Method and apparatus for transmitting data in non-terrestrial network

Abstract

A method of a UE according to the present disclosure may comprise the steps of: receiving, from a serving satellite operating in a first mode having a service link and a feeder link, system information including first switching time information indicating a time at which the serving satellite switches from the first mode to a second mode; and transferring, to a NAS of the UE, the first switching time acquired by an AS of the UE, wherein the second mode may be a store-and-forward mode operation.

Description

Method and device for data transmission in a non-terrestrial network

[0001] The present disclosure relates to data transmission technology in wireless communication systems, and more specifically, to data transmission technology in non-terrestrial network-based communication systems.

[0002] Communication networks (e.g., 5G communication networks, 6G communication networks, etc.) are being developed to provide communication services that are improved over existing communication networks (e.g., LTE (long term evolution), LTE-A (advanced), etc.). 5G communication networks (e.g., NR (new radio) communication networks) can support frequency bands above 6 GHz as well as frequency bands below 6 GHz. That is, 5G communication networks can support the FR1 band and / or FR2 band. 5G communication networks can support a wider variety of communication services and scenarios compared to LTE communication networks. For example, usage scenarios for 5G communication networks may include eMBB (enhanced Mobile BroadBand), URLLC (Ultra Reliable Low Latency Communication), mMTC (massive Machine Type Communication), etc.

[0003] 6G communication networks can support a wider variety of communication services and scenarios compared to 5G communication networks. 6G communication networks can meet the requirements for ultra-high performance, ultra-bandwidth, ultra-spatial, ultra-precision, ultra-intelligence, and / or ultra-reliability. 6G communication networks can support a wide range of frequency bands and can be applied to various usage scenarios (e.g., terrestrial communication, non-terrestrial communication, sidelink communication, etc.).

[0004] Communication networks (e.g., LTE, LTE-A, 5G communication networks, 6G communication networks, etc.) can provide communication services to terminals located on the ground. There is an increasing demand for communication services for aircraft, drones, satellites, etc., located not only on the ground but also non-ground, and technologies for non-terrestrial networks (NTN) are being discussed to meet this demand. Non-terrestrial networks can be implemented based on LTE, LTE-A, 5G communication technologies, 6G communication technologies, etc. For example, in a non-terrestrial network, communication between a satellite and a communication node located on the ground or a communication node located non-terrestrial (e.g., an aircraft, a drone, etc.) can be performed based on LTE, LTE-A, 5G communication technologies, 6G communication technologies, etc.

[0005] A method is required to efficiently transmit data from a non-terrestrial network to a terrestrial terminal or a non-terrestrial terminal.

[0006] The objective of the present disclosure to address the above-mentioned requirements is to provide a method and apparatus for transmitting data in a non-terrestrial network.

[0007] A method of user equipment (UE) according to one embodiment of the disclosure for achieving the above-mentioned purpose may include: receiving system information including first transition time information indicating a time for the serving satellite to transition from the first mode to a second mode from a serving satellite operating in a first mode having both a service link and a feeder link; and transmitting the first transition time obtained in the access stratum (AS) of the UE to the non-access stratum (NAS) of the UE, wherein the second mode may be a store and forward mode operation.

[0008] The above system information may further include neighbor satellite information, and may further include a step of measuring signals received from one or more neighbor satellites indicated by the neighbor satellite information for satellite (re)selection before the mode switching time of the serving satellite to the second mode based on the first switching time.

[0009] The method may further include a step of determining a first satellite to (re)select among the one or more neighboring satellites based on the result of measuring signals received from the one or more neighboring satellites.

[0010] Based on the result of measuring signals received from one or more neighboring satellites, the UE can connect to both the satellite operating in the first mode and the satellite operating in the second mode, and the satellite operating in the first mode can be determined as the first satellite.

[0011] Based on the result of measuring signals received from one or more neighboring satellites, and based on all satellites that the UE can connect to operating in the second mode, the satellite that operates for a short time in the second mode may be determined as the first satellite.

[0012] Based on the fact that the first satellite is a satellite operating in the second mode, the method may further include the step of performing one or more operations among neighbor cell search or paging monitoring during the time that the UE is located within the beam reception range of the satellite operating in the second mode.

[0013] The above system information may further include neighbor satellite information, and may further include a step of determining whether the UE belongs to the service area of ​​the satellite based on the service start time of each satellite and the service end time of the serving satellite based on the neighbor satellite information; and a step of suspending one or more operations of neighbor cell search or paging monitoring during the time when the UE is not included in the service area of ​​the satellite based on the determination of whether the UE belongs to the service area of ​​the satellite.

[0014] The above system information may further include second transition time information indicating the time when the serving satellite switches from the second mode to the first mode.

[0015] The NAS of the above UE may further include the step of driving a timer to stop the transmission of a mobile originated (MO) signaling message during the second mode based on the first switching time; and the step of waiting for the transmission of an MO signaling message generated in the NAS while the timer is driven.

[0016] Based on the expiration of the above timer, the method may further include a step of retrying the transmission procedure of the MO signaling message generated in the NAS and waiting.

[0017] User equipment (UE) according to one embodiment of the disclosure for achieving the above-mentioned purpose comprises at least one processor, wherein the at least one processor may cause the UE to: receive system information including first transition time information indicating a time for the serving satellite to transition from the first mode to a second mode from a serving satellite operating in a first mode having both a service link and a feeder link; and cause the first transition time obtained in the access stratum (AS) of the UE to be transmitted to the non-access stratum (NAS) of the UE, wherein the second mode may be a store and forward mode operation.

[0018] The above system information may further include neighbor satellite information, and the at least one processor may further cause the UE to measure signals received from one or more neighbor satellites indicated by the neighbor satellite information for satellite (re)selection before the mode switching time of the serving satellite to the second mode based on the first switching time.

[0019] The above at least one processor may further cause the UE to determine a first satellite to (re)select among the one or more neighboring satellites based on the result of measuring signals received from the one or more neighboring satellites.

[0020] Based on the result of measuring signals received from one or more neighboring satellites, the UE can connect to both the satellite operating in the first mode and the satellite operating in the second mode, and the satellite operating in the first mode can be determined as the first satellite.

[0021] Based on the result of measuring signals received from one or more neighboring satellites, and based on all satellites that the UE can connect to operating in the second mode, the satellite that operates for a short time in the second mode may be determined as the first satellite.

[0022] The above at least one processor may further cause the UE to perform one or more operations of neighbor cell search or paging monitoring during the time the UE is located within the coverage of the satellite operating in the second mode, based on the fact that the first satellite is a satellite operating in the second mode.

[0023] The above system information may further include neighbor satellite information, and the at least one processor may determine whether the UE belongs to the service area of ​​the satellite based on the service start time of each satellite based on the neighbor satellite information and the service end time of the serving satellite; and may further cause one or more operations of neighbor cell search or paging monitoring to be stopped during the time when the UE is not included in the service area of ​​the satellite based on the determination of whether the UE belongs to the service area of ​​the satellite.

[0024] The above system information may further include second transition time information indicating the time when the serving satellite switches from the second mode to the first mode.

[0025] The above at least one processor may further cause the UE: the UE’s NAS to drive a timer that stops the transmission of a mobile originated (MO) signaling message during the second mode based on the first switching time; and to wait for the transmission of an MO signaling message generated in the NAS while the timer is driven.

[0026] The above at least one processor may further cause the UE to retry the transmission procedure of the MO signaling message that is generated in the NAS and is waiting based on the expiration of the timer.

[0027] According to one embodiment of the present disclosure, when a satellite in the NTN operates in a second mode having only a service link, this is notified to the upper layer, thereby enabling the non-connection layer to operate correctly in a satellite environment where the satellite operates in the second mode. Additionally, when switching from the first mode to the second mode, a measurement procedure for connecting to a new satellite before switching to the second mode can be performed based on adjacent satellite information transmitted by the satellite, thereby minimizing service interruption. Furthermore, when the serving satellite switches to the second mode, a method is provided for the terminal to connect to the optimal adjacent satellite.

[0028] FIG. 1 is a conceptual diagram illustrating a first embodiment of a non-ground network.

[0029] FIG. 2 is a conceptual diagram illustrating a second embodiment of a non-ground network.

[0030] FIG. 3 is a block diagram illustrating a first embodiment of an entity constituting a non-ground network.

[0031] Figure 4 is a conceptual diagram illustrating various forms of non-ground networks.

[0032] Figure 5a is a conceptual diagram illustrating a quasi-Earth fixed cell based on a beam formed by a quasi-Earth fixed satellite in the NTN.

[0033] Figure 5b is a conceptual diagram illustrating an Earth-mobile cell based on a beam formed by an Earth-mobile satellite in NTN.

[0034] Figure 6 is a conceptual diagram illustrating the flow of data transmission according to the store-and-forward method in NTN.

[0035] Figure 7 is a flowchart illustrating the operation of a cell and a terminal when a cell transmits mode switching information to a terminal in an NTN.

[0036] Figure 8 is a flowchart for explaining the operation of a cell and a terminal when a cell transmits mode switching information and neighbor cell information to a terminal in NTN.

[0037] FIG. 9a is a conceptual diagram of an information structure according to a first embodiment for a system information block that includes information about a neighboring satellite among the system information blocks broadcast by a satellite.

[0038] FIG. 9b is a conceptual diagram of an information structure according to a second embodiment for a system information block that includes information about a neighboring satellite among the system information blocks broadcast by a satellite.

[0039] FIG. 9c is a conceptual diagram of an information structure according to a third embodiment for a system information block that includes information about a neighboring satellite among the system information blocks broadcast by a satellite.

[0040] The present disclosure is capable of various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present disclosure to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the present disclosure.

[0041] Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. Such terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present disclosure, the first component may be named the second component, and similarly, the second component may be named the first component. The term "and / or" includes a combination of a plurality of related described items or any of a plurality of related described items.

[0042] When it is stated that one component is "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to that other component, there may also be other components in between. On the other hand, when it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0043] The terms used in this disclosure are used merely to describe specific embodiments and are not intended to limit this disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this disclosure, terms such as “comprising” or “having” are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0044] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which this disclosure pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this disclosure.

[0045] A communication system to which embodiments according to the present disclosure are applied will be described. The communication system to which embodiments according to the present disclosure are applied is not limited to the details described below, and embodiments according to the present disclosure may be applied to various communication systems. Here, the term "communication system" may be used interchangeably with "communication network."

[0046] Throughout the specification, a network may include, for example, wireless internet such as WiFi (wireless fidelity), mobile internet such as WiBro (wireless broadband internet) or WiMAX (world interoperability for microwave access), 2G mobile communication networks such as GSM (global system for mobile communication) or CDMA (code division multiple access), 3G mobile communication networks such as WCDMA (wideband code division multiple access) or CDMA2000, 3.5G mobile communication networks such as HSDPA (high speed downlink packet access) or HSUPA (high speed uplink packet access), 4G mobile communication networks such as LTE (long term evolution) networks or LTE-Advanced networks, and 5G mobile communication networks.

[0047] Throughout the specification, the term "terminal" may refer to a mobile station, mobile terminal, subscriber station, portable subscriber station, user equipment, access terminal, etc., and may include all or part of the functions of a terminal, mobile station, mobile terminal, subscriber station, portable subscriber station, user equipment, access terminal, etc.

[0048] Here, a desktop computer, laptop computer, tablet PC, wireless phone, mobile phone, smartphone, smart watch, smart glass, e-book reader, PMP (portable multimedia player), portable game console, navigation device, digital camera, DMB (digital multimedia broadcasting) player, digital audio recorder, digital audio player, digital picture recorder, digital picture player, digital video recorder, digital video player, etc., capable of communicating with a terminal can be used.

