.323.

[0203] - The PDCP layer device stores at least one PDCP SDU with a COUNT value greater than the number of discarded PDCP SDU(s).

[0204] - The discarded PDCP SDU(s) have not yet been submitted to a lower layer (e.g., MAC layer) by the RLC layer that has an association with the corresponding PDCP layer device. For example, in case of a split bearer, the RLC layer may mean all RLC layer devices that have an association with the corresponding split bearer. For example, the discarded PDCP SDU(s) may not have been forwarded to the lower layer by any RLC layer device. For example, in case of a split bearer, the RLC layer may mean at least one RLC layer device that has an association with the corresponding split bearer. For example, the discarded PDCP SDU(s) may not have been forwarded to the lower layer by at least one RLC layer device.

[0205] At step 470, when the PDCP SN Gap Report is triggered, the transmitting PDCP layer device can compile the PDCP SN Gap Report as follows.

[0206] At step 480, the transmitting PDCP layer device may transmit a PDCP SN Gap Report to the base station.

[0207] At step 490, the PDCP SN Gap Report can be handled by the receiving PDCP layer device.

[0208] In one embodiment, a PDCP transmitting device may discard a particular PDCP SDU when the discardTimer or discardTimerForLowImportance of the particular PDCP SDU expires.

[0209] In one embodiment, a PDCP transmitting device may perform PDCP SDU discard as follows, but is not limited to the following examples.

[0210] PDCP SDU discard behavior:

[0211] When the discardTimer or discardTimerForLowImportance expires for a PDCP SDU, the transmitting PDCP entity shall:

[0212] - ifpdu-SetDiscardis configured (if pdu-SetDiscard is set):

[0213] - Discard all PDCP SDUs belonging to the PDU Set to which the PDCP SDU belongs along with the corresponding PDCP Data PDUs;

[0214] NOTE 1: PDCP SDUs subsequently received from upper layers are also discarded if they belong to the PDU Set.

[0215] - else:

[0216] - Discard the PDCP SDU along with the corresponding PDCP Data PDU.

[0217] If the corresponding PDCP Data PDU has already been submitted to lower layers, the discard is indicated to lower layers.

[0218] For SRBs, when upper layers request a PDCP SDU discard, the PDCP entity shall discard all stored PDCP SDUs and PDCP PDUs.

[0219] In one embodiment of the present disclosure, if a PDCP transmitter confirms successful delivery of a PDCP SDU through a PDCP Status Report, the PDCP SDU and the corresponding PDCP Data PDU may be discarded. For example, the following operation may be performed.

[0220] - When the successful delivery of a PDCP SDU is confirmed by the PDCP status report, the transmitting PDCP entity shall discard the PDCP SDU along with the corresponding PDCP Data PDU.

[0221] At this time, even if a successfully delivered PDCP SDU is discarded, it may not generate an SN Gap. Therefore, the SN / COUNT that generated an SN Gap reported through the PDCP SN Gap Report may not include the SN / COUNT corresponding to a PDCP SDU whose successful delivery was confirmed by the PDCP Status Report. In one embodiment, since discarding a PDCP SDU whose successful delivery was confirmed by the PDCP Status Report may not generate an SN Gap, the PDCP SN Gap Report may not be triggered either.

[0222] In one embodiment of the present disclosure, the problem of PDCP SN Gap Report being transmitted too frequently can be solved by an internal implementation of the terminal.

[0223] FIG. 5 illustrates a PDCP SN Gap Report format in a wireless communication system according to one embodiment of the present disclosure.

[0224] Referring to FIG. 5, when a PDCP SN Gap Report is triggered, the transmitting PDCP layer device can compile the PDCP SN Gap Report as follows.

[0225] - The transmitting PDCP layer device may set the FDC (First Discarded COUNT, 520) field to the smallest COUNT value among the discarded PDCP SDU(s).

[0226] - If there are two or more discarded PDCP SDUs:

[0227] - The transmitting PDCP layer device can allocate the Discard Bitmap (560, 570) field. For example, the length of the Discard Bitmap field (560, 570) can be determined as the smallest value among the multiples of 8 bits that can include the COUNT of the next PDCP SDU excluding the first discarded PDCP SDU and the last discarded PDCP SDU. At this time, if the size of the corresponding PDCP Control PDU exceeds 9000 bytes, the transmitting PDCP layer device can compile the PDCP Control PDU by limiting its size to 9000 bytes.

[0228] - The transmitting PDCP layer device may set the bits corresponding to PDCP SDUs that have not yet been discarded among the Discard Bitmap fields (560, 570) to '0'.

