Device and method for managing terminal context in wireless communication system

Abstract

The present disclosure relates to a wireless communication system and, more particularly, to a method for operating a first base station in a wireless communication system, the method comprising the steps of: determining whether to transmit a terminal context to a first core network on the basis of a terminal context transmission condition; receiving a retrieval request for the terminal context on the basis of whether an Xn interface exists between the first base station and a second base station when a terminal performs resumption of an RRC connection with the second base station; and transmitting a retrieval response for the terminal context.

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 determining whether to transmit a terminal context to a core network based on terminal context transmission conditions.

[0005] The present disclosure is intended to provide an apparatus and method for receiving a request to search for a terminal context based on whether an Xn interface exists between base stations when a terminal performs a request to resume an RRC connection with a base station.

[0006] The present disclosure is intended to provide an apparatus and method for transmitting a search response of a terminal context based on whether the terminal context is stored.

[0007] The present disclosure is intended to provide an apparatus and method for setting a transition to an RRC disabled state of a terminal as a terminal context transmission condition, identifying an RNA change of a first base station, identifying a trigger to remove an NG interface with a core network, and identifying a base station's departure from a predetermined area.

[0008] The present disclosure is intended to provide an apparatus and method for transmitting a terminal context to a core network when a terminal is switched to an RRC disabled state.

[0009] The present disclosure is intended to provide an apparatus and method for transmitting a terminal context to a core network when an RNA change of a base station is identified.

[0010] The present disclosure is intended to provide an apparatus and method for determining the RNA of a base station according to a coverage mapping of a ground area and a base station to which a pre-set RNA identifier is assigned.

[0011] The present disclosure is intended to provide an apparatus and method for transmitting a terminal context to a core network when an NG interface removal trigger with a core network is identified.

[0012] The present disclosure is intended to provide an apparatus and method for receiving a terminal context search request from a base station when an Xn interface exists between base stations.

[0013] The present disclosure is intended to provide an apparatus and method for a core network to request a search for a terminal context from a base station when an Xn interface between base stations is nonexistent and a terminal context is nonexistent in the core network.

[0014] 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 the steps of determining whether to transmit a terminal context to a first core network based on a terminal context transmission condition, receiving a request to search for a terminal context based on whether an Xn interface exists between the first base station and the second base station when the terminal performs an RRC connection resumption with a second base station, and transmitting a search response for the terminal context.

[0015] According to one embodiment of the present disclosure, the terminal context transmission condition may include at least one of transitioning the terminal to an RRC disabled state, identifying a change in the RNA (RAN Notification Area) of the first base station, identifying a trigger to remove the NG interface with the core network, and identifying a departure from a predetermined area of ​​the first base station.

[0016] According to another embodiment of the present disclosure, the step of determining whether to transmit the terminal context to the first core network may include the step of the first base station transmitting the terminal context to the first core network when the terminal is switched to an RRC disabled state.

[0017] According to another embodiment of the present disclosure, the step of determining whether to transmit the terminal context to a first core network may include, when an RNA change of the first base station is identified, the first base station transmitting the terminal context to the first core network.

[0018] According to another embodiment of the present disclosure, the RNA of the first base station may be determined by mapping the coverage of the first base station and a ground area to which a preset RNA identifier is assigned.

[0019] According to another embodiment of the present disclosure, the step of determining whether to transmit the terminal context to a first core network may include the step of the first base station transmitting the terminal context to the first core network when an NG interface removal trigger with the first core network is identified.

[0020] According to another embodiment of the present disclosure, the step of receiving a search request for the terminal context may include receiving a search request for the terminal context from the second base station when an Xn interface exists between the first base station and the second base station, and receiving a search request for the terminal context from the first core network when an Xn interface between the first base station and the second base station does not exist and the terminal context does not exist in the first core network.

[0021] According to another embodiment of the present disclosure, the existence of an Xn interface between the first base station and the second base station may be determined based on whether the coverage of the first base station and the second base station is mapped to the same RNA.

[0022] According to another embodiment of the present disclosure, the step of transmitting a search response of the terminal context may include the step of transmitting the terminal context to the second base station when a search request for the terminal context is received from the second base station.

[0023] According to another embodiment of the present disclosure, the step of transmitting a search response of the terminal context may include the step of transmitting the terminal context to the first core network when a search request for the terminal context is received from the first core network.

[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, the processor determines whether to transmit a terminal context to a first core network based on a terminal context transmission condition, and when a terminal performs an RRC connection resumption with a second base station, receives a search request for the terminal context based on whether an Xn interface exists between the first base station and the second base station, and transmits a search response for the terminal context.

[0025] 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 receiving a request to resume an RRC connection from a terminal, transmitting a search for a terminal context based on whether an Xn interface exists between the second base station and the first base station, receiving a response to the search for the terminal context, and performing an RRC connection resumption based on the terminal context.

[0026] According to one embodiment of the present disclosure, the step of transmitting a search of the terminal context may include, when an Xn interface exists between the first base station and the second base station, transmitting a search request of the terminal context to the second base station, and when an Xn interface does not exist between the first base station and the second base station, transmitting a search request of the terminal context to the first core network.

[0027] According to another embodiment of the present disclosure, the existence of an Xn interface between the first base station and the second base station may be determined based on whether the coverage of the first base station and the second base station is mapped to the same RNA.

[0028] According to another embodiment of the present disclosure, the step of receiving a search response of the terminal context may include receiving a search response of the terminal context from the second base station when an Xn interface exists between the first base station and the second base station, and receiving a search response of the terminal context to the first core network when an Xn interface does not exist between the first base station and the second base station.

[0029] According to another embodiment of the present disclosure, the terminal context may be transmitted to the second base station or the first core network based on terminal context transmission conditions.

[0030] According to another embodiment of the present disclosure, the terminal context transmission condition may include at least one of transitioning the terminal to an RRC disabled state, identifying an RNA change of the first base station, identifying a trigger to remove the NG interface with the core network, and identifying a departure from a predetermined area of ​​the first base station.

[0031] According to another embodiment of the present disclosure, when the terminal is switched to an RRC disabled state, the terminal context is transmitted to a first core network, and when an RNA change of the first base station is identified, the terminal context is transmitted to the first core network, and when an NG interface removal trigger with the first core network is identified, the terminal context can be transmitted to the first core network.

[0032] 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, and the processor receives an RRC connection resumption request from a terminal, transmits a search for a terminal context based on whether an Xn interface exists between the second base station and the first base station, receives a search response for the terminal context, and can perform an RRC connection resumption based on the terminal context.

[0033] According to another aspect of the present disclosure, a method of operating a first core network in a wireless communication system is disclosed, the method may include receiving a terminal context search request from a second base station, checking whether the terminal context is stored, obtaining the terminal context from the first base station based on whether the terminal context is stored, and transmitting the terminal context to the second base station.

[0034] According to embodiments of the present disclosure, terminal context management can be effectively performed in a wireless communication system.

[0035] FIG. 1 illustrates an example of a satellite network according to one embodiment of the present disclosure.

[0036] FIG. 2 illustrates another example of a satellite network according to one embodiment of the present disclosure.

[0037] FIG. 3 illustrates the configuration of a device in a wireless communication system according to one embodiment of the present disclosure.

[0038] FIG. 4 illustrates an example of an RRC connection resumption procedure according to one embodiment of the present disclosure.

[0039] FIG. 5 illustrates an example of an RRC connection resumption procedure according to another embodiment of the present disclosure.

[0040] FIG. 6 illustrates an example of an RRC connection resumption procedure according to another embodiment of the present disclosure.

[0041] Figure 7 illustrates an example of terminal context search failure due to satellite mobility.

[0042] Figure 8 illustrates an example of terminal context search failure due to the absence of an inter-satellite Xn interface.

[0043] Figure 9 illustrates another example of terminal context search failure due to the absence of the Xn interface between satellites.

[0044] Figure 10 illustrates another example of terminal context search failure due to the absence of an inter-satellite Xn interface.

[0045] Figure 11 illustrates an example of a terminal context transmission procedure according to the mobility of the satellite.

[0046] FIG. 12 illustrates an example of a terminal context transmission procedure according to one embodiment of the present disclosure.

[0047] FIG. 13 illustrates an example of terminal context transmission according to one embodiment of the present disclosure.

[0048] FIG. 14 illustrates an example of a terminal context transmission procedure according to another embodiment of the present disclosure.

[0049] FIG. 15 illustrates an example of terminal context transmission according to another embodiment of the present disclosure.

[0050] FIG. 16 illustrates an example of a terminal context transmission procedure according to another embodiment of the present disclosure.

[0051] FIG. 17 illustrates an example of a procedure for transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0052] FIG. 18 illustrates another example of a procedure for transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0053] FIG. 19 illustrates another example of transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0054] FIG. 20 illustrates another example of a procedure for transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0055] FIG. 21 illustrates another example of transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0056] FIG. 22 illustrates another example of a procedure for transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0057] FIG. 23 illustrates an example of an operation procedure of a first base station according to one embodiment of the present disclosure.

[0058] FIG. 24 illustrates an example of an operation procedure of a second base station according to one embodiment of the present disclosure.

