Device and method for managing terminal contexts in wireless communication system

Abstract

The present disclosure relates to a wireless communication system, and particularly to an operation method of a second base station in a wireless communication system, the method comprising the steps of: classifying terminal contexts on the basis of a timer; transmitting a relocation request for the terminal contexts on the basis of the classification; receiving a relocation response for the terminal contexts; and releasing an RRC connection with terminals to which the terminal contexts have been relocated.

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 a terminal context management device and method in a wireless communication system.

[0005] The present disclosure is intended to provide an apparatus and method for classifying terminal contexts based on a timer.

[0006] The present disclosure is intended to provide an apparatus and method for transmitting a request for the relocation of terminal contexts to base stations based on classification.

[0007] The present disclosure is intended to provide an apparatus and method for receiving relocation responses from base stations in which terminal contexts have been relocated.

[0008] The present disclosure is intended to provide an apparatus and method for performing RRC disconnection with terminals in which terminal contexts have been relocated.

[0009] The present disclosure is intended to provide an apparatus and method for determining a first timer indicating a RAN-based Notification Area Update (RNAU) timer of a terminal and a second timer indicating a service provision timer of a non-ground base station.

[0010] The present disclosure is intended to provide an apparatus and method for classifying terminal contexts into a first group when a first timer exceeds a second timer.

[0011] The present disclosure is intended to provide an apparatus and method for classifying terminal contexts into a second group when the first timer is less than the second timer.

[0012] The present disclosure is intended to provide an apparatus and method for transmitting terminal contexts included in a first group to a third base station, which is a ground base station.

[0013] The present disclosure is intended to provide an apparatus and method for transmitting terminal contexts included in a second group to a first base station connected by a satellite link.

[0014] According to one aspect of the present disclosure, when a method of operation of a second base station in a wireless communication system is disclosed, the method may include the steps of classifying terminal contexts based on a timer, transmitting a relocation request for the terminal contexts based on the classification, receiving a relocation response for the terminal contexts, and performing RRC disconnection with the terminals to which the terminal contexts have been relocated.

[0015] According to one embodiment of the present disclosure, the timer may include a first timer indicating a RAN-based Notification Area Update (RNAU) timer of a terminal and a second timer indicating a service provision timer of a non-ground base station.

[0016] According to another embodiment of the present disclosure, the step of classifying the terminal contexts may include classifying the terminal contexts into a first group when the first timer exceeds the second timer, and classifying the terminal contexts into a second group when the first timer is less than the second timer.

[0017] According to another embodiment of the present disclosure, the step of transmitting a relocation request for the terminal contexts may include transmitting the terminal contexts included in the first group to a third base station.

[0018] According to another embodiment of the present disclosure, the step of transmitting a relocation request for the terminal contexts may include transmitting the terminal contexts included in the second group to the first base station.

[0019] According to another embodiment of the present disclosure, the method may further include the step of transmitting the terminal context from the first base station when the first base station receives an RRC connection resumption request from a terminal and the terminal context of the terminal is included in the first group.

[0020] According to another aspect of the present disclosure, a second base station is disclosed in a wireless communication system, the second base station comprises a transceiver and a processor connected to the transceiver, the processor classifying terminal contexts based on a timer, transmitting a relocation request for the terminal contexts based on the classification, receiving a relocation response for the terminal contexts, and performing RRC disconnection with the terminals to which the terminal contexts have been relocated.

[0021] According to another aspect of the present disclosure, a method of operation of a third base station in a wireless communication system is disclosed, wherein the third base station may include the steps of receiving a request for relocation of terminal contexts classified based on a timer from a second base station, transmitting a response for relocation of the terminal contexts to the second base station, receiving a request to search for the terminal context of the terminal from the first base station in response to a request to resume an RRC connection of the terminal to the first base station, transmitting the terminal context to the first base station, and receiving a release of the terminal context from the first base station.

[0022] According to another aspect of the present disclosure, a third base station in a wireless communication system comprises a transceiver and a processor connected to the transceiver, wherein the processor receives a request for relocation of terminal contexts classified based on a timer from a second base station, transmits a response for relocation of the terminal contexts to the second base station, receives a request for retrieval of the terminal context from the first base station in response to a request for resumption of RRC connection of the terminal to the first base station, transmits the terminal context to the first base station, and receives a release of the terminal context from the first base station.

[0023] According to another aspect of the present disclosure, a method of operation of a first base station in a wireless communication system may include: receiving a relocation request for terminal contexts classified based on a timer from a second base station; transmitting a relocation response for the terminal contexts to the second base station; receiving an RRC connection resumption request from a terminal; transmitting a terminal context search request for the terminal to the second base station or a third base station based on the classification of the terminal contexts; and transmitting an RRC connection resumption response based on the terminal context.

[0024] 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 receives a request for relocation of terminal contexts classified based on a timer from a second base station, transmits a response for relocation of the terminal contexts to the second base station, receives a request for resumption of RRC connection from a terminal, transmits a request for retrieval of the terminal context of the terminal to the second base station or a third base station based on the classification of the terminal contexts, and transmits a response for resumption of RRC connection based on the terminal context.

[0025] According to another aspect of the present disclosure, a method of operation of a terminal in a wireless communication system is disclosed, the method comprising: receiving an RRC release from a second base station; requesting a first base station to resume an RRC connection based on identifying the need for an RRC connection; receiving an RRC connection resumption response from the first base station; and transmitting a completion of the RRC connection resumption to the first base station, wherein the first base station may receive a terminal context of the terminal from the second base station or the third base station according to the rearrangement of terminal contexts classified based on a timer.

[0026] According to embodiments of the present disclosure, terminal context management can be effectively performed in a wireless communication system.

[0027] FIG. 1 illustrates an example of a satellite network according to one embodiment of the present disclosure.

