Method and device for satellite switching in wireless communication system

Abstract

The present invention provides technology for satellite switching in a wireless communication system. A method performed by a terminal comprises the steps of: acquiring target satellite-related information from a source satellite; performing satellite switching from the source satellite to the target satellite on the basis of the target satellite-related information; and communicating with the target satellite on the basis of the target satellite-related information after performing the satellite switching.

Description

Satellite switching method and device in a wireless communication system

[0001] The present disclosure relates to a satellite switching technology in a wireless communication system, and more particularly, to a satellite switching technology in a wireless communication system that enables changing a satellite while maintaining a physical cell identifier (PCI) unchanged.

[0002] Advances in information and communication technology (ICT) can lead to the development of various wireless communication technologies. Representative wireless communication technologies include LTE (long term evolution), NR (new radio), and 6G (6th Generation), all of which are defined by the 3rd Generation Partnership Project (3GPP) standards. LTE can be one of the 4th Generation (4G) wireless communication technologies, and NR can be one of the 5th Generation (5G) wireless communication technologies.

[0003] In order to process the rapidly increasing amount of wireless data following the commercialization of 4G communication systems (e.g., communication systems supporting LTE), 5G communication systems (e.g., communication systems supporting NR) that use a higher frequency band (e.g., a frequency band higher than 6 GHz) than the frequency band of the 4G communication system (e.g., a frequency band below 6 GHz) may be considered. 5G communication systems may support enhanced Mobile Broadband (eMBB), Ultra-Reliable and Low Latency Communication (URLLC), and massive Machine Type Communication (mMTC).

[0004] Such wireless communication systems can be designed considering a variety of scenarios, service requirements, and potential system compatibility. In particular, discussions are actively underway on 5G NR systems and beyond 5G systems, both based on terrestrial networks (TNs) and non-terrestrial networks (NTNs), and these are expected to be used.

[0005] Conventional wireless communication systems (e.g., LTE) are TN-based wireless communication systems, meaning that both base stations (e.g., eNB, gNB) and terminals (e.g., user equipment (UE)) that make up the wireless communication system are located on the ground. On the other hand, NTN can refer to a network in which at least one of the base stations and terminals is not located on the ground. For example, TN-based communication may experience service interruptions in disaster situations such as fires, earthquakes, and tsunamis. In addition, there may be limitations in providing services in suburban, rural, remote, and remote areas with low demand density, due to reasons such as high CAPEX / OPEX (capital expenditures / operating expenses) compared to operator profits. NTN can be a technology applied to overcome these limitations of TN. In such NTN-based systems, a technology that can switch satellites without changing the physical cell identifier (PCI) may be required.

[0006] The purpose of the present disclosure to solve the above problems is to provide a satellite switching method and device in a wireless communication system that enables changing satellites while maintaining a physical cell identifier (PCI) unchanged.

[0007] In order to achieve the above object, a method for switching satellites in a wireless communication system according to a first embodiment of the present disclosure may include, as a terminal method, a step of obtaining target satellite-related information from a source satellite; a step of performing satellite switching from the source satellite to the target satellite based on the target satellite-related information; and a step of performing communication with the target satellite based on the target satellite-related information after performing the satellite switching.

[0008] Here, the step of performing communication with the target satellite may include a step of connecting to the target satellite without random access based on the target satellite-related information; and a step of performing communication with the target satellite based on the target satellite-related information.

[0009] Here, the source satellite and the target satellite are connected to the same base station, the source satellite forms a first quasi-Earth fixed cell, the target satellite forms a second quasi-Earth fixed cell, the PCI (physical cell identifier) ​​of the first quasi-Earth fixed cell and the PCI of the second quasi-Earth fixed cell are the same, and the frequency of the first SSB (synchronization signal block) transmitted by the source satellite and the frequency of the second SSB transmitted by the target satellite may be the same.

[0010] Here, the step of performing communication with the target satellite may include: a step of interrupting the communication service of the source satellite based on the satellite switching; a step of connecting to the target satellite based on the target satellite-related information; and a step of performing communication with the target satellite through the service link of the target satellite based on the target satellite-related information.

[0011] Here, the step of performing communication with the target satellite may include: a step of connecting to the target satellite based on the target satellite-related information; a step of stopping communication on the service link of the source satellite after connecting to the target satellite; and a step of performing communication with the target satellite through the service link of the target satellite based on the target satellite-related information.

[0012] Here, the terminal can determine the uplink TA (timing advance) of the target satellite based on the target satellite-related information, and apply the determined uplink TA to the communication with the target satellite.

[0013] Here, the target satellite related information may include at least one of an epoch time, uplink timing advance information, ephemeris information, uplink synchronization validity period, cell-specific scheduling offset, network scheduling offset, timing advance report information, downlink polarization information, or uplink polarization information in non-terrestrial network configuration information for the target satellite.

[0014] Here, the target satellite-related information includes a time at which the communication service of the source satellite is interrupted, and the terminal may hold an uplink HARQ (hybrid automatic repeat request) buffer without emptying it when the communication service is interrupted at the time at which the communication service of the source satellite is interrupted, and may resume an uplink HARQ operation to the target satellite when a step of performing communication with the target satellite is started.

[0015] Here, the target satellite-related information may be included in a SIB (system information block) that the terminal obtains from the source satellite.

[0016] Here, if the target satellite-related information is included in the non-terrestrial network-related SIB, the terminal may perform the satellite switching, and if the target satellite-related information is not included in the non-terrestrial network-related SIB, the terminal may not perform the satellite switching.

[0017] Meanwhile, a satellite switching method in a wireless communication system according to a second embodiment of the present disclosure for achieving the above object includes a step of providing target satellite-related information to a terminal through a source satellite connected to the base station, as a method of a base station; a step of performing satellite switching from the source satellite to the target satellite at a time when provision of a communication service of the source satellite is interrupted; and a step of providing a communication service to the terminal through the target satellite after performing the satellite switching, wherein the base station can provide the communication service to the terminal through the target satellite without performing a random access procedure between the target satellite and the terminal.

[0018] Here, the target satellite-related information may be included in a SIB (system information block) transmitted to the terminal.

[0019] Here, the target satellite related information may include at least one of an epoch time, uplink timing advance information, ephemeris information, uplink synchronization validity period, cell-specific scheduling offset, network scheduling offset, timing advance report information, downlink polarization information, or uplink polarization information in non-terrestrial network configuration information for the target satellite.

[0020] Here, the target satellite-related information may be included in a non-terrestrial network-related SIB to instruct the terminal to perform the satellite switching, and the target satellite-related information may be not included in the non-terrestrial network-related SIB to instruct the terminal not to perform the satellite switching.

[0021] Meanwhile, in a wireless communication system according to a third embodiment of the present disclosure for achieving the above purpose, a satellite switching device includes a processor as a terminal, and the processor can cause the terminal to obtain target satellite-related information from a source satellite; perform satellite switching from the source satellite to the target satellite based on the target satellite-related information; and perform communication with the target satellite based on the target satellite-related information after performing the satellite switching.

[0022] Here, in the step of performing communication with the target satellite based on the target satellite-related information after performing the satellite switching, the processor can cause the terminal to connect to the target satellite without random access based on the target satellite-related information; and to perform communication with the target satellite based on the target satellite-related information.

[0023] Here, in the step of performing communication with the target satellite based on the target satellite-related information after performing the satellite switching, the processor may cause the terminal to: interrupt the communication service of the source satellite based on the satellite switching; connect to the target satellite based on the target satellite-related information; and perform communication with the target satellite through the service link of the target satellite based on the target satellite-related information.

[0024] Here, the target satellite-related information includes a time at which the communication service of the source satellite is interrupted, and the processor can cause the terminal to hold an uplink HARQ (hybrid automatic repeat request) buffer without emptying it if the communication service is interrupted at the time at which the communication service of the source satellite is interrupted, and to resume an uplink HARQ operation to the target satellite when a step of performing communication with the target satellite is started.

[0025] Here, the target satellite-related information may be included in a SIB (system information block) that the terminal obtains from the source satellite.

[0026] Here, if the target satellite-related information is included in the non-terrestrial network-related SIB, the processor can cause the terminal to perform the satellite switching, and if the target satellite-related information is not included in the non-terrestrial network-related SIB, the processor can cause the terminal not to perform the satellite switching.

[0027] According to the present disclosure, when a terminal performs satellite switching from a source satellite to a target satellite, the terminal may not perform a separate random access procedure, thereby resolving the RACH (random access channel) congestion problem through the random access procedure. Furthermore, according to the present disclosure, the terminal may be able to perform uplink transmission to a base station if it can recognize a pre-corrected timing advance (TA) associated with the target satellite without performing random access immediately after satellite switching. Furthermore, according to the present disclosure, the terminal may correct the TA based on TA correction value information received from the base station, thereby enabling smooth communication through the target satellite.

[0028] Figure 1 is a conceptual diagram illustrating one embodiment of a communication system.

[0029] Figure 2 is a block diagram illustrating one embodiment of a communication node constituting a communication system.

[0030] Figure 3 is a conceptual diagram illustrating a first embodiment of a wireless interface protocol structure in a communication system.

[0031] Figure 4 is a conceptual diagram illustrating an example of a time resource through which a wireless signal is transmitted in a communication system.

[0032] FIG. 5 is a conceptual diagram for explaining the time difference between the reception timing of the #i-th downlink frame and the transmission timing of the #i-th uplink frame in one embodiment of a communication system.

[0033] Figure 6 is a structural diagram illustrating an embodiment of a time / frequency resource grid of a communication system.

[0034] FIG. 7 is a structural diagram illustrating an embodiment of a synchronization signal and physical broadcast channel block (SSB) of a communication system.

[0035] Figure 8 is a conceptual diagram illustrating a first embodiment of a non-terrestrial network.

[0036] Figure 9 is a conceptual diagram illustrating a second embodiment of a non-terrestrial network.

[0037] Figure 10 is a conceptual diagram illustrating embodiments of a satellite switching method in a quasi-earth fixed cell.

[0038] Figure 11 is a conceptual diagram illustrating embodiments of a hard satellite switching method in a quasi-earth fixed cell.

[0039] Figure 12 is a conceptual diagram illustrating embodiments of a soft satellite switching method in a quasi-earth fixed cell.

[0040] Figure 13 is a conceptual diagram illustrating embodiments of a non-alternative PCI (physical cell identifier) ​​satellite switching method.

[0041] Figure 14 is a conceptual diagram illustrating embodiments of a reference point, common timing advance, and terminal specific timing advance.

[0042] Figure 15 is a conceptual diagram for explaining a synchronization signal block and beam sweeping operation in a wireless communication system.

[0043] Figure 16 is a conceptual diagram illustrating a first embodiment of a method for indicating required system information using an indicator included in a SIB (system information block).

[0044] Figure 17 is a conceptual diagram illustrating a second embodiment of a method for indicating required system information using an indicator included in SIB.

[0045] Figure 18 is a conceptual diagram illustrating a first embodiment of a method for providing necessary system information immediately after switching independently from SIB.

[0046] Figure 19 is a conceptual diagram showing a first embodiment of satellite switching time based on hard satellite switching.

[0047] Fig. 20 is a flowchart showing a first embodiment of terminal operation in a satellite switching method in a wireless communication system.

[0048] This disclosure may be subject to various modifications and various embodiments. Specific embodiments are illustrated and described in detail in the drawings. However, this is not intended to limit the disclosure to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the disclosure.

[0049] While terms such as "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present disclosure, a first component could be referred to as a "second component," and similarly, a second component could also be referred to as a "first component." The term "and / or" includes a combination of multiple related items described herein or any of multiple related items described herein.

[0050] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0051] The terminology used in this disclosure is only used to describe specific embodiments and is not intended to limit the present disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this disclosure, it should be understood that the terms "comprises" or "has" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0052] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which this disclosure pertains. 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 shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0053] A communication system to which embodiments according to the present disclosure are applied will be described. The communication system to which embodiments according to the present disclosure are applied is not limited to the scope described below, and embodiments according to the present disclosure can be applied to various communication systems. Here, the term "communication system" may be used interchangeably with "communication network."

[0054] Throughout the specification, the network may include, for example, wireless internet such as WiFi (wireless fidelity), mobile internet such as WiBro (wireless broadband internet) or WiMax (world interoperability for microwave access), 2G mobile communication networks such as GSM (global system for mobile communication) or CDMA (code division multiple access), 3G mobile communication networks such as WCDMA (wideband code division multiple access) or CDMA2000, 3.5G mobile communication networks such as HSDPA (high speed downlink packet access) or HSUPA (high speed uplink packet access), 4G mobile communication networks such as LTE (long term evolution) or LTE-Advanced, and 5G mobile communication networks.

[0055] Throughout the specification, a terminal may refer to a mobile station, a mobile terminal, a subscriber station, a portable subscriber station, a user equipment, an access terminal, etc., and may include all or part of the functions of a terminal, a mobile station, a mobile terminal, a subscriber station, a portable subscriber station, a user equipment, an access terminal, etc.

[0056] Here, a desktop computer, laptop computer, tablet PC, wireless phone, mobile phone, smart phone, smart watch, smart glass, e-book reader, portable multimedia player (PMP), portable game console, navigation device, digital camera, digital multimedia broadcasting (DMB) player, digital audio recorder, digital audio player, digital picture recorder, digital picture player, digital video recorder, digital video player, etc. capable of communicating with the terminal can be used.

[0057] Throughout the specification, a base station may also refer to an access point, a radio access station, a node B, an evolved node B, a base transceiver station, a mobile multihop relay (MMR)-BS, etc., and may include all or part of the functions of a base station, an access point, a radio access station, a node B, an eNodeB, a base transceiver station, an MMR-BS, etc.

[0058] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the attached drawings. In order to facilitate an overall understanding in describing the present disclosure, identical reference numerals will be used for identical components in the drawings, and redundant descriptions of identical components will be omitted.

[0059] Figure 1 is a conceptual diagram illustrating one embodiment of a communication system.

[0060] Referring to FIG. 1, a communication system (100) may include a plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6). The plurality of communication nodes may support 4G communication (e.g., long term evolution (LTE), advanced LTE-A (LTE-A), 5G communication (e.g., new radio (NR)), etc.) specified in the 3rd generation partnership project (3GPP) standard. 4G communication may be performed in a frequency band of 6 GHz or less, and 5G communication may be performed in a frequency band of 6 GHz or more as well as a frequency band of 6 GHz or less.