[0229] - The transmitting PDCP layer device can set the bits corresponding to already discarded PDCP SDUs in the Discard Bitmap field (560, 570) to '1'.

[0230] - The transmitting PDCP layer device can forward the PDCP SN Gap Report to the lower layer by the Uu interface operation of section 5.2.1 of TS 38.323.

[0231] Referring to FIG. 5, in one embodiment of the present disclosure, each field of the PDCP SN Gap Report may have the following meanings.

[0232] - PDU Type (510): It can have a length of 3 bits. As shown in Table 1, this field can indicate with a specific field value that the type of control information of the corresponding PDCP Control PDU is PDCP SN Gap Report.

[0233]

[0234] - FDC (First Discarded COUNT): It can be 32 bits long. This field can indicate the COUNT value of the PDCP SDU with the smallest COUNT value among the discarded PDCP SDU(s).

[0235] - Discard Bitmap: The length can be variable, including 0. Each bit in this field can indicate whether the corresponding PDCP SDU has been discarded by the transmitting PDCP layer device. The COUNT value of the PDCP SDU corresponding to each bit can be defined as in Table 2. For example, the bit position in the Nth bit of the Discard Bitmap can be N.

[0236]

[0237] In one embodiment of the present disclosure, a receiving PDCP layer device that receives a PDCP SN Gap Report from a lower layer may operate as follows.

[0238] - PDCP SDUs that are set to '1' in the Discard Bitmap or that correspond to the COUNT value indicated in the FDC field may be considered discarded.

[0239] - If RX_DELIV is less than or equal to the COUNT of the PDCP SDU with the largest COUNT value among the discarded PDCP SDUs:

[0240] -- If RX_NEXT is less than or equal to the COUNT of the last discarded PDCP SDU (the one with the largest COUNT among the discarded PDCP SDUs):

[0241] --- RX_NEXT can be updated to the value of the COUNT of the PDCP SDU with the largest COUNT value among the discarded PDCP SDUs plus 1.

[0242] -- If RX_DELIV is equal to the COUNT of a specific PDCP SDU among the discarded PDCP SDUs:

[0243] --- deliver to upper layers in ascending order of the associated COUNT value after performing header decompression, if not decompressed before:

[0244] ---- all stored PDCP SDU(s) with consecutively associated COUNT values ​​starting from COUNT = RX_DELIV + 1, where consecutively associated COUNT value(s) include COUNT value(s) of both the stored PDCP SDU(s) and PDCP SDU(s) which are considered as discarded(COUNT = RX_DELIV + 1);

[0245] --- update RX_DELIV to the COUNT value of the first PDCP SDU which has not been delivered to upper layers and is not considered as discarded, with COUNT value > RX_DELIV;

[0246] -- if t-Reordering is running, and if RX_DELIV >= RX_REORD:

[0247] --- stop and reset t-Reordering(stop and reset t-Reordering);

[0248] -- if t-Reordering is not running (includes the case when t-Reordering is stopped due to actions above), and RX_DELIV < RX_NEXT (includes the case when t-Reordering is stopped due to actions above), and RX_DELIV < RX_NEXT):

[0249] --- update RX_REORD to RX_NEXT(Update RX_REORD to RX_NEXT);

[0250] --- start t-Reordering.

[0251] FIG. 6 illustrates a terminal handover operation in a wireless communication system according to one embodiment of the present disclosure.

[0252] In one embodiment of the present disclosure, a terminal handover procedure performed without modification of AMF and UPF may be performed in the following order.

[0253] - A terminal (600) in RRC_CONNECTED state (615) can transmit a measurement report to the base station according to the measurement settings (620) set by the source base station (605).

[0254] - The source base station (605) may decide to handover the terminal to the target base station (610) based on the measurement report and RRM (Radio Resource Management) information transmitted by the terminal (625).

[0255] - The source base station can transmit a Handover Request message to the target base station (630). The Handover Request message can include an RRC container. The RRC container can include information necessary for the target base station to prepare for the Handover. For example, the information can include at least one of a target cell ID, KgNB* key management gNodeB), C-RNTI of the source base station of the corresponding terminal, a mapping relationship between the current QoS Flow of the corresponding terminal and DRB, SIB1 information of the source base station, capability information for multiple RATs (Radio Access Technology) of the corresponding terminal, PDU session related information, or measurement information reported by the terminal.

[0256] - The target base station can perform Admission Control (635).

[0257] - After the target base station prepares for handover through the L1 / L2 layer, it can transmit a Handover Request Acknowledge message (640) to the source base station. The Handover Request Acknowledge message (640) can include a Transparent Container including an RRC message transmitted to the terminal during handover.