[0049] Throughout the specification, the term "base station" may refer to an access point, a radio access station, a node B, an evolved node B, a base transceiver station, a mobile multihop relay (MMR)-BS, etc., and may include all or part of the functions of a base station, access point, radio access station, node B, eNodeB, base transceiver station, MMR-BS, etc.

[0050] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the attached drawings. In order to facilitate an overall understanding of the present disclosure, the same reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted.

[0051] In the present disclosure, a phrase containing "~ case (e.g., when ~)" may be expressed as a phrase containing "~ based on (e.g., based on ~)" or a phrase containing "~ in response to (e.g., in response to ~)". In other words, a phrase containing "~ case" may be interpreted as identical or similar to a phrase containing "~ based on" or a phrase containing "~ in response to".

[0052] A non-terrestrial network (NTN) to be described in this disclosure is described below. A terrestrial network (TN) may refer to a communication system in which all of the base stations, relay nodes, and terminals constituting the communication system are located on the ground. A non-terrestrial network may refer to a network in which at least one of the base stations, relay nodes, or terminals constituting the communication system is not located on the ground. Here, a relay node may refer to one or more of a satellite, a transmission and reception point (TRP), a radio unit (RU), a radio remote head (RRH), or a relay node (RN).

[0053] FIG. 1 is a conceptual diagram illustrating a first embodiment of a non-ground network.

[0054] Referring to FIG. 1, the non-ground network may include a satellite (110), a communication node (120), a gateway (130), a data network (140), etc. The non-ground network illustrated in FIG. 1 may be a non-ground network based on a transparent payload. The satellite (110) may be a low earth orbit (LEO - altitude 300 to 1,500 km) satellite, a medium earth orbit (MEO - altitude 7,000 to 25,000 km) satellite, a geostationary earth orbit (GEO - altitude approximately 35,786 km) satellite, a high elliptical orbit (HEO) satellite, or an unmanned aircraft system (UAS) platform. The UAS platform may include a high altitude platform station (HAPS).

[0055] The communication node (120) may include a communication node located on the ground (e.g., UE (user equipment), terminal) and a communication node located off the ground (e.g., airplane, drone). A service link may be established between the satellite (110) and the communication node (120), and the service link may be a radio link. The satellite (110) may provide communication services to the communication node (120) using one or more beams. The shape of the receiving range (footprint) of the satellite (110) beam may be elliptical.

[0056] A communication node (120) can communicate with a satellite (110) (e.g., downlink communication, uplink communication) using LTE technology, NR technology and / or 6G technology. If dual connectivity (DC) is supported, the communication node (120) can be connected to another base station (e.g., a base station supporting LTE and / or NR functions) as well as the satellite (110), and can perform DC operations based on the technology defined in the LTE, NR and / or 6G specifications.

[0057] The gateway (130) may be located on the ground, and a feeder link may be established between the satellite (110) and the gateway (130). The feeder link may be a wireless link. The gateway (130) may be referred to as a "non-terrestrial network (NTN) gateway." The gateway (130) may be connected to a data network (140). A "core network" may exist between the gateway (130) and the data network (140). In this case, the gateway (130) may be connected to the core network, and the core network may be connected to the data network (140). The core network may support NR technology. For example, the core network may include an access and mobility management function (AMF), a user plane function (UPF), a session management function (SMF), etc.

[0058] Alternatively, a base station and a core network may exist between the gateway (130) and the data network (140). In this case, the gateway (130) may be connected to the base station, the base station may be connected to the core network, and the core network may be connected to the data network (140). The base station and the core network may support NR technology and / or 6G technology.

[0059] The satellite (110) exemplified in FIG. 1 may be a transparent satellite as previously described. When the transparent satellite (110) transmits data received from the gateway (130) to a terminal via a downlink, it may simply perform analog signal processing such as frequency conversion and power amplification. In other words, the transparent payload mounted on the satellite (110) does not perform the function of a base station.

[0060] FIG. 2 is a conceptual diagram illustrating a second embodiment of a non-ground network.

[0061] Referring to FIG. 2, the non-ground network may include satellite #1 (211), satellite #2 (212), a communication node (220), a gateway (230), a data network (240), etc. The non-ground network illustrated in FIG. 2 may be a regenerative payload-based non-ground network. For example, each of satellites #1-2 (211, 212) may perform a regenerative operation (e.g., demodulation, decoding, re-coding, re-modulation, and / or filtering) on ​​a payload received from other entities constituting the non-ground network (e.g., communication node (220), gateway (230)), and may transmit the regenerative payload.

[0062] Each of satellites #1-2 (211, 212) may be a LEO satellite, MEO satellite, GEO satellite, HEO satellite, or UAS platform. A UAS platform may include a HAPS. Satellite #1 (211) may be connected to satellite #2 (212), and an inter-satellite link (ISL) may be established between satellite #1 (211) and satellite #2 (212). The ISL may operate in a radio frequency (RF) frequency or optical band. The ISL may be established optionally. Communication nodes (220) may include communication nodes located on the ground (e.g., UE, terminal) and communication nodes located off the ground (e.g., airplane, drone). A service link (e.g., wireless link) may be established between satellite #1 (211) and communication nodes (220). Satellite #1 (211) can provide communication services to a communication node (220) using one or more beams.

[0063] The communication node (220) can communicate with satellite #1 (211) (e.g., downlink communication, uplink communication) using LTE technology, NR technology, and / or 6G technology. If DC is supported, the communication node (220) can be connected to satellite #1 (211) as well as other base stations (e.g., base stations supporting LTE, NR, and / or 6G functions), and can perform DC operations based on the technology defined in the LTE, NR, and / or 6G specifications.

[0064] The gateway (230) may be located on the ground, and a feeder link may be established between satellite #1 (211) and the gateway (230), and a feeder link may be established between satellite #2 (212) and the gateway (230). The feeder link may be a wireless link. If an ISL is not established between satellite #1 (211) and satellite #2 (212), a feeder link between satellite #1 (211) and the gateway (230) may be established mandatorily.

[0065] The gateway (230) can be connected to a data network (240). A "core network" may exist between the gateway (230) and the data network (240). In this case, the gateway (230) can be connected to the core network, and the core network can be connected to the data network (240). The core network may support NR technology. For example, the core network may include AMF, UPF, SMF, etc.

[0066] Alternatively, a base station and a core network may exist between the gateway (230) and the data network (240). In this case, the gateway (230) may be connected to the base station, the base station may be connected to the core network, and the core network may be connected to the data network (240). The base station and the core network may support NR technology and / or 6G technology.

[0067] The satellites (211, 212) exemplified in FIG. 2 may be regenerative satellites as previously described. The regenerative satellites (211, 212) can perform base station operations when transmitting data received from the gateway (230) to a terminal via a downlink. In other words, the regenerative satellites (211, 212) can perform functions such as conversion of encoding methods and / or modulation methods, and processing of analog signals.

[0068] Meanwhile, the entities constituting the non-terrestrial network shown in FIGS. 1 and 2 (e.g., satellite, communication node, gateway, etc.) can be configured as follows.

[0069] FIG. 3 is a block diagram illustrating a first embodiment of an entity constituting a non-ground network.

[0070] Referring to FIG. 3, the entity (300) may include at least one processor (310), a memory (320), and a transceiver (330) that communicates by being connected to a network. Additionally, the entity (300) may further include an input interface device (340), an output interface device (350), a storage device (360), etc. Each component included in the entity (300) may communicate with one another by being connected by a bus (370).

[0071] However, each component included in the entity (300) may be connected via individual interfaces or individual buses centered around the processor (310), rather than via a common bus (370). For example, the processor (310) may be connected via a dedicated interface to at least one of a memory (320), a transmission / reception device (330), an input interface device (340), an output interface device (350), and a storage device (360).

[0072] The processor (310) can execute a program command stored in at least one of the memory (320) and the storage device (360). The processor (310) may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which the methods according to embodiments of the present disclosure are performed. Each of the memory (320) and the storage device (360) may be composed of at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory (320) may be composed of at least one of read-only memory (ROM) and random access memory (RAM).

[0073] Figure 4 is a conceptual diagram illustrating various forms of non-ground networks.

[0074] In FIG. 4, the arrows may indicate directions for indicating altitude in a non-ground network. An unmanned aerial vehicle (411) can provide communication services to a ground station (or terminal) at a low altitude of about 300 m. An aircraft (412) can communicate with a ground station (or terminal) at an altitude of about 10 km, and a high-altitude platform radio station (413) can communicate with a ground station (or terminal) at an altitude of about 20 km. Additionally, a satellite (414) can communicate with a ground station (or terminal) at an altitude of about 600 km or more. The satellite (414) exemplified in FIG. 4 may be an example of a LEO satellite. MEO satellites, GEO satellites, or HEO satellites can communicate with a ground station (or terminal) at a higher altitude than the satellite (414) exemplified in FIG. 4.

[0075] The non-ground nodes exemplified in FIG. 4 (e.g., unmanned aerial vehicle (411), airplane (412), high-altitude platform radio station (413), satellite (414)) can be connected to a core network and / or a data network through a gateway. The satellite (414) and the high-altitude platform radio station (413) exemplified in FIG. 4 can each be connected to a ground station (422) through gateways (423, 425). It should be noted that gateways connecting the unmanned aerial vehicle (411) and airplane (412), excluding the satellite (414) and the high-altitude platform radio station (413) in FIG. 4 have been omitted for the sake of complexity of the drawing. FIG. 4 illustrates, as an example, that a vessel (424) may also be included in the communication node where a service link is established with the satellite (414).

[0076] Non-ground networks considered by 3GPP may be configured by placing base stations on a high-altitude platform (413) or on a satellite (414), as exemplified in FIG. 4 (in the case of a regenerative satellite). Additionally, other non-ground networks considered by 3GPP may be configured by placing base stations on the ground (in the case of a transparent satellite).

[0077] For convenience of explanation, the following description will assume that the non-ground node is a satellite. However, as illustrated in FIG. 4, the non-ground node may include not only satellites but also various forms of levitating or moving airborne objects, such as unmanned aerial vehicles (411), airplanes (412), and high-altitude platform radio stations (413). Levitating or moving airborne objects may be referred to as non-ground nodes.

[0078] As examined above, non-ground nodes can be located at different altitudes. When a non-ground node is a satellite, it can be divided into cells having the following three types of service links.

[0079] 1) Earth-fixed service link: An earth-fixed service link may be a case where the service link is provided by a beam that always covers the same geographic area. Satellites with an earth-fixed service link may include, for example, service links provided by geostationary orbit (GSO) satellites.

[0080] 2) Quasi-Earth-fixed service link: A quasi-Earth-fixed service link may be a case where the service link is provided by beam(s) that cover one geographic area for a limited period and another geographic area for a different period. A quasi-Earth-fixed service link may be, for example, a service link provided by non-geostationary orbit (NGSO) satellites that generate steerable beams.

[0081] 3) Earth-moving service link: An earth-moving service link may be a case where the coverage area where the satellite provides the service link moves over the surface of the Earth. An earth-moving service link may be, for example, a service link provided by an NGSO satellite using a fixed beam or a non-stearable beam.

[0082] As described above, in the case of an NTN with an NGSO satellite, services can be provided to terminals located on the ground via a quasi-Earth fixed service link or an Earth mobile service link, and in the case of an NTN with a GSO satellite, services can be provided to terminals located on the ground via an Earth fixed service link.

[0083] Cells with three types of service links in NTN can also be classified into three types of cells.

[0084] 1) Earth-fixed cell: An earth-fixed cell may refer to a cell having an earth-fixed service link. Therefore, an earth-fixed cell may include service links provided by geostationary satellites (GSO satellites).

