Method and apparatus for configuring timing group for handover in non-terrestrial network

Abstract

A method and apparatus for configuring a timing group for handover in a non-terrestrial network are disclosed. A method performed by a user equipment (UE) may comprise the steps of: receiving timing group configuration information for a timing group including the UE from a first satellite based on a beam point supported by the first satellite; receiving a handover command message including timing information on the UE from the first satellite according to a timing group index included in the timing group configuration information; acquiring timing advance (TA) information using the timing information; and transmitting a handover completion message using the TA information.

Description

Technical Field

[0001] The present invention relates to a technology for configuring a group for handover in a non-terrestrial network, and more particularly, to a technology for configuring a timing group for random access channel-less (RACH-less) handover. Background Art

[0002] When a handover process is performed in a terrestrial network or a non-terrestrial network, the timing advance (TA) of the source cell and the TA of the target cell may be different. In this case, when the handover process is performed, if the terminal does not know the TA of the target cell, the terminal may obtain the TA of the target cell through a random access process. The process of the terminal obtaining the TA of the target cell through a random access process may cause a delay in the handover process. In order to reduce the delay in the handover process, a handover without a random access channel (RACH-less) may be proposed in the terrestrial network. In this case, the target base station may send information about the timing difference of the TA of the target cell to the terminal. In addition, the source base station may send information about the timing difference of the TA of the source cell to the terminal.

[0003] In a terrestrial network environment, a handover process may occur due to the mobility of the terminal. Therefore, in a terrestrial network environment, a timing control method using separate signaling for the terminal by the base station may be appropriate.

[0004] In a non-terrestrial network environment, the handover process may occur mainly due to the movement of the satellite. In addition, in a non-terrestrial network environment, the handover process may occur at the same time or at similar times in a large number of terminals. Due to the large number of handover processes, a large number of random access processes may be performed. Due to the large number of random access processes, signaling overhead may occur. In a non-terrestrial network environment, a RACH-free handover process can reduce the signaling load and signaling delay caused by a large number of random access processes. However, in a non-terrestrial network environment, signaling overhead may occur when timing control signaling is performed on a terminal-by-terminal basis. In a non-terrestrial network, a large number of terminals may request to switch to a base station at the same time or at similar times. Therefore, the present invention proposes a method for configuring a terminal group with similar timing information required for a RACH-free handover process.

[0005] Since signaling is performed on a group basis for groups with similar timing information, signaling overhead can be reduced. Therefore, the present invention proposes a method for configuring groups with similar timing in situations such as feeder link switching, an Earth Fixed Beam (EFB) environment, or an Earth Mobile Beam (EMB) environment. Summary of the Invention

[0006] Technical issues

[0007] The present invention is directed to providing a method and apparatus for configuring a timing group for handover in a non-terrestrial network.

[0008] Technical Solution

[0009] A method of a user equipment (UE) according to a first exemplary embodiment of the present invention may include: receiving timing group configuration information for a timing group including the UE from a first satellite, the timing group being configured based on a beam spot supported by the first satellite; receiving a handover command message including timing information of the UE from the first satellite according to a timing group index included in the timing group configuration information; acquiring timing advance (TA) information using the timing information; and sending a handover complete message using the TA information.

[0010] The timing group configuration information may include a timing group index, and the timing group index is used to: when a difference between a timing value of the UE and a timing value of a center position of a configuration distance defined by a base station associated with a first satellite falls within a first TA range configured by the base station, identify a timing group including UEs within the first TA range.

[0011] The timing group configuration information may include a timing group index, which is used to identify the timing group including the UE within the distance range configured by the base station from the center position of the beam spot when the UE is within the distance range from the center position of the beam spot.

[0012] The timing group configuration information may include a timing group index, and the timing group index is used to: when the cell remaining time falls within the time range configured by the first satellite, identify the timing group including the UE whose cell remaining time is within the time range, and the cell remaining time is the time for providing communication services of the beam point to the UE.

[0013] When obtaining TA information using timing information, TA information can be obtained by using a timing difference corresponding to a difference between a first path and a second path, wherein the first path includes a path between the first satellite and the center position of the timing group and a path between the first satellite and the base station, and the second path includes a path between the second satellite and the center position of the timing group and a path between the second satellite and the base station.

[0014] Obtaining TA information using timing information may include: determining a UE-specific TA value; and updating the UE's TA information by using the UE-specific TA value and at least one of a common TA value equally applied to all UEs of the source cell included in the timing information, a common TA value equally applied to all UEs of the target cell, or a timing difference caused by a difference in reference points (RP) between the source cell and the target cell, thereby obtaining the TA information.

[0015] Using timing information to obtain TA information may include: receiving at least one of the UE's position information, the first satellite's position information, or satellite ephemeris information from a first satellite; using the UE's position information, the first satellite's position information, and at least one of the satellite ephemeris information to calculate a timing adjustment value for the UE; and using the timing adjustment value and the timing information to obtain TA information.

[0016] A method of a base station according to a second exemplary embodiment of the present invention may include: configuring timing group configuration information for a timing group including a user equipment (UE) based on a beam spot supported by a first satellite; sending a handover command message including timing information of the timing group to which the UE belongs to the UE according to a timing group index included in the timing group configuration information; and receiving a handover completion message from the UE that performs a handover procedure based on the timing information of the timing group to which the UE belongs.

[0017] Configuring the timing group configuration information may include configuring the UE into the timing group in response to a difference between a timing value of the UE and a timing value of a center location of a configuration distance defined by the base station communicating via the first satellite being equal to or less than a second TA value defined by the base station for the timing group.

[0018] Configuring the timing group configuration information may include configuring the UE into the timing group in response to a cell remaining time falling within a time range configured by the first satellite, wherein the cell remaining time is a time during which a communication service of the beam spot is provided to the UE.

[0019] The timing information may include at least one of a common TA value equally applied to all UEs of a source cell, a common TA value equally applied to all UEs of a target cell, or a timing difference caused by a difference in reference points (RPs) between the source cell and the target cell.

[0020] A user equipment (UE) according to a second exemplary embodiment of the present invention may include: at least one processor, wherein the at least one processor may cause the UE to execute: receiving timing group configuration information for a timing group including the UE from a first satellite, the timing group being configured based on beam spots supported by the first satellite; receiving a handover command message including timing information of the UE from the first satellite according to a timing group index included in the timing group configuration information; acquiring timing advance (TA) information using the timing information; and sending a handover complete message using the TA information.

[0021] The timing group configuration information may include a timing group index, and the timing group index is used to: when a difference between a timing value of the UE and a timing value of a center position of a configuration distance defined by a base station associated with a first satellite falls within a first TA range configured by the base station, identify a timing group including UEs within the first TA range.

[0022] The timing group configuration information may include a timing group index, which is used to identify the timing group including the UE within the distance range configured by the base station from the center position of the beam spot when the UE is within the distance range from the center position of the beam spot.

[0023] The timing group configuration information may include a timing group index, and the timing group index is used to: when the cell remaining time falls within the time range configured by the first satellite, identify the timing group including the UE whose cell remaining time is within the time range, and the cell remaining time is the time for providing communication services of the beam point to the UE.

[0024] When obtaining TA information using timing information, TA information can be obtained by using a timing difference corresponding to a difference between a first path and a second path, wherein the first path includes a path between the first satellite and the center position of the timing group and a path between the first satellite and the base station, and the second path includes a path between the second satellite and the center position of the timing group and a path between the second satellite and the base station.

[0025] When acquiring TA information using timing information, the at least one processor may further cause the UE to perform: determining a UE-specific TA value; and updating the UE's TA information by using the UE-specific TA value and at least one of a common TA value equally applied to all UEs of the source cell included in the timing information, a common TA value equally applied to all UEs of the target cell, or a timing difference value caused by a difference in a reference point (RP) between the source cell and the target cell, thereby acquiring the TA information.

[0026] When using timing information to obtain TA information, the at least one processor can further cause the UE to execute: receiving at least one of the UE's position information, the first satellite's position information, or satellite ephemeris information from the first satellite; calculating the UE's timing adjustment value using the UE's position information, the first satellite's position information, and at least one of the satellite ephemeris information; and obtaining TA information using the timing adjustment value and the timing information.

[0027] Beneficial effects

[0028] According to the present invention, to achieve coexistence between a non-terrestrial communication network (NTN) and a terrestrial communication network (TN), the NTN and TN can use the same frequency. By using the same frequency, the NTN and TN can provide services in the same area. In the NTN, signaling for handover procedures is performed on a group basis for terminals with similar timing information, thereby reducing signaling overhead. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1a is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0030] Figure 1b is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0031] Figure 2a is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0032] Figure 2b is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0033] Figure 2c is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0034] Figure 3 is a block diagram illustrating an exemplary embodiment of communication nodes comprising a non-terrestrial network.

[0035] Figure 4 is a block diagram illustrating an example embodiment of a communication node performing communications.

[0036] Figure 5a is a block diagram illustrating an exemplary embodiment of a transmit path.

[0037] Figure 5b is a block diagram illustrating an exemplary embodiment of a receive path.