[0258] - The source base station can trigger a Uu handover by transmitting an RRCReconfiguration message (645) to the UE on the Uu interface. For example, the RRCReconfiguration message (645) can include at least one of the following information: a target cell ID, a new C-RNTI, an indicator of a Security Algorithm selected by the target base station, a plurality of Dedicated RACH resources, an association between each RACH resource and SSB(s), an association between each RACH resource and UE-specific CSI-RS configuration, a plurality of Common RACH resources, or system information of the target base station.

[0259] - For example, in order to transmit the uplink PDCP SN reception status and the downlink PDCP SN transmission status of each DRB (i.e., AM DRB) to which PDCP status preservation is applied among the DRBs of the corresponding terminal, the source base station may transmit an SN Status Transfer message (650) to the target base station. For example, the uplink PDCP SN reception status may include at least the PDCP SN of the first missing UL PDCP SDU, and may include a bitmap for the reception status of an out-of-sequence UL PDCP SDU that the UE should retransmit in the target cell. For example, the downlink PDCP SN transmission status may include the next PDCP SN that the target base station should assign to a new PDCP SDU that does not yet have a PDCP SN.

[0260] - During a handover, user data can be forwarded from the source base station to the target base station. For example, data forwarding can be performed the moment the source base station receives a packet from the UPF, or sequentially for packets already present at the source base station.

[0261] - For example, the terminal can complete RRC handover by synchronizing with the target cell and transmitting an RRCReconfigurationComplete message (660).

[0262] - For example, after completing handover, the terminal can perform a PDCP re-establishment procedure (670).

[0263] In one embodiment of the present disclosure, the SN Status Transfer message may include at least one of the following information for each DRB, although the present disclosure is not limited to the following examples.

[0264] - DRB ID

[0265] - Receive Status of PDCP SDU (for UL): The IE is used in case of 12-bit or 18-bit long PDCP-SN. The first bit indicates the status of the SDU after the First Missing UL PDCP SDU. The Nth bit indicates the status of the UL PDCP SDU in position (N + First Missing SDU Number) modulo (1 + the maximum value of the PDCP-SN). Value 0 indicates PDCP SDU has not been received. Value 1 indicates PDCP SDU has been received correctly. (Received status of PDCP SDU (for UL): For PDCP-SN of 12 or 18 bits long, IE can be used. The first bit can indicate the status of the SDU after the first missing UL PDCP SDU. The Nth bit can indicate the status of the UL PDCP SDU at position (N + first missing SDU number) modulo (1 + maximum value of PDCP-SN). 0 can indicate that the PDCP SDU has not been received. 1 can indicate that the PDCP SDU has been received correctly.)

[0266] - UL COUNT Value: PDCP-SN and Hyper Frame Number of the first missing UL SDU in case of 12-bit or 18-bit long PDCP-SN

[0267] - DL COUNT Value: PDCP-SN and Hyper Frame Number that the target NG-RAN node (handover) or the NG-RAN node to which the DRB context is transferred (dual connectivity) should assign for the next DL SDU not having an SN yet in case of 12-bit or 18-bit long PDCP-SN.

[0268] In one embodiment of the present disclosure, the SN Status Transfer message may include at least one of the following PDCP SDU discard information for each DRB, although the present disclosure is not limited to the following examples.

[0269] - DRB ID

[0270] - First discarded COUNT (FDC) for DL: This field indicates the smallest COUNT value among the COUNT value(s) associated with the discarded PDCP SDU(s) for DL.

[0271] - Discard bitmap for DL: This field indicates which PDCP SDUs are discarded and which SDUs are not discarded in the source NG-RAN node for DL. The bit position of the Nth bit in the Discard Bitmap is N, ie, the bit position of the first bit in the Discard Bitmap is 1. The value 0 indicates PDCP SDU with COUNT = (FDC + bit position) modulo 2 32 is not discarded. The value 1 indicates PDCP SDU with COUNT = (FDC + bit position) modulo 2 32 is discarded (Discard Bitmap for DL: This field can indicate which PDCP SDUs are discarded and which are not discarded at the source NG-RAN node for DL. The bit position of the Nth bit in the discard bitmap can be N, i.e. the bit position of the first bit in the discard bitmap can be 1. 0 is COUNT = (FDC + bit position) modulo 2 32 can indicate that the PDCP SDU is not discarded. 1 is COUNT = (FDC + bit position) modulo 2 32 (This may indicate that a PDCP SDU is discarded.)

[0272] In one embodiment of the present disclosure, the source base station may convey the DL PDCP SDU discard information to the target base station via a message type other than SN Status Transfer. For example, a new message (e.g., SN Gap Status Transfer) conveyed via the Xn interface may include at least one of the following information for each DRB.