[0028] FIG. 2 illustrates another example of a satellite network according to one embodiment of the present disclosure.

[0029] FIG. 3 illustrates the configuration of a device in a wireless communication system according to one embodiment of the present disclosure.

[0030] FIG. 4 illustrates an example of a terminal context management method procedure in a wireless communication system according to one embodiment of the present disclosure.

[0031] FIG. 5 illustrates an example of a procedure for relocating a terminal context in a wireless communication system according to one embodiment of the present disclosure.

[0032] FIG. 6 illustrates an example of a procedure for performing RRC connection resumption in a wireless communication system according to one embodiment of the present disclosure.

[0033] FIG. 7 illustrates an example of an operation procedure of a second base station according to one embodiment of the present disclosure.

[0034] FIG. 8 illustrates an example of a procedure for relocating a terminal context at a second base station according to one embodiment of the present disclosure.

[0035] FIG. 9 illustrates an example of an operation procedure of a third base station according to one embodiment of the present disclosure.

[0036] FIG. 10 illustrates an example of an operation procedure of a first base station according to one embodiment of the present disclosure.

[0037] FIG. 11 illustrates an example of an operation procedure of a terminal according to one embodiment of the present disclosure.

[0038] FIG. 12 illustrates an example of a connection point between a terminal and base stations according to one embodiment of the present disclosure.

[0039] 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.

[0040] 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.

[0041] 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.

[0042]

[0043] The present disclosure relates to a non-terrestrial network (NTN) system and to a method for efficiently partitioning and managing the terminal context 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.

[0044] The 3GPP 5G NR (New Radio) system defines an RRC disabled state (RRC_INACTIVE) in addition to the RRC connected state (RRC_CONNECTED) and RRC idle state (RRC_IDLE) to reduce battery consumption of terminals and decrease signaling overhead.

[0045] The RRC disabled state refers to a state where only the radio connection is disconnected while the terminal and the base station (gNodeB or gNB) maintain a mutual terminal context, and the terminal can quickly return to the RRC connected state through the RRC Resume procedure when data transmission and reception are required.

[0046] In a terrestrial network (TN) environment, base stations operate from fixed locations, so even if a terminal moves, the procedures for exchanging or retrieving terminal context between adjacent base stations via the Xn or X2 interfaces can be performed relatively stably. On the other hand, in non-terrestrial network environments utilizing low-orbit satellites, satellites acting as base stations move at high speeds. Consequently, there is a possibility that by the time a terminal that was in an RRC-inactive state wakes up and requests the RRC resumption procedure, the previous satellite storing the terminal context may have already moved out of the terminal's communication range. Additionally, if the connection status of the link between satellites is unstable, the new base station may not be able to properly acquire the terminal context from the previous satellite. In such situations, the RRC resumption procedure fails, and the terminal must re-execute the RRC setup procedure; as a result, service delays may increase and unnecessary signaling traffic may be generated.

[0047] Accordingly, the present disclosure aims to provide a method for partitioning and 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.

[0048]

[0049] FIG. 1 illustrates an example of a satellite network according to one embodiment of the present disclosure.

[0050] 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).

[0051] 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.

[0052] 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 second base station, and satellite (120-2) may mean a first base station. Satellite (120-1) may mean a base station currently connected to the terminal (110) to provide services. Meanwhile, satellite (120-2) may mean a base station newly connected to the terminal (110) to provide services after satellite (120-1). Gateway (130) provides the satellites (120-1, 120-2) with a link to access a network. That is, 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).

[0053] 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.

[0054] 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.

[0055] Each of the satellites (120-1, 120-2) according to the present disclosure can provide a cell with a coverage of a certain size to a terminal. Additionally, each of the satellites (120-1, 120-2) can be connected to a gateway (130) via a feeder link. Here, the link may be a link based on NR standards. Alternatively, a newly defined link 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.

[0056] 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).

[0057] The satellite (120-2) may refer to a satellite that is replaced by a serving satellite when the signal strength received by the terminal (110) satisfies the handover condition as the terminal (110) moves out of the beam coverage of the serving satellite or is located near the boundary. 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.

[0058]

[0059] 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).

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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).

[0065]

[0066] 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).

[0067] Referring to FIG. 3, the device may include a processor (310), a communication unit (220), and a memory (330).

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072]

[0073] Due to satellite mobility, the serving satellite servicing a terminal continuously changes, which can frequently necessitate the transfer of the terminal context to a new satellite. For the new satellite to re-establish the RRC connection with the terminal or perform paging procedures, the satellite currently servicing the terminal must receive the terminal context from the previous satellite.

[0074] In such an environment, if the terminal context of all RRC-disabled terminals is transmitted collectively via inter-satellite links or feeder links, a massive concentration of signaling may occur, potentially leading to a signaling storm. This raises concerns that link capacity may be exceeded or overall network performance may degrade. In particular, if inter-satellite link connections are unstable or disconnected, or if satellites are located in positions where inter-satellite communication is impossible, the transmission of the terminal context itself becomes impossible, making it difficult to guarantee service continuity for RRC-disabled terminals.

[0075] Accordingly, the present disclosure aims to provide a technique for solving the aforementioned problems by comparing timers associated with a terminal and a base station and determining where to maintain the terminal's context information based on the comparison result. Specifically, the present disclosure provides a Hybrid UE Context Relocation technique that selectively determines whether to maintain the terminal's context information within a satellite network or to back it up to a terrestrial fixed network node. In this case, the terrestrial fixed network node may include, for example, an Anchor gNB or an Access and Mobility Management Function (AMF) of the core network.

[0076] According to the present disclosure, the RRC resumption procedure of a terminal can be successfully performed even in an environment where no inter-satellite link exists or the connection state is unstable, thereby preventing service delays caused by the re-execution of the RRC setup. In addition, according to the present disclosure, efficient utilization of network resources can be promoted by minimizing unnecessary terrestrial network signaling.

