Apparatus and method for managing user equipment context in wireless communication system

Abstract

The present disclosure relates to a wireless communication system and, particularly, to an operation method of a first base station in a wireless communication system, the method comprising the steps of: receiving an RRC connection resume request from a user equipment; transmitting, to a core network, a search request for user equipment context of the user equipment; and receiving a search response for the user equipment context on the basis of confirmation of removal of an NG interface between the core network and a second base station.

Description

Terminal context management device and method in a wireless communication system

[0001] The present disclosure relates to a wireless communication system, and in particular to an apparatus and method for managing a terminal context in a wireless communication system.

[0002] With the advancement of mobile communication services, Non-Terrestrial Networks (NTNs), which are free from spatial constraints, are attracting attention, and low-orbit satellites, in particular, are expected to play a major role. Accordingly, 3GPP (3 rd The Generation Partnership Project is proceeding with standardization for non-terrestrial networks without spatial constraints to provide effective communication services.

[0003] For example, in 5G NR (New Radio) systems, the RRC_INACTIVE state was introduced to reduce terminal power consumption and support rapid connection resumption. Meanwhile, as satellites in non-terrestrial network environments orbit the Earth at high speeds, the satellite servicing the terminal (User Equipment, UE) may continuously change due to satellite mobility. Consequently, due to this satellite mobility, situations may frequently occur where the terminal context of a terminal in the RRC_INACTIVE state must be transferred to a new satellite.

[0004] The present disclosure is intended to provide an apparatus and method for receiving a terminal context from a core network based on the removal of an NG interface between a core network and a second base station.

[0005] The present disclosure is intended to provide an apparatus and method for storing a terminal context in a core network based on a request to remove an NG interface to a core network of a second base station.

[0006] The present disclosure is intended to provide an apparatus and method for releasing a terminal context based on a NG interface removal response of a core network.

[0007] The present disclosure is intended to provide an NG interface removal request message that includes a list of terminal contexts of terminals in an RRC disabled state.

[0008] The present disclosure is intended to provide an apparatus and method for a core network to directly transmit a RAN paging request to a first base station based on RNA of a terminal obtained from a terminal context.

[0009] According to one aspect of the present disclosure, a method of operation of a first base station in a wireless communication system is disclosed. The method may include receiving a request to resume an RRC connection from a terminal, transmitting a request to search for the terminal context of the terminal to a core network, and receiving a search response for the terminal context based on confirmation of removal of an NG interface between the core network and a second base station.

[0010] According to one embodiment of the present disclosure, the terminal context may be stored in the core network based on a request to remove the NG interface to the core network of the second base station.

[0011] According to another embodiment of the present disclosure, the second base station may release the terminal context based on the NG interface removal response of the core network.

[0012] According to another embodiment of the present disclosure, the NG interface removal request may include a list of terminal contexts of terminals in an RRC disabled state.

[0013] According to another embodiment of the present disclosure, the method may further include the steps of receiving a RAN paging request from the core network based on the RNA (RAN Notification Area) of the terminal obtained from the terminal context, and performing RAN paging with the terminal.

[0014] According to another aspect of the present disclosure, a first base station is disclosed in a wireless communication system. The first base station comprises a transceiver and a processor connected to the transceiver, and the processor may receive an RRC connection resumption request from a terminal, transmit a request to search for the terminal context of the terminal to a core network, and receive a search response for the terminal context based on the NG interface removal confirmation between the core network and a second base station.

[0015] According to another aspect of the present disclosure, a method of operation of a second base station in a wireless communication system is disclosed. The method may include the steps of performing an RRC disable procedure with a terminal, performing an NG interface removal procedure with a core network, and transmitting to the core network the completion of the release of the terminal context for the terminal in an RRC disable state.

[0016] According to one embodiment of the present disclosure, the terminal context is stored in the core network based on a request to remove an NG interface to the core network of the second base station, and when the first base station transmits a request to retrieve the terminal context, it may be transmitted to the first base station based on confirmation of the removal of the NG interface with the second base station of the core network.

[0017] According to another embodiment of the present disclosure, the step of transmitting the completion of release of the terminal context to the core network may include the step of releasing the terminal context based on the NG interface removal response of the core network.

[0018] According to another embodiment of the present disclosure, the NG interface removal request may include a list of terminal contexts of terminals in an RRC disabled state.

[0019] According to another embodiment of the present disclosure, the first base station may further include the steps of receiving a RAN paging request from the core network based on the RNA of the terminal obtained from the terminal context and performing RAN paging with the terminal.

[0020] According to another aspect of the present disclosure, a second base station is disclosed in a wireless communication system. The second base station includes a transceiver and a processor connected to the transceiver, and the processor may perform an RRC disable procedure with a terminal, perform an NG interface removal procedure with a core network, and transmit to the core network the completion of the release of the terminal context for the terminal in an RRC disable state.

[0021] According to another aspect of the present disclosure, a method of operating a core network in a wireless communication system is disclosed. The method may include the steps of performing a procedure to remove an NG interface with a second base station, receiving from the second base station completion of the release of a terminal context for a terminal in an RRC disabled state, receiving a request to retrieve the terminal context from a first base station that has received a request to resume an RRC connection from the terminal, and transmitting a response to retrieve the terminal context based on confirmation of the removal of the NG interface with the second base station.

[0022] According to one embodiment of the present disclosure, the step of performing the NG interface removal procedure may be stored in the core network based on the NG interface removal request of the second base station.

[0023] According to another embodiment of the present disclosure, the method may further include the steps of receiving downlink data and transmitting a RAN paging request to the first base station based on the RNA of the terminal obtained from the terminal context.

[0024] According to another aspect of the present disclosure, a core network is disclosed in a wireless communication system. The core network includes a transceiver and a processor connected to the transceiver, and the processor performs an NG interface removal procedure with a second base station, receives from the second base station completion of the release of a terminal context for a terminal in an RRC disabled state, receives a request to retrieve the terminal context from a first base station that has received a request to resume an RRC connection from the terminal, and transmits a response to retrieve the terminal context based on confirmation of the removal of the NG interface with the second base station.

[0025] According to embodiments of the present disclosure, terminal context management can be effectively performed in a wireless communication system.

[0026] FIG. 1 illustrates an example of a satellite network according to one embodiment of the present disclosure.

[0027] FIG. 2 illustrates another example of a satellite network according to one embodiment of the present disclosure.

[0028] FIG. 3 illustrates the configuration of a device in a wireless communication system according to one embodiment of the present disclosure.

[0029] FIG. 4 illustrates an example of an RRC rejection procedure according to one embodiment of the present disclosure.

[0030] FIG. 5 illustrates an example of an RRC setup procedure according to another embodiment of the present disclosure.