[0273] - DRB ID

[0274] - First discarded COUNT (FDC) for DL: This field indicates the smallest COUNT value among the COUNT value(s) associated with the discarded PDCP SDU(s) for DL.

[0275] - Discard bitmap for DL: This field indicates which PDCP SDUs are discarded and which SDUs are not discarded in the source NG-RAN node for DL. The bit position of the Nth bit in the Discard Bitmap is N, ie, the bit position of the first bit in the Discard Bitmap is 1. The value 0 indicates PDCP SDU with COUNT = (FDC + bit position) modulo 2 32 is not discarded. The value 1 indicates PDCP SDU with COUNT = (FDC + bit position) modulo 2 32 is discarded (Discard Bitmap for DL: This field can indicate which PDCP SDUs are discarded and which are not discarded at the source NG-RAN node for DL. The bit position of the Nth bit in the discard bitmap can be N, i.e. the bit position of the first bit in the discard bitmap can be 1. 0 is COUNT = (FDC + bit position) modulo 2 32can indicate that the PDCP SDU is not discarded. 1 is COUNT = (FDC + bit position) modulo 2 32 (This may indicate that a PDCP SDU is discarded.)

[0276] As one embodiment of the present disclosure, referring to FIG. 6, a source base station can transmit downlink PDCP SDU discard information per DRB to a target base station through an SN Status Transfer message (650) or an SN Gap Status Transfer message. After a handover, a terminal can reduce a re-ordering delay that occurs during a downlink PDCP SDU reception operation of the corresponding DRB. Referring to FIG. 6, the source base station can notify the target base station through the SN Status Transfer or SN Gap Status Transfer message that a PDCP SDU with a downlink PDCP SN / COUNT value of f+2 for a specific DRB has already been discarded. Accordingly, after the handover is completed, the target base station can transmit a PDCP SN Gap Report (680) to the terminal for the corresponding DRB, notifying that a PDCP SDU with a PDCP SN / COUNT value of f+2 has already been discarded. At this time, the terminal may not perform the re-ordering operation that occurs due to the PDCP SDU after receiving a discard instruction for the PDCP SDU with the SN / COUNT value of f+2.

[0277] In one embodiment of the present disclosure, when a PDCP Status Report is triggered, a receiving PDCP layer device can compile a PDCP Status Report as follows.

[0278] - setting the FMC field to RX_DELIV;

[0279] - if RX_DELIV < RX_NEXT:

[0280] -- allocating a Bitmap field of length in bits equal to the number of COUNTs from and not including the first missing PDCP SDU up to and including the last out-of-sequence PDCP SDU or last PDCP SDU considered as discarded, whichever comes last, rounded up to the next multiple of 8, or up to and including a PDCP SDU for which the resulting PDCP Control PDU size is equal to 9000 bytes, whichever comes first;

[0281] -- setting in the bitmap field as '0' for all PDCP SDUs that have not been received and also not considered as discarded, and optionally PDCP SDUs for which decompression have failed;

[0282] -- setting in the bitmap field as '1' for all PDCP SDUs that have been received or considered as discarded;

[0283] - Submit the PDCP status report to lower layers as the first PDCP PDU for transmission via the transmitting PDCP entity.

[0284] FIG. 7 illustrates a terminal handover operation in a wireless communication system according to one embodiment of the present disclosure.

[0285] Referring to Fig. 7, a terminal handover procedure performed without modification of AMF and UPF can be performed in the following order.

[0286] - A terminal (700) in RRC_CONNECTED state (715) can transmit a measurement report (720) to the base station according to the measurement settings (720) set by the source base station (705).

[0287] - The source base station (705) may decide to handover the terminal to the target base station (710) based on the measurement report and RRM (Radio Resource Management) information transmitted by the terminal (725).

[0288] - The source base station can transmit a Handover Request message (730) to the target base station (730). The Handover Request message can include an RRC container. The RRC container can include information necessary for the target base station to prepare for the handover. For example, the information can include at least one of a target cell ID, KgNB*, a C-RNTI at the source base station of the corresponding terminal, a mapping relationship between the current QoS Flow of the corresponding terminal and the DRB, SIB1 information of the source base station, capability information for multiple RATs (Radio Access Technology) of the corresponding terminal, PDU session related information, or measurement information reported by the terminal.

[0289] - The target base station can perform Admission Control (735).

[0290] - After the target base station prepares for handover through the L1 / L2 layer, it can transmit a Handover Request Acknowledge message (740) to the source base station. The Handover Request Acknowledge message (740) can include a Transparent Container including an RRC message transmitted to the terminal during handover.

