Apparatus and method for store-and-forward in IoT non-terrestrial networks

Abstract

This invention provides a device and method for appropriately performing S&F (Store and Forward) mode communication in an NTN (Non-Terrestrial Network). [Solution] In a wireless communication system, the satellite equipment identifies the S&F mode while connected to the UE (User Equipment) via RRC (Radio Resource Control), sends a message to the UE indicating that the satellite is operating in S&F mode, then receives a request signal from the UE to disconnect the RRC connection, and requests the UE to send an RRC disconnection message to disconnect the RRC connection. The RRC disconnection message includes a cause value for RRC disconnection. The message includes an indicator that the cells provided by the satellite support S&F mode, information about the validity period of the satellite's feeder link, or information about the conditions that trigger the request to disconnect the RRC connection.

Description

Technical Field

[0001] The present disclosure relates to a non-terrestrial network (NTN) that provides a wireless communication service via a satellite located in the Earth's orbit or an aerial vehicle flying at a high altitude, rather than a ground base station. More specifically, it relates to an apparatus and method for store and forward in an IoT (Internet of Everything) NTN (non-terrestrial network).

Background Art

[0002] A non-terrestrial network (NTN) has been introduced to complement a terrestrial network that provides a wireless communication system. The non-terrestrial network can provide communication services even in areas where it is difficult to construct a terrestrial network or in disaster situations. Furthermore, due to the recent reduction in satellite launch costs, it has become possible to provide an efficient access network environment.

Summary of the Invention

Means for Solving the Problems

[0003] Embodiments of this disclosure provide a satellite device configured to provide NTN (non-terrestrial network) access and perform the functions of an evolved node B (eNB). The device may include a memory containing instructions; at least one processor; and at least one transceiver. When executed by the at least one processor, the instructions may cause the device to identify store and forward (S&F) mode while connected to a user equipment (UE) via radio resource control (RRC), send a message to the UE indicating that the satellite is operating in S&F mode, receive a request signal from the UE to disconnect the RRC connection after sending the message, and cause the UE to send a disconnect message to disconnect the RRC connection. The disconnect message may include a cause value for disconnecting the RRC connection. The message may include at least one of the following: an indicator that a cell provided by the satellite supports S&F mode, information about the validity period of the satellite's feeder link, or information about conditions for triggering the request to disconnect the RRC connection.

[0004] Embodiments of this disclosure provide user equipment (UE) for performing NTN (non-terrestrial network) access. The UE may include memory containing instructions; at least one processor; and at least one transceiver. When the instructions are executed by the at least one processor, the UE may receive a message from a satellite configured to perform the functions of an evolved node B (eNB) in a radio resource control (RRC) connection state, indicating that the satellite is operating in store and forward (S&F) mode; after receiving the message, send a request signal to the satellite to disconnect the RRC connection; and receive an RRC disconnection message from the satellite to disconnect the RRC connection. The RRC disconnection message may include a cause value for disconnecting the RRC connection. The message may include at least one of the following: an indicator indicating that a cell provided by the satellite supports S&F mode; information regarding the validity period of the satellite's feeder link; or information regarding conditions for triggering the request to disconnect the RRC connection.

[0005] Embodiments of this disclosure provide a method performed by a satellite configured to provide NTN (non-terrestrial network) access and perform the functions of an evolved node B (eNB). The method includes: identifying store and forward (S&F) mode in a radio resource control (RRC) connection state with user equipment (UE); sending a message to the UE indicating that the satellite is operating in S&F mode; receiving a request signal from the UE for disconnecting the RRC connection after sending the message; and sending an RRC disconnection message to the UE for disconnecting the RRC connection, the RRC disconnection message may include a cause value for disconnecting the RRC connection. The message may include at least one of the following: an indicator indicating that a cell provided by the satellite supports S&F mode; information regarding the validity period of the satellite's feeder link; or information regarding conditions for triggering the request for disconnecting the RRC connection.

[0006] Embodiments of this disclosure provide a method performed by user equipment (UE) for performing NTN (non-terrestrial network) access. This method may include receiving a message from a satellite configured to perform the function of an evolved node B (eNB) in a radio resource control (RRC) connection state, indicating that the satellite is operating in store and forward (S&F) mode; sending a request signal to the satellite for disconnecting the RRC connection after receiving the message; and receiving an RRC disconnection message from the satellite for disconnecting the RRC connection. The RRC disconnection message may include a cause value for disconnecting the RRC connection. The message may include at least one of the following: an indicator indicating that a cell provided by the satellite supports S&F mode; information regarding the validity period of the satellite's feeder link; or information regarding conditions for triggering the request for disconnecting the RRC connection. [Brief explanation of the drawing]

[0007] [Figure 1] This shows a wireless communication system. [Figure 2a] An example of a non-terrestrial network (NTN) is shown. [Figure 2b] An example of a non-terrestrial network (NTN) is shown. [Figure 3a] An example of a control plane (C-plane) is shown. [Figure 3b] An example of a user plane (U-plane) is shown. [Figure 4] This shows an example of a resource structure in the time-frequency domain in a wireless communication system. [Figure 5]This example shows the S&F (store and forward) mode in IoT (Internet of Everything) NTN (non-terrestrial network). [Figure 6] This shows the signaling information regarding the effective time of the S&F mode. [Figure 7] This shows an example of the RRC (Radio Resource Control) connection status of an IoT UE (user equipment). [Figure 8a] This shows an example of disconnecting the RRC connection in S&F mode. [Figure 8b] This shows an example of a request to disconnect the RRC connection in S&F mode. [Figure 9] Here are some examples of UE components. [Figure 10] Examples of satellite components are shown. [Modes for carrying out the invention]

[0008] The terms used in this disclosure are used solely to describe specific embodiments and are not intended to limit the scope of other embodiments. Singular expressions can, in context, include plural expressions unless otherwise specified. Terms used herein, including technical or scientific terms, may have the same meaning as generally understood by a person of ordinary skill in the art described herein. Terms used herein that are defined in a general dictionary may be interpreted as having the same or similar meaning as in the context of the relevant art, and not as ideally or excessively formal unless expressly defined herein. In some cases, terms defined herein may not be interpreted in a way that excludes embodiments of this disclosure.

[0009] The various embodiments of the Disclosure described below illustrate hardware-based approaches as examples. However, since the various embodiments of the Disclosure include techniques that use both hardware and software, the various embodiments of the Disclosure do not exclude software-based approaches.

[0010] The terms used in the following description, such as those referring to signals (e.g., signal, information, message, signaling), resources (e.g., symbol, slot, subframe, radio frame, subcarrier, RE (resource element), RB (resource block), BWP (bandwidth part), occasion), operational states (e.g., step, operation, procedure), data (e.g., packet, user stream, information, bit, symbol, codeword), channels, network entities, and device components, are provided as examples for illustrative purposes only. Therefore, this disclosure is not limited to the terms described below, and other terms with equivalent technical meanings may be used.

[0011] In the following description, the terms "physical channel" and "signal" may be used interchangeably with "data" or "control signal." For example, PDSCH (physical downlink shared channel) is a term referring to a physical channel through which data is transmitted, but PDSCH may also be used to refer to data. In other words, in this disclosure, the expression "transmit a physical channel" may be interpreted as equivalent to the expression "transmit data or a signal over a physical channel."

[0012] Hereinafter, in this disclosure, "upper signaling" means a signal transmission method transmitted from a base station to a terminal using a physical layer downlink data channel, or from a terminal to a base station using a physical layer uplink data channel. Upper signaling may be understood as RRC (radio resource control) signaling or MAC control element (hereinafter referred to as "CE").

[0013] Furthermore, this disclosure may use expressions greater than or less than to determine whether a particular condition is satisfied or fulfilled, but this is merely an illustrative example and does not preclude the use of greater than or less than expressions. Conditions described as "greater than or equal to" may be replaced with "greater than or equal to," conditions described as "less than or equal to" may be replaced with "less than or equal to," and conditions described as "greater than or equal to and less than" may be replaced with "greater than and less than or equal to." Also, hereafter, "A" to "B" means at least one of the elements from A to B (including A). Hereinafter, "C" and / or "D" means including at least one of "C" or "D," i.e., {"C", "D", "C", and "D"}.

[0014] The signal quality in the present disclosure can be at least one of, for example, RSRP (reference signal received power), BRSRP (beam reference signal received power), RSRQ (reference signal received quality), RSSI (received signal strength indicator), SINR (signal to interference and noise ratio), CINR (carrier to interference and noise ratio), SNR (signal to noise ratio), EVM (error vector magnitude), BER (bit error rate), and BLER (block error rate). Needless to say, in addition to the above examples, other terms having the same technical meaning or other metrics representing channel quality can be used. Hereinafter, in the present disclosure, a high signal quality means a case where the signal quality value related to the signal size is large or the signal quality value related to the error rate is small. A higher signal quality may mean that a smoother wireless communication environment is guaranteed. Note that the optimal beam may mean the beam with the highest signal quality among the beams.

[0015] The present disclosure describes various embodiments using terms used in some communication standards (for example, 3GPP (3rd Generation Partnership Project), ETSI (European Telecommunications Standards Institute)), but this is merely an example for explanation. Various embodiments of the present disclosure can be easily modified and applied in other communication systems.

[0016] FIG. 1 shows a wireless communication system.

[0017] Referring to FIG. 1, FIG. 1 shows a radio interface of a radio access technology (RAT), and shows a terminal 110 and a base station 120 as part of a node that utilizes a radio channel in a radio communication system using EUTRAN (evolved UMTS (Universal Mobile Telecommunications System) radio access network) or NR (New Radio). Although FIG. 1 shows only one base station, the radio communication system may further include other base stations that are the same as or similar to the base station (e.g., LTE eNB or NR gNB) 120.