[0061] For example, for 4G communication and 5G communication, multiple communication nodes can support a communication protocol based on CDMA (code division multiple access), a communication protocol based on WCDMA (wideband CDMA), a communication protocol based on TDMA (time division multiple access), a communication protocol based on FDMA (frequency division multiple access), a communication protocol based on OFDM (orthogonal frequency division multiplexing), a communication protocol based on Filtered OFDM, a communication protocol based on CP (cyclic prefix)-OFDM, a communication protocol based on DFT-s-OFDM (discrete Fourier transform-spread-OFDM), a communication protocol based on OFDMA (orthogonal frequency division multiple access), a communication protocol based on SC (single carrier)-FDMA, a communication protocol based on NOMA (Non-orthogonal Multiple Access), a communication protocol based on GFDM (generalized frequency division multiplexing), a communication protocol based on FBMC (filter bank multi-carrier), a communication protocol based on UFMC (universal filtered multi-carrier), a communication protocol based on SDMA (Space Division Multiple Access), etc.

[0062] In addition, the communication system (100) may further include a core network. If the communication system (100) supports 4G communication, the core network may include a serving gateway (S-GW), a packet data network (PDN) gateway (P-GW), a mobility management entity (MME), etc. If the communication system (100) supports 5G communication, the core network may include a user plane function (UPF), a session management function (SMF), an access and mobility management function (AMF), etc.

[0063] Meanwhile, each of the plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6) constituting the communication system (100) may have the following structure.

[0064] Figure 2 is a block diagram illustrating one embodiment of a communication node constituting a communication system.

[0065] Referring to FIG. 2, a communication node (200) may include at least one processor (210), a memory (220), and a transmission / reception device (230) that is connected to a network and performs communication. In addition, the communication node (200) may further include an input interface device (240), an output interface device (250), a storage device (260), etc. Each component included in the communication node (200) may be connected by a bus (270) and communicate with each other.

[0066] However, each component included in the communication node (200) may be connected through an individual interface or individual bus centered around the processor (210), rather than a common bus (270). For example, the processor (210) may be connected to at least one of a memory (220), a transmission / reception device (230), an input interface device (240), an output interface device (250), and a storage device (260) through a dedicated interface.

[0067] The processor (210) can execute program commands stored in at least one of the memory (220) and the storage device (260). The processor (210) may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor in which the methods according to embodiments of the present disclosure are performed. Each of the memory (220) and the storage device (260) may be configured with at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory (220) may be configured with at least one of a read-only memory (ROM) and a random access memory (RAM).

[0068] Referring again to FIG. 1, the communication system (100) may include a plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) and a plurality of terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6). The communication system (100) including the base stations (110-1, 110-2, 110-3, 120-1, 120-2) and the terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) may be referred to as an “access network.” The first base station (110-1), the second base station (110-2), and the third base station (110-3) can each form a macro cell. The fourth base station (120-1) and the fifth base station (120-2) can each form a small cell. The fourth base station (120-1), the third terminal (130-3), and the fourth terminal (130-4) can be within the cell coverage of the first base station (110-1). The second terminal (130-2), the fourth terminal (130-4), and the fifth terminal (130-5) can be within the cell coverage of the second base station (110-2). The fifth base station (120-2), the fourth terminal (130-4), the fifth terminal (130-5), and the sixth terminal (130-6) may be within the cell coverage of the third base station (110-3). The first terminal (130-1) may be within the cell coverage of the fourth base station (120-1). The sixth terminal (130-6) may be within the cell coverage of the fifth base station (120-2).

[0069] Here, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be referred to as a NodeB, an evolved NodeB, a BTS (base transceiver station), a radio base station, a radio transceiver, an access point, an access node, an RSU (road side unit), a RRH (radio remote head), a TP (transmission point), a TRP (transmission and reception point), an eNB, a gNB, etc.

[0070] Each of the plurality of terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) may be referred to as a UE (user equipment), a terminal, an access terminal, a mobile terminal, a station, a subscriber station, a mobile station, a portable subscriber station, a node, a device, an IoT (Internet of Things) device, an onboard device (mounted module / device / terminal or onboard device / terminal, etc.).

[0071] Meanwhile, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may operate in a different frequency band or may operate in the same frequency band. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be connected to each other via an ideal backhaul link or a non-ideal backhaul link, and may exchange information with each other via the ideal backhaul link or the non-ideal backhaul link. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be connected to the core network via the ideal backhaul link or the non-ideal backhaul link. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can transmit a signal received from the core network to the corresponding terminal (130-1, 130-2, 130-3, 130-4, 130-5, 130-6), and can transmit a signal received from the corresponding terminal (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) to the core network.

[0072] Additionally, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may support MIMO transmission (e.g., single user (SU)-MIMO, multi user (MU)-MIMO, massive MIMO, etc.), coordinated multipoint (CoMP) transmission, carrier aggregation (CA) transmission, transmission in an unlicensed band, device to device communication (D2D) (or, proximity services (ProSe)), etc. Here, each of the plurality of terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) can perform an operation corresponding to the base station (110-1, 110-2, 110-3, 120-1, 120-2) and an operation supported by the base station (110-1, 110-2, 110-3, 120-1, 120-2). For example, the second base station (110-2) can transmit a signal to the fourth terminal (130-4) based on the SU-MIMO scheme, and the fourth terminal (130-4) can receive a signal from the second base station (110-2) by the SU-MIMO scheme. Alternatively, the second base station (110-2) can transmit signals to the fourth terminal (130-4) and the fifth terminal (130-5) based on the MU-MIMO method, and each of the fourth terminal (130-4) and the fifth terminal (130-5) can receive signals from the second base station (110-2) based on the MU-MIMO method.

[0073] Each of the first base station (110-1), the second base station (110-2), and the third base station (110-3) can transmit a signal to the fourth terminal (130-4) based on the CoMP scheme, and the fourth terminal (130-4) can receive a signal from the first base station (110-1), the second base station (110-2), and the third base station (110-3) based on the CoMP scheme. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can transmit and receive a signal with terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) within its cell coverage based on the CA scheme. Each of the first base station (110-1), the second base station (110-2), and the third base station (110-3) can control D2D between the fourth terminal (130-4) and the fifth terminal (130-5), and each of the fourth terminal (130-4) and the fifth terminal (130-5) can perform D2D under the control of the second base station (110-2) and the third base station (110-3).

[0074] Next, methods for setting up and managing a wireless interface in a communication system will be described. Even if a method (e.g., signal transmission or reception) performed by a first communication node among communication nodes is described, a corresponding second communication node can perform a method (e.g., signal reception or transmission) corresponding to the method performed by the first communication node. That is, if the operation of a terminal is described, the corresponding base station can perform an operation corresponding to the operation of the terminal. Conversely, if the operation of a base station is described, the corresponding terminal can perform an operation corresponding to the operation of the base station.

[0075] FIG. 3 is a conceptual diagram illustrating a first embodiment of a radio interface protocol architecture in a communication system.

[0076] Referring to FIG. 3, the wireless interface protocol structure (300) of the communication system may be configured to include an RRC (radio resource control) layer (310), a MAC (medium access control) layer (320), a physical (PHY) layer (330), etc. The wireless interface protocol structure (300) illustrated in FIG. 3 may correspond to various interface embodiments, such as an interface between a terminal and a base station, an interface between an IAB-node DU (distributed unit) of an IAB (integrated access backhaul) network and an IAB-node MT (mobile terminal), an interface between an IAB-node DU and a lower node, an interface between an IAB-node MT and an upper node, and an interface between a plurality of terminals.

[0077] Near the PHY layer (330), an RRC layer (310) and a MAC layer (320) may be placed above the PHY layer (330). For example, the MAC layer (320) may be placed above the PHY layer (330). The RRC layer (310) may be placed above the MAC layer (320).

[0078] The MAC layer (320) can be connected to a higher layer (e.g., the RRC layer (310)) through logical channels (315). The PHY layer (330) can be connected to the higher MAC layer (320) through transport channels (325). The PHY layer (330) can exchange control information or measurement information (350) with the RRC layer (310).

[0079] The PHY layer (330) may be referred to as 'layer 1' or 'L1'. The MAC layer (320) may be referred to as 'layer 2' or 'L2'. The RRC layer (310) may be referred to as 'layer 3' or 'L3'. The RRC layer (310) and the MAC layer (320) may be collectively referred to as 'upper layers'.

[0080] In this specification, 'L1 signaling' may refer to signaling such as downlink control information (DCI) transmitted through a physical downlink control channel (PDCCH), which is a PHY layer (330) channel, uplink control information (UCI) transmitted through a physical uplink control channel (PUCCH), and sidelink control information (SCI) transmitted through a physical sidelink control channel (PSCCH). Similarly, 'upper layer signaling' in this specification may include L2 signaling transmitted through a MAC control element (CE), L3 signaling transmitted through RRC signaling, etc. Although omitted in FIG. 3 for convenience of explanation, information that may be included in an interface between base stations, or an interface between base station components such as a distributed unit (DU) and a central unit (CU) (e.g., F1, NG (next generation) interface, etc.) may also be collectively referred to as upper layer signaling together with L2 signaling or L3 signaling.

[0081] In communication systems such as 5G, one or more of the numerologies in Table 1 may be used for various purposes, such as reducing inter-carrier interference (ICI) according to frequency band characteristics and reducing latency according to service characteristics.

[0082]

[0083] Table 1 is only an example for convenience of explanation, and embodiments of numerologies used in a communication system may not be limited thereto. Each numerology μ may correspond to information on subcarrier spacing (SCS) Δf and cyclic prefix (CP). The terminal can check the numerology μ and CP values ​​applied to the downlink bandwidth part or the uplink bandwidth part based on the upper layer parameters such as 'subcarrierSpacing' and 'cyclicPrefix'. Fig. 4 is a conceptual diagram illustrating an embodiment of a time resource for transmitting a wireless signal in a communication system.

[0084] Referring to FIG. 4, the time resource for transmitting a wireless signal in a communication system is one or more ( ) a frame (430) consisting of a subframe (420), one or more ( ) a sub-frame (420) consisting of a slot (410), and (For example, it can be expressed as a slot (410) consisting of 14 OFDM symbols. At this time, each variable , , The values ​​may follow the values ​​in Table 2 in the case of a regular cyclic prefix, or follow the values ​​in Table 3 in the case of an extended cyclic prefix, depending on the set numerology. OFDM symbols included in one slot may be distinguished as 'downlink', 'flexible', or 'uplink' by upper layer signaling or a combination of upper layer signaling and L1 signaling.

[0085]

[0086]

[0087] In a 5G NR communication system, a frame (430) may have a length of 10 ms, and a subframe (420) may have a length of 1 ms. Each frame (430) may be divided into two half-frames having the same length, and the first half-frame (half-frame 0) may be composed of sub-frames (420) numbered 0 to 4, and the second half-frame (half-frame 1) may be composed of sub-frames (420) numbered 5 to 9. One carrier may have a set of frames for uplink (uplink frames) and a set of frames for downlink (downlink frames). FIG. 5 is a conceptual diagram for explaining a time difference between the reception timing of the #i-th downlink frame and the transmission timing of the #i-th uplink in one embodiment of a communication system.

[0088] Referring to FIG. 5, the time difference between the reception timing of the #i-th downlink frame (500) and the transmission timing of the #i-th uplink frame (510) is T TA (520) can be. Accordingly, the terminal can compare T with the start time of reception of downlink frame #i (500). TA Transmission for uplink frame #i (510) can be started at an earlier point in time. Such TTA can be named as timing advance or timing adjustment (TA). The base station informs the terminal of T through upper layer signaling or L1 signaling. TA You can instruct it to change the value, for example: It can be promised to be applied as follows. For 5G NR, case T c Is can be defined as , and is Δf max can be 480kHz, N f can be 4096, N TA,offset can be a value set by L3 signaling, and N TA is the value T indicated by L2 signaling A It can be a value determined by the following mathematical formula 1.

[0089]

[0090] Here, N TA,offset and N TA The description may be an example for a specific situation, and various other options may exist, but not all possible cases may be listed in this disclosure so as not to obscure the gist of the description.

[0091] Figure 6 is a structural diagram illustrating an embodiment of a time / frequency resource grid of a communication system.

[0092] Referring to Figure 6, the time / frequency resource grid of the communication system is subcarriers and It can be composed of OFDM symbols. The resource grid can be defined for each numeral and carrier. In this case, may be a common resource block (CRB) location indicated by upper layer signaling. may mean the number of resource blocks (RBs) (610) starting from the CRB, i.e., the carrier bandwidth. and / or can have different values ​​for each link direction (uplink, downlink, sidelink) or for each numerology (μ). Here, the numerology (μ) may be referred to by other terms, such as subcarrier spacing (SCS) settings, as needed.

[0093] Each element within the resource grid for antenna port p and subcarrier spacing (SCS) setting (μ) may be referred to as a resource element (RE) (620). Each location can be uniquely defined. Here, k can be a frequency axis index, and l can mean a symbol position on the time axis. RE is a physical channel or signal complex value may correspond to physical resources used to transmit. One resource block (610) is continuous on the frequency axis. =Can be defined with 12 subcarriers.

[0094] 5G NR communication systems can introduce the concept of a bandwidth part (BWP) to reduce the high terminal implementation complexity and power consumption due to the increased carrier bandwidth compared to 3G / 4G communication systems. A bandwidth part can be composed of consecutive common resource blocks, and the starting resource block location of the bandwidth part and the number of resource blocks that make up the corresponding bandwidth portion. can satisfy mathematical expressions 2 and 3.

[0095]

[0096]

[0097] A terminal can configure up to four downlink bandwidth segments within a single component carrier (CC), and can only activate one bandwidth segment at a time. The terminal may not receive physical downlink shared channel (PDSCH), physical downlink control channel (PDCCH), channel state information reference signal (CSI-RS), etc. received outside of the activated bandwidth segment.