[0085] 2) Quasi-Earth-fixed cell: A quasi-Earth-fixed cell may refer to a cell using a quasi-Earth-fixed service link. A quasi-Earth-fixed cell may be a case where an NGSO satellite generating steerable beams services a fixed area of ​​the ground cell for a limited time.

[0086] 3) Earth-moving cell: An earth-moving cell may refer to a cell that provides an earth-moving service link. For example, it may be a satellite defined in Release 18 of the 3GPP new radio (NR) NTN specifications, which assumes the case where the satellite uses a fixed beam.

[0087] Figure 5a is a conceptual diagram illustrating a quasi-Earth fixed cell based on a beam formed by a quasi-Earth fixed satellite in the NTN.

[0088] Referring to FIG. 5a, it should be noted that the quasi-earth fixed satellite (511) at time T0 and the quasi-earth fixed satellite (511) at time T1 have different brightness levels.

[0089] A quasi-Earth-fixed cell (521) can be formed at time T0. The quasi-Earth-fixed satellite (511) may be an NGSO satellite capable of generating steerable beams as previously described. Thus, by adjusting the beam steering angle for a specific geographical area for a limited time, a quasi-Earth-fixed cell (521) can be formed within the same or similar area. In other words, at time T1, the quasi-Earth-fixed satellite (511) may be located in a different geographical / spatial area than at time T0. However, the quasi-Earth-fixed cell (522) formed by the quasi-Earth-fixed satellite (511) at time T1 may be in the same geographical area or a generally similar geographical area as the quasi-Earth-fixed cell (521) formed by the quasi-Earth-fixed satellite (511) at time T0. In the example of FIG. 5a, a case was illustrated in which the cell (521) area formed by the semi-Earth fixed satellite (511) at time T0 and the cell (522) area formed at time T1 were not identical. However, as described above, it should be noted that the cell (521) area formed by the semi-Earth fixed satellite (511) at time T0 may be identical to the cell (522) area formed at time T1. The degree of similarity between the geographical area of ​​the semi-Earth fixed cell (521) at time T0 and the semi-Earth fixed cell (522) at time T1 can be determined by how accurately the semi-Earth fixed satellite (511) can steer the beam.

[0090] Figure 5b is a conceptual diagram illustrating an Earth-mobile cell based on a beam formed by an Earth-mobile satellite in NTN.

[0091] Referring to FIG. 5b, it should be noted that the Earth-mobile satellite (512) at time T0 and the Earth-mobile satellite (512) at time T1 have different brightness levels.

[0092] As previously described, the Earth-moving satellite (512) may be an NGSO satellite that uses a fixed beam or a non-steerable beam. Therefore, the Earth-moving satellite (512) may form a fixed beam or a non-steerable beam. The coverage area formed by the beam of the Earth-moving satellite (512) may be called an Earth-moving cell. Since the Earth-moving satellite (512) uses a fixed beam, the Earth-moving cell (531) serviced by the Earth-moving satellite (512) at time T0 may have a different geographical location from the Earth-moving cell (532) serviced by the Earth-moving satellite (512) at time T1.

[0093] Meanwhile, FIG. 5a describes a quasi-Earth fixed cell using a quasi-Earth fixed satellite, and FIG. 5b describes a Earth-moving cell using an Earth-moving satellite. Although the Earth fixed satellite is not illustrated in the drawings, it can be located in a fixed area above a specific area on the ground. Therefore, although the Earth fixed cell using an Earth fixed satellite is not illustrated in the drawings, it can be inferred from the examples in FIG. 5a and FIG. 5b and the description of the Earth fixed cell and the Earth fixed service link.

[0094] <Satellite structure with store and forward operation applied>

[0095] The satellite according to the present disclosure described below may include a satellite that performs a store and forward (S&F) operation. Additionally, the satellite that performs the store and forward operation may be a satellite having a regenerative payload. The structure of the satellite that performs the store and forward operation described in the present disclosure and has a regenerative payload may be one or more of the following cases.

[0096] 1. In the case where the satellite has a payload that performs only some of the full functions of the base station

[0097] 2. When the satellite has a payload that performs the full function of a base station

[0098] 3. Where the satellite has a payload that performs the full-function of a base station and part of the core network functions (e.g., NR's 5GC or LTE's evolved packet core (EPC)).

[0099] 3-1. Cases where a satellite in an LTE system has some functions of a base station (eNB) and a mobility management entity (MME) may be included in case 3.

[0100] 4. When the satellite has a payload that performs the entire full-function and core network functions of a base station

[0101] Among the four cases (five cases including 3-1) described above, the case where the first exemplified satellite has a payload that performs only some of the full-functions of a base station, or the case where the second exemplified satellite has a payload that performs the full-functions of a base station, may be a case where there is no core network. However, in the first case, if the remaining functions of the base station and at least part of the core network exist on another satellite and the satellites are connected via an inter-satellite link (ISL), it can be understood as the same as the third or fourth case. Likewise, in the second case, if at least part of the core network exists on another satellite and the satellites are connected via an ISL, it can be understood as the same as the third or fourth case.

[0102] In NTN, a base station (e.g., a satellite) can broadcast SIB2, SIB3, … etc., containing various system information, including a system information block (SIB1) containing initial access system information broadcast within a cell. A terminal receives SIB1 broadcast by the base station and can obtain the transmission period and channel information for various SIBs such as SIB2, SIB3, … by decoding the received SIB1. Therefore, the terminal can receive various system information such as SIB2, SIB3, … based on SIB1.

[0103] These SIBs may include parameters related to the service time of semi-Geographic fixed cells and / or Earth-mobile cells. More specifically, they may include "t-Service parameters" and "t-ServiceStart parameters".

[0104] The t-Service parameter can be defined as time information regarding when to stop service for the area currently covered by the NTN cell. The t-Service parameter can be applied to the service link switch of an NTN semi-earth fixed cell. Additionally, the t-Service parameter can be applied to the feeder link switch for NTN semi-earth fixed cells and earth mobile cells.

[0105] The t-ServiceStart parameter can be defined as information about the service start time of the next satellite providing service to the corresponding area of ​​the quasi-Earth fixed cell.

[0106] Meanwhile, in the case of an LTE-based NTN system, information regarding neighboring cells of a quasi-Earth fixed cell or an Earth mobile cell can be broadcast via SIB33. SIB33 broadcast by a base station (e.g., a satellite) can also be broadcast based on other system information (SI) scheduling information included in SIB1, as previously described. Therefore, a terminal can receive SIB33 based on SIB1. SIB33 broadcast by a base station may include a "t-ServiceStartNeigh parameter".

[0107] The t-ServiceStartNeigh parameter can be defined as the time when a neighbor cell comes to cover the area currently served by the serving cell. In other words, the t-ServiceStartNeigh parameter can be defined as the time when a neighbor cell begins to provide service to the currently served area. Therefore, the terminal can determine the time when it can receive service from a neighbor cell based on the t-ServiceStartNeigh parameter. Additionally, the t-ServiceStartNeigh parameter may be indicated by a satellite identifier (satelliteId) to identify the satellite forming the neighbor cell. This t-ServiceStartNeigh parameter may exist only to represent quasi-Earth fixed neighbor cell information in NTN.

[0108] In the present disclosure, the store and forward (S&F) method may be understood as an accumulate and forward method.

[0109] Figure 6 is a conceptual diagram illustrating the flow of data transmission according to the store-and-forward method in NTN.

[0110] Referring to FIG. 6, a satellite (611), a terminal (601), an NTN gateway (621), and ground network entity(s) (630) of a serving PLMN are illustrated.

[0111] The satellite (611) exemplified in FIG. 6 may be a satellite forming a semi-Earth fixed cell. As previously described, the position of the satellite forming the semi-Earth fixed cell may change over time. In other words, the satellite (611) may be a satellite orbiting the surface of the Earth while maintaining a constant altitude above sea level.

[0112] In FIG. 6, the satellite (611) forming a semi-earth fixed cell at satellite location L1 at the first time may be a location where a service link can be formed with the terminal (601), but a feeder link cannot be formed with the ground NTN gateway (621).

[0113] In the second time, at satellite location L2, the satellite (611) may form a feeder link with the NTN gateway (621). In this case, the satellite (611) may not be able to form a service link with the ground terminal (601). However, the satellite (611) may form a service link with another terminal (not shown in FIG. 6) within the cell formed by a beam steered to a different region than the terminal (601) exemplified in FIG. 6.

[0114] In FIG. 6, the dotted line 690 may be a virtual line to distinguish between cases where the satellite (611) has only a service link to the terminal (601) and cases where it has only a feeder link to the NTN gateway (621).

[0115] In the present disclosure, data transmitted and received via a service link between a terminal (601) and a satellite (611) may include one or more of user plane data and control plane data. Accordingly, data transmitted via a feeder link between a satellite (611) and an NTN gateway (621) may also include one or more of user plane data and control plane data. In the following description, a signal (or data) transmitted and received via a service link may include one or more of user plane data and / or control plane data, and a signal (or data) transmitted and received via a feeder link may also include one or more of user plane data and / or control plane data.

[0116] A signal transmitted by the terminal (601) via an uplink can be referred to as a "mobile originated (MO)" signal, and a signal transmitted to the terminal (601) via a downlink can be referred to as a "mobile terminated (MT)" signal. Accordingly, the terminal (601) can transmit an MO signal to the satellite (611) at the L1 location via an uplink (641), and the satellite (611) at the L1 location can transmit an MT signal to the terminal (601) via a downlink (651).

[0117] Below, with reference to FIG. 6, the save and forward (S&F) operation is described.

[0118] Even if the satellite (611) at the L1 location receives an MO signal directed toward the terrestrial network (TN) from a terminal (601) within the satellite coverage, it cannot transmit the MO signal to the terrestrial NTN gateway (621) because there is no feeder link with the NTN gateway (621). Therefore, the satellite (611) that supports Store and Forward (S&F) operations can store the MO signal received via the uplink in the satellite (611). This may be the case where the satellite (611) has a service link with the terminal (611) but is no longer able to maintain a feeder link due to the distance from the NTN gateway (621), or where the feeder link with the terrestrial gateway (621) is disconnected for a specific reason.

[0119] If the satellite (611) cannot transmit the MO data received from the terminal (601) at the L1 location to the NTN gateway (621), it can store the MO data received from the terminal (601). The satellite (611) can wait until a feeder link is connected with the NTN gateway (621).

[0120] As previously explained, the satellite (611) can rotate around the Earth along a preset path at a constant altitude. Thus, the satellite (611) can move to an L2 location where the feeder link with the NTN gateway (621) can be reused. When the feeder link with the NTN gateway (621) is connected at the L2 location, the satellite (611) can forward the stored MO signal to the NTN gateway (621) via the feeder link (642) directed toward the NTN gateway.

[0121] Next, we will examine the case of an MT signal directed from the TN to the terminal (601). The satellite (611) at the L2 location can receive the MT signal transmitted from the ground gateway to the terminal (601) via a feeder link (652) directed to the satellite (611). In this case, if a service link is not established with the terminal (601), the satellite (611) can store the MT signal received from the gateway (621). As previously explained, the satellite (611) can rotate around the Earth along a preset path at a certain altitude. Therefore, if the terminal (601) is located within the coverage of the satellite (611), the satellite (611) can forward the stored MT signal to the terminal (601) via a downlink (651).

[0122] In the case where the terminal (601) enters the coverage area of ​​the satellite (611) at the L1 location and the satellite (611) does not have a feeder link with the TN (i.e., a feeder link with the NTN gateway (621)), the terminal (601) cannot be provided with NTN services by normal means. In such a case where NTN services cannot be provided, if the satellite (611) supports a store and forward (S&F) operation, the terminal (601) can transmit MO data (or signals) and receive MT data (or signals).