[0077]

[0078] FIG. 4 illustrates an example of a terminal context management method procedure in a wireless communication system according to one embodiment of the present disclosure.

[0079] Referring to FIG. 4, in step S401, base stations (420, 430, 440) perform terminal context relocation. For example, base stations (420, 430, 440) may classify terminal contexts based on the characteristics of terminal (410) and relocate terminal contexts based on the classification results. According to an embodiment, base stations (420, 430, 440) may determine a group of terminal contexts based on the report timer of terminal (410) and the service timer of base stations (420, 430, 440). At this time, according to an embodiment, the location where the terminal context of terminal (410) is delivered or stored may be determined by the group containing the terminal context. For example, the second base station (430) may control the delivery of the terminal context to the first base station (420) or storage on the side of the third base station (440) based on the group containing the context of terminal (410).

[0080] Meanwhile, the first base station (420) may refer to a satellite that is replaced by a serving satellite when the timer for service provision is satisfied, when the serving satellite moves out of beam coverage, or when the signal strength received by the terminal (410) satisfies the handover condition. The second base station (430) may refer to a satellite currently connected to the terminal (410) to provide communication. The third base station (440) may refer to a fixed network node on the ground, such as an anchor base station or a core network (e.g., an AMF). The base stations (420, 430, 440) may be connected to each other via inter-satellite links or feeder links. According to an embodiment, the first base station (420) and the second base station (430) may be connected via inter-satellite links, and the second base station (430) and the third base station (440) may be connected via feeder links.

[0081] That is, in step S401, the second base station (430) classifies terminal contexts before leaving the service area and transmits the terminal contexts to the next satellite, the first base station (420), via the Xn interface (e.g., inter-satellite link), or transmits them to the ground fixed network node, the third base station (440), via the NG interface (e.g., feeder link). Additionally, according to the embodiment, the second base station (430) may store the terminal contexts as they are. Thus, if the terminal context of a terminal requiring RRC connection resumption is stored in the first base station (420), the first base station (420) can perform the RRC connection resumption procedure using the stored terminal context. Additionally, if the terminal context of a terminal requiring RRC connection resumption is stored in the third base station (440), the first base station (430) can perform the RRC connection resumption procedure using the terminal context stored in the third base station (440).

[0082] In step S403, the third base station (440) transmits a path switch request to the core network (450). Specifically, the second base station (440) transmits a path switch request message to the core network (450). For example, the third base station (440) may transmit a path switch request message to the core network (450) to switch the paths of the User Plane and Control Plane for the terminal (410) as the serving base station of the terminal (410) is changed or released.

[0083] In step S405, the third base station (440) receives a path switch request confirmation from the core network (450). Specifically, the core network (450) confirms that the transmission paths of the user plane and control plane for the terminal (410) have been updated based on the path switch request message transmitted by the third base station (440), and can transmit a confirmation message to the third base station (440).

[0084] In step S407, the second base station (430) transmits an RRC release to the terminal (410). For example, specifically, the second base station (430) may perform an RRC deactivation procedure to disconnect the wireless connection with the terminal (410) and transition to an RRC deactivation state when data transmission and reception do not occur for a certain period of time or when an RRC connection release is required according to network control.

[0085] In step S409, the terminal (410) changes to an RRC disabled state. For example, the terminal (410) transitions to an RRC disabled state upon receiving an RRC release from the second base station (430), and disconnects the wireless connection while maintaining the terminal context corresponding to the RRC disabled state.

[0086] In the case of resuming the connection by the terminal, at step S411, the terminal (410) checks for the occurrence of RNAU (RAN-based Notification Area Update) or uplink data. The terminal (410) monitors whether uplink data has occurred in a data session or service flow and can recognize if uplink data has occurred. If the occurrence of uplink data is confirmed, the terminal (410) can prepare a procedure to perform RRC connection resumption with the first base station (420) or the second base station (430).

[0087] In step S413, the terminal (410) performs an RRC connection resumption. For example, if the first base station (420) is located in the service area of ​​the terminal (410), the terminal (410) can perform an RRC connection resumption with the first base station (420). At this time, if the terminal context of the terminal (410) for which an RRC connection resumption is required is stored in the first base station (420), the first base station (420) can perform an RRC connection resumption procedure using the stored terminal context. Additionally, if the terminal context of the terminal (410) for which an RRC connection resumption is required is stored in the third base station (440), the first base station (430) can perform an RRC connection resumption procedure using the terminal context stored in the third base station (440). Additionally, for example, if the second base station (430) is still located in the service area of ​​the terminal (410), the terminal (410) can perform an RRC connection resumption with the second base station (430). At this time, the second base station (430) can perform an RRC connection resumption procedure using the previously stored terminal context.

[0088] In the case of resuming the connection by the core network, at step S415, the core network (450) confirms the occurrence of downlink data. Specifically, the core network (450) monitors whether downlink data has been received in a data session or service flow corresponding to the terminal (410), and can recognize if downlink data has occurred. If the occurrence of downlink data is confirmed, the core network (450) can prepare a paging procedure or a data delivery procedure for the terminal (410).

[0089] In step S417, the third base station (430) can transmit a RAN paging message to the first base station (420) or the second base station (430). For example, if the first base station (420) is located in the service area of ​​the terminal (410), the third base station (440) can transmit a RAN paging message to the first base station (420). Also, for example, if the second base station (430) is located in the service area of ​​the terminal (410), the third base station (440) can transmit a RAN paging message to the second base station (430).

[0090] In step S419, the first base station (420) transmits a paging request message to the terminal (410). Specifically, the first base station (420) can transmit a paging message in accordance with the paging occasions available to the terminal (410) by using terminal identification information and paging-related parameters. According to an embodiment, if the second base station (430) is located in the service area of ​​the terminal (410), the second base station (430) can transmit a paging request message to the terminal (410).