[0098] A terminal can configure up to four uplink bandwidth segments within a single component carrier, and can only activate one bandwidth segment at a time. A terminal may not transmit PUSCH (physical uplink shared channel), PUCCH (physical uplink control channel), or SRS (sounding reference signal) outside of the activated bandwidth segment.

[0099] FIG. 7 is a structural diagram illustrating an embodiment of a synchronization signal and physical broadcast channel block (SSB) of a communication system.

[0100] Referring to FIG. 7, the SS / PBCH block of the communication system may be composed of a primary synchronization signal (PSS) transmitted in the middle 127 subcarriers of the first OFDM symbol, a secondary synchronization signal (SSS) transmitted in the middle 127 subcarriers of the third OFDM symbol, and a physical broadcast channel (PBCH) transmitted in the second, third, and fourth OFDM symbols. The PBCH, which occupies the widest bandwidth, may be transmitted over 20 RBs, which may be 3.6 MHz based on a 15 kHz SCS. The base station transmits one SSB using the same beam, and if there is a need to operate multiple beams, such as when the number of base station antennas increases or more than one analog beam is applied to support high frequencies, multi-beam operation can be supported by transmitting multiple SSBs. The above 'beam' can be expressed in various terms such as transmission precoding or spatial transmission filter in actual application, but in order not to obscure the main point of the explanation, it can be referred to as beam.

[0101] For example, a base station may transmit multiple SSBs (730, 740, 750, 760) to represent multiple beams (e.g., beam #1, beam #2, beam #3, beam #4). At this time, it may be possible for multiple SSBs (730, 740, 750, 760) to be transmitted in one slot according to a pre-arranged pattern for each numerology. SSBs (730, 740, 750, 760) to which different beams are applied may be included in an SS burst (720) and grouped into one set. A terminal may assume a half-frame window having a length of 5 ms at the time of monitoring an SSB. An SS burst set (715) configured by upper layer signaling within a half frame may include one or more SS bursts (720). When performing initial access (IA), if the RRC configuration values ​​are unknown or unavailable, the terminal can receive or measure SSB by assuming a period of 20 ms for the SS burst set (710). For example, the terminal can receive SSB by referring to the SSB configuration information below.

[0102] Figure 8 is a conceptual diagram illustrating a first embodiment of a non-terrestrial network.

[0103] Referring to FIG. 8, the non-terrestrial network may include a satellite (810), a communication node (820), a gateway (830), a data network (840), etc. The non-terrestrial network illustrated in FIG. 8 may be a transparent payload-based non-terrestrial network. The satellite (810) may be a LEO (low earth orbit, altitude 300 to 1,500 km) satellite, a MEO (medium earth orbit, altitude 7,000 to 25,000 km) satellite, a GEO (geostationary earth orbit, altitude approximately 35,786 km) satellite, a HEO (high elliptical orbit) satellite, or an unmanned aircraft system (UAS) platform. The UAS platform may include a HAPS (high altitude platform station).

[0104] The communication node (820) may include a communication node located on the ground (e.g., a user equipment (UE), a terminal) and a communication node located off the ground (e.g., an airplane, a drone). A service link may be established between the satellite (810) and the communication node (820), and the service link may be a radio link. The satellite (810) may provide a communication service to the communication node (820) using one or more beams. The shape of the beam reception area (footprint) of the satellite (810) may be elliptical.

[0105] The communication node (820) can perform communication (e.g., downlink communication, uplink communication) with the satellite (810) using LTE technology and / or NR technology. Communication between the satellite (810) and the communication node (820) can be performed using an NR-Uu interface. When DC (dual connectivity) is supported, the communication node (820) can be connected to not only the satellite (810) but also other base stations (e.g., base stations supporting LTE and / or NR functions), and can perform DC operations based on technologies defined in the LTE and / or NR standards.

[0106] The gateway (830) may be located on the ground, and a feeder link may be established between the satellite (810) and the gateway (830). The feeder link may be a wireless link. The gateway (830) may be referred to as a "non-terrestrial network (NTN) gateway." Communication between the satellite (810) and the gateway (830) may be performed based on a NR-Uu interface or a satellite radio interface (SRI). The gateway (830) may be connected to a data network (840). A "core network" may exist between the gateway (830) and the data network (840). In this case, the gateway (830) may be connected to the core network, and the core network may be connected to the data network (840). The core network may support NR technology. For example, the core network may include an access and mobility management function (AMF), a user plane function (UPF), a session management function (SMF), etc. Communication between the gateway (830) and the core network may be performed based on the NG-C / U interface.

[0107] Alternatively, a base station and a core network may exist between the gateway (830) and the data network (840). In this case, the gateway (830) may be connected to the base station, the base station may be connected to the core network, and the core network may be connected to the data network (840). The base station and the core network may support NR technology. Communication between the gateway (830) and the base station may be performed based on the NR-Uu interface, and communication between the base station and the core network (e.g., AMF, UPF, SMF) may be performed based on the NG-C / U interface.

[0108] Figure 9 is a conceptual diagram illustrating a second embodiment of a non-terrestrial network.

[0109] Referring to FIG. 9, the non-terrestrial network may include satellite #1 (911), satellite #2 (912), a communication node (920), a gateway (930), a data network (940), etc. The non-terrestrial network illustrated in FIG. 9 may be a regenerative payload-based non-terrestrial network. For example, each of satellites #1-2 (911, 912) may perform a regenerative operation (e.g., a demodulation operation, a decoding operation, a re-encoding operation, a re-modulation operation, and / or a filtering operation) on a payload received from another entity constituting the non-terrestrial network (e.g., a communication node (920), a gateway (930)) and transmit the regenerated payload.

[0110] Each of satellites #1-2 (911, 912) may be a LEO satellite, MEO satellite, GEO satellite, HEO satellite, or UAS platform. The UAS platform may include HAPS. Satellite #1 (911) may be connected to satellite #2 (912), and an inter-satellite link (ISL) may be established between satellite #1 (911) and satellite #2 (912). The ISL may operate in a radio frequency (RF) frequency or an optical band. The ISL may be configured as optional. The communication node (920) may include a communication node located on the ground (e.g., a UE, terminal) and a communication node located off the ground (e.g., an airplane, a drone). A service link (e.g., a wireless link) may be established between satellite #1 (911) and the communication node (920). Satellite #1 (911) may provide communication services to a communication node (920) using one or more beams.

[0111] The communication node (920) can perform communication (e.g., downlink communication, uplink communication) with satellite #1 (911) using LTE technology and / or NR technology. Communication between satellite #1 (911) and the communication node (920) can be performed using an NR-Uu interface. If DC is supported, the communication node (920) can be connected to not only satellite #1 (911) but also other base stations (e.g., base stations supporting LTE and / or NR functions), and can perform DC operations based on technologies defined in the LTE and / or NR standards.

[0112] The gateway (930) may be located on the ground, and a feeder link may be established between satellite #1 (911) and the gateway (930), and a feeder link may be established between satellite #2 (912) and the gateway (930). The feeder link may be a wireless link. If an ISL is not established between satellite #1 (911) and satellite #2 (912), a feeder link between satellite #1 (911) and the gateway (930) may be established mandatorily.

[0113] Communication between each of satellites #1-2 (911, 912) and the gateway (930) may be performed based on the NR-Uu interface or SRI. The gateway (930) may be connected to a data network (940). A "core network" may exist between the gateway (930) and the data network (940). In this case, the gateway (930) may be connected to the core network, and the core network may be connected to the data network (940). The core network may support NR technology. For example, the core network may include AMF, UPF, SMF, etc. Communication between the gateway (930) and the core network may be performed based on the NG-C / U interface.

[0114] Alternatively, a base station and a core network may exist between the gateway (930) and the data network (940). In this case, the gateway (930) may be connected to the base station, the base station may be connected to the core network, and the core network may be connected to the data network (940). The base station and the core network may support NR technology. Communication between the gateway (930) and the base station may be performed based on the NR-Uu interface, and communication between the base station and the core network (e.g., AMF, UPF, SMF) may be performed based on the NG-C / U interface.

[0115] Meanwhile, entities constituting the non-terrestrial network illustrated in FIGS. 8 and 9 (e.g., satellites, communication nodes, gateways, etc.) may include at least one processor, memory, and a transceiver connected to the network to perform communication. In addition, the entity may further include an input interface device, an output interface device, a storage device, etc. Each component included in the entity may be connected by a bus to perform communication with each other. However, each component included in the entity may be connected through individual interfaces or individual buses centered around the processor, rather than a common bus. For example, the processor may be connected to at least one of the memory, the transceiver, the input interface device, the output interface device, and the storage device through a dedicated interface. The processor may execute program commands stored in at least one of the memory and the storage device. The processor may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present disclosure are performed. Each of the memory and storage devices may comprise at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory may comprise at least one of a read-only memory (ROM) and a random access memory (RAM).

[0116] Meanwhile, in non-terrestrial networks, scenarios can be defined as shown in Table 4 below.

[0117] NTN shown in Fig. 8 NTNGEO shown in Fig. 9 Scenario A Scenario BLEO (steerable beam) Scenario C1 Scenario D1 LEO (beam moving with satellite) Scenario C2 Scenario D2

[0118] In the non-terrestrial network illustrated in FIG. 8, if the satellite (810) is a GEO satellite (e.g., a GEO satellite supporting a transparent function), this may be referred to as “Scenario A.” In the non-terrestrial network illustrated in FIG. 9, if satellites #1-2 (911, 912) are GEO satellites (e.g., a GEO supporting a regenerative function), this may be referred to as “Scenario B.” In the non-terrestrial network illustrated in FIG. 8, if the satellite (810) is a LEO satellite having steerable beams, this may be referred to as “Scenario C1.” In the non-terrestrial network illustrated in FIG. 8, if the satellite (810) is a LEO satellite having beams move with the satellite, this may be referred to as “Scenario C2.” In the non-terrestrial network illustrated in FIG. 9, if satellites #1-2 (911, 912) are LEO satellites with steerable beams, this may be referred to as "Scenario D1." In the non-terrestrial network illustrated in FIG. 9, if satellites #1-2 (911, 912) are LEO satellites with beams that move together with the satellites, this may be referred to as "Scenario D2." Parameters for the scenarios defined in Table 4 may be defined as shown in Table 5 below.

[0119] Scenario A and B Scenario C and D Altitude 35,786 km 600 km 1,200 km Spectrum (service link) < 6 GHz (e.g. 2 GHz) > 6 GHz (e.g. DL 20 GHz, UL 30 GHz) Maximum channel bandwidth capability (service link) 30 MHz for band < 6 GHz 1 GHz for band > 6 GHz Maximum distance between satellite and communication node (e.g., UE) at minimum elevation angle 40,581 km 1,932 km (600 km altitude) 3,131 km (1,200 km altitude) Maximum round trio delay (RTD) (propagation delay only) Scenario A: 541.46 ms (service and feeder links) Scenario B: 270.73 ms (service link only) Scenario C: (Transparent payload: service feeder links) - 5.77 ms (600 km altitude) - 41.77ms (1,200km altitude) Scenario D: (Regenerated payload: only service link) - 12.89ms (600km altitude) - 20.89ms (1,200km altitude) Maximum delay variation within a beam 16ms 4.44ms (600km altitude) 6.44ms (1,200km altitude) Maximum differential delay within a cell 10.3ms 3.12ms (600km altitude) 3.18ms (1,200km altitude) Service link NR defined in 3GPP Feeder link Radio interface defined in 3GPP or non-3GPP

[0120] Additionally, in the scenarios defined in Table 4, the delay constraint can be defined as shown in Table 6 below.

[0121] Scenario A Scenario B Scenario C1-2 Scenario D1-2 Satellite altitude 35,786 km 600 km Maximum RTD on the air interface between the base station and the UE 541.75 ms (worst case) 270.57 ms 28.41 ms 12.88 ms Minimum RTD on the air interface between the base station and the UE 477.14 ms 238.57 ms 8 ms 4 ms

[0122]

[0123] Meanwhile, the terminal can support the calculation of a specific timing advance (TA) of the terminal based on the position and serving satellite ephemeris obtained from the global navigation satellite system (GNSS). For example, N TA can be defined as 0 for PRACH (physical random access channel). N TA can be updated based on the TA command field of the msg2 / msgB and MAC (medium access control) CE (control element) TA command. N TA, UE-specific It may be a terminal self-estimated TA to compensate for service link delay in advance, and N TA,common As a network control common TA, it may include any timing offset deemed necessary by the network and may support a value of 0.

[0124] N TA,offset may be a fixed offset used to calculate the timing advance. The terminal may assume that the round trip time (RTT) between the terminal and the base station (gNB) is not equal to the TA calculated for Msg1 / MsgA. The validity duration configured in the network for the satellite ephemeris data may indicate the maximum time that the terminal can apply the satellite ephemeris without acquiring a new satellite ephemeris. N based on the TA command field of Msg2 / msgB and the MAC CE TA command. TA The update can be used to correct the uplink timing alignment as follows: When a timing advance command (TAC) is received in Msg2 / msgB, the terminal can receive the first adjustment, and N TA can be updated as shown in the following mathematical expression 4.

[0125]

[0126] Here T A can be in the TAC field of msg2 / msgB. When the TAC (TA) provided by MAC CE is received, N TA can be updated as in the following mathematical expression 5. In other words, the terminal is the previous N TA In N TA,old to N TA_new can be updated.

[0127]

[0128] Here, TA can be a value in the TAC field of the MAC CE. The common TA can include parameters indicating timing drift. The terminal applies the common TA according to the parameters provided by the network (if any), and when defining the uplink timing error requirement, the offset between the common TA according to the parameters provided by the network and the actual feeder link RTT may not be considered.

[0129] The terminal uses scheduling offset (K) to improve timing relationship. offset ) can be introduced to improve the timing relationship. It can be configured in the system information and K used for initial connection. offset For at least one cell, a cell-specific K is used in all beams. offset The configuration can be supported. Along with this, K for MAC-CE offset Scheduling offsets other than K mac can be defined as

[0130] Downlink and uplink frame timing can be aligned to the gNB. In this case, the terminal operation and assumptions for the downlink and uplink configurations indicated by the MAC CE command on the PDSCH are as follows: macThis may not be necessary. For terminal operation and assumptions about the downlink configuration indicated by the MAC-CE command on the PDSCH when the downlink and uplink frame timings are not aligned at the gNB, K mac This may be required. The terminal can receive system information from the gNB and K included in the system information. mac Information can be obtained.