[0291] - The source base station can trigger a Uu handover by transmitting an RRCReconfiguration message (745) to the UE on the Uu interface. For example, the RRCReconfiguration message (745) can include at least one of the following information: a target cell ID, a new C-RNTI, an indicator of a Security Algorithm selected by the target base station, a plurality of Dedicated RACH resources, an association between each RACH resource and SSB(s), an association between each RACH resource and a UE-specific CSI-RS configuration, a plurality of Common RACH resources, or system information of the target base station.

[0292] - For example, in order to transmit the uplink PDCP SN reception status and the downlink PDCP SN transmission status of each DRB (i.e., AM DRB) to which PDCP status preservation is applied among the DRBs of the corresponding terminal, the source base station may transmit an SN Status Transfer message (750) to the target base station. For example, the uplink PDCP SN reception status may include at least the PDCP SN of the first missing UL PDCP SDU, and may include a bitmap for the reception status of an out-of-sequence UL PDCP SDU that the UE should retransmit in the target cell. For example, the downlink PDCP SN transmission status may include the next PDCP SN that the target base station should assign to a new PDCP SDU that does not yet have a PDCP SN.

[0293] - During a handover, user data can be forwarded from the source base station to the target base station. For example, data forwarding can be performed the moment the source base station receives a packet from the UPF, or sequentially for packets already present at the source base station.

[0294] - For example, the terminal can complete RRC handover by synchronizing with the target cell and transmitting an RRCReconfigurationComplete message (760).

[0295] - For example, after handover is completed, the terminal can perform a PDCP re-establishment procedure (770).

[0296] In one embodiment of the present disclosure, the SN Status Transfer message may include at least one of the following information for each DRB:

[0297] - DRB ID

[0298] - Receive Status of PDCP SDU (for UL): The IE is used in case of 12-bit or 18-bit long PDCP-SN. The first bit indicates the status of the SDU after the First Missing UL PDCP SDU. The Nth bit indicates the status of the UL PDCP SDU in position (N + First Missing SDU Number) modulo (1 + the maximum value of the PDCP-SN). Value 0 indicates PDCP SDU has not been received and also not considered as discarded. Value 1 indicates PDCP SDU has been received correctly or considered as discarded (Received status of PDCP SDU (for UL): For PDCP-SN of 12 or 18 bits long, this IE may be used. The first bit may indicate the status of the SDU after the first missing UL PDCP SDU. The Nth bit may indicate the status of the UL PDCP SDU at position (N + first missing SDU number) modulo (1 + maximum value of PDCP-SN). A value of 0 may indicate that the PDCP SDU has not been received and is not considered as discarded. A value of 1 may indicate that the PDCP SDU has been received correctly or is considered as discarded.).

[0299] - UL COUNT Value: PDCP-SN and Hyper Frame Number of the first missing and not considered as discarded UL SDU in case of 12-bit or 18-bit long PDCP-SN

[0300] - DL COUNT Value: PDCP-SN and Hyper Frame Number that the target NG-RAN node (handover) or the NG-RAN node to which the DRB context is transferred (dual connectivity) should assign for the next DL SDU not having an SN yet in case of 12-bit or 18-bit long PDCP-SN.

[0301] In one embodiment of the present disclosure, the SN Status Transfer message may include, for each DRB, at least one of the following PDCP SDU discard information.

[0302] - DRB ID

[0303] - First discarded COUNT (FDC) for UL: This field indicates the smallest COUNT value among the COUNT value(s) associated with the discarded PDCP SDU(s) for UL.

[0304] - Discard bitmap for UL: This field indicates which PDCP SDUs are discarded and which SDUs are not discarded in the UE for UL. The bit position of the Nth bit in the Discard Bitmap is N, ie, the bit position of the first bit in the Discard Bitmap is 1. The value 0 indicates PDCP SDU with COUNT = (FDC + bit position) modulo 2 32 is not discarded. The value 1 indicates PDCP SDU with COUNT = (FDC + bit position) modulo 2 32 is discarded (Discard Bitmap for UL: This field can indicate PDCP SDUs that are discarded and SDUs that are not discarded by the UE for UL. The bit position of the Nth bit in the Discard Bitmap can be N, i.e. the bit position of the first bit in the Discard Bitmap can be 1. 0 is COUNT = (FDC + bit position) modulo 2 32 can indicate that the PDCP SDU is not discarded. 1 is COUNT = (FDC + bit position) modulo 2 32 (This may indicate that a PDCP SDU is being deleted.)