[0059] FIG. 25 illustrates an example of an operation procedure of a core network according to one embodiment of the present disclosure.

[0060] 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.

[0061] 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.

[0062] 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.

[0063]

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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-inactive state must be transferred to a new satellite. Meanwhile, for a terminal to resume the RRC connection or receive paging, the satellite currently servicing the terminal must receive the terminal context of that terminal from the previous satellite. Therefore, the present disclosure aims to provide a method for partitioning and managing terminal contexts by considering the characteristics of terminals in an RRC-inactive state, in order to efficiently utilize limited satellite network resources and ensure stable service continuity for terminals in an RRC-inactive state.

[0069]

[0070] FIG. 1 illustrates an example of a satellite network according to one embodiment of the present disclosure.

[0071] 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).

[0072] 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.

[0073] 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).

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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).

[0078] 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.

[0079]

[0080] 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).

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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).

[0086]

[0087] 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).

[0088] Referring to FIG. 3, the device may include a processor (310), a communication unit (220), and a memory (330).

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093]

[0094] Due to satellite mobility, the serving satellite servicing a terminal continuously changes; consequently, situations may frequently arise where the terminal context for a terminal in an RRC-deactivated state must be passed to a new satellite. For a terminal to resume the RRC connection or receive paging, the satellite currently servicing the terminal must receive the terminal context from the previous satellite.

[0095] 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.

[0096] Accordingly, in order to efficiently utilize limited satellite network resources and ensure stable service continuity for terminals in an RRC-disabled state, a method for transmitting and managing terminal contexts by dividing them based on the characteristics of terminals in an RRC-disabled state is disclosed below.

[0097]

[0098] FIG. 4 illustrates an example of an RRC connection resumption procedure according to one embodiment of the present disclosure.

[0099] The present disclosure relates to a method and apparatus for managing the exchange of terminal contexts between base stations for a terminal in an inactive state, depending on the active status of the inter-satellite link, in a non-terrestrial network environment including a regenerated relay payload of an onboard gNB structure, and for improving the RRC Connection Resume and RRC Connection Re-establishment schemes defined in existing NR systems. A terminal in an RRC inactive state is a state defined in 3GPP standards and refers to an intermediate state between the RRC Connected (RRC_CONNECTED) state and the RRC Idle (RRC_IDLE) state. In the RRC inactive state, the terminal can operate in a state where it maintains the CM_CONNECTED state and is not registered in the NG-RAN but can move within the RNA (Registration Area). A terminal in an RRC inactive state does not require a full network connection even when moving between cells, and terminal context information is maintained for subsequent connection resumption. Specifically, the last base station to provide service maintains the terminal context and the NG connections associated with the terminal (e.g., connections with AMF and UPF).

[0100] According to the 3GPP standard document TS 38.300, the RRC disabled state is a concept introduced for efficient network resource management. When a terminal is in the RRC disabled state, it does not immediately transition to a fully disabled state, and the gNB and AMF maintain the terminal context. Consequently, the terminal does not need to repeat the entire connection setup procedure when returning to the RRC connected state. The 3GPP standard document TS 38.300 defines key operations related to terminal RRC disabled, and representative operations are as follows.

[0101] Referring to FIG. 4, in step S401, the terminal (410) can perform an RRC deactivation procedure. 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 first base station (420), which is the serving base station, and transitions to an RRC deactivation state.

[0102] Meanwhile, the first base station (420) may refer to a satellite currently connected to the terminal (410) to provide communication. The second base station (420) may refer to a satellite that is replaced as a serving satellite when the first base station (420), which is a serving satellite, moves out of beam coverage or when the signal strength received by the terminal satisfies the handover condition.

[0103] In step S403, the first base station (420) identifies a RAN paging trigger. For example, the first base station (420) may identify a RAN paging trigger based on receiving downlink data or a signal from the core network (440). Specifically, when the first base station (420) receives downlink data from the User Plane Function (UPF) of the core network or receives a downlink terminal association signal from the Access and Mobility Management Function (AMF), it may perform cell-level paging for the RNA belonging to the terminal (410).

[0104] In step S405, the first base station (420) can transmit a RAN paging message to the second base station (430). Specifically, the AMF of the core network (440) transmits a RAN paging request message to the first base station (420) for processing the paging request, and the first base station (420) can transmit a RAN paging request message to the second base station (430) via XnAP RAN paging.

[0105] In step S407, the second base station (430) can perform a paging procedure with the terminal (410). The second base station (430) 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 included in the terminal context.

[0106] In step S409, the terminal (410) can perform an RRC connection resumption procedure. Specifically, the terminal (410) can transmit an RRC connection request message to the second base station (430). By configuring the RRC connection request message to include previously stored terminal identification information and connection-related parameters, the terminal (410) enables the second base station (430) to perform connection resumption for the terminal (410). The second base station (430) can quickly perform connection resumption for the terminal (410) by utilizing the terminal context of the terminal (410).

[0107] Meanwhile, regarding the paging procedure, the context of the terminal may be released. Specifically, when a terminal context release command (UE Context Release Command) or request message is received from the core network (440), the last base station may perform paging in the cell corresponding to RNA and, if necessary, transmit XnAP RAN paging to an adjacent base station to explicitly release the terminal. Here, the last base station and the adjacent base station may refer to the first base station (420) and the second base station (430), respectively. Additionally, regarding the paging procedure, when the last base station receives an NG RESET message, the last base station may perform paging for the relevant terminal and, if necessary, transmit XnAP RAN paging to an adjacent base station to release the relevant terminal. Meanwhile, if the paging-related operation fails, the operation is defined to be handled in accordance with 3GPP standard document TS 23.501.

[0108]

[0109] The procedure for the terminal to return to a direct RRC connection state will be explained in detail below with reference to Fig. 5.

[0110] FIG. 5 illustrates an example of an RRC connection resumption procedure according to another embodiment of the present disclosure.

[0111] Referring to FIG. 5, in step S501, the terminal (510) can perform an RRC deactivation procedure. 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 first base station (520), which is the serving base station, and transitions to an RRC deactivation state.

[0112] Meanwhile, the first base station (520) may refer to a satellite currently connected to the terminal (510) to provide communication. The second base station (530) may refer to a satellite that is replaced as a serving satellite when the first base station (520), which is the serving satellite, moves out of beam coverage or when the signal strength received by the terminal satisfies the handover condition.

[0113] In step S503, the terminal (510) transmits an RRC connection resumption request to the second base station (530). Specifically, in order for the terminal to return to the RRC connection state directly, the process may begin with the step of transmitting an RRC connection resumption request message to a base station that the terminal can connect to. The RRC connection resumption request message may include an I-RNTI (Temporary Identifier) ​​assigned by the first base station (520) that previously provided the last service. Meanwhile, the second base station (530), upon receiving the RRC connection resumption request message, verifies the identifier (ID) of the first base station (520) based on the I-RNTI included in the message.

[0114] In step S505, if the second base station (530) succeeds in identifying the first base station (520), it can send a terminal context search request to the first base station (520).

[0115] In step S507, the first base station (520) may transmit a terminal context search response based on a terminal context search request. The terminal context for which search was requested may be transmitted to the second base station (530) via the Xn interface.

[0116] In step S509, the second base station (530) transmits an RRC connection resumption response to the terminal (510). Based on the received terminal context, the second base station (530) transmits an RRC connection resumption response (RRC Resume Response) to the terminal (510) to complete the resumption of the RRC connection with the terminal (510).

[0117] In step S511, the terminal (510) changes to an RRC connection state. That is, the terminal (510) transitions to an RRC connection state in accordance with the RRC connection resumption response received from the first base station (530).

[0118] In step S513, the terminal (510) transmits a connection resumption completion to the second base station (530). That is, the terminal (510) transmits a connection resumption completion message to the second base station (530) indicating that the RRC connection resumption has been completed.

[0119] The second base station (530), having received the terminal context through the above-described procedure, can complete the RRC connection recovery procedure for the terminal, and the terminal can return to the RRC connection state and operate.

[0120] In step S515, the second base station (530) may transmit an Xn-U address indicator to the first base station (520). Specifically, the Xn-U address indicator may be used to provide a forwarding address from the first base station (520) to the first base station (530) for a configured Packet Data Unit (PDU) session resource. To prevent downlink data loss, downlink data buffered at the first base station (520) may be forwarded to the second base station (530) based on the Xn-U address indicator. Meanwhile, the second base station (530) may also provide a forwarding address for downlink data transmission to the first base station (520) to prevent downlink data loss.

[0121] In step S517, the second base station (530) transmits a route change request to the core network (540). For example, the second base station (530) may transmit a route change request message to the core network (540) to switch the paths of the user plane and control plane for the terminal (510) as the serving base station of the terminal (510) changes to the second base station (530).

[0122] In step S519, the second base station (530) receives a route change response message from the core network (540). Specifically, the core network (540) confirms that the transmission paths of the user plane and control plane for the terminal (510) have been updated based on the route switch request message transmitted by the second base station (530), and can transmit a confirmation message to the second base station (530).

[0123] In step S521, the second base station (530) transmits a terminal context release to the first base station (520). After the resumption of the RRC connection with the terminal (510) is completed, the second base station (530) transmits a terminal context release request to the first base station (520) to clean up the terminal context that is no longer needed to be maintained.