[0038] Figure 6a is a conceptual diagram illustrating an exemplary embodiment of a protocol stack for a user plane in a non-terrestrial network based on transparent payload.

[0039] Figure 6bis a conceptual diagram illustrating an exemplary embodiment of a protocol stack for a control plane in a non-terrestrial network based on transparent payload.

[0040] Figure 7a is a conceptual diagram illustrating an exemplary embodiment of a protocol stack for a user plane in a non-terrestrial network based on a regenerative payload.

[0041] Figure 7b is a conceptual diagram illustrating an exemplary embodiment of a protocol stack for a control plane in a non-terrestrial network based on a regenerative payload.

[0042] Figure 8 is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0043] Figure 9 is a conceptual diagram illustrating an exemplary embodiment of an uplink time synchronization procedure.

[0044] Figure 10a is a conceptual diagram illustrating an exemplary embodiment of a handover process.

[0045] Figure 10b is a conceptual diagram illustrating an exemplary embodiment of a handover process.

[0046] Figure 11 is a conceptual diagram illustrating an exemplary embodiment of beam foot print in an EFB environment.

[0047] Figure 12 is a conceptual diagram illustrating an exemplary embodiment of an EMB.

[0048] Figure 13a is a conceptual diagram illustrating an exemplary embodiment of handover in a non-terrestrial network.

[0049] Figure 13b is a conceptual diagram illustrating an exemplary embodiment of handover in a non-terrestrial network.

[0050] Figure 14a is a conceptual diagram illustrating an exemplary embodiment of a feeder link switching environment.

[0051] Figure 14b is a conceptual diagram illustrating an exemplary embodiment of a feeder link switching environment.

[0052] Figure 15 is a conceptual diagram illustrating an exemplary embodiment of a timing group configuration.

[0053] Figure 16 is a conceptual diagram illustrating an exemplary embodiment of a handover process in an EMB environment.

[0054] Figure 17is a conceptual diagram illustrating an exemplary embodiment of a handover process in an EMB environment.

[0055] Figure 18 is a conceptual diagram illustrating an exemplary embodiment of a handover process in an EMB environment. DETAILED DESCRIPTION

[0056] While the present invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will be described in detail herein. However, it should be understood that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Throughout the description of the drawings, like reference numerals refer to like elements.

[0057] It will be understood that although the terms first, second, etc. can be used herein to describe each element, these elements should not be limited by these terms. These terms are only used to distinguish an element from another element. For example, without departing from the scope of the present invention, the first element can be referred to as the second element, and similarly, the second element can be referred to as the first element. As used in this article, the term "and / or" includes any combination and all combinations of one or more related enumeration items.

[0058] In the present invention, “at least one of A and B” may mean “at least one of A or B” or “at least one of a combination of one or more of A and B”. Furthermore, in an exemplary embodiment of the present invention, “one or more of A and B” may mean “one or more of A or B” or “one or more of a combination of one or more of A and B”.

[0059] In the present invention, "(re)transmission" may mean "transmission", "retransmission" or "transmission and retransmission", "(re)configuration" may mean "configuration", "reconfiguration" or "configuration and reconfiguration", "(re)connection" may mean "connection", "reconnection" or "connection and reconnection", and "(re)access" may mean "access", "reaccess" or "access and reaccess".

[0060] It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements.

[0061] The terms used in this article are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in this article, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. It will be further understood that when the terms "comprise" and / or "comprising" are used in this article, it indicates the presence of the described features, values, steps, operations, elements, components or combinations thereof, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components and / or combinations thereof.

[0062] Unless otherwise defined, all terms (including technical and scientific terms) used in this document have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It will be further understood that terms (e.g., terms defined in commonly used dictionaries) should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology and will not be interpreted as idealized or overly formal unless explicitly defined as such in this document.

[0063] Hereinafter, the exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In order to promote overall understanding when describing the present invention, the same components in the drawings are represented by the same reference numerals, and repeated descriptions thereof will be omitted. In addition to the exemplary embodiments clearly described in the present invention, operations can also be performed according to combinations of exemplary embodiments, expansions of exemplary embodiments, and / or modifications of exemplary embodiments. The execution of some operations can be omitted, and the execution order of operations can be changed.

[0064] Even when describing a method performed at a first communication node among communication nodes (e.g., transmission or reception of a signal), the corresponding second communication node may also perform a method corresponding to the method performed at the first communication node (e.g., reception or transmission of a signal). That is, when describing the operation of a user equipment (UE), the base station corresponding to the UE may perform an operation corresponding to the operation of the UE. Conversely, when describing the operation of a base station, the UE corresponding to the base station may perform an operation corresponding to the operation of the base station. In a non-terrestrial network (NTN) (e.g., a payload-based NTN), the operation of the base station may refer to the operation of the satellite, and the operation of the satellite may refer to the operation of the base station.

[0065] A base station may refer to a node B, an evolved node B (eNodeB), a next generation node B (gNodeB), a gNB, a device, an apparatus, a node, a communication node, a base transceiver station (BTS), a radio remote head (RRH), a transmission reception point (TRP), a radio unit (RU), a roadside unit (RSU), a radio transceiver, an access point, an access node, etc. A UE may refer to a terminal, a device, an apparatus, a node, a communication node, an end node, an access terminal, a mobile terminal, a station, a subscriber station, a mobile station, a portable subscriber station, an on-broad unit (OBU), etc.

[0066] In the present invention, signaling may be at least one of higher layer signaling, medium access control (MAC) signaling, or physical (PHY) signaling. A message used for higher layer signaling may be referred to as a "higher layer message" or a "higher layer signaling message." A message used for MAC signaling may be referred to as a "MAC message" or a "MAC signaling message." A message used for PHY signaling may be referred to as a "PHY message" or a "PHY signaling message." Higher layer signaling may refer to the transmission and reception operations of system information (e.g., a master information block (MIB), a system information block (SIB)) and / or an RRC message. MAC signaling may refer to the transmission and reception operations of a MAC control element (CE). PHY signaling may refer to the transmission and reception operations of control information (e.g., downlink control information (DCI), uplink control information (UCI), and sidelink control information (SCI)).

[0067] In the present invention, “configuring an operation (e.g., sending an operation)” may mean “signaling configuration information (e.g., information element or parameter) of the operation and / or information instructing to perform the operation.” “Configuring an information element (e.g., parameter)” may mean “signaling a corresponding information element.” In the present invention, “signal and / or channel” may mean signal, channel, or “signal and channel,” and “signal” may be used to mean “signal and / or channel.”

[0068] The communication system may include at least one of a terrestrial network, a non-terrestrial network, a 4G communication network (e.g., a Long Term Evolution (LTE) communication network), a 5G communication network (e.g., a New Radio (NR) communication network), or a 6G communication network. Each of the 4G communication network, the 5G communication network, and the 6G communication network may include a terrestrial network and / or a non-terrestrial network. The non-terrestrial network may operate based on at least one of the LTE communication technology, the 5G communication technology, or the 6G communication technology. The non-terrestrial network may provide communication services in various frequency bands.

[0069] The communication network to which the exemplary embodiment is applied is not limited to the content described below, and the exemplary embodiment can be applied to various communication networks (e.g., 4G communication network, 5G communication network and / or 6G communication network). Here, the communication network can be used in the same sense as the communication system.

[0070] Figure 1a is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0071] like Figure 1a As shown, the non-terrestrial network (NTN) may include a satellite 110, a communication node 120, a gateway 130, a data network 140, etc. A unit including the satellite 110 and the gateway 130 may correspond to a remote radio unit (RRU). Figure 1a The NTN shown may be a transparent payload-based NTN. Satellite 110 may be a low earth orbit (LEO) satellite, a medium earth orbit (MEO) satellite, a geostationary earth orbit (GEO) 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). Non-GEO satellites may be LEO satellites and / or MEO satellites.

[0072] The communication nodes 120 may include communication nodes located at terrestrial locations (e.g., user equipment (UE) or terminals) and communication nodes located in non-terrestrial space (e.g., aircraft, drones). 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 coverage area of ​​the beam of the satellite 110 may be elliptical or circular.

[0073] In non-terrestrial networks, the following three types of service links can be supported.

[0074] - Earth-fixed: The service link may be provided by a beam that continuously covers the same geographical area at all times (e.g., a geosynchronous orbit (GSO) satellite).

[0075] - Quasi-Earth-Fixed: The service link may be provided by a beam covering one geographical area during a defined period and by a beam covering another geographical area during another period (e.g. a non-GSO (NGSO) satellite forming a steerable beam).

[0076] - Earth-moving: The service link may be provided by a beam that moves over the surface of the Earth (e.g., an NGSO satellite forming a fixed or non-steerable beam).

[0077] The communication node 120 may perform communication (e.g., downlink communication and uplink communication) with the satellite 110 using 4G communication technology, 5G communication technology, and / or 6G communication technology. Communication between the satellite 110 and the communication node 120 may be performed using an NR-Uu interface and / or a 6G-Uu interface. When dual connectivity (DC) is supported, the communication node 120 may be connected to other base stations (e.g., base stations supporting 4G, 5G, and / or 6G functions) as well as the satellite 110, and perform DC operations based on the technologies defined in the 4G, 5G, and / or 6G technical specifications.