[0305] In one embodiment of the present disclosure, the source base station may convey the UL PDCP SDU discard information to the target base station via a message type other than SN Status Transfer. For example, a new message (e.g., SN Gap Status Transfer) conveyed via the Xn interface may include at least one of the following information for each DRB.

[0306] - DRB ID

[0307] - First discarded COUNT (FDC) for UL: This field indicates the smallest COUNT value among the COUNT value(s) associated with the discarded PDCP SDU(s) for UL.

[0308] - Discard bitmap for UL: This field indicates which PDCP SDUs are discarded and which SDUs are not discarded in the UE for UL. The bit position of the Nth bit in the Discard Bitmap is N, ie, the bit position of the first bit in the Discard Bitmap is 1. The value 0 indicates PDCP SDU with COUNT = (FDC + bit position) modulo 2 32 is not discarded. The value 1 indicates PDCP SDU with COUNT = (FDC + bit position) modulo 2 32is discarded (Discard Bitmap for UL: This field can indicate PDCP SDUs that are discarded and SDUs that are not discarded by the UE for UL. The bit position of the Nth bit in the discard bitmap can be N, i.e. the bit position of the first bit in the discard bitmap can be 1. 0 is COUNT = (FDC + bit position) modulo 2 32 may indicate that the PDCP SDU is not discarded. A value of 1 indicates that COUNT = (FDC + bit position) modulo 2. 32 (This may indicate that a PDCP SDU is being deleted.)

[0309] In one embodiment of the present disclosure, referring to FIG. 7, if a source base station can transmit uplink PDCP SDU discard information per DRB to a target base station through an SN Status Transfer message (750) or an SN Gap Status Transfer message, after a handover, the target base station can reduce a re-ordering delay that occurs during an uplink PDCP SDU reception operation of the corresponding DRB. Referring to FIG. 7, the source base station can notify the target base station through the SN Status Transfer or SN Gap Status Transfer message that, for a specific DRB, a PDCP SDU having an uplink PDCP SN / COUNT value of f+2 has already been discarded. Accordingly, after the handover is completed, the target base station may not perform a re-ordering operation that occurs due to the PDCP SDU after receiving a discard instruction for the PDCP SDU having an SN / COUNT value of f+2.

[0310] In one embodiment of the present disclosure, the AM DRB of a terminal configured to send a PDCP SN Gap Report may trigger a PDCP SN Gap Report in the following cases:

[0311] - upper layer requests a PDCP entity re-establishment;

[0312] - upper layer requests a PDCP data recovery;

[0313] - upper layer requests a uplink data switching;

[0314] - upper layer reconfigures the PDCP entity to release DAPS and daps-SourceRelease is configured in TS 38.331.

[0315] For AM DRBs in the sidelink, the transmitting PDCP entity shall trigger a PDCP SN Gap report when:

[0316] - upper layer requests a PDCP entity re-establishment.

[0317] For AM MRBs configured by upper layers to send a PDCP SN Gap report in the uplink, the transmitting PDCP entity shall trigger a PDCP SN Gap report when:

[0318] - upper layer requests a PDCP entity re-establishment;

[0319] - upper layer requests a PDCP data recovery.

[0320] FIG. 8 illustrates a configuration of a terminal according to various embodiments of the present disclosure. According to one embodiment, the terminal of FIG. 8 may include at least one of a user terminal, a terminal, an electronic device, or a user equipment (UE), as conveniently referred to. For example, the terminal may include a terminal or UE in the embodiments described above.

[0321] A terminal according to one embodiment of the present disclosure may include a processor (or controller) (820) that controls the overall operation of the terminal, a transceiver (800) including a transmitter and a receiver, and a memory (810). Of course, the terminal is not limited to the above-described examples, and the terminal may include more or fewer components than those illustrated in FIG. 8.

[0322] According to one embodiment of the present disclosure, the transceiver (800) can transmit and receive signals with a base station or other devices. The signals transmitted and received by the terminal may include control information and data. Furthermore, the transceiver (800) can receive signals via a wireless channel, output them to the processor (820), and transmit the signals output from the processor (820) via the wireless channel.

[0323] According to one embodiment of the present disclosure, the processor (820) can control the terminal to perform any one of the operations described above. Meanwhile, the processor (820), the memory (810), and the transceiver (800) do not necessarily have to be implemented as separate modules, and of course, they can be implemented as a single component in the form of a single chip. In addition, the processor (820) and the transceiver (800) can be electrically connected. In addition, the processor (820) can include an Application Processor (AP), a Communication Processor (CP), a circuit, an application-specific circuit, a controller, or at least one processor.

