Method and apparatus for performing improved communications in a wireless communication system

Abstract

Disclosed are communication technologies and systems for fusing a 5G communication system using IoT technology to support a higher data transmission rate than a 4G system. The disclosure can be applied to intelligent services (e.g., smart homes, smart buildings, smart cities, smart cars, connected cars, healthcare, digital education, retail, security and safety services, etc.) based on 5G communication technology and IoT-related technology. One embodiment of the present invention relates to a method by which a terminal updates system information and a terminal for performing the method, the method including the steps of acquiring first system information and second system information from a first cell, starting a timer corresponding to the second system information, determining whether a second cell is a cell that shares the second system information with the first cell if the terminal has moved from the first cell to the second cell, and updating the second system information based on the determination result.

Description

[0001] This application is a divisional application of the Chinese Invention Patent Application No. 201880024868.1, filed on January 26, 2018, entitled “Method and apparatus for performing improved communication in wireless communication system” with the same title. TECHNICAL FIELD

[0002] The disclosure relates to a method for performing different handover operations according to a type of a base station in a wireless communication system.

[0003] In addition, the disclosure relates to a radio link failure in case of applying multiple connections in a next-generation mobile communication system.

[0004] In addition, the disclosure relates to discontinuous reception (DRX) and paging establishment in a next-generation mobile communication system.

[0005] In addition, the disclosure relates to system information update in a next-generation mobile communication system. BACKGROUND

[0006] To meet the demand for wireless data traffic having increased since the 4G communication system has been commercialized, efforts are made to develop an improved 5G communication system or a pre-5G communication system. Therefore, the 5G communication system or the pre-5G communication system is also called a "beyond 4G network communication system" or a "post LTE system". The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease the pathloss of radio waves and increase the transmission distance of radio waves in the mmWave bands, the following technologies are discussed in the 5G wireless communication system: beamforming, massive Multiple-Input Multiple-Output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, analog beam forming, and large scale antenna. In addition, in the 5G communication system, development for system network improvement is under way based on technologies such as evolved small cell, advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, device-to-device communication (D2D), wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like. Also, in the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as an advanced access technology are under development.

[0007] Meanwhile, the Internet, which has been a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, or "things," exchange and process information. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged as a new paradigm for the IoT. As technology elements, such as "sensing technology", "wired / wireless communication and network infrastructure", "service interface technology", and "security technology" have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth, have been researched. An IoT environment can provide intelligent Internet technology services that create a new value through collection and analysis of data generated from connected things. The IoT can be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances, and advanced medical services through the convergence and combination of existing Information Technology (IT) and various industrial applications.

[0008] In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies, such as a sensor network, Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth, have been applied to a 5G communication technical, such as beamforming, MIMO, and array antennas. The application of a cloud Radio Access Network (cloud RAN) as the above-described Big Data processing technology can also be considered as an example of convergence between the 5G technology and the IoT technology.

[0009] Meanwhile, during communication between a terminal and a base station, a current base station (serving cell) can determine handover of a terminal from the current base station to another base station according to signal strength / quality information of the current base station and a neighboring base station reported by the terminal due to movement of the terminal or the like. In this case, since there can be various types of base stations, the terminal needs different operations for performing handover with respect to different kinds of base stations. SUMMARY

[0010] TECHNICAL PROBLEM

[0011] An aspect of the disclosure is to provide a method of processing data without loss even when different handover operations are performed according to types of base stations in a wireless communication system.

[0012] In addition, another aspect of the disclosure is to provide a method of processing data without loss when handover between heterogeneous systems, such as handover from LTE to New Radio (NR) or handover from NR to LTE, is performed in a wireless communication system.

[0013] In addition, another aspect of the disclosure will provide a new procedure that can consider the performance of multiple radio links as a whole in a multi-connection case in which a primary base station and a secondary base station can transmit and receive duplicated data, unlike conventional LTE.

[0014] In addition, another aspect of the disclosure will propose a procedure in which, when a terminal in an inactive radio resource control (RRC) state applies discontinuous reception (DRX), a base station configures a DRX cycle and operation of the terminal according to a type of paging.

[0015] In addition, another aspect of the disclosure will provide a method for updating system information in a next-generation mobile communication system.

[0016] Technical Solution

[0017] According to an embodiment of the disclosure, a method performed by a terminal in a communication system, the method comprising: receiving a radio resource control (RRC) message related to an RRC inactive state; entering the RRC inactive state based on the RRC message; receiving a paging message in the RRC inactive state; entering an RRC idle state from the RRC inactive state in case that the paging message includes an identity matching an S-temporary mobile subscriber identity (S-TMSI); and generating an access stratum (AS) message for a radio access network (RAN) paging in case that the paging message includes an identity matching a resume identity.

[0018] According to an embodiment of the disclosure, a terminal in a communication system, the terminal comprising: a transceiver; and at least one processor coupled with the transceiver and configured to: receive a radio resource control (RRC) message related to an RRC inactive state; enter the RRC inactive state based on the RRC message; receive a paging message in the RRC inactive state; enter an RRC idle state from the RRC inactive state in case that the paging message includes an identity matching an S-temporary mobile subscriber identity (S-TMSI); and generate an access stratum (AS) message for a radio access network (RAN) paging in case that the paging message includes an identity matching a resume identity.

[0019] According to an embodiment of the disclosure, a method performed by a base station in a communication system, the method including: transmitting a paging message to a terminal that has entered an RRC inactive state based on a radio resource control (RRC) message; in a case where the paging message includes an identity matching an S-temporary mobile subscriber identity (S-TMSI), receiving a non-access stratum (NAS) message from the terminal that has entered an RRC idle state from the RRC inactive state based on the paging message; and in a case where the paging message includes an identity matching a resume identity, receiving an access stratum (AS) message for a radio access network (RAN) paging from the terminal in the RRC inactive state.

[0020] According to an embodiment of the disclosure, a base station in a communication system, the base station including: a transceiver; and at least one processor coupled with the transceiver and configured to: transmit a paging message to a terminal that has entered an RRC inactive state based on a radio resource control (RRC) message; in a case where the paging message includes an identity matching an S-temporary mobile subscriber identity (S-TMSI), receive a non-access stratum (NAS) message from the terminal that has entered an RRC idle state from the RRC inactive state based on the paging message; and in a case where the paging message includes an identity matching a resume identity, receive an access stratum (AS) message for a radio access network (RAN) paging from the terminal in the RRC inactive state.

[0021] According to an embodiment of the disclosure, a method of a terminal for updating system information can include: acquiring first system information and second system information from a first cell; starting a timer corresponding to the second system information; if the terminal moves from the first cell to a second cell, determining whether the second cell shares the second system information with the first cell; and updating the second system information based on a result of the determination.

[0022] In addition, according to an embodiment of the disclosure, a terminal can include: a transceiver configured to transmit and receive a signal; and a controller configured to acquire first system information and second system information from a first cell, start a timer corresponding to the second system information, determine whether a second cell shares the second system information with the first cell if the terminal moves from the first cell to the second cell, and update the second system information based on a result of the determination.

[0023] Beneficial technical effects

[0024] According to an embodiment of the disclosure, a terminal performs different handover operations according to a type of a base station, thereby reducing packets lost during handover.

[0025] In addition, according to another embodiment of the disclosure, even when a terminal performs handover to a base station of a heterogeneous system, it is possible to prevent data loss.

[0026] In addition, according to another embodiment of the disclosure, in a case where multiple connections are used in a next-generation mobile communication system, it is possible to stably support a connection state between a terminal and a base station by specifying a radio link failure declaration procedure.

[0027] In addition, according to another embodiment of the disclosure, it is possible to solve a security problem that can occur in a case where a base station independently generates a paging.

[0028] In addition, according to another embodiment of the disclosure, it is possible to effectively update system information according to a change in a cell to which a terminal belongs. BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG. 1A FIG. 1 is a diagram illustrating a structure of an LTE system according to an embodiment of the disclosure.

[0030] FIG. 1B FIG. 2 is a diagram illustrating a radio protocol structure of an LTE system according to an embodiment of the disclosure.

[0031] FIG. 1C FIG. 3 is a diagram illustrating a message flow between a terminal and a base station according to an embodiment of the disclosure.

[0032] FIG. 1D FIG. 4 is a diagram illustrating an operation of a terminal according to an embodiment of the disclosure.

[0033] FIG. 1E FIG. 5 is a block diagram illustrating a configuration of a terminal according to an embodiment of the disclosure.

[0034] FIG. 1F FIG. 6 is a diagram illustrating options for separating a central unit (CU) and a distributed unit (DU) according to an embodiment of the disclosure.

[0035] FIG. 2A FIG. 7 is a diagram illustrating a structure of an LTE system according to an embodiment of the disclosure.

[0036] FIG. 2B FIG. 8 is a diagram illustrating a radio protocol structure of an LTE system according to an embodiment of the disclosure.

[0037] FIG. 2C FIG. 9 is a diagram illustrating a message flow between a terminal and a base station according to an embodiment of the disclosure.

[0038] FIG. 2D FIG. 10 is a diagram illustrating an operation of a terminal according to an embodiment of the disclosure.

[0039] FIG. 2E FIG. 11 is a block diagram illustrating a configuration of a terminal according to an embodiment of the disclosure.

[0040] FIG. 3Ais a diagram illustrating a structure of an LTE system according to an embodiment of the disclosure.

[0041] FIG. 3B is a diagram illustrating a radio protocol structure of an LTE system according to an embodiment of the disclosure.

[0042] FIG. 3C is a diagram illustrating a structure of a next-generation mobile communication system according to an embodiment of the disclosure.

[0043] FIG. 3D is a diagram schematically illustrating RRC diversity operation in multi-connectivity according to an embodiment of the disclosure.

[0044] FIG. 3E is a diagram illustrating radio link monitoring operation and radio link failure operation in LTE according to an embodiment of the disclosure.

[0045] FIG. 3F is a diagram illustrating overall operation of radio link monitoring (RLM) and radio link failure (RLF) of a primary cell (PCell) and a primary secondary cell (PSCell) in case RRC diversity is applied according to an embodiment of the disclosure.

[0046] FIG. 3G is a diagram illustrating RLM and RLF procedures of a terminal in a PCell in case RRC diversity is applied according to an embodiment of the disclosure.

[0047] FIG. 3H is a diagram illustrating RLM and RLF procedures of a terminal in a PSCell in case RRC diversity is applied according to an embodiment of the disclosure.

[0048] FIG. 3I is a block diagram illustrating a structure of a terminal according to an embodiment of the disclosure.

[0049] FIG. 3J is a block diagram illustrating a configuration of an NR base station according to an embodiment of the disclosure.

[0050] FIG. 4A is a diagram illustrating a structure of a next-generation mobile communication system according to an embodiment of the disclosure.

[0051] FIG. 4B is a conceptual diagram illustrating a paging time in LTE technology according to an embodiment of the disclosure.

[0052] FIG. 4C is a diagram illustrating a process of determining a DRX cycle of a terminal in LTE technology according to an embodiment of the disclosure.

[0053] FIG. 4Dis a diagram illustrating a transition of a radio access state in a next-generation mobile communication system according to an embodiment of the disclosure.

[0054] FIG. 4E is a flowchart illustrating a process of transmitting a paging message when a terminal is in an RRC inactive state according to an embodiment of the disclosure.

[0055] FIG. 4F is a diagram illustrating an operation of a terminal according to an embodiment of the disclosure.

[0056] FIG. 4G is a diagram illustrating an operation of a base station according to an embodiment of the disclosure.

[0057] FIG. 4H is a block diagram illustrating a structure of a terminal according to an embodiment of the disclosure.

[0058] FIG. 4I is a block diagram illustrating a configuration of a base station according to an embodiment of the disclosure.

[0059] FIG. 5A is a diagram illustrating a structure of a next-generation mobile communication system according to an embodiment of the disclosure.

[0060] FIG. 5B is a diagram illustrating a method of providing system information in an LTE system according to an embodiment of the disclosure.

[0061] FIG. 5C is a diagram illustrating a method for updating system information in an LTE system according to an embodiment of the disclosure.

[0062] FIG. 5D is a diagram illustrating a method of providing system information in a next-generation mobile communication system according to an embodiment of the disclosure.

[0063] FIG. 5E is a diagram illustrating a method for updating system information according to an embodiment of the disclosure.

[0064] FIG. 5F is a diagram illustrating an operation of a terminal for operating cell-based or area-based system information and a validity timer corresponding thereto according to an embodiment of the disclosure.

[0065] FIG. 5G is a diagram illustrating a method of performing system information update according to an embodiment of the disclosure.

[0066] FIG. 5H is a diagram illustrating an operation of a terminal for performing system information update according to an embodiment of the disclosure.

[0067] FIG. 5Iis a view illustrating an operation of a terminal for performing system information update according to an embodiment of the disclosure.

[0068] FIG. 5J is a view illustrating a method of providing access barring configuration information as system information according to an embodiment of the disclosure.

[0069] FIG. 5K is a view illustrating an operation of a base station for providing access barring configuration information as system information according to an embodiment of the disclosure.

[0070] FIG. 5L is a block diagram illustrating a structure of a terminal according to an embodiment of the disclosure.

[0071] FIG. 5M is a block diagram illustrating a configuration of a base station according to an embodiment of the disclosure. DETAILED DESCRIPTION

[0072] Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. In the following description of the disclosure, it will be omitted to describe in detail the known functions or configurations incorporated herein when the detailed description of the known functions or configurations incorporated herein can make the subject matter of the disclosure not very clear. The terms to be described below are terms defined in consideration of the functions in the disclosure, and can be different according to users, user's intention, or habits. Therefore, the definition of the terms should be made based on the content of the entire specification.

[0073] The advantages and features of the disclosure and the means for achieving them will be clear by referring to the embodiments described below in detail in conjunction with the accompanying drawings. However, the disclosure is not limited to the embodiments set forth below, but can be implemented in various different forms. The following embodiments are provided only to completely disclose the disclosure and to inform the skilled in the art of the scope of the disclosure, and the disclosure is limited only by the scope of the appended claims. Throughout the specification, the same or similar reference numerals denote the same or similar elements.

[0074] <First Embodiment>

[0075] Hereinafter, for the convenience of explanation, terms for identifying connection nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, terms referring to various identification information, and the like will be used as examples. Therefore, the disclosure is not limited to the terms used herein, and other terms referring to objects having equivalent technical meanings can be used.

[0076] For the convenience of explanation, the terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard, which is the latest communication standard among existing communication standards, will be used in the present disclosure. However, the present disclosure is not limited to the above terms and names, and the present disclosure can be applied to systems conforming to other standards in the same manner. In particular, the present disclosure is applicable to 3GPP New Radio (NR) (a 5th generation mobile communication standard).

[0077] FIG. 1A is a diagram illustrating a structure of an LTE system according to an embodiment of the present disclosure.

[0078] Referring to FIG. 1A The wireless communication system includes a plurality of base stations 1a-05, 1a-10, 1a-15, and 1a-20, a mobility management entity (MME) 1a-25, and a serving gateway (S-GW) 1a-30. A user equipment (hereinafter, referred to as "UE" or "terminal") 1a-35 accesses an external network through the base stations 1a-05, 1a-10, 1a-15, and 1a-20 and the S-GW 1a-30.

[0079] The base stations 1a-05, 1a-10, 1a-15, and 1a-20 provide wireless access to terminals accessing a network as access nodes of a cellular network. That is, in order to serve traffic of a user, the base stations 1a-05, 1a-10, 1a-15, and 1a-20 collect state information such as a buffer state of a terminal, an available transmission power state, a channel state, and the like, and perform scheduling, thereby supporting connection between a terminal and a core network (CN). The MME 1a-25 performs various control functions and a mobility management function for a terminal and is connected to a plurality of base stations. The S-GW 1a-30 provides a data bearer. In addition, the MME 1a-25 and the S-GW 1a-30 can further perform authentication and bearer management for terminals accessing a network and can process packets received from the base stations 1a-05, 1a-10, 1a-15, and 1a-20 or packets to be transmitted to the base stations 1a-05, 1a-10, 1a-15, and 1a-20.

[0080] FIG. 1B is a diagram illustrating a wireless protocol structure of an LTE system according to an embodiment of the present disclosure. The wireless protocol structure in the diagram can be partially different from a wireless protocol structure of an NR system to be defined later, but the wireless protocol structure in the diagram will be described for the convenience of explanation of the present disclosure.

[0081] Referring to FIG. 1BThe radio protocol of the LTE system includes a packet data convergence protocol (PDCP) 1b-05 or 1b-40, a radio link control (RLC) 1b-10 or 1b-35, and a medium access control (MAC) 1b-15 or 1b-30 in the terminal and the ENB, respectively. The packet data convergence protocol (PDCP) 1b-05 or 1b-40 performs operations such as IP header compression / decompression, and the radio link control (hereinafter, also referred to as "RLC") 1b-10 or 1b-35 reconfigures a PDCP PDU (packet data unit) to an appropriate size. The MAC 1b-15 or 1b-30 is connected to a plurality of RLC entities (configured in a single terminal), multiplexes RLC PDUs into a MAC PDU, and demultiplexes RLC PDUs from a MAC PDU. The physical (PHY) layer 1b-20 or 1b-25 channel-encodes and modulates high layer data, and converts it into an OFDM symbol that will then be transmitted through a wireless channel, or demodulates and channel-decodes an OFDM symbol received through a wireless channel so as to then be transmitted to a high layer. In addition, hybrid-ARQ (HARQ) is also used for additional error correction in the physical layer 1b-20 or 1b-25, and the receiving end transmits 1-bit information indicating whether a packet transmitted from the transmitting end has been received. This is referred to as HARQ ACK / NACK information. Downlink HARQ ACK / NACK information regarding uplink transmission can be transmitted through a physical hybrid-ARQ indicator channel (PHICH), and uplink HARQ ACK / NACK information regarding downlink transmission can be transmitted through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).

[0082] Although not shown in the drawing, a radio resource control (hereinafter, referred to as "RRC") layer exists in a high layer of the PDCP layer of the terminal and the base station, respectively. The RRC layer can transmit and receive a configuration control message for radio resource control related to access / measurement. For example, the terminal can be instructed to perform measurement using an RRC layer message, and the terminal can report a measurement result to the base station using an RRC layer message.