[0124] That is, through the path change process described above, the data transmission paths of the UPF and AMF are changed, and in conjunction with this, terminal context release is performed at the first base station (520).

[0125] Meanwhile, if the request to resume the RRC connection is not immediately accepted by the second base station (530), the terminal may maintain the RRC disabled state without resuming the connection, or may operate to perform a new RRC connection.

[0126]

[0127] The procedure for the terminal to return to an RRC connection state to perform an RNA update is explained in detail through Fig. 6.

[0128] FIG. 6 illustrates an example of an RRC connection resumption procedure according to another embodiment of the present disclosure.

[0129] Referring to FIG. 6, in step S601, the terminal (610) can perform an RRC deactivation procedure. 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 first base station (620), which is the serving base station, and transitions to an RRC deactivation state.

[0130] Meanwhile, the first base station (620) may refer to a satellite currently connected to the terminal (610) to provide communication. The second base station (630) may refer to a satellite that is replaced as a serving satellite when the first base station (620), which is the serving satellite, moves out of beam coverage or when the signal strength received by the terminal satisfies the handover condition.

[0131] In step S603, the terminal (610) transmits an RRC connection resumption request to the second base station (630). Specifically, in order for the terminal (610) 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 to a base station to which the terminal (610) can connect. The RRC connection resumption request message may include an I-RNTI assigned by the first base station (620) that previously provided the last service. Meanwhile, the second base station (630), upon receiving the RRC connection resumption request message, verifies the identifier (ID) of the first base station (620) based on the I-RNTI included in the message.

[0132] In step S605, if the second base station (630) succeeds in identifying the first base station (620), it can send a terminal context search request to the first base station (620).

[0133] In step S607, the first base station (620) may transmit a terminal context search response based on a terminal context search request. The terminal context for which search was requested may be transmitted to the second base station (630) via the Xn interface.

[0134] Meanwhile, the second base station (630) may transmit an RRC Resume Response to the terminal (610) to complete the resumption of the RRC connection with the terminal (610) based on the received terminal context. Accordingly, the terminal (610) changes to an RRC connection state. That is, the terminal (610) transitions to an RRC connection state according to the RRC Resume Response received from the first base station (630). Subsequently, the terminal (610) may transmit the completion of the connection resumption to the second base station (630). The second base station (630), having received the terminal context through the above-described procedure, can complete the RRC connection recovery procedure for the terminal, and the terminal can return to the RRC connection state and operate.

[0135] In step S609, the second base station (630) can transmit an Xn-U address indicator to the first base station (620). Additionally, the second base station (630) can provide the first base station (620) with an address for downlink data transmission to prevent downlink data loss.

[0136] In step S611, the second base station (630) transmits a route change request to the core network (640). For example, the second base station (630) may transmit a route change request message to the core network (640) 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 second base station (630).

[0137] In step S613, the second base station (630) 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 second base station (630), and can transmit a confirmation message to the second base station (630).

[0138] In step S615, the second base station (630) may transmit an RRC release to the terminal (610). Specifically, the second base station (630) may transmit an RRC release message to disconnect the wireless connection with the terminal (610) and transition to an RRC disabled state if an RRC disconnection is required according to network control based on RNAU completion.

[0139] In step S617, the second base station (630) transmits a terminal context release to the first base station (620). The second base station (630) transmits a terminal context release request to the first base station (620) to clean up terminal contexts that are no longer needed.

[0140]

[0141] Meanwhile, in existing terrestrial network environments, gNBs between RANs are connected via Xn interfaces, which are wired interfaces in the form of optical cables, and gNBs are geographically fixed in specific areas. Considering these characteristics, it is possible to verify the Xn interfaces between fixed gNBs, the NG connection structure, and the connection range. Accordingly, CN Paging, RAN Paging, and UE context delivery procedures utilizing RNA (RAN Notification Area) have been standardized.

[0142] However, communication based on playback payloads in non-terrestrial network environments has several structural differences compared to existing terrestrial network environments, and in particular, gives rise to unique technical problems in the process of managing and transmitting the context of terminals in an RRC-disabled state.

[0143] Specifically, low-orbit satellites have rapid orbital movement characteristics and require frequent handovers to maintain connection continuity with terminals. Due to these characteristics, an adaptive mechanism is required in non-terrestrial network environments that considers context delivery for terminals in an RRC-disabled state.

[0144] Meanwhile, low-orbit satellites orbit the Earth at a speed of approximately 7.5 km / s, causing connected satellites to be replaced within about 10 to 15 minutes. Consequently, the context of a terminal in an RRC-inactive state must continuously shift from the currently serviced satellite to the next. However, if the inter-satellite link is not active or is unstable, the transmission path of the terminal context may be forced to pass through a terrestrial network (e.g., a core network). Furthermore, if a terminal remains in an RRC-inactive state for an extended period, the NG interface containing the connection with the AMF of the last serviced low-orbit satellite may be removed. In such cases, requests for the terminal context via the AMF become impossible, resulting in the problem of the terminal having to reconstruct a new connection through the RRC setup procedure.

[0145] Meanwhile, in a non-terrestrial network environment where regenerated payloads are applied, the Xn interface can be activated by utilizing inter-satellite links between satellite base stations. However, depending on the clustering pattern of satellite base stations, the direction of movement within orbit, and changes in relative position, surrounding satellites can change dynamically at every moment, which implies continuous variability of the Xn interface. When a terminal requests reconnection to a new satellite base station after a base station deployed on a non-geostationary (Non-GEO) satellite has switched the terminal to an RRC-deactivated state, a terminal context search procedure is initiated. However, the success of this procedure may depend on the availability of inter-satellite links or feeder links between the base station (e.g., Anchor gNB) and the current base station. As such, in a non-terrestrial network environment, the availability of the terminal context transmission path changes moment by moment, and as a result, problems may arise where it is difficult to apply terminal context management procedures designed based on conventional terrestrial networks as they are. For example, the problems arising from the existing procedure are illustrated in Figure 7 below.

[0146]

[0147] Figure 7 illustrates an example of terminal context search failure due to satellite mobility.

[0148] Referring to FIG. 7, the first base station (710) may include a satellite base station operating in a non-ground network environment. Likewise, the second base station (720) may include a satellite base station operating in a non-ground network environment.

[0149] At time T1, the moving satellite first base station (710) switches the terminal to an RRC disabled state and maintains the terminal context for the terminal. At this time, the terminal can move freely within RNA. Meanwhile, at time T2, as the moving first base station (710) moves to the opposite side of the Earth, the terminal may face a situation where a resuming procedure or subsequent action in response to a network request is required. Possible scenarios related to this are classified as follows.

[0150] Case 1 is a case where the terminal directly performs an RRC connection reset. When the terminal transmits a request to resume the RRC connection, the second base station (720) corresponding to the current location of the terminal receives the request. However, if the second base station (720) is unable to communicate with the first base station (710) of the moving satellite, the procedure for searching for the terminal context is impossible. As a result, a problem may occur in which the RRC connection reset procedure cannot be completed.

[0151] Case 2 is a situation based on network-initiated downlink data or downlink signaling. When the network intends to perform paging to deliver downlink data or downlink signals to a terminal, the first satellite base station (710) in motion must deliver a RAN paging message to the second base station (720). However, if the inter-satellite link or feeder link between the first base station (710) and the second base station (720) is not available, paging fails, and as a result, a problem arises in which the downlink data or downlink signals cannot be delivered to the terminal. This problem can be understood as being caused by the fact that the inter-satellite link directly connecting the two satellites (710, 720) is not activated, or that the activation status of the inter-satellite link configured in a hop-by-hop manner is uncertain.

[0152] Case 3 corresponds to Mobile Terminated (MT) communication and is based on the premise that a satellite link or feeder link can be activated between the first base station (710) and the second base station (720) while in motion. In the case of Mobile Terminated (MT) communication, the AMF or UPF transmits a downlink signal or downlink data to the first base station (710) while in motion, and subsequently, the first base station (710) transmits a RAN Paging message to the second base station (720). After receiving the paging, the terminal performs an RRC connection reset procedure. However, in the scenario described above, delays may accumulate during the data and signaling transmission process, and as a result, transmission delays may become prolonged, leading to a problem where the Quality of Service (QoS) deteriorates. Below, an example of a procedure in which terminal context search fails in the scenario described above is explained.

[0153]

[0154] Figure 8 illustrates an example of terminal context search failure due to the absence of an inter-satellite Xn interface.

[0155] Referring to FIG. 8, in step S801, the terminal (810) can perform an RRC deactivation procedure. 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 first base station (820), which is the serving base station, and transitions to an RRC deactivation state.

[0156] The first base station (820) may refer to a satellite currently connected to and providing communication with the terminal (810). The second base station (830) may refer to a satellite that is replaced as a serving satellite when the first base station (820), which is the serving satellite, moves out of beam coverage or when the signal strength received by the terminal satisfies the handover condition.

[0157] In step S803, the terminal (810) transmits an RRC connection resumption request to the second base station (830). The RRC connection resumption request message may include an I-RNTI assigned by the first base station (820) that previously provided the last service.