[0091] In step S421, the terminal (410) performs an RRC connection resumption. For example, if the first base station (420) is located in the service area of ​​the terminal (410), the terminal (410) can perform an RRC connection resumption with the first base station (420). At this time, if the terminal context of the terminal (410) for which an RRC connection resumption is required is stored in the first base station (420), the first base station (420) can perform an RRC connection resumption procedure using the stored terminal context. Additionally, if the terminal context of the terminal (410) for which an RRC connection resumption is required is stored in the third base station (440), the first base station (430) can perform an RRC connection resumption procedure using the terminal context stored in the third base station (440). Additionally, for example, if the second base station (430) is still located in the service area of ​​the terminal (410), the terminal (410) can perform an RRC connection resumption with the second base station (430). At this time, the second base station (430) can perform an RRC connection resumption procedure using the previously stored terminal context.

[0092]

[0093] FIG. 5 illustrates an example of a procedure for relocating a terminal context in a wireless communication system according to one embodiment of the present disclosure.

[0094] The first base station (510) may refer to a satellite that is replaced by a serving satellite when the timer for service provision is satisfied, when the serving satellite moves out of beam coverage, or when the signal strength received by the terminal satisfies the handover condition. The second base station (520) may refer to a satellite currently connected to the terminal to provide communication. The third base station (530) may refer to a fixed network node on the ground, such as an anchor base station or a core network (e.g., an AMF). The base stations (510, 520, 230) may be connected to each other via inter-satellite links or feeder links. According to an embodiment, the first base station (510) and the second base station (520) may be connected via inter-satellite links, and the second base station (520) and the third base station (530) may be connected via feeder links.

[0095] Referring to FIG. 5, in step S501, the second base station (520) classifies terminal contexts based on a timer. According to an embodiment, the location where the terminal context of a terminal is to be delivered or stored may be determined by the group to which the terminal context is included. For example, the second base station (520) may control the delivery of the terminal context to the first base station (510) or to store it on the side of the third base station (530) based on the group to which the terminal is included.

[0096] For example, the second base station (520) may classify the terminal context using a first timer indicating the terminal's RNAU timer and a second timer indicating the service provision timer of the non-ground base station. According to an embodiment, the first timer may refer to a timer that determines the wake-up cycle for the terminal to periodically report its location, the RNA (RAN Notification Area), to the network while in an inactive state. For example, the first timer may be specified differently according to the service policy, such as 5 minutes, 10 minutes, 20 minutes, and 30 minutes. The first timer may be specified to the terminal through the periodicRNAU-TimerValue field within the suspendConfig of the RRC release message. Meanwhile, according to an embodiment, the second timer may refer to the time remaining until the serving satellite currently servicing the terminal can no longer provide service to the terminal due to orbital movement. That is, the second timer may refer to the remaining time until a handover to the next satellite occurs.

[0097] In step S503, the second base station (520) transmits a terminal context relocation request to the first base station (510) or the third base station (530). For example, the second base station (520) may transmit the terminal context relocation request to the first base station (510) if, through a comparison of the first timer and the second timer, it is expected that the time when the terminal wakes up for the RNAU will remain at the second base station (520), which is the current serving satellite, or will change to the first base station (510). Additionally, for example, the second base station (520) may transmit the terminal context relocation request to the third base station (530) if, through a comparison of the first timer and the second timer, the time when the terminal wakes up for the RNAU is after the service provision timer of the second base station (520), which is the current serving satellite, and the first base station (510).

[0098] That is, when the terminal wakes up for RNAU, if the second base station (520) can resume RRC connection with the second base station (520), which is the current serving satellite, or the first base station (510), which is directly connected to the second base station (520) via a satellite link, in order to save unnecessary ground backhaul traffic, the terminal context may not be transmitted to the third base station (530), which is a fixed node on the ground, but may be stored as is or transmitted to the first base station (510). Additionally, when the terminal wakes up for RNAU, if the second base station (520) cannot resume RRC connection with the second base station (520), which is the current serving satellite, or the first base station (510), which is directly connected to the second base station (520) via a satellite link, due to the expiration of the service provision timer, the terminal context may be transmitted to the third base station (530), which is a fixed node on the ground.

[0099] In step S505, the second base station (520) receives a terminal context response. The second base station (520) receives a response to the terminal context relocation request from the first base station (510) or the third base station (530), and confirms that the transfer or storage of the terminal context has been successfully completed based on the response.

[0100]

[0101] FIG. 6 illustrates an example of a procedure for performing RRC connection resumption in a wireless communication system according to one embodiment of the present disclosure.

[0102] The first base station (610) may refer to a satellite that is replaced by a serving satellite when the timer for service provision is satisfied, when the serving satellite moves out of beam coverage, or when the signal strength received by the terminal satisfies the handover condition. The second base station (620) may refer to a satellite currently connected to the terminal to provide communication. The third base station (630) may refer to a fixed network node on the ground, such as an anchor base station or a core network (e.g., an AMF). The base stations (610, 620, 630) may be connected to each other via inter-satellite links or feeder links. According to an embodiment, the first base station (610) and the second base station (620) may be connected via inter-satellite links, and the second base station (620) and the third base station (630) may be connected via feeder links. Below, the description will focus on the case where the serving satellite is replaced from the second base station (630) to the first base station (620).

[0103] Referring to FIG. 6, in step S601, the terminal (610) transmits an RRC Resume Request to the first base station (620). For example, the terminal (610) monitors whether uplink data has occurred in a data session or service flow, and if uplink data has occurred, it can transmit an RRC Resume Request to the first base station (620). Additionally, for example, the terminal (610) can transmit an RRC Resume Request to the first base station (620) based on the recognition of downlink data occurrence from the core network (650).