[0031] FIG. 6 illustrates an example of a terminal context transmission procedure according to one embodiment of the present disclosure.

[0032] FIG. 7 illustrates an example of a terminal context transmission procedure according to another embodiment of the present disclosure.

[0033] FIG. 8 illustrates an example of a terminal context transmission procedure according to another embodiment of the present disclosure.

[0034] FIG. 9 illustrates an example of an operation procedure of a first base station according to one embodiment of the present disclosure.

[0035] FIG. 10 illustrates an example of an operation procedure of a second base station according to one embodiment of the present disclosure.

[0036] FIG. 11 illustrates an example of an operation procedure of a core network according to one embodiment of the present disclosure.

[0037] The terms used in these embodiments have been selected to be as widely used and general as possible, taking into account the functions within these embodiments; however, these terms may vary depending on the intent of those skilled in the art, case law, the emergence of new technologies, etc. Additionally, in specific cases, the applicant has arbitrarily selected terms, and in such cases, their meanings will be described in detail in the relevant sections. Therefore, the terms used in these embodiments should be defined not merely by their names, but based on their meanings and the content throughout these embodiments.

[0038] The embodiments are subject to various modifications and may take various forms; therefore, some embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the embodiments to the specific disclosed forms, and it should be understood that the embodiments include all modifications, equivalents, and substitutions that fall within the spirit and scope of the embodiments. The terms used herein are for the description of the embodiments only and are not intended to limit the embodiments.

[0039] Unless otherwise defined, the terms used in these embodiments have the same meaning as generally understood by those skilled in the art to which these embodiments pertain. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in these embodiments.

[0040]

[0041] The present disclosure relates to a Non-Terrestrial Network (NTN) system and to a method for efficiently partitioning and managing a terminal context corresponding to the Radio Resource Control Inactive (RRC_INACTIVE) state of a User Equipment (UE) in an environment where a base station (gNB) is mounted on a Low Earth Orbit (LEO) satellite. In one embodiment, the present disclosure may be configured to distribute, store, transmit, or maintain the terminal context by utilizing an Xn interface between satellites and an NG interface between a satellite and an Access and Mobility Management Function (AMF) of a core network.

[0042] In 5G NR (New Radio) systems, an RRC-inactive (RRC_INACTIVE) state was introduced to reduce terminal power consumption and support rapid connection resumption. When a terminal is in the RRC-inactive state, the radio connection with the base station (RAN) is terminated, but the connection information (Context) with the AMF, which performs core network access and mobility management functions, is maintained. At this time, the base station stores and manages the terminal context corresponding to the terminal.

[0043] In a conventional terrestrial mobile communication network environment, since base stations are fixed, when downlink data occurs, the core network transmits a paging request to the base station that last serviced the terminal, and the corresponding base station can perform paging for the terminal and initiate data transmission.

[0044] However, in a non-terrestrial network environment based on regenerative payloads where base stations are mounted on satellites, technical problems different from those of terrestrial networks arise because the location of the base station continuously changes as the satellite orbits the Earth.

[0045] Specifically, due to satellite mobility, the serving satellite servicing a terminal continuously changes, and consequently, situations frequently arise where the terminal context for a terminal in an RRC-disabled state must be transferred to a new satellite. Meanwhile, for a terminal to perform an RRC connection resume or receive paging, the satellite currently servicing the terminal must receive the terminal context of that terminal from the last satellite. Therefore, the present disclosure aims to provide a method for managing terminal contexts by considering the characteristics of terminals in an RRC-disabled state in order to efficiently utilize limited satellite network resources and ensure stable service continuity for terminals in an RRC-disabled state.

[0046]

[0047] FIG. 1 illustrates an example of a satellite network according to one embodiment of the present disclosure.

[0048] Referring to FIG. 1, the satellite network includes a terminal (110), satellites (120-1, 120-2), and a gateway (130). The terminal (110) is a user device equipped with hardware and software that receives cellular data from a satellite (120-1), and may be a mobile or fixed device. For example, the terminal (110) may include a mobile phone, a smartphone, a wearable device, or a UE (User Equipment). Furthermore, the terminal (110) is not limited to the examples described above, and may include any electronic device capable of cellular communication, such as a laptop or tablet PC. The terminal (110) is not limited to the examples described above. Although the satellite network in FIG. 1 is depicted as including only a single terminal (110), this is merely an exemplary embodiment and is not limited thereto, and it is obvious that it may include multiple terminals (110).

[0049] Specifically, the terminal (110) can support communication protocols defined in 3GPP (3rd generation partnership project) standards (e.g., LTE communication protocol, LTE-A communication protocol, NR communication protocol, etc.). Multiple communication nodes (110 to 130) can support CDMA (code division multiple access) technology, WCDMA (wideband CDMA) technology, TDMA (time division multiple access) technology, FDMA (frequency division multiple access) technology, OFDM (orthogonal frequency division multiplexing) technology, Filtered OFDM technology, CP (cyclic prefix)-OFDM technology, DFT-s-OFDM (discrete Fourier transform-spread-OFDM) technology, OFDMA (orthogonal frequency division multiple access) technology, SC (single carrier)-FDMA technology, NOMA (non-orthogonal multiple access) technology, GFDM (generalized frequency division multiplexing) technology, FBMC (filter bank multi-carrier) technology, UFMC (universal filtered multi-carrier) technology, SDMA (space division multiple access) technology, etc.

[0050] Satellites (120-1, 120-2) fly in a fixed orbit and can provide a cell with coverage of a certain size by forming a beam toward the ground. In relation to the present disclosure, satellite (120-1) may mean a serving satellite and satellite (120-2) may mean a target satellite. A gateway (130) provides the satellites (120-1, 120-2) with a link to access a network. That is, the gateway (130) can provide a connection between the satellites (120-1, 120-2) and the core network. The satellites (120-1, 120-2) can interact with the Access and Mobility Management Function (AMF) of the core network through the gateway (130).

[0051] The link between the terminal (110) and the satellite (120-1) is called a service link and may be based on NR standards defined by 3GPP. The link between the satellites (120-1, 120-2) and the gateway (130) is called a feeder link and may be based on a 3GPP or non-3GPP wireless interface. An inter-satellite link (ISL) may be used mainly for regenerative satellites.

[0052] For transparent satellites based on an NR-RAN architecture, the satellite radio interfaces of the feeder link and service link may be NR-Uu. For transparent satellites, the satellite performs radio frequency filtering, frequency conversion, and amplification functions. For regenerative satellites, onboard functions are built into the satellite, and accordingly, the satellite can perform radio frequency filtering, frequency conversion, and amplification, as well as some or all of the base station functions such as switching and routing, coding and modulation, and decoding and demodulation.