[0018] The terminal 110 is a device used by a user and communicates with the base station 120 via a radio channel. The link from the base station 120 to the terminal 110 is called the downlink (DL), and the link from the terminal 110 to the base station 120 is called the uplink (UL). Although not shown in FIG. 1, the terminal 110 and other terminals can communicate with each other via a radio channel. In this case, the link (device-to-device link, D2D) between the terminal 110 and other terminals is called the sidelink, and this sidelink can be mixed with the PC5 interface. In some other embodiments, the terminal 110 can be operated without user involvement. According to one embodiment, the terminal 110 is a device that executes machine type communication (MTC) and may not be carried by a user. Further, according to one embodiment, the terminal 110 can be a NB (Narrowband)-IoT (Internet of thing) device.

[0019] In describing the systems and methods described herein, terminal 110 may be an electronic device used to communicate voice and / or data to base station 120, which in turn can communicate with a network of devices (e.g., a public switched telephone network (PSTN), the Internet, etc.).

[0020] Furthermore, terminal 110 may be referred to as "user equipment (UE)", "vehicle", "customer premises equipment (CPE)", "mobile station", "subscriber station", "remote terminal", "wireless terminal", "electronic device", or "user device", "access terminal", "mobile terminal", "remote station", "user terminal", "subscriber unit", "mobile device", or other terms with equivalent technical meaning.

[0021] Examples of terminal 110 include mobile phones, smartphones, personal digital assistants (PDAs), laptop computers, netbooks, e-readers, and wireless modems. In the 3GPP standard, terminal 110 is typically referred to as a UE. However, since the scope disclosed herein should not be limited to the 3GPP standard, the terms “UE” and “terminal” may be used interchangeably herein to mean the more general term “wireless communication device.” A UE may more generally be referred to as a terminal equipment device.

[0022] A base station 120 is network infrastructure that provides wireless connectivity to terminals 110. Terminals 110 have coverage defined based on the distance over which they can transmit signals. In 3GPP standards, base stations 120 may be referred to as "Node B," "Evolved Node B (eNodeB, eNB)," "5G node (5th generation node)," "Next generation node B (gNB)," "Home Enhanced or Evolved Node B (HeNB)," as well as "Access point (AP)," "Wireless point," "Transmission / reception point (TRP)," or other terms with equivalent technical meaning.

[0023] Since the scope of what is disclosed herein should not be limited to 3GPP standards, the terms “base station,” “node B,” “eNB,” and “HeNB” may be used interchangeably herein to mean the more general term “base station.” Furthermore, the term “base station” may be used to represent an access point. An access point may be an electronic device that provides access to a network for wireless communication devices (e.g., a local area network (LAN), the Internet, etc.). The term “communication device” may be used to represent both a wireless communication device and / or a base station. An eNB or gNB may be more generally referred to as a base station device.

[0024] The base station 120 can communicate with the core network entity 130. For example, the core network entity 130 may include a mobility management entity (MME) responsible for the control plane, such as terminal 110 connectivity and mobility control functions, and a serving gateway (S-GW) responsible for control functions over user data.

[0025] Terminal 110 can perform beamforming with base station 120. Terminal 110 and base station 120 can transmit and receive radio signals in relatively low frequency bands (e.g., NR FR1 (frequency range 1)). Terminal 110 and base station 120 can also transmit and receive radio signals in relatively high frequency bands (e.g., NR FR2 (or FR2-1, FR2-2, FR2-3), FR3) and millimeter wave (mmWave) bands (e.g., 28GHz, 30GHz, 38GHz, 60GHz). To improve channel gain, terminal 110 and base station 120 can perform beamforming. Here, beamforming may include transmit beamforming and / or receive beamforming. Terminal 110 and base station 120 can impart directionality to the transmitted or received signal. For this purpose, terminal 110 and base station 120 can select a serving beam through a beam search or beam management procedure. After the serving beam is selected, communication may be carried out through a resource that has a Quasi Co-Location (QCL) relationship with the resource that transmitted the serving beam.

[0026] If the large-scale characteristics of the channel that transmitted the symbol on the first antenna port can be inferred from the channel that transmitted the symbol on the second antenna port, then the first and second antenna ports can be evaluated as being in a QCL relationship. For example, the large-scale characteristics may include at least one of the following: delay spread, Doppler spread, Doppler shift, average gain, average delay, and spatial receiver parameter.

[0027] Both terminal 110 and base station 120 can perform beamforming, but the embodiments of this disclosure are not necessarily limited thereto. In some embodiments, terminal 110 may or may not perform beamforming. Similarly, base station 120 may or may not perform beamforming. That is, either terminal 110 or base station 120 may perform beamforming alone, or neither terminal 110 nor base station 120 may perform beamforming.

[0028] In this disclosure, "beam" means the spatial flow of a signal in a radio channel, which is formed by one or more antennas (or antenna elements), and such formation process may be referred to as beamforming. Beamforming may include at least one of analog beamforming or digital beamforming (e.g., precoding). Reference signals transmitted based on beamforming may include, for example, DM-RS (demodulation-reference signal), CSI-RS (channel state information-reference signal), SS / PBCH (synchronization signal / physical broadcast channel), and SRS (sounding reference signal). Furthermore, an information element (IE), such as a CSI-RS resource or an SRS resource, may be used as the configuration of each reference signal, and such a configuration may include information associated with the beam. Beam-related information can mean whether the configuration (e.g., a CSI-RS resource) uses the same spatial domain filter as other configurations (e.g., other CSI-RS resources within the same CSI-RS resource set), or uses a different spatial domain filter, or which reference signal it is quasi-co-located with, and if so, what type of quasi-co-located

[0029] In the following description of the embodiments, the terminal may be referred to as UE110, and the base station may be referred to as eNB120 or gNB120. In this disclosure, eNB120 is described as an example of a node providing an access network in order to describe IoT NTN for IoT UE, but it goes without saying that the same or similar methods can be applied to gNB120.

[0030] Figures 2a and 2b illustrate examples of non-terrestrial networks (NTNs). Figure 2a shows an example of a non-terrestrial network (NTN) utilizing transparent satellites. Figure 2b shows an example of a non-terrestrial network (NTN) utilizing regenerative satellites. NTN refers to an access network that provides non-terrestrial access to UEs (such as UE110) via NTN payloads and NTN gateways mounted on airborne or space-borne NTN vehicles. The access network may be provided via one or more eNBs (e.g., eNB120).

[0031] Referring to Figure 2a, NTN200 represents the network environment provided by the transparent satellite. NTN200 may include NTN payload 221 and NTN gateway 223 as eNB120. NTN payload 221 is a network node mounted on a satellite or HAPS (high altitude platform station) that provides connectivity between a service link (described later) and a feeder link (described later). NTN gateway 223 is an earth station located on the Earth's surface that provides connectivity to NTN payload 221 using the feeder link. NTN gateway 223 is a TNL (transport network layer) node. NTN200 can provide non-terrestrial access to UE110. NTN200 can provide non-terrestrial access to UE110 via NTN payload 221 and NTN gateway 223. The link between NTN payload 221 and UE110 may be referred to as a service link. The link between the NTN gateway 223 and the NTN payload 221 may be referred to as a feeder link. A feeder link may correspond to a wireless link.

[0032] The NTN payload 221 can receive radio protocol data from the UE 110 via the service link. The NTN payload 221 can transparently transmit the radio protocol data to the NTN gateway 223 via the feeder link. Therefore, from the perspective of the UE 110, the NTN payload 221 and the NTN gateway 223 can appear as a single eNB 120. The NTN payload 221 and the NTN gateway 223 can communicate with the UE 110 via the Uu interface, which is a common radio protocol. That is, the NTN payload 221 and the NTN gateway 223 can communicate with the UE 110 via radio protocol, just like a single eNB 120. The NTN gateway 223 can communicate with the core network entity 235 (MME (mobility management entity) or S-GW (serving gateway)) via the S1 interface.

[0033] According to one embodiment, the NTN payload 221 and NTN gateway 223 can use the wireless protocol stack in the control plane shown in Figure 3a, which will be described later. Furthermore, according to one embodiment, the NTN payload 221 and NTN gateway 223 can use the wireless protocol stack in the user plane shown in Figure 3b.

[0034] Figure 2a illustrates one NTN payload 221 and one NTN gateway 223 included in the eNB 120, but embodiments of the present disclosure are not limited thereto. For example, an eNB may include multiple NTN payloads. Furthermore, for example, an NTN payload may be provided by multiple eNBs. In other words, the implementation scenario shown in Figure 2a is an example and does not limit embodiments of the present disclosure.

[0035] Referring to Figure 2b, NTN250 represents the network environment provided by the regenerative satellite. NTN250 may include satellite 260 operating as eNB120. Satellite 260 represents a space-borne vehicle carrying a regenerative payload communications transmitter located in low-earth orbit (LEO), medium-earth orbit (MEO), or geostationary earth orbit (GEO). Satellite 260 may be referred to as a regenerative payload or regenerative satellite. Satellite 260 represents a payload configured to convert and amplify uplink RF signals before transmitting them downlink, and the conversion of such signals may mean digital processing that includes demodulation, decoding, recoding, remodulation, and / or filtering. NTN250 may include NTN Gateway 265, which is a ground-based entity connected to satellite 260. NTN Gateway 265 is an earth station located on the Earth's surface that provides connectivity to satellite 260 using the feeder link. NTN250 can provide non-terrestrial access to UE110. NTN250 can provide non-terrestrial access to UE110 via satellite 260 and NTN Gateway 265.