[0104] In step S603, the first base station (620) requests a terminal context search from the second base station (630) or the third base station (640). For example, if the terminal context of the terminal (610) is stored in the third base station (640), the first base station (620) may request a terminal context search from the third base station (640). Also, for example, if the terminal context of the terminal (610) is stored in the second base station (630), the first base station (620) may request a terminal context search from the second base station (630). Also, for example, if the terminal context of the terminal (610) is stored in the first base station (620), the first base station (620) may perform an RRC connection resumption procedure using the stored terminal context. The first base station (620) may check whether the terminal context is stored in it based on its cache. Additionally, according to an embodiment, the first base station (620) may request terminal context search from both the second base station (630) and the third base station (640).

[0105] In step S605, the first base station (620) receives a terminal context response from the second base station (630) or the third base station (640). For example, if the first base station (620) requests a terminal context search from the third base station (640), it may receive a terminal context response from the third base station (640). Also, for example, if the first base station (620) requests a terminal context search from the second base station (630), it may receive a terminal context response from the second base station (630). The terminal context response may include the terminal context of the terminal (610). Additionally, according to an embodiment, if the first base station (620) transmits a terminal context search request to both the second base station (630) and the third base station (640), the terminal context response may include the terminal context of the terminal (610) or include information indicating that there is no terminal context.

[0106] In step S607, the first base station (620) transmits an RRC connection resumption response to the terminal (610). Based on the received terminal context, the first base station (620) transmits an RRC connection resumption response (RRC Resume Response) to the terminal (610) to complete the resumption of the RRC connection with the terminal (610).

[0107] In step S609, 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).

[0108] In step S611, 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.

[0109] In step S613, the first base station (620) transmits a path switch request to the core network (650). For example, the first base station (620) may transmit a path switch request message to the core network (650) to switch the paths of the user plane and control plane for the terminal (610) as the serving base station of the terminal (610) changes to the first base station (620).

[0110] In step S615, the first base station (620) receives a path switch response message from the core network (650). Specifically, the core network (650) confirms that the transmission paths of the user plane and control plane for the terminal (610) have been updated based on the path switch request message transmitted by the first base station (620), and can transmit a confirmation message to the first base station (620).

[0111] In step S617, the first base station (620) transmits a terminal context release to the second base station (630) or the third base station (640). After the resumption of the RRC connection with the terminal (610) is completed, the first base station (620) transmits a terminal context release request to the second base station (630) or the third base station (640) to clean up the terminal context that is no longer needed to be maintained.

[0112]

[0113] FIG. 7 illustrates an example of an operation procedure of a second base station according to one embodiment of the present disclosure. The operating entity of FIG. 7 is described as a second base station, and the second base station may refer to a serving satellite currently connected to a terminal and providing communication services.

[0114] Referring to FIG. 7, in step S701, the second base station classifies terminal contexts based on a timer. According to an embodiment, the location where the terminal context of a terminal is to be delivered or stored may be determined by the group to which the terminal context is included. For example, the second base station may control the delivery of the terminal context to the first base station or storage at the third base station based on the group to which the terminal is included.

[0115] The first base station may, for example, be a base station configured to serve a terminal after the service provider for the terminal has changed from the second base station. Here, the first base station refers to a base station that performs the role of serving the terminal after the second base station, and may include at least one base station selected to perform service provision to the terminal after the second base station has left the service area, among base stations connected to the second base station via a satellite link. The third base station is a fixed network node on the ground and may refer to an anchor base station or a core network (e.g., an AMF).

[0116] For example, a second base station may classify the terminal context using a first timer indicating the terminal's RNAU timer and a second timer indicating the service provision timer of a non-ground base station. According to an embodiment, the first timer may refer to a timer that determines the wake-up cycle for the terminal to periodically report its location, the RNA (RAN Notification Area), to the network while in an inactive state. Meanwhile, according to an embodiment, the second timer may refer to the time remaining until the serving satellite currently serving the terminal can no longer provide service to the terminal due to orbital movement.

[0117] In step S703, the second base station transmits a request for the relocation of terminal contexts. For example, the second base station may transmit a request for the relocation of terminal contexts to the first base station if, through a comparison of the first timer and the second timer, it is expected that the time when the terminal wakes up for the RNAU will remain at the second base station, which is the current serving satellite, or will change to the first base station. Additionally, for example, the second base station may transmit a request for the relocation of terminal contexts to the third base station if, through a comparison of the first timer and the second timer, it is expected that the time when the terminal wakes up for the RNAU is after the service provision timer of the second base station, which is the current serving satellite, and the first base station. That is, before leaving the service area, the second base station classifies the terminal contexts and transmits the terminal contexts to the next satellite, the first base station, via the Xn interface (e.g., inter-satellite link), or transmits them to the third base station, which is a fixed network node on the ground, via the NG interface (e.g., feeder link).

[0118] In step S705, the second base station receives a response regarding the relocation of terminal contexts. The second base station receives a response to the request for terminal context relocation from the first base station or the third base station, and confirms that the transfer or storage of the terminal context has been successfully completed based on the response.

[0119] In step S707, the second base station disconnects the RRC connection with the terminal. For example, specifically, if data transmission and reception do not occur for a certain period of time or if disconnection of the RRC connection is required by network control, the second base station may perform an RRC deactivation procedure to disconnect the wireless connection with the terminal and transition to an RRC deactivation state.

[0120]

[0121] FIG. 8 illustrates an example of a procedure for relocating a terminal context at a second base station according to an embodiment of the present disclosure. The operating entity of FIG. 8 is described as a second base station, and the second base station may refer to a serving satellite currently connected to the terminal and providing communication services.