[0078] The gateway 130 may be located at a ground location, and a feeder link may be established between the satellite 110 and the gateway 130. The feeder link may be a radio link. The gateway 130 may be referred to as a "non-terrestrial network (NTN) gateway". Communication between the satellite 110 and the gateway 130 may be performed based on an NR-Uu interface, a 6G-Uu interface, or a satellite radio interface (SRI). The gateway 130 may be connected to the data network 140. A "core network" may exist between the gateway 130 and the data network 140. For example, 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 4G communication technology, 5G communication technology, and / or 6G communication 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), and the like. Communication between the gateway 130 and the core network may be performed based on an NG-C / U interface or a 6G-C / U interface.

[0079] like Figure 1b As shown in the exemplary embodiment of FIG, in the NTN based on transparent payload, a “core network” may exist between the gateway 130 and the data network 140.

[0080] Figure 1b is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0081] like Figure 1b As shown, the gateway can be connected to the base station, the base station can be connected to the core network, and the core network can be connected to the data network. Each of the base station and the core network can support 4G communication technology, 5G communication technology and / or 6G communication technology. The communication between the gateway and the base station can be performed based on the NR-Uu interface or the 6G-Uu interface, and the communication between the base station and the core network (e.g., AMF, UPF, SMF, etc.) can be performed based on the NG-C / U interface or the 6G-C / U interface.

[0082] Figure 2a is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0083] like Figure 2a As shown, the non-terrestrial network may include a first satellite 211, a second satellite 212, a communication node 220, a gateway 230, a data network 240, and the like. Figure 2aThe NTN shown may be an NTN based on a regenerated payload. For example, each of satellite 211 and satellite 212 may perform a regeneration operation (e.g., demodulation, decoding, re-encoding, re-modulation, and / or filtering) on ​​a payload received from another entity (e.g., communication node 220 or gateway 230) and transmit the regenerated payload.

[0084] Each of satellite 211 and satellite 212 can be a LEO satellite, a MEO satellite, a GEO satellite, a HEO satellite or a UAS platform. The UAS platform can include a HAPS. Satellite 211 can be connected to satellite 212, and an inter-satellite link (ISL) can be established between satellite 211 and satellite 212. The ISL can operate in an RF band or an optical band. The ISL can be optionally established. The communication node 220 can include a ground communication node (e.g., a UE or terminal) and a non-ground communication node (e.g., an aircraft or a drone). A service link (e.g., a radio link) can be established between satellite 211 and communication node 220. Satellite 211 can provide communication services to communication node 220 using one or more beams.

[0085] The communication node 220 can perform communication (e.g., downlink communication or uplink communication) with the satellite 211 using 4G communication technology, 5G communication technology, and / or 6G communication technology. Communication between the satellite 211 and the communication node 220 can be performed using an NR-Uu interface or a 6G-Uu interface. When DC is supported, the communication node 220 can be connected to other base stations (e.g., base stations supporting 4G, 5G, and / or 6G functions) and the satellite 211, and can perform DC operations based on the technologies defined in the 4G, 5G, and / or 6G technical specifications.

[0086] Gateway 230 may be located on the ground. A feeder link may be established between satellite 211 and gateway 230, and a feeder link may be established between satellite 212 and gateway 230. The feeder link may be a radio link. When an ISL is not established between satellite 211 and satellite 212, a feeder link may be established between satellite 211 and gateway 230. Communication between each of satellite 211 and satellite 212 and gateway 230 may be performed based on an NR-Uu interface, a 6G-Uu interface, or SRI. Gateway 230 may be connected to a data network 240.

[0087] like Figure 2b and Figure 2c As shown in the exemplary embodiment of FIG, a “core network” may exist between the gateway 230 and the data network 240.

[0088] Figure 2bis a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network, Figure 2c is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0089] like Figure 2b and Figure 2c As shown, the gateway can be connected to the core network, and the core network can be connected to the data network. The core network can support 4G communication technology, 5G communication technology and / or 6G communication technology. For example. The core network may include AMF, UPF, SMF, etc. The communication between the gateway and the core network can be performed based on the NG-C / U interface or the 6G-C / U interface. The functions of the base station can be performed by the satellite. That is, the base station can be located on the satellite. The payload can be processed by the base station located on the satellite. Base stations located on different satellites can be connected to the same core network. A satellite can have one or more base stations. In Figure 2b In non-terrestrial networks, it may not be possible to establish ISLs between satellites. Figure 2c In non-terrestrial networks, ISLs between satellites can be established.

[0090] On the other hand, the composition Figure 1a 、 Figure 1b 、 Figure 2a 、 Figure 2b and / or Figure 2c The entities of the non-terrestrial network shown (eg, satellite, base station, UE, communication node, gateway, etc.) may be configured as follows: In the present invention, the entity may be referred to as a communication node.

[0091] Figure 3 is a block diagram illustrating an exemplary embodiment of communication nodes comprising a non-terrestrial network.

[0092] like Figure 3 As shown, the communication node 300 may include at least one processor 310, a memory 320, and a transceiver 330 connected to a network to perform communication. In addition, the communication node 300 may further include an input interface device 340, an output interface device 350, a storage device 360, etc. The components included in the communication node 300 may be connected to communicate with each other via a bus 370.

[0093] However, each component included in the communication node 300 may be connected to the processor 310 through a separate interface or a separate bus instead of the common bus 370. For example, the processor 310 may be connected to at least one of the memory 320, the transceiver 330, the input interface device 340, the output interface device 350, and the storage device 360 ​​through a dedicated interface.

[0094] The processor 310 can execute at least one instruction stored in at least one of the memory 320 and the storage device 360. The processor 310 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which the method according to the exemplary embodiment of the present invention is executed. Each of the memory 320 and the storage device 360 ​​can be configured as at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 320 can be configured with at least one of a read-only memory (ROM) and a random access memory (RAM).

[0095] On the other hand, a communication node that performs communication in a communication network (eg, a non-terrestrial network) may be configured as follows. Figure 4 The communication nodes shown may be Figure 3 A specific exemplary embodiment of a communication node is shown.

[0096] Figure 4 is a block diagram illustrating an example embodiment of a communication node performing communications.

[0097] like Figure 4 As shown, each of the first communication node 400a and the second communication node 400b can be a base station or a UE. The first communication node 400a can send a signal to the second communication node 400b. The transmission processor 411 included in the first communication node 400a can receive data (e.g., data units) from the data source 410. The transmission processor 411 can receive control information from the controller 416. The control information may include at least one of system information, RRC configuration information (e.g., information configured by RRC signaling), MAC control information (e.g., MAC CE), or PHY control information (e.g., DCI, SCI).

[0098] The transmit processor 411 may generate data symbols by performing processing operations on data (e.g., encoding operations, symbol mapping operations, etc.). The transmit processor 411 may generate control symbols by performing processing operations on control information (e.g., encoding operations, symbol mapping operations, etc.). In addition, the transmit processor 411 may generate synchronization / reference symbols for synchronization signals and / or reference signals.

[0099] The Tx MIMO processor 412 may perform spatial processing operations (e.g., precoding operations) on data symbols, control symbols, and / or synchronization / reference symbols. The output of the Tx MIMO processor 412 (e.g., a symbol stream) may be provided to a modulator (MOD) included in transceivers 413a to 413t. The modulator may generate modulation symbols by performing processing operations on the symbol stream and may generate signals by performing additional processing operations (e.g., analog-to-analog conversion operations, amplification operations, filtering operations, upconversion operations, etc.) on the modulation symbols. The signals generated by the modulators of transceivers 413a to 413t may be transmitted via antennas 414a to 414t.

[0100] The signal transmitted by the first communication node 400a can be received at antennas 464a to 464r of the second communication node 400b. The signals received at antennas 464a to 464r can be provided to a demodulator (DEMOD) included in transceivers 463a to 463r. The demodulator (DEMOD) can obtain samples by performing processing operations (e.g., filtering, amplification, down-conversion, digital conversion, etc.) on the signal. The demodulator can perform additional processing operations on the samples to obtain symbols. The MIMO detector 462 can perform MIMO detection operations on the symbols. The receive processor 461 can perform processing operations (e.g., deinterleaving, decoding, etc.) on the symbols. The output of the receive processor 461 can be provided to the data sink 460 and the controller 466. For example, data can be provided to the data sink 460, and control information can be provided to the controller 466.

[0101] On the other hand, the second communication node 400b can transmit a signal to the first communication node 400a. The transmit processor 468 included in the second communication node 400b can receive data (e.g., data units) from the data source 467 and perform processing operations on the data to generate data symbols. The transmit processor 468 can receive control information from the controller 466 and perform processing operations on the control information to generate control symbols. In addition, the transmit processor 468 can generate reference symbols by performing processing operations on reference signals.