[0123] As explained above, store-and-forward operation can be a method that enables service provision to terminals located within the satellite's service link coverage area but without a usable feeder link. However, store-and-forward operation may involve a latency greater than that of general wireless communication methods and NTNs. Therefore, store-and-forward operation has a limitation in that service must be restricted to delay-tolerant traffic.

[0124] Store-and-forward operations can be used, for example, when a satellite is traversing open seas such as the ocean and communicating with a terminal located on a vessel. When the satellite is traversing the sea, there may be no feeder link, or a service link may be able to be established. In addition, store-and-forward operations can be used in various cases where the satellite's feeder link is disconnected.

[0125] In the disclosure described below, a normal mode in which Save and Forward (S&F) operations are not performed will be referred to as the first mode, and a mode in which Save and Forward (S&F) operations are performed will be referred to as the second mode. Accordingly, the normal mode may mean a mode in which Save and Forward is not performed. The satellite described below may operate in either the first mode (normal mode) or the second mode (S&F mode). The cell described in the disclosure below may be understood as equivalent even if replaced with a satellite. Conversely, the satellite may be understood as equivalent even if replaced with a cell.

[0126] In addition, as illustrated in FIGS. 1 and 2 above, a single satellite can form multiple beams, and the beams formed by the satellite can have multiple beam footprints. Each of the multiple beam footprints may be understood as a single cell. In this way, when a single satellite has multiple cells, a first mode or a second mode can be independently set for each of the cells.

[0127] As another example, a single satellite may have only one cell. Even if a single satellite has multiple beam reception ranges, all beam reception ranges may be understood as a single cell. Therefore, it should be noted that the cells described in this disclosure may be understood as being replaced by satellites.

[0128] As defined above, in this disclosure, a satellite may operate in either a first mode or a second mode. In the case of a satellite that supports both first mode operation and second mode operation, a satellite operating in the first mode may be switched to the second mode, and a satellite operating in the second mode may be switched to the first mode. The switching from the first mode to the second mode may be understood as a transition from normal mode to S&F mode, and the switching from the second mode to the first mode may be understood as a transition from S&F mode to normal mode.

[0129] When a satellite is operating in a second mode (S&F mode), the satellite may broadcast system information to notify terminals that it is operating in a second mode. For example, in the case of a 3GPP Internet of Things (IoT) NTN, the cell may broadcast that it is operating in a second mode through system information (e.g., SIB). In other words, the SIB broadcast by the satellite may include a "second mode operation indication" field or a "S&F operation indication" field.

[0130] When a mode switch is performed, the satellite may broadcast the time of the mode switch via system information (e.g., SIB). For example, the satellite may broadcast the time when the satellite's operating mode changes from a second mode to a first mode as system information. In this disclosure, the time of the mode switch from the second mode to the first mode may be understood as the time of the transition from S&F mode to normal mode (S&F to normal). For example, in the case of 3GPP IoT NTN, the time of the mode switch from the second mode to the first mode may be broadcast via a SIB. The expression format for the time of the mode switch from the second mode to the first mode may use an absolute time format, such as Coordinated Universal Time (UTC), for example. The time of the mode switch from the second mode to the first mode expressed in an absolute time format is It can be expressed as.

[0131] Meanwhile, the communication coverage provided by the network in NTN may be discontinuous. In the disclosure described below, this is referred to as "discontinuous coverage." Discontinuous coverage may mean spatial discontinuity or temporal discontinuity. In NTN, discontinuous coverage generally refers to temporal discontinuity.

[0132] As previously explained, NGSO satellites can be satellites orbiting the Earth at a constant altitude. Since NGSO satellites orbit the Earth, a single satellite cannot always provide coverage for a specific point on the Earth's surface. For NTNs utilizing NGSO satellites, multiple NGSO satellites must be deployed to provide continuous communication coverage to a specific location. However, deploying multiple satellites at a high density entails complexity and very high costs. Due to these practical constraints, a phenomenon may occur where satellites fail to cover specific areas. Such areas where service is not provided by satellites can be referred to as "coverage holes." The frequency of coverage hole formation and their duration can vary depending on the satellite constellation. Temporal discontinuous coverage in NTNs can be considered a characteristic unique to NTNs that distinguishes them from TNs. For example, even if a terminal is located out of coverage due to a coverage hole, it may be located back in coverage after a certain period of time as another satellite orbits the Earth. The opposite is also possible.

[0133] When the terminal is located in a coverage hole, that is, when the terminal is located outside of coverage, a series of operations performed in idle mode is unnecessary. Operations in idle mode may include, for example, cell search for cell selection and / or cell re-selection and paging monitoring. Cell search operations may include measuring signals received from neighboring cells. When the terminal is located outside of coverage, even if the terminal performs these idle mode operations, no results are obtained, and it only consumes unnecessary battery power.

[0134] According to the 3GPP standard regarding discontinuous coverage, to address the problem of unnecessary battery consumption, cells can broadcast information related to discontinuous coverage through system information. Terminals can receive this information regarding discontinuous coverage and, based on it, predict and determine whether they are located within or outside the coverage area. For example, in the case of LTE-based NTN under the 3GPP standard, information related to discontinuous coverage can be broadcast to terminals through SIB32, which is system information. SIB32 transmitted by a satellite may include a satellite information list (satelliteInfoList). The satellite information list included in SIB32 may include not only information on multiple satellites but also a satellite identifier (satelliteId) for each of the multiple satellites, service information (serviceInfo) regarding when the satellite will provide service, and information on the satellite's beam reception range (footprintinfo).

[0135] When the terminal receives SIB32 from a satellite, it can check the list of one or more satellite information contained in the SIB32. Additionally, the terminal can obtain the satellite identifier, service information, and beam reception range information for each satellite included in the satellite information list. Furthermore, based on the SIB32 information, the terminal can predict and determine whether it is located within or outside the satellite's coverage. If it is determined that the terminal is located outside the satellite's coverage, the terminal may not perform the operations required in idle mode as previously described. Through this, the terminal achieves the effect of preventing unnecessary battery consumption. On the other hand, if it is determined that the terminal is located within the satellite's coverage, the terminal performs the operations required in idle mode as previously described.

[0136] [First Embodiment: Mode change from first mode to second mode]

[0137] According to the present disclosure, a satellite (or cell) may transition its operating mode from a first mode (e.g., normal mode) to a second mode (e.g., Save and Forward (S&F) mode). Below, the operation of the satellite and the terminal is described when the satellite transitions from the first mode to the second mode (normal to S&F).

[0138] Figure 7 is a flowchart illustrating the operation of a cell and a terminal when a cell transmits mode switching information to a terminal in an NTN.

[0139] Before describing FIG. 7, it should be noted that a cell can be understood as a satellite as described above. However, it should be noted that for the convenience of explanation in describing FIG. 7, it is described as a cell. Additionally, in FIG. 7, the terminal and the satellite may include all or part of the configuration of the entity described earlier in FIG. 3. Furthermore, in the case of a satellite, in addition to the configuration exemplified in FIG. 3, it may include additional configurations for communicating with an NTN gateway, configurations for communicating between satellites, etc. In the case of a terminal, in addition to the configuration exemplified in FIG. 3, it may include additional configurations for user convenience.

[0140] Referring to FIG. 7, at step S700, the cell can determine whether the conditions for transmitting system information are satisfied. The conditions for transmitting system information may be satisfied if one or more of the following conditions are satisfied. First, system information may be transmitted when a preset broadcasting cycle arrives. Second, system information may be broadcast or transmitted to a specific terminal when a request for system information is received from a terminal. Here, the system information may be, for example, a System Information Block (SIB).

[0141] If the conditions of step S700 are satisfied, the cell can configure system information in step S702. For the sake of convenience, the following description assumes that system information is transmitted periodically and that the corresponding period has arrived. However, it should be noted that cases where system information is transmitted at the request of a terminal are not excluded.

[0142] System information configured by the cell in step S702 may include the time when the cell transitions from a first mode to a second mode (normal to S&F). The time when the cell's operating mode changes from the first mode to the second mode may be in an absolute time format such as Coordinated Universal Time (UTC) or in a relative time format. The time information when the cell's operating mode changes from the first mode to the second mode may be broadcast to all terminals within the cell via the SIB.

[0143] The relative time at which the mode transition from the first mode to the second mode occurs It is called, and the time expressed in absolute time If so, the relationship between absolute time and relative time can have the relationship of mathematical formula 1 or mathematical formula 2 below.

[0144]

[0145]

[0146] According to the present disclosure, the time at which a mode transition from a first mode to a second mode occurs may differ from the time at which the use of the feeder link becomes impossible. According to the present disclosure, the time at which a mode transition from a first mode to a second mode occurs may differ from the time provided by the t-Service parameter, which is defined as time information regarding the time at which service for the area currently covered by the cell is discontinued.

[0147] In step S704, the cell may broadcast system information (e.g., SIB) containing mode transition time information from the first mode to the second mode (normal to S&F). According to one embodiment of the present disclosure, the cell may broadcast system information containing mode transition time information from the first mode to the second mode (normal to S&F) regardless of the cell's operating mode. In this case, the mode transition time information from the first mode to the second mode (normal to S&F) included in the system information may include the time closest to the present time among the times when the cell transitions from the first mode to the second mode.

[0148] In step S704, the terminal can receive system information broadcast by the cell. The terminal can demodulate and decode the received system information to obtain mode transition time information from the first mode to the second mode (normal to S&F) included in the system information.

[0149] In step S706, the terminal can transmit mode transition time information from the first mode to the second mode (normal to S&F) to an upper layer within the terminal. For example, the access stratum (AS) layer of the terminal can transmit mode transition time information from the first mode to the second mode (normal to S&F) to the non-access stratum (NAS) layer. The terminal obtaining the transition time information from the first mode to the second mode and transmitting it to the upper layer can be used to ensure that the non-access layer operates correctly in a satellite environment where it operates in the second mode.

[0150] For example, in the signaling procedure of the non-connection layer, the mode transition time transmitted from the terminal's connection layer to the terminal's non-connection layer may be used. Some of the terminal originating (MO) NAS signaling messages sent from the UE's non-connection layer to the network may depend on the availability of the feeder link, i.e., the operating mode of the satellite. In this disclosure, the feeder link availability information may be mode transition information. For example, when the mode is switched from a first mode to a second mode, the feeder link may be in an unavailable state. On the other hand, when the mode is switched from a second mode to a first mode, the feeder link may be in an available state. Therefore, the feeder link availability information may be understood as being substituted for the mode transition information. The UE's non-connection layer must know the operating mode of the satellite. Furthermore, the availability of the feeder link is information that the non-connection layer present in the satellite cannot know. According to this disclosure, the feeder link availability information may be transmitted to the UE's connection layer as system information related to the satellite's operating mode broadcast by the base station. After the UE's connection layer receives information on the availability of the feeder link and forwards it to the UE's non-connection layer, the UE's non-connection layer can transmit a terminal outgoing (MO) NAS signaling message suitable for the satellite's operating mode to the network.

[0151] As another example, the terminal acquiring information on the transition time from the first mode to the second mode and transmitting it to the upper layer may be for the purpose of managing the store-and-forward wait timer managed by the UE's non-connection layer. The store-and-forward wait timer may be a timer configured to wait without proceeding with the signaling procedure of the non-connection layer while the satellite is operating in the second mode. As previously explained, the UE's non-connection layer cannot know the operating mode of the satellite. However, according to the present disclosure, the UE's non-connection layer can activate the store-and-forward wait timer during the time the satellite is operating in the second mode by utilizing mode transition time information (or information on the availability of the feeder link) provided by the UE's connection layer. Furthermore, when the timer expires, the UE's non-connection layer can retry the non-connection layer signaling procedure that was waiting without proceeding.