[0158] In step S805, if the second base station (830) succeeds in identifying the first base station (820), it may send a terminal context search request to the first base station (820). However, if the second base station (820) is unable to communicate with the first base station (810), the procedure for searching for the terminal context is impossible. As a result, a problem may occur in which the RRC connection reset procedure cannot be completed.

[0159] In step S807, the second base station (830) transmits an RRC rejection to the terminal (810). For example, the RRC rejection message may include cause information indicating that the terminal context is unavailable. Upon receiving the RRC rejection, the terminal (810) may recognize that immediate resumption of the RRC connection through the second base station (830) is not possible.

[0160] In step S809, the terminal (810) may perform an RRC connection resumption after the timer expires. Specifically, after receiving an RRC rejection message, the terminal (810) 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 (810) may re-transmit an RRC connection resumption request to the same base station or a new serving base station, or perform a new RRC connection setup procedure.

[0161]

[0162] Figure 9 illustrates another example of terminal context search failure due to the absence of the Xn interface between satellites.

[0163] Referring to FIG. 9, in step S901, the terminal (910) can perform an RRC deactivation procedure. 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 (910) disconnects the wireless connection with the first base station (920), which is the serving base station, and transitions to an RRC deactivation state.

[0164] The first base station (920) may refer to a satellite currently connected to and providing communication with the terminal (910). The second base station (930) may refer to a satellite that is replaced as a serving satellite when the first base station (920), which is the serving satellite, moves out of beam coverage or when the signal strength received by the terminal satisfies the handover condition.

[0165] In step S903, the terminal (910) transmits an RRC connection resumption request to the second base station (930). The RRC connection resumption request message may include an I-RNTI assigned by the first base station (920) that previously provided the last service.

[0166] In step S905, if the second base station (930) succeeds in identifying the first base station (920), it may send a terminal context search request to the first base station (920). However, if the second base station (920) is unable to communicate with the first base station (910), the procedure for searching for the terminal context is impossible. For example, if a satellite link is not established between the first base station (920) and the second base station (930), or if a feeder link with a ground base station is not available, a failure occurs in transmitting the RAN paging message when attempting to perform paging to deliver a downlink signal to the terminal. Consequently, the terminal (910) faces the problem of having to reconstruct a new connection with the second base station (930) through an RRC setup procedure.

[0167] Accordingly, in step S907, the second base station (930) transmits an RRC setup request message to the terminal (910), and in step S909, the terminal (910) performs the RRC setup procedure.

[0168] In step S911, the first base station (920) releases the terminal context. The first base station (920) releases the terminal context to clean up the terminal context that is no longer needed to be maintained after the RRC between the second base station (930) and the terminal (910) has been set up.

[0169]

[0170] Figure 10 illustrates another example of terminal context search failure due to the absence of an inter-satellite Xn interface.

[0171] Referring to FIG. 10, in step S1001, the terminal (1010) can perform an RRC deactivation procedure. 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 (1010) disconnects the wireless connection with the first base station (1020), which is the serving base station, and transitions to an RRC deactivation state.

[0172] In step S1003, the first base station (1020) fails to transmit a RAN paging message to the second base station (1030). For example, in a situation based on network-driven downlink data or downlink signals, when the network intends to perform paging to deliver downlink data or downlink signals to a terminal, the first base station (1010) must transmit a RAN paging message to the second base station (1020). However, if the satellite link or feeder link between the first base station (1010) and the second base station (1020) is not available, paging fails.

[0173] In step S1005, the first base station (1020) requests the core network (1040) to release the terminal context. Specifically, the first base station (1020) releases the terminal context to clean up the terminal context that is no longer needed to be maintained.

[0174]

[0175] Below, with reference to FIG. 11, a method for efficiently managing terminal context despite satellite mobility is described.

[0176] Figure 11 illustrates an example of a terminal context transmission procedure according to the mobility of the satellite.

[0177] Referring to FIG. 11, in the case of Option A, at step S1101, the terminal (1110) performs an RRC deactivation procedure. The terminal (1110) performs a procedure to disconnect the RRC connection with the first base station (1120) and transition to an RRC deactivation state when data transmission and reception do not occur for a certain period of time or according to network control. At this time, the terminal (1110) recognizes that the terminal context for resuming the connection in the future is maintained on the network side while maintaining the RRC deactivation state.

[0178] In step S1103, the first base station (1120) and the core network (1130) remove the NG. The first base station (1120) and the core network (1130) remove the NG interface depending on satellite mobility or the inability to maintain the NG interface. This process may be performed without separate notification to the terminal, and the core network (1130) becomes a state where there is no RAN context for the terminal.

[0179] In step S1105, the core network (1130) performs connection resumption. Specifically, when downlink data is received or a request for connection resumption from the terminal occurs, the core network (1130) initiates a connection resumption procedure. For example, the core network (1130) may transmit a core network-based paging or connection resumption related signal to call the terminal (1110). Through this, the terminal is activated from an inactive state via a paging procedure and can transmit the terminal context to the next satellite. This method does not rely on terrestrial network infrastructure and does not affect the NG interface. Additionally, it can provide the lowest latency during UE reconnection and suspend events. However, support for the inter-satellite link is essential for this procedure. In particular, this procedure requires a periodic suspend procedure longer than the minimum period specified in the standard, which may cause the terminal to unnecessarily switch to an RRC connection state and reduce the efficiency of the RRC inactive state. Furthermore, the above method has the disadvantage of increased signal overhead due to frequent paging and state switching. The above method can be referred to as Page and relocate UE context to the next satellite.

[0180] Meanwhile, in the Pro-actively move UE context method, where the first base station (1120) transmits the terminal's context to the next satellite without notifying the terminal (1110), the accuracy and stability of the satellite orbit prediction (SA3) may become a major challenge.

[0181] Next is Option B, in step S1109, the first base station (1120) performs a paging procedure and releases the terminal context. Specifically, the first base station (1120) performs a paging procedure for the terminal (1110) when satellite movement or service termination is scheduled, and releases the terminal context regardless of whether a paging response is received. In this step, multiple terminals may become targets for paging and relocation within a short period of time, which may increase the signaling load.

[0182] In step S1111, the first base station (1120) and the core network (1130) remove the NG. The first base station (1120) releases all RAN and core linkage information for the terminal (1110), and the terminal (1110) performs a reconnection procedure through a new serving satellite or network node.

[0183]

[0184] In the case of a method that transfers terminal contexts to the core network or a representative gNB, terminal context management is separated from dependencies on inter-satellite links, and terminal contexts with all RRC disabled can be stored in an AMF within the core network or a specific base station. Accordingly, the complexity associated with direct inter-satellite communication can be mitigated.

[0185] Due to the configuration of introducing a new storage, the above method requires large-scale terminal data processing when all terminal contexts are stored in the AMF, which can significantly increase the storage load of the AMF or a specific base station. In particular, if frequent exchange of terminal contexts occurs between the AMF and the base station, the NGAP procedure must be expanded, and in situations involving multiple terminals, increased load on the core network and latency issues may occur. Additionally, when using the representative base station method, the process of selecting a suitable representative base station to store terminal contexts can become complex, and there is a disadvantage that the XnAP procedure must be expanded to support this.

[0186] Meanwhile, the NG-Based UE Context Retrieval Procedure utilizes existing NG interfaces to search for and manage terminal contexts, offering the advantage of minimizing protocol changes. However, if the NG interface is removed, the above method cannot perform terminal context retrieval, increasing the risk of failure. In particular, system reliability may be compromised because terminal contexts cannot be retrieved during NG removal situations. Additionally, since the AMF must be traversed during the terminal context retrieval procedure, it may result in the longest procedure delay among the proposed options. This acts as a disadvantage, as it takes a relatively long time to transmit data and control signals and to complete the resumption of the terminal connection.

[0187]

[0188] In order to manage terminal mobility and terminal context with RRC disabled in a non-terrestrial network environment, it is required to select an appropriate solution or use a combination of multiple solutions. Therefore, it is necessary to devise a terminal context management method suitable for a non-terrestrial network environment by comprehensively considering the examples described in Fig. 11.

[0189] The present disclosure proposes a method for managing terminal context in an RRC-inactive state using RNA (Registration Area) based Xn and NG interfaces. Specifically, the present disclosure proposes a technology to solve terminal context management problems arising from rapid inter-satellite mobility, uncertainty of inter-satellite links, and dependency on NG interfaces in non-terrestrial network environments. Specifically, the proposed technology aims to stably manage and transmit terminal context in an RRC-inactive state by selectively utilizing Xn interfaces and NG interfaces based on RNA and TA (Tracking Area).

[0190] According to existing discussions, the major issues arising in non-terrestrial network environments are the uncertainty of inter-satellite links and the deactivation of Xn interface functions. This acts as a primary cause preventing the existing terminal context retrieval procedure (UE Context Retrieve Request / Response) from being properly delivered depending on whether inter-satellite links are enabled. In particular, since satellites are constantly moving in non-terrestrial network environments, connections with terminals may be severed if inter-satellite links are not supported or are unstable. This leads to increased dependency on the NG interface, resulting in a problem where the load on the AMF increases. In such environments, the following technical considerations are required to reliably deliver terminal contexts in an RRC-deactivated state even when RNA and TA are changed. For example, a clear definition of the possible range of Xn interface connectivity based on inter-satellite links, a method for managing and delivering terminal contexts in an RRC-deactivated state based on RNA and TA, and an efficient RRC protocol update method while minimizing dependency on the NG interface must be considered. Accordingly, this disclosure proposes the following solution in consideration of the aforementioned technical matters.