[0036] Satellite 260 may be configured to regenerate signals received from terminal 110 or an earth station (e.g., NTN gateway 265). A Uu interface may be defined between satellite 260 and terminal 110. A satellite radio interface (SRI) on the feeder link may be defined between satellite 260 and NTN gateway 265. Although not shown in Figure 2b, satellite 260 can provide inter-satellite links (ISL). The ISL is an inter-satellite transmission link and may be a 3GPP or non-3GPP defined radio interface (e.g., X2 interface or XN interface) or an optical interface. Satellite 260 can communicate with core network entity 235 (e.g., MME or S-GW) via the S1 interface based on NTN gateway 265. According to one embodiment, satellite 260 can utilize the radio protocol stack in the control plane of Figure 3a, described later. Furthermore, according to one embodiment, satellite 260 can utilize the radio protocol stack in the user plane shown in Figure 3b.

[0037] Figure 2b illustrates satellite 260 operating as eNB120, but embodiments of the present disclosure are not limited thereto. An eNB120 according to embodiments of the present disclosure can be implemented in a distributed deployment utilizing a centralized unit (CU) configured to perform upper layer functions of the access network (e.g., PDCP (packet data convergence protocol), RRC (radio resource control)) and distributed units (DUs) configured to perform lower layer functions. The interface between the CU and the distributed unit may be referred to as an F1 interface. The centralized unit (CU) is connected to one or more DUs and can perform functions higher than those of the DUs. For example, the CU may be responsible for the RRC (radio resource control) and PDCP (packet data convergence protocol) layers, while the DU and RU (radio unit) are responsible for lower layer functions. The DU may be responsible for the RLC (radio link control), MAC (media access control), and PHY (physical) layer functions. In this distributed configuration, satellite 260 can be used as a CU or DU constituting eNB120.

[0038] Figure 3a shows an example of a control plane (C-plane). At least some of the following description of eNB120 may be understood to apply to satellite 260.

[0039] Referring to Figure 3a, in the C plane, the UE110 and AMF235 can perform NAS (non-access stratum) signaling. In the C plane, the UE110 and eNB120 can communicate according to the protocols specified in the RRC layer, PDCP layer, RLC layer, MAC layer, and PHY layer, respectively.

[0040] In NTN Access, the main functions of the RRC layer include at least some of the following: - AS (Access Stratum) and NAS-related system information broadcasting - Paging - Setting up, maintaining, and disconnecting RRC connections between the UE and the access network, including, more specifically, controlling RLC, MAC, and PHY: - Adding, modifying, and removing Carrier Aggregations - Adding, modifying, and removing dual connectivity between NR or E-UTRA and NR. - Security features including key management - Setting up, configuring, maintaining, and deactivating SRB (Signaling Radio Bearer) and DRB (Data Radio Bearer) - Includes the following mobility features: - Handover and context transmission - Selection and re-selection of UE cells, and control of cell selection and re-selection. - Mobility between RATs - QoS (Quality of Service) management function - Reporting and control of UE measurement - Detection and recovery of radio link failures. - Send messages from / to the UE, to / from the NAS, and to the NAS.

[0041] In NTN Access, the main functions of the PDCP layer include at least some of the following functions: - Header compression and decompression function (ROHC only) - User data transmission function - Sequential delivery of upper layer PDUs - Out-of-sequence delivery of upper layer PDUs - Duplicate detection function (Duplicate detection of lower layer SDUs) - Retransmission function (Retransmission of PDCP SDUs) - Encryption and deciphering functions - Timer-based SDU discard function (SDU discard in uplink).

[0042] In NTN Access, the main functions of the RLC layer include at least some of the following: - Data transmission function (Transfer of upper layer PDUs) - Sequential delivery of upper layer PDUs - Out-of-sequence delivery of upper layer PDUs - ARQ function (Error Correction through ARQ) - Concatenation, segmentation, and reassembly of RLC SDUs - Re-segmentation function (RLC data PDUs) - Reordering function for RLC data PDUs - Duplicate detection function - Error detection function (Protocol error detection) - RLC SDU deletion function (RLC SDU discard) - RLC re-establishment function.

[0043] In NTN access, the MAC layer may be connected to several RLC layer devices configured in a single terminal, and the main functions of the MAC may include at least some of the following: - Mapping function between logical channels and transport channels - MAC SDU multiplexing and demultiplexing functionality - Scheduling information reporting function - Error correction through HARQ functionality - Priority handling between logical channels of one UE (Unified Element) - Priority handling between UEs by means of dynamic scheduling - MBMS service identification function - Transport format selection function - Padding function.

[0044] In NTN Access, each entity in the physical layer (e.g., terminal 110, eNB120) can perform operations such as channel coding and modulation of higher-layer data, generating OFDM symbols and transmitting them to the radio channel, or demodulating OFDM symbols received via the radio channel, channel decoding them, and transmitting them to the higher layer.

[0045] Figure 3b shows an example of a user plane (U-plane). At least some of the following explanation of eNB120 can be understood as relating to satellite 260.

[0046] Referring to Figure 3b, in the U-plane, UE110 and eNB120 can communicate according to the protocols specified in the PDCP layer, RLC layer, MAC layer, and PHY layer, respectively. For details on the PDCP layer, RLC layer, MAC layer, and PHY layer, please refer to the explanation in Figure 3a.

[0047] Figure 4 shows an example of a time-frequency domain resource structure supported by a wireless communication system to which embodiments proposed herein may be applied. While Figure 4 illustrates an example resource structure for an LTE network for IoT NTN, embodiments of this disclosure are not limited thereto. It goes without saying that signaling and related operations according to embodiments of this disclosure may also be applied to NR systems.

[0048] Referring to Figure 4, the horizontal axis represents the time domain, and the vertical axis represents the frequency domain. The smallest transmission unit in the time domain is the OFDM symbol, N symbA collection of OFDM symbols 402 constitutes one slot 406 (for example, seven in an LTE system). Referring to Figure 4, in a wireless communication system to which the present invention is applied, one radio frame 414 may be defined as having a length of 10 ms, consisting of 10 subframes, each having the same length of 1 ms. A radio frame 414 may be divided into 5 ms half-frames, each half-frame containing 5 subframes. In Figure 4, slot 406 consists of 7 OFDM symbols, although the length of the slot may vary depending on the subcarrier spacing. The radio resources supported in a wireless communication system to which the invention proposed herein may be applied consist of multiple time resources, which are symbols, and multiple frequency resources, which are subcarriers, and each time resource and frequency resource may be represented as a two-dimensional resource grid. In Figure 4, one of the smallest physical resources, a rectangle consisting of one subcarrier and one symbol within the resource grid, is referred to as Resource Element (RE) 412.

[0049] In a wireless communication system to which the invention proposed herein may be applied, the smallest transmission unit in the frequency domain is a subcarrier, and the carrier bandwidth constituting the resource grid is N BWIt may consist of multiple subcarriers 404. The basic unit of resource in the time-frequency domain is a resource element (RE) 412, which can be represented as an OFDM symbol index and a subcarrier index. A resource block 408 can contain multiple resource elements 412. In a wireless communication system to which the invention proposed herein may be applied, a resource block 408 (or physical resource block (PRB)) is N in the time domain. symb A sequence of OFDM symbols (for example, 7 symbols), and N in the frequency domain. SC RB It can be defined as 12 consecutive subcarriers. The data rate may increase in proportion to the number of RBs scheduled to the terminal. In a frequency division duplex (FDD) system where downlink and uplink are operated on separate frequencies, the downlink transmit bandwidth and the uplink transmit bandwidth may be different from each other. The channel bandwidth represents the RF (radio frequency) bandwidth corresponding to the system transmit bandwidth. For example, the channel bandwidth may be one of the following: 1.4 MHz (e.g., 6 PRB), 3 MHz (e.g., 15 PRB), 5 MHz (e.g., 25 PRB), 10 MHz (e.g., 50 PRB), 15 MHz (e.g., 75 PRB), or 20 MHz (e.g., 100 PRB).

[0050] E-UTRAN can support wireless access via a non-terrestrial network (NTN) not only for general UEs but also for BL (Bandwidth-Limited) UEs, CE (Coverage Enhancement) UEs, and NB-IoT UEs. Support for non-terrestrial networks may include platforms that provide wireless access via geostationary orbit (GSO), non-geostationary orbit (NGSO) (including low Earth orbit (LEO) and medium Earth orbit (MEO)), or high-altitude platform stations (HAPS).

[0051] In the transparent payload system, the NTN gateway and the NTN payload (i.e., the satellite) work together to perform the role of the eNB, while in the regenerative payload system, the NTN payload (i.e., the satellite) can perform the role of the eNB.

[0052] A transparent NTN payload transparently forwards the radio protocol received from the UE (over the service link) to the NTN gateway (over the feeder link), and vice versa. A regenerative payload can be terminated with the Uu interface (over the service link), S1, and X2 interfaces. An NTN gateway can support multiple transparent or regenerative NTN payloads. A transparent or regenerative NTN payload can be serviced by multiple eNBs. A regenerative NTN payload can be terminated with one or more intersatellite links leading to other regenerative payloads. As an example, a transparent NTN payload may change its carrier frequency before retransmitting over the service link, and vice versa (over the feeder links, respectively). In a non-terrestrial network, a tracking area may correspond to a fixed geographical area. In a non-terrestrial network, the same value may be used when the satellite ID refers to the same satellite in both the AS and the NAS.

[0053] In non-terrestrial networks, three types of service links may be supported. ● Earth-fixed: Provisioned with a beam that continuously covers the same geographical area (e.g., GSO satellites). ● Quasi-Earth-fixed: Provisioned with a beam that covers one geographical region for a limited period and another geographical region for other periods (e.g., when the NGSO satellite generates a steerable beam). ● Earth-moving: The coverage area is provisioned with a beam that moves as if gliding across the Earth's surface (e.g., when the NGSO satellite generates a fixed or uncontrollable beam).

[0054] eNBs using NGSO satellites may provide quasi-Earth-fixed cell coverage or Earth-moving cell coverage, while eNBs using GSO satellites may provide Earth-fixed cell coverage or quasi-Earth-fixed cell coverage.