[0102] The Tx MIMO processor 469 may perform spatial processing operations (e.g., precoding operations) on data symbols, control symbols, and / or reference symbols. The output of the Tx MIMO processor 469 (e.g., a symbol stream) may be provided to a modulator (MOD) included in transceivers 463a to 463t. The modulator may generate modulation symbols by performing processing operations on the symbol stream and may generate signals by performing additional processing operations (e.g., analog-to-analog conversion operations, amplification operations, filtering operations, upconversion operations, etc.) on the modulation symbols. The signals generated by the modulators of transceivers 463a to 463t may be transmitted via antennas 464a to 464t.

[0103] The signal transmitted by the second communication node 400b can be received at the antenna 414a to the antenna 414r of the first communication node 400a. The signal received at the antenna 414a to the antenna 414r can be provided to the demodulator (DEMOD) included in the transceiver 413a to the transceiver 413r. The demodulator can obtain samples by performing processing operations on the signal (e.g., filtering operations, amplification operations, down-conversion operations, digital conversion operations, etc.). The demodulator can perform additional processing operations on the samples to obtain symbols. The MIMO detector 420 can perform MIMO detection operations on the symbols. The receiving processor 419 can perform processing operations on the symbols (e.g., deinterleaving operations, decoding operations, etc.). The output of the receiving processor 419 can be provided to the data sink. 418 and controller 416. For example, data may be provided to data sink 418 and control information may be provided to controller 416.

[0104] Memory 415 and memory 465 may store data, control information, and / or program codes. Scheduler 417 may perform scheduling operations for communications. Figure 4 The processors 411, 412, 419, 461, 468, and 469 and the controllers 416 and 466 shown may be Figure 3 The processor 310 shown can be used to execute the methods described in the present invention.

[0105] Figure 5a is a block diagram illustrating an exemplary embodiment of a transmit path, Figure 5b is a block diagram illustrating an exemplary embodiment of a receive path.

[0106] like Figure 5a and Figure 5bAs shown, the transmission path 510 can be implemented in a communication node that transmits a signal, and the reception path 520 can be implemented in a communication node that receives a signal. The transmission path 510 can include a channel coding and modulation block 511, a serial-to-parallel (S to P) block 512, an N-point inverse fast Fourier transform (IFFT) block 513, a parallel-to-serial (P to S) block 514, a cyclic prefix (CP) addition block 515, and an up-converter (UC) 516. The reception path 520 can include a down-converter (DC) 521, a CP removal block 522, an S to P block 523, an N-point FFT block 524, a P to S block 525, and a channel decoding and demodulation block 526. Here, N can be a natural number.

[0107] In the transmit path 510, information bits may be input to a channel coding and modulation block 511. The channel coding and modulation block 511 may perform encoding operations (e.g., low-density parity check (LDPC) encoding operations, polar coding operations, etc.) and modulation operations (e.g., quadrature phase shift keying (OPSK), quadrature amplitude modulation (QAM), etc.) on the information bits. The output of the channel coding and modulation block 511 may be a modulation symbol sequence.

[0108] The S-to-P block 512 may convert the frequency-domain modulation symbols into parallel symbol streams to generate N parallel symbol streams. N may be the IFFT size or the FFT size. The N-point IFFT block 513 may generate a time-domain signal by performing an IFFT operation on the N parallel symbol streams. The P-to-S block 514 may convert the output of the N-point IFFT block 513 (e.g., the parallel signal) into a serial signal to generate a serial signal.

[0109] The CP adding block 515 may insert a CP into the signal. The UC 516 may up-convert the frequency of the output of the CP adding block 515 to a radio frequency (RF) frequency. In addition, the output of the CP adding block 515 may be filtered in baseband before up-conversion.

[0110] The signal transmitted from the transmit path 510 can be input to the receive path 520. The operations in the receive path 520 can be the opposite of those in the transmit path 510. The DC 521 can down-convert the frequency of the received signal to the baseband frequency. The CP removal block 522 can remove the CP from the signal. The output of the CP removal block 522 can be a serial signal. The S to P block 523 can convert the serial signal into a parallel signal. The N-point FFT block 524 can generate N parallel signals by performing an FFT algorithm. The P to S block 525 can convert the parallel signals into a modulation symbol sequence. The channel decoding and demodulation block 526 can perform a demodulation operation on the modulation symbols and can recover the data by performing a decoding operation on the result of the demodulation operation.

[0111] exist Figure 5a and Figure 5b In the present invention, discrete Fourier transform (DFT) and inverse DFT (IDFT) can be used instead of FFT and IFFT. Figure 5a and Figure 5b Each of the blocks (eg, components) in the embodiment may be implemented by at least one of hardware, software, or firmware. For example, Figure 5a and Figure 5b Some blocks in the may be implemented by software, and other blocks may be implemented by hardware or a combination of hardware and software. Figure 5a and Figure 5b In the , a block can be subdivided into multiple blocks, multiple blocks can be integrated into one block, some blocks can be omitted, and blocks that support other functions can be added.

[0112] On the other hand, the NTN reference scenario can be defined as shown in Table 1 below.

[0113] [Table 1]

[0114] NTN shown in Figure 1 NTN shown in Figure 2 GEO Scenario A Scenario B LEO (Leading Emission Oriented) Scenario C1 Scene D1 LEO (beam that moves with the satellite) Scenario C2 Scene D2

[0115] when Figure 1a and / or Figure 1b When the satellite 110 in the NTN shown is a GEO satellite (e.g., a GEO satellite supporting transparency functionality), this may be referred to as "Scenario A." Figure 2a 、 Figure 2b and / or Figure 2c When satellite 211 and satellite 212 in the illustrated NTN are GEO satellites (eg, GEOs supporting regeneration functionality), this may be referred to as "Scenario B."

[0116] when Figure 1a and / or Figure 1bWhen the satellite 110 in the NTN shown is a LEO satellite with a steerable beam, this may be referred to as "Scenario C1". Figure 1a and / or Figure 1b When the satellite 110 in the NTN shown is a LEO satellite with a beam that moves with the satellite, this may be referred to as "Scenario C2". Figure 2a 、 Figure 2b and / or Figure 2c When satellite 211 and satellite 212 in the NTN shown are LEO satellites with steerable beams, this can be referred to as "Scenario D1". Figure 2a 、 Figure 2b and / or Figure 2c When satellite 211 and satellite 212 in the NTN are shown as LEO satellites with beams that move with the satellites, this may be referred to as "scenario D2."

[0117] Parameters for the NTN reference scenario defined in Table 1 may be defined as shown in Table 2 below.

[0118] [Table 2]

[0119]

[0120]

[0121] In addition, in the scenario defined in Table 1, the delay constraint may be defined as shown in Table 3 below.

[0122] [Table 3]

[0123]

[0124]

[0125] Figure 6a is a conceptual diagram illustrating an exemplary embodiment of a protocol stack for a user plane in a non-terrestrial network based on transparent payload, Figure 6b is a conceptual diagram illustrating an exemplary embodiment of a protocol stack for a control plane in a non-terrestrial network based on transparent payload.

[0126] like Figure 6a and Figure 6b As shown, user data can be sent and received between the UE and the core network (e.g., UPF), and control data (e.g., control information) can be sent and received between the UE and the core network (e.g., AMF). Each of the user data and the control data can be sent and received via a satellite and / or a gateway. Figure 6a The protocol stack of the user plane shown can be applied identically or similarly to a 6G communication network. Figure 6b The control plane protocol stack shown can be applied identically or similarly to a 6G communication network.

[0127] Figure 7a is a conceptual diagram illustrating an exemplary embodiment of a protocol stack for a user plane in a non-terrestrial network based on a regenerative payload, Figure 7b is a conceptual diagram illustrating an exemplary embodiment of a protocol stack for a control plane in a non-terrestrial network based on a regenerative payload.

[0128] like Figure 7a and Figure 7b As shown, each of user data and control data (e.g., control information) can be sent and received through an interface between a UE and a satellite (e.g., a base station). User data can refer to user protocol data units (PDUs). A satellite radio interface (SRI) protocol stack can be used to send and receive user data and / or control data between a satellite and a gateway. User data can be sent and received between a satellite and a core network via a general packet radio service (GPRS) tunneling protocol (GTP)-U tunnel.

[0129] On the other hand, in a non-terrestrial network, the base station may transmit system information (e.g., SIB19) including satellite assistance information for NTN access. The UE may receive the system information (e.g., SIB19) from the base station, identify the satellite assistance information included in the system information, and perform communication (e.g., non-terrestrial communication) based on the satellite assistance information. SIB19 may include the information elements defined in Table 4 below.

[0130] [Table 4]

[0131]

[0132]

[0133] The NTN-Config defined in Table 4 may include the information elements defined in Table 5 below.

[0134] [Table 5]

[0135]

[0136] EphemerisInfo defined in Table 5 may include information elements defined in Table 6 below.

[0137] [Table 6]

[0138]

[0139]

[0140] During a handover process in a terrestrial network environment or a non-terrestrial network environment, the source cell timing advance (TA) and the target cell TA may be different. When the terminal does not know the TA value of the target cell during the handover process, the terminal can obtain the TA value of the target cell through a random access process. Accordingly, the terminal can perform a system information acquisition process, an initial timing estimation process, and a fine-tuning process through preamble transmission, which is the same as the initial cell access process in the idle state (RRC_IDLE). When the terminal performs the fine-tuning process, the handover of the terminal may be delayed. In order to reduce the delay of the handover, the terminal can perform a handover process without a random access channel (RACH) in the terrestrial network. In the RACH-free handover process, the terminal can separately receive information about the timing difference between the TA of the target cell and the TA of the source cell. In a terrestrial network environment, handover may occur due to the movement of the terminal. Therefore, the timing control method in the terrestrial network can be performed by separate signaling for each terminal.