[0083] FIG. 1C FIG. 1 is a diagram illustrating a message flow between a terminal and a base station when a handover method according to an embodiment of the disclosure is used.

[0084] In FIG. 1CIn the middle, the terminal 1c-01 in the idle mode (RRC_IDLE) accesses the base station (1c-11) after generating transmission data or the like. Since the terminal is disconnected from the network to save power or the like, data cannot be transmitted in the idle mode. Therefore, in order to transmit data, it is necessary to switch to the connected mode (RRC_CONNECTED). If the terminal 1c-01 successfully connects to the base station 1c-03, the terminal 1c-01 switches to the connected mode (RRC_CONNECTED), and then the base station 1c-03 configures a data radio bearer (DRB) to the terminal 1c-01 for data transmission and reception (1c-13), and the terminal 1c-01 transmits its acknowledgement message to the base station 1c-03 (1c-15), so that the terminal 1c-01 in the connected mode can transmit and receive data to and from the base station 1c-03 (1c-17). In order to configure the DRB, an "RRCConnectionReconfiguration" message of the RRC layer can be used, and as the acknowledgement message, an "RRCConnectionReconfigurationComplete" can be used. In addition, the DRB configuration can include configuration information of the PDCP and RLC layers for each bearer. More specifically, the DRB configuration can indicate the operation mode of the RLC layer {more specifically, the acknowledgement mode (AM) and the unacknowledgement mode (UM)} or the like, and the configuration information of the PDCP layer can include an indicator indicating whether or not a status report needs to be transmitted after handover or when the PDCP layer is reconfigured for each bearer. That is, "statusReportRequired" information is included in the PDCP configuration. As described above, the bearer for which the PDCP status report needs to be transmitted is referred to as a "first bearer". That is, with respect to the first bearer, "statusReportRequired" is configured as "TRUE". "StatusReportRequired" can be configured only for RLC-AM for which retransmission can be performed when data is lost.

[0085] During communication between the terminal 1c-01 and the base station 1c-03, the current base station (serving cell) 1c-03 can determine handover in which the terminal 1c-01 moves to another base station 1c-05, according to signal strength / quality information of the current base station 1c-03 and the neighboring base station 1c-05, which is reported by the terminal 1c-01 due to movement of the terminal 1c-01 or the like (1c-19).

[0086] Meanwhile, NR can have various types of base stations. In the existing LTE system, a base station called "eNB" has the above FIG. 1BAll of the layers in the MAC, RLC, PDCP, and RRC layers described in the middle. On the other hand, in the NR system, like the eNB, the gNB can include all functions. Alternatively, the gNB can be divided into a central unit (CU) and a distribution unit (DU) and the MAC, RLC, PDCP, and RRC layers can be logically divided into the CU and the DU. FIG. 1F Options for separating the CU and the DU are described.

[0087] Referring to the CU-DU separation option 2, the RRC and the PDCP exist in the CU, and the RLC, the MAC, and the physical layer exist in the DU. Referring to the CU-DU separation option 3, the RRC, the PDCP, and the High-RLC exist in the CU, and the Low-RLC, the MAC, and the physical layer exist in the DU. Among the functions of the RLC, the High-RLC includes a function of performing retransmission in the case of data loss, such as the functions of ARQ and packet sequence reordering; and the low RLC includes a function of segmenting or concatenating packets according to a given transmission resource. Meanwhile, one CU can have one or more DUs, and thus, according to the movement of a terminal, only the DU can change while the CU remains unchanged.

[0088] Therefore, handover can be performed so that both the DU and the CU change, or so that only the DU changes according to the movement of a terminal while the CU remains unchanged. In addition, even in the case where only the DU changes while the CU remains unchanged, operations need to be performed differently according to the CU-DU separation option.

[0089] Therefore, in an embodiment of the disclosure, a base station determines a terminal for which handover is to be performed and the handover to be performed. In an embodiment of the disclosure, the handover is classified as follows.

[0090] - First handover: handover between gNBs (handover in which both the CU and the DU change)

[0091] - Second handover: RLC moving (repositioning) handover in gNB (HO under the same base station. After the HO, the RLC changes: that is, handover in which the CU does not change but the DU changes because the gNB has the structure of option 2, and the PDCP does not change)

[0092] - Third handover: RLC fixed handover in gNB (HO under the same base station. The same RLC is used even after the HO: that is, handover in which the CU does not change but the DU changes because the gNB has the structure of option 3)

[0093] The base station 1c-03 determines the type of handover according to the above classification, and the base station 1c-03 transmits a handover command (1c-21) to the terminal 1c-01 according to it. The handover command can be transmitted by an "RRCConnectionReconfiguration" message of the RRC layer, and the handover command message includes mobility control information (MCI) (MobilityControlInfo) indicating the base station to which this handover is directed. In addition, according to the type of handover, the RRC message can include or can not include the following information.

[0094] - Information related to security key reconfiguration: This includes counter information for generating a new key.

[0095] - RLC re-establishment indicator: This is an indicator indicating whether RLC re-establishment is required.

[0096] The terminal 1c-01 that has received the handover command determines the type of handover indicated by the base station 1c-03 among the above types of handover (1c-23). In an embodiment of the present disclosure, if there is information related to security key reconfiguration, the terminal 1c-01 can determine that the first handover is indicated; if there is no information related to security key reconfiguration and if there is an RLC re-establishment indicator, it can be determined that the second handover is indicated; and if there is no information related to security key reconfiguration and if there is no RLC re-establishment indicator, it can be determined that the third handover is indicated.

[0097] Thereafter, the terminal 1c-01 receives a synchronization signal of the target cell 1c-05 indicated by the RRC message, performs synchronization, and initializes the MAC layer of the terminal 1c-01. This is due to the fact that in all types of handover, the MAC layer is directed to the new base station (or new DU).

[0098] In addition, the terminal 1c-01 performs an operation conforming to the type of handover according to the determination result (1c-25). More specifically, PDCP re-establishment and RLC re-establishment are performed in the case of the first handover, PDCP is maintained and RLC re-establishment is performed in the case of the second handover, and PDCP and RLC are maintained without re-establishment in the case of the third handover.

[0099] In addition, the terminal 1c-01 applies the terminal identifier (C-RNTI for the LTE standard) received through the handover command in the target base station 1c-05, adopts a new security key to perform update according to the received information in the case of the first handover, and maintains the secret key of the existing base station 1c-03 (which has been used in the existing CU) in the case of the second or third handover.

[0100] Thereafter, the terminal 1c-01 performs random access to the target base station 1c-05, synchronizes with the base station 1c-05 in uplink, receives an uplink resource allocation from the target base station 1c-05 (1c-27) and transmits an RRC message confirming the handover completion to the target base station 1c-05 based on the allocated resources (1c-29). The RRC message can be an "RRCConnectionReconfigurationComplete message".

[0101] The terminal 1c-01 performs operations (1c-31) after the handover completion depending on the type of the handover. More specifically, in the case of the first handover, the terminal 1c-01 generates and transmits a PDCP status report for the first bearer to the base station 1c-05 (1c-33). The PDCP status report intends to inform the base station 1c-05 of the received packets because there is a possibility that packets can be lost during the handover of the terminal 1c-01 and thus the base station 1c-05 can retransmit the lost packets.

[0102] In addition, in the case of the second handover, the terminal 1c-01 also generates and transmits a PDCP status report for the first bearer to the base station 1c-05. This is due to the fact that there is still a possibility that the terminal 1c-01 can lose packets due to the movement of the RLC to the target base station 1c-05.

[0103] On the other hand, in the case of the third handover, the terminal 1c-01 does not generate a PDCP report even for the first bearer. This is due to the fact that since the High RLC remains unchanged in the case of the third handover, the RLC re-establishment is not performed; and since the High RLC has a function of performing recovery in the case of data loss such as ARQ, there is no need to retransmit a separate PDCP status report. Thus, the base station can retransmit data that the terminal 1c-01 failed to receive and then the terminal 1c-01 can transmit / receive data to / from the target base station 1c-05 (1c-41).

[0104] FIG. 1D FIG. 1c-01 is a diagram illustrating an operation sequence of a terminal according to an embodiment of the disclosure.

[0105] In FIG. 1DIn the middle, it is assumed that the terminal is in a connected mode (RRC_CONNECTED) (1d-01). Thereafter, the terminal receives a configuration of a data radio bearer (DRB) for data transmission and reception from the base station, transmits an acknowledgement message to the base station in response to this, so that the terminal in the connected mode can transmit data to the base station and receive data from the base station (1d-03). To configure the DRB, an "RRCConnectionReconfiguration" message of the RRC layer can be used and an "RRCConnectionReconfigurationComplete" message can be used as the acknowledgement message. In addition, the DRB configuration can include configuration information of the PDCP and RLC layers for each bearer. More specifically, the DRB configuration can indicate an operation mode of the RLC layer {e.g., an acknowledgement mode (AM) and a non-acknowledgement mode (UM)} and the like, and the configuration information of the PDCP layer can include an indicator indicating whether a status report is required after handover or when the PDCP layer is reconfigured for each bearer. That is, "statusReportRequired" information is included in the PDCP configuration. As described above, a bearer for which a PDCP status report is required is referred to as a "first bearer". That is, with respect to the first bearer, "statusReportRequired" is configured as "TRUE". "StatusReportRequired" can be configured only for RLC-AM, which can perform retransmission when data is lost.

[0106] Thereafter, the terminal can receive a handover command from the base station due to movement of the terminal or the like (1d-05). As described above, the NR can have various types of base stations, and thus, in the present disclosure, handover is classified as follows.

[0107] - First handover: handover between gNBs (handover in which both CU and DU are changed)

[0108] - Second handover: RLC moving (repositioning) handover in gNB (HO under the same base station. After the HO, the RLC is changed: that is, a handover in which, because the gNB has an option 2 structure, the CU is not changed but the DU is changed, and the PDCP is not changed)

[0109] - Third handover: RLC fixed handover in gNB (HO under the same base station. The same RLC is used even after the HO: that is, a handover in which, because the gNB has an option 3 structure, the CU is not changed but the DU is changed)

[0110] The handover command can be transmitted through an "RRCConnectionReconfiguration" message of the RRC layer, and the handover command message includes mobility control information (MCI) (MobilityControlInfo) indicating a base station to which the handover is directed. In addition, the RRC message can include or can not include the following information according to the type of the handover.

[0111] - Information related to security key reconfiguration: This includes counter information for generating a new key.

[0112] - RLC re-establishment indicator: This is an indicator indicating whether RLC re-establishment is required.

[0113] The terminal that has received the handover command determines the type of the handover indicated by the base station among the above-described types of the handover (1d-07). In an embodiment of the disclosure, if there is information related to security key reconfiguration, the terminal can determine that the first handover is indicated; if there is no information related to security key reconfiguration and if there is an RLC re-establishment indicator, the second handover can be determined to be indicated, and if there is no information related to security key reconfiguration and if there is no RLC re-establishment indicator, the third handover can be determined to be indicated.

[0114] According to the determination result, the terminal performs an operation conforming to the type of the handover (1d-11, 1d-13, and 1d-15). More specifically, in all types of the handover, the terminal receives a synchronization signal of a target cell indicated through the RRC message, performs synchronization, and initializes the MAC layer of the terminal. Thereafter, in the case of the first handover, PDCP re-establishment and RLC re-establishment are performed, in the case of the second handover, PDCP is maintained and RLC re-establishment is performed, and in the case of the third handover, PDCP and RLC are maintained without re-establishment.

[0115] In addition, for the corresponding type of the handover, the terminal applies a terminal identifier (C-RNTI for the LTE standard) received through the handover command in the target base station. The terminal generates a new security key according to the received information in the case of the first handover, and maintains a secret key of the existing base station (already used in the existing CU) in the case of the second handover or the third handover.

[0116] Thereafter, the terminal performs random access to the target base station, performs uplink synchronization with the base station, receives an uplink resource allocation from the target base station, and transmits an RRC message (1d-17) confirming completion of the handover to the base station using the allocated resource. The RRC message can be an "RRCConnectionReconfigurationComplete" message.

[0117] Thereafter, the terminal performs an operation according to the type of the handover after the handover is completed (1d-19). More specifically, in the case of the first handover, the terminal generates a PDCP status report for the first bearer and transmits it to the base station (1d-33). The PDCP status report informs the base station of the received packets because there is a possibility that the packets can be lost in the process of the handover of the terminal, and thus the base station can retransmit the lost packets. In addition, in the case of the second handover, the terminal also generates a PDCP status report for the first bearer and transmits it to the base station. This is due to the fact that there is still a possibility that the terminal can lose packets due to the movement of the RLC to the target base station. On the other hand, in the case of the third handover, the terminal does not generate a PDCP report even for the first bearer. This is due to the fact that the RLC re-establishment is not performed because the High RLC remains unchanged in the case of the third handover; and because the High RLC has a function of performing recovery in the case of data loss such as ARQ, a separate PDCP status report does not need to be retransmitted. Thus, the base station can retransmit the data that the terminal failed to receive, and then the terminal can transmit / receive data to / from the target base station.

[0118] FIG. 1E is a block diagram illustrating a configuration of a terminal according to an embodiment of the disclosure.

[0119] Reference FIG. 1E The terminal includes a radio frequency (RF) processor 1e-10, a baseband processor 1e-20, a storage unit 1e-30, and a controller 1e-40.

[0120] The RF processor 1e-10 performs a function of transmitting and receiving a signal through a wireless channel, such as band conversion and signal amplification. That is, the RF processor 1e-10 up-converts a baseband signal provided from the baseband processor 1e-20 into an RF band signal, thus transmitting it through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 1e-10 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Although only one antenna is illustrated in FIG. 1e-10, the terminal can have a plurality of antennas. In addition, the RF processor 1e-10 can include a plurality of RF chains. Furthermore, the RF processor 1e-10 can perform beamforming. To perform beamforming, the RF processor 1e-10 can adjust the phase and amplitude of signals transmitted and received through a plurality of antennas or antenna elements. FIG. 1E

[0121] ​The baseband processor 1e-20 performs a function of conversion between a baseband signal and a bit string according to a physical layer specification of a system. For example, in the case of data transmission, the baseband processor 1e-20 encodes and modulates a transmission bit string, thereby generating a complex symbol. Also, when receiving data, the baseband processor 1e-20 demodulates and decodes a baseband signal provided from the RF processor 1e-10, thus recovering a reception bit string. For example, in the case of applying an orthogonal frequency division multiplexing (OFDM) scheme, when transmitting data, the baseband processor 1e-20 generates a complex symbol by encoding and modulating a transmission bit string, maps the complex symbol to a subcarrier, and then configures an OFDM symbol through an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion. Also, when receiving data, the baseband processor 1e-20 divides a baseband signal provided from the RF processor 1e-10 into an OFDM symbol unit, recovers a signal mapped to a subcarrier through a fast Fourier transform (FFT) operation, and then recovers a reception bit string through demodulation and decoding.

[0122] As described above, the baseband processor 1e-20 and the RF processor 1e-10 transmit and receive a signal. Accordingly, the baseband processor 1e-20 and the RF processor 1e-10 can be referred to as a "transmitter", a "receiver", a "transceiver", or a "communication unit". Further, at least one of the baseband processor 1e-20 and the RF processor 1e-10 can include different communication modules to process signals of different frequency bands. The different frequency bands can include a super high frequency (SHF) (e.g., 2.5 GHz or 5 GHz) band and a millimeter wave (e.g., 60 GHz) band.

[0123] The storage unit 1e-30 stores data such as a basic program for terminal operation, an application program, and configuration information.

[0124] The controller 1e-40 controls overall operations of the terminal. For example, the controller 1e-40 transmits and receives a signal through the baseband processor 1e-20 and the RF processor 1e-10. Also, the controller 1e-40 records and reads data in and from the storage unit 1e-30. To this end, the controller 1e-40 can include at least one processor. For example, the controller 1e-40 can include a communication processor (CP) for controlling communication and an application processor (AP) for controlling a higher layer such as an application program. According to an embodiment of the disclosure, the controller 1e-40 can include a multi-connection processor 1e-42 for performing a process for operating in a multi-connection mode. For example, the controller 1e-40 can perform control so that the terminal performs FIG. 1E the illustrated operations.

[0125] According to embodiments of the disclosure, a terminal can individually perform a handover operation according to a handover command received from a base station, thereby ensuring communication without data loss even when performing handover to a different type of base station.

[0126] The method according to the embodiments described in the claims or specification of the disclosure can be implemented in hardware, software, or a combination thereof.

[0127] When the method is implemented in software, a computer-readable storage medium storing one or more programs (software modules) can be provided. The one or more programs stored in the computer-readable storage medium are configured to be executed by one or more processors in an electronic device. The one or more programs include instructions that allow the electronic device to execute the method according to the embodiments described in the claims or specification of the disclosure.

[0128] The programs (software modules or software) can be stored in random access memory, non-volatile memory including flash memory, ROM (Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), magnetic disc storage devices, CD-ROMs (Compact Disc - ROMs), DVDs (Digital Versatile Discs), other types of optical storage devices, or magnetic cassettes. Alternatively, the programs can be stored in a memory configured as a combination of some or all of the above. In addition, a plurality of memories can be included.

[0129] In addition, the above programs can be stored in an attachable storage device accessible through a communication network such as the Internet, an intranet, a LAN (Local Area Network), a WLAN (Wide Area LAN), or a SAN (Storage Area Network), or a communication network configured as a combination thereof. Such a storage device can be connected to a device for executing embodiments of the disclosure via an external port. In addition, a separate storage device in the communication network can be connected to a device for executing embodiments of the disclosure.

[0130] <Second Embodiment>

[0131] Hereinafter, the operation principle of the disclosure will be described in detail with reference to the accompanying drawings. Hereinafter, if a detailed description of functions and configurations incorporated herein obscures the subject matter of the disclosure, a detailed description of functions and configurations incorporated herein will be omitted. In addition, the terms used herein are defined in consideration of the functions of the disclosure, and can vary according to the intention or practice of a user or operator, etc. Therefore, the definition should be based on the content throughout the specification.