[0131] After initial connection, the terminal is K offset can be updated. The terminal receives the timing advance command K offset Uplink transmission timing adjustment can be supplemented by introducing K after initial connection. offset Terminal specific K for update offset can be provided and updated by the network using MAC CE. Cell-specific K configured in system information offset You can choose one of the following two options:

[0132] Option 1 may be signaled by a single offset value. For example, one offset value may include the round-trip delay (RTT) of the service link and the RTT between the service satellite and the reference point. Option 2 may consist of a first offset value and a second offset value. K offset may be the sum of the first offset value and the second offset value. For example, the first offset value may be the RTT (or determined by the common timing advance (TA)) between the serving satellite and the reference point, and the second offset value may be the RTT of the serving link.

[0133] K other than the value signaled in the system information offset If this is not provided, the K signaled in the system information offset can be applied to all timing relationship improvements. K for MAC-CE offset K is a scheduling offset other than maccan be provided to the terminal by the network. The network provides the terminal with a scheduling offset K mac may not provide. In such a case, the terminal may not provide K mac can be assumed to be 0.

[0134] The estimate of UE-gNB RTT is based on the UE's T A Wow K mac may be equal to the sum of T . For reference, the TA of the terminal is T TA Based on and the estimate of gNB-satellite RTT is N TA,common × T c Wow K mac may be equal to the sum of the terminals K mac If the value is not provided from the network, the terminal mac can be assumed to be 0.

[0135] NTN ephemeris can be divided into ephemeris of the serving cell and ephemeris of its neighbors. Information about when a cell will cease local service and / or timing information (e.g., timers or absolute time) about new incoming cells can be supported, at least in a quasi-earth-stationary NTN scenario. If both types of information are needed, they can be obtained from system information and / or ephemeris. At least for uplink scheduling adaptation, the UE can report information about UE-specific TA pre-calibration. The UE can report UE-specific TA pre-calibration to the base station during a random access (RA) procedure using the RACH using the MAC CE.

[0136] If enabled by the network, the UE may report information about UE-specific TA pre-calibration during a random access procedure (MSGA / MSG3 or MSG5) using MAC CE. The content of UE-specific TA pre-calibration reported in an RA procedure using MAC CE may be UE-specific TA. UE-specific TA reporting during an RA procedure using RACH may be enabled / disabled by system information (SI). Reporting of information about UE-specific TA may be supported in connected mode. Event triggering for reporting information about UE-specific TA may be supported in connected mode. If configured, the UE may report information about UE-specific TA pre-calibration to a target cell during random access.

[0137] If UE location information cannot be reported in connected mode, the content of the UE-specific TA reported in connected mode may be UE-specific TA pre-correction. If the content of the information about the reported UE-specific TA is UE location information in connected mode, RRC signaling may be used to report it. If UE location information can be reported in connected mode, for TA reporting purposes in connected mode, the network may configure the UE to report either UE-specific TA pre-correction or UE location information. If the content of the information about the reported UE-specific TA is a TA pre-correction value in connected mode, it may be reported using MAC CE.

[0138] Event-triggered UE location reporting can be configured by the gNB to obtain UE location updates for mobile UEs in radio resource control (RRC) connected mode. Periodic location reporting can also be configured by the gNB to obtain UE location updates for mobile UEs in RRC connected mode.

[0139] A new indication in RRC reconfiguration using synchronization may not necessarily be required to configure the UE to report information about a specific TA during a handover procedure. SI information indicating whether TA reporting is enabled / disabled in the target cell may be conveyed via the handover (HO) command.

[0140] For RA procedures triggered by a "request for other SI (system information)", information about UE-specific TA pre-calibration may not be reported. The event trigger for reporting information about a UE-specific TA may be based on a TA value. A TA offset threshold may be used for event trigger reporting, and at least the offset threshold may be between the current information about the UE-specific TA and the last successfully reported information about the UE-specific TA.

[0141] At least for quasi-Earth-fixed and Earth-fixed cell scenarios, timing information regarding when a cell will cease serving its area is required to support cell reselection in the NTN, and the timing information regarding when a cell will cease serving its area can be broadcast to UEs via system information. The broadcast of cell downtime in the SIB may only apply to quasi-Earth-fixed cells and may not apply to mobile cells. At least for quasi-Earth-fixed cells, the timing information regarding when a cell will cease serving its area can be used to determine when to perform measurements for neighboring cells. For quasi-Earth-fixed cells, the reference location of the cell (serving cell or neighboring cell) may be broadcast in the system information. The reference location may be the cell center.

[0142] For quasi-terrestrial fixed cells, the terminal may begin measurements of neighboring cells before the serving cell ceases to cover the current area. For quasi-terrestrial fixed cells, the broadcasted "information on when the cell will cease to serve the area" may refer to the time when the cell ceases to cover the current area. For quasi-terrestrial fixed cells, the terminal specifies the broadcast stop time of the serving cell, i.e., the time before which measurements of neighboring cells must begin, and the exact time to begin measurements may depend on the terminal implementation.

[0143] Meanwhile, non-terrestrial networks can support the following three types of service links:

[0144] 1) Earth-fixed service link: An Earth-fixed service link may be a service link provided by a beam that always covers the same geographic area. For example, a service link provided by a geostationary orbit (GSO) satellite may be an Earth-fixed service link.

[0145] 2) Quasi-Earth-fixed service links: Quasi-Earth-fixed service links may cover one geographic area for a limited period and may be provided by beam(s) that cover different geographic areas for different periods. For example, a service link provided by a non-geostationary orbit (NGSO) satellite that generates steerable beams may be a quasi-Earth-fixed service link.

[0146] 3) Earth-moving service links: An Earth-moving service link may be one in which the coverage area provided by the satellite moves over the Earth's surface. For example, a service link provided by an NGSO satellite using a fixed or non-stearable beam may be an Earth-moving service link.

[0147] NTN can provide quasi-earth fixed service links or earth mobile service links via NGSO satellites. Furthermore, NTN can provide earth fixed service links via GSO satellites. Depending on the type of service link, the following three cell types can be supported in NTN.

[0148] 1) Earth-fixed cell: An Earth-fixed cell may be a cell that uses an Earth-fixed service link.

[0149] 2) Quasi-Earth-fixed cell: A quasi-Earth-fixed cell may be a cell that uses a quasi-Earth-fixed service link.

[0150] 3) Earth-moving cell: An earth-moving cell may be a cell that uses an earth-moving service link.

[0151] Terminal mobility can be supported in NTN. Specifically, NTN can support mobility for terminals in idle or inactive mode through cell reselection. For example, to support mobility for terminals in idle or inactive mode in TN, the terminal can measure surrounding cells and reselect a cell on which to camp based on the measurement results. In NTN, terminals in idle or inactive mode can also support mobility through cell reselection using the same mechanism as in TN. In this way, NTN can support mobility for terminals in idle or inactive mode through cell reselection.

[0152] On the other hand, connected mode terminals can perform handovers, which can support mobility. For example, in TN, to support mobility for terminals in connected mode, the terminal can measure cells surrounding the cell it is currently connected to (i.e., the source cell) and, based on the measurement results, perform a handover to a selected cell (i.e., the target cell). In NTN, terminals in connected mode can also support mobility through handovers using a mechanism fundamentally identical to that of TN.

[0153] Figure 10 is a conceptual diagram illustrating embodiments of a satellite switching method in a quasi-earth fixed cell.

[0154] Referring to Fig. 10, the first satellite (1010) and the second satellite (1020) may be NGSO satellites moving along an orbit. The cell area (1030) may be serviced by the first satellite (1010). As the first satellite (1010) moves, the satellite providing service to the cell area (1030) may be switched from the first satellite (1010) to the second satellite (1020). In other words, Fig. 10 may be a satellite switch scenario of a quasi-earth fixed cell, but may not be limited to that scenario. In the following, in the satellite switching process, the satellite before switching may be referred to as a source satellite, and the satellite after switching may be referred to as a target satellite, but this is for convenience of explanation and may not be limited to those terms.

[0155] Satellite switching methods for quasi-earth fixed cells can be categorized into hard satellite switching and soft satellite switching, depending on whether service links are provided simultaneously during the switching process. These terms, hard satellite switching and soft satellite switching, are for convenience of explanation and may not be limited to these terms.

[0156] Figure 11 is a conceptual diagram illustrating embodiments of a hard satellite switching method in a quasi-earth fixed cell.

[0157] Referring to FIG. 11, in a hard satellite switching method, before switching, a first satellite (1110) may provide a service link to terminals using a quasi-earth fixed cell (1130). After switching, a second satellite (1120) may provide a service link to terminals using a quasi-earth fixed cell (1140). However, during switching, the first satellite (1110) and the second satellite (1120) may not provide communication services to terminals. Accordingly, during switching, terminals may be located in a geographic area (1150) where communication services are not provided.

[0158] Figure 12 is a conceptual diagram illustrating embodiments of a soft satellite switching method in a quasi-earth fixed cell.

[0159] Referring to FIG. 12, in a soft satellite switching method, before switching, a first satellite (1210) can provide communication services to terminals using a quasi-Earth-stationary cell (1230). After switching, a second satellite (1220) can provide communication services to terminals using a quasi-Earth-stationary cell (1240). During switching, both the first satellite (1210) and the second satellite (1220) can provide communication services to terminals simultaneously. Accordingly, during switching, terminals can be located in a geographic area where two communication services are provided.

[0160] In this soft satellite switching case, communication service by the target satellite can be provided before communication service by the source satellite is interrupted. Afterwards, communication service for the source satellite can be interrupted. In other words, communication service by two satellites can be maintained during the switching time. For example, if a first satellite (1210) is providing communication service in a cell area and is switched to a second satellite (1220) through satellite switching, the communication service of the second satellite (1220) can be provided before the communication service of the first satellite (1210) is interrupted, and the communication service of the first satellite (1210) can be interrupted after the communication service of the second satellite (1220) is provided.

[0161] The present disclosure may consider a non-interchangeable PCI (unchanged physical cell identifier) ​​satellite switching scenario in relation to the above-described satellite switching scenario. The non-interchangeable PCI satellite switching method may be a hard satellite switching method or a soft satellite switching method in a satellite switching method of a quasi-earth fixed cell. Furthermore, in the non-interchangeable PCI satellite switching method, satellites before and after satellite switching may be connected to the same base station. Furthermore, in the non-interchangeable PCI switching method, the PCI may be used identically before and after switching. Furthermore, in the non-interchangeable PCI switching method, the frequency for transmitting a synchronous signal block (SSB) may be used identically before and after switching. Here, the PCI may be a cell identifier that enables different cells to be distinguished. In addition, the SSB may include a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a physical broadcast channel (PBCH).

[0162] The following describes a non-replaceable PCI satellite switching scenario, but it may not be limited thereto and may be applicable to other scenarios. In addition, the non-replaceable PCI satellite switching scenario may be a satellite switch with re-synchronization scenario. For example, the non-replaceable PCI satellite switching scenario may be a satellite switch with re-synchronization scenario because the frequency for transmitting PCI and SSB in the same or similar area is the same as that of a satellite switch of a quasi-earth fixed cell. In addition, the non-replaceable PCI satellite switching scenario may not be limited to a specific name as a scenario under the conditions described above and may be referred to by other names. In other words, the non-replaceable satellite switching scenario may not be limited to a specific name and may be applied in a scenario that operates based on the above and may not be limited to a specific form. In the following, for the convenience of explanation, it may be referred to as a satellite switch with re-synchronization PCI satellite switching scenario.

[0163] Fig. 13 is a conceptual diagram showing a first embodiment of a non-alternative PCI (physical cell identifier) ​​satellite switching method.

[0164] Referring to FIG. 13, the first satellite (1310) and the second satellite (1320) may be orbiting satellites. In this case, the second satellite (1320) may be connected to the same gateway (1350) and / or base station (1360) as the first satellite (1310). Satellite switching may be performed from the first satellite (1310), which is the source satellite, to the second satellite (1320), which is the target satellite.

[0165] For example, a first satellite (1310) may provide services to terminals (1370) using a quasi-earth fixed cell (1330). As the first satellite (1310) moves, it may stop providing services to the terminals (1370) using the quasi-earth fixed cell (1330). Then, a second satellite (1320) may take over services to the terminals (1370) using the quasi-earth fixed cell (1340). In this way, the first satellite (1310) and the second satellite (1320) may perform hard satellite switching. At this time, the second satellite (1320) may be connected or connected to a gateway (1350) or base station (1360) to which the first satellite (1310) is already connected. Therefore, the second satellite (1320) can service the same service area as the first satellite (1310) previously serviced using a quasi-earth fixed cell (1340).

[0166] Accordingly, the satellite serving the terminals (1370) may be hard-switched from the first satellite (1310) to the second satellite (1320). Accordingly, after the satellite serving the terminals (1370) is switched from the first satellite (1310) to the second satellite (1320), the PCI, frequency, etc. may not change.

[0167] As another example, a first satellite (1310) may provide communication services to terminals (1350) using a quasi-Earth-stationary cell (1330). After switching, a second satellite (1320) may provide communication services to terminals (1350) using a quasi-Earth-stationary cell (1340). During the switching, both the first satellite (1310) and the second satellite (1320) may provide communication services to terminals (1350) simultaneously. Accordingly, during the switching, terminals (1350) may be located in a geographic area with two communication services.

[0168] In this soft satellite switching case, communication service by the target satellite can be provided before communication service by the source satellite is interrupted. Afterwards, communication service for the source satellite can be interrupted. In other words, communication service by both satellites can be maintained during the switching time. For example, if a first satellite (1310) is providing communication service in a cell area and is switched to a second satellite (1320) through satellite switching, the communication service of the second satellite (1320) can be provided before the communication service of the first satellite (1310) is interrupted, and the communication service of the first satellite (1310) can be interrupted after the communication service of the second satellite (1320) is provided. Such a non-switched PCI satellite switching scenario can be as shown in Table 7.