[0055] The store-and-forward (S&F) mode may be used to provide communication services to a UE when the serving satellite has a discontinuous connection to a ground network and that connection is unavailable when the satellite interacts with the UE. The eNB can indicate whether the cell is operating in store-and-forward mode. The store-and-forward mode means an operating mode in which the service satellite has a discontinuous connection to an NTN gateway and provides communication services to the UE when the connection to the NTN gateway is unavailable when the satellite interacts with the UE.

[0056] Figure 5 shows an example of the S&F (store and forward) mode in IoT (Internet of Everything) NTN (non-terrestrial network).

[0057] Referring to Figure 5, UE510 can communicate with satellite 520. UE510 may be referred to as terminal 110 in Figure 1. Satellite 520 may be referred to as base station 120 or a network entity performing at least some of the functions of base station 120. According to one embodiment, satellite 520 may be an eNB providing IoT NTN. Satellite 520 can provide E-UTRAN for IoT devices (e.g., UE510). UE510 can connect to satellite 520 via E-UTRAN. The connection between satellite 520 and UE510 may be referred to as a service link. Satellite 520 can move along a designated orbit. Depending on the movement of satellite 520, satellite 520 may connect to a ground-based network entity (hereinafter referred to as a ground segment) (e.g., NTN gateway 530). The connection between satellite 520 and NTN gateway 530 may be referred to as a feeder link. The NTN gateway 530 may be connected to the core network 550 via the transmission network 540. As the satellite 520 repeatedly moves along the designated orbit, the service link may be available or unavailable. As the satellite 520 repeatedly moves along the designated orbit, the feeder link may be available or unavailable.

[0058] Satellite 520 can support S&F (store and forward) mode. S&F (store and forward) mode can represent an operating mode of a system that is capable of satellite access. Delay-tolerant communication services can be provided via S&F (store and forward) mode. When satellite access is intermittently or temporarily unavailable (for example, when serving a UE510 located in a coverage area where the feeder link to the ground segment (e.g., NTN Gateway 530) is not simultaneously activated), a level of service that stores and forwards data can be provided. According to one embodiment, satellite 520 can be used to provide delay-tolerant IoT services via NGSO (non-geostationary satellite orbit) (e.g., LEO (low earth orbit)). According to one embodiment, satellite 520 can provide satellite access to a UE510 that does not have a GNSS (global navigation satellite system) receiver or has difficulty connecting to GNSS services. As a non-restrictive example, satellite 520 can perform UE-satellite-UE communication with UE510. For example, UE510 can communicate with satellite 520 without communicating with the ground segment (e.g., NTN gateway 530) to avoid long latency and limited data rates and reduce resource consumption. S&F mode can be used for latency-tolerant and / or interruption-tolerant services. For example, in a 3GPP context, SMS (short message service) may be used for S&F mode, and end-to-end connectivity between endpoints (e.g., UE510 and application server) may not be required. Only connectivity between the endpoint (e.g., UE510) and an intermediate node (e.g., SMSC (short message service center)) may be required.

[0059] In S&F mode, the service link between UE510 and satellite 520 can alternate between available and unavailable states. When the service link between UE510 and satellite 520 is available, it indicates that satellite 520 is located within the range where it can provide service to the area (e.g., footprint) where UE510 is located on satellite 520's orbit (hereinafter referred to as the "service-available orbit segment"). When the service link between UE510 and satellite 520 is unavailable, it indicates that satellite 520 is located within the range where it is difficult to provide service to the area (e.g., footprint) where UE510 is located on satellite 520's orbit (hereinafter referred to as the "service-unavailable orbit segment"). In S&F mode, the feeder link between satellite 520 and the ground segment (e.g., NTN Gateway 530) can alternate between available and unavailable states. The availability of the feeder link between satellite 520 and the ground segment (e.g., NTN Gateway 530) indicates that the satellite 520 is located within the range (e.g., footprint) of the area where the ground segment (e.g., NTN Gateway 530) is located on satellite 520's orbit, where service can be provided (hereinafter referred to as the "feeder-available orbit segment"). The unavailability of the service link between satellite 520 and the ground segment (e.g., NTN Gateway 530) indicates that the satellite 520 is located within the range (e.g., footprint) of the area where the ground segment (e.g., NTN Gateway 530) is located on satellite 520's orbit, where service is difficult to provide (hereinafter referred to as the "feeder-unavailable orbit segment"). With respect to UE510, the availability of the service link and the availability of the feeder link do not necessarily occur simultaneously. For example, even if the status of the service link changes from available to unavailable, the status of the feeder link does not change. For example, even if the status of the feeder link changes from available to unavailable, the status of the service link does not change.

[0060] According to one embodiment, UE510 can transmit a signal. The signal may be MO (mobile originated) data. For example, in operation 591, UE510 can transmit uplink data (e.g., PUSCH) to satellite 520 when the service link is available. Satellite 520 can receive the uplink data from UE510. Since the feeder link is not available, satellite 520 can store the uplink data. Satellite 520 can then move. In response to the move, the state of the feeder link may change from available to unavailable. In operation 592, satellite 520 can transmit the uplink data via a network entity located on the ground (e.g., NTN gateway 530). The uplink data can be transmitted to the data network via the core network 550. Hereinafter, in S&F mode, the service to which a message originating from UE510 via satellite 520 is transmitted may be referred to as an MO service.

[0061] According to one embodiment, satellite 520 can transmit a signal to UE 510. The signal may be MT (mobile terminated) data. For example, in operation 593, while the feeder link is available, satellite 520 can receive data from external devices (e.g., servers, other UEs) via the data network and core network 550 (e.g., UPF). Satellite 520 can move. Depending on the movement of satellite 520, the state of the feeder link may be changed from available to unavailable. Depending on the movement of satellite 520, the state of the service link between satellite 520 and UE 510 may be changed from unavailable to available. In operation 594, when the service link is available, satellite 520 can transmit downlink data (e.g., PDSCH) to UE 510. Hereinafter, in S&F mode, the service of messages transmitted from UE 510 via satellite 520 may be referred to as MT service.

[0062] 1. Indication signaling related to S&F mode For S&F mode, the UE510 can receive indications on the system information broadcast from the serving satellite (e.g., satellite 520) indicating whether the serving satellite is currently operating in S&F mode. In satellite systems using S&F mode, the feeder link state across various RRC states can affect the operation of the UE510. From the perspective of the UE510, the following three scenarios are possible:

[0063] 1) Normal operation: Service link and feeder link are available simultaneously. 2) S&F operation: Only service link is possible. 3) Coupling operation: The state of the feeder link changes at specific points in time within the coverage path period. For example, an earth-moving cell (where the received coverage of the Earth's surface fluctuates as the satellite moves). To effectively manage scenarios, the UE510 needs to be able to identify the current operating mode through the indications provided in the system information. Therefore, the UE510 is required to know the following information:

[0064] - Whether the service satellite supports S&F connectivity. - Service satellite feeder status, - Remaining duration of the current feeder link state By providing the aforementioned information, the UE510 can perform appropriate operations under various conditions. If the service satellite supports S&F connectivity, the UE510's operation may differ depending on the status of the satellite's feeder link.

[0065] If the feeder link is available, the remaining duration can correspond to the validity period of the normal operation mode (hereinafter referred to as normal mode). If the feeder link is unavailable, the remaining duration can correspond to the validity period of the S&F operation mode (i.e., S&F mode). Furthermore, if the service link is available, the service link duration can correspond to the validity period of the S&F operation mode (i.e., S&F mode). Similarly, if the service link is unavailable, the service link duration can correspond to the start time of the S&F operation mode (i.e., S&F mode). The UE510 can know the status of the service link, but it cannot directly know the status of the feeder link; therefore, it is required to know the status of the feeder link. Furthermore, the UE510 is required to know the duration of the service link. In embodiments of this disclosure, the following describes signaling techniques provided from the network side to determine how UE510 operates with respect to a service satellite (e.g., satellite 520) under different scenarios.

[0066] According to embodiments of the present disclosure, a network (e.g., eNB) can instruct a terminal (e.g., UE) to enter store-and-forward mode via an SIB1 message. For example, an SIB1 message may contain an 'sf-OperationMode' IE (information element). The IE may indicate that a cell is operating in store-and-forward mode. If the field is present, a UE supporting store-and-forward operation may ignore cellBarred-NTN and cellBarred. The IE may have a value of 'barred' or 'notBarred'. The value 'barred' means that the cell is barred from NTN connections via store-and-forward operation, as defined in TS 36.304. The value 'notBarred' means that the cell allows access from a UE supporting store-and-forward operation. If this field is not present, the SIB1 message may indicate that an NTN cell is operating in normal mode, i.e., in a mode other than store-and-forward mode.

[0067] According to embodiments of the present disclosure, a network (e.g., eNB) can instruct a terminal (e.g., UE) via SIB31 time information related to store-and-forward mode. SIB31 may include satellite assistance information relating to the serving cell. The satellite assistance information may include ephemeris information, satellite ID, and reference position information in SIB31. According to one embodiment, the SIB31 message may include switching time information (e.g., t-ModeSwitching) IE. If sf-OperationMode is present in SIB1, this field indicates the time information for when the NTN cell switches from store-and-forward operating mode to normal mode. Otherwise, this field indicates the time information for when the NTN cell switches from normal mode to store-and-forward mode.

[0068] Figure 6 shows signaling information regarding the validity period of the S&F mode. Satellite 520 may be configured to perform the functions of an eNB. For example, the eNB may be located on the board of satellite 520, and entities of the core network (e.g., core network 550) may be located on the ground. For example, the eNB and some of the entities of the core network (or some of a specific entity (e.g., MME (mobile management entity))) may be located on the board of satellite 520, and other entities of the core network may be located on the ground.