[0132] Hereinafter, for the convenience of explanation, terms for identifying connection nodes, terms for referring to network entities, terms for referring to messages, terms for referring to interfaces between network entities, terms for referring to various pieces of identification information, and the like will be used as examples. Accordingly, the disclosure is not limited to the terms used herein, and other terms referring to objects having equivalent technical meanings can be used.

[0133] For the convenience of explanation, in the disclosure, terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard, which is the latest communication standard among existing communication standards, will be used. However, the disclosure is not limited to the above-described terms and names, and the disclosure can be equally applied to systems conforming to other standards. In particular, the disclosure is applicable to 3GPP New Radio (NR) (a 5th generation mobile communication standard).

[0134] The disclosure relates to a method for performing handover between heterogeneous systems without data loss in a wireless communication system.

[0135] FIG. 2A is a diagram showing the structure of an LTE system according to an embodiment of the disclosure.

[0136] Reference FIG. 2A The wireless communication system includes a plurality of base stations 2a-05, 2a-10, 2a-15, and 2a-20, a mobility management entity (MME) 2a-25, and a serving gateway (S-GW) 2a-30. A user equipment (hereinafter, referred to as "UE" or "terminal") 2a-35 accesses an external network through the base stations 2a-05, 2a-10, 2a-15, and 2a-20 and the S-GW 2a-30.

[0137] The base stations 2a-05, 2a-10, 2a-15, and 2a-20 provide wireless access to terminals accessing a network as access nodes of a cellular network. That is, in order to serve traffic of a user, the base stations 2a-05, 2a-10, 2a-15, and 2a-20 collect state information such as a buffer state of a terminal, an available transmission power state, a channel state, and the like, and perform scheduling, thereby supporting connection between a terminal and a core network (CN). The MME 2a-25 performs various control functions as well as a mobility management function for a terminal, and is connected to a plurality of base stations. The S-GW 2a-30 provides a data bearer. A bearer is a logical path through which data passes, and there can be a plurality of bearers in one terminal. In addition, the MME 2a-25 and the S-GW 2a-30 can further perform authentication and bearer management for terminals accessing a network, and can process packets received from the base stations 2a-05, 2a-10, 2a-15, and 2a-20 or packets to be transmitted to the base stations 2a-05, 2a-10, 2a-15, and 2a-20.

[0138] FIG. 2B is a diagram illustrating a radio protocol structure of an LTE system according to an embodiment of the disclosure. The radio protocol structure in the diagram can be partially different from a radio protocol structure of an NR system to be defined later, but the radio protocol structure in the diagram will be described for the convenience of explanation of the disclosure.

[0139] Reference FIG. 2B , the radio protocol of the LTE system includes a packet data convergence protocol (PDCP) 2b-05 or 2b-40, a radio link control (RLC) 2b-10 or 2b-35, and a medium access control (MAC) 2b-15 or 2b-30 in the terminal and the ENB, respectively. The packet data convergence protocol (PDCP) 2b-05 or 2b-40 performs operations such as IP header compression / decompression, and the radio link control (hereinafter, also referred to as "RLC") 2b-10 or 2b-35 reconfigures a PDCP PDU (packet data unit) to an appropriate size. In addition, an automatic repeat request (ARQ) operation for retransmission of data requiring reliability is also performed in the RLC layer, which is limited to operate in an acknowledgement mode (AM) among the RLC layers. As a corresponding concept, a non-acknowledgement mode (UM) is also defined. The MAC 2b-15 or 2b-30 is connected to a plurality of RLC entities (configured in a single terminal), multiplexes RLC PDUs into a MAC PDU, and demultiplexes RLC PDUs from the MAC PDU. The physical layer 2b-20 or 2b-25 channel-encodes and modulates high layer data, and converts it into an OFDM symbol to be then transmitted through a wireless channel, or demodulates and channel-decodes an OFDM symbol received through a wireless channel so as to then transmit to a high layer. In addition, a hybrid ARQ (HARQ) is also used for additional error correction in the physical layer, and a receiving end transmits 1-bit information indicating whether a packet transmitted from a transmitting end has been received. This is referred to as HARQ ACK / NACK information. Downlink HARQ ACK / NACK information regarding uplink transmission can be transmitted through a physical hybrid ARQ indicator channel (PHICH), and uplink HARQ ACK / NACK information regarding downlink transmission can be transmitted through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).

[0140] Although not shown in the diagram, Radio Resource Control (RRC) layers exist at higher levels of the PDCP layer in both the terminal and the base station. The RRC layer can send and receive configuration control messages related to access / measurement for radio resource control. For example, it can instruct the terminal to perform measurements using RRC layer messages, and the terminal can use RRC layer messages to report measurement results to the base station.

[0141] FIG. 2C This is a diagram illustrating the message flow between a terminal and a base station when using the handover method between different systems as proposed in the embodiments of this disclosure.

[0142] exist FIG. 2C In the diagram, terminal 2c-01, which supports both NR and LTE and is in idle mode (RRC_IDLE), connects to the adjacent NR base station 2c-03 (2c-11) after generating and transmitting data. (Although for ease of explanation, it is assumed that the terminal connects to an NR base station, the terminal can also connect to an LTE base station.) Because the terminal disconnects from the network to save power, it cannot transmit data in idle mode. Therefore, in order to transmit data, it needs to switch to connected mode (RRC_CONNECTED). If terminal 2c-01 successfully connects to base station 2c-03, terminal 2c-01 switches to connected mode (RRC_CONNECTED), and then terminal 2c-01 and base station 2c-03 can send and receive data (2c-13).

[0143] During communication between the terminal 2c-01 and the base station 2c-03, the current base station (serving cell) 2c-03 can determine handover in which the terminal 2c-01 moves to another base station 2c-05 according to signal strength / quality information of the current base station 2c-03 and neighboring base stations, which is reported by the terminal 2c-01 due to movement of the terminal 2c-01 or the like (2c-15). In an embodiment of the disclosure, it is assumed that the LTE base station 2c-05 is the most suitable cell for handover around the terminal, and thus, the NR gNB 2c-03 transmits a command to instruct the terminal 2c-01 to perform handover to the LTE base station 2c-05 (2c-17). The handover command can be transmitted through an "RRCConnectionReconfiguration" message of an RRC layer, and the handover command message includes mobility control information (MCI) (MobilityControlInfo) indicating a base station to which the handover is directed (i.e., the target cell is the LTE base station cell). In addition, the RRC message can further include an indicator (e.g., losslessHandover) indicating lossless handover, and can include configuration information received from the target LTE cell regarding PDCP, RLC, and MAC layers of LTE to be operated in the target LTE cell.

[0144] The lossless handover indicator indicates that the terminal applies lossless handover (to be described later) to a first bearer satisfying a predetermined first condition, and even if the lossless handover indicator is configured (true), the lossless handover is not applied to a second bearer not satisfying the first condition (or satisfying a second condition). The first bearer and the second bearer are defined as follows.

[0145] - The first bearer: a bearer in which the length of a sequence number (SN) in the NR PDCP layer before handover among RLC-AM bearers is less than or equal to the length of the LTE PDCP SN after handover (i.e., there is no loss of data included in the length before handover because the length after handover is greater than the length before handover)

[0146] - The second bearer: a bearer in which the length of the NR PDCP SN before handover is greater than the length of the LTE PDCP SN after handover among all signaling radio bearers (SRBs) (i.e., signaling radio bearers for control signals), all RLC-UM bearers, and RLC-AM bearers (i.e., there is loss of data included in the length before handover because the length after handover is less than the length before handover)

[0147] Hereinafter, for the convenience of description, the PDCP SN length before the handover is referred to as "source PDCP SN length", and the PDCP SN length after the handover is referred to as "target PDCP SN length".

[0148] According to the above classification, the terminal 2c-01 performs different operations according to the type of the bearer (i.e., the first bearer or the second bearer) among the bearers possessed by the terminal 2c-01 (2c-19). That is, the terminal 2c-01 applies the following first operation to the first bearer.

[0149] - generating LTE PDCP and LTE RLC layers to be used in the target

[0150] - processing PDCP PDUs stored in the NR PDCP into PDCP SDUs (i.e., converting encrypted packets into decrypted packets), and then transmitting them to the generated LTE PDCP

[0151] - configuring a hyper frame number (TX_HFN) and RX_HFN in the generated LTE PDCP layer, considering the values (e.g., the same values) used in the NR, and storing the received PDCP SDUs in a reordering buffer according to the PDCP SN

[0152] o TX_HFN is an HFN value internally managed when a packet is transmitted in the PDCP layer. The HFN value and the PDCP SN included in the header of the packet to be transmitted are combined to generate a 32-bit COUNT value of the packet.

[0153] o RX_HFN is an HFN value internally managed when a packet is received in the PDCP layer. The HFN value and the PDCP SN included in the header of the packet to be received are combined to generate a 32-bit COUNT value of the packet.

[0154] - canceling the previous NR PDCP and NR RLC

[0155] Meanwhile, the terminal 2c-01 applies the following second operation to the second bearer.

[0156] - generating LTE PDCP and LTE RLC

[0157] - configuring initial values of TX_HFN and RX_HFN of the LTE PDCP (e.g., set to 0)

[0158] - processing PDCP PDUs stored in the NR PDCP into PDCP SDUs, and transmitting them to the generated LTE PDCP layer

[0159] - canceling the previous NR PDCP and NR RLC

[0160] Thereafter, the terminal 2c-01 performs synchronization and random access with the target cell 2c-05 to perform downlink and uplink synchronization (2c-21), generates a new security key if the random access is successful, and then configures the generated LTE PDCP to use the new security key (2c-23). In addition, the terminal 2c-01 transmits a message of the RRC layer encrypted with the new security key and integrity protected to the target base station 2c-05 to inform that the handover has been successfully completed (2c-25). The message of the RRC layer can be an "RRCConnectionReconfigurationComplete" message.

[0161] Thereafter, the terminal 2c-01 generates a PDCP status report message of a first format for the PDCP of the first bearer among the bearers configured to transmit the PDCP status report and transmits it to the target base station 2c-05 (2c-27). The PDCP status report of the first format includes a first missing SN (FMS) field and a bitmap. The first missing PDCP SN value is written in the FMS field, and the length of the PDCP SN follows the length of the target PDCP SN. Accordingly, the terminal 2c-01 can transmit information about lost packets with respect to the first bearer to the target base station 2c-05, and thus the target base station 2c-05 can retransmit the lost packets to the terminal 2c-01 (2c-29), thereby performing lossless handover.

[0162] Subsequently, for the convenience of description, operations opposite to the above-described operations (i.e., the case where handover from an LTE base station to an NR base station is performed) will be described with reference to the accompanying drawings.

[0163] As described above, during the communication between the terminal 2c-01 and the base station 2c-05, the current base station (serving cell) 2c-05 can determine a handover in which the terminal 2c-01 switches to another base station 2c-03 according to the signal strength / quality information of the current base station 2c-05 and the neighboring base stations, which is reported by the terminal 2c-01 due to the movement of the terminal 2c-01 or the like (2c-35). In this example, it is assumed that the NR base station 2c-03 is the most suitable cell for the handover around the terminal, and thus the LTE eNB 2c-05 transmits a command message to instruct the terminal 2c-01 to perform the handover to the NR base station 2c-03 (2c-37). The handover command can be transmitted through an "RRCConnectionReconfiguration" message of the RRC layer, and the handover command message includes mobility control information (MCI) (MobilityControlInfo) indicating the base station to which the handover is directed, i.e., the target cell is the NR base station cell. In addition, the RRC message can also include an indicator indicating lossless handover (e.g., losslessHandover), and can include configuration information received from the target NR cell regarding the PDCP layer, RLC layer, and MAC layer of the NR to be operated in the target NR cell.

[0164] As described above, the first bearer performing the lossless handover according to the lossless handover indicator and the second bearer not performing the lossless handover can be defined as follows.

[0165] - First bearer: a bearer satisfying a first condition: a bearer among RLC-AM bearers in which the source PDCP SN length is less than or equal to the target PDCP SN length

[0166] - Second bearer: a bearer satisfying a second condition: a bearer among all SRBs, all UM bearers, and AM bearers in which the source PDCP SN length is greater than the target PDCP SN length

[0167] According to the above classification, the terminal 2c-01 performs different operations according to the type of the bearer (i.e., the first bearer or the second bearer) among the bearers possessed by the terminal 2c-01 (2c-39). That is, the terminal 2c-01 applies the following first operation to the first bearer.

[0168] - Generating NR PDCP and NR RLC layers to be used in the target

[0169] - Reassembling (e.g., split) RLC PDUs stored in the LTE RLC into RLC SDUs and transmitting the same to the LTE PDCP

[0170] - process (e.g., encrypted) PDCP PDUs stored in the LTE PDCP into PDCP SDUs (i.e., convert encrypted packets into decrypted packets), and then send them to the generated NR PDCP

[0171] - configure TX_HFN and RX_HFN in the generated NR PDCP layer taking into account the values used in LTE (e.g., the same values), and store received PDCP SDUs in a reordering buffer of according to PDCP SN

[0172] o TX_HFN is the HFN value internally managed when a packet is transmitted in the PDCP layer. The HFN value and PDCP SN included in the header of a packet to be transmitted are combined to generate a 32-bit COUNT value of the packet.

[0173] o RX_HFN is the HFN value internally managed when a packet is received in the PDCP layer. The HFN value and PDCP SN included in the header of a packet to be received are combined to generate a 32-bit COUNT value of the packet.

[0174] - cancel the previous LTE PDCP and LTE RLC

[0175] Meanwhile, the terminal 2c-01 applies the following second operation to the second bearer.

[0176] - generate LTE PDCP and LTE RLC

[0177] - configure initial values of TX_HFN and RX_HFN of the LTE PDCP (e.g., set to 0)

[0178] - process PDCP PDUs stored in the NR PDCP into PDCP SDUs, and send them to the generated LTE PDCP layer

[0179] - cancel the previous LTE PDCP and LTE RLC

[0180] Thereafter, the terminal 2c-01 performs synchronization and random access with the target cell 2c-03 to perform downlink and uplink synchronization (2c-41), generates a new security key if the random access is successful, and then configures the generated NR PDCP to use the new security key (2c-43). In addition, the terminal 2c-01 transmits a message of the RRC layer encrypted with the new security key and integrity protected to the target base station 2c-03 to inform that the handover has been successfully completed (2c-45). The message of the RRC layer can be an "RRCConnectionReconfigurationComplete" message.

[0181] Thereafter, the terminal 2c-01 generates a PDCP status report message in a second format for a PDCP of a first bearer among bearers configured to transmit a PDCP status report and transmits it to the target base station (2c-47). The PDCP status report in the second format includes an FMS field and a bitmap. The first missing COUNT value is written in the FMS field and COUNT has 32 bits. Accordingly, the terminal 2c-01 can transmit information about lost packets with respect to the first bearer to the target base station 2c-03, and thus the target base station 2c-03 can retransmit the lost packets to the terminal 2c-01 (2c-49), thereby performing lossless handover.

[0182] FIG. 2D FIG. 2c is a diagram illustrating a sequence of operations of a terminal when the present disclosure is applied.

[0183] In FIG. 2D In FIG. 2d, it is assumed that the terminal is in a connected mode (RRC_CONNECTED) (2d-01). Thereafter, the terminal receives configuration of a data radio bearer (DRB) for data transmission and reception from the base station, transmits an acknowledgement message to the base station in response thereto, so that the terminal in the connected mode can transmit data to the base station and receive data from the base station (2d-03). To configure the DRB, an "RRCConnectionReconfiguration" message of an RRC layer can be used, and an "RRCConnectionReconfigurationComplete" message can be used as the acknowledgement message. In addition, the DRB configuration can include configuration information of a PDCP and an RLC layer for each bearer. More specifically, the DRB configuration can indicate an operation mode {e.g., an acknowledgement mode (AM) and a non-acknowledgement mode (UM)} of the RLC layer, etc., and the configuration information of the PDCP layer can include an indicator indicating whether a status report needs to be transmitted after handover or when the PDCP layer is reconfigured for each bearer. That is, "statusReportRequired" information is included in the PDCP configuration. As described above, a bearer for which a PDCP status report needs to be transmitted is referred to as a "first bearer." That is, with respect to the first bearer, "statusReportRequired" is configured as "TRUE." The "StatusReportRequired" can be configured only for an RLC-AM for which retransmission can be performed when data is lost.

[0184] Thereafter, the terminal can receive a handover command from the base station due to movement of the terminal or the like (2d-05). The handover command can be transmitted through an "RRCConnectionReconfiguration" message of the RRC layer, and the handover command message includes mobility control information (MCI) (MobilityControlInfo) indicating the base station to which the handover is directed, that is, whether the target base station is an LTE base station or an NR base station. In the embodiment of the disclosure, detailed description of handover from NR to NR (2d-11) will be omitted, and the following detailed description will be made based on handover from NR to LTE and handover from LTE to an NR base station. As described above, in the case of performing handover between base stations of different systems, the embodiment of the disclosure also provides an indicator for lossless handover (e.g., losslessHandover). As described above, if the lossless handover indicator is configured, operations can be performed according to the type of the bearer. As described above, the first bearer performing lossless handover according to the lossless handover indicator and the second bearer not performing lossless handover can be defined as follows.

[0185] - First bearer: a bearer satisfying a first condition: a bearer among RLC-AM bearers, the source PDCP SN length of which is less than or equal to the target PDCP SN length

[0186] - Second bearer: a bearer satisfying a second condition: a bearer among all SRBs, all UM bearers, and AM bearers, the source PDCP SN length of which is greater than the target PDCP SN length

[0187] According to the above classification, in the case of performing handover from NR to LTE, the terminal applies the following first operation to the first bearer (2d-13).

[0188] - Generating LTE PDCP and LTE RLC layers to be used in the target

[0189] - Processing PDCP PDUs stored in the NR PDCP into PDCP SDUs (i.e., converting encrypted packets into decrypted packets), and then transmitting them to the generated LTE PDCP

[0190] - Configuring TX_HFN and RX_HFN in the generated LTE PDCP layer, considering the values (e.g., the same values) used in NR, and storing the received PDCP SDUs in the reordering buffer according to the PDCP SN

[0191] o TX_HFN is an HFN value internally managed when a packet is transmitted in the PDCP layer. The HFN value and the PDCP SN included in the header of the packet to be transmitted are combined to generate a 32-bit COUNT value of the packet.