[0169] - In non-alternative PCI satellite switching, the cells provided by the two satellites can be quasi-earth fixed cells. - Non-alternative PCI satellite switching can be hard satellite switching or soft satellite switching. - In non-alternative PCI satellite switching, the feeder links before and after switching can be connected to the same base station. - In non-alternative PCI satellite switching, the frequencies transmitting SSB before and after switching can be the same. - In non-alternative PCI satellite switching, the PCI before and after switching can be the same.

[0170] The non-alternative PCI satellite switching method may not be a network-involved L3 (layer 3) handover (HO) method or an L3 conditional handover (CHO) method. For convenience of explanation, the handover (or conditional handover) may be described as (C)HO in the following. In addition, the cell that the terminal is connected to before (C)HO is referred to as the source cell, and the cell that the terminal wants to connect to after (C)HO is referred to as the target cell, but these names may not be limited. For example, when providing a service to a terminal through a quasi-earth fixed cell using an NGSO satellite, the satellite covering a given terrestrial area may continuously change. A terminal in a connected mode belonging to a quasi-earth fixed cell can generally perform an L3 handover or an L3 conditional handover when such a satellite is changed. However, in the non-alternative PCI method, a terminal in a connected mode may not perform an L3 handover or an L3 conditional handover. For example, based on a non-alternative PCI satellite switching scenario, a terminal operating in connected mode can overcome the disadvantages of (C)HO by not performing (C)HO. In other words, in a non-alternative PCI satellite switching method, a terminal operating in connected mode does not require RRC (radio resource control) signaling required for handover or conditional handover, thereby reducing signaling overhead. As a specific example, in the case of a handover in a quasi-terrestrial fixed cell, all terminals within the cell may perform handover almost simultaneously. As a result, RRC signaling may be overwhelmed in an instant. In other words, a handover storming phenomenon may occur. Moreover, the time interval between satellite switching in a quasi-terrestrial fixed cell may be short. Accordingly, the probability of handover failure may increase.However, a non-replaceable PCI satellite switching method can avoid such handover failures at the terminal. The non-replaceable PCI satellite switching method can also avoid random access channel (RACH) congestion. After switching, the terminal can pre-compensate for the uplink timing advance (TA) with the target satellite.

[0171] In such cases, the terminal may omit the random access (RA) required immediately after a handover or conditional handover to the target cell. This omission of the random access may be due to the fact that regular communication, even if not optimal, is possible within the acceptable TA range of the base station, even without TA alignment through RA. If the random access is omitted, the terminal can synchronize timing advance while performing regular communication after switching.

[0172] In the case of a handover in a quasi-terrestrial fixed cell, since all terminals within the cell perform a handover almost simultaneously, simultaneous random accesses may occur immediately after the handover. As a result, RACH capacity may be insufficient. This problem can be referred to as the RACH contention problem. The RACH contention problem can be avoided by omitting random access in the non-alternative PCI satellite switching method. If random access can be omitted in the non-alternative PCI satellite switching method, terminals in the quasi-terrestrial fixed cell can save power. Power can be saved because the terminals can avoid L3 (conditional) handovers or random accesses due to satellite movement in the quasi-terrestrial fixed cell.

[0173] For example, the non-replaceable PCI method could allow NTN operators to configure quasi-earth fixed cells using NGSO satellites. This would allow NTN operators to service specific areas of the Earth using the same base station, providing benefits such as flexibility and lower costs in NTN configuration.

[0174] Next, the present disclosure may consider system information (SI). System information may be information required for a terminal to connect to a base station and communicate with the connected base station. System information can be broadly divided into a master information block (MIB) and a system information block (SIB). The terminal can receive the MIB from the base station via a physical broadcast channel (PBCH). Furthermore, the terminal can receive the SIB from the base station via a physical downlink shared channel (PDSCH). The base station can periodically broadcast the SIB. The terminal can then receive the SIB periodically broadcast from the base station. The terminal can request the required SIB information from the base station. The base station can then receive a request for the required SIB information from the terminal. The base station can then transmit the requested information to the terminal. Accordingly, the terminal can receive the required SIB information from the base station. This method 2 may be an on-demand method.

[0175] SIBs can be divided into the form of SIBx according to the broadcast cycle, importance, or relevance. Here, x can be an integer greater than or equal to 1. Unlike TN cells, SIB19 can exist in NTN cells. The terminal can also distinguish whether it is a TN cell or an NTN cell based on the presence or absence of SIB19. Table 8 can represent SIB19. For example, Table 8 below can be SIB 19 information presented based on 3GPP Release 17, but is not limited thereto and can be applied to other versions as well.

[0176] -- ASN1START-- TAG-SIB19-STARTSIB19-r17 ::= SEQUENCE {ntn-Config-r17 NTN-Config-r17 OPTIONAL, -- Need Rt-Service-r17 INTEGER (0..549755813887) OPTIONAL, -- Need RreferenceLocation-r17 ReferenceLocation-r17 OPTIONAL, -- Need RdistanceThresh-r17 INTEGER(0..65525) OPTIONAL, -- Need Rntn-NeighCellConfigList-r17 NTN-NeighCellConfigList-r17 OPTIONAL, -- Need RlateNonCriticalExtension OCTET STRING OPTIONAL,...,[[ntn-NeighCellConfigListExt-v1720 NTN-NeighCellConfigList-r17 OPTIONAL -- Need R]]}NTN-NeighCellConfigList-r17 ::= SEQUENCE (SIZE(1..maxCellNTN-r17)) OF NTN-NeighCellConfig-r17NTN-NeighCellConfig-r17 ::= SEQUENCE {ntn-Config-r17 NTN-Config-r17 OPTIONAL, -- Need RcarrierFreq-r17 ARFCN-ValueNR OPTIONAL, -- Need RphysCellId-r17 PhysCellId OPTIONAL -- Need R}-- TAG-SIB19-STOP-- ASN1STOP

[0177] In a 3P NTN cell, a terminal can receive SIB19 from a satellite as described above. The description of each field in Table 8 can be as in Table 9.

[0178] -t-Service: When the current cell is an NTN quasi-terrestrial fixed cell, this may be time information about when the current cell's service will be interrupted. In other words, t-Service may be the cell interruption time, which may be the service termination time of the serving cell. This service termination time of the serving cell may be used for time-based measurement initiation of a terminal in idle mode or deactivated mode. Time-based measurement initiation may refer to the operation of the terminal to initiate measurement of other surrounding cells before the service termination time of the current serving cell received by the terminal. -referenceLocation: When the serving cell is an NTN quasi-terrestrial fixed cell (or an NTN terrestrial mobile cell in the case of 3GPP Release-18), this may be the reference location of the serving cell. Here, the reference location of the serving cell may be used for location-based measurement initiation of a terminal in idle mode or deactivated mode. Location-based measurement initiation may mean an operation of a terminal to initiate measurements of other neighboring cells until it is a threshold distance away from a reference location of a serving cell received by the terminal. -distanceThresh: This may be a threshold distance required for the terminal to initiate location-based measurements. A terminal in idle mode or inactive mode may initiate measurements of other neighboring cells until it is a threshold distance away from a reference location. -ntn-NeighCellConfigList: This may be a non-terrestrial network neighboring cell configuration list consisting of maxCellNTN non-terrestrial network cell configuration (i.e., NTN-Config) information elements (IEs), which are values ​​configured by the base station.Each of the non-terrestrial network cell settings in the list can be a non-terrestrial network cell setting of a neighbor cell of the current cell. maxCellNTN can be the maximum number of non-terrestrial cells and can be a positive integer. -NTN-Config: can be an IE configured as in Table 10 below, and each field can be as in Table 11.

[0179] For example, referring to Table 9, the NTN-related SIB may include NTN-config as NTN configuration information, and NTN-config may be an IE (information element) configured as in Table 10 below, and each field may be as in Table 11.

[0180] -- ASN1START-- TAG-NTN-CONFIG-STARTNTN-Config-r17 ::= SEQUENCE {epochTime-r17 EpochTime-r17 OPTIONAL, -- Need Rntn-UlSyncValidityDuration-r17 ENUMERATED{ s5, s10, s15, s20, s25, s30, s35,s40, s45, s50, s55, s60, s120, s180, s240, s900} OPTIONAL, -- Cond SIB19cellSpecificKoffset-r17 INTEGER(1..1023) OPTIONAL, -- Need Rkmac-r17 INTEGER(1..512) OPTIONAL, -- Need Rta-Info-r17 TA-Info-r17 OPTIONAL, -- Need Rntn-PolarizationDL-r17 ENUMERATED {rhcp,lhcp,linear} OPTIONAL, -- Need Rntn-PolarizationUL-r17 ENUMERATED {rhcp,lhcp,linear} OPTIONAL, -- Need RephemerisInfo-r17 EphemerisInfo-r17 OPTIONAL, -- Need Rta-Report-r17 ENUMERATED {enabled} OPTIONAL, -- Need R...}EpochTime-r17 ::= SEQUENCE {sfn-r17 INTEGER(0..1023),subFrameNR-r17 INTEGER(0..9)}TA-Info-r17 ::= SEQUENCE {ta-Common-r17 INTEGER(0..66485757),ta-CommonDrift-r17 INTEGER(-257303..257303) OPTIONAL, -- Need Rta-CommonDriftVariant-r17 INTEGER(0..28949) OPTIONAL -- Need R}-- TAG-NTN-CONFIG-STOP-- ASN1STOP

[0181] The description of each field in Table 10 may be as shown in Table 11 below.

[0182] - The epochTime field may be a field providing the epoch time of the NTN assistance information. - The ntn-UlSyncValidityDuration field may be a field providing the uplink synchronization validity period. - The cellSpecificKoffset field may be a field providing a cell-specific scheduling offset. Here, the cell-specific scheduling offset may be a scheduling offset value used for a modified timing relationship for the NTN. This cell-specific scheduling offset field may be omitted. Then, the terminal may assume the cell-specific scheduling offset to be 0. - The kmac field may be a field providing a network scheduling offset value provided by the network when the downlink and uplink frame timings are not aligned at the base station. If the kmac field is omitted, the terminal may assume the network scheduling offset value to be 0. - The ta-Info field may be a field providing uplink timing advance information used by the terminal to pre-compensate the uplink timing. The terminal can estimate the common TA in the NTN at time t by using the Taylor approximation as in the following mathematical expression 6 using the satellite's ephemeris information (ephemerisInfo), epoch time (epochTime), and the current time of the terminal. Here, the epoch time may be the epoch time when ta-Info is received. - Each of the ntn-PolarizationDL field and the ntn-PolarizationUL field may be a field for providing polarization information of the service downlink and uplink. - The ephemerisInfo field may be a field for providing the satellite ephemeris in the form of a position and velocity state vector or an orbit parameter format. The IE of ephemerisInfo may be as in Table 12.The value tag of SIB1 may not change due to a change in ephemerisInfo. The -ta-Report field may not be omitted and, if included, may be a field to provide that TA reporting is enabled during random access due to RRC (radio resource control) connection establishment or RRC connection resume.

[0183] In Table 11, support information can include all information related to serving and / or neighboring satellite ephemeris, uplink timing advance information, etc. This support information can be information contained in NTN-Config or SIB19 containing NTN-Config. In other words, the epoch time can be time information provided by NTN-Config through SIB or dedicated signaling. Therefore, the epoch time can change differently each time the terminal receives NTN support information. However, the value tag in SIB1 may not change due to a change in the epoch time.

[0184] Additionally, in Table 11, the uplink synchronization validity period may refer to the maximum time duration from the epoch time during which assistance information can be applied without the terminal acquiring new assistance information. This uplink synchronization validity period may be updated only when at least one of the epoch time, uplink timing advance, and satellite ephemeris is updated. However, a change in the uplink synchronization validity period may not change the value tag of SIB1. The satellite ephemeris information may be expressed as ephemerisInfo. And, the uplink timing advance information may be expressed as ta-Info.

[0185] Also, in Table 11, mathematical expression 6 can be as follows. Here, t can be a real number.

[0186]

[0187] Additionally, as an example, ephemerisInfo, which is orbit-related information included in NTN-config, may include satellite ephemeris information in the form of position and velocity state vectors or orbital parameters, as shown in Table 12.

[0188] -- ASN1START-- TAG-EPHEMERISINFO-STARTEphemerisInfo-r17 ::= CHOICE {positionVelocity-r17 PositionVelocity-r17,orbital-r17 Orbital-r17}PositionVelocity-r17 ::= SEQUENCE {positionX-r17 PositionStateVector-r17,positionY-r17 PositionStateVector-r17,positionZ-r17 PositionStateVector-r17,velocityVX-r17 VelocityStateVector-r17,velocityVY-r17 VelocityStateVector-r17,velocityVZ-r17 VelocityStateVector-r17}Orbital-r17 ::= SEQUENCE {semiMajorAxis-r17 INTEGER (0..8589934591),eccentricity-r17 INTEGER (0..1048575),periapsis-r17 INTEGER (0..268435455),longitude-r17 INTEGER (0..268435455),inclination-r17 INTEGER (-67108864..67108863),meanAnomaly-r17 INTEGER (0..268435455)}PositionStateVector-r17 ::= INTEGER (-33554432..33554431)VelocityStateVector-r17 ::= INTEGER (-131072..131071)-- TAG-EPHEMERISINFO-STOP-- ASN1STOP

[0189] Figure 14 is a conceptual diagram illustrating a first embodiment of a reference point, a common timing advance, and a terminal-specific timing advance. Referring to Figure 14, a common TA is a TA related to the time delay between a reference point and a satellite (1410) and may be common to all terminals within a cell. A terminal-specific TA is a TA related to the time delay between a satellite (1410) and a terminal (1420) and may have a value that may be different for each terminal within a cell. Here, the reference point may be a point where a downlink frame and an uplink frame are aligned.

[0190] The above-described pre-compensation may mean that the terminal derives a portion of the uplink TA in an open loop manner, and the terminal may determine the uplink TA by the method of the following mathematical expression 7.

[0191]

[0192] Here, N TA is a TA obtained by a closed loop method and may be a TA updated by a timing advance command MAC CE. And, N TA, offset The values ​​may be determined by the frequency used and the duplex method. The remaining common TA and terminal-specific TA may be values ​​derived from the support information contained in the system information received by the terminal using an open loop method and the location information and time information possessed by the terminal. The terminal deriving the common TA and terminal-specific TA may be referred to as pre-calibration.