[0141] In a non-terrestrial network environment, handover may occur mainly due to the movement of the satellite. Therefore, in a non-terrestrial network environment, a large number of terminals may undergo handover at the same time or at similar times. For example, in order to reduce the signaling load and / or signaling delay that occurs in a non-terrestrial network environment, RACH-free handover may be proposed. The TA value of the source cell and the TA value of the target cell may be different. Accordingly, for the RACH-free handover process, the source base station may send the timing information of the target cell to the terminal in the source cell. For example, the source base station may send the timing information of the target cell to the terminal in the source cell before the terminal initiates the handover process. In a terrestrial network environment, each terminal may undergo handover individually. In a terrestrial network environment, the timing of handover may be distributed. In contrast, in a non-terrestrial network environment, a large number of terminals may undergo handover. In this case, a large number of terminals may request a handover process to the same target satellite. Therefore, in a non-terrestrial network environment, the handover process may occur at the same time or at similar times. For example, in an earth fixed beam (EFB) environment, terminals included in the same beam point may request a handover process to the same target satellite at the same time or at similar times. In an Earth Moving Beam (EMB) environment, terminals within a satellite's beam spot can continuously request handovers to a target satellite based on the satellite's movement. Accordingly, in an EMB environment, handovers can occur in a distributed manner at various times. Furthermore, in an EMB environment, handovers can occur due to satellite movement according to a relatively predetermined pattern, unlike handovers in a TN environment, which occur due to the individual movement of terminals.

[0142] In non-terrestrial network environments, the signaling caused by individual handovers of terminals can generate a high signaling load. Therefore, to efficiently handle RACH-free handovers in non-terrestrial network environments, satellites can transmit timing information through group-based signaling. Group-based signaling can reduce the signaling overhead during handovers.

[0143] To utilize group-based signaling, a satellite can configure groups of terminals with similar timing. Groups with similar timing information can be signaled on a group basis, reducing signaling overhead. Therefore, the present invention provides a method for configuring groups with similar timing in scenarios such as feeder link switching, EFB environments, or EMB environments.

[0144] Figure 8 is a conceptual diagram illustrating an exemplary embodiment of a non-terrestrial network.

[0145] like Figure 8 As shown, the satellite can perform a method for improving uplink time synchronization and uplink frequency synchronization of the NR non-terrestrial network. The terminal can perform a method for controlling timing in a radio resource control (RRC) idle state (RRC_IDLE) or an RRC inactive state (RRC_INACTIVE). The terminal can obtain initial timing information by utilizing system information provided by the satellite for public TA calculation and by utilizing the global navigation satellite system (GNSS) function. The terminal can obtain the initial TA before sending a physical random access channel (PRACH) preamble to the satellite. For the uplink timing synchronization of the terminal, the timing error may need to be within half of the preamble cyclic prefix (CP). The timing error may refer to the timing error after pre-compensation for the delay before the initial RACH preamble transmission.

[0146] This invention proposes open-loop TA in the NR NTN, including a common TA and a UE-specific TA. The common TA can change over time. The network can calculate the common TA. Furthermore, the network can transmit the common TA value to the terminal. The terminal can use the common TA parameters transmitted from the network to estimate and predict the common TA that changes over time according to defined rules. The UE-specific TA may refer to the TA estimated by the terminal to pre-compensate for service link delay. The positions of the satellite and the terminal can be transmitted to the terminal to enable TA estimation.

[0147] NR NTN may differ from 5G NR in the presence or absence of open-loop TA and related parameters (i.e., common TA parameters and satellite ephemeris information). In order to enable the terminal to access the network in the RRC idle state (RRC_IDLE) or the RRC inactive state (RRC_INACTIVE), the open-loop TA parameters may be included in the system information block (SIB) message. The open-loop TA parameters may include information about the period (e.g., which may be greater than 20ms) of the synchronization signal (SS) / physical broadcast channel (PBCH) block (i.e., SSB). The valid duration of the common TA parameters and satellite ephemeris information may be configured by the base station. In NR NTN, the terminal may perform an uplink time synchronization process. The uplink time synchronization process is described as follows.

[0148] Figure 9 is a conceptual diagram illustrating an exemplary embodiment of an uplink time synchronization procedure.

[0149] like Figure 9 As shown, the base station may send an SSB to the terminal (S910). The SSB may include at least one of DL time information, DL frequency information, and synchronization information. The terminal may receive the SSB sent by the base station.

[0150] The base station may transmit data to the terminal by utilizing control resource set (CORESET) #0 (S920). CORESET #0 may refer to physical resources used to carry PDCCH / DCI. In other words, CORESET #0 may refer to a specific type of CORESET used to carry PDCCH / DCI for SIBs. The detected SIBs may include at least one of PRACH resources, common TA parameters, satellite ephemeris information, and absolute time information. The terminal may receive physical resources from the base station through CORESET #0.

[0151] The terminal can utilize the common TA included in the SIB. The terminal can estimate the UE-specific TA. For preamble transmission, the terminal can utilize the estimated UE-specific TA.

[0152] The terminal may transmit Message 1 (Msg1) or Message A (MsgA) to the base station (S930). Message 1 (Msg1) or Message A (MsgA) may include a preamble. The base station may receive Message 1 (Msg1) or Message A (MsgA) transmitted by the terminal.

[0153] The base station may send Message 2 (Msg2) or Message B (MsgB) to the terminal (S940). Message 2 (Msg2) or Message B (MsgB) may include a random access response (RAR) message. The RAR may include a timing advance command (TAC) field. The terminal may receive Message 2 (Msg2) or Message B (MsgB) sent by the base station.

[0154] For uplink synchronization, the terminal may utilize at least one of a common TA included in the SIB, a UE-specific TA, or a TAC included in the RAR.

[0155] In the RRC connected state, the terminal and the base station may perform the following process. The base station may send a MAC CE including a TAC to the terminal (S950). The terminal may receive the TAC sent by the base station. The terminal may perform an uplink synchronization process by using at least one of the TAC, common TA, or UE-specific TA of the received MAC CE.

[0156] The base station may send an SSB or dedicated signaling to the terminal (S960). The terminal may receive the SSB or dedicated signaling sent by the base station. The terminal may update common TA parameters using the SSB or dedicated signaling. The terminal may update satellite ephemeris information using the SSB or dedicated signaling. The terminal may update absolute time using the SSB or dedicated signaling.

[0157] On the other hand, when performing RACH-free handover in an NTN, the base station can schedule the initial PUSCH transmission using reference signal (RS) resources that use the same beam (e.g., the same beam index) as the SS / PBCH block. The RS resources associated with the SS / PBCH block index can have a quasi-co-location (QCL) relationship with the SS / PBCH block, which can be used for PDCCH reception.

[0158] Figure 10a is a conceptual diagram illustrating an exemplary embodiment of a handover process.

[0159] like Figure 10a As shown, in an EFB environment, satellites (i.e., a first satellite and a second satellite) can form cell coverage. In this case, beam coverage can be formed by at least one or more beam areas (e.g., beam spots). A beam area may refer to an area covered by a beam. In other words, a satellite can form one or more beam areas (beam spots).

[0160] In an EFB environment, all terminals in the same beam spot can send handover procedure requests to the satellite at the same or similar times. Terminals in the same beam spot can have the same cell remaining time value. Based on this same cell remaining time value, the satellite can configure all terminals in the same beam spot into the same group.

[0161] Figure 10b is a conceptual diagram illustrating an exemplary embodiment of a handover process.

[0162] like Figure 10a and Figure 10b As shown, in an EFB-based NTN (hereinafter referred to as "EFB NTN"), each of a first satellite and a second satellite can move over time (e.g., from a first time to a second time) and can support an earth-fixed beam. The second time can be after the first time. The handover process can be divided into an intra-satellite (intra-SAT) handover process and an inter-satellite (inter-SAT) handover process. The intra-satellite handover process and the inter-satellite handover process can each be a conventional handover process or a conditional handover (CHO) process. In the intra-satellite handover process, a terminal can perform a handover process between cells of the same satellite. That is, the intra-satellite handover process can be performed by beam switching in the same satellite. For example, in the intra-satellite handover process, all terminals connected to the first cell of the first satellite can be switched to the second cell of the first satellite. In this case, all terminals can be switched to the second cell at the same time or at similar times. EFB can be supported by beam steering in the same satellite.

[0163] During an inter-satellite handover procedure, a terminal can perform a handover procedure between different satellites. During an inter-satellite handover procedure, all terminals connected to a first satellite (e.g., a specific cell of the first satellite) can be handed over to a second satellite (e.g., a specific cell of the second satellite). In this case, all terminals can be handed over to the second satellite at the same time or at similar times. The handover procedure performed from the first time to the second time may correspond to an inter-satellite handover procedure. EFB can be supported by a new cell of a new satellite (e.g., a second satellite).