[0192] o RX_HFN is an HFN value internally managed when a packet is received in the PDCP layer. An HFN value included in the header of a packet to be received and a PDCP SN are combined to generate a 32-bit COUNT value of the packet.

[0193] - cancel the previous NR PDCP and NR RLC

[0194] Meanwhile, the terminal applies the following second operation to the second bearer (2d-13).

[0195] - generate LTE PDCP and LTE RLC

[0196] - configure initial values of TX_HFN and RX_HFN of the LTE PDCP (for example, set to 0)

[0197] - process the PDCP PDU stored in the NR PDCP as a PDCP SDU and transmit it to the generated LTE PDCP layer

[0198] - cancel the previous NR PDCP and NR RLC

[0199] Thereafter, the terminal performs synchronization and random access with the target cell to perform downlink and uplink synchronization, generates a new security key if the random access is successful, and then configures the generated LTE PDCP to use the new security key (2d-15). In addition, the terminal transmits a message of the RRC layer encrypted with the new security key and protected by integrity to the target base station to inform that the handover has been successfully completed.

[0200] Thereafter, the terminal generates a PDCP status report message of a first format for the PDCP of the first bearer among the bearers configured to transmit the PDCP status report and transmits it to the target base station (2d-17). The PDCP status report of the first format includes an FMS field and a bitmap. A first missing PDCP SN value is written in the FMS field, and the length of the PDCP SN follows the length of the target PDCP SN. Accordingly, the terminal can transmit information about the missing packets with respect to the first bearer to the target base station, and thus the target base station can retransmit the missing packets to the terminal, thereby performing lossless handover.

[0201] Meanwhile, in the case of performing handover from LTE to NR, the terminal applies the following first operation to the first bearer (2d-21).

[0202] - generate NR PDCP and NR RLC layers to be used in the target

[0203] - reassembles (e.g., split) RLC PDUs stored in the LTE RLC into RLC SDUs and sends them to the LTE PDCP

[0204] - processes (e.g., encrypted) PDCP PDUs stored in the LTE PDCP into PDCP SDUs (i.e., converts encrypted packets into decrypted packets), and then sends them to the generated NR PDCP

[0205] - configures TX_HFN and RX_HFN of the generated NR PDCP layer considering values (e.g., same values) used in the LTE, and stores received PDCP SDUs in a reordering buffer according to PDCP SN

[0206] o TX_HFN is an HFN value internally managed when a packet is transmitted in the PDCP layer. The HFN value and PDCP SN included in the header of a packet to be transmitted are combined to generate a 32-bit COUNT value of the packet.

[0207] o RX_HFN is an HFN value internally managed when a packet is received in the PDCP layer. The HFN value and PDCP SN included in the header of a packet to be received are combined to generate a 32-bit COUNT value of the packet.

[0208] - cancels the previous LTE PDCP and LTE RLC

[0209] Meanwhile, the terminal applies the following second operation to the second bearer (2d-21).

[0210] - generates LTE PDCP and LTE RLC

[0211] - configures initial values (e.g., set to 0) of TX_HFN and RX_HFN of the LTE PDCP

[0212] - processes PDCP PDUs stored in the NR PDCP into PDCP SDUs and sends them to the generated LTE PDCP layer

[0213] - cancels the previous LTE PDCP and LTE RLC

[0214] Thereafter, the terminal performs synchronization and random access with the target cell for downlink and uplink synchronization, generates a new security key if the random access is successful, and then configures the generated NR PDCP to use the new security key (2d-23). In addition, the terminal transmits a message of the RRC layer encrypted with the new security key and integrity protected to the target base station to inform that the handover has been successfully completed.

[0215] Thereafter, the terminal generates a PDCP status report message in a second format for a PDCP of a first bearer among bearers configured to transmit a PDCP status report, and transmits it to the target base station (2d-25). The PDCP status report in the second format includes an FMC field and a bitmap. The first missing COUNT value is written in the FMS field, and the COUNT has 32 bits. Accordingly, the terminal can transmit information about missing packets with respect to the first bearer to the target base station, and thus the target base station can retransmit the missing packets to the terminal, thereby performing lossless handover.

[0216] FIG. 2E is a block diagram illustrating a configuration of a terminal according to an embodiment of the disclosure.

[0217] Reference FIG. 2E The terminal includes a radio frequency (RF) processor 2e-10, a baseband processor 2e-20, a storage unit 2e-30, and a controller 2e-40.

[0218] The RF processor 2e-10 performs a function of transmitting and receiving a signal through a wireless channel, such as band conversion and signal amplification. That is, the RF processor 2e-10 up-converts a baseband signal provided from the baseband processor 2e-20 into an RF band signal, and thus transmits it through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 2e-10 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Although only one antenna is illustrated in FIG. 2E However, the terminal can have a plurality of antennas. In addition, the RF processor 2e-10 can include a plurality of RF chains. Furthermore, the RF processor 2e-10 can perform beamforming. To perform beamforming, the RF processor 2e-10 can adjust phases and amplitudes of signals transmitted and received through a plurality of antennas or antenna elements.

[0219] The baseband processor 2e-20 performs a conversion function between a baseband signal and a bit string according to a physical layer specification of a system. For example, in the case of data transmission, the baseband processor 2e-20 encodes and modulates a transmission bit string, thereby generating a complex symbol. Also, when receiving data, the baseband processor 2e-20 demodulates and decodes a baseband signal provided from the RF processor 2e-10, thus recovering a reception bit string. For example, in the case of applying an orthogonal frequency division multiplexing (OFDM) scheme, when transmitting data, the baseband processor 2e-20 generates a complex symbol by encoding and modulating a transmission bit string, maps the complex symbol to a subcarrier, and then configures an OFDM symbol through an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion. Also, when receiving data, the baseband processor 2e-20 divides a baseband signal provided from the RF processor 2e-10 into an OFDM symbol unit, recovers a signal mapped to a subcarrier through a fast Fourier transform (FFT) operation, and then recovers a reception bit string through demodulation and decoding.

[0220] As described above, the baseband processor 2e-20 and the RF processor 2e-10 transmit and receive signals. Accordingly, the baseband processor 2e-20 and the RF processor 2e-10 can be referred to as a "transmitter", a "receiver", a "transceiver", or a "communication unit". Further, at least one of the baseband processor 2e-20 and the RF processor 2e-10 can include different communication modules to process signals of different frequency bands. The different frequency bands can include a super high frequency (SHF) (e.g., 2.5 GHz or 5 GHz) band and a millimeter wave (e.g., 60 GHz) band.

[0221] The storage unit 2e-30 stores data such as a basic program for terminal operation, an application program, and configuration information.

[0222] The controller 2e-40 controls the overall operation of the terminal. For example, the controller 2e-40 transmits and receives signals through the baseband processor 2e-20 and the RF processor 2e-10. Also, the controller 2e-40 records and reads data in and from the storage unit 2e-30. To this end, the controller 2e-40 can include at least one processor. For example, the controller 2e-40 can include a communication processor (CP) for controlling communication and an application processor (AP) for controlling a higher layer such as an application program. According to an embodiment of the disclosure, the controller 2e-40 can include a multi-connection processor 2e-42 for performing a process for operating in a multi-connection mode. For example, the controller 2e-40 can perform control so that the terminal performs FIG. 2E the operations shown.

[0223] According to embodiments of the disclosure, if a terminal receives a lossless handover command from a base station to a base station of another system, the terminal can perform the above-described operation according to the type of a bearer, thereby preventing packet loss.

[0224] The method according to the embodiments described in the claims or specification of the disclosure can be implemented in hardware, software, or a combination thereof.

[0225] When the method is implemented in software, a computer-readable storage medium storing one or more programs (software modules) can be provided. The one or more programs stored in the computer-readable storage medium are configured to be executed by one or more processors in an electronic device. The one or more programs include instructions that allow the electronic device to execute the method according to the embodiments described in the claims or specification of the disclosure.

[0226] The programs (software modules or software) can be stored in random access memory, non-volatile memory including flash memory, ROM (Read-Only Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), a magnetic disc storage device, a CD-ROM (Compact Disc - ROM), a DVD (Digital Versatile Disc), another type of optical storage device, or a magnetic cassette. Alternatively, the programs can be stored in a memory configured as a combination of some or all of the above. In addition, a plurality of memories can be included.

[0227] In addition, the above-described programs can be stored in an attachable storage device accessible through a communication network such as the Internet, an intranet, a LAN (Local Area Network), a WLAN (Wide Area LAN), or a SAN (Storage Area Network), or a communication network configured as a combination thereof. Such a storage device can be connected to a device for executing embodiments of the disclosure via an external port. In addition, a separate storage device in the communication network can be connected to a device for executing embodiments of the disclosure.

[0228] <Third Embodiment>

[0229] Hereinafter, the operation principle of the disclosure will be described in detail with reference to the accompanying drawings. Hereinafter, if the detailed description of the functions and configurations incorporated herein obscures the subject matter of the disclosure, the detailed description of the functions and configurations incorporated herein will be omitted. In addition, the terms used herein are defined in consideration of the functions of the disclosure, and can be changed according to the intention or practice of a user or an operator, etc. Therefore, the definition should be based on the content throughout the present specification.

[0230] Hereinafter, for the convenience of explanation, terms for identifying connection nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, terms referring to various identification information, etc. will be used as examples. Accordingly, the present disclosure is not limited to the terms used herein, and other terms referring to objects having equivalent technical meanings can be used.

[0231] For the convenience of explanation, in the present disclosure, terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard, which is the latest communication standard among existing communication standards, will be used. However, the present disclosure is not limited to the above-described terms and names, and the present disclosure can be equally applied to systems conforming to other standards.

[0232] If multi-connection is used in the next generation mobile communication system, the primary base station and the secondary base station can transmit and receive duplicated data. In this case, the terminal must be able to transmit the same RRC message to multiple base stations and receive the same RRC from multiple base stations. In the existing LTE, if the radio link quality from one base station is not good, radio link failure is declared and the subsequent procedure is performed. However, in order to apply the above-described system, the radio link must be declared by considering multiple radio links as a whole, which requires a new procedure. The present disclosure proposes a procedure for applying radio link failure to the case where multi-connection is used in the next generation mobile communication system, and illustrates the operation of the terminal.

[0233] FIG. 3A is a diagram showing the structure of an LTE system according to an embodiment of the present disclosure.

[0234] Referring to FIG. 3A The wireless communication system includes a plurality of base stations 3a-05, 3a-10, 3a-15, and 3a-20, a mobility management entity (MME) 3a-25, and a serving gateway (S-GW) 3a-30. A user equipment (hereinafter, referred to as "UE" or "terminal") 3a-35 accesses an external network through the base stations 3a-05, 3a-10, 3a-15, and 3a-20 and the S-GW 3a-30.

[0235] The base stations 3a-05, 3a-10, 3a-15, and 3a-20 provide wireless access to terminals of the access network as access nodes of a cellular network. That is, in order to serve traffic of users, the base stations 3a-05, 3a-10, 3a-15, and 3a-20 collect status information such as a buffer status of a terminal, an available transmission power status, a channel status, and the like, and perform scheduling, thereby supporting connection between a terminal and a core network (CN). The MME 3a-25 performs various control functions and a mobility management function for terminals and is connected to a plurality of base stations. The S-GW 3a-30 provides a data bearer. In addition, the MME 3a-25 and the S-GW 3a-30 can further perform authentication and bearer management for terminals of the access network and can process packets received from the base stations 3a-05, 3a-10, 3a-15, and 3a-20 or to be transmitted to the base stations 3a-05, 3a-10, 3a-15, and 3a-20.

[0236] FIG. 3B FIG. 1 is a diagram illustrating a radio protocol structure of an LTE system according to an embodiment of the disclosure.

[0237] Reference FIG. 3B The radio protocol of the LTE system includes a packet data convergence protocol (PDCP) 3b-05 or 3b-40, a radio link control (RLC) 3b-10 or 3b-35, and a medium access control (MAC) 3b-15 or 3b-30 in the terminal and the eNB, respectively. The PDCP 3b-05 or 3b-40 performs operations such as IP header compression / decompression, and the like. The main functions of the PDCP are summarized as follows.

[0238] - header compression and decompression (ROHC only)

[0239] - transfer of user data

[0240] - in-sequence delivery of upper layer PDUs at PDCP re-establishment for RLC AM

[0241] - sequence number reordering (split bearer in DC (RLC AM only) supported: PDCP PDU routing for transmission and PDCP PDU reordering for reception)

[0242] - duplicate detection of lower SDU at PDCP re-establishment for RLC AM

[0243] - retransmission of PDCP SDUs at handover, and for RLC AM, of PDCP PDUs at PDCP data recovery procedure for split bearer in DC

[0244] - ciphering and deciphering

[0245] - Discard of timer-based SDU in uplink.

[0246] Radio link control (hereinafter referred to as "RLC") 3b-10 or 3b-35 reconfigures a PDCP PDU (Packet Data Unit) to an appropriate size and performs an ARQ operation, etc. The main functions of RLC are summarized as follows.

[0247] - Data transfer function (transfer of higher layer PDU)

[0248] - ARQ function (error correction through ARQ (only for AM data transfer))

[0249] - Concatenation, segmentation, and reassembly of RLC SDU (only for UM and AM data transfer)

[0250] - Re-segmentation of RLC data PDU (only for AM data transfer)

[0251] - Reordering of RLC data PDU (only for UM and AM data transfer)

[0252] - Duplicate detection (only for UM and AM data transfer)

[0253] - Protocol error detection (only for AM data transfer)

[0254] - RLC SDU discard (only for UM and AM data transfer)

[0255] - RLC re-establishment

[0256] MAC 3b-15 or 3b-30 is connected to a plurality of RLC entities (configured in a single terminal), multiplexes RLC PDUs into a MAC PDU, and demultiplexes RLC PDUs from a MAC PDU. The main functions of MAC are summarized as follows.

[0257] - Mapping between logical channels and transport channels

[0258] - Multiplexing of MAC SDUs belonging to one or different logical channels into transport blocks (TBs) to be delivered to the physical layer on the transport channel / demultiplexing of MAC SDUs from transport blocks (TBs) from the physical layer on the transport channel into MAC SDUs belonging to one or different logical channels

[0259] - Scheduling information reporting

[0260] - HARQ function (error correction through HARQ)

[0261] - Priority handling between logical channels of one UE

[0262] - Priority handling among UEs by dynamic scheduling

[0263] - MBMS service identity

[0264] - Transport format selection

[0265] - Padding

[0266] The physical layer 3b-20 or 3b-25 channel-codes and modulates upper layer data and converts it into OFDM symbols that will then be transmitted through a wireless channel, or demodulates and channel-decodes OFDM symbols received through a wireless channel in order to then transmit to a higher layer.

[0267] Although not shown in the figure, there is a radio resource control (hereinafter, referred to as "RRC") layer in the upper layer of the PDCP layer of the terminal and the base station, respectively. The RRC layer can transmit and receive configuration control messages related to access / measurement for radio resource control.

[0268] FIG. 3C is a diagram showing the structure of a next-generation mobile communication system according to an embodiment of the disclosure.

[0269] Referring to FIG. 3C , the radio access network of the next-generation mobile communication system includes a new radio node B (hereinafter, referred to as "NR gNB" or "NR base station") 3c-10 and a new radio core network (NR CN) 3c-05, as shown in the figure. A new radio user equipment (hereinafter, referred to as "NR UE" or "terminal") 3c-15 accesses an external network through the NR gNB 3c-10 and the NR CN 3c-05.

[0270] In FIG. 3CIn the middle, the NR gNB 3c-10 corresponds to an evolved Node B (eNB) of the existing LTE system. The NR gNB 3c-10 is connected to the NR UE 3c-15 through a wireless channel, and can provide a more superior service than the service of the existing Node B. In the next-generation mobile communication system, since all user traffic is serviced through a shared channel, a device for collecting state information such as a buffer state of a UE, an available transmission power state, and a channel state and performing scheduling is required. The NR gNB 3c-10 serves as such a device. One NR gNB 3c-10 generally controls multiple cells, and includes a central unit (CU) for performing control and signaling and a distributed unit (DU) for performing transmission and reception of signals. In order to achieve a super-high data rate compared to the existing LTE system, the next-generation mobile communication system can have a bandwidth equal to or greater than the maximum bandwidth of the existing system, can employ orthogonal frequency division multiplexing (hereinafter referred to as "OFDM") as a wireless access technology, and in addition thereto, can employ a beamforming technique. In addition, an adaptive modulation and coding (hereinafter referred to as "AMC") scheme is applied to determine a modulation scheme and a channel coding rate according to the channel state of the terminal. The NR CN 3c-05 performs functions such as mobility support, bearer configuration, and QoS configuration. The NR CN 3c-05 is a device that performs various control functions as well as a mobility management function for the terminal 3c-15, and is connected to multiple base stations. In addition, the next-generation mobile communication system can interwork with the existing LTE system, and the NR CN 3c-05 is connected to the MME 3c-25 through a network interface. The MME 3c-25 is connected to the eNB 3c-30, which is an existing base station.

[0271] Embodiments of the disclosure relate to RRC diversity techniques. RRC diversity is a technique in which a terminal transmits the same RRC message to multiple base stations and receives the same RRC message from multiple base stations, thereby increasing the likelihood of receiving the RRC message. RRC diversity can also be referred to as "packet duplication." RRC diversity can be classified into downlink (DL) RRC diversity and uplink (UL) RRC diversity. In the case of DL RRC diversity, a terminal receives the same RRC message from multiple base stations. According to embodiments, DL RRC diversity is particularly effective in handover processing in which reception signal strength is unstable. In the case of UL RRC diversity, a terminal transmits the same RRC message to multiple base stations. Likewise, the likelihood of successfully transmitting the RRC message can be increased in a cell boundary area.

[0272] FIG. 3D FIG. 1 is a diagram schematically illustrating RRC diversity operation in multi-connection according to an embodiment of the disclosure.

[0273] Reference FIG. 3D In a case where the base station 1 (3d-05) transmits / receives a carrier of a center frequency f1 and the base station 2 (3d-15) transmits / receives a carrier of a center frequency f2, if the terminal 3d-01 combines a forward carrier of the center frequency f1 and a forward carrier of the center frequency f2, one terminal can transmit / receive data to / from two or more base stations. The LTE system supports the above operation, which is called "dual connectivity" (hereinafter, referred to as "DC").