[0122] Referring to FIG. 8, in step S801, the second base station determines whether the terminal's timer exceeds the satellite switch timer. The terminal's timer may refer to a first timer indicating the terminal's RNAU timer. According to an embodiment, the first timer may refer to a timer that determines the cycle for the terminal to wake up periodically to report its RNA, which is its location, to the network while in an inactive state. The satellite switch timer may refer to a second timer indicating the time remaining until the serving satellite currently serving the terminal can no longer provide service to the terminal due to orbital movement.

[0123] For example, the first timer may include a T380 timer, which means an RNAU timer. The T380 timer may be assigned any one of the periodicRNAU-TimerValues ​​defined in the 3GPP standard. For example, the first timer may be assigned 5 minutes, 10 minutes, 20 minutes, and 30 minutes, etc., but is not limited to the examples described above.

[0124] Meanwhile, the second timer can be obtained by calculating by the second base station based on satellite orbit information (Ephemeris data) configured from the network management system (Operation, Administration and Maintenance, OAM) and the terminal's location information. Specifically, the network management system may provision orbit parameters to the second base station that include at least one of the satellite's orbital inclination angle, altitude, and movement speed, and the second base station may predict the time of loss of coverage when a terminal at a specific location leaves the coverage of the second base station by using the orbit parameters and the terminal's location information. The second base station may determine the second timer based on the time when each satellite leaves the coverage.

[0125] In step S803, if the terminal's timer exceeds the satellite switching timer, the second base station classifies the terminal context into the first group and transmits the terminal context to the third base station. If the terminal's timer exceeds the satellite switching timer, the time at which the terminal wakes up for the RNAU corresponds to a state where the second base station cannot provide communication services to the terminal because the time at which the terminal wakes up exceeds the communication service availability time of the second base station. Therefore, if the second base station anticipates that at the time the terminal wakes up for the RNAU, it will be impossible to resume the RRC connection with the second base station, which is the current serving satellite, or with the first base station, which is directly connected via a link between the second base station and the satellite, due to the expiration of the satellite switching timer, the terminal context may be transmitted to the third base station, which is a fixed node on the ground.

[0126] In step S805, if the terminal's timer is less than the satellite switching timer, the second base station classifies the terminal context into a second group and transmits the terminal context to the first base station. If the terminal's timer is less than the satellite switching timer, the time when the terminal wakes up for the RNAU exists within the communication service availability time of the second base station, so it corresponds to a state where the second base station can provide communication services to the terminal. That is, if the terminal and the second base station can resume the RRC connection, the second base station may not transmit the terminal context to the third base station, which is a fixed node on the ground, in order to save unnecessary ground backhaul traffic, but may store it as is or transmit it to the first base station.

[0127] That is, the second base station can predict the terminal's short-term or long-term sleep relative to the satellite switching time based on the terminal's timer and satellite switching timer, and reassign terminal contexts.

[0128] In step S807, the second base station receives a relocation response for the terminal contexts. The second base station receives a response regarding the transmitted terminal contexts from the first base station or the third base station and confirms that the delivery or storage of the terminal contexts has been successfully completed.

[0129]

[0130] FIG. 9 illustrates an example of an operation procedure of a third base station according to one embodiment of the present disclosure. The operating entity of FIG. 9 is described as a third base station, and the third base station may include a ground base station connected by a feeder link to a serving satellite currently connected to a terminal and providing communication services.

[0131] Referring to FIG. 9, in step S901, the third base station receives a relocation request for terminal contexts from the second base station. The second base station may refer to a serving satellite currently connected to the terminal and providing communication services. Specifically, the third base station may receive a relocation request including the terminal context of the terminal from the second base station if, through a comparison of the first timer and the second timer, the time when the terminal wakes up for the RNAU is after the service provision timer of the second base station, which is the current serving satellite, and the first base station, which is the next serving satellite.

[0132] In step S903, the third base station transmits a relocation response of terminal contexts to the second base station. The third base station may transmit a relocation response to the second base station that includes information indicating that the terminal contexts have been successfully received.

[0133] In step S905, the third base station receives a terminal context search request from the first base station. For example, if the terminal context of a terminal is stored in the third base station, the third base station may receive a terminal context search from the first base station. Specifically, if the terminal's timer exceeds the satellite switching timer, the first base station determines that the terminal context of the terminal belongs to the first group and may transmit a terminal context search request to the third base station.

[0134] In step S907, the third base station transmits the terminal context to the first base station. Specifically, the third base station transmits the stored terminal context to the first base station so that the first base station can perform an RRC connection resumption procedure with the terminal based on the terminal context.

[0135] In step S909, the third base station receives the release of the terminal context from the first base station. That is, the third base station may receive a request to release the terminal context from the first base station to clean up the terminal context that is no longer needed after the first base station has completed the resumption of the RRC connection with the terminal.

[0136]

[0137] FIG. 10 illustrates an example of an operation procedure of a first base station according to an embodiment of the present disclosure. The operating entity of FIG. 10 is described as the first base station, and the first base station may include, for example, a base station that performs a serving role for a terminal after a second base station which is currently a serving base station.

[0138] Referring to FIG. 10, in step S1001, the first base station receives a relocation request for terminal contexts from the second base station. The second base station may refer to a serving satellite currently connected to the terminal and providing communication services. Specifically, the first base station may receive a relocation request including the terminal context of the terminal from the second base station if, through a comparison of the first timer and the second timer, the time when the terminal wakes up for the RNAU is prior to the time when the service provision timer of the second base station, which is the current serving satellite, and the service provision timer of the first base station, which is the next serving satellite, are prior.

[0139] In step S1003, the first base station transmits a relocation response of terminal contexts to the second base station. The third base station may transmit a relocation response to the second base station that includes information indicating that the terminal contexts have been successfully received.

[0140] In step S1005, the first base station receives an RRC connection resumption request from the terminal. For example, the terminal monitors whether uplink data has occurred in a data session or service flow, and if uplink data has occurred, it may transmit an RRC connection resumption request to the first base station. Additionally, for example, the terminal may transmit an RRC connection resumption request to the first base station based on the detection of downlink data from the core network.