[0191] In the present disclosure, when an inter-satellite link is possible, the most preferable method is to directly transmit the terminal context to the final serving base station via the Xn interface in response to a terminal context request. Accordingly, the present disclosure proposes a method for determining whether an inter-satellite link is active based on whether it is within the same RNA region, and a procedure for performing an Xn interface-based RRC deactivation terminal context exchange with the final serving base station when the inter-satellite link is connected as a result of the RNA region-based determination.

[0192] In this regard, RNA may consist of a single base station or multiple base stations, and an Xn interface may be provided between base stations within the same RNA. Accordingly, when an inter-satellite link is activated for satellites within the same RNA, direct terminal context requests and transmissions between satellites are possible using the Xn interface. Therefore, a satellite or base station that receives a connection resumption request from a final serving base station holding the terminal context can directly receive the terminal context via the Xn interface if the terminal is located within the same RNA. On the other hand, if the terminal has moved to a different RNA, direct transmission via the Xn interface is difficult, so the minimum terminal context is transmitted through the XnAP procedure. The above procedure is explained in detail with reference to FIG. 12.

[0193]

[0194] FIG. 12 illustrates an example of a terminal context transmission procedure according to one embodiment of the present disclosure. FIG. 12 is described on the premise that an Xn interface is established as the first base station (1220) and the second base station (1230) exist within the same RNA.

[0195] Referring to FIG. 12, in step S1201, the terminal (1210) performs an RRC deactivation procedure. 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 (1210) disconnects the wireless connection with the first base station (1220), which is the serving base station, and transitions to an RRC deactivation state.

[0196] Meanwhile, the first base station (1220) may refer to a satellite currently connected to the terminal (1210) to provide communication. The second base station (1230) may refer to a satellite that is replaced by a serving satellite when the signal strength received by the terminal satisfies the handover condition.

[0197] Additionally, the first base station (1220) and the second base station (1220) may be base stations existing in the same RNA. Whether they exist in the same RNA can be determined by mapping the coverage of the first base station to the ground area to which a pre-set RNA identifier is assigned. That is, as the coverage of the first base station (1220) and the second base station (1220) corresponds identically to the ground area to which the RNA identifier is assigned, the same RNA identifier may be assigned to the first base station (1220) and the second base station (1220). That is, the first base station (1220) and the second base station (1220) are base stations mapped to the same RNA identifier, and an Xn interface is set.

[0198] In step S1203, the terminal (1210) transmits an RRC connection resumption request to the second base station (1230). Specifically, in order for the terminal to return to a direct RRC connection state, the process may begin with the step of transmitting an RRC connection resumption request message to a base station to which the terminal can connect. The RRC connection resumption request message may include an I-RNTI (Temporary Identifier) ​​assigned by the first base station (1220) that previously provided the last service. Meanwhile, the second base station (1230) that receives the RRC connection resumption request message verifies the identifier (ID) of the first base station (1220) based on the I-RNTI included in the message.

[0199] In step S1205, if the second base station (1230) succeeds in identifying the first base station (1220), it can send a terminal context search request to the first base station (1220).

[0200] In step S1207, the first base station (1220) may transmit a terminal context search response based on a terminal context search request. The terminal context for which search was requested may be transmitted to the second base station (1230) via the Xn interface.

[0201] In step S1209, the second base station (1230) transmits an RRC connection resumption response to the terminal (1210). The second base station (1230) transmits an RRC connection resumption response to the terminal (1210) to complete the resumption of the RRC connection with the terminal (1210) based on the terminal context received through the Xn interface.

[0202] In step S1211, the terminal (1210) changes to an RRC connection state. That is, the terminal (1210) transitions to an RRC connection state in accordance with the RRC connection resumption response received from the first base station (1230).

[0203] In step S1213, the terminal (1210) transmits a connection resumption completion to the second base station (1230). That is, the terminal (1210) transmits a connection resumption completion message to the second base station (1230) indicating that the RRC connection resumption has been completed.

[0204] In step S1215, the second base station (1230) may transmit an Xn-U address indicator to the first base station (1220). Specifically, the Xn-U address indicator may be used to provide a forwarding address from the first base station (1220) to the first base station (1230) for a configured Packet Data Unit (PDU) session resource. To prevent downlink data loss, downlink data buffered at the first base station (1220) may be forwarded to the second base station (1230) based on the Xn-U address indicator.

[0205] In step S1217, the second base station (1230) transmits a route change request to the core network (1240). For example, the second base station (1230) may transmit a route change request message to the core network (1240) to switch the paths of the user plane and control plane for the terminal (1210) as the serving base station of the terminal (1210) changes to the second base station (1230).

[0206] In step S1219, the second base station (1230) receives a route change response message from the core network (1240). Specifically, the core network (1240) confirms that the transmission paths of the user plane and control plane for the terminal (1210) have been updated based on the route switch request message transmitted by the second base station (1230), and can transmit a confirmation message to the second base station (1230).

[0207] In step S1221, the second base station (1230) transmits a terminal context release to the first base station (1220). After the resumption of the RRC connection with the terminal (1210) is completed, the second base station (1230) transmits a terminal context release request to the first base station (1220) to clean up the terminal context that is no longer needed to be maintained.

[0208]

[0209] The present disclosure provides an embodiment for assigning RNA identifiers to satellite base stations. Specifically, discussions regarding the definition method of Tracking Area (TA) and RAN Notification Area (RNA) in NR-based non-terrestrial network environments have been ongoing, centered around the 3GPP RAN3 conference, but no clearly established method exists. In existing terrestrial network environments, TA and RNA have been defined by logically grouping multiple terrestrial base stations as units, and based on this, terminal location management and paging efficiency have been performed. However, in satellite-based non-terrestrial network environments, since coverage areas continuously change over time due to satellite mobility, there are conflicting opinions: one argues that the existing fixed definition of areas is not suitable, while the other argues that area information defined based on terrestrial standards should be maintained.

[0210] Considering the characteristics of such non-terrestrial network environments, 3GPP is currently discussing a method to utilize cell-based Mapped Cell ID and geographic information-based Geographical Service Area Information in parallel. In particular, for service units such as Self-Organizing Network (SO / MDT) functions or Multicast / Broadcast Service (MBS), the need for defining areas based on geographical service coverage is continuously being raised. Against this backdrop of discussion, the present invention is based on a structure that defines RNA and TA areas in fixed spatial units based on the ground rather than satellites.

[0211] Specifically, the present disclosure divides a specific region on Earth into predetermined units, assigns a fixed RNA identifier (RAN Notification Area ID) corresponding to each divided region, and configures all satellites covering the region to share the same RNA ID. That is, by defining RNA in fixed area units based on ground coordinates rather than in satellite units, the RNA to which a satellite belongs is dynamically determined according to the coverage of the ground area currently being covered by the satellite. This can be understood as a structure in which RNA is automatically mapped according to the ground area being covered by a satellite, departing from the conventional concept of RNA based on ground base station bundles. In other words, whether each satellite exists in the same RNA can be determined by the mapping of the ground area to which a pre-configured RNA identifier is assigned and the coverage of the base station. For example, as the coverage of each base station corresponds identically to the ground area to which the RNA identifier is assigned, the same RNA identifier can be assigned to those base stations.

[0212] Additionally, according to the present disclosure, each satellite periodically receives an RNA-GRID Mapping Table containing RNA-GRID mapping information from the AMF of the core network, thereby maintaining a minimal list of satellites corresponding to the RNA it currently covers. Each satellite is configured to minimize unnecessary Xn interface connections by setting or unsetting the Xn interface for satellites corresponding to RNAs it does not cover, based on the RNA-GRID Mapping Table. That is, an Xn interface is established between base stations assigned the same RNA identifier.

[0213]

[0214] FIG. 13 illustrates an example of terminal context transmission according to one embodiment of the present disclosure.

[0215] Referring to FIG. 13, a situation is illustrated in which multiple satellites move along a trajectory and sequentially cover a ground area. On the ground, RNA and TA defined based on ground standards are set as fixed areas, and each RNA can be composed of a sub-region of TA.

[0216] A terminal is located within a specific RNA with RRC disabled, and a satellite having coverage corresponding to that RNA region acts as the terminal's serving base station. Meanwhile, between multiple satellites covering the same RNA, a satellite link is activated, and the terminal context can be directly transmitted via the Xn interface between satellites. In this case, as illustrated in Option 1 of the drawing, when the terminal performs a reset procedure, the satellite currently covering the terminal can receive the terminal context from the previous serving satellite using the Xn interface and quickly process the resumption of the terminal's connection. That is, according to the present disclosure, since the RNA is defined as a fixed area based on the ground rather than on a satellite unit, the terminal context can be efficiently transferred via the Xn interface even when a satellite is replaced within the same RNA.