[0053] Each of the satellites (120-1, 120-2) according to the present disclosure may provide a cell having a coverage of a certain size to a terminal. Additionally, each of the satellites (120-1, 120-2) may be connected to a gateway (130) via a feeder link. Herein, the link may be a link based on NR standards. Alternatively, a link newly defined in an advanced next-generation wireless communication system may be adaptively applied, or a link based on various interfaces of a communication system introduced by industry needs that are not NR standards may be applied. In the following, in relation to the present disclosure, a serving cell, a target cell, and a candidate cell may be mentioned, each corresponding to a serving satellite, a target satellite, and a candidate satellite, and may be used interchangeably.

[0054] A satellite (120-1) may refer to a satellite currently connected to a terminal in a satellite network to provide communication. For example, a satellite (120-1) may include a geostationary satellite, a low-orbit satellite, a medium-orbit satellite, a polar orbit satellite, an elliptical orbit satellite, etc., and is not limited to any type. In addition, the satellites presented in this disclosure are not limited to a specific satellite configuration and may include any satellite or combination of satellites capable of providing a functional connection between the gateway (130) and the terminal (110).

[0055] The satellite (120-2) may refer to a new satellite that replaces the serving satellite when the terminal (110) is out of the beam coverage of the serving satellite or is located near the boundary, and the signal strength received by the terminal (110) satisfies the handover condition. The satellite (120-2) may refer to a satellite that can be selected as a target satellite in a satellite network. That is, the satellite (120-2) may be determined based on at least the satellite's visibility, signal strength, connection stability, latency, and network load.

[0056]

[0057] FIG. 2 illustrates another example of a satellite network according to one embodiment of the present disclosure. FIG. 2 illustrates an example of an NTN providing non-ground access to a UE (210) using an NTN payload (220) and an NTN gateway (230). Here, the UE (210) may be substantially the same configuration as the terminal (110) described in FIG. 1. Referring to FIG. 2, the link between the NTN payload (220) and the UE (210) is a service link and may be based on a Uu interface. The link between the NTN payload (220) and the NTN gateway (230) is a feeder link. The link between the NTN gateway (230) and the AMF / UPF (240) may be based on an NG interface. The NTN payload (220) can transparently forward wireless protocols received from the UE (210) to the NTN gateway (230) via the service link. Similarly, the NTN payload (220) can transparently forward wireless protocols received from the NTN gateway (230) via a feeder link to the UE (210).

[0058] To this end, the following connectivity may be supported by the NTN payload (220). A base station may service multiple NTN payloads. An NTN payload may be serviced by multiple base stations.

[0059] The NTN payload (220) can change the carrier frequency before retransmitting data on the service link. That is, the NTN payload (220) can use different carrier frequencies on the service link and the feed link. For the NTN, at least one of the following may be used as a network identifier: AMF name, NCGI (NR cell global identifier), CgNB ID (identifier), global gNB ID, TAI (tracking area identity), S-NSSAI (Single Network Slice Selection Assistance information), NSAG (Network Slice AS Group), NID (Network Identifier), CAG (Closed Access Group) ID, and local NG-RAN node ID (identifier). Additionally, a mapped cell ID may be used. Here, the tracking area may correspond to a fixed geographical area.

[0060] Non-geosynchronous orbits (NGSO) include a low Earth orbit at an altitude of about 300 km to 1500 km and a medium Earth orbit at an altitude of about 7000 km to 25000 km.

[0061] Service links can be classified into the following three types: earth-fixed, quasi-earth-fixed, and earth-moving. The earth-fixed type provides beam(s) that continuously cover the same geographical area at all times. For example, a satellite in a geosynchronous orbit (GSO) can provide an earth-fixed type service link. The quasi-earth-fixed type provides beam(s) that continuously cover the same geographical area for a limited period and beams that cover different geographical areas during different periods. For example, a satellite in a non-earth-synchronous orbit can provide a quasi-earth-fixed type service link using steerable beams. The earth-moving type provides beams where the coverage area slides across the Earth's surface. For example, a satellite with a non-Earth-synchronous orbit can provide an Earth-moving type service link using fixed or steerable beams.

[0062] By using a satellite with a non-Earth-synchronous orbit, the base station can provide quasi-Earth-fixed cell coverage or Earth-mobile cell coverage. By using a satellite with an Earth-synchronous orbit, the base station can provide Earth-fixed cell coverage. In the case of a non-Earth-synchronous orbit, a switch of the service link may be referred to a switch of the satellite (120-1).

[0063]

[0064] FIG. 3 illustrates the configuration of a device in a wireless communication system according to one embodiment of the present disclosure. The device of FIG. 3 may be understood as a part of the structure of any one of the devices described with reference to FIG. 1, for example, a terminal (110), satellites (120-1, 120-2), and a gateway (130).

[0065] Referring to FIG. 3, the device may include a processor (310), a communication unit (220), and a memory (330).

[0066] The processor (310) can control the overall function and operation of the device. The processor (310) may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits, and / or data processing devices.

[0067] The communication unit (320) is connected to the processor (310) to transmit and receive wireless signals. The communication unit (320) may include a baseband circuit for processing wireless signals. For example, the communication unit (320) may include a short-range communication unit, a mobile communication unit, and a broadcast reception unit. In one embodiment, the communication unit (320) may transmit and receive data to and from other devices, such as a base station, a satellite, etc.

[0068] Memory (330) is hardware that stores various data processed by the processor (310). For example, the memory (330) may store SIR values ​​for the transmission target terminals of the transmitting terminals, information regarding transmission target terminal groups for each transmitting terminal, etc. Additionally, the memory (330) may store applications, drivers, etc. to be driven by the processor (310). The memory (330) may include random access memory (RAM), such as dynamic random access memory (DRAM) and static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), CD-ROM, Blu-ray or other optical disc storage, hard disk drive (HDD), solid state drive (SSD), or flash memory.

[0069] The structure of FIG. 3 can be understood as at least part of a terminal, base station, satellite, or gateway. If the structure of FIG. 3 is part of a satellite, the satellite may further include other hardware devices necessary for orbiting in addition to the components exemplified in FIG. 3. If the structure of FIG. 3 is part of a gateway or base station, the gateway or base station may further include components that support wired communication, etc.