[0324] According to one embodiment of the present disclosure, the memory (810) can store data such as basic programs, application programs, and setting information for the operation of the terminal. In particular, the memory (810) provides the stored data upon request of the processor (820). The memory (810) can be configured as a storage medium or a combination of storage media such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD. In addition, there can be a plurality of memories (810). In addition, the processor (820) can perform the above-described embodiments based on a program for performing the above-described embodiments of the present disclosure stored in the memory (810).

[0325] FIG. 9 illustrates a configuration of a base station according to various embodiments of the present disclosure. According to one embodiment, the base station of FIG. 9 may include at least one of a base station or a gNB, as referred to for convenience. For example, the base station may include a base station or gNB (source gNB or target gNB) in the embodiments described above.

[0326] A base station according to one embodiment of the present disclosure may include a processor (or controller) (920) that controls the overall operation of the base station, a transceiver (900) including a transmitter and a receiver, and a memory (910). Of course, the present invention is not limited to the above-described example, and the network entity may include more or fewer components than the configuration illustrated in FIG. 9.

[0327] According to one embodiment of the present disclosure, the transceiver (900) can transmit and receive signals with at least one of network entities or other devices. The signals transmitted and received by the base station can include control information and data.

[0328] According to one embodiment of the present disclosure, the processor (920) can control the base station to perform any one of the operations described above. Meanwhile, the processor (920), the memory (910), and the transceiver (900) do not necessarily have to be implemented as separate modules, and of course, they can be implemented as a single component in the form of a single chip. In addition, the processor (920) and the transceiver (900) can be electrically connected. In addition, the processor (920) can include an Application Processor (AP), a Communication Processor (CP), a circuit, an application-specific circuit, a controller, or at least one processor.

[0329] According to one embodiment of the present disclosure, the memory (910) can store data such as basic programs, application programs, and setting information for the operation of the base station. In particular, the memory (910) provides the stored data upon request of the processor (920). The memory (910) can be configured as a storage medium or a combination of storage media such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD. In addition, there can be a plurality of memories (910). In addition, the processor (920) can perform the above-described embodiments based on a program for performing the above-described embodiments of the present disclosure stored in the memory (910).

[0330] It should be noted that the aforementioned configuration diagrams, examples of control / data signal transmission methods, examples of operational procedures, and configuration diagrams are not intended to limit the scope of the present disclosure. That is, not all components, entities, or operational steps described in the embodiments of the present disclosure should be construed as essential components for implementing the disclosure, and implementations may be made without detracting from the essence of the disclosure even if only some components are included. Furthermore, each embodiment may be combined and operated as needed. For example, parts of the methods proposed in the present disclosure may be combined to operate network entities and terminals.

[0331] The operations of the base station or terminal described above can be realized by providing a memory device storing the corresponding program code in any component within the base station or terminal device. That is, the control unit of the base station or terminal device can execute the operations described above by reading and executing the program code stored in the memory device using a processor or CPU (Central Processing Unit).

[0332] The various components and modules of the entity, base station or terminal device described in this specification may be operated using hardware circuits, such as logic circuits based on complementary metal oxide semiconductors, firmware, software and / or hardware and firmware and / or software embedded in a machine-readable medium. For example, various electrical structures and methods may be implemented using electrical circuits such as transistors, logic gates and application-specific semiconductors.

[0333] When implemented in software, a computer-readable storage medium storing one or more programs (software modules) may be provided. The one or more programs stored in the computer-readable storage medium are configured for execution by one or more processors within an electronic device. The one or more programs include instructions that cause the electronic device to execute methods according to the embodiments described in the claims or specification of the present disclosure.

[0334] These programs (software modules, software) may be stored in random access memory, non-volatile memory including flash memory, read only memory (ROM), electrically erasable programmable read only memory (EEPROM), magnetic disc storage device, compact disc ROM (CD-ROM), digital versatile discs (DVDs) or other forms of optical storage device, magnetic cassette. Or, they may be stored in a memory configured as a combination of some or all of these. In addition, each configuration memory may be included in multiple numbers.

[0335] Additionally, the program may be stored in an attachable storage device that is accessible via a communication network such as the Internet, an intranet, a local area network (LAN), a wide local area network (WLAN), a storage area network (SAN), or a combination thereof. Such a storage device may be connected to a device performing an embodiment of the present disclosure via an external port. Additionally, a separate storage device on the communication network may be connected to a device performing an embodiment of the present disclosure.

[0336] In the specific embodiments of the present disclosure described above, components included in the disclosure are expressed singularly or plurally, depending on the specific embodiment presented. However, the singular or plural expressions are selected to suit the presented situation for convenience of explanation, and the present disclosure is not limited to singular or plural components. Components expressed in plural may be composed of singular elements, or components expressed in singular may be composed of plural elements.