[0141] In step S1007, the first base station determines whether the terminal's timer exceeds the satellite switching timer. If the terminal's timer exceeds the satellite switching timer, the time when the terminal wakes up for the RNAU exceeds the communication service availability time of the second base station, and thus the second base station is unable to provide communication services to the terminal. On the other hand, if the terminal's timer is less than the satellite switching timer, the time when the terminal wakes up for the RNAU exists within the communication service availability time of the second base station, and thus the second base station is able to provide communication services to the terminal.

[0142] In step S1009, if the terminal's timer exceeds the satellite switching timer, the first base station transmits a terminal context search request to the third base station. Meanwhile, in step S1011, if the terminal's timer is less than the satellite switching timer, the first base station transmits a terminal context search request to the second base station. According to an embodiment, if the terminal context of the terminal is stored in the first base station, the first base station may perform an RRC connection resumption procedure using the stored terminal context.

[0143] In step S1013, the first base station transmits an RRC connection resumption response based on the terminal context. Based on the received terminal context, the first base station transmits an RRC connection resumption response to the terminal to complete the resumption of the RRC connection with the terminal.

[0144]

[0145] FIG. 11 illustrates an example of an operation procedure of a terminal according to one embodiment of the present disclosure.

[0146] Referring to FIG. 11, in step S1101, the terminal receives an RRC release from the second base station. Specifically, if data transmission and reception do not occur for a certain period of time or if an RRC connection release is required according to network control, the terminal may perform an RRC deactivation procedure to release the wireless connection with the second base station and transition to an RRC deactivation state. Meanwhile, the second base station may be a serving base station that provides communication services to the terminal.

[0147] In step S1103, the terminal may transmit a request to resume the RRC connection to the first base station based on the identification of the need for an RRC connection. For example, the terminal may transmit a request to resume the RRC connection to the first base station upon confirmation of the occurrence of RNAU or uplink data. The first base station may include a base station that performs the role of serving the terminal after the second base station, which is currently serving the terminal. That is, if the provision of service to the terminal by the second base station is terminated according to the control protocol, the terminal may transmit a request to resume the RRC connection to the first base station. Additionally, according to another embodiment, the terminal may transmit a request to resume the RRC connection to the second base station upon confirmation of the occurrence of RNAU or uplink data. For example, if the need for an RRC connection is identified and the second base station is capable of providing service to the terminal according to the control protocol, the terminal may transmit a request to resume the RRC connection to the second base station.

[0148] In step S1105, the terminal receives an RRC connection resumption response from the first base station. Specifically, the first base station may transmit an RRC connection resumption response to the terminal to complete the resumption of the RRC connection with the terminal based on the terminal context. According to an embodiment, the first base station may obtain a terminal context from the second base station or the third base station based on the relocation of terminal contexts classified based on a timer. Meanwhile, the third base station may be a fixed network node on the ground.

[0149] In step S1107, the terminal transmits the completion of RRC connection resumption to the first base station. That is, the terminal transmits a connection resumption completion message to the first base station indicating that the RRC connection resumption has been completed.

[0150]

[0151] FIG. 12 illustrates an example of a connection point between a terminal and base stations according to one embodiment of the present disclosure.

[0152] Referring to Fig. 12, Serving Sat refers to the serving base station connected to the terminal. Sat 2 may refer to the satellite base station connected to the terminal after Serving Sat due to the expiration of t_sat switch1. t_sat switch1 refers to a timer at which Serving Sat can no longer provide service to the terminal, and when t_sat switch1 expires at a specific point in time, the terminal handovers from Serving Sat to Sat 2. Sat 3 may refer to the satellite base station connected to the terminal after Sat 1 due to the expiration of t_sat switch2. t_sat switch2 refers to a timer at which Sat 1 can no longer provide service to the terminal, and when t_sat switch 2 expires at a specific point in time, the terminal handovers from Sat 1 to Sat 2.

[0153] Meanwhile, according to one embodiment of the present disclosure, based on the present, prior to RRC release, Serving Sat relocates the context of the terminal. For example, Serving Sat may classify terminal contexts based on a timer, and the timer may include a first timer indicating the terminal's RNAU timer and a second timer indicating the service provision timer of a non-terrestrial base station. For example, the first timer may include T380, which is a period in which the terminal is paginated to periodically report its RNA to the network.

[0154] According to an embodiment, Serving Sat may classify terminal contexts into a first group when the first timer exceeds the second timer, and classify terminal contexts into a second group when the first timer is less than the second timer. Serving Sat may transmit terminal contexts included in the first group to a ground base station, and terminal contexts included in the second group to Sat 2.

[0155] For example, Serving Sat can determine that the time when the terminal is paginated is included within the time connected to Serving Sat because the T380 of the first terminal (UE 1) is less than t_sat switch1. Accordingly, Serving Sat can save the terminal context of the first terminal as is or transmit it to Sat 2. Additionally, for example, Serving Sat can determine that the target for pagination of the terminal is Sat 2 because the T380 of the second terminal (UE 1) is greater than t_sat switch1 and less than t_sat switch2. Accordingly, Serving Sat can transmit the terminal context of the second terminal to the ground base station. Additionally, for example, Serving Sat can determine that the target for pagination of the terminal is Sat 3 because the T380 of the third terminal (UE 3) is greater than t_sat switch2. Accordingly, Serving Sat can transmit the terminal context of the third terminal to the ground base station.

[0156] According to an embodiment, when the second terminal performs an RRC connection resumption with Sat 2, Sat 2 may obtain the terminal context of the second terminal from the ground base station. Likewise, when the third terminal performs an RRC connection resumption with Sat 3, Sat 3 may obtain the terminal context of the third terminal from the ground base station.