[0070]

[0071] The 3GPP 5G NR system supports the RRC_INACTIVE state to conserve terminal battery power and improve signaling efficiency. In a terrestrial network (TN), base stations are fixed, allowing for the transmission and reception of terminal contexts via the Xn interface between base stations or the stable reception of data via the core network. However, in non-terrestrial network environments utilizing low-orbit satellites, particularly in regenerative relay payload environments where base station functions are embedded in satellites, satellites are constantly moving. For example, if the last-serving gNB that serviced a terminal in an RRC-inactive state moves to the other side of the Earth, the terminal may move out of the last satellite's service range. In this case, an NG Removal procedure is performed to disconnect the connection with the core network. According to conventional technology, when a terminal attempts to re-establish the RRC connection by connecting to a new gNB, the new gNB can request the terminal context of that terminal from the last gNB via the core network. However, if the last satellite has already disconnected from the core network through the NG Removal procedure, the core network cannot deliver a terminal context request to the last satellite, causing the RRC connection reset procedure to fail. This results in not only the failure of the RRC connection reset but also unnecessary reconnection attempts (e.g., RRC Setup) and paging failures, thereby degrading service quality and wasting wireless resources. Specifically, the limitations of the existing procedure will be explained through Figures 4 and 5 below.

[0072]

[0073] FIG. 4 illustrates an example of an RRC rejection procedure according to one embodiment of the present disclosure.

[0074] Referring to FIG. 4, in step S401, the terminal (410) can perform an RRC deactivation procedure with the second base station (430). Specifically, if data transmission and reception do not occur for a certain period of time or if RRC connection disconnection is required according to network control, the terminal (410) disconnects the wireless connection with the second base station (430), which is the serving base station, and transitions to an RRC deactivation state.

[0075] Meanwhile, the second base station (430) may refer to a satellite currently connected to the terminal (410) to provide communication. The first base station (420) may refer to a satellite that is replaced by a serving satellite when the serving satellite, the second base station (430), moves out of beam coverage or when the signal strength received by the terminal satisfies the handover condition.

[0076] In step S403, the second base station (430) transmits an NG removal request to the core network (440). For example, the second base station (430) may identify that it is out of service coverage area due to mobility or cannot maintain an NG interface with the existing core network (440), and transmit an NG interface removal request to the core network (440).

[0077] In step S405, the second base station (430) receives an NG removal response from the core network (440). Specifically, the second base station (430) may receive an NG removal response indicating that NG removal with the core network (440) has been completed.

[0078] In step S407, the first base station (420) receives an RRC connection resumption request from the terminal (410). For example, the terminal (410) may transmit an RRC connection resumption request to the first base station (420) based on an RNAU (RAN-based Notification Area Update) or uplink data generation. Specifically, to return the terminal (410) to the RRC connection state directly, the terminal (410) transmits an RRC connection resumption request message to a connectable base station. The RRC connection resumption request may be transmitted to the first base station (420) as the satellite that replaces the serving satellite when the second base station (430), which is the last serving satellite, moves out of beam coverage or when the signal strength received by the terminal (410) satisfies the handover condition. Meanwhile, the RRC connection resumption request message may include an I-RNTI (Temporary Identifier) ​​assigned by the second base station (430) that previously provided the last service.

[0079] In step S409, the first base station (420) transmits a terminal context search request to the core network (440). Specifically, the first base station (420) transmits a terminal context search request to the core network (440) to obtain the terminal context of the terminal that requested the resumption of the RRC connection.

[0080] In step S411, the core network (440) transmits a terminal context search request to the second base station (430). However, since the NG interface with the core network (440) is disabled, the request fails.

[0081] Accordingly, at step S413, the core network (413) transmits a terminal context search response to the first base station (420) including a failure to acquire the terminal context, and at step S415, the first base station (420) transmits an RRC rejection to the terminal (410). For example, the RRC rejection message may include cause information indicating that the terminal context is unavailable. Upon receiving the RRC rejection, the terminal (410) may recognize that immediate resumption of the RRC connection through the first base station (420) is not possible.

[0082] In step S415, the terminal (410) may perform an RRC connection resumption after the timer expires. Specifically, after receiving an RRC rejection message, the terminal (410) may wait until a pre-set retry timer expires and then re-perform the RRC connection resumption procedure. For example, after the timer expires, the terminal (410) may re-transmit an RRC connection resumption request to the same base station or a new serving base station.

[0083]

[0084] FIG. 5 illustrates an example of an RRC setup procedure according to another embodiment of the present disclosure.

[0085] Referring to FIG. 5, in step S501, the terminal (510) can perform an RRC deactivation procedure with the second base station (530). Specifically, if data transmission and reception do not occur for a certain period of time or if RRC connection disconnection is required according to network control, the terminal (510) disconnects the wireless connection with the second base station (530), which is the serving base station, and transitions to an RRC deactivation state.

[0086] Meanwhile, the second base station (530) may refer to a satellite currently connected to the terminal (510) to provide communication. The first base station (520) may refer to a satellite that is replaced by a serving satellite when the serving satellite, the second base station (530), moves out of beam coverage or when the signal strength received by the terminal satisfies the handover condition.

[0087] In step S503, the second base station (530) transmits an NG removal request to the core network (540). For example, the second base station (530) may identify that it is out of service coverage area due to mobility or cannot maintain an NG interface with the existing core network (540), and transmit an NG interface removal request to the core network (540).

[0088] In step S505, the second base station (530) receives an NG removal response from the core network (540). Specifically, the second base station (530) may receive an NG removal response indicating that NG removal with the core network (540) has been completed.

[0089] In step S507, the first base station (520) receives an RRC connection resumption request from the terminal (510). For example, the terminal (510) may transmit an RRC connection resumption request to the first base station (520) based on RNAU or uplink data generation. Specifically, to return the terminal (510) to a direct RRC connection state, the terminal (510) transmits an RRC connection resumption request message to a connectable base station. The RRC connection resumption request may be transmitted to the first base station (520) as the satellite that replaces the serving satellite when the second base station (530), which is the last serving satellite, moves out of beam coverage or when the signal strength received by the terminal (510) satisfies the handover condition. Meanwhile, the RRC connection resumption request message may include an I-RNTI assigned by the second base station (530) that previously provided the last service.

[0090] In step S509, the first base station (520) transmits a terminal context search request to the core network (540). Specifically, the first base station (520) transmits a terminal context search request to the core network (540) to obtain the terminal context of the terminal that requested the resumption of the RRC connection.

[0091] In step S511, the core network (540) transmits a terminal context search request to the second base station (530). However, since the NG interface with the core network (540) is disabled, the request fails.

[0092] Accordingly, in step S513, the core network (513) transmits a terminal context search response including failure to acquire terminal context to the first base station (520), and in step S515, the first base station (520) transmits an RRC setup to the terminal (510).

[0093] In step S517, the terminal (510) can perform an RRC setup procedure with the first base station (520) and a new RRC connection setup procedure.