[0274] Hereinafter, in the embodiments of the disclosure, an operation in which a terminal receives data through an arbitrary forward carrier or transmits data through an arbitrary uplink carrier means that the terminal transmits / receives data using a control channel and a data channel provided from a cell corresponding to a center frequency and a frequency band (which characterizes a carrier). In the embodiments of the disclosure, a set of serving cells controlled by the same base station is defined as a cell group (CG). The cell group is divided into a master cell group (MCG) and a secondary cell group (SCG). The MCG refers to a set of serving cells controlled by a base station (master eNB, MeNB) which controls a primary cell (PCell), and the SCG refers to a set of serving cells controlled by a base station (secondary eNB, SeNB) which controls only a secondary cell (SCell) other than the base station which controls the PCell. In a process of configuring corresponding serving cells, the base station informs a terminal of whether a specific serving cell belongs to the MCG or the SCG. The PCell or the SCell indicates a type of a serving cell configured with respect to the terminal. There are some differences between the PCell and the SCell. For example, the PCell is always in an active state, but the SCell is shifted between the active state and the inactive state according to an instruction of the base station. The mobility of the terminal is controlled by the PCell, and the SCell can be understood as an additional serving cell for data transmission and reception. The PCell and the SCell in the embodiments of the disclosure mean the PCell and the SCell defined in the LTE standard 36.331 or 36.321.

[0275] Reference back to FIG. 3DIf the base station 1 (3d-05) is the MeNB and the base station 2 (3d-15) is the SeNB, the serving cell 3d-10 having the center frequency f1 belongs to the MCG and the serving cell 3d-20 having the center frequency f2 belongs to the SCG. In addition, it can be impossible to actually transmit the HARQ feedback and the CSI of the SCG SCell through the physical uplink control channel (PUCCH) of the PCell. The HARQ feedback must be delivered within a HARQ round trip time (RTT) (typically 8 ms), because the transmission delay between the MeNB 3d-10 and the SeNB 3d-15 can be greater than the HARQ RTT. Due to the above-described problem, the PUCCH transmission resource is configured in the cell belonging to the SCell of the SCG (i.e., the primary SCell (PSCell)), and the HARQ feedback and the CSI for the SCG SCell are transmitted through the PUCCH.

[0276] In the present disclosure, in the case where the RRC diversity is applied, the terminal 3d-01 can simultaneously receive the RRC message including the same information from two base stations, i.e., the MeNB 3d-05 and the SeNB 3d-15. The RRC message to be transmitted to the terminal 3d-01 can be exchanged through the Xn backhaul connected to the MeNB 3d-05 and the SeNB 3d-15. The two base stations 3d-05 and 3d-15 can use the same or different frequencies.

[0277] FIG. 3E is a diagram for explaining a radio link monitoring operation and a radio link failure operation in LTE according to an embodiment of the present disclosure.

[0278] Reference FIG. 3EA procedure in which a terminal performs a radio link monitoring (RLM) operation and a radio link failure (RLF) operation in a PCell will be described. A terminal in an RRC connected state (3e-05) can perform normal operation with a PCell (3e-10), and can not receive a signal with sufficient strength from an MeNB. Such a situation can frequently occur when a terminal moves quickly from a serving cell to a target cell, or when the quality of a radio link suddenly degrades. In this case, the terminal receives an "out-of-sync" signal from a physical layer indicating that it is no longer served by the MeNB (3e-15). If the signal is received N310 times, the terminal recognizes a radio connection problem with the MeNB, and starts a T310 timer (3e-20). While the timer is operating, the terminal does not perform a radio link recovery operation. If the timer expires, the terminal declares an RLF (3e-25) and performs an RRC connection reestablishment procedure. For the RRC connection reestablishment procedure, the terminal performs cell selection, MAC reset, RB suspension, etc. In addition, if the RRC connection reestablishment procedure is started, the terminal starts a T311 timer, and does not perform a radio link recovery operation while the timer is operating (3e-30). If the RRC connection reestablishment is not performed while the timer is operating and if the timer expires, the terminal transitions to an RRC idle state (3e-35).

[0279] FIG. 3F FIG. 3f-01 is a diagram illustrating overall operations of RLM and RLF of a PCell and a PSCell in case that RRC diversity is applied according to an embodiment of the disclosure.

[0280] A terminal 3f-01 establishes an RRC connection with an MgNB 3f-03 after receiving system information from the MgNB 3f-03 (3f-05). The system information includes time information on N310 and T310 timers in LTE. The terminal 3f-01 performs radio link monitoring in a PCell by applying the received N310 and T310 (3f-15). Meanwhile, if certain conditions are met, the MgNB 3f-02 can determine that the terminal 3f-01 applies DC to an SgNB 3f-03 (3f-20). Examples of the conditions are that the terminal periodically or according to a configuration of the base station measures a neighbor cell, and transmits a measurement value indicating that multi-connection for handover is required. That is, the conditions can include an event in which the strength of a signal received by the terminal from a source base station decreases and the strength of a signal received by the terminal from a target base station increases, and the source base station that receives the conditions can recognize the mobility of the terminal and can prepare for handover.

[0281] The MgNB 3f-03 transmits an SCG configuration control message including T313, N313, and an RRC diversity indicator to the terminal 3f-01 (3f-25). The timer intends for RLM in the PSCell, and the RRC diversity indicator indicates whether to apply RRC diversity in the configured DC. Thereafter, the terminal 3f-01 detects a radio link problem due to the expiration of T310 in the PCell (3f-35). If RLF occurs in the existing LTE PCell, the RRC connection reestablishment operation is started as described above. However, in the RRC diversity environment, even if RLF occurs in the PCell, the following method can be performed considering the situation, instead of immediately starting the RRC connection reestablishment. FIG. 3E The RRC connection reestablishment operation is started as described above. However, in the RRC diversity environment, even if RLF occurs in the PCell, the following method can be performed considering the situation, instead of immediately starting the RRC connection reestablishment.

[0282] - In the case where RRC diversity is not applied: RLF operation 1 is performed.

[0283] - In the case where RRC diversity is applied: RLF operation 1 or RLF operation 2 is started according to the situation of the PSCell.

[0284] RLF operation 1 indicates an operation of resetting the MAC, stopping SRB 1 and 2 and all DRBs, and releasing the MCG SCell. RLF operation 2 includes interrupting uplink transmission and reporting RLF.

[0285] Referring again to step 3f-35, if T310 expires in the PCell without the RRC diversity indication from the MgNB 3f-02, the terminal 3f-01 performs RLF operation 1. That is, the terminal resets the MAC, stops SRB 1 and 2 and all DRBs, and releases the MCG SCell. On the other hand, if the terminal 3f-01 receives the indication of RRC diversity from the MgNB 3f-02, and if T310 expires in the PCell, the RLF operation is different depending on the condition of the PSCell. If the PSCell quality is good and if normal transmission / reception is performed in the PSCell, the terminal 3f-01 performs RLF operation 1. However, if the PSCell quality is poor and if transmission / reception is not normally performed (if T313 is in operation or if RLF 1 was declared in the PSCell recently for n ms), the terminal 3f-01 performs RLF operation 2. RLF operation 2 can correspond to the case where radio link problems occur in both the PCell and the PSCell, and only in this case, the terminal 3f-01 declares and reports RLF.

[0286] If the RLF operation 2 starts, the terminal 3f-01 transmits a control message for reporting the RLF 2 to the SgNB 3f-03 (3f-40). Alternatively, the terminal can also transmit the corresponding information to the MgNB 3f-02. The control message for reporting the RLF 2 can include the following information.

[0287] - an indicator indicating the PCell or the PSCell

[0288] - FailureType: timer expiration, random access problem, maximum RLC delivery count problem, SCG change problem, etc.

[0289] - measResultServFreqList: a serving frequency identifier and information on a measured SCell quality (RSRP and RSRQ), etc.

[0290] After that, the MgNB 3f-02 determines a new PCell with reference to the "measResultServFreqList" received from the terminal 3f-01, and transmits a handover RRC message indicating a change of the PCell to the terminal 3f-01 (3f-50). The terminal 3f-01 performs handover to the indicated new PCell (3f-55), and performs RLM in the PCell (3f-60). In addition, the terminal 3f-01 can also perform radio link problem detection in the PSCell in parallel with the RLM and the RLF procedure in the PCell, that is, the RLF declaration operation. That is, if T313 expires in the PSCell without an indication of RRC diversity from the MgNB 3f-02, the terminal 3f-01 performs the RLF operation 1. The RLF operation 1 refers to an operation of resetting the MAC, stopping SRB 1 and 2 and all DRBs, and releasing the SCG SCell. On the other hand, if the terminal 3f-01 receives an indication of RRC diversity from the MgNB 3f-02, and if T313 expires in the PSCell, the RLF operation is different depending on the conditions of the PCell. If the PCell quality is good and if normal transmission / reception is performed in the PCell, the terminal performs the RLF operation 2. However, if the PCell quality is poor and if transmission / reception is not normally performed (if T310 is in operation or if RLF 1 was recently declared in the PCell for n ms), the terminal performs the RLF operation 1. The RLF operation 1 can correspond to a case where radio link problems occur in both the PCell and the PSCell, and only in this case, the terminal 3f-01 declares and reports the RLF (3f-65).

[0291] FIG. 3Gis a diagram illustrating an RLM and RLF procedure of a terminal in a PCell in case RRC diversity is applied according to an embodiment of the disclosure.

[0292] The terminal in an RRC connected state performs RLM in a PCell with reference to N310 and T310 timer information received from system information of a base station (3g-05). Thereafter, the terminal receives an SCG configuration control message from the base station under certain conditions (3g-10), and performs RLM in a PSCell corresponding to the received configuration (3g-15). Upon receiving a consecutive out-of-sync (OOC) indication of N310 from a physical layer (3g-20), the terminal starts a T310 timer (3g-25). While the timer is operating, the terminal does not perform an operation for radio link recovery (3g-30). If an SCG configuration control message is received from the base station, subsequent operations of the terminal differ depending on whether RRC diversity is configured or not.

[0293] First, if the RRC diversity operation is not configured and if the T310 timer expires, the terminal performs RLF operation 1. RLF operation 1 refers to an operation of resetting a MAC, stopping SRB 1 and 2 and all DRBs, and releasing MCG SCells. On the other hand, if the RRC diversity operation is configured and if the T310 timer expires, the terminal performs a different RLF operation according to a condition of a PSCell (3g-45). If the PSCell quality is good and if normal transmission / reception is performed in the PSCell, the terminal performs RLF operation 2 (3g-50). However, if the PSCell quality is poor and if transmission / reception is not normally performed (if T313 is operating or if RLF 1 was declared in the PSCell most recently in n ms), the terminal performs RLF operation 1 (3g-55). RLF operation 1 includes interrupting uplink transmission and reporting RLF. That is, only in the case where radio link problems occur in both the PCell and the PSCell (in the case where RLF 1 is started), the terminal declares and reports RLF to the base station.

[0294] FIG. 3H is a diagram illustrating an RLM and RLF procedure of a terminal in a PSCell in case RRC diversity is applied according to an embodiment of the disclosure.

[0295] The terminal in the RRC connected state performs RLM in the PCell with reference to the N313 and T313 timer information received from the system information of the base station (3h-05). Thereafter, the terminal receives an SCG configuration control message from the base station under certain conditions (3h-10), and performs RLM in the PSCell corresponding to the received configuration (3h-15). Upon receiving a consecutive out-of-sync indication of N313 from the physical layer (3h-20), the terminal starts the T313 timer (3h-25). While the timer is operating, the terminal does not perform an operation for radio link recovery (3h-30). If the SCG configuration control message is received from the base station, the subsequent operation of the terminal differs depending on whether the RRC diversity is configured or not.

[0296] First, if the RRC diversity operation is not configured and if the T313 timer expires, the terminal performs RLF operation 1. The RLF operation 1 refers to an operation of resetting the MAC, stopping SRB 1 and 2 and all DRBs, and releasing the SCG SCell. On the other hand, if the RRC diversity operation is configured and if the T313 timer expires, the terminal performs a different RLF operation according to the condition of the PCell (3h-45). If the PCell quality is good and if the normal transmission / reception is performed in the PCell, the terminal performs RLF operation 2 (3h-50). However, if the PCell quality is poor and if the transmission / reception is not normally performed (if T310 is in operation or RLF 1 was recently declared in the PCell for n ms), the terminal performs RLF operation 1 (3h-55). The RLF operation 1 includes interrupting the uplink transmission and reporting RLF. That is, only in the case where radio link problems occur in both the PCell and the PSCell (in the case where RLF 1 is started), the terminal declares and reports RLF to the base station.

[0297] FIG. 3I is a block diagram illustrating a structure of a terminal according to an embodiment of the disclosure.

[0298] Reference FIG. 3I The terminal includes a radio frequency (RF) processor 3i-10, a baseband processor 3i-20, a storage unit 3i-30, and a controller 3i-40.

[0299] The RF processor 3i-10 performs a function of transmitting and receiving a signal through a wireless channel, such as band conversion and signal amplification. That is, the RF processor 3i-10 up-converts a baseband signal provided from the baseband processor 3i-20 into an RF band signal, thus transmitting it through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 3i-10 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Although only one antenna is shown in FIG. 3I The terminal can have a plurality of antennas. In addition, the RF processor 3i-10 can include a plurality of RF chains. Furthermore, the RF processor 3i-10 can perform beamforming. To perform beamforming, the RF processor 3i-10 can adjust phases and amplitudes of signals transmitted and received through a plurality of antennas or antenna elements. In addition, the RF processor can perform MIMO, and can receive a plurality of layers when performing a MIMO operation.

[0300] The baseband processor 3i-20 performs a conversion function between a baseband signal and a bit string according to a physical layer specification of a system. For example, in the case of data transmission, the baseband processor 3i-20 encodes and modulates a transmission bit string, thus generating a complex symbol. In addition, when receiving data, the baseband processor 3i-20 demodulates and decodes a baseband signal provided from the RF processor 3i-10, thus recovering a reception bit string. For example, in the case of applying an orthogonal frequency division multiplexing (OFDM) scheme, when transmitting data, the baseband processor 3i-20 generates a complex symbol by encoding and modulating a transmission bit string, maps the complex symbol to a subcarrier, and then configures an OFDM symbol through an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion. In addition, when receiving data, the baseband processor 3i-20 divides a baseband signal provided from the RF processor 3i-10 into an OFDM symbol unit, recovers a signal mapped to a subcarrier through a fast Fourier transform (FFT) operation, and then recovers a reception bit string through demodulation and decoding.

[0301] As described above, the baseband processor 3i-20 and the RF processor 3i-10 transmit and receive signals. Accordingly, the baseband processor 3i-20 and the RF processor 3i-10 can be referred to as a "transmitter", a "receiver", a "transceiver", or a "communication unit". Furthermore, at least one of the baseband processor 3i-20 and the RF processor 3i-10 can include a plurality of communication modules to support a plurality of different radio access technologies. In addition, at least one of the baseband processor 3i-20 and the RF processor 3i-10 can include different communication modules to process signals of different frequency bands. For example, the different radio access technologies can include a wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. In addition, the different frequency bands can include a super high frequency (SHF) (e.g., 2.NRHz or NR hz) band and a millimeter wave (e.g., 60 GHz) band.

[0302] The storage unit 3i-30 stores data such as basic programs for terminal operations, application programs, and configuration information. Specifically, the storage unit 3i-30 can store information related to a second access node for performing wireless communication using a second radio access technology. In addition, the storage unit 3i-30 provides the stored data according to a request of the controller 3i-40.

[0303] The controller 3i-40 controls the overall operation of the terminal. For example, the controller 3i-40 transmits and receives signals through the baseband processor 3i-20 and the RF processor 3i-10. In addition, the controller 3i-40 records and reads data in and from the storage unit 3i-30. To this end, the controller 3i-40 can include at least one processor. For example, the controller 3i-40 can include a communication processor (CP) for controlling communication and an application processor (AP) for controlling a high layer such as an application program.

[0304] FIG. 3J is a block diagram illustrating a configuration of an NR base station according to an embodiment of the disclosure.

[0305] As illustrated, the base station includes an RF processor 3j-10, a baseband processor 3j-20, a backhaul communication unit 3j-30, a storage unit 3j-40, and a controller 3j-50.

[0306] The RF processor 3j-10 performs functions of transmitting and receiving a signal through a wireless channel, such as band conversion and signal amplification. That is, the RF processor 3j-10 up-converts a baseband signal provided from the baseband processor 3j-20 into an RF band signal, and thus transmits it through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 3j-10 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is shown in the drawing, the first access node can have a plurality of antennas. In addition, the RF processor 3j-10 can include a plurality of RF chains. Furthermore, the RF processor 3j-10 can perform beamforming. To perform the beamforming, the RF processor 3j-10 can adjust phases and amplitudes of signals transmitted and received through a plurality of antennas or antenna elements. The RF processor can perform a downlink MIMO operation by transmitting one or more layers.

[0307] The baseband processor 3j-20 performs a conversion function between a baseband signal and a bit string according to a physical layer specification of the first radio access technology. For example, in the case of transmitting data, the baseband processor 3j-20 encodes and modulates a transmission bit string, thereby generating a complex symbol. In addition, when receiving data, the baseband processor 3j-20 demodulates and decodes a baseband signal provided from the RF processor 3j-10, thus recovering a reception bit string. For example, in the case of applying an OFDM scheme, when transmitting data, the baseband processor 3j-20 generates a complex symbol by encoding and modulating a transmission bit string, maps the complex symbol to a subcarrier, and then configures an OFDM symbol through an IFFT operation and CP insertion. In addition, when receiving data, the baseband processor 3j-20 divides a baseband signal provided from the RF processor 3j-10 into an OFDM symbol unit, recovers a signal mapped to a subcarrier through an FFT operation, and then recovers a reception bit string through demodulation and decoding. As described above, the baseband processor 3j-20 and the RF processor 3j-10 transmit and receive a signal. Accordingly, the baseband processor 3j-20 and the RF processor 3j-10 can be referred to as a "transmitter", a "receiver", a "transceiver", a "communication unit", or a "wireless communication unit".