[0152] In step S708, the terminal can initiate signal measurement for cell selection or cell re-selection based on mode switching time information from the first mode to the second mode (normal to S&F).

[0153] If a terminal that does not support the operation of the second mode (S&F mode) receives the time of mode transition from the first mode to the second mode, it cannot communicate with the current cell because the current cell operates in the second mode after the time of mode transition from the first mode to the second mode. Therefore, even if the wireless channel quality of the current cell is not poor, if a terminal that does not support the operation of the second mode (S&F mode) receives the time of mode transition from the first mode to the second mode, it can search for a signal received from another cell before the time of mode transition from the first mode to the second mode and start measuring the signal received from the other cell, thereby preparing for cell selection or cell re-selection in advance.

[0154] In other words, when a terminal that does not support operation in the second mode receives a mode switching time from the first mode to the second mode, it may start measuring a signal from another cell for cell selection or cell re-selection before the mode switching time, and if there is a neighbor cell operating in the first mode, it may perform communication with the neighbor cell operating in the first mode after (or before) the mode switching time from the first mode to the second mode.

[0155] In addition, even if a terminal supports operation in the second mode, upon receiving the mode transition time from the first mode to the second mode, the terminal supporting operation in the second mode may start measuring signals for cell selection or cell re-selection before the mode transition time. This is because, even for a terminal supporting operation in the second mode, it may be more advantageous to operate in the first mode than to operate in the second mode. Therefore, if a terminal supporting operation in the second mode also receives the mode transition time from the first mode to the second mode, it may start measuring signals received from other cells for cell selection or cell re-selection before the mode transition time, and if there is a neighbor cell operating in the first mode, it may perform communication with the neighbor cell operating in the first mode after (or before) the mode transition time from the first mode to the second mode.

[0156] Meanwhile, the system information configured in step S702 of Fig. 7 was described only in the case where the time for the cell to transition from the first mode to the second mode (normal to S&F) is included.

[0157] According to one embodiment of the present disclosure, system information may be broadcast along with the mode transition time from the second mode to the first mode (S&F to normal) and the mode transition from the first mode to the second mode (normal to S&F). In this case, the terminal may know the length of time the cell operates in the second mode (S&F mode) by calculating the difference between the two times.

[0158] According to the first embodiment of the present disclosure, if the system information includes the mode transition time from the first mode to the second mode (normal to S&F) of the cell, the mode transition time from the second mode to the first mode (S&F to normal) may not be included. In this case, a terminal capable of obtaining the mode transition time information from the first mode to the second mode (normal to S&F) from the system information broadcast by the cell and using (understanding) it may be a terminal that supports the second mode. In the case of a terminal that supports the second mode, upon receiving system information that includes the mode transition time information from the first mode to the second mode, it can determine that the current cell is operating in the first mode (normal mode). In other words, the terminal can determine that the current cell is operating in the first mode if the received system information includes only the mode transition time information from the first mode to the second mode (normal to S&F).

[0159] The terminal can perform a cell (re)selection procedure based on mode switching time information from the first mode to the second mode. For example, the terminal can initiate a measurement for cell (re)selection before the current cell switches from the first mode to the second mode, and can perform a connection procedure with a neighboring cell based on the measurement result.

[0160] [Second Embodiment: Enhancement of Cell Selection and Re-selection Criteria]

[0161] In the disclosure described below, it is assumed that a cell broadcasts a mode transition time from a first mode (e.g., normal mode) to a second mode (e.g., Save and Forward (S&F) mode). In the disclosure described below, a method for utilizing received information is described when a terminal receives information regarding the mode transition time from the first mode to the second mode through system information.

[0162] Figure 8 is a flowchart for explaining the operation of a cell and a terminal when a cell transmits mode switching information and neighbor cell information to a terminal in NTN.

[0163] Before describing FIG. 8, it should be noted that a cell can be understood as a satellite as described above. However, it should be noted that for the convenience of explanation in describing FIG. 8, it is described as a cell. Additionally, in FIG. 8, the terminal and the satellite may include all or part of the configuration of the entity described earlier in FIG. 3. Furthermore, in the case of a satellite, in addition to the configuration exemplified in FIG. 3, it may include additional configurations for communicating with an NTN gateway, configurations for communicating between satellites, etc. In the case of a terminal, in addition to the configuration exemplified in FIG. 3, it may include additional configurations for user convenience.

[0164] Referring to FIG. 8, the first system information configured by the cell in step S802 may include the time when the cell transitions from a first mode to a second mode (normal to S&F). Here, if the system information is a SIB, the first system information may not mean SIB1. In other words, it may mean a specific SIBx. Here, x may be an integer greater than or equal to 1. The time when the cell's operating mode changes from the first mode to the second mode may use an absolute time format, such as Coordinated Universal Time (UTC), as previously described in FIG. 7, or one of the relative time formats. The time information when the cell's operating mode changes from the first mode to the second mode may be broadcast to all terminals within the cell through a specific SIB.

[0165] In step S804, the cell may broadcast first system information (e.g., a specific SIB) containing mode transition time information from a first mode to a second mode (normal to S&F). According to one embodiment of the present disclosure, the cell may broadcast first system information containing mode transition time information from a first mode to a second mode (normal to S&F) regardless of the cell's operating mode. In this case, the mode transition time information from a first mode to a second mode (normal to S&F) included in the first system information may be the time closest in the future from the current time among the times when the cell transitions from the first mode to the second mode.

[0166] According to another embodiment of the present disclosure, a cell may broadcast first system information including mode transition time information from the first mode to the second mode (normal to S&F) only when the cell is in the first mode (normal mode). Even in this case, the mode transition time information from the first mode to the second mode (normal to S&F) included in the first system information may include the time closest to the present time among the times when the cell transitions from the first mode to the second mode.

[0167] In step S804, the terminal can receive first system information broadcast by the cell. In step S806, the terminal can demodulate and decode the received first system information to obtain mode transition time information from the first mode to the second mode (normal to S&F) included in the first system information. Meanwhile, although not exemplified in FIG. 8, as described in FIG. 7, the terminal may transmit the mode transition time information from the first mode to the second mode (normal to S&F) obtained from the first system information to an upper layer. Since this has already been explained in FIG. 7, a redundant explanation is omitted.

[0168] Meanwhile, the first system information of step S804 described above may be transmitted together with the second system information to be described below. In other words, even if transmitted through the same system information or through different system information, it may be transmitted through a single data channel. When transmitted through the same system information, the mode switching time information included in the first system information described in step S804 may be included and transmitted together with the second system information. It should be noted that step S804 is illustrated with a dotted line to represent this.

[0169] In step S812, the second system information configured by the cell may be criteria enhancement information that the target cell can refer to in addition to the wireless channel state to enhance the effect of cell selection / reselection. The criteria enhancement information may be, for example, one or more of the target cell's operating mode, the remaining operating time of the target cell's first mode, or the operating time length of the target cell's second mode. Here, the target cell may be, for example, a neighboring cell. In other words, the criteria enhancement information included in the second system information may be information of a neighboring cell.

[0170] When the reference reinforcement information according to the present disclosure is neighbor cell information, the neighbor cell information may include, for example, one or more of the following: an operating mode of a neighbor cell, a mode transition time of the neighbor cell from a first mode to a second mode, or a mode transition time of the neighbor cell from a second mode to a first mode.

[0171] For example, the operation mode of a neighbor cell may be the "second mode operation indication (S&F operation indication)" of the neighbor cell in the 3GPP IoT NTN as previously described. The operation mode of the neighbor cell included in the second system information may be information that is included in the second system information only when the neighbor cell is in the second mode (S&F mode), and is not included when the neighbor cell is in the first mode (e.g., normal mode).

[0172] As another example, if the neighbor cell operation mode is set to 1 bit, it may indicate either the first mode or the second mode. For instance, if the 1 bit indicating the neighbor cell operation mode is set to a value of "zero (0)", the neighbor cell operation mode may be the first mode, and if the 1 bit indicating the neighbor cell operation mode is set to a value of "1", the neighbor cell operation mode may be the second mode. The bit value may also be set in the opposite way to the above description.

[0173] In step S812, the cell may broadcast second system information including criteria enhancement information configured as above. Accordingly, in step S812, the terminal may receive the second system information configured by the cell. The terminal may obtain the criteria enhancement information included in the second system information by demodulating and decoding the received second system information.

[0174] In step S816, the terminal may perform cell selection or cell re-selection based on the first system information received in step S804 and the second system information received in step S814. At this time, as previously described, the first system information and the second system information may be transmitted through the same SIB. It should be noted that if mode switching time information and criteria reinforcement information for cell (re)selection are received through the same SIB, they may be transmitted through a single SIB in step S814 instead of step S804. For the sake of convenience of explanation, the following description assumes that steps S804 and S814 are performed separately.

[0175] In step S804, the terminal may perform a procedure for cell (re)selection based on the received mode switching time information and the reference reinforcement information received in step S814. As previously described, the mode switching time information may refer only to the mode switching time from the first mode (normal mode) to the second mode (S&F mode), or it may refer to both the mode switching time from the first mode to the second mode and the mode switching time from the second mode to the first mode.

[0176] The terminal may measure signals received from neighboring cells to perform cell (re)selection in advance prior to the time when the serving cell transitions from the first mode (normal mode) to the second mode (S&F mode). In this case, the terminal may utilize reference enhancement information transmitted as second system information. If the reference enhancement information is neighboring cell information, one or more neighboring cell information may be received. As previously described, neighboring cell information may include, for example, the operating mode of the neighboring cell, the time when the neighboring cell transitions from the first mode to the second mode, or the time when the neighboring cell transitions from the second mode to the first mode. Accordingly, the terminal may (re)select a neighboring cell based on the received neighboring cell information through one of the priority determination methods below or a combination of the priority determination methods below. As previously described, the timing of neighboring cell (re)selection may be performed prior to the time when the serving cell transitions from the first mode to the second mode.

[0177] Priority Determination Method #1: A cell currently operating in Mode 1 (Normal Mode) may have a higher priority in cell selection or cell reselection than a cell currently operating in Mode 2 (S&F Mode).

[0178] Priority Determination Method #2: Among the cells currently operating in the first mode (normal mode), cells with a longer remaining time to operate in the first mode may have a higher priority when (re)selecting a cell. Here, the remaining time to operate in the first mode can be calculated based on the difference between the current time and the time when neighboring cells transition from the first mode to the second mode.

[0179] Priority Determination Method #3: Among the cells currently operating in the first mode (normal mode), cells with shorter operating times in the second mode (S&F mode) may have a higher priority during cell (re)selection. Here, the length of time a cell operates in the second mode can be calculated based on the mode transition time information of neighboring cells from the first mode to the second mode and the mode transition time information of the same cell from the second mode to the first mode.

[0180] In the case of a terminal whose radio channel has been released in radio resource control (RRC) idle mode in the same cell as the current cell, if the current cell operates in a second mode (S&F mode), other cells belonging to the same satellite serving the current cell may not be re-selected.

[0181] The terminal in the present disclosure may perform cell (re)selection using one or more of priority determination methods #1 to priority determination methods #3.

[0182] For example, the terminal can check whether there is a cell operating in the first mode among the cells capable of cell (re)selection based on priority determination method #1. In this case, if there are two or more cells capable of cell (re)selection, the terminal can determine the selected cell as the cell for cell (re)selection according to the existing cell selection / reselection criteria. Here, the existing cell selection / reselection criteria can determine the cell with the best wireless channel condition with the target cell as the cell for (re)selection based on measurement results such as reference signal received power (RSRP) and reference signal received quality (RSRQ).