[0217]

[0218] Meanwhile, when a terminal moves outside of RNA, a situation may arise where connectivity of the Xn interface through inter-satellite links is not guaranteed, or where it is impossible to form hop-by-hop links between satellites. In such cases, it is difficult to perform exchange procedures, such as terminal context requests and delivery according to the existing method. Additionally, a determination is required as to which path, the Xn interface or the NG interface, to initiate the terminal context request procedure.

[0219] Accordingly, the present disclosure first determines whether the Xn interface via the inter-satellite link is available based on RNA, and if the inter-satellite link is not supported or a network change occurs, discloses a procedure to search for and transmit a terminal context from another base station via the AMF of the terrestrial core network. Meanwhile, the present disclosure provides a method of transmitting the terminal context to the AMF via the NG interface in situations where the inter-satellite link is not supported, and the method of transmitting and receiving the terminal context to the core network via the NG interface may have the advantage of providing relatively low latency. Under these assumptions, the present disclosure determines that the inter-satellite link is unavailable when the RNA is different, and configures a basic protocol to immediately direct the target of the terminal context request procedure to the AMF.

[0220] Specifically, the present disclosure determines a suitable search path between the Xn interface and the AMF based on RNA to resolve the problem where control message transmission is impossible due to the lack of a satellite link or an Xn interface. In this case, when passing through the AMF, the present disclosure additionally sets conditions to allow for faster processing of the terminal context if the AMF stores the terminal context. Hereinafter, with reference to FIG. 14, the RNA determination-based terminal context transmission and reception procedure will be described.

[0221]

[0222] FIG. 14 illustrates an example of a terminal context transmission procedure according to another embodiment of the present disclosure.

[0223] Referring to FIG. 14, in step S1401, the terminal (1410) performs an RRC deactivation procedure. 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 (1410) disconnects the wireless connection with the first base station (1420), which is the serving base station, and transitions to an RRC deactivation state.

[0224] Meanwhile, the first base station (1420) may refer to a satellite currently connected to the terminal (1410) to provide communication. The second base station (1430) may refer to a satellite that is replaced by a serving satellite when the signal strength received by the terminal satisfies the handover condition.

[0225] However, the first base station (1420) and the second base station (1420) may be base stations assigned different RNA identifiers. Accordingly, the second base station (1430) may determine that there is no Xn interface with the first base station (1420). RNA identifiers for surrounding base stations may be stored in advance in the second base station (1420).

[0226] In step S1403, the terminal (1410) requests the second base station (1430) to resume the RRC connection.

[0227] In S1405, the second base station (1430) transmits a terminal context search request to the core network (1440). That is, the second base station (1430) first determines whether the Xn interface via the inter-satellite link is available based on RNA, and if the inter-satellite link is not supported or a network change occurs, it initiates a procedure to search for and transmit a terminal context from another base station via the AMF itself or via the AMF of the terrestrial core network (1440). That is, if the second base station (1430) is assigned an RNA identifier different from that of the first base station (1420), the second base station (1430) configures a basic protocol to immediately direct the target of the terminal context request procedure to the core network (1440).

[0228] In step S1407, the core network (1440) transmits a terminal context search response. If the terminal context of the terminal (1410) is stored within the core network (1440), the core network (1440) may transmit the terminal context of the terminal (1410) to the second base station (1430). On the other hand, if the terminal context of the terminal (1410) is not stored within the core network (1440), the core network (1440) may transmit a response to the second base station (1430) indicating that the terminal context does not exist.

[0229] If the terminal context of the terminal (1410) does not exist in the core network (1440), in step S1409, the core network (1440) transmits a terminal context search request to the first base station (1420).

[0230] In step S1411, the core network (1440) receives a terminal context search response from the first base station (1420), and in step S1413, can transmit a terminal context release request to the first base station (1420).

[0231] In step S1415, the core network (1440) transmits a terminal context search response to the second base station (1430). Specifically, the core network (1440) can transmit the terminal context obtained from the first base station (1420) through step S1411 to the second base station (1430).

[0232] In step S1417, the terminal (1410) can perform an RRC connection resumption procedure. Specifically, the terminal (1410) can transmit an RRC connection request message to the second base station (1430). By configuring the RRC connection request message to include previously stored terminal identification information and connection-related parameters, the terminal (1410) enables the second base station (1430) to perform connection resumption for the terminal (1410). At this time, the second base station (1430) can perform connection resumption for the terminal (110) using the core network (1440) or the terminal context obtained through the core network (1440).

[0233]

[0234] FIG. 15 illustrates an example of terminal context transmission according to another embodiment of the present disclosure.

[0235] Referring to Fig. 15, RNA and TA defined by ground standards are set as fixed regions on the ground, and the terminal intends to perform a reset procedure in an RRC disabled state.

[0236] If a terminal transmits a reset request to a base station, but the RNA where the terminal is located and the final serving base station holding the terminal context belong to different RNAs, Xn interface connectivity via the inter-satellite link may not be guaranteed, or direct transfer of the terminal context via the inter-satellite Hop-by-Hop method may be impossible.

[0237] Accordingly, the present disclosure selects a procedure that passes through a terrestrial core network without performing direct terminal context transfer through the Xn interface in the situation described above.

[0238] For example, Option 2 includes a method in which the terminal context is stored in advance in the AMF of the core network, and when a reset request occurs from the terminal, the AMF directly transmits the terminal context to the base station covering the current terminal. The above method transmits the terminal context through the NG interface and can reduce the delay occurring during the relay phase.

[0239] Additionally, Option 3 includes a method in which, upon a terminal reset request, the AMF identifies the last serving base station holding the terminal context, retrieves the terminal context from that base station, and transmits it to the current serving base station. This method utilizes existing NG interface-based procedures, thereby minimizing protocol changes, but because it must pass through the AMF, the latency may increase relatively.

[0240]

[0241] Below, a procedure for determining the search start path of a terminal context based on whether the RNA identifier is identical is described in detail through FIG. 16.

[0242] FIG. 16 illustrates an example of a terminal context transmission procedure according to another embodiment of the present disclosure.

[0243] Referring to FIG. 16, in step S1601, the terminal (1610) performs an RRC deactivation procedure. 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 (1610) disconnects the wireless connection with the first base station (1620), which is the serving base station, and transitions to an RRC deactivation state.

[0244] Meanwhile, the first base station (1620) may refer to a satellite currently connected to the terminal (1610) to provide communication. The second base station (1630) may refer to a satellite that is replaced by a serving satellite when the signal strength received by the terminal satisfies the handover condition.

[0245] In step S1603, the terminal (1610) transmits an RRC connection resumption request to the second base station (1630). Specifically, in order for the terminal to return to a direct RRC connection state, the process may begin with the step of transmitting an RRC connection resumption request message to a base station to which the terminal can connect. The RRC connection resumption request message may include an I-RNTI (Temporary Identifier) ​​assigned by the first base station (1620) that previously provided the last service. Meanwhile, the second base station (1630), upon receiving the RRC connection resumption request message, verifies the identifier (ID) of the first base station (1620) based on the I-RNTI included in the message.

[0246] In step S1605, the second base station (1630) determines whether the first base station (1620) and the second base station (1630) belong to the same RNA. Whether they belong to the same RNA can be determined based on the RNA identifier assigned to each base station (1620, 1630).

[0247] If they belong to the same RNA, in step S1607, the second base station (1630) can send a terminal context search request to the first base station (1620).

[0248] Accordingly, in step S1609, the first base station (1620) can transmit a terminal context search response to the second base station (1630) based on a terminal context search request. As the same RNA identifier is assigned to each base station (1620, 1630), the terminal context for which search was requested can be transmitted to the second base station (1230) via the Xn interface.

[0249] Meanwhile, if it does not belong to the same RNA, in step S1611, the second base station (1630) transmits a terminal context search request to the core network (1640). The second base station (1630) determines only the identity of the RNA, and if the determination result indicates that it is not the same RNA, it configures the protocol to transmit a terminal context search request to the core network (1640).

[0250] In step S1613, the core network (1640) determines whether a terminal context exists.

[0251] If the terminal context is stored in the core network (1640), in step S1615, the core network (1640) may transmit the terminal context of the terminal (1610) to the second base station (1630). On the other hand, if the terminal context of the terminal (1610) is not stored in the core network (1640), the core network (1640) may transmit a response to the second base station (1630) indicating that the terminal context is not present.

[0252] If the terminal context is not present, in step S1617, the core network (1640) sends a terminal context search request to the first base station (1620).

[0253] In step S1619, the core network (1640) receives a terminal context search response from the first base station (1620), and in step S1621, can transmit a terminal context release request to the first base station (1620).

[0254] In step S1621, the core network (1640) transmits a terminal context search response to the second base station (1630). Specifically, the core network (1640) can transmit the terminal context obtained from the first base station (1620) through step S1619 to the second base station (1630).

[0255] In step S1623, the terminal (1610) may perform an RRC connection resumption procedure. Specifically, the terminal (1610) may transmit an RRC connection request message to the second base station (1630). At this time, the second base station (1630) may perform connection resumption for the terminal (1610) using the first base station (1620), the core network (1640), or the terminal context obtained through the core network (1640).