[0308] The backhaul communication unit 3j-30 provides an interface for performing communication with other nodes in a network. That is, the backhaul communication unit 3j-30 converts a bit string transmitted from the master base station to other nodes such as a secondary base station, a core network, etc., into a physical signal, and converts a physical signal received from the other nodes into a bit string.

[0309] The storage unit 3j-40 stores data such as basic programs for operation of the master base station, application programs, and configuration information. Specifically, the storage unit 3j-40 can store information on bearers allocated to connected terminals, measurement results reported from connected terminals, and the like. In addition, the storage unit 3j-40 can store information that is a criterion for determining whether to provide a plurality of connections to a terminal or release a plurality of connections. In addition, the storage unit 3j-40 provides stored data in response to a request from the controller 3j-50.

[0310] The controller 3j-50 controls the overall operation of the master base station. For example, the controller 3j-50 transmits and receives signals through the baseband processor 3j-20 and the RF processor 3j-10 or the backhaul communication unit 3j-30. In addition, the controller 3j-50 records and reads data in and from the storage unit 3j-40. To this end, the controller 3j-50 can include at least one processor.

[0311] Embodiments of the disclosure can be configured to have the following configurations.

[0312] A method of configuring RRC diversity in a terminal supporting DC such that the RLF declaration procedure is different depending on the RRC diversity configuration

[0313] -> In the case where RRC diversity is not configured in the terminal, if a radio link problem is detected in the PCell or the PSCell, a method of performing RLF operation 1

[0314] -> In the case where RRC diversity is configured in the terminal, if a radio link problem is detected in the PCell, a method of declaring RLF differently depending on the radio link and operation state of the PSCell

[0315] ---> If the PSCell is in a good radio state or the PSCell is in normal operation, a method of performing RLF operation 1

[0316] ---> If the PSCell is not in a good radio state or the PSCell is not in normal operation, a method of performing RLF operation 2

[0317] ---> RLF operation 1 includes the operation of resetting the MAC, stopping SRB 1 and 2 and all DRBs, and releasing the MCG SCell.

[0318] ---> RLF operation 2 includes the operation of stopping uplink transmission and reporting RLF.

[0319] If the PSCell is not in a good radio state or if the PSCell is not in normal operation, a method of performing RLF operation 2

[0320] -> In the case where RRC diversity is configured, if a radio link problem is detected in the PCell, a method of declaring RLF differently according to the radio link and operation state of the PSCell

[0321] ---> If the PCell is in a good radio state or the PCell is in normal operation, a method of performing RLF operation 1

[0322] ---> If the PCell is not in a good radio state or the PSCell is not in normal operation, a method of performing RLF operation 2

[0323] ---> RLF operation 1 includes the operation of resetting the MAC, stopping SRB 1 and 2 and all DRBs, and releasing the MCG SCell.

[0324] ---> RLF operation 2 includes the operation of stopping uplink transmission and reporting RLF.

[0325] <Fourth Embodiment>

[0326] Hereinafter, a detailed description of functions and configurations incorporated herein known will be omitted if it obscures the subject matter of the present disclosure. Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0327] FIG. 4A is a diagram illustrating a structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0328] Referring to FIG. 4A , a radio access network of a next-generation mobile communication system includes a new radio node B (hereinafter, referred to as "NR NB") 4a-10 and a new radio core network (NR CN) 4a-05, as illustrated. A new radio user equipment (hereinafter, referred to as "NR UE" or "terminal") 4a-15 accesses an external network through the NR NB 4a-10 and the NR CN 4a-05.

[0329] In FIG. 4AIn the middle, the NR NB 4a-10 corresponds to an evolved Node B (eNB) of the existing LTE system. The NR NB is connected to the NR UE 4a-15 through a wireless channel and can provide a more superior service than that of the existing Node B. In the next-generation mobile communication system, since all user traffic is serviced through a shared channel, a device for collecting state information such as a buffer state of a UE, an available transmission power state, and a channel state and performing scheduling is required. The NR NB 4a-10 serves as such a device. One NR NB 4a-10 generally controls a plurality of cells. To achieve a super-high data rate compared to the existing LTE system, the next-generation mobile communication system can have a bandwidth equal to or greater than the maximum bandwidth of the existing system, can employ orthogonal frequency division multiplexing (hereinafter referred to as "OFDM") as a wireless access technology, and in addition thereto, can employ a beamforming technique. In addition, an adaptive modulation and coding (hereinafter referred to as "AMC") scheme is applied to determine a modulation scheme and a channel coding rate according to a channel state of a terminal. The NR CN 4a-05 performs functions such as mobility support, bearer configuration, and QoS configuration. The NR CN 4a-05 is a device that performs various control functions as well as a mobility management function for a terminal, and is connected to a plurality of base stations. In addition, the next-generation mobile communication system can interwork with the existing LTE system, and the NR CN 4a-05 is connected to the MME 4a-25 through a network interface. The MME 4a-25 is connected to the eNB 4a-30 which is an existing base station.

[0330] One of the methods for improving power consumption is to increase a DRX cycle. The terminal performs a reception operation to receive a paging signal from the base station. However, since the paging signal is transmitted infrequently, the reception operation performed by the terminal during a time period in which the paging signal is not received can increase power consumption. Therefore, in order to reduce power consumption, the terminal can perform an operation of receiving a paging signal only during a specific time period periodically, which is called "DRX". In the LTE system, the DRX operation of the terminal in an idle mode is performed using Equation 1 below. A system frame number (SFN) is increased by 1 every radio frame. If a paging signal is transmitted in a radio frame satisfying the equation, the terminal performs a reception operation through DRX. The radio frame is called a "paging frame (PF)".

[0331] < Equation 1 >

[0332] SFN mod T = (T div N) * (UE_ID mod N)

[0333] Here,

[0334] SFN: System Frame Number. 10 bits (MSB 8 bits explicit and LSB 2 bits implicit)

[0335] T: DRX cycle of the UE. Transmitted on SIB2. Enumerated as {rf32, rf64, rf128, rf256}

[0336] N: min(T, nB)

[0337] nB: Transmitted on SIB2. Enumerated as {4T, 2T, T, T / 2, T / 4, T / 8, T / 16, T / 32}.

[0338] UE_ID: IMSI mod 1024 (IMSI is a unique number assigned to each terminal)

[0339] The 8-bit representation of the SFN of the Master Information Block (MIB) of the Physical Broadcast Channel (PBCH). T and nB are values provided from the base station, which are included in SIB2 (System Information Block Type 2) at the same time. T can have one of {rf32, rf64, rf128, rf256}, where r32 denotes the length of 32 radio frames. That is, r32 means 320 ms.

[0340] FIG. 4B A paging time in the LTE technology according to an embodiment of the disclosure is conceptually illustrated. The SFN is increased by 1 for each radio frame (4b-05). Every 1024 cycles, the value of the SFN is reset to 0 (4b-10). According to Equation 1, the same paging pattern is repeated every SFN cycle (4b-15). According to the above equation, it can be seen that the maximum DRX cycle in the current LTE standard is 2.56 seconds, and even if the DRX cycle is maximally increased, it is impossible to exceed the SFN cycle, i.e., 10.24 seconds. In other words, in order to increase the DRX cycle to 10.24 seconds or more to reduce power consumption, it is also necessary to increase the SFN cycle.

[0341] In an embodiment of the disclosure, in order to increase the SFN period, additional SFN bits are included in an existing or new SIB, and a terminal receives the additional SFN bits, which will be described below. The SFN bits are incremented by 1 every SFN period. In addition, the SIB including the additional SFN bits does not need to be received by all terminals, and it is characterized in that only a terminal to which a very long DRX cycle is applied can attempt to receive the additional SFN bits. In addition, the following values are not affected by the change in the SFN bit value: a "systemInfoValueTag" value (IE included in SIB 1) that is generally incremented by 1 every time SIB information is changed, and a "systemInfoModification" IE included in a paging and informing whether system information is changed. That is, even if the SFN bit value is changed, the "systemInfoValueTag" IE is not updated, and the "systemInfoModification" IE is not transmitted through paging.

[0342] FIG. 4C is a diagram for explaining a process of determining a DRX cycle of a terminal in an LTE technology according to an embodiment of the disclosure.

[0343] The base station 4c-05 provides a default DRX value to the terminal 4c-00 using SIB 1, which is a piece of broadcast system information (4c-15). If the terminal desires a shorter DRX cycle than the default DRX value, the terminal provides a desired DRX value as a UE-specific DRX value to the MME 4c-10 through an ATTACH process (4c-20). If there is a paging with respect to the terminal 4c-00, the MME 4c-10 transmits the UE-specific DRX value provided from the terminal 4c-00 together with the paging to the base station 4c-05. The terminal 4c-00 determines the smaller one of the UE-specific DRX value transmitted to the MME 4c-10 and the default DRX value provided from the base station 4c-05 as a DRX cycle (4c-30). The base station 4c-05 also determines the smaller one of the UE-specific DRX value received from the MME 4c-10 and the default DRX value broadcast by the base station 4c-10 as a DRX cycle (4c-35). Accordingly, the terminal 4c-00 and the base station 4c-05 select the same DRX cycle, and the base station 4c-05 determines a PF based on the DRX cycle and transmits a paging message to the terminal 4c-00.

[0344] FIG. 4D is a diagram for explaining a transition of a radio access state in a next-generation mobile communication system according to an embodiment of the disclosure.

[0345] The next generation mobile communication system has three radio connection states (RRC states). The connected mode (RRC_CONNECTED) 4d-05 is a radio access state in which a terminal can transmit and receive data. The idle mode (RRC_IDLE) 4d-30 is a radio access state in which a terminal monitors whether a paging message is received. The above two modes are radio access states applicable to the existing LTE system, and their detailed descriptions are the same as those of the existing LTE system. In the next generation mobile communication system, the RRC_INACTIVE radio access state (4d-15) is newly defined. In this wireless access state, the UE context is maintained in the base station and the terminal, and RAN-based paging is supported. The functions of the new radio access state are listed below.

[0346] - Cell reselection mobility;

[0347] - CN-NR RAN connection (both C / U-planes) has been established for the UE;

[0348] - UE AS context is stored in at least one gNB and the UE;

[0349] - Paging is initiated by the NR RAN;

[0350] - RAN-based notification area is managed by the NR RAN; and

[0351] - The NR RAN knows the RAN-based notification area to which the UE belongs.

[0352] The new inactive radio access state can be converted to the connected mode or the idle mode using a specific procedure. According to the connection activation, the inactive mode is converted to the connected mode, and the connected mode is converted to the inactive mode using the connection inactivation procedure (4d-10). The connection activation / inactivation procedure is performed through one or more RRC messages between the terminal and the base station, and includes one or more steps. The inactive mode can also be converted to the idle mode according to a specific procedure (4d-20). Various methods based on a specific message exchange or a timer or an event can be considered as the above specific procedure. The conversion between the connected mode and the idle mode follows the existing LTE technology. That is, the conversion between the modes is performed through the connection establishment or release procedure (4d-25).

[0353] Embodiments of the disclosure propose a procedure in which a base station configures a DRX cycle when a terminal in an RRC inactive state applies DRX, and a terminal's operation according to a type of paging. As described above, the existing LTE system applies UE_ID when calculating a paging frame (PF) and a paging occasion (PO). In LTE, UE_ID is defined as IMSI mod 1024. The MME provides the terminal with UE_ID information, not IMSI. This is intended to maintain high security. The international mobile subscriber identity (IMSI) is a unique ID representing a user, and the MME is provided from a mobile communication service provider server. The IMSI can have a size of 15 bits or more, and includes "MCC+MNC+MSIN". The MCC (mobile country code) is a country code, the MNC (mobile network code) is a service provider code, and the MSIN (mobile subscriber identification number) is a user code allocated by a service provider. In addition, the base station has only UE_ID information, and calculates a time at which to transmit a paging message to the terminal, i.e., the PF and the PO. In a next-generation mobile communication system, the base station can independently generate paging. This means that the base station can independently configure the PF or the PO. However, if the base station has IMSI when configuring the PF or the PO, it can be vulnerable in terms of security. Therefore, in embodiments of the disclosure, the base station and the core network (e.g., the NG core in embodiments of the disclosure) use the same PF and PO, and for this, they also use the same UE_ID. In addition, embodiments of the disclosure propose using a SAE temporary mobile subscriber identity (S-TMSI) instead of IMSI in order to maintain high security. The S-TMSI is a unique ID indicating a specific terminal in a single MME group, and its length (40 bits) is smaller than that of IMSI. The S-TMSI includes "MMEC+M-TMSI". The MMEC (MME code) is an ID indicating a specific MME in a single service provider network, and the M-TMSI (MME mobile subscriber identity) is an ID indicating a specific terminal in a single MME. In the disclosure, UE_ID is used as the following equation.

[0354] UE_ID = S-TMSI mod N

[0355] N is a positive integer in the above equation, and can be, for example, 1024. In a next-generation mobile communication system, it is assumed that since the NG core corresponds to the MME, the NG core of the next-generation mobile communication system can be employed instead of the definition of the S-TMSI; and it is assumed that even if the length of the ID can be different from that of LTE, the concept of the ID can be maintained.

[0356] The procedure of determining the DRX cycle in the existing LTE system has been described above. In the next generation mobile communication system, it is assumed that the base station triggered paging has the same paging cycle as the core network triggered paging or has a common multiple relationship. This is intended to eliminate unnecessary complexity and minimize the power consumption of the terminal. In order to make the base station triggered paging have the same paging cycle as the core network triggered paging or have a common multiple relationship, the base station must know the paging cycle (DRX cycle) derived through the predetermined procedure between the core network and the terminal. For this, in the present disclosure, the terminal reports the UE-specific DRX cycle or eDRX cycle to the base station according to the request of the base station. Alternatively, the base station can request the UE-specific DRX cycle, eDRX cycle, or paging cycle information derived through the predetermined procedure with the terminal to the NG core, and the NG core can report the information to the base station. In the embodiment of the present disclosure, the terminal can receive two types of paging, i.e., the paging triggered by the base station and the paging triggered by the core network. Therefore, the terminal performs different operations according to the type of the received paging. If the terminal receives the paging triggered by the core network, the terminal performs the service request. If the terminal receives the paging triggered by the base station, the terminal performs the RAN area update.

[0357] FIG. 4E FIG. 1 is a flowchart illustrating a procedure of transmitting a paging message when a terminal is in an RRC inactive state according to an embodiment of the present disclosure.

[0358] The terminal 4e-05 is connected with a base station (gNB) 4e-10 (4e-15). In this case, the base station 4e-10 determines that the terminal 4g-05 will transition to an inactive state (4e-20). The base station 4g-10 requests the terminal 4g-05 of DRX cycle information of the terminal 4g-05 using a predetermined RRC message (4e-25). The DRX cycle information refers to a UE-specific DRX cycle or eDRX cycle value of the terminal. The terminal 4e-05 receiving the request transmits the DRX cycle information to the base station 4e-10 using a predetermined RRC message (4e-30). The base station 4e-10 derives a DRX cycle to be applied by the terminal 4e-05 in the inactive state using the DRX cycle information reported by the terminal 4e-05 (4e-35). The derived DRX cycle is the same as or has a common multiple relationship with the DRX cycle determined by the terminal 4e-05 and the core network. The base station 4e-10 instructs the terminal 4e-05 to transition to the inactive state using a predetermined RRC message (4e-40). The message includes a DRX cycle value to be applied by the terminal 4e-05 in the inactive state and paging area information. The terminal 4e-05 receiving the message transitions to the inactive state and determines the timing of transmitting a paging triggered by the base station 4e-10, i.e., PF and PO, using the configuration information and UE_ID (= S-TMSI mod N) previously provided from the core network (4e-45). The terminal 4e-05 can receive both a paging 4e-50 triggered by the base station 4e-10 and a paging 4e-55 triggered by the core network. When the terminal 4e-05 receives a paging message at the above PF / PO, the terminal 4e-05 determines a paging ID included in the paging message. The terminal 4e-05 performs one of the following operations according to the paging ID (4e-60). If the paging ID is a second identifier (IMSI or S-TMSI), the terminal performs a first operation. The first operation is as follows.

[0359] - transition from the inactive state to the idle state

[0360] - generate a NAS message for a paging response after maintaining the current cell without performing a cell selection process. The NAS message is a service request.

[0361] If the paging ID is a third identifier (e.g., RESUME ID), the terminal performs a second operation. The second operation is as follows.

[0362] - maintain the inactive state

[0363] - generate an AS message for a RAN paging response

[0364] The inactive UE can move to LTE. At this time, the terminal performs inter-RAT cell reselection, omits cell selection processing, and transitions to the IDLE mode. In this case, the fourth identifier (IMSI) and the CN paging cycle (the shorter one of the default DRX cycle and the UE DRX cycle or eDRX cycle) are used to determine the paging timing (PF / PO).

[0365] FIG. 4F is a diagram for explaining the operation of a terminal according to an embodiment of the disclosure.

[0366] In step 4f-05, the terminal receives a predetermined RRC message requesting DRX cycle information of the terminal from the base station. In step 4f-10, the terminal that has received the request transmits the DRX cycle information to the base station using the predetermined RRC message. In step 4f-15, the terminal receives a predetermined RRC message from the base station, which instructs the terminal to transition to the inactive state. In step 4f-20, the terminal transitions to the inactive state. The message includes the DRX cycle value and paging area information to be applied by the terminal in the inactive state. In step 4f-25, the terminal determines the timing, i.e., PF and PO, at which the base station 4e-10 triggers a paging message, using the configuration information previously provided from the core network and the UE_ID (= S-TMSI mod N) in the paging area indicated above. In step 4f-30, the terminal determines whether a paging message has been received. If one paging message is received, the terminal checks the identifier included in the paging message in step 4f-35. The terminal can receive both a base station-triggered paging message and a core network-triggered paging message. The base station-triggered paging message includes the third identifier, and the core network-triggered paging message includes the second identifier. If the paging ID is the second identifier (IMSI or S-TMSI), the terminal performs a first operation in step 4f-40. The first operation has been described above. If the paging ID is the third identifier (e.g., RESUME ID), the terminal performs a second operation in step 4f-45. The second operation has been described above.

[0367] FIG. 4G is a diagram for explaining the operation of a terminal according to an embodiment of the disclosure.