[0069] Referring to Figure 6, in operation 601, satellite 520 can transmit information regarding the S&F mode validity period to UE 510. The S&F mode validity period can represent the time during which satellite 520's S&F mode is active. For example, the S&F mode validity period can represent the remaining period during which satellite 520's feeder link is unavailable and until the feeder link becomes available. In this case, the S&F mode validity period can be satellite-specific or cell-specific. Since the feeder link is the connection between satellite 520 and the ground station, the state of the feeder link between satellite 520 and the ground station can be determined depending on the orbit of satellite 520. Therefore, satellite 520 can know when the feeder link is expected to be restored. The S&F mode validity period can be indicated independently of the service link state.

[0070] According to one embodiment, the effective time of the S&F mode can indicate the point in time when the feeder link connection is restored. This point in time may be indicated as an absolute time. 3GPP defines a “t-service” IE (information element) to indicate the service time of a cell provided by satellite 520. The “t-service” IE indicates time information regarding the time during which a cell provided through the NTN system will interrupt service in the area it currently serves. The IE may be applied to service link switching of the NTN quasi-Earth fixed system and to feeder link switching for both the NTN quasi-Earth fixed system and the NTN Earth moving system. The IE expresses time in multiples of 10ms after 00:00:00 on January 1, 1900 (midnight between Sunday, December 31, 1899 and Monday, January 1, 1900) in the Gregorian calendar. The exact stop time is between the time indicated by the value of this field minus 1 and the time indicated by the value of this field. The reference point of the IE is the cell's uplink time synchronization reference point. The validity period of S&F mode can be indicated in this manner. For example, the validity period of S&F mode can be indicated as an absolute point in time, such as the "t-service" IE. In another example, the validity period of S&F mode can be indicated in a manner such as HFN (hyper frame number), SFN (system frame number), RF (radio frame), SF (subframe), and / or symbol index. In one example, the validity period of S&F mode can be indicated as follows:

[0071] [Table 1] JPEG2026100835000003.jpg245170JPEG2026100835000004.jpg67170

[0072] The "t-feederStart-r19" IE can indicate the point in time when the feeder link for a cell provided by satellite 520 (i.e., an NTN cell) is initiated.

[0073] In addition to the feeder link to the serving satellite, the start time of the feeder link to the adjacent satellite may be specified to indicate the effective duration of the S&F mode to the adjacent satellite.

[0074] [Table 2] JPEG2026100835000006.jpg213170

[0075] The "t-feederStartNeigh-r19" IE can indicate the point in time when the feeder link of a satellite adjacent to satellite 520 is initiated.

[0076] For information representing absolute time, the UTC format may be used. The following table may be referenced for the UTC format.

[0077] [Table 3]

[0078] In another embodiment, the validity period of S&F mode may be expressed as a relative time. For example, the relative time may represent the difference between the point at which service by the NTN cell ends (e.g., "t-service" IE) and the point at which the feeder link connection is restored. In other words, the validity period of S&F mode may be expressed as a relative time (e.g., an offset). In one example, the validity period of S&F mode may be expressed as a value relative to an absolute value expressed via "t-service".

[0079] Satellite 520 can transmit information regarding the validity period of the S&F mode. According to one embodiment, satellite 520 can broadcast information regarding the validity period of the S&F mode via system information. For example, the system information may be SIB31. For example, the system information may be SIB32. As another example, satellite 520 can broadcast information regarding the validity period of the S&F mode of an adjacent satellite via SIB33. According to another embodiment, satellite 520 can transmit information regarding the validity period of the S&F mode via RRC messages (e.g., RRC reconfiguration messages). If a ground station connected to satellite 520 via a feeder link is changed, or if satellite 520 is changed from normal mode to S&F mode, satellite 520 can change the RRC configuration of the cell while maintaining the RRC connection state.

[0080] Satellite 520 can transmit information regarding the validity period of the S&F mode along with other information. According to one embodiment, satellite 520 can transmit information regarding the validity period of the S&F mode along with the operating mode of satellite 520 via a message (e.g., an SI (system information) message or an RRC message). The operating mode may include an indicator indicating whether it is in normal mode or S&F mode. In one example, if the operating mode represents S&F mode, information regarding the validity period of S&F mode may be included in the message. According to one embodiment, satellite 520 can transmit information regarding the current feeder link status along with a message (e.g., an SI (system information) message or an RRC message). The information regarding the feeder link status may include an indicator indicating whether the current feeder link status is available or unavailable. In one example, if the information indicates that the feeder link status is unavailable, information regarding the validity period of S&F mode may be included in the message.

[0081] 2. S&F mode and RRC states When the satellite switches to S&F mode, it is necessary to define how the UE510 behaves in RRC connected mode. This is because, in S&F mode, the network cannot acquire new downlink data to the UE. On the other hand, for uplink data, the UE510 can continue transmitting data to the network as long as the network allows it. Since satellite 520 acts as a RAN node, it can release the DRB which requires strict latency if the feeder link is disconnected. Once data transmission is complete, satellite 520 can disconnect the UE's RRC connection for power saving purposes. In the case of UE510 in RRC connected mode, the network may not automatically transition the UE510 to idle mode when it switches to S&F mode. Through the network configuration, it is possible to ensure that only DRBs with acceptable latency are maintained when satellite 520 switches to S&F mode.

[0082] Figure 7 shows an example of the RRC (Radio Resource Control) connection status of IoTUE (user equipment).

[0083] Referring to Figure 7, the RRC layer can be responsible for signal management between the UE 510 and the satellite 520. The RRC layer can handle tasks such as setting up, maintaining, and disconnecting wireless connections, as well as mobility and security. The states of the RRC layer (hereinafter referred to as RRC states) can include an RRC connected state 710 corresponding to a connected mode and an RRC idle state 720 corresponding to a standby mode. Each state serves a different purpose in the communication process, and through transitions between states, battery consumption can be managed while the UE communicates efficiently with the network. The UE 510 can perform transitions between the RRC connected state 710 and the RRC idle state 720 in response to network activity. Such transitions can be triggered on the network side by factors such as user data requests, signaling activity, or power saving requests. For example, a transition from the RRC idle state 720 to the RRC connected state 710 occurs when the UE 510 needs to send or receive data. The UE 510 can transition to the connected state by sending an RRC connection request. For example, the transition from RRC connected state 710 to RRC idle state 720 may occur when UE510 is no longer involved in active communication. When the network side (e.g., satellite 520) releases its radio resources, UE520 can return to standby mode to conserve battery power.

[0084] In RRC idle state 720, the UE510 does not actively send or receive user data and may not be allocated dedicated resources on the network. However, the UE510 can still monitor network paging messages and system information. The UE510 can maintain battery life by using only minimal power. In RRC idle state 720, the UE510 can continuously monitor the signal strength of adjacent cells and, if necessary, perform cell reselection to switch to a better cell. Furthermore, in RRC idle state 720, the UE510 can perform paging reception to check for incoming phone, SMS, or mobile end data session information by receiving paging messages from the network (e.g., satellite 520). The UE510 can perform discontinuous reception (DRX), which saves power by periodically waking up to check for paging messages and then remaining inactive for the rest of the time. When the UE510 moves between different tracking areas, it can perform a tracking area update (TAU) procedure to update its position to the network (e.g., satellite 520) and allow the network to track the UE510 for future communications.

[0085] Figure 8a shows an example of RRC connection termination in S&F mode. Satellite 520 may be configured to perform the functions of an eNB. In one example, the eNB may be located on the board of satellite 520, and entities of the core network (e.g., core network 550) may be located on the ground. In one example, the eNB and some of the entities of the core network (or some of a specific entity (e.g., MME (mobile management entity))) may be located on the board of satellite 520, and other entities of the entities of the core network may be located on the ground.

[0086] Referring to Figure 8a, in operation 810, UE510 and satellite 520 can communicate in an RRC connection state (e.g., RRC connection state 710).

[0087] In operation 801, satellite 520 can operate in S&F mode. When transitioning to S&F mode, satellite 520 can decide whether or not to disconnect the RRC connection with UE 510. In S&F mode, satellite 520 cannot acquire new downlink data. However, satellite 520 can acquire uplink data from UE 510. Satellite 520 can decide whether or not to disconnect the RRC connection based on the communication services connected to UE 510. According to one embodiment, satellite 520 can decide whether or not to disconnect the RRC connection based on the status of the feeder link. In one example, the status of the feeder link may include the expected recovery time of the feeder link, the channel capacity of the feeder link, the time the feeder link has been disconnected, and / or the time the feeder link has been unavailable. According to one embodiment, satellite 520 can decide whether or not to disconnect the RRC connection based on the status of the service link. In one example, if the channel quality measured on the service link (e.g., RSRP, CQI, SINR) is below a threshold, satellite 520 can decide to disconnect the RRC connection. According to one embodiment, satellite 520 can decide whether or not to disconnect the RRC connection based on the DRB. In one example, if the QCI of the DRB indicates that the packet delay budget is below a threshold, satellite 520 can decide to disconnect the RRC connection. According to one embodiment, satellite 520 can decide whether or not to disconnect the RRC connection based on the QoS flow. In one example, if the allowable delay time is below a threshold according to the 5QI related to the QoS flow, satellite 520 can decide to disconnect the RRC connection. According to one embodiment, satellite 520 can decide whether or not to disconnect the RRC connection based on the network slice. For example, if the SST (slice service type) and / or SD (slice differentiator) of the network slice indicate a delay-sensitive service (e.g., if the SST indicates URLLC), satellite 520 can decide to disconnect the RRC connection.Under the following circumstances, satellite 520 may decide to disconnect the RRC connection with UE510.

[0088] In operation 803, satellite 520 may transmit a control signal to UE 510. Satellite 520 may transmit a control signal to disconnect the RRC connection. According to one embodiment, the control signal may be an RRC message for disconnecting the RRC connection. According to one embodiment, the RRC message may include configuration information for configuring S&F mode.

[0089] [Table 4] JPEG2026100835000009.jpg245170JPEG2026100835000010.jpg245170JPEG2026100835000011.jpg153170

[0090] According to one embodiment, an RRC message for disconnecting an RRC connection may include "StoreandForward" as the cause value for disconnection.