[0256]

[0257] In order to store a terminal context in a terrestrial core network, it is necessary to define the timing and procedure for a base station possessing the terminal context to transmit it to the core network. Hereinafter, a method for transmitting a terminal context according to the present disclosure will be described with reference to FIGS. 17 to 22.

[0258] FIG. 17 illustrates an example of a procedure for transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0259] Referring to FIG. 17, in step S1701, the first base station (1720) transmits a Suspend Indication to the terminal (1710).

[0260] In step S1703, the terminal (1710) switches to an RRC disabled state. When the terminal (1710) switches to an RRC disabled state, in step S1705, the first base station (1720) transmits a terminal context transfer request to the core network (1730), and in step S1707, receives a terminal context transfer acknowledgment from the core network (1730). The terminal context transfer request includes information requesting whether terminal context storage is possible in the core network (1730), and the terminal context transfer acknowledgment includes a response thereto.

[0261] In step S1709, the first base station (1720) transmits the terminal context to the core network (1730). The core network (1730) stores the terminal context.

[0262] In step S1711, the core network (1730) transmits a terminal context transmission confirmation to the first base station (1720). After verifying the integrity and suitability of the transmitted terminal context, the core network (1730) may transmit a response message regarding the completion of terminal context storage to the first base station (1720).

[0263] In step S1713, the first base station (1720) releases the terminal context. The first base station (1720) releases the terminal context of the corresponding terminal it held by confirming that the terminal context delivery is complete. Accordingly, the first base station (1720) reduces the burden of storing the terminal context, and the subsequent procedure to resume the connection of the terminal can be performed based on the terminal context stored in the core network (1730).

[0264]

[0265] When a base station's RNA changes, the Xn interfaces formed between base stations belonging to the existing RNA are removed (Xn Removal), and Xn interfaces are established between base stations belonging to the new RNA (Xn Setup). During this process, the existing base station transfers its terminal context to the AMF for storage.

[0266] In the above procedure, terminal context transfer may include UE Context Transfer Request, UE Context Transfer Request Acknowledgement, UE Context Transfer, and Save UE Context procedures, and through these message exchanges, the last serving gNB reliably transfers the terminal context it holds to the AMF. Subsequently, when terminal context transfer is completed, the base station releases the terminal context.

[0267] As described above, the series of procedures for transferring terminal context from the base station to the AMF can be referred to as the UE CONTEXT TRANSFER PROCEDURE, and will be explained in detail below through FIG. 18.

[0268] FIG. 18 illustrates another example of a procedure for transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0269] Referring to FIG. 18, in step S1801, the first base station (1810) identifies an RNA change. Specifically, the first base station (1810) may be assigned a new RNA identifier due to mobility. Accordingly, when a new RNA identifier is assigned, the first base station (1810) may determine that the RNA at its location has changed.

[0270] In step S1803, the first base station (1810) transmits a terminal context transmission request to the core network (1830), and in step S1805, receives a terminal context transmission acknowledgment from the core network (1830). The terminal context transmission request includes information requesting whether the core network (1830) can store the terminal context, and the terminal context transmission acknowledgment includes a response thereto.

[0271] In step S1807, the first base station (1810) transmits the terminal context to the core network (1830). The core network (1830) stores the terminal context.

[0272] In step S1809, the core network (1830) transmits a terminal context transmission confirmation to the first base station (1810). After verifying the integrity and suitability of the transmitted terminal context, the core network (1830) may transmit a response message regarding the completion of terminal context storage to the first base station (1810).

[0273] In step S1811, the first base station (1810) releases the terminal context. The first base station (1810) releases the terminal context of the corresponding terminal it held by confirming that the terminal context delivery is complete. Accordingly, the first base station (1810) reduces the burden of storing the terminal context, and the subsequent procedure to resume the connection of the terminal can be performed based on the terminal context stored in the core network (1830).

[0274] In step S1813, the first base station (1810) transmits a request to remove Xn to the second base station (1820), and in step S1815, receives a response to remove Xn from the second base station (1820). That is, the first base station transfers the terminal context to the terrestrial core network (1830) before the RNA change is identified and the Xn interface with the surrounding satellite base station, the second base station (1820), is removed.

[0275]

[0276] FIG. 19 illustrates another example of transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0277] Referring to Fig. 19, multiple satellites are moving along an orbit and covering the ground area, and each satellite can be logically classified according to RNA and TA defined based on the ground.

[0278] In the case of satellite base stations, RNA can be changed depending on their mobility. Specifically, if a satellite no longer belongs to the existing RNA due to movement, the Xn interface formed between satellites belonging to the existing RNA may be removed. Subsequently, when the satellite enters a new RNA, a new Xn interface is established between the satellites belonging to that RNA.

[0279] According to the present disclosure, when such an RNA change occurs, the base station transfers the terminal context it possesses to the AMF of the core network. That is, the base station transmits the terminal context to the AMF using the RNA change as a trigger, and the AMF stores the transferred terminal context. This process can be performed in accordance with the previously defined UE CONTEXT TRANSFER PROCEDURE.

[0280]

[0281] Below, we describe the procedure for transmitting a terminal context when the trigger for removing the NG interface with the core network is identified, that is, when switching of the core network occurs. This transmission of the terminal context can be performed simultaneously with the time when the NG interface removal with the existing AMF is performed, before the base station leaves the service area or connects to a new AMF.

[0282] Since existing procedures are standardized with a legacy method similar to Option 3, which allows the terminal context to be stored by the final serving base station, there is no defined procedure for the AMF to separately store the terminal context or to transfer the terminal context to the AMF. Accordingly, the present disclosure proposes a new procedure for transferring the terminal context held by the base station to the AMF in order to ensure the continuity of the terminal context even when AMF switching occurs.

[0283]

[0284] FIG. 20 illustrates another example of a procedure for transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0285] In step S2001, the first base station (2010) identifies an NG removal trigger. Specifically, the first base station (2010) may remove the NG with the first core network (2020), where the existing NG interface is set up due to mobility, and may require an NG setup with the second core network (2030), which is a new network.

[0286] In step S2003, the first base station (2010) transmits a terminal context transmission request to the first core network (2020), and in step S2005, receives a terminal context transmission confirmation from the first core network (2020). The terminal context transmission request includes information requesting whether terminal context storage is possible in the first core network (2020), and the terminal context transmission confirmation includes a response thereto.

[0287] In step S2007, the first base station (2010) transmits the terminal context to the first core network (2030). The first core network (2030) stores the terminal context.

[0288] In step S2009, the first core network (2030) transmits a terminal context transmission confirmation to the first base station (2010). After verifying the integrity and suitability of the transmitted terminal context, the first core network (2030) may transmit a response message regarding the completion of terminal context storage to the first base station (2010).

[0289] In step S2011, the first base station (2010) releases the terminal context. The first base station (2010) releases the terminal context of the corresponding terminal it held by confirming that the terminal context delivery is complete. Accordingly, the first base station (2010) reduces the burden of storing the terminal context, and the subsequent procedure to resume the connection of the terminal can be performed based on the terminal context stored in the core network (2030).

[0290] In step S2013, the first base station (2010) transmits an NG removal request to the first core network (2020), and in step S2015, receives an NG removal response from the first core network (2020). Accordingly, the NG interface established between the first base station (2010) and the first core network (2020) is released.

[0291] In step S2017, the first base station (2010) transmits an NG setup request to the second core network (2030). The first base station (2010) establishes a new NG interface with the second core network (2030) through the NG setup request, and subsequently, the procedure for resuming the connection of terminals existing in the RNA of the first base station and the exchange of control signals can be performed based on the terminal context stored in the first core network (2030).

[0292]

[0293] FIG. 21 illustrates another example of transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0294] FIG. 21 illustrates an AMF switching situation in which the AMF changes as the satellite base station moves. Specifically, when the satellite base station moves out of the service area of ​​the existing AMF and enters the area of ​​the new AMF, the NG interface with the existing AMF is removed, and an NG interface with the new AMF can be established. According to the present disclosure, when AMF switching occurs, the base station performs a procedure to remove the NG with the existing AMF and, at the same time, transfers the terminal context it possesses to the AMF of the core network.

[0295]

[0296] FIG. 22 illustrates another example of a procedure for transmitting a terminal context based on the terminal context transmission conditions of the present disclosure.

[0297] Referring to FIG. 22, in step S2201, the first base station (2210) can identify deviation from a predetermined area. Here, the predetermined area may include RNA, but is not limited thereto, and may be designated as a specific region according to the system settings.

[0298] In step S2203, the first base station (2210) transmits a terminal context storage request to the core network (2220). The terminal context storage request includes information requesting the core network (2220) whether terminal context storage is possible, and includes the terminal context.

[0299] In step S2205, the first base station (2210) receives confirmation of terminal context storage from the core network (2220). After verifying the integrity and suitability of the transmitted terminal context, the core network (2220) may send a response message regarding the completion of terminal context storage to the first base station (2210).

[0300] In step S2207, the first base station (2210) releases the terminal context. The first base station (2210) releases the terminal context of the corresponding terminal it held by confirming that the terminal context transfer is complete.