[0164] Due to the high altitude in NTNs, RSRP-based handover procedures may not be effective. Therefore, a handover procedure suitable for NTNs is needed. Even when a satellite moves in an EFB NTN, the cell area on the ground can be maintained. That is, a satellite can support a fixed cell area. Intra-satellite handover procedures and / or inter-satellite handover procedures can be performed simultaneously for terminals (e.g., all or some terminals) in the same cell. An efficient handover procedure that takes into account the characteristics of the EFB NTN described above is needed.

[0165] Even when the satellites (first and second satellites) move in an EFB environment, the existing beam coverage 860 on the ground can be maintained. The beam coverage can be referred to as a cell area on the ground. In an EFB environment, the satellites (first and second satellites) can maintain the cell area in a fixed manner through beam steering or beam switching. As the existing satellites move, the cell area can be served by a new satellite. When the cell area begins to be served by the new satellite, the elevation angle between the cell area and the new satellite may be minimal. The elevation angle may increase as the satellite moves. After the elevation angle increases, it may decrease again as the satellite moves further. In this case, the distance between the satellite and the cell may decrease or increase depending on the change in elevation angle.

[0166] Figure 11 is a conceptual diagram illustrating an exemplary embodiment of beam foot print in an EFB environment.

[0167] like Figure 11 As shown, a satellite (or unmanned aerial vehicle (UAV) platform) 1110 can support multiple beams. The satellite can form cell coverage using multiple beams. The satellite can form a beam coverage area, which is included in the cell coverage formed by the satellite. For example, the radius of the cell coverage formed by the satellite can be tens of kilometers. Furthermore, the satellite can move at a speed of 7.56 km / s.

[0168] Figure 12 is a conceptual diagram illustrating an exemplary embodiment of an EMB.

[0169] like Figure 12 As shown, the beam of the satellite may have EMB characteristics. In an EMB environment, when satellite 1210 and satellite 1220 move, the cell coverage 1260 and cell coverage 1270 on the ground may change according to the movement of the satellite. Therefore, the satellite serving the terminal in a specific area may change continuously. In this case, for the terminal included in the beam coverage of a specific satellite, the data service time of the specific satellite may vary according to the location of the beam coverage. In other words, the remaining cell time of the terminal may vary according to the location of the terminal. The remaining cell time may refer to the remaining time that the terminal is served in the corresponding cell according to the location of the terminal within the beam coverage. In other words, the remaining cell time may be the time during which communication services can be provided to the corresponding terminal in the cell where the terminal is located. When the remaining cell service time expires, the terminal may need to perform a process of (re)selecting another cell.

[0170] Figure 13a is a conceptual diagram illustrating an exemplary embodiment of handover in a non-terrestrial network.

[0171] like Figure 13a As shown, during an intra-satellite handover process, both the serving link and / or the feeder link may be changed.

[0172] Figure 13b is a conceptual diagram illustrating an exemplary embodiment of handover in a non-terrestrial network.

[0173] like Figure 13b As shown, during the inter-satellite handover process, the serving link may not be changed, but the feeder link may be changed.

[0174] On the other hand, NTN satellite systems can operate in either EFB or EMB environments, depending on changes in beam coverage on the ground caused by satellite movement. Applying the same grouping method to both scenarios may be inefficient. In other words, it may be difficult to achieve the effect of reducing handover signaling through grouping. Therefore, during handovers in NTN, satellites can transmit a changed TA to terminals when changing base stations.

[0175] On the other hand, TA information for terminals in an NTN can be configured as follows. Satellites can perform RACH-free handovers in the NTN. Satellites can configure TA information when performing a RACH-free handover procedure. When performing a RACH-free handover procedure in an NTN environment, timing difference information may be different for each terminal. Based on the timing information of the source cell and the timing information of the target cell, the timing difference information may include the difference between the timing value of the source cell and the timing value of the target cell. To calculate the timing difference information, the satellite can obtain the timing information of each cell. In the NTN, the timing information can be as shown in the following equation 1.

[0176] [Equation 1]

[0177]

[0178] T TA Can represent timing information. TA,common It can represent the delay between the reference point (RP) and the satellite. TA,common It can be called a public TA. TA,UE-specific It can represent the delay of the service link. TA,UE-specific It can represent the TA value estimated by the terminal. TA,UE-specific It can be called UE-specific TA. UE-specific TA can represent the round trip delay (RTD) between the terminal and the satellite. In other words, T TA,UE-specific It can represent the delay between the terminal and the satellite. On the other hand, the terminal can perform a closed-loop timing control process through the TA command message sent by the base station.

[0179] N TA It can perform the same role as in the terrestrial network. For the TA information in the NTN, N can be additionally defined. TA,offset . N TA,offset It can represent the TA value usually applied to the terminal, and T c It can be a time base unit constant mainly used in the NR physical layer and can represent (4096×480×1000) -1 Second.

[0180] The timing difference information may include a common TA difference. The timing difference information may represent a difference between different common TA values. For example, the difference between different common TA values ​​may represent a difference between a common TA value of a source cell and a common TA value of a target cell.

[0181] The common TA can be calculated based on the RP of each cell. When the terminal changes cells through the handover process, the common TA value may change. Accordingly, the terminal can use the timing difference information for the common TA of the source cell and the common TA of the target cell to perform the handover process.

[0182] Timing difference information for the common TA value can be sent to the terminal via a handover command message. The terminal can receive the handover command message sent by the base station. The handover command message may include the difference between the common TA values. The terminal can calculate the UE-specific TA value on its own. The terminal can obtain the timing information of the target cell based on the common TA difference and the UE-specific TA value. Alternatively, the terminal can use the timing information of the target cell to perform a RACH-free handover.

[0183] On the other hand, when the RPs of the source cell and the target cell are configured differently, the base station may send the timing difference caused by the different RPs to the terminal.

[0184] The timing difference for a common TA and the timing difference caused by different RPs can be sent to the terminal using two parameters. Alternatively, the timing difference for a common TA and the timing difference caused by different RPs can be sent to the terminal using a single parameter. For example, FL_TA_diff can be defined to include the common TA difference and the timing difference caused by different RPs. Furthermore, the satellite can redefine and use a common TA.

[0185] On the other hand, in case of feeder link switching, TA information may be updated as follows.

[0186] Figure 14a is a conceptual diagram illustrating an exemplary embodiment of a feeder link switching environment, and Figure 14b is a conceptual diagram illustrating an exemplary embodiment of a feeder link switching environment.

[0187] like Figure 14aand Figure 14b As shown, when a base station performs a feeder link handover, the base station can update the TA value. T1 can represent the time when the satellite connected to gateway 1. Alternatively, T1 can represent the time immediately before the satellite performed the handover. T2 can represent the time when the satellite connected to gateway 2. T2 can represent the time immediately after the satellite performed the handover. The satellite can change gateways during the handover process. In other words, the satellite can perform a feeder link handover.

[0188] Feeder link switching can refer to changing the gateway or base station (gNB) connected to a satellite to another gateway or base station. In other words, feeder link switching can mean changing the gateway or base station without changing the satellite. When a satellite performs a feeder link switching procedure, service link delay and / or feeder link delay differences may occur. Here, the service link delay can be a common value.

[0189] The feeder link delay difference can be calculated based on the satellite's location and the location of the gateway or base station. During a handover, the satellite can transmit information about the feeder link delay difference to all terminals in the cell supported by the satellite. A parameter representing the feeder link delay difference can be defined as FL_TA_diff. The satellite can generate a handover command message including FL_TA_diff and transmit the handover command message to the terminal.

[0190] In this case, FL_TA_diff may have a range of [-X, +X]. X may be a parameter pre-configured through an RRC message. For example, FL_TA_diff may be a parameter with a range of 2 N It can be defined by using a table with 2 N The index of the table containing the entries sends FL_TA_diff to the terminal.

[0191] The RP of the feeder link formed by gateway 1 may be located at gateway 1. The RP may represent a location (or time point) on the feeder link between the gateway (or ground base station) and the satellite. The RP of the feeder link formed by gateway 2 may be located at gateway 2. The common TA value may correspond to the value between the base station and the RP. In this case, FL_TA_diff may be equal to the difference between the common TA values ​​(the difference between the common TA value for gateway 1 and the common TA value for gateway 2).

[0192] The RP may be located in at least one of a base station, satellite, feeder link, or serving link for uplink synchronization. The location of the RP may not be restricted. Information about the location of the RP may not be transmitted to the terminal. Therefore, the terminal may not estimate the common TA, and the network may calculate the common TA.

[0193] When the feeder link formed by the gateway has RPs at different locations, FL_TA_diff may be different from the difference between the common TA values. In this case, FL_TA_diff may include the difference between the common TA values ​​and the timing difference caused by the different locations of the RPs.

[0194] The satellite may generate an RRC message including the difference between common TAs and the timing difference caused by the different locations of RPs instead of the single parameter FL_TA_diff, and may send the RRC message to the terminal.