[0091] [Table 5] JPEG2026100835000013.jpg201170

[0092] As a non-limiting example, contrary to what is shown in Figure 8a, satellite 520 may also send configuration information for configuring S&F mode to UE510 as a separate message from the RRC message for disconnecting the RRC connection.

[0093] In operation 805, UE510 may disconnect the RRC connection. In response to the control signal, UE510 may perform a procedure to disconnect the RRC connection. As the RRC connection is disconnected, the connection state of UE510 may change from the RRC connected state to the RRC idle state.

[0094] In operation 820, UE510 may be in an RRC idle state (e.g., RRC idle state 720). UE510 may be configured to perform operations in RRC idle state 710 as shown in Figure 7. For example, UE510 may monitor paging messages and / or system information. For example, UE510 may perform cell reselection.

[0095] Figure 8a illustrates an example of RRC connection disconnection, but embodiments of this disclosure are not limited thereto. For example, in addition to disconnecting the RRC connection, a low-power mode of the UE510 may be triggered via MAC CE or DCI. In another example, an inactivity timer for S&F mode may be configured. The inactivity timer may induce the disconnection of the RRC connection of the UE510 if there is no data transmission for a certain period of time.

[0096] Figure 8b shows an example of a request to disconnect the RRC connection in S&F mode. Satellite 520 may be configured to perform the functions of an eNB. In one example, the eNB may be located on the board of satellite 520, and entities of the core network (e.g., core network 550) may be located on the ground. In one example, the eNB and some of the entities of the core network (or some of a specific entity (e.g., MME (mobile management entity))) may be located on the board of satellite 520, and other entities of the entities of the core network may be located on the ground.

[0097] Referring to Figure 8b, in operation 810, UE510 and satellite 520 can communicate in an RRC connection state (e.g., RRC connection state 710).

[0098] In operation 851, satellite 520 can operate in S&F mode. In S&F mode, satellite 520 cannot acquire new downlink data. However, satellite 520 can acquire uplink data from UE 510. Whether or not the RRC connection is terminated can be determined by the presence or absence of uplink data from UE 510. If there is no data transmission or reception for a certain period of time, satellite 520 can terminate the RRC connection via a pre-configured parameter (e.g., an inactivity timer). For example, if there is no traffic with UE 510, the eNB of satellite 520 can send a UE context de-context request to the MME and receive a UE context de-context completion message from the MME. After that, satellite 520 can send an RRC connection termination message. However, such a procedure not only requires waiting for the inactivity timer to expire, but may also take more time to terminate the RRC connection. Therefore, satellite 520 can monitor the status of UE 510 and, based on a request from UE 510, determine whether or not to terminate the RRC connection.

[0099] In operation 853, satellite 520 may send a message to UE 510 to indicate the operation of satellite 520 in S&F mode. According to one embodiment, the message may include a message related to an operating condition. For example, the operating condition may represent a trigger condition for UE 510 to request the disconnection of the RRC connection. For example, the message may include a list of data services to maintain the RRC connection without disconnecting it, even in S&F mode. As an example, the list may include a DRB list, a QoSFlow list, a list of S-NSSAI (Single Network Slice Selection Assistance Information), and / or a list of resource areas (e.g., BWP, PRB, subband). For example, the message may include a threshold for a metric (e.g., RSRP, SINR). If the channel quality is measured to be above the threshold for the metric, UE 510 can perform communication without requesting the disconnection of the RRC connection. If the channel quality is measured to be below the threshold for the metric, UE 510 can request the disconnection of the RRC connection. For example, the message may include a threshold for data traffic. If the amount of data to be transmitted (e.g., the amount of data held in the buffer, TBS (transport block size)) is less than the data traffic threshold, the UE510 can perform communication without requesting the RRC connection to be terminated. If the amount of data to be transmitted is greater than or equal to the data traffic threshold, the UE510 can request the RRC connection to be terminated.

[0100] In operation 855, UE510 can verify the operating conditions. Based on the message received in operation 853, UE510 can determine whether the operating conditions are met. Based on the message received in operation 853, if the operating conditions are met, UE510 can execute operation 857. For example, if the channel quality measured is below a metric threshold, UE510 can execute operation 857. For example, if the amount of data to be transmitted is greater than or equal to the data traffic threshold, UE510 can execute operation 857. As a non-limiting example, UE510 can verify that there is no further data after completing an uplink transmission. UE510 can determine that the operating conditions are met. According to one embodiment, after completing the uplink transmission, if a period of time equal to the non-activity timer has elapsed, the RRC connection may be terminated even if there is no request from UE510. Therefore, a request from UE510 may be meaningful if made within a time period shorter than the non-activity timer. UE510 can determine whether the operating conditions are met based on the time of the non-activity timer (for example, by comparing the time related to the round-trip time (RTT) between UE510 and UE510 with the time of the non-activity timer). Although not shown in Figure 8b, UE510 can perform uplink data communication if the operating conditions are not met. After repeatedly determining whether the operating conditions are met, operation 875 can be executed when the operating conditions are met.

[0101] In operation 857, UE 510 may transmit a request signal in response to a determination that the operating conditions have been met. To request the disconnection of the high-speed RRC connection, UE 510 may transmit the request signal. For example, the request signal may include an indicator that directly requests the disconnection of the RRC. For example, the request signal may include an indicator that the conditions set in the message of operation 853 have been met. Based on the indicator, satellite 520 may decide whether or not to transmit an RRC disconnection message. For example, the request signal may transmit information about the measured channel quality. Based on the information, satellite 520 may decide whether or not to transmit an RRC disconnection message. For example, the request signal may include the size of the amount of data moored in UE 510's uplink buffer. Based on the size, satellite 520 may decide whether or not to transmit an RRC disconnection message.

[0102] The request signal according to various embodiments of this disclosure may be executed via one of various procedures. According to one embodiment, the request signal may be executed via an RRC message. In S&F mode, another RRC message may be defined to request the disconnection of the RRC connection. According to one embodiment, the request signal may execute a random access procedure. The request to disconnect the RRC connection may be instructed via a random access preamble or message 3. According to one embodiment, the request signal may be executed via a predefined sequence. UE510 may provide satellite 520 with a request to disconnect the RRC connection by transmitting a predefined sequence (e.g., m value, cs (cycle shift) value, pattern) on PUCCH. According to one embodiment, the request signal may be executed via a MAC CE (control element). For example, the MAC CE may include a BSR (buffer status reporting) MAC CE (control element). The BSR may be used to request the disconnection of the RRC connection as well as the amount of uplink data. As the amount of uplink data below a threshold (e.g., 0 or a specified value) is included in the BSR MAC CE, satellite 520 can indirectly identify that the BSR MAC CE is a request to disconnect the RRC connection.

[0103] Based on the request signal, satellite 520 can decide whether or not to disconnect the RRC connection. Once satellite 520 decides to disconnect the RRC connection, satellite 520 can send an RRC disconnection message to UE 510.

[0104] In operation 820, UE510 may be in an RRC idle state (e.g., RRC idle state 720). UE510 may be configured to perform operations in RRC idle state 710 as shown in Figure 7. For example, UE510 may monitor paging messages and / or system information. For example, UE510 may perform cell reselection.

[0105] Figure 8a illustrates an example of RRC connection termination, but embodiments of this disclosure are not limited thereto. For example, in addition to a request to terminate the RRC connection, a low-power mode of the UE510 may be triggered via MAC CE or DCI. In another example, an inactivity timer for S&F mode may be configured. The inactivity timer for S&F mode can induce the termination of the RRC connection of the UE510 if there is no data transmission for a certain period of time. The length of the inactivity timer for S&F mode may be set shorter than the length of an inactivity timer set for normal operation and / or between a general ground base station and a terminal, which is possible for both service links and feeder links.

[0106] Figure 9 shows an example of the components of a UE (e.g., UE510).

[0107] Referring to Figure 9, the UE510 may include a transceiver 901, a processor 903, and memory 905. The transceiver 901 performs the function of sending and receiving signals over a radio channel. For example, the transceiver 901 upconverts a baseband signal to an RF band signal and transmits it via an antenna, and downconverts the RF band signal received via the antenna back to a baseband signal. For example, the transceiver 901 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC (digital to analog converter), an ADC (analog to digital converter), etc.

[0108] The transceiver 901 may include multiple transmit / receive paths. Furthermore, the transceiver 901 may include an antenna section. The transceiver 901 may include at least one antenna array composed of multiple antenna elements. From a hardware perspective, the transceiver 901 may consist of digital and analog circuits (e.g., an RFIC (radio frequency integrated circuit)). Here, the digital and analog circuits may be implemented as a single package. Furthermore, the transceiver 901 may include multiple RF chains. The transceiver 901 can perform beamforming. The transceiver 901 may apply beamforming weights to signals to impart directionality to the signals to be transmitted or received according to the settings of the processor 903. According to one embodiment, the transceiver 901 may include an RF (radio frequency) block (or RF section). According to one embodiment, the transceiver 901 can support satellite communications. The UE 510 can transmit signals to or receive signals from a satellite (e.g., satellite 520) via the transceiver 901.

[0109] The transceiver 901 can transmit and receive signals over a radio access network. For example, the transceiver 901 can receive downlink signals. Downlink signals may include synchronization signals (SS), reference signals (RS) (e.g., CRS (cell-specific reference signal), DM (demodulation)-RS), system information (e.g., MIB, SIB, RMSI (remaining system information), OSI (other system information)), configuration messages, control information, or downlink data. Furthermore, for example, the transceiver 901 can transmit uplink signals. The uplink signal may include random access-related signals (e.g., random access preamble (RAP) (or Msg1 (message 1)), Msg3 (message 3)), reference signals (e.g., SRS (sounding reference signal), DM-RS), uplink control information (UCI) (e.g., CSI (channel state information), HARQ (hybrid automatic repeat request), SR (scheduling request)), or power headroom reports (PHR). Although only the transceiver 901 is shown in Figure 9, according to another embodiment, the UE510 may include two or more RF transceivers.