[0094]

[0095] To solve the problem described above, the present disclosure below proposes a method for transferring and backing up the terminal context in advance when the last serving satellite performs the NG removal procedure with the core network due to satellite mobility. Through this, the present disclosure enables a new satellite to obtain the terminal context from the core network even after the NG interface has been removed, thereby ensuring the success of RRC connection reset, RNAU, and paging procedures and preventing service interruption.

[0096]

[0097] FIG. 6 illustrates an example of a terminal context transmission procedure according to one embodiment of the present disclosure.

[0098] Referring to FIG. 6, in step S601, the terminal (610) can perform an RRC deactivation procedure with the second base station (630). Specifically, if data transmission and reception do not occur for a certain period of time or if RRC connection disconnection is required according to network control, the terminal (610) disconnects the wireless connection with the second base station (630), which is the serving base station, and transitions to an RRC deactivation state.

[0099] Meanwhile, the second base station (630) may refer to a satellite currently connected to the terminal (610) to provide communication. The first base station (620) may refer to a satellite that is replaced by a serving satellite when the serving satellite, the second base station (630), moves out of beam coverage or when the signal strength received by the terminal satisfies the handover condition.

[0100] In step S603, the second base station (630) transmits an NG removal request to the core network (640). For example, the second base station (630) may identify that it is out of service coverage area due to mobility or cannot maintain an NG interface with the existing core network (640), and transmit an NG interface removal request to the core network (640).

[0101] Meanwhile, according to an embodiment of the present disclosure, the second base station (630) may transmit a terminal context based on the transmission of an NG removal request message to the core network (640). For example, the second base station (630) may include information regarding the terminal contexts of terminals in an RRC disabled state in the NG removal request message. That is, the second base station (630) may transmit information regarding the terminal contexts of terminals in an RRC disabled state to the core network (640) as at least part of the NG removal request message. Additionally, according to an embodiment, the second base station (630) may generate a protocol for transmitting the terminal context to the core network (640) in conjunction with the NG removal request message transmission procedure. That is, the second base station (630) may transmit the NG removal request message to the core network (640) and transmit a message containing the terminal context to the core network (640). According to the embodiment described above, the second base station (630) can transmit the terminal context of the terminal (610) to the core network (640).

[0102] In step S605, the second base station (630) receives an NG removal response from the core network (640). Specifically, the core network (640) may save the terminal context based on the NG interface removal request of step S603 and transmit an NG removal response indicating that NG removal with the second base station (630) is complete. That is, through the NG removal response, the NG interface is removed, and the NG removal response may include a message indicating that the terminal context has been saved to the core network (640).

[0103] In step S607, the second base station (630) transmits the completion of terminal context release to the core network (640). Specifically, the second base station (630) releases the terminal context based on the transmission of an NG removal response from the core network (640) and transmits the completion of terminal context release to the core network (640). That is, as the terminal context of the terminal (610) is stored in the core network (640), the second base station (630) releases the terminal context to clean up the terminal context that is no longer needed to be maintained, and transmits the result to the core network (640).

[0104] In step S609, the first base station (620) receives an RRC connection resumption request from the terminal (610). Specifically, in order for the terminal (610) to return to the RRC connection state directly, the terminal (610) transmits an RRC connection resumption request message to a connectable base station. Meanwhile, since the first base station (620) is the satellite that replaces the second base station (630), which is the last serving satellite, the RRC connection resumption request may be transmitted to the first base station (620). Meanwhile, the RRC connection resumption request message may include an I-RNTI assigned by the second base station (630), which previously provided the last service.

[0105] In step S611, the first base station (620) transmits a terminal context search request to the core network (640). Specifically, the first base station (620) transmits a terminal context search request to the core network (640) to obtain the terminal context of the terminal (610) that requested the resumption of the RRC connection.

[0106] In step S613, the core network (640) confirms that the NG has been removed. Specifically, the core network (640) confirms with the second base station (630) that transmitted the terminal context of the RRC connection resumption target terminal (610) whether the NG has been removed. The above step can be understood as a procedure in which the core network (640) receives the terminal context from the second base station (630) and confirms that storage is complete.

[0107] In step S615, the core network (640) transmits a terminal context search response to the first base station (620). Specifically, the core network (640) transmits the terminal context of the RRC connection resumption target terminal (610) to the first base station (620). Meanwhile, according to an embodiment, if NG removal is not confirmed in step S613, the core network (640) may transmit a terminal context search response indicating that the terminal context is non-existent.

[0108] In step S617, the first base station (620) transmits an RRC connection resumption to the terminal (610). Specifically, the first base station (620) transmits an RRC connection resumption response to the terminal (610) to complete the RRC connection resumption with the terminal (610) using the received terminal context.

[0109] In step S619, the terminal (610) changes to an RRC connection state. That is, the terminal (610) transitions to an RRC connection state in accordance with the RRC connection resumption response received from the first base station (620).

[0110] In step S621, the terminal (610) transmits a connection resumption completion to the first base station (620). That is, the terminal (610) transmits a connection resumption completion message to the first base station (620) indicating that the RRC connection resumption has been completed.

[0111] In step S623, the first base station (620) transmits a route change request to the core network (640). For example, as the serving base station of the terminal (610) changes to the first base station (620), the first base station (620) may transmit a route change request message to the core network (640) to switch the paths of the user plane and the control plane for the terminal (610).

[0112] In step S625, the first base station (620) receives a route change response message from the core network (640). Specifically, the core network (640) confirms that the transmission paths of the user plane and control plane for the terminal (610) have been updated based on the route switch request message transmitted by the first base station (620), and can transmit a confirmation message to the first base station (620).

[0113]

[0114] An NG removal request message according to one embodiment of the present disclosure may include information regarding terminal contexts of terminals in an RRC disabled state. That is, information regarding terminal contexts of terminals in an RRC disabled state may be included as at least part of the NG removal request message. For example, information regarding terminal contexts may include a list of terminal contexts of terminals in an RRC disabled state (or, an inactive terminal context list; Inactive UE context List). That is, the NG removal request message may be defined by adding an inactive terminal context list field as a new information element (IE). The configuration of the NG removal request message including the terminal context list field as a new information element is as shown in Table 1 below.

[0115] IE / Group Name Presence IE Type and Reference Semantics Description Message Type M9.3.1.1 Identification of message type Global RAN Node IDM9.3.1.1 Global ID of the satellite base station to be disconnected Inactive UE Context List O (New) Field added according to the present invention > Inactive UE Item M Information item per terminal >> AMF UE NGAP IDM9.3.1.1 Terminal identifier within AMF >> NG-RAN node UE NGAP IDM9.3.1.2 Terminal identifier within the base station >> UE Context Information M9.2.2.1 3 in 3GPP TS 38.426 AS (Access Stratum) terminal context information required for RRC Resume (including RRC settings, security key, C-RNTI, I-RNTI, etc.)