[0195] In the present invention, timing groups can be configured to improve the performance of the handover process in an NTN environment.

[0196] Figure 15 is a conceptual diagram illustrating an exemplary embodiment of a timing group configuration.

[0197] like Figure 15 As shown in FIG. 1 , when an inter-satellite handover is requested from a terminal in an EFB environment, the feeder link and the service link may change. When performing a handover process in an EFB environment, the transmission path may differ before and after the handover. The satellite can perform the handover process by utilizing four linearly configured timing groups (TGs).

[0198] A timing group may refer to a group of terminals with similar timing information. A timing group may be configured with terminals. A timing group may include terminals whose difference between a reference value and a timing value is within ΔT.

[0199] The reference value may refer to a timing value at the center position of a configuration distance defined by a base station associated with the satellite. For example, the reference value for timing group 1 may be Tref1. Tref1 may represent a timing value corresponding to the center position of timing group 1. Tref1 may be expressed as Tref1 = ΔT. Tref2 may represent a reference value for timing group 2. Tref2 may represent a timing value corresponding to the center position of timing group 2. Tref2 may be expressed as Tref2 = Tref1 + 2ΔT. Additionally, Tref3 may represent a reference value for timing group 3. Tref3 may represent a timing value corresponding to the center position of timing group 3. Tref3 may be expressed as Tref3 = Tref2 + 2ΔT. Tref4 may represent a reference value for timing group 4. Tref4 may represent a timing value corresponding to the center position of timing group 4. Tref4 may be expressed as Tref4 = Tref3 + 2ΔT. ΔT may represent a parameter preconfigured via an RRC message. ΔT may represent a first TA range. The base station may configure the first TA range.

[0200] Accordingly, the base station may configure the timing group using timing group configuration information. The timing group configuration information may include the timing group index of the terminal. In other words, the base station may send the configured timing group index to each terminal. The base station may send the timing group index configured by the base station to each terminal via RRC signaling. The timing group index may include the identification number of the group configured for the terminal. The terminal may receive the timing group index sent by the base station. The terminal may identify the timing group of the terminal using the timing group index.

[0201] A timing group can be configured with terminals within a certain distance from a location corresponding to a reference value. Timing groups can be configured based on ΔT. Alternatively, timing groups can be configured based on a certain distance from a location corresponding to a reference value. In other words, a timing group can be configured using at least one of ΔT and a certain distance from a location corresponding to a reference value. The center location of the timing group can be obtained using the location information of the terminals. For example, each terminal can obtain its location information using GNSS.

[0202] When terminals are concentrated in a narrow area, the satellite can configure timing groups using the timing value at the center of the area (i.e., the narrow area) as a reference value. The satellite can configure the same timing group for terminals within a certain distance from the center of the area. The satellite can also configure the same timing group for terminals whose timing values ​​differ from the center of the area by a predetermined value.

[0203] In other words, the base station can configure a timing group for terminals whose timing values ​​(e.g., the terminal's reference value minus the timing value) differ by a value within ΔT. The reference value can represent the timing value at the center of the area or a value configured by the base station (e.g., Tref1, Tref2, Tref3, Tref4). The reference value can also be a fixed value configured by the base station.

[0204] When the terminal performs a handover process, the terminal may receive changed timing information from the base station. The base station may select a method for transmitting the changed timing information to the terminal.

[0205] Each terminal in a timing group may have the same common TA. When a handover process is performed, the common TA value may change. Accordingly, the base station may send the difference in the common TA value to the terminals in the timing group. The common TA value may be included in a handover command message. The base station may send a handover command message to the terminals in the timing group. The base station may send the handover command message to the terminals in the timing group via group-based signaling. In other words, the base station may send the handover command message to the terminals in the timing group via common signaling, such as multicast.

[0206] The common TA can be calculated based on the RP of each cell. Therefore, when a handover procedure is performed to change cells, the common TA can change. Accordingly, when the terminal performs the handover procedure, the terminal can receive information about the difference between the common TA of the source cell and the common TA of the target cell. The base station can send information about the difference between the common TAs to the terminal via a handover command message. The terminal can obtain the timing information of the target cell based on the information about the difference between the common TAs sent from the base station and the UE-specific TA value calculated by the terminal. In addition, the terminal can perform RACH-free handover using the obtained timing information of the target cell.

[0207] When the RP changes, the base station may generate a handover command message including additional timing information and may send the handover command message to the terminal.

[0208] On the other hand, the base station can configure the center point of the timing group. The center point of the timing group can represent a geographical center location. In addition, the center point of the timing group can represent the median value of the timing values ​​of the terminals in the timing group. The base station can send a timing difference based on the center point (e.g., a reference value) to the terminal. The base station can generate a switching command message including the timing difference based on the center point (e.g., a reference value) and can send the switching command message to the terminal. For example, the base station can send to the terminal the difference between the timing of the path from the center point (e.g., the reference value) via satellite 1 to the base station and the timing of the path from the center point (e.g., the reference value) via satellite 2 to the base station.

[0209] On the other hand, in an NTN environment, the base station can perform an open-loop timing control procedure by utilizing a common TA value and a UE-specific TA value. In a terrestrial network environment, the base station can perform a closed-loop timing control procedure. The reason for introducing the open-loop timing control procedure in the NTN environment can be to utilize the parameter N used in the open-loop timing control procedure. TA and N TA,offset To perform the timing control process in the NTN environment. In this case, the parameter N TA and N TA,offset Can have a fixed length.

[0210] However, since the handover command message has no restriction on the length change of the parameter, the base station can send the timing difference value based on the center point of each timing group to the terminal.

[0211] In densely populated areas, terminals may be concentrated in a narrow area. Therefore, the base station can send a timing value based on the center point of the timing group to the terminals in the timing group. The terminal can perform a RACH-free handover procedure by using the timing value based on the center point of the timing group sent by the base station.

[0212] For example, when configuring timing groups based on half the signal CP length, with an SCS of 15 kHz, since the CP length is 4.7 microseconds, the base station can consider the propagation delay corresponding to half the CP length (i.e., 2.35 microseconds) and configure terminals within 705 meters into the same timing group. In other words, the base station can configure terminals within a radius of approximately 705 meters into the same timing group. Terminals within 705 meters can perform initial access using the same timing value.

[0213] The base station may send a timing difference based on the center point of the timing group and information about the center point of the timing group to the terminal. The terminal may calculate an additional timing adjustment value using the terminal's location information and satellite ephemeris information. The terminal may use the timing adjustment value to perform RACH-free handover. If the terminal does not have GNSS functionality, the terminal may use the timing adjustment value to perform RACH-free handover.

[0214] Figure 16 is a conceptual diagram illustrating an exemplary embodiment of a handover process in an EMB environment.

[0215] like Figure 16 As shown, in an EMB environment, the remaining time of the terminals included in the beam spot may be different from each other. The remaining time may refer to the time remaining until the handover request time of the terminal belonging to the beam spot. The remaining time may vary according to the location of the terminal belonging to the beam spot. For example, the beam spot 1611 may include multiple terminals. For the sake of convenience, in Figure 16 In FIG, multiple terminals may be shown as a circle (e.g., 1621), a square (e.g., 1622), and a triangle (e.g., 1623). In this case, considering the direction of movement of the satellite, terminal 1621 is able to receive service for the longest time compared to other terminals (i.e., terminal 1622 and terminal 1623). In other words, terminal 1621 can perform the switching process at the latest time compared to other terminals (i.e., terminal 1622 and terminal 1623). Therefore, terminal 1621 can have a larger remaining time compared to other terminals (i.e., terminal 1622 and terminal 1623). Terminals belonging to beam spot 1611 can perform the switching process in order of smaller remaining time values.

[0216] On the other hand, even when the terminals have the same remaining time depending on their locations, the target satellites used for the handover process may be different from each other. For example, even when the terminals 1621 and 1622 have the same remaining time, the terminals 1621 and 1622 may belong to different beam spots. Therefore, the handover process for the terminals 1621 and 1622 may be performed for different target satellites.

[0217] Therefore, the base station can configure a group so that terminals in the group can perform a handover procedure using common signaling. The base station can configure terminals into groups by utilizing the remaining time value and additional information. Group configuration can be performed at the base station. Information about the configured group can be sent to the terminal by sending a group index. In this case, when performing a handover procedure, the terminal can select a target satellite. Once the terminal determines the target satellite, the base station can configure the group using the target satellite's ID. The base station can also configure the group using the terminal's location information and the satellite's ephemeris information.

[0218] Figure 17 is a conceptual diagram illustrating an exemplary embodiment of a handover process in an EMB environment.

[0219] like Figure 17 As shown, in an EMB environment, handover can occur sequentially for terminals based on satellite movement. In other words, the base station can perform the handover process based on the index of the timing group. The satellite's beam spots can correspond to timing groups with a common TA. In an NTN, the base station can predetermine the satellite's movement (speed, direction, altitude). The base station can predict or calculate the TA information for the next area by utilizing the TA information for the previous area.

[0220] Figure 18 is a conceptual diagram illustrating an exemplary embodiment of a handover process in an EMB environment.