[0193] Figure 15 is a conceptual diagram for explaining a synchronization signal block and beam sweeping operation in a wireless communication system.

[0194] Referring to FIG. 15, a method for selecting a downlink beam when a terminal communicates with a base station can be considered. For example, the terminal and the base station can determine a downlink beam for communication. Here, the initial selection of the downlink beam can be performed during the random access process of the initial access performed by the terminal to connect to the base station. The terminal can select a downlink beam during the random access process.

[0195] A base station (e.g., a gNB) can transmit a synchronization signal block (SSB) (1510) to a terminal via a beam that sweeps within an SSB burst. The terminal can select a beam to use for downlink transmission based on the SSB (1510) transmitted by the base station. Specifically, one SSB (1510) can be a resource unit used for transmitting a synchronization signal used to synchronize downlink. Here, the beam directions used for synchronization transmission in each synchronization signal block within one synchronization signal burst can be different from each other.

[0196] Each beam swept by the base station can be allocated and used for each synchronization signal block within a synchronization signal burst. The terminal can select an optimal synchronization signal block (e.g., a synchronization block having the largest RSRP (reference signal received power) estimated from the synchronization signal of the synchronization signal block) among the synchronization signal blocks within the synchronization signal burst. Thereafter, the terminal can transmit a random access message (e.g., MSG 1) to the base station using a random access resource (e.g., a random access channel occasion, RACH occasion) associated with the synchronization signal block.

[0197] The base station can receive MSG 1. And, the base station can identify the resource (e.g., RACH occasion) in which MSG 1 is received. Specifically, the base station can check which frequency-time resource was used for transmission of MSG 1 of the terminal, and thereby can recognize the beam selected by the terminal. Here, one random access resource (e.g., RACH occasion) is associated with a specific beam, and the base station can recognize the associated beam by identifying the resource (e.g., RACH occasion) in which MSG 1 is received.

[0198] Thereafter, the base station can transmit MSG 2 to the terminal in response to MSG 1. Here, the base station can transmit MSG 2 to the terminal using the downlink beam recognized through the resource (e.g., RACH occasion) in which MSG 1 was received. In addition, the base station can transmit the downlink signal to be transmitted to the terminal after MSG 2 through the above-described downlink beam.

[0199] Based on the above, a wireless communication system operating in NTN may have limitations in supporting non-replaceable PCI satellite switching scenarios for terminals. Specifically, terminal behavior based on 3GPP NTN technology may make it difficult for terminals to support non-replaceable PCI satellite switching scenarios.

[0200] Referring again to FIG. 10, in an existing wireless communication system, a satellite providing services to a terminal in connected mode may be switched from a first satellite to a second satellite. As the satellite switches from the first satellite to the second satellite, the uplink TA may become different. For example, in an L3 handover or L3 conditional handover, the terminal may pre-compensate for the uplink TA of the neighboring cell to be handed over. This pre-compensation may be possible because the terminal receives the neighboring cell configuration IE (i.e., NTN-NeighCellConfig IE) in the NTN neighboring cell configuration list in SIB19 of the current cell to which the terminal is connected.

[0201] In contrast, the non-alternative PCI satellite switching method may not be an L3 handover or conditional handover. Therefore, in existing wireless communication systems, even if the communication service of the first satellite is interrupted under a non-alternative PCI satellite switching scenario, the terminal may not perform any procedures related to an L3 handover or an L3 conditional handover. In other words, after the terminal switches from the first satellite to the second satellite, the pre-calibration at the terminal may mean using the values ​​of the SIB19 received via the first satellite, which is the source satellite before the switching, until the terminal receives SIB19 again from the second satellite.

[0202] In the above-described situation, the terminal can perform pre-calibration using NTN-related information received from the source satellite. Accordingly, the terminal can operate based on values ​​that are not suitable for the target satellite (i.e., the second satellite) using the existing common TA and terminal-specific TA until NTN-related system information is received from the target satellite (i.e., the second satellite) through satellite switching. In addition, the terminal can perform cell-specific K offset ,K macAnd since other NTN-related field values ​​also use the values ​​of the source satellite, they may use incorrect values ​​until new NTN-related system information is acquired from the second satellite. In other words, terminals operating on existing wireless communication systems may experience significant degradation in uplink transmission performance or failure of uplink transmission based on incorrect values ​​when satellites are switched based on a non-replacement PCI satellite switching scenario.

[0203] Below, considering the above-described points, an operating method in a non-replaceable PCI satellite switching scenario can be described. For example, based on a non-replaceable PCI satellite switching scenario, a terminal can obtain system information from a source satellite prior to satellite switching for communicating with a base station via a target satellite immediately after satellite switching. For example, the terminal can refer to the system information required for communicating with a base station via a target satellite as "system information required by the terminal immediately after switching." As another example, the terminal can refer to the system information required for communicating with a base station via a target satellite as "satellite switching-related application information."

[0204] Here, the system information required by the terminal immediately after switching may refer to the system information required when the terminal switches to a target satellite based on satellite switching and then communicates with the base station via the target satellite. This term may not be limited to this term, and other terms may be used. However, for convenience of explanation, the above-described system information may be referred to as the system information required by the terminal immediately after switching.

[0205] System information required by the terminal immediately after switching may be information required for TA pre-calibration related to the target satellite. The terminal can receive the system information required by the terminal immediately after switching via the service link provided by the source satellite prior to switching. Specifically, since the terminal must communicate with the base station via the service link provided by the target satellite immediately after satellite switching, the terminal can obtain the system information required by the terminal immediately after switching via the service link provided by the source satellite prior to satellite switching. Here, the system information required by the terminal immediately after switching may include the aforementioned TA pre-calibration information.

[0206] For example, a base station may periodically broadcast a SIB containing system information. A terminal may receive the SIB from the base station and obtain the necessary system information immediately after the switching required by the terminal. Alternatively, a terminal may request the base station for the necessary system information. The base station may receive a request for system information from the terminal and transmit the necessary system information to the terminal immediately after the requested switching. The terminal may receive the necessary system information from the base station immediately after the switching. The terminal may obtain the necessary system information immediately after the switching based on at least one of the above-described methods, and may not be limited to a specific form.

[0207] For example, system information required by a terminal immediately after switching may be included in a single SIB. For example, system information required by a terminal immediately after switching may be included in a single SIB. For example, system information required by a terminal immediately after switching may be included in an NTN-related SIB (e.g., SIB 19) and delivered to the terminal. In another example, system information required by a terminal immediately after switching may be divided and included in multiple SIBs, and may not be limited to a specific format.

[0208] The system information required by the terminal immediately after switching may be information included in the SIB. Alternatively, the system information required by the terminal immediately after switching may be information configured separately from the SIB. For example, the system information required by the terminal immediately after switching may be indicated through an indicator within a specific SIB. Here, the indicator within the specific SIB may indicate whether any cell information in the neighboring cell list contains the system information required by the terminal immediately after switching. For example, the indicator indicating which cell information in the neighboring cell list contains the system information required by the terminal immediately after switching may be a field or IE of the SIB. As a specific example, the indicator may indicate the PCI (physical cell ID) of the neighboring cell in the neighboring cell list. For example, the PCI may be physCellId.

[0209] As another example, the indicator may indicate a neighboring cell based on a neighboring cell index in a list of neighboring cells, where the index may be one of integer values ​​from 1, 2, …, maxCellNTN. As an example, the list of neighboring cells may be, but is not limited to, NTN-NeighCellConfigList or NTN-NeighCellConfigListExt.

[0210] In other words, an indicator within a SIB can indicate a specific neighboring cell within a neighboring cell list. Here, the entirety of the neighboring cell information indicated by the indicator within the SIB may be system information required by the terminal immediately after switching. As another example, a portion of the neighboring cell information indicated by the indicator within the SIB may be system information required by the terminal immediately after switching, and may not be limited to a specific format.

[0211] In addition, as an example, the above-described indicator may be included in the SIB only in the above-described non-alternative PCI satellite switching scenario. Therefore, the terminal can recognize that the NTN system operates based on the non-alternative PCI satellite switching scenario based on whether the indicator is included in the SIB. For example, the SIB may be an NTN-related SIB. More specifically, the SIB may be SIB 19. In other words, if the NTN-related SIB includes the indicator, the terminal can recognize that the NTN system operates based on the non-alternative PCI satellite switching scenario. On the other hand, if the NTN-related SIB does not include the indicator, the terminal can recognize that the NTN system operates based on a scenario other than the non-alternative PCI satellite switching scenario. In other words, whether it is a non-alternative PCI satellite switching scenario can be implicitly indicated based on whether the NTN-related SIB includes the indicator.

[0212] As another example, system information required by the terminal immediately after switching may be independently configured within a specific SIB. For example, the specific SIB may be an NTN-related SIB. As a more specific example, the specific SIB may be, but is not limited to, SIB 19. Here, the terminal may recognize that the NTN system operates based on a non-alternative PCI satellite switching scenario based on whether the system information required by the terminal immediately after the independently configured switching is included in the NTN-related SIB. For example, the SIB may be an NTN-related SIB. As a more specific example, the SIB may be SIB 19. In other words, if the system information required by the terminal immediately after the independently configured switching is included in the NTN-related SIB, the terminal may recognize that the NTN system operates based on a non-alternative PCI satellite switching scenario. On the other hand, if the NTN-related SIB does not include the system information required by the terminal immediately after the independently configured switching, the terminal may recognize that the NTN system operates based on a scenario other than the non-alternative PCI satellite switching scenario. In other words, whether it is a non-replacement PCI satellite switching scenario can be implicitly indicated by whether the NTN-related SIB includes the corresponding indicator.

[0213] For example, system information required by a terminal immediately after switching can be indicated via an indicator included in the SIB. The indicator can indicate that the system information required by the terminal immediately after switching is included in the information of any one cell included in the neighbor cell list within the SIB.

[0214] Figure 16 is a conceptual diagram illustrating a first embodiment of a method for indicating required system information using an indicator included in a SIB.

[0215] Referring to FIG. 16, an indicator (1611) indicating system information required for a terminal immediately after switching may be included in an SIB (1610). Specifically, the indicator (1611) may indicate that the system information required for a terminal immediately after switching is included in the information (1612, 1613, …) of a cell included in the neighbor cell list within the SIB (1610). For example, n in SIBn may be an integer indicating the index of the SIB.

[0216] The indicator can indicate which cell information in the neighboring cell list within the same SIB contains the system information necessary for the terminal immediately after switching. As a specific example, in FIG. 16, SIBn (1610) may be SIB 19. In other words, the terminal can recognize that one cell information in the neighboring cell list contains the system information necessary for the terminal immediately after switching through the indicator included in the same SIB.

[0217] Here, the terminal can receive SIBn (1610) before switching via the service link of the source satellite. In other words, the terminal can receive system information necessary for the terminal from immediately after switching, before switching, via the service link of the source satellite. Specifically, the terminal can receive SIBn before switching. The terminal can check the indicator in the SIBn and check the specific neighboring cell information indicated by the indicator from the neighboring cell list. The terminal can determine that all or part of the checked specific neighboring cell information is system information necessary for the terminal from immediately after switching. As another example, the system information necessary for the terminal from immediately after switching can be indicated via an indicator included in the SIB. The indicator can indicate that the system information necessary for the terminal from immediately after switching is included in the information of any cell in the neighboring cell list included in another SIB different from the corresponding SIB.

[0218] Figure 17 is a conceptual diagram illustrating a second embodiment of a method for indicating required system information using an indicator included in SIB.

[0219] Referring to FIG. 17, an indicator (1711) indicating system information necessary for the terminal immediately after switching may be included in the first SIB (SIBk) (1710). Here, the second SIB (SIBn) (1720) may include neighboring cell list information, and the indicator (1711) included in the first SIB (1710) may indicate that system information necessary for the terminal immediately after switching is included in any one cell information in the neighboring cell list (1721, 1722, ...) included in the second SIB (1720). For example, in SIBn and SIBk, k and n are integers indicating indices of SIBs and may be different values. In other words, the indicator may indicate whether system information necessary for the terminal immediately after switching is included in any one cell information in the neighboring cell list in another SIB other than the SIB including the indicator.

[0220] Specifically, the terminal can receive SIBk and SIBn before switching. In other words, the terminal can receive SIBk and SIBn through the service link of the source satellite before switching. Here, SIBk may be an SIB associated with SIBn, which includes the most up-to-date neighboring cell list. The terminal can check an indicator in SIBk and check specific neighboring cell information indicated by the indicator from the neighboring cell list in SIBn. The terminal can obtain all or part of the checked specific neighboring cell information as system information required by the terminal immediately after switching. As another example, the system information required by the terminal immediately after switching may be independently configured within the SIB. In other words, the system information required by the terminal immediately after switching may not be indicated through the above-described indicator, but may be configured individually.

[0221] Figure 18 is a conceptual diagram illustrating a first embodiment of a method for providing necessary system information immediately after switching independently from SIB.

[0222] Referring to FIG. 18, SIBn (1810) may include system information (1811) required by the terminal immediately after switching. In SIBn, n may be an integer representing the index of the SIB. In other words, the system information required by the terminal immediately after switching may not be indicated by an indicator and may be configured separately within the corresponding SIB. For example, the system information (1811) required by the terminal immediately after switching may be information required for TA pre-calibration of the target satellite. Accordingly, the system information (1811) required by the terminal immediately after switching may be configured with one or more fields within SIBn. Alternatively, the system information (1811) required by the terminal immediately after switching may be an information element (IE) within SIBn and may not be limited to a specific embodiment.

[0223] The terminal can receive the SIBn from the service link of the source satellite before switching. Then, the terminal can check the system information required for the terminal immediately after switching within the SIBn, and apply the checked switching information immediately after switching. In addition, as an example, the system information required for the terminal immediately after switching can be included in the SIB in the non-alternative PCI satellite switching scenario described above. Here, the SIB can be an NTN-related SIB. In other words, the terminal can determine whether the NTN system is operating based on the non-alternative PCI satellite switching scenario based on whether the system information required for the terminal immediately after switching exists in the NTN-related SIB. Specifically, if the system information required for the terminal immediately after switching exists in the NTN-related SIB, the terminal can recognize that the NTN system is operating based on the non-alternative PCI satellite switching scenario. On the other hand, if the system information required for the terminal immediately after switching does not exist in the NTN-related SIB, the terminal can recognize that the NTN system is operating based on a different scenario.