[0183] As another example, the terminal can check whether there is a cell operating in the first mode among the cells capable of cell (re)selection based on priority determination method #1. In this case, if there are two or more cells capable of cell (re)selection, the terminal can determine the cell with the longer remaining time to operate in the first mode as the cell for cell (re)selection based on priority determination method #2.

[0184] As another example, the terminal can check whether there is a cell operating in the first mode among the cells capable of cell (re)selection based on priority determination method #1. In this case, if there are two or more cells capable of cell (re)selection, the terminal can determine the selected cell as the cell for cell (re)selection according to the existing cell selection / reselection criteria. Here, the existing cell selection / reselection criteria can determine the cell with the higher ranking or priority as the cell for (re)selection by comparing the ranking of the target cell determined by the system, the priority of the frequency used by the target cell, and the priority according to the radio access technology (RAT) used by the target cell.

[0185] As another example, the terminal can check whether there is a cell operating in the first mode among the cells capable of cell (re)selection based on priority determination method #1. In this case, if two or more cells capable of cell (re)selection are all cells operating in the second mode, the terminal can determine the cell with the shortest duration of operation in the second mode as the cell for cell (re)selection based on priority determination method #3.

[0186] As described above, the priority determination method may use only one method or two or more methods together. When a specific cell is selected by one or more priority determination methods, the terminal may perform a connection procedure with that cell (e.g., a random access procedure).

[0187] The priority may be associated with or mapped to the frequency or frequency band used by the cell or the satellite serving the cell.

[0188] After being associated with or mapped to a frequency or frequency band, the priority may be associated with or mapped to a specific cell using that frequency or frequency band.

[0189] If the priority determining terminal described above is a terminal capable of operating in a second mode (S&F mode), the terminal capable of operating in the second mode can measure a signal even for neighboring cells whose operating mode of the received neighboring cells is the second mode. When the terminal (re)selects a cell, it can (re)select one of the neighboring cells by giving a different priority according to the operating mode of the neighboring cell received from the serving cell.

[0190] [Third Embodiment: Broadcasting of neighbor cell information considering second mode (S&F mode) operation]

[0191] As described above, when the second mode (S&F mode) operation is performed in the serving cell, the terminal may perform cell (re)selection depending on whether the second mode operation of the neighboring cell is performed. Therefore, when the serving cell broadcasts information about the neighboring cell to the terminal, it may also broadcast information about the second mode operation of the neighboring cell.

[0192] As previously described, in all embodiments of the present disclosure, the serving cell may be a satellite. Accordingly, information about neighboring satellites to a specific terminal may be broadcast within the satellite's coverage area via a System Information Block (SIB). Accordingly, all terminals communicating with the satellite within the serving satellite's coverage area may receive the SIB broadcast by the serving satellite. Below, the SIB broadcast by the serving satellite is described according to the third embodiment of the present disclosure.

[0193] FIG. 9a is a conceptual diagram of an information structure according to a first embodiment for a system information block that includes information about a neighboring satellite among the system information blocks broadcast by a satellite.

[0194] Referring to FIG. 9a, a system information block (SIB) (900) may include information (910) about neighboring satellites. The information about neighboring satellites (910) may include a list (911) of each satellite, and additional information may be transmitted in correspondence with the list of each satellite. In the example of FIG. 9, it is illustrated that satellite information for each of n neighboring satellites is included within the SIB (900). In other words, information about satellite #1, information about satellite #2, ..., information about satellite #n among the neighboring satellites may each be included within the information about neighboring satellites (910). Information about satellite #1, information about satellite #2, ... Each piece of information regarding satellite #n may include one or more of the following: an identifier of the satellite, information (or an indicator) indicating the operation mode of the satellite (e.g., first mode (normal mode) operation or second mode (S&F mode)), mode transition time information from the second mode to the first mode, or mode transition time information from the first mode to the second mode. The information indicating the operation mode of the satellite may be the “second mode operation indicator” field described above or may be indicated through a 1-bit indicator.

[0195] Therefore, when the terminal receives the SIB (900) from the serving satellite, it can obtain one or more of the neighboring satellites of the serving satellite, mode information of the neighboring satellites, and mode switching times of the neighboring satellites.

[0196] When the terminal receives mode transition time information from the serving satellite, which is the time when the serving satellite transitions from the first mode to the second mode (normal to S&F), it can perform cell (re)selection based on individual neighbor satellite information included in the SIB (900) before the mode transition time to the second mode. At this time, both the terminal that supports the operation of the second mode and the terminal that does not support the operation of the second mode can perform cell (re)selection based on the neighbor satellite information.

[0197] At this time, a terminal supporting operation in the second mode can perform a signal measurement procedure for cell (re)selection of the neighboring satellite even if the neighboring satellite is a satellite operating in the second mode. This is because operation in the second mode is possible when the neighboring satellite is (re)selected, even if the neighboring satellite is a serving satellite (a satellite operating in the second mode) that only has a service link. Accordingly, the serving satellite can configure the SIB (900) by considering terminals capable of operating in the second mode. The satellite can then broadcast the configured SIB (900).

[0198] When a terminal supporting operation in the second mode receives a SIB (900) from a serving satellite to be switched to the second mode, it may perform (re)selection of a neighbor satellite (or cell (re)selection) based on information regarding each neighbor satellite included in the received SIB (900), even if the neighbor satellite is a satellite operating in the second mode. At this time, one or more of the priority determination methods described above may be used for the (re)selection of the satellite.

[0199] Information about all neighboring satellites may exist in the form of a collection of information about individual neighboring satellites within the SIB (900), as exemplified in FIG. 9a. Each element constituting the information collection may consist of information about each individual neighboring satellite (in other words, information about each individual satellite).

[0200] In this case, the data structure or information element (IE) of the element used for each neighboring satellite information may differ depending on whether the satellite supports the second mode (S&F mode). For example, if the data structure or IE of an element for a satellite that does not support second mode operation is Type A, then the data structure or IE of an element for a satellite that supports second mode (S&F mode) operation may use Type B.

[0201] In this way, by having different data structures depending on whether the neighboring satellite information included in the SIB broadcast by the satellite supports the operation of the second mode (S&F mode), a terminal that does not support the operation of the second mode can perform signal measurement for neighboring satellite (re)selection based on the satellite information of type A. A terminal that does not support the operation of the second mode can be prevented from understanding the satellite information of type B, or even if it understands the satellite information of type B, it can be prevented from performing satellite (re)selection for a satellite that has the satellite information of type B.

[0202] However, as previously explained, in the case of a terminal supporting second mode operation, it can understand both Type A satellite information and Type B satellite information, and can perform satellite (re)selection based on both Type A satellite information and Type B satellite information. Performing satellite (re)selection may include a procedure for measuring signals received from a target satellite.

[0203] Type A satellite information and Type B satellite information may include a "t-ServiceStartNeigh parameter" indicating the service start time of a neighboring satellite.

[0204] In the case of Type A satellite information, the t-ServiceStartNeigh parameter, which indicates the service start time of a neighboring satellite, can be set to the earliest point in time when the neighboring satellite covers the area of ​​the cell to which the terminal belongs as a service area.

[0205] In the case of B-type satellite information, the t-ServiceStartNeigh parameter, which indicates the service start time of a neighboring satellite, can be set to the earliest time when the service link provided by the satellite covers the area where the terminal is located, even if the neighboring satellite operates in the first mode (normal mode) as well as the second mode (S&F mode).

[0206] According to another embodiment of the present disclosure, information about all neighboring satellites may exist in the form of a collection of information about individual neighboring satellites within the SIB (900), as illustrated in FIG. 9a. In this case, each element constituting the collection of information may be composed of information about each individual neighboring satellite. However, the type of information internally included in the element used for each individual neighboring satellite information may differ depending on whether the second mode (S&F mode) is operating. For example, information about a neighboring satellite that is operating in the second mode or is scheduled to operate in the second mode may be configured to have additional information compared to a neighboring satellite that is not operating in the second mode, that is, one that operates only in the first mode.

[0207] Information regarding a neighboring satellite that is operating in or is scheduled to operate in second mode may include the "t-SnFServiceStartNeigh parameter." The t-SnFServiceStartNeigh parameter may be set to the earliest time when the neighboring cell provided by the neighboring satellite covers the area serviced by the current serving cell, even if the neighboring satellite is operating in second mode. In other words, the t-SnFServiceStartNeigh parameter may be set to the earliest time when the area where the service link of the neighboring satellite operating in second mode is provided covers the area where the terminal serviced by the current serving cell is located.

[0208] Information regarding neighboring satellites that support second mode operation may include the t-ServiceStartNeigh parameter if it further includes time information for when the satellite operates in first mode (normal mode). For example, if a neighboring cell provided by a neighboring satellite services the area currently served by the serving cell in second mode and then provides service in first mode after a specific point in time, information regarding that satellite may include both the t-SnFServiceStartNeigh parameter and the t-ServiceStartNeigh parameter. In this case, the value of the t-ServiceStartNeigh parameter can be set to the earliest time when the neighboring cell provided by the neighboring satellite covers the area currently served by the serving cell in first mode (normal mode).

[0209] FIG. 9b is a conceptual diagram of an information structure according to a second embodiment for a system information block that includes information about a neighboring satellite among the system information blocks broadcast by a satellite.

[0210] Referring to FIG. 9b, the system information block (SIB) (900) may include information about neighboring satellites as previously described. According to the embodiment of FIG. 9b, the SIB (900) may include information about neighboring satellites divided into information (921) about neighboring satellites that do not support the second mode (S&F mode) and information (922) about neighboring satellites that support the second mode. In other words, the information may be divided and included in two different data structures or IEs within the SIB (900).

[0211] Information (921) about neighboring satellites that do not support the second mode may be a collection of information about individual neighboring satellites that do not support the second mode. On the other hand, information (922) about neighboring satellites that support the second mode may be a collection of information about individual neighboring satellites that support the second mode. Therefore, information (922) about neighboring satellites that support the second mode may include the previously described t-SnFServiceStartNeigh parameter for each individual satellite.

[0212] If a terminal that receives an SIB (900) as in FIG. 9b is a terminal that does not support the second mode, the terminal may only utilize information (921) regarding neighboring satellites that do not support the second mode. Therefore, signal measurement for satellite (re)selection can be performed using only the information of the satellites included in the information (921) regarding neighboring satellites that do not support the second mode. At this time, if the terminal is a terminal that does not support the second mode, it may not understand the information (921) regarding neighboring satellites that do not support the second mode, or even if it understands it, it may not perform signal measurement for satellite (re)selection for the neighboring satellites included in the information (921) regarding neighboring satellites that do not support the second mode. Here, signal measurement may mean measuring a signal received from another satellite.

[0213] On the other hand, if the terminal is a terminal that supports the second mode, the terminal can understand both the information (921) regarding neighboring satellites that do not support the second mode and the information (922) regarding neighboring satellites that support the second mode. Additionally, as previously described, the terminal that supports the second mode can perform signal measurements for satellite (re)selection on all neighboring satellites included in the information (921) regarding neighboring satellites that do not support the second mode and the information (922) regarding neighboring satellites that support the second mode.

[0214] FIG. 9c is a conceptual diagram of an information structure according to a third embodiment for a system information block that includes information about a neighboring satellite among the system information blocks broadcast by a satellite.