[0221] like Figure 18 As shown, in an EMB environment, handover can occur on a cell basis or on a beam basis. However, in an EMB environment, handover can occur continuously. Figure 18 A method for updating timing information during handovers that occur continuously in an EMB environment is shown.

[0222] In an EMB environment, the base station may configure a timing group for a terminal (S1810). A terminal may refer to a terminal located in the same beam spot. The base station may configure the terminal into a timing group by utilizing the remaining time. The remaining time may be configured as [reference value, reference value + △T]. The base station may configure terminals with the same target cell into a timing group. For example, when the reference value of timing group 1 is 0, the reference value of timing group 2 may be △T, and the reference value of timing group 3 may be 2△T. Therefore, the remaining time of timing group 1 may be [0, △T]. The remaining time of timing group 2 may be [△T, 2△T]. The remaining time of timing group 3 may be [2△T, 3△T]. In other words, timing group 2 may include terminals with a remaining time of [△T, 2△T].

[0223] The base station may assign numbers to the corresponding timing groups (S1820). The base station may assign numbers to the timing groups in order of smaller remaining time values.

[0224] The base station may send TA information to all terminals in a specific timing group at a specific time (S1830). The specific time may refer to a value configured by the base station. The specific time may be referred to as t. In this case, the TA information may refer to the TA information at the specific time.

[0225] The terminal may use the same TA information during ΔT ( S1840 ).

[0226] The base station may send TA information to all terminals in the next timing group (S1850). The base station may send TA information to all terminals in the next timing group after ΔT has passed. In this case, the TA information may refer to TA information of a time obtained by adding ΔT to a specific time.

[0227] The base station may determine whether the timing group of the terminal to which the TA information has been transmitted is the last timing group (S1860). When the timing group of the terminal is not the last timing group, the base station and the terminal may perform steps S1840 and S1850 again. When the timing group is the last timing group, the base station may terminate the process.

[0228] The operation of the method according to the exemplary embodiment of the present invention can be implemented as a computer-readable program or code in a computer-readable recording medium. The computer-readable recording medium may include all types of recording devices storing data that can be read by a computer system. In addition, the computer-readable recording medium can store and execute programs or codes, which can be distributed among computer systems connected via a network and read by computers in a distributed manner.

[0229] Computer readable recording media may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, or flash memory. Program instructions may include not only machine language codes created by a compiler, but also high-level language codes that can be executed by a computer using an interpreter.

[0230] Although some aspects of the present invention have been described in the context of an apparatus, these aspects can be indicated according to the corresponding description of the method, and a block or apparatus can correspond to the steps of the method or the features of the steps. Similarly, the aspects described in the context of the method can be represented as the features of the corresponding blocks or items or corresponding apparatus. Some or all steps of the method can be performed by (or using) a hardware device such as a microprocessor, a programmable computer or an electronic circuit. In some embodiments, one or more of the most important steps of the method can be performed by such an apparatus.

[0231] In some exemplary embodiments, a programmable logic device such as a field programmable gate array (FPGA) may be used to perform some or all of the functions of the methods described herein. In some exemplary embodiments, the FPGA may be operated with a microprocessor to perform one of the methods described herein. Typically, the methods are preferably performed by specific hardware devices.

[0232] The description of the present invention is merely exemplary in nature, and therefore variations that do not depart from the essence of the present invention are intended to be within the scope of the present invention. Such variations should not be considered to depart from the spirit and scope of the present invention. Therefore, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope defined by the appended claims.

Claims

1. A method of a user equipment (UE), comprising: receiving, from a first satellite, timing group configuration information for a timing group including the UE, the timing group being configured based on beam spots supported by the first satellite; receiving, from the first satellite, a handover command message including timing information of the UE according to a timing group index included in the timing group configuration information; Utilize timing information to obtain timing advance (TA) information; as well as The TA information is used to send a handover complete message.

2. The method according to claim 1, wherein The timing group configuration information includes a timing group index, and the timing group index is used to: when a difference between a timing value of the UE and a timing value of a center position of a configuration distance defined by a base station associated with a first satellite falls within a first TA range configured by the base station, identify a timing group including UEs within the first TA range.

3. The method according to claim 1, wherein The timing group configuration information includes a timing group index, which is used to identify the timing group including the UE within the distance range configured by the base station from the center position of the beam point when the UE is within the distance range from the center position of the beam point.

4. The method according to claim 1, wherein The timing group configuration information includes a timing group index, and the timing group index is used to: when the cell remaining time falls within the time range configured by the first satellite, identify the timing group of the UE including the cell remaining time within the time range, and the cell remaining time is the time for providing communication services of the beam point to the UE.

5. The method according to claim 1, wherein When obtaining TA information using timing information, TA information is obtained by using a timing difference corresponding to a difference between a first path and a second path, wherein the first path includes a path between the first satellite and the center position of the timing group and a path between the first satellite and the base station, and the second path includes a path between the second satellite and the center position of the timing group and a path between the second satellite and the base station.

6. The method according to claim 1, wherein Using timing information to obtain TA information includes: determining a UE-specific TA value; and The TA information of the UE is acquired by updating the TA information of the UE using a UE-specific TA value and at least one of a common TA value equally applied to all UEs of the source cell included in the timing information, a common TA value equally applied to all UEs of the target cell, or a timing difference value caused by a difference in reference points (RP) between the source cell and the target cell.

7. The method according to claim 1, wherein Using timing information to obtain TA information includes: receiving at least one of location information of the UE, location information of the first satellite, or satellite ephemeris information from the first satellite; Calculating a timing adjustment value of the UE using at least one of the position information of the UE, the position information of the first satellite, and the satellite ephemeris information; and The TA information is obtained using the timing adjustment value and the timing information.

8. A method for a base station, comprising: configuring timing group configuration information for a timing group including a user equipment (UE) based on beam spots supported by a first satellite; sending, to the UE, a handover command message including timing information of the timing group to which the UE belongs, according to the timing group index included in the timing group configuration information; as well as A handover complete message is received from the UE that performed the handover procedure based on the timing information of the timing group to which the UE belongs.

9. The method according to claim 8, wherein The configuring the timing group configuration information includes configuring the UE into the timing group in response to a difference between a timing value of the UE and a timing value of a center position of a configuration distance defined by the base station communicating via the first satellite being equal to or less than a second TA value defined by the base station for the timing group.

10. The method according to claim 8, wherein The configuring timing group configuration information includes configuring the UE into the timing group in response to a cell remaining time falling within a time range configured by the first satellite, wherein the cell remaining time is a time for providing communication services of the beam point to the UE.

11. The method according to claim 8, wherein The timing information includes at least one of a common TA value equally applied to all UEs of a source cell, a common TA value equally applied to all UEs of a target cell, or a timing difference caused by a difference in Reference Points (RPs) between the source and target cells.

12. A user equipment (UE), comprising at least one processor, wherein: The at least one processor causes the UE to execute: receiving, from a first satellite, timing group configuration information for a timing group including the UE, the timing group being configured based on beam spots supported by the first satellite; receiving, from the first satellite, a handover command message including timing information of the UE according to a timing group index included in the timing group configuration information; Utilize timing information to obtain timing advance (TA) information; as well as The TA information is used to send a handover complete message.

13. The UE according to claim 12, wherein: The timing group configuration information includes a timing group index, and the timing group index is used to: when a difference between a timing value of the UE and a timing value of a center position of a configuration distance defined by a base station associated with a first satellite falls within a first TA range configured by the base station, identify a timing group including UEs within the first TA range.

14. The UE according to claim 12, wherein: The timing group configuration information includes a timing group index, which is used to identify the timing group including the UE within the distance range configured by the base station from the center position of the beam point when the UE is within the distance range from the center position of the beam point.

15. The UE according to claim 12, wherein: The timing group configuration information includes a timing group index, and the timing group index is used to: when the cell remaining time falls within the time range configured by the first satellite, identify the timing group of the UE including the cell remaining time within the time range, and the cell remaining time is the time for providing communication services of the beam point to the UE.

16. The UE according to claim 12, wherein: When obtaining TA information using timing information, TA information is obtained by using a timing difference corresponding to a difference between a first path and a second path, wherein the first path includes a path between the first satellite and the center position of the timing group and a path between the first satellite and the base station, and the second path includes a path between the second satellite and the center position of the timing group and a path between the second satellite and the base station.

17. The UE according to claim 12, wherein: When acquiring the TA information using the timing information, the at least one processor further causes the UE to execute: Determine UE-specific TA value; as well as The TA information of the UE is acquired by updating the TA information of the UE using a UE-specific TA value and at least one of a common TA value equally applied to all UEs of the source cell included in the timing information, a common TA value equally applied to all UEs of the target cell, or a timing difference value caused by a difference in reference points (RP) between the source cell and the target cell.

18. The UE according to claim 12, wherein: When acquiring the TA information using the timing information, the at least one processor further causes the UE to execute: receiving at least one of location information of the UE, location information of the first satellite, or satellite ephemeris information from the first satellite; calculating a timing adjustment value of the UE using at least one of the position information of the UE, the position information of the first satellite, and the satellite ephemeris information; as well as The TA information is obtained using the timing adjustment value and the timing information.

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