[0337] While the detailed description of the present disclosure has described specific embodiments, it should be understood that various modifications are possible without departing from the scope of the present disclosure. Therefore, the scope of the present disclosure should not be limited to the described embodiments, but should be determined not only by the scope of the claims described below but also by equivalents thereof. In other words, it will be apparent to those skilled in the art that other modifications based on the technical idea of ​​the present disclosure are possible. In addition, the above-described embodiments can be combined and operated with each other as needed. For example, parts of the methods proposed in the present disclosure can be combined with each other to operate a base station and a terminal. In addition, although the above-described embodiments have been presented based on a 5G, NR system, other modifications based on the technical idea of ​​the above-described embodiments can be implemented with other systems such as LTE, LTE-A, and LTE-A-Pro systems.

Claims

1. A method performed by a first base station in a wireless communication system, A step of transmitting a first message including information regarding discarding an uplink PDCP (packet data convergence protocol) SDU (service data unit) to a second base station, A method, wherein the information regarding the discarding of the above uplink PDCP SDU includes first information for indicating the PDCP SDU to be discarded at the terminal.

2. In paragraph 1, The above first information includes a bitmap for indicating whether to discard or not for each DRB, and A method wherein the bitmap includes at least one bit indicating whether at least one uplink PDCP SDU is discarded.

3. In paragraph 2, If at least one bit above is assigned a value of 0, it indicates that at least one uplink PDCP SDU is not discarded, A method, wherein if a value of 1 is assigned to at least one bit, the at least one uplink PDCP SDU is indicated to be discarded.

4. In paragraph 1, The above first base station is a source base station, A method wherein the second base station is a target base station for the terminal to hand over.

5. In a method performed by a second base station of a wireless communication system, A step of receiving a first message including information about discarding an uplink PDCP (packet data convergence protocol) SDU (service data unit) from a first base station, A method, wherein the information regarding the discarding of the above uplink PDCP SDU includes first information for indicating the PDCP SDU to be discarded at the terminal.

6. In paragraph 5, The above first information includes a bitmap for indicating whether to discard or not for each DRB, and A method wherein the bitmap includes at least one bit indicating whether at least one uplink PDCP SDU is discarded.

7. In paragraph 6, If at least one bit above is assigned a value of 0, it indicates that at least one uplink PDCP SDU is not discarded, A method, wherein if a value of 1 is assigned to at least one bit, the at least one uplink PDCP SDU is indicated to be discarded.

8. In paragraph 5, The above first base station is a source base station, A method wherein the second base station is a target base station for the terminal to hand over.

9. At the first base station: At least one transceiver; At least one processor communicatively coupled to said at least one transceiver; and At least one memory communicatively coupled to said at least one processor and storing instructions, The above commands are executed individually or in any combination by the at least one processor, so that the first base station: To the second base station, transmit a first message including information regarding the discarding of an uplink PDCP (packet data convergence protocol) SDU (service data unit), A first base station, wherein the information regarding the discarding of the above uplink PDCP SDU includes first information for indicating the PDCP SDU to be discarded at the terminal.

10. In paragraph 9, The above first information includes a bitmap for indicating whether to discard or not for each DRB, and A first base station, wherein the bitmap includes at least one bit indicating whether at least one uplink PDCP SDU is discarded.

11. In paragraph 10, If at least one bit above is assigned a value of 0, it indicates that at least one uplink PDCP SDU is not discarded, A first base station, wherein if a value of 1 is assigned to at least one bit, the at least one uplink PDCP SDU is indicated to be discarded.

12. In paragraph 9, The above first base station is a source base station, The second base station is a first base station, which is a target base station for the terminal to hand over.

13. At the second base station: At least one transceiver; At least one processor communicatively coupled to said at least one transceiver; and At least one memory communicatively coupled to said at least one processor and storing instructions, The above commands are executed individually or in any combination by the at least one processor so that the second base station: Receive a first message from a first base station that includes information about discarding an uplink PDCP (packet data convergence protocol) SDU (service data unit), A second base station, wherein the information regarding the discarding of the above uplink PDCP SDU includes first information for indicating the PDCP SDU to be discarded at the terminal.

14. In paragraph 13, The above first information includes a bitmap for indicating whether to discard or not for each DRB, and A second base station, wherein the bitmap includes at least one bit indicating whether at least one uplink PDCP SDU is discarded.

15. In paragraph 13, If at least one bit above is assigned a value of 0, it indicates that at least one uplink PDCP SDU is not discarded, A second base station, wherein if a value of 1 is assigned to at least one bit, the at least one uplink PDCP SDU is indicated to be discarded.

Images