[0110] The processor 903 controls the overall operation of the UE510. The processor 903 may be referred to as the control unit. For example, the processor 903 transmits and receives signals via the transceiver 901. The processor 903 also writes and reads data to and from the memory 905. Furthermore, the processor 903 can perform the functions of the protocol stack required by the communication standard. Although only the processor 903 is shown in Figure 9, according to another embodiment, the UE510 may include two or more processors. The processor 903 may be an instruction / code or memory area storing instructions / code that resides at least temporarily in the processor 903 as an instruction set or code stored in the memory 905, or it may be part of the circuitry that constitutes the processor 903. In addition, the processor 903 may include various modules for performing communication. The processor 903 can control the UE510 to perform the operations according to the embodiment.

[0111] Memory 905 stores data such as basic programs, application programs, and configuration information for the operation of the UE510. Memory 905 may be referred to as a storage unit. Memory 905 may consist of volatile memory, non-volatile memory, or a combination of volatile and non-volatile memory. Memory 905 then provides the stored data in response to requests from processor 903. According to one embodiment, memory 905 may include memory for conditions, instructions, or settings related to satellite communication transmission schemes.

[0112] Figure 10 shows an example of the components of a satellite (e.g., satellite 520).

[0113] Referring to Figure 10, satellite 520 may include at least one transceiver 1001, at least one processor 1003, and at least one memory 1005. Hereafter, components are described singly, but implementations of multiple components or subcomponents are not excluded.

[0114] The transceiver 1001 performs the function of transmitting and receiving signals via a wireless channel. For example, the transceiver 1001 performs the function of converting between baseband signals and bit sequences according to the system's physical layer standard. For example, when transmitting data, the transceiver 1001 generates complex symbols by encoding and modulating the transmitted bit sequence. When receiving data, the transceiver 1001 demodulates and decodes the baseband signal to restore the received bit sequence. The transceiver 1001 also upconverts the baseband signal to an RF (radio frequency) band signal and transmits it via the antenna, and downconverts the RF band signal received via the antenna back to a baseband signal. For this purpose, the transceiver 1001 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC (digital to analog converter), an ADC (analog to digital converter), etc. Furthermore, the transceiver 1001 may include multiple transmit and receive paths. Furthermore, the transceiver 1001 may include at least one antenna array composed of multiple antenna elements. From a hardware perspective, the transceiver 1001 may consist of a digital unit and an analog unit, and the analog unit may consist of multiple sub-units depending on the operating power, operating frequency, etc. The transceiver 1001 transmits and receives signals as described above. Therefore, the transceiver 1001 may be referred to as the "transmitting unit," the "receiving unit," or the "transmitting / receiving unit."

[0115] The transceiver 1001 does not exclude the ability to transmit or receive signals not only via wireless channels but also via backhaul networks, optical communications, Ethernet, and other wired paths. For example, the transceiver 1001 can support optical communications for satellite 520 to signal with other satellites. Satellite 520 can communicate with other satellites using optical communications by using lasers via the transceiver 1001. For example, wired communications between components within satellite 520 may be supported. The transceiver 1001 can convert bit streams transmitted to other nodes in satellite 520, such as other connection nodes, other base stations, higher-level nodes, core networks, etc., into physical signals, and can convert physical signals received from other nodes into bit streams.

[0116] The transceiver 1001 can support communication between satellite 520 and UE 510. The transceiver 1001 can support communication not only between satellite 520 and UE 510, but also between satellite 520 and the ground segment (e.g., NTN gateway 530, network entities of core network 550). As a non-limiting example, circuits for communication with UE 510 and circuits for communication with the ground segment (e.g., NTN gateway 530, network entities of core network 550) can be distinguished within the transceiver 1001.

[0117] The processor 1003 can control the overall operation of the satellite 520. For example, the processor 1003 writes to and reads data from the memory 1005. For example, the processor 1003 transmits and receives signals via the transceiver 1001. Figure 10 shows one processor, but embodiments of the present disclosure are not limited thereto. The satellite 520 may include at least one processor (e.g., multiple processors) to perform embodiments of the present disclosure. The processor 1003 may be referred to as a control unit or control means. According to embodiments of the present disclosure, the processor 1003 can control the satellite 520 to perform at least one of the operations or methods according to embodiments of the present disclosure.

[0118] Memory 1005 can store data such as basic programs, application programs, and configuration information for the operation of satellite 520. Memory 1005 can store various data used by at least one component (e.g., transceiver 1001, processor 1003). The data may include, for example, software and input or output data for related instructions. Memory 1005 may consist of volatile memory, non-volatile memory, or a combination of volatile and non-volatile memory. Memory 1005 can then provide the stored data to the processor 1003 upon request.

[0119] Embodiments of the present disclosure provide a satellite device configured to provide NTN (non-terrestrial network) access and perform the functions of an evolved node B (eNB). The device may include a memory containing instructions; at least one processor; and at least one transceiver. When executed by the at least one processor, the instructions may cause the device to identify store and forward (S&F) mode while connected to a user equipment (UE) via radio resource control (RRC), send a message to the UE indicating that the satellite is operating in S&F mode, receive a request signal from the UE to disconnect the RRC connection after sending the message, and cause the UE to send a disconnect message to disconnect the RRC connection. The disconnect message may include a cause value for disconnecting the RRC connection. The message may include at least one of the following: an indicator that a cell provided by the satellite supports S&F mode, information about the validity period of the satellite's feeder link, or information about conditions for triggering the request to disconnect the RRC connection.

[0120] According to one embodiment, the message may include a data inactivity timer for the S&F mode. The value of the data inactivity timer may be set to a value shorter than the inactivity timer used to disconnect the RRC connection in modes other than the S&F mode.

[0121] According to one embodiment, the information regarding the conditions for triggering a request to disconnect the RRC connection may include at least one of the following: a DRB (data radio bearer) list, a QoS (quality of service) flow list, an S-NSSAI (Single Network Slice Selection Assistance Information) list, a BWP (bandwidth part) list, a PRB (physical resource block) list, a subband list, an uplink data volume threshold, or a metric threshold for channel quality.

[0122] According to one embodiment, the request signal may correspond to a BSR (buffer status reporting), MAC (medium access control), and CE (control element) that include the amount of uplink data of the UE.

[0123] According to one embodiment, the cause value for disconnecting the RRC connection can indicate the S&F mode.

[0124] Embodiments of this disclosure provide user equipment (UE) for performing NTN (non-terrestrial network) access. The UE may include memory containing instructions; at least one processor; and at least one transceiver. When the instructions are executed by the at least one processor, the UE may receive a message from a satellite configured to perform the functions of an evolved node B (eNB) in a radio resource control (RRC) connection state, indicating that the satellite is operating in store and forward (S&F) mode; after receiving the message, send a request signal to the satellite to disconnect the RRC connection; and receive an RRC disconnection message from the satellite to disconnect the RRC connection. The RRC disconnection message may include a cause value for disconnecting the RRC connection. The message may include at least one of the following: an indicator indicating that a cell provided by the satellite supports S&F mode; information regarding the validity period of the satellite's feeder link; or information regarding conditions for triggering the request to disconnect the RRC connection.

[0125] According to one embodiment, the message may include a data inactivity timer for the S&F mode. The value of the data inactivity timer may be set to a value shorter than the inactivity timer used to disconnect the RRC connection in modes other than the S&F mode.

[0126] According to one embodiment, the information regarding the conditions for triggering a request to disconnect the RRC connection may include at least one of the following: a DRB (data radio bearer) list, a QoS (quality of service) flow list, an S-NSSAI (Single Network Slice Selection Assistance Information) list, a BWP (bandwidth part) list, a PRB (physical resource block) list, a subband list, an uplink data volume threshold, or a metric threshold for channel quality.

[0127] According to one embodiment, the request signal may correspond to a BSR (buffer status reporting), MAC (medium access control), and CE (control element) that include the amount of uplink data of the UE.

[0128] According to one embodiment, the cause value for disconnecting the RRC connection can indicate the S&F mode.

[0129] Embodiments of the present disclosure provide a method performed by a satellite configured to provide NTN (non-terrestrial network) access and perform the functions of an evolved node B (eNB). The method includes: identifying store and forward (S&F) mode in a radio resource control (RRC) connection state with user equipment (UE); sending a message to the UE indicating that the satellite is operating in S&F mode; receiving a request signal from the UE to disconnect the RRC connection after sending the message; and sending an RRC disconnection message to the UE to disconnect the RRC connection, the RRC disconnection message may include a cause value for disconnecting the RRC connection. The message may include at least one of the following: an indicator indicating that a cell provided by the satellite supports S&F mode; information regarding the validity period of the satellite's feeder link; or information regarding conditions for triggering the request to disconnect the RRC connection.

[0130] According to one embodiment, the message may include a data inactivity timer for the S&F mode. The value of the data inactivity timer may be set to a value shorter than the inactivity timer used to disconnect the RRC connection in modes other than the S&F mode.

[0131] According to one embodiment, the information regarding the conditions for triggering a request to disconnect the RRC connection may include at least one of the following: a DRB (data radio bearer) list, a QoS (quality of service) flow list, an S-NSSAI (Single Network Slice Selection Assistance Information) list, a BWP (bandwidth part) list, a PRB (physical resource block) list, a subband list, an uplink data volume threshold, or a metric threshold for channel quality.

[0132] According to one embodiment, the request signal may correspond to a BSR (buffer status reporting), MAC (medium access control), and CE (control element) that include the amount of uplink data of the UE.

[0133] According to one embodiment, the cause value for disconnecting the RRC connection can indicate the S&F mode.