[0116] The following describes a procedure in which a new satellite obtains a terminal context from the core network and ensures the success of the paging procedure, even after the NG interface has been removed.

[0117] FIG. 7 illustrates an example of a terminal context transmission procedure according to another embodiment of the present disclosure.

[0118] In step S701, the terminal (710) can perform an RRC deactivation procedure with the second base station (730). Specifically, if data transmission and reception do not occur for a certain period of time or if RRC disconnection is required according to network control, the terminal (710) disconnects the wireless connection with the second base station (730), which is the serving base station, and transitions to an RRC deactivation state.

[0119] Meanwhile, the second base station (730) may refer to a satellite currently connected to the terminal (710) to provide communication. The first base station (720) may refer to a satellite that is replaced by a serving satellite when the serving satellite, the second base station (730), moves out of beam coverage or when the signal strength received by the terminal satisfies the handover condition.

[0120] In step S703, the second base station (730) transmits an NG removal request to the core network (740). For example, the second base station (730) may identify that it is out of service coverage area due to mobility or cannot maintain an NG interface with the existing core network (740), and transmit an NG interface removal request to the core network (740).

[0121] Meanwhile, according to an embodiment of the present disclosure, the second base station (730) may transmit a terminal context based on the transmission of an NG removal request message to the core network (740). For example, the second base station (730) may include information regarding the terminal contexts of terminals in an RRC disabled state in the NG removal request message. That is, the second base station (730) may transmit information regarding the terminal contexts of terminals in an RRC disabled state to the core network (740) as at least part of the NG removal request message. Additionally, according to an embodiment, the second base station (730) may generate a protocol for transmitting the terminal context to the core network (740) in conjunction with the NG removal request message transmission procedure. That is, the second base station (730) may transmit the NG removal request message to the core network (740) and transmit a message containing the terminal context to the core network (740). According to the embodiment described above, the second base station (730) can transmit the terminal context of the terminal (710) to the core network (740).

[0122] In step S705, the second base station (730) receives an NG removal response from the core network (740). Specifically, the core network (740) may save the terminal context based on the NG interface removal request of step S703 and transmit an NG removal response indicating that NG removal with the second base station (730) is complete. That is, through the NG removal response, the NG interface is removed, and the NG removal response may include a message indicating that the terminal context has been saved to the core network (740).

[0123] In step S707, the second base station (730) transmits the completion of terminal context release to the core network (670). Specifically, the second base station (730) releases the terminal context based on the transmission of an NG removal response from the core network (740) and transmits the completion of terminal context release to the core network (740). That is, as the terminal context of the terminal (710) is stored in the core network (740), the second base station (730) releases the terminal context to clean up the terminal context that is no longer needed to be maintained, and transmits the result to the core network (740).

[0124] In step S709, the core network (740) receives downlink data. Specifically, the core network (740) may receive downlink data to be delivered to the terminal (710) from an external data network or a user plane function within the core network.

[0125] In step S711, the core network (740) confirms that the NG has been removed. Specifically, the core network (740) confirms with the second base station (730) that transmitted the terminal context of the RRC connection resumption target terminal (710) whether the NG has been removed. The above step can be understood as a procedure in which the core network (740) receives the terminal context from the second base station (730) and confirms that storage is complete.

[0126] In step S713, the core network (740) transmits a RAN paging request to the first base station (720). The core network (740) recognizes that a terminal context for the terminal (710) is already stored in the core network (740) and can perform delivery processing for the corresponding downlink data based on the stored terminal context. Specifically, the core network (740) can use the stored terminal context to transmit a RAN paging request to the first base station (720) capable of serving the terminal (710). According to an embodiment, the RAN paging request may include a terminal context for the terminal (710).

[0127] In step S715, the first base station (720) identifies a RAN paging trigger. For example, the first base station (720) may identify a RAN paging trigger based on receiving downlink data or a RAN paging request from the core network (740). Specifically, when the first base station (720) receives downlink data from the User Plane Function (UPF) of the core network (740) or receives a downlink terminal association signal from the Access and Mobility Management Function (AMF), it may perform cell-level paging for the terminal (710).

[0128] In step S717, the first base station (720) performs RAN paging with the terminal (710). Specifically, the first base station (720) can transmit a paging message according to the paging occasions available to the terminal (710) by using terminal identification information and paging-related parameters included in the terminal context.

[0129]

[0130] The following describes a procedure in which a new satellite acquires a terminal context from the core network and ensures the success of the terminal's RNAU, even after the NG interface has been removed.

[0131] FIG. 8 illustrates an example of a terminal context transmission procedure according to another embodiment of the present disclosure.

[0132] Referring to FIG. 8, in step S801, the terminal (810) can perform an RRC deactivation procedure with the second base station (830). Specifically, if data transmission and reception do not occur for a certain period of time or if RRC connection disconnection is required according to network control, the terminal (810) disconnects the wireless connection with the second base station (830), which is the serving base station, and transitions to an RRC deactivation state.

[0133] Meanwhile, the second base station (830) may refer to a satellite currently connected to the terminal (810) to provide communication. The first base station (820) may refer to a satellite that is replaced by a serving satellite when the serving satellite, the second base station (830), moves out of beam coverage or when the signal strength received by the terminal satisfies the handover condition.

[0134] In step S803, the second base station (830) transmits an NG removal request to the core network (840). For example, the second base station (830) may identify that it is out of service area due to mobility or cannot maintain an NG interface with the existing core network (840), and transmit an NG interface removal request to the core network (840).

[0135] Meanwhile, according to an embodiment of the present disclosure, the second base station (830) may transmit a terminal context based on the transmission of an NG removal request message to the core network (840). For example, the second base station (830) may include information regarding the terminal contexts of terminals in an RRC disabled state in the NG removal request message. That is, the second base station (830) may transmit information regarding the terminal contexts of terminals in an RRC disabled state to the core network (840) as at least part of the NG removal request message. Additionally, according to an embodiment, the second base station (830) may generate a protocol for transmitting the terminal context to the core network (840) in conjunction with the NG removal request message transmission procedure. That is, the second base station (830) may transmit the NG removal request message to the core network (840) and transmit a message containing the terminal context to the core network (840). According to the embodiment described above, the second base station (830) can transmit the terminal context of the terminal (810) to the core network (840).

[0136] In step S805, the second base station (830) receives an NG removal response from the core network (840). Specifically, the core network (840) may save the terminal context based on the NG interface removal request of step S803 and transmit an NG removal response indicating that NG removal with the second base station (830) is complete. That is, through the NG removal response, the NG interface is removed, and the NG removal response may include a message indicating that the terminal context has been saved to the core network (840).