[0215] Referring to FIG. 9c, the system information block (SIB) (900) may include information about neighboring satellites as previously described. According to the embodiment of FIG. 9c, the SIB (900) may include information (931) of neighboring satellites currently operating in a first mode and information (932) of satellites operating in a second mode. Accordingly, the information (932) of satellites operating in a second mode may include the previously described t-SnFServiceStartNeigh parameter for each individual satellite.

[0216] Neighbor satellites operating in the first mode may include neighbor satellite(s) that support only the first mode. In other words, information about neighbor satellite(s) that do not support the second mode may be included. Additionally, neighbor satellites operating in the first mode may include neighbor satellite(s) that support the second mode but are currently operating in the first mode. In other words, information (931) about neighbor satellites operating in the first mode may include both neighbor satellites that support only the first mode and neighbor satellites that support the second mode but are currently operating in the first mode.

[0217] Information (932) about neighboring satellites operating in second mode may include only neighboring satellite(s) that support second mode and are currently operating in second mode.

[0218] As exemplified in FIG. 9c, the data structure or IE of the information (931) of neighboring satellites operating in the first mode included in the SIB (900) and the data structure or IE of the information (932) of satellites operating in the second mode may be different from each other.

[0219] If the terminal that received the SIB (900) is a terminal that does not support second mode operation, the terminal may perform signal measurement for satellite (re)selection based on information (931) of neighboring satellites operating in first mode. At this time, the terminal that does not support second mode operation may not be able to understand the information (932) of the satellites operating in second mode, or even if it understands it, it may not use the information of the satellites for signal measurement for satellite (re)selection.

[0220] On the other hand, a terminal supporting the second mode can understand both the information (931) of neighboring satellites operating in the first mode and the information (932) of neighboring satellites operating in the second mode included in the received SIB (900). Therefore, as described above, a terminal supporting the second mode can perform signal measurement for satellite (re)selection for both neighboring satellites currently operating in the first mode and neighboring satellites operating in the second mode.

[0221] The t-SnFServiceStartNeigh parameter may be expressed (or provided) in a different form. Below, a method for expressing (or providing) the t-SnFServiceStartNeigh parameter in a different form and the operation of the terminal accordingly are described.

[0222] According to one embodiment of the present disclosure, the t-SnFServiceStartNeigh parameter may be expressed as a combination of the following two pieces of information.

[0223] (a) 1st parameter: Time information on when service is initiated for the area where neighboring satellites currently provide service to the terminal.

[0224] (b) Second parameter: Information indicating that the neighboring satellite is in second mode operation

[0225] The first parameter may be the previously described t-ServiceStartNeigh parameter or t-ServiceStart parameter.

[0226] The application time of the second mode may be the time when the second parameter is provided. As another example, the application time of the second mode may be from the time when a neighboring cell provides service to the area where the terminal is currently receiving service based on the first parameter.

[0227] When t-SnFServiceStartNeigh is expressed based on a combination of the first parameter and the second parameter, the terminal may operate as follows.

[0228] When a terminal supporting second mode (S&F) operation receives the t-SnFServiceStartNeigh parameter from the base station via the SIB (900), it can measure the signal of the neighboring satellite from the time t-ServiceStartNeigh.

[0229] According to another embodiment of the present disclosure, when a terminal supporting a second mode operation receives from a base station via an SIB (900) a first parameter including a time for providing service to an area where the terminal is currently receiving service, and a second parameter including information indicating that a neighbor cell is in second mode operation, the terminal may measure a signal from the neighbor satellite from after the first parameter.

[0230] The serving satellite currently providing services to the terminal may directly notify the terminal of the operating mode of a neighboring satellite or indirectly. The following describes the method by which the serving satellite directly or indirectly notifies the neighboring satellite of its operating mode and the corresponding operation of the terminal.

[0231] The base station can directly notify the operating mode of neighboring satellites through the SIB. For example, if the SIB includes an indicator to indicate whether a neighboring satellite is operating in Mode 1 (Normal Mode) or Mode 2 (S&F Mode), the terminal can use that indicator to indicate the mode of each neighboring satellite(s). In this way, when the SIB includes an indicator for the operating mode of a neighboring satellite, the terminal can identify whether the neighboring satellite is operating in Mode 1 or Mode 2 by checking the corresponding operating mode indicator in the neighboring satellite information included in the SIB. Based on the identification of the neighboring satellite's mode, the terminal can select or exclude the neighboring satellite as a target for (re)selection.

[0232] As another example, the base station can indirectly inform the terminal of the operating mode of neighboring satellites via the SIB. For instance, if there is information that is included only when the second mode (S&F mode) is present, the base station may include such information regarding neighboring satellite(s) operating in the second mode in the individual neighboring satellite information within the SIB. In other words, such information is not included in the SIB for neighboring satellite(s) operating in the first mode. Therefore, a terminal receiving the SIB from the base station can determine that neighboring satellites containing information specific to those operating in the second mode are satellites operating in the second mode, and can determine that the other neighboring satellite(s) are satellites operating in the first mode.

[0233] Meanwhile, even if a terminal supports only the first mode, a terminal capable of interpreting information regarding the second mode may exclude satellites operating in the second mode from signal measurement targets for satellite (re)selection. To this end, even if a signal is received from a satellite operating in the second mode, the signal from that satellite may be excluded from measurement targets. Generally, a terminal can measure a signal when it is received from a satellite (or cell). However, in the case of a satellite operating in the second mode, although signal measurement of the service link is possible, a feeder link does not exist; therefore, a terminal operating in the first mode cannot receive services from a satellite operating in the second mode.

[0234] If a terminal operating in a first mode performs satellite (re)selection or handover based on a signal received from a satellite operating in a second mode, the terminal cannot receive normal service from the satellite operating in the second mode. Therefore, in the present disclosure, service interruption can be prevented by ensuring that a terminal operating in a first mode does not perform measurement for satellite (re)selection or handover even if a signal is received from a satellite operating in a second mode. Furthermore, power consumption of the terminal can be reduced by ensuring that the terminal does not perform unnecessary measurement procedures for received signals.

[0235] [Fourth Embodiment: Operation in Second Mode (S&F)]

[0236] A satellite can provide information to a terminal in RRC idle mode to identify whether the satellite is operating in a first mode (normal mode) or a second mode (S&F mode). For example, a satellite operating in a second mode can notify terminals that it is currently operating in a second mode by broadcasting a second mode operation indication parameter to the area covered by the satellite.

[0237] The terminal can recognize (or confirm or determine) that the satellite is operating in the second mode if the information broadcast by the satellite operating in the second mode includes a second mode operation indication (S&F operation indication) parameter.

[0238] A terminal in an RRC idle state may be prevented from performing at least one of the operations of monitoring paging messages and / or measuring for reselection when it recognizes that a satellite covering the area where the terminal is located is operating in a second mode (S&F mode). According to current 3GPP standards, monitoring of paging messages and measuring for cell reselection are required to be performed even for a terminal in an RRC idle state. However, since a satellite operating in a second mode does not have a feeder link, there may be no transmission of paging messages. Therefore, unnecessary power consumption of the terminal can be prevented by preventing the terminal in an RRC idle state from performing monitoring of paging messages and / or measuring for cell reselection when it is located within the coverage of a satellite operating in a second mode.

[0239] In the case of a terminal released from an RRC idle state, if the satellite providing the service link to the terminal is a satellite operating in second mode, the terminal may be prevented from performing one or more of paging messages and / or signal measurements for satellite (re)selection. Since this case can be understood as identical to what was explained above, a redundant explanation is omitted.

[0240] In the case of a satellite that has switched from the first mode to the second mode, there may still be data to be transmitted to a terminal (MT described in FIG. 6) even after the satellite has switched to the second mode. This is because, before the feeder link is disconnected, data to be transmitted to the terminal may be transmitted to the satellite via the feeder link, and the MT may not be fully transmitted to the terminal until the satellite switches to the second mode. Therefore, if there is MT to be transmitted to the terminal, the satellite switched to the second mode can transmit the MT to the terminal via the service link. At this time, the MT may be user plane data and / or control plane data. Once the satellite switched to the second mode has transmitted all the MT, it may no longer transmit data to the terminal via the service link. Therefore, after the satellite operating in the second mode has transmitted all the MT, it can release all terminals in the RRC connected state within the satellite coverage to the RRC idle state.

[0241] A satellite operating in second mode may set up cell barring after releasing all terminals in the RRC connected state from the RRC idle state. Cell barring is a setting intended to restrict cell connections. In other words, cell barring may refer to a setting that prevents a terminal from (re)selecting a specific cell. For example, cell barring information may consist of system information (e.g., SIB1) and be broadcast to all terminals within the satellite coverage area of ​​second mode.

[0242] Cell barring settings can be configured in three ways.

[0243] The first method may use a cell barring configuration that supports all terminals. For example, information indicating the cell-barred cell may be provided in the system information (e.g., SIB1) broadcast to all terminals.

[0244] The second method may utilize a cell barring setting that supports all terminals capable of connecting to the NTN. In other words, the cell barring setting of the second method may provide information indicating a barred cell (cellBarred_NTN) configured to restrict NTN access in system information (e.g., SIB1) broadcast to all terminals. That is to say, a cell barring method valid only for terminals capable of connecting to the NTN may be used. The second method may be a cell barring method designed to restrict access to a specific cell for all terminals capable of connecting to the NTN.

[0245] A third method may use a cell barring method that supports only terminals that support operation in the second mode among terminals capable of connecting to the NTN. For example, the cell barring of the third method may be a method in which, at the time of switching to the second mode, the satellite sets up cell barring targeting only terminals that do not support operation in the second mode, thereby restricting access to the corresponding cell at the base station to only terminals that do not support operation in the second mode.

[0246] [Fifth Embodiment: Discontinuous Coverage Considering Second Mode (S&F Mode)]

[0247] In the disclosure described below, a situation of discontinuous coverage is described. As previously explained, discontinuous coverage may refer to spatial discontinuity or temporal discontinuity, but in NTN, discontinuous coverage generally refers to temporal discontinuity.

[0248] According to one embodiment of the present disclosure, if a terminal capable of operating in a second mode (S&F mode) is located in discontinuous coverage and the terminal is located within the beam reception range of a satellite operating in the second mode, the terminal can be determined to be within satellite coverage.

[0249] The terminal must be able to determine such a situation, and the satellite must provide information to enable the terminal to recognize that it is located within the satellite's coverage area. The following description explains the information that the satellite must provide to enable the terminal to recognize the above situation, and the method by which the terminal uses said information to determine the situation.

[0250] A terminal may receive system information from a satellite, for example, the information described below via an SIB. It should be noted that the terminal receiving the information below implies a procedure in which the satellite (or base station) configures and transmits said information.

[0251] The terminal can receive system information (e.g., SIB) broadcast by the satellite. The system information may include the following information.

[0252] (a1) Operation mode of the satellites

[0253] (a2) Start time when each satellite provides communication services

[0254] (a3) Satellite's second mode change time

[0255] (a4) Satellite identification information

[0256] (a5) Satellite beam reception range information

[0257] (a6) Satellite frequency information

[0258] (a1) The operation mode of the satellites can be notified to the terminal as follows.

[0259] The operating modes of the satellites may directly or implicitly include the operating modes of the satellite transmitting system information and the neighboring satellite(s). As described above, the operating mode of a satellite may be either the first mode (general mode) or the second mode (S&F mode). If an indicator indicating the operating mode is set, the satellite transmitting system information may indicate its own operating mode and the operating modes of the neighboring satellite(s) through the corresponding indicator. Accordingly, a terminal using an indicator indicating the operating mode of a satellite can determine the operating modes of the satellites based on the operating mode indicators for the serving satellite and the neighboring satellite(s), respectively, from the system information.