[0157] According to the present disclosure, the terminal context can be reliably retrieved through a fixed network node on the ground even when a satellite link does not exist or is disconnected, thereby reducing dependency on the satellite link. Additionally, by enabling the terminal to resume the connection through an RRC connection resumption procedure without re-executing the RRC setup procedure, the latency required for resuming the wireless connection can be reduced and service responsiveness can be improved. Furthermore, by processing the terminal context within the satellite network when the time the terminal wakes up falls within the satellite's service provision time, and transmitting it to a fixed network node on the ground only in other cases, unnecessary ground backhaul traffic can be suppressed and the network load can be effectively distributed.

[0158]

[0159] 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.

[0160] 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 second base station in a wireless communication system, A step of classifying terminal contexts based on a timer; A step of transmitting a request for relocation of the terminal contexts based on the above classification; A step of receiving a relocation response of the above terminal contexts; and A method comprising the step of performing RRC disconnection with the terminals to which the above terminal contexts have been relocated.

2. In Paragraph 1, The above timer is, A method comprising a first timer indicating a RNAU (RAN-based Notification Area Update) timer of a terminal and a second timer indicating a service provision timer of a non-ground base station.

3. In Paragraph 2, The step of classifying the above terminal contexts is, When the first timer exceeds the second timer, a step of classifying the terminal contexts into a first group; and A method comprising the step of classifying the terminal contexts into a second group when the first timer is less than the second timer.

4. In Paragraph 3, The step of transmitting a request for relocation of the above terminal contexts is: A method comprising the step of transmitting the terminal contexts included in the first group to a third base station.

5. In Paragraph 3, The step of transmitting a request for relocation of the above terminal contexts is: A method comprising the step of transmitting the terminal contexts included in the second group to a first base station.

6. In Paragraph 3, The above method is, A method comprising the step of a first base station receiving an RRC connection resumption request from a terminal, and, if the terminal context of the terminal is included in the first group, transmitting the terminal context from the first base station.

7. 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, Classify terminal contexts based on a timer, and Based on the above classification, a request for the relocation of the above terminal contexts is transmitted, and Receive a relocation response of the above terminal contexts, and A second base station that performs RRC disconnection with the terminals to which the above terminal contexts have been relocated.

8. In a method of operating a third base station in a wireless communication system, A step of receiving a request for relocation of terminal contexts classified based on a timer from a second base station; A step of transmitting a relocation response of the terminal contexts to the second base station; A step of receiving a terminal context search request from the first base station in response to a request from the terminal to resume an RRC connection to the first base station; The step of transmitting the terminal context to the first base station; and A method comprising the step of receiving the release of the terminal context from the first base station.

9. In Paragraph 8, The above timer is, A method comprising a first timer indicating an RNAU timer of a terminal and a second timer indicating a service provision timer of a non-ground base station.

10. In Paragraph 9, The above terminal contexts are, If the first timer exceeds the second timer, the terminal contexts are classified into a first group, and A method in which, when the first timer is less than the second timer, the terminal contexts are classified into a second group.

11. In Paragraph 10, The step of receiving a relocation request for the above-described classified terminal contexts is: A method comprising the step of receiving a relocation request for the terminal contexts included in the first group.

12. In Paragraph 10, The step of receiving the above terminal context search request is, A method comprising the step of receiving a terminal context search request from the first base station in response to a request to resume the RRC connection of the terminal to the first base station when the terminal context of the terminal is included in the first group.

13. In a third 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, Receive a request for the relocation of terminal contexts classified based on a timer from the second base station, and Transmitting a relocation response of the terminal contexts to the second base station, and In response to a request from a terminal to resume an RRC connection to a first base station, a terminal context search request from the terminal is received from the first base station, and Transmit the above terminal context to the first base station, and A third base station receiving the release of the terminal context from the first base station.

14. In a method of operating a first base station in a wireless communication system, A step of receiving a request for relocation of terminal contexts classified based on a timer from a second base station; A step of transmitting a relocation response of the terminal contexts to the second base station; A step of receiving an RRC connection resumption request from a terminal; Based on the classification of the above terminal contexts, the step of transmitting a terminal context search request of the terminal to the second base station or the third base station; and A method comprising the step of transmitting an RRC connection resumption response based on the above terminal context.

15. In Paragraph 14, The above timer is, A method comprising a first timer indicating an RNAU timer of a terminal and a second timer indicating a service provision timer of a non-ground base station.

16. In Paragraph 15, The above terminal contexts are, If the first timer exceeds the second timer, the terminal contexts are classified into a first group, and A method in which, when the first timer is less than the second timer, the terminal contexts are classified into a second group.

17. In Paragraph 16, The step of transmitting a terminal context search request of the above terminal is, A method comprising the step of transmitting a request to search for the terminal context of the terminal to the third base station when the terminal context of the terminal is included in the first group.

18. In Paragraph 16, The step of transmitting a terminal context search request of the above terminal is, A method comprising the step of transmitting a request to search for the terminal context of the terminal to the first base station when the terminal context of the terminal is included in the second group.

19. 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, Receive a request for relocation of terminal contexts classified based on a timer from the second base station; Transmitting a relocation response of the terminal contexts to the second base station; Receive a request to resume the RRC connection from the terminal; Based on the classification of the above terminal contexts, a terminal context search request of the terminal is transmitted to the second base station or the third base station; and A first base station that transmits an RRC connection resumption response based on the above terminal context.

20. In a method of operation of a terminal in a wireless communication system, A step of receiving RRC release from the second base station; A step of requesting the resumption of RRC connection to the first base station based on the identification of the need for an RRC connection; A step of receiving an RRC connection resumption response from the first base station; and The method includes the step of transmitting the completion of RRC connection resumption to the first base station, A method in which the first base station receives the terminal context of the terminal from the second base station or the third base station according to the rearrangement of terminal contexts classified based on a timer.

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