[0224] For example, the system information required by the terminal immediately after switching may be NTN configuration information (e.g., NTN-config) consisting of values ​​for the target satellite. As another example, the system information required by the terminal immediately after switching may be some fields of the NTN configuration information (e.g., NTN-config) or an IE consisting of some fields of the NTN configuration information (e.g., NTN-config). Here, some of the fields described above may be values ​​for the target satellite. As a specific example, some fields of the NTN configuration information (e.g., NTN-config) may include the fields of Table 13 as information required for TA pre-calibration related to the target satellite. Specifically, some fields of the NTN configuration information (e.g., NTN-config) may include an epochTime field providing information about epoch time, a ta-info field providing information related to TA, and an ephemerisInfo field providing information related to ephemeris.

[0225] epochTimeta-infoephemerisInfo

[0226] In addition, some fields of NTN configuration information (e.g., NTN-config) may include fields of Table 14, which are fields that include one or more information among the NTN configuration information (e.g., NTN-config) fields. Specifically, some fields of NTN configuration information (e.g., NTN-config) may include the ntn-UlSyncValidityDuration field for providing uplink synchronization validity period information in NTN, and the cell-specific K offset cellSpecificKoffset field to provide information, K macIt may include a kmac field for providing information, a ta-Report field for providing TA reporting information, and an ntn-PolarizationDL field or ntn-PolarizationUL field for providing NTN polarization information.

[0227] ntn-UlSyncValidityDurationcellSpecificKoffsetkmacta-Reportntn-PolarizationDL, ntn-PolarizationUL

[0228] In other words, the system information required by the terminal immediately after switching may include NTN configuration information (e.g., NTN-config) related to the target satellite or some fields of the NTN configuration information (e.g., NTN-config) and at least one of Tables 13 and 14, and may not be limited to a specific form. Here, the system information required by the terminal immediately after switching may further include information of Table 15 in relation to at least one of Tables 13 and 14 as NTN configuration information (e.g., NTN-config) related to the target satellite or some fields of the NTN configuration information (e.g., NTN-config). For example, Table 15 may be information on a start time or a length of time related to satellite switching. In other words, the system information required by the terminal immediately after switching may further include time information related to satellite switching.

[0229] - The time when the communication service of the source satellite is interrupted may be referred to as t-Service. - The time when the communication service of the target satellite begins may be referred to as t-Start. - The time interval between the time when the communication service of the target satellite begins and the time when the communication service of the source satellite is interrupted may be referred to as t-Gap.

[0230] For example, the terminal can apply system information required for the terminal immediately after switching to the target satellite, and perform operations and updates based thereon. Here, the system information required for the terminal immediately after switching may include ntn-UlSyncValidityDuration as described in Table 14 above, and ntn-UlSyncValidityDuration may also be applied to the terminal when the communication service of the target satellite is initiated immediately after switching to the target satellite. For example, ntn-UlSyncValidityDuration may indicate a period during which uplink synchronization is valid in the NTN system, and a timer may be operated based thereon. Accordingly, the terminal may start a timer according to ntn-UlSyncValidityDuration when the communication service of the target satellite is initiated immediately after switching to the target satellite, but is not limited to this embodiment. The terminal may operate based on a non-switchable PCI satellite switching scenario in the NTN system as described above. Here, the non-alternative PCI satellite switching can be performed based on hard satellite switching or soft satellite switching in a satellite switching scenario of a quasi-earth fixed cell, and the source satellite and the target satellite can be connected to the same base station so that the PCI (physical cell ID) can be used identically before and after switching, and the SSB frequency can be used identically before and after switching, which can be as shown in Table 7 described above. The terminal needs to recognize whether the system is operating in the non-alternative PCI satellite switching scenario in order to support system operation according to the non-alternative PCI satellite switching scenario.

[0231] Specifically, the terminal can recognize the non-alternative PCI satellite switching scenario through the presence of an indicator indicating system information required for the terminal immediately after switching. In other words, the terminal can recognize the presence of the indicator and recognize that it operates based on the non-alternative PCI satellite switching scenario when, based on FIG. 16, the indicator included in the same SIB indicates that the system information required for the terminal immediately after switching is included in information about one cell in the neighboring cell list, and when, based on FIG. 17, the indicator included in another SIB indicates that the system information required for the terminal immediately after switching is included in information about one cell in the neighboring cell list.

[0232] As another example, based on the above-described Figure 18, the terminal can recognize that it operates based on a non-alternative PCI satellite switching scenario if system information required by the terminal is independently configured in the SIB immediately after switching. In other words, the terminal can recognize that it operates based on a non-alternative PCI satellite switching scenario based on whether system information required by the terminal exists in the SIB immediately after independently configured switching.

[0233] As another example, the terminal may recognize that it is operating under a non-alternative PCI satellite switching scenario based on the presence or absence of a t-Gap associated with the start time of providing communication services on the target satellite. As another example, the terminal may recognize that it is operating under a non-alternative PCI satellite switching scenario based on the presence or absence of a t-Start associated with the start time of providing communication services on the target satellite.

[0234] For example, recognizing that a terminal is operating based on a non-replaceable PCI satellite switching scenario may mean that the terminal recognizes in advance that satellite switching is performed based on hard satellite switching or soft satellite switching, and may perform corresponding actions.

[0235] For example, when hard satellite switching is performed, the terminal may connect to the service link of the target satellite after the communication service provided by the source satellite has been discontinued. In other words, the terminal may not be connected to both satellites simultaneously. Since the TA may have different values ​​before and after satellite switching, failure to recognize the TA may hinder smooth communication. Therefore, the terminal needs to discontinue uplink transmission when the communication service provided by the source satellite ends. To this end, the terminal needs to recognize the termination time of the communication service provided by the source satellite.

[0236] Specifically, the terminal can recognize that satellite switching has occurred according to the non-replacement PCI satellite switching scenario based on the above, but the method by which the terminal recognizes the non-replacement PCI satellite switching scenario may not be limited to the above. Thereafter, the terminal can receive information about the time when the communication service of the source satellite ends through the communication service of the source satellite. For example, the time when the communication service of the source satellite ends may be the time designated by the t-service described above, but may not be limited thereto. The terminal can recognize the time when the communication service of the source satellite ends based on the above.

[0237] As another example, the terminal may recognize that a satellite switch occurs according to a non-replacement PCI satellite switching scenario based on the above, but the method by which the terminal recognizes the non-replacement PCI satellite switching scenario may not be limited to the above. Thereafter, the terminal may receive, through the source satellite, the time at which the ephemeris of the source satellite and other assistance information of the source satellite were acquired. Here, the time at which the ephemeris of the source satellite and other assistance information of the source satellite were acquired may be, but is not limited to, the time specified by epochTime. The terminal may receive, through the service link of the source satellite, information about the length of the validity period based on the time at which the ephemeris of the source satellite and other assistance information of the source satellite were acquired. As an example, the length of the validity period may be, but is not limited to, the time indicated by ntn-UlSyncValidityDuration. The terminal can recognize that the communication service of the source satellite is terminated when the validity period has elapsed based on the time at which the ephemeris of the source satellite and other assistance information of the source satellite were acquired. In other words, the terminal can recognize the termination time of the communication service of the source satellite. As a specific example, the terminal can recognize the termination time of the communication service of the source satellite based on "the time specified by epochTime + the time period specified by ntn-UlSyncValidityDuration", but may not be limited to the above embodiment.

[0238] Satellite switching based on a non-replaceable PCI satellite switching scenario may be a hard satellite switching scenario, as described above. Therefore, there may be a period of time during which the terminal cannot use both the source satellite's service link and the target satellite's service link. This time may be the satellite switching time. However, this term is for convenience of explanation and may not be limited to this term. For convenience of explanation, it may be described as the satellite switching time below.

[0239] Figure 19 is a conceptual diagram showing a first embodiment of satellite switching time based on hard satellite switching.

[0240] Referring to FIG. 19, during the satellite switching time period (1910), the terminal may not be able to communicate with the base station. In addition, if a communication service is provided by the target satellite, the terminal may apply pre-correction of the TA related to the target satellite when performing uplink transmission. Considering the above, the terminal may need to recognize the start time and end time of the satellite switching time period (1910). In other words, the terminal may need to recognize the time when the communication service of the source satellite ends and the time when the communication service of the target satellite starts. Here, the terminal may confirm the start time of the satellite switching time period (1910) period (i.e., the end time of the provision of the communication service of the source satellite) through the method of recognizing the end time of the communication service of the source satellite described above, but may not be limited to the above-described embodiment.

[0241] Additionally, the terminal may need to recognize the end time of the satellite switching time (1910) (i.e., the start time of the communication service provision of the target satellite). Specifically, based on the above, the terminal may operate based on the non-switched PCI satellite switching scenario and recognize the end time of the communication service provision of the source satellite.

[0242] Here, the terminal can receive the t-Gap time, which is defined as the time required for satellite switching, through the service link provided by the source satellite. The terminal can recognize the time required for satellite switching through "the time when the communication service of the source satellite ends + the t-Gap time described above." In other words, the terminal can recognize the time when the communication service of the target satellite begins to be provided. As another example, the terminal can recognize that it operates based on a non-switched PCI satellite switching scenario. Here, the terminal can receive t-Start time information, which is defined as the time when the communication service of the target satellite begins to be provided, through the service link of the source satellite, and thereby recognize the time when the communication service of the target satellite begins to be provided.

[0243] As another example, the terminal may recognize that it operates based on a non-switchable PCI satellite switching scenario. Here, if the system information that the terminal acquires from the service link provided by the source satellite does not include the t-Gap time or t-Start time information, the terminal may recognize the time when the communication service of the source satellite ends as the communication service start time of the target satellite. In other words, if there is no indication information about the communication service start time of the target satellite, the terminal may recognize the communication service end time of the source satellite as the communication service start time of the target satellite. Here, the terminal may acquire the t-Gap time or t-Start time described above from the base station. As an example, information about the t-Gap time or t-Start time may be included in the system information required by the terminal immediately after switching, as shown in Table 15. For example, the terminal can receive system information necessary for the terminal immediately after switching via the service link of the source satellite before satellite switching, and the t-Gap time and t-Start time can also be received via the service link of the source satellite before satellite switching.

[0244] When satellite switching occurs according to a non-alternative PCI satellite switching scenario, the terminal can perform communication with the base station by receiving the service link of the target satellite after the communication service of the source satellite is terminated, as described above. Here, the terminal can receive system information necessary for the terminal through the service link of the source satellite immediately after switching until the communication service of the source satellite is terminated. The terminal can recognize whether the non-alternative PCI satellite switching scenario is applied through the system information necessary for the terminal immediately after switching before receiving it, as described above.

[0245] The terminal can update system information related to the target satellite using system information required by the terminal from immediately after switching, received prior to satellite switching, after the start time of providing the target satellite's communication service. Specifically, the terminal can update some or all of the information in Table 16 using system information required by the terminal immediately after switching. In other words, the terminal can update target satellite-related information obtained through the service link of the source satellite after the start of providing the target satellite's communication service.

[0246] -NTN-Config part or all, that is, part or all of epochTime, ntn-UlSyncValidityDuration, cellSpecificKoffset, kmac, ta-info, ntn-PolarizationDL, ntn-PolarizationUL, ephmerisInfo, ta-Report -t-Service-referenceLocation-distanceThresh-ntn-NeighCellConfigList-ntn-NeighCellConfigListExt

[0247] Specifically, the terminal can determine a pre-compensated TA related to the target satellite using the system information required by the terminal immediately after switching, and can apply the TA to communication with the base station from the start of providing the communication service of the target satellite. Therefore, the terminal may not perform a separate random access to perform communication with the base station from the start of providing the communication service of the target satellite. For example, the random access may be a random access performed by the terminal to align an uplink TA for communication with the base station from the start of providing the communication service of the target satellite, but may not be limited thereto. In other words, the terminal may not perform a separate random access procedure when performing satellite switching from a source satellite to a target satellite, and thereby solve the RACH (random access channel) congestion problem by the random access procedure. More specifically, if the terminal can recognize the pre-compensated TA related to the target satellite even without performing a random access immediately after satellite switching, uplink transmission to the base station may be possible. Therefore, the terminal may not perform the procedure of matching the TA through random access.

[0248] The random access procedure may be a procedure to find the optimal TA in relation to the uplink TA and apply it to the uplink, but if pre-compensation of the TA is possible, uplink transmission to the target satellite may be possible. Thereafter, the terminal may align the TA within the TA error range through communication with the base station. Specifically, the terminal may transmit an uplink signal (e.g., a sounding reference signal (SRS)) to the base station through uplink transmission, and the base station may correct the TA based on the received signal and instruct the terminal. For example, the corrected TA may be instructed using a timing advance command (TAC) medium access control (MAC) command element (CE). The terminal may correct the TA based on the TA correction value information received from the base station, thereby performing smooth communication through the target satellite.

[0249] As another example, the terminal may cause a timer indicating the validity of system information to expire when switching satellites. Here, if the timer indicating the validity of system information expires (or is stopped), the terminal may recognize that uplink synchronization is lost. For example, if the terminal switches to a target satellite, existing system information may no longer be used, so the timer indicating the validity of system information may expire when the terminal switches to the target satellite. In other words, the terminal may stop the timer indicating the validity of system information when switching satellites. As a specific example, the timer may be a 3GPP T430 timer, but the present invention is not limited to this embodiment. As an example, the time at which the terminal expires (or stops) the timer indicating the validity of system information based on a satellite switch may be the time at which the source satellite terminates providing communication services. As another example, the time at which the terminal expires (or stops) the timer indicating the validity of system information based on satellite switching may be the time at which the target satellite begins providing communication services, but may not be limited to this embodiment.

[0250] For example, when a timer indicating the validity of system information expires (or is interrupted), the terminal may suspend an ongoing uplink transmission at the termination time of the communication service of the source satellite. Thereafter, the terminal may resume the suspended uplink transmission at the initiation time of the communication service of the target satellite. As a specific example, if uplink data exists in the uplink HARQ (hybrid automatic repeat request) buffer of the terminal, the terminal may not flush the buffer and may suspend it. Thereafter, the terminal may resume transmitting the uplink data in the uplink HARQ buffer at the initiation time of the communication service of the target satellite, thereby maintaining the uplink transmission even in the event of satellite switching.