[0134] Embodiments of this disclosure provide a method performed by user equipment (UE) for performing NTN (non-terrestrial network) access. This method includes receiving a message from a satellite configured to perform the function of an evolved node B (eNB) in a radio resource control (RRC) connection state, indicating that the satellite is operating in store and forward (S&F) mode; sending a request signal to the satellite for disconnecting the RRC connection after receiving the message; and receiving an RRC disconnection message from the satellite for disconnecting the RRC connection. The RRC disconnection message may include a cause value for disconnecting the RRC connection. The message may include at least one of the following: an indicator indicating that a cell provided by the satellite supports S&F mode; information regarding the validity period of the satellite's feeder link; or information regarding conditions for triggering the request for disconnecting the RRC connection.

[0135] According to one embodiment, the message may include a data inactivity timer for the S&F mode. The value of the data inactivity timer may be set to a value shorter than the inactivity timer used to disconnect the RRC connection in modes other than the S&F mode.

[0136] According to one embodiment, the information regarding the conditions for triggering a request to disconnect the RRC connection may include at least one of the following: a DRB (data radio bearer) list, a QoS (quality of service) flow list, an S-NSSAI (Single Network Slice Selection Assistance Information) list, a BWP (bandwidth part) list, a PRB (physical resource block) list, a subband list, an uplink data volume threshold, or a metric threshold for channel quality.

[0137] According to one embodiment, the request signal may correspond to a BSR (buffer status reporting), MAC (medium access control), and CE (control element) that include the amount of uplink data of the UE.

[0138] According to one embodiment, the cause value for disconnecting the RRC connection can indicate the S&F mode.

[0139] The methods described in the claims or specifications of this disclosure may be implemented in the form of hardware, software, or a combination of hardware and software.

[0140] When implemented as software, a computer-readable storage medium containing one or more programs (software modules) may be provided. The one or more programs stored on the computer-readable storage medium are configured for execution by one or more processors in an electronic device. The one or more programs include instructions that cause the electronic device to perform the methods according to the claims or specifications of this disclosure.

[0141] Such programs (software modules, software) may be stored in random access memory, non-volatile memory including flash memory, read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), magnetic disc storage devices, compact disc-ROMs (CD-ROMs), digital versatile discs (DVDs), or other forms of optical storage devices, magnetic cassettes, or in memory composed of some or all of these. Furthermore, each constituent memory may include multiple instances.

[0142] Furthermore, the program may be stored in an attachable storage device that is accessible via a communication network such as the Internet, Intranet, LAN (local area network), WAN (wide area network), SAN (storage area network), or a combination thereof. Such a storage device may be connected via an external port to an apparatus performing an embodiment of the disclosure. In addition, a separate storage device on the communication network may also be connected to an apparatus performing an embodiment of the disclosure.

[0143] In the specific embodiments of the present disclosure described above, the components included in the disclosure are represented singly or plurally according to the particular embodiment presented. However, the singly or plural representations are selected for the purposes of the present context, and the disclosure is not limited to singly or plural components. Components represented plural may consist of singular components, and components represented singly may consist of plural components.

[0144] While specific embodiments have been described in the detailed description of this disclosure, it goes without saying that various modifications are possible as long as they do not deviate from the scope of this disclosure.

Claims

1. In a satellite instrument configured to provide NTN (non-terrestrial network) access and perform the functions of an eNB (evolved node B), Memory containing instructions; at least one processor; and Includes at least one transceiver, When the instruction is executed by the at least one processor, the device: In the RRC (radio resource control) connection state with UE (user equipment), identify the S&F (store and forward) mode. The satellite sends a message to the UE indicating that it is operating in S&F mode. After sending the aforementioned message, the UE receives a request signal to terminate the RRC connection. This causes the UE to send an RRC disconnection message to disconnect the RRC connection. The RRC connection disconnection message includes the cause value for disconnecting the RRC connection. The device wherein the message includes at least one of the following: an indicator that a cell provided by the satellite supports S&F mode; information regarding the validity period of the satellite's feeder link; or information regarding conditions for triggering a request to disconnect the RRC connection.

2. The message includes a data non-activity timer for the S&F mode, The apparatus according to claim 1, wherein the value of the data inactivity timer is set to a value shorter than the inactivity timer used to disconnect the RRC connection in a mode different from the S&F mode.

3. The apparatus according to claim 1, wherein the information relating to the conditions for triggering the request to disconnect the RRC connection includes at least one of the following: a DRB (data radio bearer) list, a QoS (quality of service) flow list, an S-NSSAI (Single Network Slice Selection Assistance Information) list, a BWP (bandwidth part) list, a PRB (physical resource block) list, a subband list, an uplink data volume threshold, or a metric threshold for channel quality.

4. The apparatus according to claim 1, wherein the request signal corresponds to a BSR (buffer status reporting), MAC (medium access control), and CE (control element) including the amount of uplink data of the UE.

5. The apparatus according to claim 1, wherein the cause value for disconnecting the RRC connection is the S&F mode.

6. In user equipment (UE) for performing NTN (non-terrestrial network) access, Memory containing instructions; at least one processor; and Includes at least one transceiver, When the instruction is executed by the at least one processor, the UE: In an RRC (radio resource control) connection state, a message is received from a satellite configured to perform the function of an eNB (evolved node B) indicating that the satellite is operating in S&F (store and forward) mode. After receiving the aforementioned message, a request signal for disconnecting the RRC connection is sent to the satellite. This causes the satellite to receive an RRC disconnection message to disconnect the RRC connection, The RRC connection disconnection message includes the cause value for disconnecting the RRC connection. The message includes at least one of the following: an indicator that the cell provided by the satellite supports S&F mode; information regarding the validity period of the satellite's feeder link; or information regarding conditions for triggering a request to disconnect the RRC connection.

7. The message includes a data non-activity timer for the S&F mode, The UE according to claim 6, wherein the value of the data non-activity timer is set to a value shorter than the non-activity timer used to disconnect the RRC connection in a mode different from the S&F mode.

8. The UE according to claim 6, wherein the information relating to the conditions for triggering the request to disconnect the RRC connection includes at least one of the following: a DRB (data radio bearer) list, a QoS (quality of service) flow list, an S-NSSAI (Single Network Slice Selection Assistance Information) list, a BWP (bandwidth part) list, a PRB (physical resource block) list, a subband list, an uplink data volume threshold, or a metric threshold for channel quality.

9. The UE according to claim 6, wherein the request signal corresponds to a BSR (buffer status reporting), MAC (medium access control), and CE (control element) including the amount of uplink data of the UE.

10. The cause value for disconnecting the RRC connection is the UE according to claim 6, which indicates the S&F mode.

11. In a method performed by a satellite configured to provide NTN (non-terrestrial network) access and perform the functions of an eNB (evolved node B), The operation to identify the S&F (store and forward) mode while connected to UE (user equipment) via RRC (radio resource control), The operation of sending a message to the UE indicating that the satellite is operating in the S&F mode, After sending the aforementioned message, the UE receives a request signal to terminate the RRC connection, This includes sending an RRC connection disconnection message to the UE to disconnect the RRC connection, The RRC connection disconnection message includes the cause value for disconnecting the RRC connection. A method wherein the message includes at least one of the following: an indicator that a cell provided by the satellite supports S&F mode; information regarding the validity period of the satellite's feeder link; or information regarding conditions for triggering a request to disconnect the RRC connection.

12. The message includes a data non-activity timer for the S&F mode, The method according to claim 11, wherein the value of the data inactivity timer is set to a value shorter than the inactivity timer used to disconnect the RRC connection in a mode different from the S&F mode.

13. The method according to claim 11, wherein the information relating to the conditions for triggering the request to disconnect the RRC connection includes at least one of a DRB (data radio bearer) list, a QoS (quality of service) flow list, an S-NSSAI (Single Network Slice Selection Assistance Information) list, a BWP (bandwidth part) list, a PRB (physical resource block) list, a subband list, an uplink data volume threshold, or a metric threshold for channel quality.

14. The method according to claim 11, wherein the request signal corresponds to a BSR (buffer status reporting), MAC (medium access control), and CE (control element) including the amount of uplink data of the UE.

15. The method according to claim 11, wherein the cause value for disconnecting the RRC connection is the S&F mode.

16. In a method performed by user equipment (UE) for NTN (non-terrestrial network) access, The operation of receiving a message from a satellite configured to perform the function of an evolved node B (eNB) while connected to RRC (radio resource control), indicating that the satellite is operating in S&F (store and forward) mode, After receiving the aforementioned message, the system performs the operation of sending a request signal to the satellite to disconnect the RRC connection, This includes the operation of receiving an RRC disconnection message from the satellite to disconnect the RRC connection, The RRC connection disconnection message includes the cause value for disconnecting the RRC connection. A method wherein the message includes at least one of the following: an indicator that a cell provided by the satellite supports S&F mode; information regarding the validity period of the satellite's feeder link; or information regarding conditions for triggering a request to disconnect the RRC connection.

17. The message includes a data non-activity timer for the S&F mode, The method according to claim 16, wherein the value of the data inactivity timer is set to a value shorter than the inactivity timer used to disconnect the RRC connection in a mode different from the S&F mode.

18. The method according to claim 16, wherein the information relating to the conditions for triggering the request to disconnect the RRC connection includes at least one of the following: a DRB (data radio bearer) list, a QoS (quality of service) flow list, an S-NSSAI (Single Network Slice Selection Assistance Information) list, a BWP (bandwidth part) list, a PRB (physical resource block) list, a subband list, an uplink data volume threshold, or a metric threshold for channel quality.

19. The method according to claim 16, wherein the request signal corresponds to a BSR (buffer status reporting), MAC (medium access control), and CE (control element) including the amount of uplink data of the UE.

20. The method according to claim 16, wherein the cause value for disconnecting the RRC connection is the S&F mode.

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