[0137] In step S807, the second base station (830) transmits the completion of terminal context release to the core network (840). Specifically, the second base station (830) releases the terminal context based on the transmission of an NG removal response from the core network (840) and transmits the completion of terminal context release to the core network (840). That is, as the terminal context of the terminal (810) is stored in the core network (840), the second base station (830) releases the terminal context to clean up the terminal context that is no longer needed to be maintained, and transmits the result to the core network (840).

[0138] In step S809, the first base station (820) receives an RRC connection resumption request from the terminal (810). In order for the terminal (810) to return to a direct RRC connection state for the RNAU upon completion of the RNAU (RAN-based Notification Area Update) timer, it is required to transmit an RRC connection resumption request message containing the RNAU to a base station that the terminal (810) can connect to. Specifically, to return the terminal (810) to a direct RRC connection state, the terminal (810) transmits an RRC connection resumption request message to a base station that can connect. Meanwhile, since the first base station (820) is the satellite that replaces the second base station (830), which is the last serving satellite, the RRC connection resumption request may be transmitted to the first base station (820). Meanwhile, the RRC connection resumption request message may include an I-RNTI assigned by the second base station (830), which previously provided the last service.

[0139] In step S811, the first base station (820) transmits a terminal context search request to the core network (840). Specifically, the first base station (820) transmits a terminal context search request to the core network (840) to obtain the terminal context of the terminal (810) that requested the resumption of the RRC connection.

[0140] In step S813, the core network (840) confirms that the NG has been removed. Specifically, the core network (840) confirms with the second base station (830) that transmitted the terminal context of the RRC connection resumption target terminal (810) whether the NG has been removed. The above step can be understood as a procedure in which the core network (840) receives the terminal context from the second base station (830) and confirms that storage is complete.

[0141] In step S815, the core network (840) transmits a terminal context search response to the first base station (820). Specifically, the core network (840) transmits the terminal context of the RRC connection resumption target terminal (810) to the first base station (820). Meanwhile, according to an embodiment, if NG removal is not confirmed in step S813, the core network (840) may transmit a terminal context search response indicating that the terminal context is non-existent. Based on the received terminal context, the first base station (820) receives an RNAU from the terminal (820) and performs an RRC deactivation procedure with the terminal (810).

[0142] In step S817, the first base station (820) transmits a route change request to the core network (840). For example, as the serving base station of the terminal (810) is changed to the first base station (820), the first base station (820) may transmit a route change request message to the core network (840) to switch the paths of the user plane and control plane for the terminal (810).

[0143] In step S819, the first base station (820) receives a route change response message from the core network (840). Specifically, the core network (840) confirms that the transmission paths of the user plane and control plane for the terminal (810) have been updated based on the route switch request message transmitted by the first base station (820), and can transmit a confirmation message to the first base station (820).

[0144] In step S821, the first base station (820) transmits a Suspend Indication to the terminal (810). Specifically, the first base station (820) may transmit the Suspend Indication to release the RRC with the terminal (810) after the RNAU.

[0145]

[0146] FIG. 9 illustrates an example of an operation procedure of a first base station according to one embodiment of the present disclosure.

[0147] Referring to FIG. 9, in step S901, the first base station receives an RRC resumption request. According to an embodiment, in order for the terminal to return to an RRC connection state directly based on the completion of an RNAU timer, etc., the terminal transmits an RRC connection resumption request message to a connectable base station. Meanwhile, since the first base station is a satellite that is replaced as a serving satellite following the second base station, which is the last serving satellite, the RRC connection resumption request may be transmitted to the first base station.

[0148] In step S903, the first base station transmits a terminal context search request to the core network. Specifically, the first base station transmits a terminal context search request to the core network to obtain the terminal context of the terminal that requested the resumption of the RRC connection.

[0149] In step S905, the first base station receives a terminal context search response based on the confirmation of the removal of the NG interface between the core network and the second base station. According to an embodiment, the terminal context may be transmitted from the second base station, which is the last serving satellite, to the core network. At this time, the terminal context may be transmitted to the core network based on the removal of the NG interface between the second base station and the core network. Meanwhile, in response to the terminal context search request, the core network may determine whether to back up the terminal context by confirming the removal of the NG interface with the second base station. That is, the core network checks whether the NG interface with the second base station has been removed, and if the NG interface has been removed, it may transmit the backed-up terminal context to the first base station. Accordingly, the first base station may perform the resumption of the RRC connection with the terminal using the acquired terminal context.

[0150]

[0151] FIG. 10 illustrates an example of an operation procedure of a second base station according to one embodiment of the present disclosure.

[0152] Referring to FIG. 10, in step S1001, the second base station performs an RRC deactivation procedure with the terminal. Specifically, if data transmission and reception to the terminal does not occur for a certain period of time or if RRC connection disconnection is required according to network control, the second base station disconnects the wireless connection with the terminal and transitions the terminal to an RRC deactivation state.

[0153] In step S1003, the second base station performs a procedure to remove the NG interface with the core network. For example, the second base station may identify that it is out of service area due to mobility or that it cannot maintain the existing NG interface with the core network, and may send a request to remove the NG interface to the core network.

[0154] Additionally, the second base station may transmit terminal contexts based on the transmission of an NG removal request message to the core network. For example, the second base station may transmit information regarding terminal contexts of terminals in an RRC disabled state to the core network as at least part of the NG removal request message.

[0155] In step S1005, the second base station transmits the completion of terminal context release to the core network. Specifically, as the terminal context is backed up to the core network, the second base station releases the terminal context to clean up the terminal context that is no longer needed to be maintained, and transmits the result thereof to the core network.

[0156]

[0157] FIG. 11 illustrates an example of an operation procedure of a core network according to one embodiment of the present disclosure.

[0158] Referring to FIG. 11, in step S1101, the core network performs a procedure to remove the NG interface with the second base station. For example, the core network may perform a procedure to remove the NG interface with the second base station when the second base station moves out of the service area due to mobility or when it is unable to maintain the NG interface with the core network.

[0159] Meanwhile, according to an embodiment of the present disclosure, the core network may receive the terminal context of the second base station in an NG removal procedure. For example, the NG removal request message transmitted from the second base station may include information regarding the terminal contexts of terminals in an RRC disabled state. That is, information regarding the terminal contexts of terminals in an RRC disabled state may be included as at least part of the NG removal request message. Additionally, the core network may store the terminal context based on the NG interface removal request and transmit an NG removal response indicating that NG removal with the second base station has been completed.