[0368] In step 4g-05, the base station transmits a predetermined RRC message requesting DRX cycle information of the terminal to the terminal. In step 4g-10, the base station receives a predetermined RRC message including the DRX cycle information from the terminal that transmitted the request for the information thereto. In step 4g-15, the base station transmits a predetermined RRC message instructing the terminal to transition to an inactive state. In step 4g-20, the base station derives a DRX cycle to be applied to the terminal in the inactive state using the reported information. In step 4g-25, the base station can transmit a paging message triggered by the base station at a PF and a PO obtained by applying the derived DRX cycle.

[0369] FIG. 4H FIG. 1 is a diagram illustrating a structure of a terminal according to an embodiment of the disclosure.

[0370] Referring to FIG. 4H , the terminal includes a radio frequency (RF) processor 4h-10, a baseband processor 4h-20, a storage unit 4h-30, and a controller 4h-40.

[0371] The RF processor 4h-10 performs a function of transmitting and receiving a signal through a wireless channel, such as band conversion and signal amplification. That is, the RF processor 4h-10 up-converts a baseband signal provided from the baseband processor 4h-20 into an RF band signal, thus transmitting it through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 4h-10 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Although only one antenna is illustrated in FIG. 4H , the terminal can have a plurality of antennas. In addition, the RF processor 4h-10 can include a plurality of RF chains. Furthermore, the RF processor 4h-10 can perform beamforming. To perform beamforming, the RF processor 4h-10 can adjust phases and amplitudes of signals transmitted and received through a plurality of antennas or antenna elements. In addition, the RF processor can perform MIMO, and can receive a plurality of layers when performing a MIMO operation.

[0372] The baseband processor 4h-20 performs a conversion function between a baseband signal and a bit string according to a physical layer specification of a system. For example, in case of data transmission, the baseband processor 4h-20 encodes and modulates a transmission bit string, thereby generating a complex symbol. Also, in case of receiving data, the baseband processor 4h-20 demodulates and decodes a baseband signal provided from the RF processor 4h-10, thus recovering a reception bit string. For example, in case of applying an orthogonal frequency division multiplexing (OFDM) scheme, when transmitting data, the baseband processor 4h-20 generates a complex symbol by encoding and modulating a transmission bit string, maps the complex symbol to a subcarrier, and then configures an OFDM symbol through an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion. Also, when receiving data, the baseband processor 4h-20 divides a baseband signal provided from the RF processor 4h-10 into an OFDM symbol unit, recovers a signal mapped to a subcarrier through a fast Fourier transform (FFT) operation, and then recovers a reception bit string through demodulation and decoding.

[0373] As described above, the baseband processor 4h-20 and the RF processor 4h-10 transmit and receive signals. Accordingly, the baseband processor 4h-20 and the RF processor 4h-10 can be referred to as a "transmitter", a "receiver", a "transceiver", or a "communication unit". Further, at least one of the baseband processor 4h-20 and the RF processor 4h-10 can include a plurality of communication modules to support a plurality of different radio access technologies. Also, at least one of the baseband processor 4h-20 and the RF processor 4h-10 can include different communication modules to process signals of different frequency bands. For example, the different radio access technologies can include a wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. Also, the different frequency bands can include a super high frequency (SHF) (e.g., 2.NR Hz or NR hz) band and a millimeter wave (e.g., 60 GHz) band.

[0374] The storage unit 4h-30 stores data such as a basic program for terminal operation, an application program, and configuration information. Specifically, the storage unit 4h-30 can store information related to a second access node for performing wireless communication using a second radio access technology. Also, the storage unit 4h-30 provides the stored data according to a request of the controller 4h-40.

[0375] The controller 4h-40 controls overall operations of the terminal. For example, the controller 4h-40 transmits and receives signals through the baseband processor 4h-20 and the RF processor 4h-10. Also, the controller 4h-40 records and reads data in and from the storage unit 4h-30. To this end, the controller 4h-40 can include at least one processor. For example, the controller 4h-40 can include a communication processor (CP) for controlling communication and an application processor (AP) for controlling a higher layer such as an application program.

[0376] FIG. 4I is a block diagram of a configuration of a base station in a wireless communication system according to an embodiment of the disclosure.

[0377] As illustrated, the base station includes an RF processor 4i-10, a baseband processor 4i-20, a backhaul communication unit 4i-30, a storage unit 4i-40, and a controller 4i-50.

[0378] The RF processor 4i-10 performs a function of transmitting and receiving a signal through a wireless channel, such as band conversion and signal amplification. That is, the RF processor 4i-10 up-converts a baseband signal provided from the baseband processor 4i-20 into an RF band signal, thus transmitting it through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 4i-10 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is illustrated in the drawing, the first access node can have a plurality of antennas. Also, the RF processor 4i-10 can include a plurality of RF chains. Further, the RF processor 4i-10 can perform beamforming. To perform the beamforming, the RF processor 4i-10 can adjust phases and amplitudes of signals transmitted and received through a plurality of antennas or antenna elements. The RF processor can perform a downlink MIMO operation by transmitting one or more layers.

[0379] The baseband processor 4i-20 performs a conversion function between a baseband signal and a bit string according to a physical layer specification of the first radio access technology. For example, in the case of data transmission, the baseband processor 4i-20 encodes and modulates a transmission bit string, thereby generating a complex symbol. Also, when receiving data, the baseband processor 4i-20 demodulates and decodes a baseband signal provided from the RF processor 4i-10, thus recovering a reception bit string. For example, in the case of applying an OFDM scheme, when transmitting data, the baseband processor 4i-20 generates a complex symbol by encoding and modulating a transmission bit string, maps the complex symbol to a subcarrier, and then configures an OFDM symbol through an IFFT operation and CP insertion. Also, when receiving data, the baseband processor 4i-20 divides a baseband signal provided from the RF processor 4i-10 into an OFDM symbol unit, recovers a signal mapped to a subcarrier through an FFT operation, and then recovers a reception bit string through demodulation and decoding. As described above, the baseband processor 4i-20 and the RF processor 4i-10 transmit and receive a signal. Accordingly, the baseband processor 4i-20 and the RF processor 4i-10 can be referred to as a "transmitter", a "receiver", a "transceiver", a "communication unit", or a "wireless communication unit".

[0380] The backhaul communication unit 4i-30 provides an interface for performing communication with other nodes in a network. That is, the backhaul communication unit 4i-30 converts a bit string transmitted from the master base station to other nodes such as a secondary base station, a core network, etc., into a physical signal, and converts a physical signal received from the other nodes into a bit string.

[0381] The storage unit 4i-40 stores data such as a basic program for operation of the master base station, an application program, and configuration information. In particular, the storage unit 4i-40 can store information on a bearer allocated to a connected terminal, a measurement result reported from a connected terminal, etc. Also, the storage unit 4i-40 can store information that is a criterion for determining whether to provide a plurality of connections to a terminal or to release a plurality of connections. Also, the storage unit 4i-40 provides stored data in response to a request from the controller 4i-50.

[0382] The controller 4i-50 controls the overall operation of the master base station. For example, the controller 4i-50 transmits and receives a signal through the baseband processor 4i-20 and the RF processor 4i-10 or the backhaul communication unit 4i-30. Also, the controller 4i-50 records and reads data in and from the storage unit 4i-40. To this end, the controller 4i-50 can include at least one processor.

[0383] <5th Embodiment>

[0384] Hereinafter, detailed descriptions of known functions and configurations incorporated herein will be omitted if it renders the subject matter of the present disclosure ambiguous. Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0385] FIG. 5A is a diagram illustrating a structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0386] Referring to FIG. 5A , a radio access network of a next-generation mobile communication system includes a new radio node B (hereinafter, referred to as "NR NB") 5a-10 and a new radio core network (NR CN) 5a-05, as illustrated. A new radio user equipment (hereinafter, referred to as "NR UE" or "terminal") 5a-15 accesses an external network through the NR NB 5a-10 and the NR CN 5a-05.

[0387] In FIG. 5A , the NR NB 5a-10 corresponds to an evolved node B (eNB) of an existing LTE system. The NR NB is connected to the NR UE 5a-15 through a wireless channel and can provide a more superior service than a service of the existing node B. In the next-generation mobile communication system, since all user traffics are serviced through a shared channel, a device for collecting state information such as a buffer state of a UE, an available transmission power state, and a channel state and performing scheduling is required. The NR NB 5a-10 serves as such a device. One NR NB generally controls a plurality of cells. In order to achieve a super-high data rate compared to the existing LTE system, the next-generation mobile communication system can have a bandwidth equal to or greater than a maximum bandwidth of the existing system, can employ orthogonal frequency division multiplexing (hereinafter, referred to as "OFDM") as a radio access technology, and in addition thereto, can employ a beamforming technology. In addition, an adaptive modulation and coding (hereinafter, referred to as "AMC") scheme is applied according to a channel state of a terminal to determine a modulation scheme and a channel coding rate. The NR CN 5a-05 performs functions such as mobility support, bearer configuration, and QoS configuration. The NR CN 5a-05 is a device performing various control functions as well as a mobility management function for a terminal and is connected to a plurality of base stations. In addition, the next-generation mobile communication system can interwork with the existing LTE system, and the NR CN 5a-05 is connected to an MME 5a-25 through a network interface. The MME 5a-25 is connected to an eNB 5a-30 which is an existing base station.

[0388] FIG. 5B is a diagram illustrating a method of providing system information in an LTE system according to an embodiment of the present disclosure.

[0389] In the LTE system, system information broadcast by the base station 5b-10 is divided into a "MasterInformationBlock" (MIB) and several "SystemInformationBlock" (SIB) which will then be transmitted to the terminal 5b-05. The MIB 5b-15 includes only limited essential information, and the essential information is periodically transmitted in order to acquire other information from the cell. SIBs other than SIB 1 (5b-15) are transmitted using a system information (SI) message, and mapping information between the SIBs and the SI message is included in SIB 1 (5b-15). Each SIB can be included in only one SI message. SIB 1 (5b-15) includes SI scheduling information necessary for receiving another SIB 5b-25. SIB 1 also includes a "systemInfoValueTag" IE as information related to SI update. The value tag information is incremented by 1 each time a SIB (except for MIB, SIB 1, SIB 10, SIB 11, SIB 12, and SIB 14) is updated. This is used for the terminal to determine whether its own system information matches the system information currently being broadcast. In the LTE system, the value tag can be configured to 5 bits, and can be counted from 0 to 31. Therefore, if the value tag is changed 32 times or more, the value tag is wrapped around to zero. Therefore, it can be inappropriate to use the value tag to determine whether stored system information is the latest version after a long time. Therefore, the terminal has a validity timer, and the timer is reset each time SI update occurs. If the timer expires, the terminal updates the system information again. In the LTE system, the duration of the timer is 3 hours.

[0390] FIG. 5C FIG. 1 is a diagram illustrating a method for updating system information in an LTE system according to an embodiment of the disclosure.

[0391] System information broadcasted by the first LTE base station (eNB1) 5c-01 (hereinafter, referred to as "first base station") is valid only in the corresponding base station (5c-05). System information broadcasted by the second base station (eNB2) 5c-02 is valid only in the corresponding base station (5c-30). If the terminal 5c-10 newly receives system information broadcasted from the first base station 5c-05, the terminal drives only one validity timer (5c-15). In addition, the terminal 5c-10 records value tag information provided in SIB 1. The value tag is incremented by 1 each time system information is updated. If the terminal 5c-10 returns from a shadow area, the terminal compares the stored value tag with the value tag included in the currently broadcasted SIB 1, and if the stored value tag is the same as the value tag included in the SIB 1, the terminal does not perform system information update. If the stored value tag is different from the value tag included in the SIB 1, it means that system information has changed while the terminal 5c-10 stayed in the shadow area, and thus the terminal 5c-10 has to receive newly updated system information. If the validity timer expires, the terminal 5c-10 acquires system information from the first base station 5c-01 again (5c-20). If the terminal 5c-10 moves to a service area of the adjacent second base station (eNB2) 5c-02, the terminal 5c-10 receives new system information broadcasted from the second base station 5c-02, and resets the validity timer in operation, thereby restarting the validity timer (5c-25). At this time, the terminal 5c-10 records value tag information provided in SIB 1 transmitted by the second base station 5c-02.

[0392] FIG. 5D FIG. 1 is a diagram illustrating a method of providing system information in a next-generation mobile communication system according to an embodiment of the disclosure.

[0393] In the next generation mobile communication system, system information broadcasted by the base station 5d-10 is divided into minimum system information (SI) and other system information. The minimum SI is periodically broadcasted (5d-15), and includes configuration information necessary for initial access and SI scheduling information necessary for receiving other SI broadcast periodically or when requested. Basically, the other SI includes all configuration information not included in the minimum SI. The other SI is broadcasted periodically (5d-20) or when the terminal requests, or provided to the terminal (UE) 5d-05 from the base station (gNB) 5d-10 using dedicated signaling (5d-25). In the case where the terminal 5d-05 requests and receives the other SI, before making the request, the terminal 5d-05 needs to check whether the other SI is valid in the cell or the other SI is currently being broadcasted (by the request of another terminal). The above check can be performed by specific information provided by the minimum SI. The terminal in the idle mode (RRC_IDLE) or in the inactive mode (RRC_INACTIVE) can request the other SI without changing the current RRC state. The terminal in the connected mode (RRC_CONNECTED) can request and receive the other SI through dedicated RRC signaling. In each configured period, the other SI is broadcasted for a predetermined period. Public warning system (PWS) information is classified as the other SI and provided as the other SI. Whether the other SI is broadcasted or whether the other SI is provided via dedicated RRC signaling depends on the network implementation.

[0394] FIG. 5E is a diagram for explaining a method for updating system information according to an embodiment of the disclosure.

[0395] As described above, in LTE, system information is re-acquired every 3 hours regardless of whether the value tag is changed. This is intended to prevent a case where the same value as the terminal 5e-10 is used, because the value tag is wrapped around for 3 hours. In addition, if the terminal 5e-10 changes a serving cell, the terminal 5e-10 re-acquires system information and resets the validity timer regardless of the change of the value tag.

[0396] Embodiments of the present disclosure show first system information applied only to one cell and second system information commonly applied to a region including a plurality of cells adjacent to each other. A specific cell provides a terminal 5e-10 with first system information and second system information (5e-05). In addition, the first system information and the second system information can respectively have: a first value tag and a first validity timer and a second value tag and a second validity timer. The first validity timer can not be used. If a timer is configured, the terminal 5e-10 can start the corresponding timer. Update of the first system information can be performed by a method of updating system information in an LTE system. Regarding the second system information, the terminal 5e-10 reacquires the second system information each time a validity timer expires in the same cell (5e-20). However, when a cell changes, the terminal reacquires the second system information only in the case where the value tag is different; and even if a cell changes, the terminal does not perform reacquisition of the second system information and resetting of the validity timer if the value tag is the same (5e-25).

[0397] If a specific region including a plurality of cells changes, the terminal 5e-10 updates the second system information regardless of the second value tag value. If the terminal 5e-10 is capable of storing system information for a corresponding cell or region, it is also capable of maintaining a validity timer corresponding to the system information. This is intended to prevent the terminal 5e-10 from unnecessarily reacquiring the same second system information when the terminal 5e-10 returns to a previous region. The following table summarizes the operation of the terminal in relation to update of system information in specific cases in the present disclosure.

[0398] [Table 1]

[0399]

[0400] FIG. 5F FIG. 1 is a diagram illustrating a terminal for operating cell-based or region-based system information and a validity timer corresponding thereto according to an embodiment of the present disclosure.

[0401] In step 5f-05, the terminal receives first system information and second system information from a base station. The system information is provided to the terminal through periodic broadcast, request-based broadcast, or dedicated signaling. The first system information can be cell-specific SI applied only to one cell, and the second system information can be region-specific SI commonly applied to a region including a plurality of cells adjacent to each other (a group including a plurality of cells). The first system information can include a master information block (MIB). In addition, the first system information can include system information block 1 (SIB1). The second system information can include system information other than the first system information.

[0402] In step 5f-10, the terminal drives a first validity timer and a second validity timer corresponding to the first system information and the second system information, respectively. In step 5f-15, the terminal stores a first value tag and a second value tag corresponding to the first system information and the second system information. The first value tag information and the second value tag information are provided as specific system information, for example, minimum SI. The first validity timer can not be configured, and in this case, the operation of driving the validity timer 1 and operations according thereto can be omitted below.

[0403] In step 5f-20, if the terminal moves to another cell in a region sharing the second system information, the terminal updates only the first system information and restarts the first validity timer corresponding thereto. In step 5f-25, if the terminal moves to another cell in a region not sharing the second system information, the terminal updates both the first system information and the second system information and restarts the validity timer corresponding thereto.

[0404] In step 5f-30, if the terminal is still within the same cell or region when a specific validity timer expires, the terminal updates the system information corresponding thereto. In step 5f-35, if the terminal is in another cell or region when a specific validity timer expires, the terminal deletes the system information corresponding thereto.

[0405] FIG. 5G is a diagram for explaining a method of performing system information update according to an embodiment of the disclosure.

[0406] Reacquiring system information every time the validity timer expires regardless of whether the value tag is changed is due to the fact that the value tag wraps around after a long time, so that the same value as the value saved by the terminal can be used. If the base station provides system information indicating that the value tag has not been changed a certain number of times within a certain period of time before the current time, the terminal can determine whether the stored value tag value is still valid even if the validity timer expires. For example, even if the validity timer expires, the value tag (length = n bits) does not need to be updated unless it has changed 2n times. Accordingly, the base station provides, using a certain system information (such as minimum SI, etc.), a value tag corresponding to the system information and 1-bit information (multipleUpdateIndicator) indicating whether the system information has been updated 2n times or more within a certain period of time before the current time (5g-05, 5g-10, and 5g-15) (5g-20). If this information is "true", it means that the system information has been updated 2n times or more. If it is "false", it means that the system information has not been updated 2n times or more. The certain period of time is shorter than the duration of the validity timer. The terminal checks the "multipleUpdateIndicator" provided from the certain system information immediately before or at the expiration of the validity timer, and if the indicator is "true", discards the system information and reacquires the system information. If the indicator is "false" and if the value tag is different, the terminal reacquires the system information. If the indicator is "false" and if the value tag is the same, the terminal applies the currently stored system information and restarts the validity timer corresponding thereto.