[0301]

[0302] FIG. 23 illustrates an example of an operation procedure of a first base station according to one embodiment of the present disclosure. The first base station may be a serving base station connected to a terminal to provide communication services.

[0303] Referring to FIG. 23, in step S2301, the first base station determines whether to transmit the terminal context to the core network based on terminal context transmission conditions. The terminal context conditions may include at least one of the transition of the terminal to an RRC disabled state, identification of RNA change of the first base station, identification of a trigger to remove the NG interface with the core network, and identification of departure from a predetermined area of ​​the first base station.

[0304] According to an embodiment, the first base station may transmit the terminal context to the core network when the RRC deactivation state of the terminal is identified. Additionally, according to an embodiment, the first base station may transmit the terminal context to the core network when an RNA change of the first base station is identified. Additionally, according to an embodiment, the first base station may transmit the terminal context to the core network when an NG interface removal trigger between the first base station and the core network is identified. Additionally, according to an embodiment, the first base station may transmit the terminal context to the core network when the first base station leaves a predetermined area. Meanwhile, if the above-described terminal context transmission conditions are not satisfied, the first base station may not transmit the terminal context and may store it.

[0305] In step S2303, the first base station receives a terminal context search request based on whether an Xn interface exists. According to an embodiment, if an Xn interface exists between the first base station and the second base station, which is the target for RRC reconnection between the first base station and the terminal, the first base station may receive a terminal context search request from the second base station. Meanwhile, if the Xn interface does not exist, the terminal context search request may be received from a core network in which an NG interface is established with the second base station. In this case, the terminal context search request transmitted from the core network may be transmitted from the core network if the corresponding terminal context is not stored in the core network.

[0306] In step S2305, the first base station transmits a terminal context search response. Specifically, the first base station may transmit the terminal context to the entity that transmitted the terminal context search request.

[0307]

[0308] FIG. 24 illustrates an example of an operation procedure of a second base station according to one embodiment of the present disclosure.

[0309] Referring to FIG. 24, in step S2401, the second base station receives an RRC connection resumption request from the terminal. Upon receiving the RRC connection resumption request message, the second base station identifies the identifier of the first base station based on the I-RNTI included in the message.

[0310] In step S2403, it is determined whether the first base station and the second base station belong to the same RNA. Whether they belong to the same RNA can be determined based on the RNA identifiers assigned to the first base station and the second base station.

[0311] If they belong to the same RNA, in step S2405, the second base station can obtain the terminal context from the first base station. Specifically, as the same RNA identifier is assigned to the first and second base stations, the terminal context can be transmitted to the second base station via the Xn interface.

[0312] If it does not belong to the same RNA, in step S2407, the second base station obtains a terminal context from the core network. For example, the second base station may send a terminal context search request to the core network and receive a terminal context stored in the core network, or receive a terminal context stored in the first base station through the core network.

[0313] In step S2409, the second base station performs RRC connection resumption. The second base station may perform RRC connection resumption for the terminal using the first base station, the core network, or a terminal context obtained through the core network.

[0314]

[0315] FIG. 25 illustrates an example of an operation procedure of a core network according to one embodiment of the present disclosure.

[0316] Referring to FIG. 25, in step S2501, the core network receives a terminal context search request from the second base station. For example, the core network may receive a terminal context search request from the second base station based on the case where the second base station and the first base station do not belong to the same RNA. That is, as the second base station does not have an Xn interface established with the first base station, and as the second base station cannot obtain the terminal context from the first base station, the second base station transmits a terminal context search request to the core network.

[0317] Meanwhile, the first base station includes a satellite connected immediately before the terminal to provide communication, and the second base station may refer to a satellite that is replaced by a serving satellite when the signal strength received by the terminal satisfies the handover condition.

[0318] In step S2503, the core network determines the existence of a terminal context. Specifically, the core network determines whether it has received and stored a terminal context in advance based on the terminal context transmission conditions.

[0319] If the terminal context is stored in the core network, in step S2505, the core network transmits a terminal context response to the second base station. The core network may transmit the stored terminal context to the second base station.

[0320] On the other hand, if the terminal context of the terminal is not stored in the core network, the core network may transmit a response to the second base station indicating that the terminal context does not exist. In addition, at step S2507, the core network may obtain the terminal context from the first base station and transmit the obtained terminal context to the second base station.

[0321]

[0322] 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.

[0323] 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 determining whether to transmit the terminal context to the first core network based on the terminal context transmission conditions; When the terminal performs the resumption of an RRC connection with the second base station, the step of receiving a search request for the terminal context based on whether an Xn interface exists between the first base station and the second base station; and A method comprising the step of transmitting a search response of the above terminal context.

2. In Paragraph 1, The above terminal context transmission conditions are, A method comprising at least one of transitioning the terminal to an RRC disabled state, identifying a change in the RNA (RAN Notification Area) of the first base station, identifying a trigger to remove the NG interface with the core network, and identifying the departure from a predetermined area of ​​the first base station.

3. In Paragraph 1, The step of determining whether to transmit the above terminal context to the first core network is, A method comprising the step of, when the terminal is switched to an RRC disabled state, the first base station transmitting the terminal context to the first core network.

4. In Paragraph 1, The step of determining whether to transmit the above terminal context to the first core network is, A method comprising the step of, when an RNA change of the first base station is identified, transmitting the terminal context to the first core network.

5. In Paragraph 4, The RNA of the first base station mentioned above is, A method determined by mapping a ground area assigned to a pre-set RNA identifier and the coverage of the first base station.

6. In Paragraph 1, The step of determining whether to transmit the above terminal context to the first core network is, A method comprising the step of, when an NG interface removal trigger with the first core network is identified, transmitting the terminal context to the first core network by the first base station.

7. In Paragraph 1, The step of receiving a search request for the above terminal context is, If an Xn interface exists between the first base station and the second base station, a step of receiving a search request for the terminal context from the second base station; and A method comprising the step of receiving a search request for the terminal context from the first core network when the Xn interface between the first base station and the second base station is nonexistent and the terminal context is nonexistent in the first core network.

8. In Paragraph 7, A method in which the existence of an Xn interface between the first base station and the second base station is determined based on whether the coverage of the first base station and the second base station is mapped to the same RNA.

9. In Paragraph 1, The step of transmitting a search response of the above terminal context is: When a search request for the terminal context is received from the second base station, A method comprising the step of transmitting the terminal context to the second base station.

10. In Paragraph 1, The step of transmitting a search response of the above terminal context is: A method comprising the step of transmitting the terminal context to the first core network when receiving a search request for the terminal context from the first core network.

11. 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, Determining whether to transmit the terminal context to the first core network based on the terminal context transmission conditions, and When the terminal performs the resumption of an RRC connection with the second base station, based on whether an Xn interface exists between the first base station and the second base station, it receives a search request for the terminal context, and A first base station that transmits a search response of the above terminal context.

12. In a method of operating a second base station in a wireless communication system, A step of receiving an RRC connection resumption request from a terminal; A step of transmitting a search for a terminal context based on whether an Xn interface exists between the second base station and the first base station; A step of receiving a search response of the above terminal context; and A method comprising the step of resuming an RRC connection based on the above terminal context.

13. In Paragraph 12, The step of transmitting the search of the above terminal context is, If an Xn interface exists between the first base station and the second base station, the step of transmitting a search request for the terminal context to the second base station; and A method comprising the step of transmitting a search request for the terminal context to the first core network when the Xn interface between the first base station and the second base station does not exist.

14. In Paragraph 13, A method in which the existence of an Xn interface between the first base station and the second base station is determined based on whether the coverage of the first base station and the second base station is mapped to the same RNA.

15. In Paragraph 12, The step of receiving a search response of the above terminal context is, If an Xn interface exists between the first base station and the second base station, the step of receiving a search response for the terminal context from the second base station; and A method comprising the step of receiving a search response of the terminal context to the first core network when the Xn interface between the first base station and the second base station does not exist.

16. In Paragraph 12, The above terminal context is, A method transmitted to the second base station or the first core network based on terminal context transmission conditions.

17. In Paragraph 16, The above terminal context transmission conditions are, A method comprising at least one of transitioning the terminal to an RRC disabled state, identifying an RNA change of the first base station, identifying a trigger to remove the NG interface with the core network, and identifying a departure from a predetermined area of ​​the first base station.

18. In Paragraph 17, When the above terminal is switched to an RRC disabled state, the terminal context is transmitted to the first core network, and When an RNA change of the first base station is identified, the terminal context is transmitted to the first core network, and A method in which, when a trigger to remove the NG interface with the first core network is identified, the terminal context is transmitted to the first core network.

19. 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, Receives a request to resume the RRC connection from the terminal, and Based on whether an Xn interface exists between the second base station and the first base station, a search for a terminal context is transmitted, and Receive a search response of the above terminal context, and A second base station that performs RRC connection resumption based on the above terminal context.

20. A method of operating a first core network in a wireless communication system, A step of receiving a terminal context search request from a second base station; A step of checking whether the above terminal context is saved; A step of obtaining the terminal context from the first base station based on whether the terminal context is stored; and A method comprising the step of transmitting the terminal context to the second base station.

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