[0160] In step S1103, the core network receives the completion of terminal context release. Specifically, as the terminal context of the terminal is stored in the core network, the second base station cleans up the terminal context that is no longer needed to be maintained and releases the terminal context, and may transmit the result thereof to the core network.

[0161] In step S1105, the core network receives a terminal context search request. Specifically, the first base station, which is a new serving base station that has received an RRC connection resumption request from a terminal, transmits a terminal context search request to the core network to obtain the terminal context of the terminal.

[0162] In step S1107, the core network transmits a terminal context search response based on confirmation of the removal of the NG interface with the second base station. Specifically, according to the embodiment, the terminal context may be transmitted to the core network from the second base station, which is the last serving satellite. At this time, the terminal context may be transmitted to the core network based on the removal of the NG interface between the second base station and the core network. Accordingly, the core network confirms the removal of the NG interface with the second base station and determines that the terminal context has been backed up. If the removal of the NG interface is confirmed, the core network confirms that the terminal context has been backed up and may transmit the stored terminal context to the first base station.

[0163]

[0164] Through the procedure described above, the present disclosure backs up the terminal context to the core network's AMF before the last base station removes the NG interface from the core network, thereby preventing failure to acquire the terminal context during RRC connection reconfiguration and RNAU even when the NG interface is removed. Furthermore, the present disclosure can shorten the service resumption time of the terminal by preventing the RRC rejection and RRC setup process caused by failure to acquire the terminal context. Additionally, the present disclosure can reduce signaling overhead by explicitly releasing the resources of the last base station in conjunction with the removal of the NG interface and subsequently omitting release procedures following unnecessary route switching. Furthermore, the present disclosure can increase the reception success rate by preventing paging attempts to disconnected base stations and enabling paging to valid satellite areas led by the core network's AMF.

[0165]

[0166] Meanwhile, those skilled in the art related to the present embodiment will understand that it may be implemented in modified forms without departing from the essential characteristics of the above description. Therefore, the disclosed methods should be considered in an illustrative rather than a restrictive sense. The scope of the present disclosure is defined by the claims, not by the foregoing description, and all variations within the scope of equivalence should be interpreted as being included in the present disclosure.

[0167]

[0168] The present disclosure relates to a wireless communication system, and in particular, can be used in a device for transmitting terminal context between base stations in a wireless communication system.

Claims

1. In a method of operating a first base station in a wireless communication system, A step of receiving an RRC connection resumption request from a terminal; The step of transmitting a search request for the terminal context of the terminal to the core network; and A method comprising the step of receiving a search response of the terminal context based on the confirmation of removal of the NG interface between the core network and the second base station.

2. In Paragraph 1, The above terminal context is, A method stored in the core network based on a request to remove the NG interface to the core network of the second base station.

3. In Paragraph 1, The above-mentioned second base station is, A method for releasing the terminal context based on the NG interface removal response of the core network.

4. In Paragraph 2, The above request to remove the NG interface is, A method comprising a list of terminal contexts of terminals in an RRC disabled state.

5. In Paragraph 1, Receiving a RAN paging request from the core network based on the RNA (RAN Notification Area) of the terminal obtained from the terminal context; and A method further comprising the step of performing RAN paging with the above terminal.

6. In a first base station of a wireless communication system, Transmitter / receiver; and It includes a processor connected to the above-mentioned transmitter and receiver, The above processor is, Receives a request to resume the RRC connection from the terminal, and Sending a search request for the terminal context of the above terminal to the core network, and A first base station receiving a search response of the terminal context based on the confirmation of removal of the NG interface between the core network and the second base station.

7. In Paragraph 6, The above terminal context is, A first base station stored in the core network based on a request to remove the NG interface to the core network of the second base station.

8. In Paragraph 6, The above-mentioned second base station is, A first base station that releases the terminal context based on the NG interface removal response from the core network.

9. In Paragraph 7, The above request to remove the NG interface is, A first base station comprising a list of terminal contexts for terminals in an RRC disabled state.

10. In Paragraph 6, The above processor is, Receive a RAN paging request from the core network based on the RNA of the terminal obtained from the terminal context, and A first base station that performs RAN paging with the above terminal.

11. In a method of operating a second base station in a wireless communication system, Step of performing the terminal and RRC disable procedure; Step of performing a procedure to remove the core network and NG interface; and A method comprising the step of transmitting to the core network the completion of releasing the terminal context for the terminal in the RRC disabled state.

12. In Paragraph 11, The above terminal context is, Based on the request to remove the NG interface to the core network of the second base station, it is stored in the core network, and A method in which, when a first base station transmits a search request for a terminal context, the request is transmitted to the first base station based on the confirmation of removal of the NG interface with the second base station of the core network.

13. In Paragraph 11, The step of transmitting the completion of release of the above terminal context to the core network is, A method comprising the step of releasing the terminal context based on the NG interface removal response of the core network.

14. In Paragraph 12, The above request to remove the NG interface is, A method comprising a list of terminal contexts of terminals in an RRC disabled state.

15. In Paragraph 12, The above-mentioned first base station is, Receiving a RAN paging request from the core network based on the RNA of the terminal obtained from the terminal context; and A method further comprising the step of performing RAN paging with the above terminal.

16. In a second base station of a wireless communication system, Transmitter / receiver; and It includes a processor connected to the above-mentioned transmitter and receiver, The above processor is, Perform the RRC disable procedure with the terminal, and Perform the procedure to remove the core network and NG interface, and A second base station that transmits to the core network the completion of the release of the terminal context for the terminal in the RRC disabled state.

17. In a method of operation of a core network in a wireless communication system, A step of performing a procedure to remove the NG interface between the second base station and the NG; A step of receiving from the second base station the completion of the release of the terminal context for a terminal in an RRC disabled state; A step of receiving a search request for the terminal context from a first base station that has received an RRC connection resumption request from the terminal; and A method comprising the step of transmitting a search response of the terminal context based on confirmation of removal of the NG interface with the second base station.

18. In Paragraph 17, The step of performing the above NG interface removal procedure is: A method stored in the core network based on a request to remove the NG interface of the second base station.

19. In Paragraph 17, Step of receiving downlink data; and A method further comprising the step of transmitting a RAN paging request to the first base station based on the RNA of the terminal obtained from the terminal context.

20. In a core network of a wireless communication system, Transmitter / receiver; and It includes a processor connected to the above-mentioned transmitter and receiver, The above processor is, Perform the procedure to remove the NG interface with the second base station, and Receive from the second base station completion of the release of the terminal context for a terminal in an RRC disabled state, and Receiving a search request for the terminal context from the first base station that received an RRC connection resumption request from the terminal, and A core network that transmits a search response of the terminal context based on confirmation of removal of the NG interface with the second base station.

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