[0260] A satellite may add information indicating that a satellite is operating in the second mode to neighboring satellite information only for those neighboring satellites that are operating in the second mode. If a satellite is operating in the first mode, the neighboring satellite information included in the system information may not include information added only when operating in the second mode. Therefore, if there is a satellite among the system information received from the satellite for which information indicating that it is operating in the second mode has been added to it, the terminal may determine that the satellite is operating in the second mode. If none of the neighboring satellite information included in the system information received from the satellite includes information indicating that the satellite is operating in the second mode, the terminal may determine that all neighboring satellites are neighboring satellites operating in the first mode.

[0261] (a2) The start time for each satellite to provide communication services may be provided to the terminal in the following manner.

[0262] If the satellite is a satellite operating in a first mode, time information regarding when the satellite operating in the first mode provides a service to a specific area can be provided to the terminal through system information. Conversely, if the satellite is a satellite operating in a second mode, time information regarding when the satellite provides a service to a specific area in the second mode can be provided to the terminal through system information. The terminal can obtain time information regarding when a service (e.g., a service in the first mode or a service in the second mode) is provided according to the satellite's operating mode included in the system information received from the satellite.

[0263] According to one embodiment of the present disclosure, in the case of (a2), the start time at which each satellite provides communication services may also be provided to the terminal in the following manner.

[0264] For example, regardless of the satellite's operating mode, the earliest time information when a neighboring cell served by the satellite covers the area currently served by the serving cell can be provided to the terminal via system information. Here, whether the satellite covers the area currently served by the satellite can also be determined using the satellite beam's reception range (footprint). The terminal can obtain the aforementioned earliest time information through system information received from the satellite.

[0265] (a3) Information on the satellite's second mode change time can be provided to the terminal in the following way.

[0266] The satellite may transmit one or more time information, among the time of mode switching from the first mode to the second mode (normal to S&F) or the time of mode switching from the second mode to the first mode (S&F to normal), to the terminal via system information. Accordingly, the terminal receives system information from the satellite and can predict (or determine) whether it is within or outside the coverage area based on the mode switching time information included in the received system information. If the terminal determines that it is outside the coverage area, the terminal may not perform the operation that is required to be performed in the idle mode described above.

[0267] (a4) Satellite identification information can be provided to the terminal in the following ways.

[0268] Each satellite may have a satellite identifier capable of identifying itself. The satellite identifier may consist of a finite bit length. Such a satellite identifier can be used to identify not only its own satellite but also neighboring satellites. Therefore, satellite identification information can be transmitted to the terminal via system information. The satellite identification information transmitted to the terminal via system information may include not only the satellite identification information of the satellite transmitting the system information but also satellite identifiers for identifying neighboring satellites. The terminal can verify the satellite identifier of the satellite currently receiving service as well as the satellite identifiers of neighboring satellites from the system information received from the satellite.

[0269] (a5) Information on the satellite's beam reception range (footprint) can be provided to the terminal in the following way.

[0270] For example, information related to a satellite's beam reception range may be elevation angle information. As another example, information related to a satellite's beam reception range may be a reference point and radius information of a circle centered on the reference point. As yet another example, information related to a satellite's beam reception range may be a finite-length satellite identifier capable of identifying the relevant satellite among multiple satellites. The satellite beam reception range information described above may be provided to a terminal through system information. The terminal obtains the satellite beam reception range information through system information and can communicate with the satellite within that range.

[0271] (a6) Satellite frequency information can be provided to the terminal in the following manner.

[0272] Satellite frequency information may refer to frequency information used by each satellite or provided by the satellite. The frequency information may be a carrier frequency or a frequency band. Satellite frequency information may be provided to a terminal through system information. In this case, the system information may be one or more of a Master Information Block (MIB), a SIB, or an RRC signaling message.

[0273] According to one embodiment of the present disclosure, a satellite (or base station) may receive "discontinuous coverage information" via a SIB from the satellite (or cell) to which the terminal is currently connected, as described above. The discontinuous coverage information may be broadcast via the SIB or delivered on-demand in response to a request from the terminal.

[0274] According to one embodiment of the present disclosure, a terminal may perform the following operations after receiving an SIB from a currently connected cell.

[0275] The terminal can predict (or determine) whether the terminal is located in-coverage or out-of-coverage by using one or more of the "discontinuous coverage information." Here, the terminal may additionally use SIB information of the current serving satellite (or cell) (e.g., SIB31 in the case of 3GPP IoT NTN), and t-Service (e.g., t-Service included in SIB3 in the case of 3GPP IoT).

[0276] According to one embodiment of the present disclosure, if a terminal is capable of operating in a second mode (S&F mode) and the terminal is located within the beam reception range of a satellite operating in the second mode, the terminal can ultimately determine that it is in coverage. This enables the overcoming of the disadvantage that conventional discontinuous coverage-related technologies do not support satellites operating in the second mode. For example, when a terminal capable of operating in the second mode is within the beam reception range of a satellite operating in the second mode, the problem of not performing operations that should be performed in idle mode by determining that the terminal is out of coverage, even though the terminal can receive services through the operation in the second mode, can be resolved.

[0277] Meanwhile, the first to fifth embodiments described above may each be used individually, or two or more embodiments may be performed in combination. Examples in which two or more embodiments are used in combination have been partially described in each embodiment. It should be noted that embodiments in which examples in which two or more embodiments are used in combination are not described in this disclosure may also be additionally implemented based on what is described in this disclosure.

[0278] The operation of the method according to an embodiment of the present disclosure can be implemented as a computer-readable program or code on a computer-readable recording medium. A computer-readable recording medium includes all types of recording devices in which information that can be read by a computer system is stored. Additionally, the computer-readable recording medium may be distributed across networked computer systems, allowing the computer-readable program or code to be stored and executed in a distributed manner.

[0279] In addition, computer-readable recording media may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, and flash memory. Program instructions may include machine code, such as that generated by a compiler, as well as high-level language code that can be executed by a computer using an interpreter, etc.

[0280] Some aspects of the present disclosure have been described in the context of a device, but may also be described according to a corresponding method, wherein a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method may also be described according to a corresponding block or item or a feature of a corresponding device. Some or all of the method steps may be performed by (or using) a hardware device, such as, for example, a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, at least one of the most important method steps may be performed by such a device.

[0281] In the embodiments, a programmable logic device (e.g., a field-programmable gate array) may be used to perform some or all of the functions of the methods described herein. In the embodiments, the field-programmable gate array may operate with a microprocessor to perform one of the methods described herein. Generally, it is preferable that the methods be performed by some hardware device.

[0282] Although the present disclosure has been described with reference to preferred embodiments, those skilled in the art will understand that various modifications and changes can be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the following claims.

Claims

1. In the method of user equipment (UE), A step of receiving system information including first transition time information indicating the time for the serving satellite to transition from the first mode to the second mode from a serving satellite operating in a first mode having both a service link and a feeder link; and The method includes the step of transmitting the first switching time obtained at the access stratum (AS) of the UE to the non-access stratum (NAS) of the UE, The above second mode is a store and forward mode operation, UE's method.

2. In Claim 1, The above system information further includes neighboring satellite information, The method further comprises the step of measuring signals received from one or more neighboring satellites indicated by the neighboring satellite information for satellite (re)selection before the mode switching time of the serving satellite to the second mode based on the first switching time. UE's method.

3. In Claim 2, The method further comprises the step of determining a first satellite to (re)select among the one or more neighboring satellites based on the result of measuring signals received from the one or more neighboring satellites. UE's method.

4. In Claim 3, Based on the result of measuring signals received from one or more neighboring satellites, the UE is connected to both the satellite operating in the first mode and the satellite operating in the second mode, and the satellite operating in the first mode is determined to be the first satellite. UE's method.

5. In Claim 3, Based on the result of measuring signals received from one or more neighboring satellites, and based on all satellites accessible to the UE operating in the second mode, the satellite with the shortest time operating in the second mode is determined as the first satellite. UE's method.

6. In Claim 3, Based on the fact that the first satellite is a satellite operating in the second mode, the method further includes the step of performing one or more operations among neighbor cell search or paging monitoring during the time when the UE is located within the beam reception range of the satellite operating in the second mode. UE's method.

7. In Claim 1, The above system information further includes neighboring satellite information, and A step of determining whether the UE belongs to the service area of ​​the satellite based on the service start time of each satellite and the service end time of the serving satellite based on the neighboring satellite information; and The method further includes the step of suspending one or more operations of neighbor cell search or paging monitoring during the time when the UE is not included in the satellite's service area, based on a determination of whether the UE belongs to the satellite's service area. UE's method.

8. In Claim 1, The above system information further includes second transition time information indicating the time when the serving satellite switches from the second mode to the first mode, UE's method.

9. In Claim 1, The NAS of the above UE drives a timer to stop the transmission of a mobile originated (MO) signaling message during the second mode based on the first switching time; and The method further includes the step of waiting for the transmission of an MO signaling message generated in the NAS while the above timer is running. UE's method.

10. In Claim 9, Based on the expiration of the above timer, the method further includes the step of retrying the transmission procedure of the MO signaling message generated in the NAS and waiting. UE's method.

11. In user equipment (UE), It includes at least one processor, wherein the at least one processor is the UE: Receiving system information including first transition time information indicating the time for the serving satellite to switch from the first mode to the second mode from a serving satellite operating in a first mode having both a service link and a feeder link; and Causing the first transition time obtained at the access stratum (AS) of the above UE to be transmitted to the non-access stratum (NAS) of the above UE, The above second mode is a store and forward mode operation, UE.

12. In Claim 11, The above system information further includes neighboring satellite information, The above at least one processor further causes the UE to measure signals received from one or more neighboring satellites indicated by the neighboring satellite information for satellite (re)selection before the mode switching time of the serving satellite to the second mode based on the first switching time. UE.

13. In Claim 12, The above at least one processor further causes the UE to determine a first satellite to (re)select among the one or more neighboring satellites based on the result of measuring signals received from the one or more neighboring satellites, UE.

14. In Claim 13, Based on the result of measuring signals received from one or more neighboring satellites, the UE is connected to both the satellite operating in the first mode and the satellite operating in the second mode, and the satellite operating in the first mode is determined to be the first satellite. UE.

15. In Claim 13, Based on the result of measuring signals received from one or more neighboring satellites, and based on all satellites accessible to the UE operating in the second mode, the satellite with the shortest time operating in the second mode is determined as the first satellite. UE.

16. In Claim 13, The above at least one processor further causes the UE to perform one or more operations of neighbor cell search or paging monitoring during the time the UE is located within the beam reception range of the satellite operating in the second mode, based on the fact that the first satellite is a satellite operating in the second mode. UE.

17. In Claim 11, The above system information further includes neighboring satellite information, and The above at least one processor is the UE: Determining whether the UE belongs to the service area of ​​the satellite based on the service start time of each satellite and the service end time of the serving satellite based on the neighboring satellite information; and Based on a determination of whether the above UE belongs to the satellite's service area, further causing one or more operations of neighbor cell search or paging monitoring to be stopped during the time when the above UE is not included in the satellite's service area, UE.

18. In Claim 11, The above system information further includes second transition time information indicating the time when the serving satellite switches from the second mode to the first mode, UE.

19. In Claim 11, The above at least one processor is the UE: The NAS of the above UE drives a timer that stops the transmission of a mobile originated (MO) signaling message during the second mode based on the first switching time; and Further causing to wait for the transmission of MO signaling messages generated in the NAS while the above timer is running, UE.

20. In Claim 19, The above at least one processor further causes the UE to retry the transmission procedure of the MO signaling message generated in the NAS and waiting based on the expiration of the timer, UE.

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