[0407] FIG. 5H is a diagram for explaining the operation of a terminal for performing system information update according to an embodiment of the disclosure.

[0408] In step 5h-05, the terminal receives system information including a "multipleUpdateIndicator" corresponding to the certain system information immediately before or at the expiration of the validity timer of the certain system information. In step 5h-10, the terminal identifies the indicator. In step 5h-15, if the indicator is "true", the terminal discards the system information and reacquires the system information. In step 5h-20, if the indicator is "false" and if the value tag is different, the terminal reacquires the system information. In step 5h-25, if the indicator is "false" and if the value tag is the same, the terminal applies the currently stored system information and restarts the validity timer corresponding thereto.

[0409] FIG. 5I is a diagram for explaining the operation of a terminal for performing system information update according to an embodiment of the disclosure.

[0410] In step 5i-05, the base station transmits specific system information including a value tag and a 1-bit information (multipleUpdateIndicator) indicating whether the system information has been updated a specific number of times or more within a specific time period before the current time. In step 5i-10, the base station calculates and includes the 1-bit information each time the specific system information including the information is transmitted. In step 5i-15, the base station does not count the value tag although the 1-bit information changes.

[0411] In LTE, carrier frequency information about surrounding frequencies is provided as inter-frequency information in SIB 5. As a result, even in the same area, SIB 5 has different contents for each frequency.

[0412] In LTE, information about intra-frequency mobility is provided through SIB 4 and information about inter-frequency mobility is provided through SIB 5. Therefore, SIB 5 changes whenever a serving frequency changes. There is no big problem in LTE because the terminal must acquire system information from a new serving cell each time a cell changes. However, in the next-generation mobile communication system, it is expected to maintain system information the same between neighboring cells. Applying this principle, it is not expected to configure SIB 5 in the same way as LTE. This is due to the fact that a change in a serving frequency also causes a change in SIB 5. The next-generation mobile communication system needs to change the definition of SIB 5 so that SIB 5 does not change even if a serving frequency changes. Embodiments of the present disclosure provide the definition of SIB 5 using information about a serving frequency and neighboring frequencies. The following table shows an example of the configuration of SIB 5 in embodiments of the present disclosure. For example, if the definition proposed in the present disclosure is applied, SIB 5 does not change even if a serving frequency changes in a system including f1, f2, f3, and f4. This means that SIB 5 does not need to be updated even if the terminal changes the frequency of the serving cell.

[0413]

[0414] FIG. 5J is a diagram for explaining a method of providing access barring configuration information as system information according to embodiments of the present disclosure.

[0415] As described above, system information broadcast by the base station 5j-10 in the next-generation mobile communication system is mainly divided into minimum system information (SI) and other system information. Since the minimum SI is periodically broadcast but has a limited size, there is a limit to including a large amount of configuration information. Although access barring configuration information is the most essential information, the configuration information has a variable size and sometimes can be very large. Therefore, it can be inefficient or impossible to include all of the access barring configuration information in the minimum SI. Therefore, in an embodiment of the disclosure, if the access barring configuration information has a certain size or more, only some of the access barring configuration information is included in the minimum SI (5j-15), and the remaining access barring configuration information is included in the other SI. The access barring configuration information always included in the minimum SI, regardless of its size, includes at least information corresponding to signaling for requesting the other SI. It is possible to consistently include only the access barring configuration information corresponding to the signaling for requesting the other SI regardless of the size of the access barring configuration information, and the remaining access barring configuration information can be transmitted through the other SI. In addition, the access barring configuration information consistently included in the minimum SI can include access barring configuration information corresponding to emergency communication.

[0416] The access barring configuration information other than the access barring configuration information corresponding to the signaling for requesting the other SI is provided to the terminal 5j-05 through the other SI through broadcast or dedicated RRC signaling (5j-20 and 5j-25).

[0417] FIG. 5K FIG. 5k-00 is a diagram for explaining an operation of a base station for providing access barring configuration information as system information according to an embodiment of the disclosure.

[0418] In step 5k-05, the base station determines whether the size of the entire access barring configuration information is equal to or greater than a predetermined value. For example, the predetermined value corresponds to an additional space other than information that must be included in the minimum SI. If the size of the entire access barring configuration information is greater than or equal to the predetermined value, in step 5k-10, the base station includes only some of the access barring configuration information in the minimum SI and includes the remaining access barring configuration information in the other SI. Otherwise, if the size of the entire access barring configuration information is less than the predetermined value, in step 5k-15, the base station includes the entire access barring configuration information in the minimum SI.

[0419] FIG. 5L FIG. 5k-01 is a diagram showing a structure of a terminal according to an embodiment of the disclosure.

[0420] Reference FIG. 5LThe terminal includes a radio frequency (RF) processor 5l-10, a baseband processor 5l-20, a storage unit 5l-30, and a controller 5l-40.

[0421] The RF processor 51-10 performs a function of transmitting and receiving a signal through a wireless channel, such as band conversion and signal amplification. That is, the RF processor 5l-10 up-converts a baseband signal provided from the baseband processor 5l-20 into an RF band signal, and thus transmits it through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 5l-10 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Although only one antenna is illustrated in FIG. 5L The terminal can have a plurality of antennas. In addition, the RF processor 51-10 can include a plurality of RF chains. Furthermore, the RF processor 5l-10 can perform beamforming. To perform beamforming, the RF processor 51-10 can adjust phases and amplitudes of signals transmitted and received through a plurality of antennas or antenna elements. In addition, the RF processor can perform MIMO, and can receive a plurality of layers when performing the MIMO operation.

[0422] The baseband processor 5l-20 performs a conversion function between a baseband signal and a bit string according to a physical layer specification of a system. For example, in the case of data transmission, the baseband processor 5l-20 encodes and modulates a transmission bit string, thereby generating a complex symbol. In addition, when receiving data, the baseband processor 5l-20 demodulates and decodes a baseband signal provided from the RF processor 5l-10, thus recovering a reception bit string. For example, in the case of applying an orthogonal frequency division multiplexing (OFDM) scheme, when transmitting data, the baseband processor 5l-20 generates a complex symbol by encoding and modulating a transmission bit string, maps the complex symbol to a subcarrier, and then configures an OFDM symbol through an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion. In addition, when receiving data, the baseband processor 5l-20 divides a baseband signal provided from the RF processor 5l-10 into an OFDM symbol unit, recovers a signal mapped to a subcarrier through a fast Fourier transform (FFT) operation, and then recovers a reception bit string through demodulation and decoding.

[0423] As described above, the baseband processor 5l-20 and the RF processor 5l-10 transmit and receive signals. Accordingly, the baseband processor 5l-20 and the RF processor 5l-10 can be referred to as a "transmitter", a "receiver", a "transceiver", or a "communication unit". Also, at least one of the baseband processor 5l-20 and the RF processor 5l-10 can include a plurality of communication modules to support a plurality of different radio access technologies. In addition, at least one of the baseband processor 5l-20 and the RF processor 5l-10 can include different communication modules to process signals of different frequency bands. For example, the different radio access technologies can include wireless LAN (e.g., IEEE 802.11), cellular network (e.g., LTE), etc. In addition, the different frequency bands can include a super high frequency (SHF) (e.g., 2.NR Hz or NR hz) band and a millimeter wave (e.g., 60 GHz) band.

[0424] The storage unit 5l-30 stores data such as basic programs for terminal operations, application programs, and configuration information. Specifically, the storage unit 5l-30 can store information related to a second access node for performing wireless communication using a second radio access technology. In addition, the storage unit 5l-30 provides the stored data according to a request of the controller 5l-40.

[0425] The controller 5l-40 controls the overall operation of the terminal. For example, the controller 5l-40 transmits and receives signals through the baseband processor 5l-20 and the RF processor 5l-10. In addition, the controller 5l-40 records and reads data in and from the storage unit 5l-30. To this end, the controller 5l-40 can include at least one processor. For example, the controller 5l-40 can include a communication processor (CP) for controlling communication and an application processor (AP) for controlling a higher layer such as an application program.

[0426] In addition, the controller 5l-40 can perform control to acquire first system information and second system information from a first cell, start a timer corresponding to the second system information, determine whether a second cell shares the second system information with the first cell if the terminal moves from the first cell to the second cell, and update the second system information based on a result of the determination.

[0427] The controller 5l-40 can perform control to update the first system information, instead of updating the second system information, if the second cell shares the second system information with the first cell. The controller 5l-40 can perform control to update the acquired second system information if a value tag of the second system information acquired in the first cell is different from a value tag of the second system information of the second cell.

[0428] In addition, the controller 51-40 can perform control so as to update the first system information and the second system information and reset and restart the timer if the second cell does not share the second system information with the first cell. In addition, the controller 51-40 can perform control so as to update the first system information if the terminal moves from the first cell to another cell, regardless of the value tag of the first system information.

[0429] The first system information can be cell-specific system information, and the second system information can be common system information for a plurality of cells. In addition, the first system information can include a master information block (MIB).

[0430] FIG. 5M FIG. 1 is a diagram illustrating a configuration of a terminal according to an embodiment of the disclosure.

[0431] As illustrated, the terminal includes an RF processor 1a-10, a baseband processor 1a-20, a storage unit 1a-30, and a controller 1a-40.

[0432] The RF processor 1a-10 performs a function of transmitting and receiving a signal through a wireless channel, such as band conversion and signal amplification. That is, the RF processor 1a-10 up-converts a baseband signal provided from the baseband processor 1a-20 into an RF band signal, thus transmitting it through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 1a-10 can include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is illustrated in the drawing, the first access node can have a plurality of antennas. In addition, the RF processor 1a-10 can include a plurality of RF chains. Furthermore, the RF processor 1a-10 can perform beamforming. To perform beamforming, the RF processor 1a-10 can adjust phases and amplitudes of signals transmitted and received through a plurality of antennas or antenna elements. The RF processor can perform a downlink MIMO operation by transmitting one or more layers.

[0433] The baseband processor 5m-20 performs a conversion function between a baseband signal and a bit string according to a physical layer specification of the first radio access technology. For example, in the case of data transmission, the baseband processor 5m-20 encodes and modulates a transmission bit string, thereby generating a complex symbol. Also, upon reception of data, the baseband processor 5m-20 demodulates and decodes a baseband signal provided from the RF processor 5m-10, thus recovering a reception bit string. For example, in the case of employing an OFDM scheme, when transmitting data, the baseband processor 5m-20 generates a complex symbol by encoding and modulating a transmission bit string, maps the complex symbol to a subcarrier, and then configures an OFDM symbol through an IFFT operation and CP insertion. Also, when receiving data, the baseband processor 5m-20 divides a baseband signal provided from the RF processor 5m-10 into an OFDM symbol unit, recovers a signal corresponding to a subcarrier through an FFT operation, and then recovers a reception bit string through demodulation and decoding. As described above, the baseband processor 5m-20 and the RF processor 5m-10 transmit and receive a signal. Accordingly, the baseband processor 5m-20 and the RF processor 5m-10 can be referred to as a "transmitter", a "receiver", a "transceiver", a "communication unit", or a "wireless communication unit".

[0434] The backhaul communication unit 5m-30 provides an interface for performing communication with other nodes in a network. That is, the backhaul communication unit 5m-30 converts a bit string transmitted from the master base station to another node such as a secondary base station, a core network, etc., into a physical signal, and converts a physical signal received from the other node into a bit string.

[0435] The storage unit 5m-40 stores data such as a basic program for operation of the master base station, an application program, and configuration information. In particular, the storage unit 5m-40 can store information on a bearer allocated to a connected terminal, a measurement result reported from a connected terminal, etc. Also, the storage unit 5m-40 can store information that is a criterion for determining whether to provide a plurality of connections to a terminal or release a plurality of connections. Also, the storage unit 5m-40 provides stored data in response to a request from the controller 5m-50.

[0436] The controller 5m-50 controls the overall operation of the master base station. For example, the controller 5m-50 transmits and receives a signal through the baseband processor 5m-20 and the RF processor 5m-10 or the backhaul communication unit 5m-30. Also, the controller 5m-50 records and reads data in and from the storage unit 5m-40. To this end, the controller 5m-50 can include at least one processor.

[0437] In the above detailed embodiments of the disclosure, components included in the disclosure are expressed in singular or plural according to the detailed embodiments presented. However, for the convenience of description, singular or plural expression is selected as appropriate to the situation presented, and the disclosure is not limited to a single or multiple elements. An element expressed in plural can be configured as singular, or an element expressed in singular can be configured as plural.

[0438] Although embodiments have been described in the detailed description of the disclosure, the disclosure can be modified in various forms without departing from the scope of the disclosure. Therefore, the scope of the disclosure should not be limited to the embodiments, but should be defined by the appended claims and equivalents thereof.

Claims

1. A method executed by a terminal in a communication system, the method comprising: Receive RRC messages related to Radio Resource Control (RRC) inactivity status; Based on the RRC message, the system enters the RRC inactive state; Receive paging messages in the RRC inactive state; If the paging message includes an identifier that matches the S-Temporary Mobile Subscriber Identity (S-TMSI), the user transitions from the RRC inactive state to the RRC idle state. as well as If the paging message includes an identifier that matches the recovery identifier, an access layer AS message for paging in the radio access network (RAN) is generated.

2. The method according to claim 1, The RRC message includes information about the RAN paging cycle and information about the RAN paging area.

3. The method according to claim 2, The RAN paging cycle is different from the core network (CN) paging cycle configured based on system information.

4. The method according to claim 1, further comprising: When inter-cell reselection of Radio Access Technology (RAT) is performed while the terminal is in the RRC inactive state, the terminal transitions from the RRC inactive state to the RRC idle state. In cases where cell selection is not performed when entering the RRC idle state is triggered based on the inter-RAT cell reselection being triggered when the terminal is in the RRC inactive state.

5. The method according to claim 1, in, If the paging message includes an identifier matching the S-TMSI, the terminal generates a Non-Access Stratum (NAS) message for paging triggered by the core network (CN), and Wherein, if the paging message includes an identifier that matches the recovery identifier, the terminal maintains the RRC inactive state and generates the AS message.

6. A terminal in a communication system, the terminal comprising: transceiver; and At least one processor, coupled to the transceiver, is configured to: Receive RRC messages related to Radio Resource Control (RRC) inactivity status; Based on the RRC message, the system enters the RRC inactive state; Receive paging messages in the RRC inactive state; If the paging message includes an identifier that matches the S-Temporary Mobile Subscriber Identity (S-TMSI), the user transitions from the RRC inactive state to the RRC idle state. as well as If the paging message includes an identifier that matches the recovery identifier, an access layer AS message for paging in the radio access network (RAN) is generated.

7. The terminal according to claim 6, The RRC message includes information about the RAN paging cycle and information about the RAN paging area.

8. The terminal according to claim 7, The RAN paging cycle is different from the core network (CN) paging cycle configured based on system information.

9. The terminal according to claim 6, in, The at least one processor is configured to transition from the RRC inactive state to the RRC idle state when inter-Radio Access Technology (RAT) cell reselection is performed while the terminal is in the RRC inactive state, and In cases where cell selection is not performed when entering the RRC idle state is triggered based on the inter-RAT cell reselection being triggered when the terminal is in the RRC inactive state.

10. The terminal according to claim 6, in, If the paging message includes an identifier matching the S-TMSI, the terminal generates a Non-Access Stratum (NAS) message for paging triggered by the core network (CN), and Wherein, if the paging message includes an identifier that matches the recovery identifier, the terminal maintains the RRC inactive state and generates the AS message.

11. A method performed by a base station in a communication system, the method comprising: Send a paging message to the terminal that has entered the RRC inactive state based on the Radio Resource Control (RRC) message; If the paging message includes an identifier that matches the S-Temporary Mobile Subscriber Identity (S-TMSI), a Non-Access Stratum (NAS) message is received from the terminal that has entered the RRC idle state from the RRC inactive state based on the paging message. as well as If the paging message includes an identifier that matches the recovery identifier, the terminal in the RRC inactive state receives an access layer AS message for paging the radio access network (RAN).

12. The method according to claim 11, The RRC message includes information about the RAN paging cycle and information about the RAN paging area.

13. The method according to claim 12, The RAN paging cycle is different from the core network (CN) paging cycle configured based on system information.

14. The method according to claim 11, in, When inter-cell reselection of Radio Access Technology (RAT) is performed while the terminal is in the RRC inactive state, the terminal transitions from the RRC inactive state to the RRC idle state, and In cases where cell selection is not performed when entering the RRC idle state is triggered based on the inter-RAT cell reselection being triggered when the terminal is in the RRC inactive state.

15. The method according to claim 11, in, The NAS message is used for paging triggered by the core network (CN), and Wherein, if the paging message includes an identifier that matches the recovery identifier, the AS message is generated when the terminal maintains the RRC inactive state.

16. A base station in a communication system, the base station comprising: transceiver; and At least one processor, coupled to the transceiver, is configured to: Send a paging message to the terminal that has entered the RRC inactive state based on the Radio Resource Control (RRC) message; If the paging message includes an identifier that matches the S-Temporary Mobile Subscriber Identity (S-TMSI), a Non-Access Stratum (NAS) message is received from the terminal that has entered the RRC idle state from the RRC inactive state based on the paging message. as well as If the paging message includes an identifier that matches the recovery identifier, the terminal in the RRC inactive state receives an access layer AS message for paging the radio access network (RAN).

17. The base station according to claim 16, The RRC message includes information about the RAN paging cycle and information about the RAN paging area.

18. The base station according to claim 17, The RAN paging cycle is different from the core network (CN) paging cycle configured based on system information.

19. The base station according to claim 16, in, When inter-cell reselection of Radio Access Technology (RAT) is performed while the terminal is in the RRC inactive state, the terminal transitions from the RRC inactive state to the RRC idle state, and In cases where cell selection is not performed when entering the RRC idle state is triggered based on the inter-RAT cell reselection being triggered when the terminal is in the RRC inactive state.

20. The base station according to claim 16, in, The NAS message is used for paging triggered by the core network (CN), and Wherein, if the paging message includes an identifier that matches the recovery identifier, the AS message is generated when the terminal maintains the RRC inactive state.

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