[0251] As described above, when the terminal performs satellite switching based on the non-alternative PCI satellite switching scenario, the terminal performs pre-compensation using the system information required for the terminal for the uplink TA required for communication with the base station immediately after the start of provision of the communication service of the target satellite immediately after the satellite switching, and thus may not perform a random access procedure for adjusting the uplink TA. However, as described above, the terminal can select the downlink beam used by the base station during the random access process for performing the initial connection, but since the random access procedure is not performed in the non-alternative PCI satellite switching scenario, an operation for this may be required.

[0252] For example, a terminal may need to change the transmission beam used for the downlink of the service link (provided by the target satellite) immediately after satellite switching. Since the terminal does not perform random access after satellite switching, a method may be needed to reselect the transmission beam used for the downlink of the service link immediately after satellite switching.

[0253] Specifically, the terminal can select the transmission beam used for the downlink of the service link immediately after switching by utilizing the mapping relationship between the beam used immediately before satellite switching and the downlink transmission beam used immediately after switching. For example, the base station can recognize the mapping relationship between the transmission beam used for a specific terminal on the source satellite and the transmission beam used for the corresponding terminal on the target satellite before satellite switching. Thereafter, when satellite switching is performed, the base station can change the service link downlink transmission beam for each terminal by utilizing the mapping relationship it has identified.

[0254] As a more specific example, a terminal may receive a communication service through a downlink transmission beam having a beam index of 1 from a source satellite. Thereafter, when the terminal receives a communication service of a target terminal based on satellite switching, the terminal may receive the service through a downlink transmission beam having a beam index of 2 from the target satellite, and the above-described case may be an optimal beam selection. Here, beam index 1 from the source satellite and beam index 2 from the target satellite may have a mapping relationship. The base station may select (change) a downlink transmission beam based on the above-described mapping relationship when the provision of a communication service by the source satellite may be terminated and the provision of a communication service by the target satellite is initiated. In other words, when the base station selects a service link downlink transmission beam to be used by a specific terminal, the base station may select a service link downlink transmission beam of a specific terminal from the target satellite by considering the mapping relationship based on the service link downlink transmission beam of the specific terminal from the source satellite.

[0255] For example, the above-described mapping relationship may be determined in advance. As a specific example, it may be determined when a quasi-earth fixed cell to which a non-alternative PCI satellite switching scenario is applied is planned on the Earth's surface, but is not limited thereto. The base station or the network may select a downlink transmission beam according to the mapping relationship based on terminal location information obtained from the terminal immediately before the terminal's satellite switching. As another example, the base station or the network may select a downlink transmission beam according to the mapping relationship based on terminal location information obtained from the terminal immediately before the terminal's satellite switching and terminal location information obtained from the target satellite immediately after the satellite switching.

[0256] As another example, the mapping relationship may be obtained from operational information that the base station or network acquires while servicing the corresponding quasi-earth fixed cell, but may not be limited thereto. Furthermore, as an example, in a non-switched PCI satellite switching scenario, the terminal may receive the SSB of the service link provided by the target satellite after satellite switching. The terminal may synchronize the downlink through the received SSB and estimate the downlink received signal strength (e.g., RSRP). If the estimated downlink received signal strength is below a preset threshold, the terminal may perform an RRC connection re-establishment procedure, but may not be limited thereto. Here, the preset threshold may be a parameter configured by the base station and broadcast as system information, but is not limited thereto. As an example, the base station may configure different threshold values ​​for each of a plurality of terminals. Specifically, the base station may set threshold values ​​for each individual terminal through parameters for threshold value configuration included in RRC dedicated signaling, and may not be limited to a specific form.

[0257] As another example, a radio link fail (RLF) may occur after a terminal performs satellite switching. In other words, if a terminal detects an RLF, indicating that communication with the base station is impossible while using the service link provided by the target satellite after performing satellite switching based on a non-switched PCI satellite switching scenario, the terminal may perform an RRC connection re-establishment procedure.

[0258] As another example, a terminal may perform operations considering a time alignment timer (TAT) in a non-alternative PCI satellite switching scenario. The TAT may be a timer that a base station provides to the terminal to manage uplink synchronization (e.g., uplink timing advance). Here, uplink timing alignment may be achieved while the timer is maintained. The TAT may be a timer for the uplink synchronization validity time. The TAT may be set to a value through a dedicated signal for each terminal (i.e., UE-specific) so that it has a different value for each terminal. As another example, the TAT may be set through a SIB broadcast by the base station so that all terminals in a cell have the same value (i.e., cell-specific), but the present invention may not be limited thereto. Here, the TAT may operate independently of satellite switching. For example, the TAT may operate independently of a timer that indicates the validity of system information (e.g., a T430 timer). In other words, TAT may not be affected by non-replacement PCI satellite switching scenarios and may operate as before.

[0259] As another example, a terminal that supports non-replaceable PCI satellite switching may report to a base station that it supports non-replaceable PCI satellite switching. As a specific example, the terminal may report to the base station that it supports non-replaceable PCI satellite switching based on terminal capability information (UE capability information). As an example, the terminal may generate a terminal capability information message indicating that the terminal supports non-replaceable PCI satellite switching. More specifically, the base station may transmit a message inquiring about terminal capability information (UE capability enquiry) to the terminal, and the terminal may include information indicating whether non-replaceable PCI satellite switching is supported in the terminal capability information message in response thereto and report it to the base station (UE capability report), but the present invention is not limited to this embodiment.

[0260] For example, if the SIB obtained through the service link of the source satellite includes system information required by the terminal immediately after switching, the terminal can recognize a non-replacement PCI satellite switching scenario. In other words, the terminal can recognize a re-synchronization satellite switching scenario, as described above. Here, the system information required by the terminal immediately after switching may be a first field (or first parameter) in the SIB. As a specific example, the first field (or first parameter) may be a re-synchronization satellite switching parameter (e.g., SatSwitchWithReSync), but may not be limited thereto. Here, the terminal can recognize a non-replacement PCI satellite switching scenario if it receives an SIB including the first field (or first parameter) through the service link of the source satellite. In addition, the SIB may further include other parameters related to the NTN system. For example, the SIB may further include parameters included in Table 9, but may not be limited thereto. Here, the terminal can recognize the non-alternative PCI satellite switching scenario based on the first field (or first parameter) described above and other parameters related to the NTN system. As a specific example, the terminal can recognize the non-alternative PCI satellite switching scenario based on the first field (or first parameter) described above included in the corresponding SIB and the t-service field (or parameter) of Table 9, which is the satellite service interruption time, but the present invention may not be limited thereto.

[0261] As another example, the terminal can recognize that the PCI will not be changed in the cell if the first field (or the first parameter) in the SIB is included as system information required by the terminal immediately after switching. As a specific example, in the non-alternative PCI satellite switching scenario described above, hard satellite switching may be performed if the PCI is not changed in the cell, but this may not be limited thereto. In other words, if the first field (or the first parameter) in the SIB is included as system information required by the terminal immediately after switching, the PCI may not be changed in the cell, and soft satellite switching may be performed. As an example, although the above description is based on the case where hard satellite switching is performed in the non-alternative PCI satellite switching scenario, the same may be applied even if the PCI is not changed and soft satellite switching is performed.

[0262] In other words, in the NTN system, the operation for the case where the terminal obtains the system information required for the terminal immediately after switching through the service link of the source satellite may be applied equally even when the PCI is not changed and soft satellite switching is performed, and is not limited to a specific form. As another example, if the terminal receives the system information required for the terminal immediately after switching from the service link of the source satellite, the terminal may perform pre-calibration of the uplink TA for the service link of the target satellite without a random access procedure, and when the service link of the target satellite is initiated, the terminal may perform an operation and an update operation based on the corresponding TA. As an example, if the terminal receives the system information required for the terminal immediately after switching from the service link of the source satellite and then obtains random access indication information, the terminal may perform a random access procedure for the target satellite. In other words, if the terminal receives the system information required for the terminal immediately after switching from the service link of the source satellite, the terminal may not perform the random access procedure. However, if the base station indicates that the random access procedure needs to be performed, the terminal may perform the random access procedure based on the indication, and may not be limited to the above embodiment.

[0263] Fig. 20 is a flowchart showing a first embodiment of terminal operation in a satellite switching method in a wireless communication system.

[0264] Referring to FIG. 20, a terminal operating in an NTN system can be connected to a base station based on a service link of a source satellite (S2010). Here, the terminal can obtain target satellite-related information through the service link of the source satellite (S2020). For example, the target satellite-related information may be system information required by the terminal immediately after the above-described switching, but may not be limited thereto. Thereafter, satellite switching from the source satellite to the target satellite can be performed (S2030), and after the satellite switching to the target satellite is performed, the terminal can communicate with the target satellite based on the target satellite-related information (S2040).

[0265] Here, for example, if the terminal does not receive random access indication information, it can connect to the target satellite's service link without random access based on satellite switching. In other words, if the terminal receives necessary system information from the source satellite's service link immediately after switching, it can connect to the target satellite without random access and perform communication via the target satellite's service link.

[0266] Here, the above-described operation may be performed based on a non-alternative PCI satellite switching scenario. For example, in a non-alternative PCI method, a terminal may be connected to a base station based on a first cell provided by a source satellite. Then, after satellite switching, the terminal may be connected to the same base station based on a second cell provided by a target satellite. The first cell and the second cell may be quasi-earth fixed cells. Here, the PCI provided by the source satellite of the first cell and the PCI provided by the target satellite of the second cell may be the same. In addition, the frequency of the SSB that the terminal receives from the source satellite based on the first cell and the frequency of the SSB that the terminal receives from the target satellite based on the second cell may also be the same.

[0267] In addition, if the service link of the target satellite is connected after the communication service of the source satellite is interrupted based on satellite switching, the terminal may perform communication with the target satellite based on information related to the target satellite after switching to the target satellite based on satellite switching. In another example, if the service link of the target satellite is connected before the communication service of the source satellite is interrupted based on satellite switching, and if the communication service of the source satellite is interrupted after the service link of the target satellite is connected, the terminal may perform communication with the target satellite based on information related to the target satellite after switching to the target satellite. In addition, the target satellite-related information acquired by the terminal may include information applied after satellite switching of the target satellite, and the terminal may determine an uplink TA (timing advance) of the target satellite based on the information applied after satellite switching of the target satellite and apply it to communication with the target satellite. Here, the information applied after satellite switching of the target satellite may include NTN-config itself or some fields within NTN-config, as described above. For example, the application information after satellite switching of the target satellite may include at least one of epochTime, TA-info, ephemerisInfo, ntn-UlSyncValidityDuration, cellSpecificK_offset, Kmac, TA-Report, ntn-PolarizationDL, and ntn-PolarizationUL in NTN-config. As another example, the application information after satellite switching of the target satellite may include at least one of t-Service, t-Start, and t-Gap, which may be as described above.

[0268] In addition, the application information after the satellite switching of the target satellite may be configured as at least one field or IE (information element) within the SIB that the terminal acquires through the service link of the source satellite. In other words, the application information after the satellite switching of the target satellite may be independently configured within the SIB, which may be as described above. In addition, the terminal receives an NTN-related SIB, and the target-related information may be included in the NTN-related SIB. For example, if the first field exists in the NTN-related SIB, the terminal may determine that the satellite switching is performed based on a re-synchronization satellite switching scenario. In another example, if the first field and the second field exist in the NTN-related SIB, the terminal may determine that the satellite switching is performed based on a re-synchronization satellite switching scenario. Here, the first field may be SatSwitchWithReSync, and the second field may be a t-service field, but may not be limited thereto. In addition, if a first field may be present in the NTN-related SIB, and if the cell where the terminal is provided with service is a quasi-earth fixed cell, the terminal may determine that satellite switching is performed based on a re-synchronization satellite switching scenario. For example, in the re-synchronization satellite switching scenario, the source satellite and the target satellite may be connected to the same base station, the physical cell identifier (PCI) of the cell may be the same in the source satellite and the target satellite, and the frequency of the synchronization signal block (SSB) received by the terminal based on the cell may be the same. In addition, if there is uplink data in the hybrid automatic repeat request (HARQ) buffer based on the service link of the source satellite, the terminal may withhold the uplink data in the uplink HARQ buffer during the satellite switching process, and may resume the operation of transmitting the uplink data in the uplink HARQ buffer after switching to the target satellite.

[0269] The operations of the method according to the embodiments of the present disclosure can be implemented as a computer-readable program or code on a computer-readable recording medium. A computer-readable recording medium includes any type of recording device that stores information readable by a computer system. Furthermore, a computer-readable recording medium can be distributed across network-connected computer systems, allowing the computer-readable program or code to be stored and executed in a distributed manner.

[0270] Additionally, the computer-readable recording medium may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, etc. The program instructions may include not only machine language codes produced by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc.

[0271] While some aspects of the present disclosure have been described in the context of a device, they may also represent a description of a corresponding method, wherein a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method may also be described as a corresponding block or item or a feature of a corresponding device. Some or all of the method steps may be performed by (or using) a hardware device, such as, for example, a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, at least one or more of the most important method steps may be performed by such a device.

[0272] In embodiments, a programmable logic device (e.g., a field-programmable gate array) may be used to perform some or all of the functions of the methods described herein. In embodiments, the field-programmable gate array may operate in conjunction with a microprocessor to perform one of the methods described herein. In general, the methods are preferably performed by some hardware device.

[0273] Although the present disclosure has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the claims below.

Claims

1. As a terminal method, A step of acquiring target satellite related information from a source satellite; A step of performing satellite switching from the source satellite to the target satellite based on the target satellite-related information; and Comprising a step of performing communication with the target satellite based on the target satellite related information after performing the satellite switching, Terminal method.

2. In claim 1, The step of performing communication with the above target satellite is: A step of connecting to the target satellite without random access based on the target satellite-related information; and Comprising a step of performing communication with the target satellite based on the target satellite-related information, Terminal method.

3. In claim 1, The source satellite and the target satellite are connected to the same base station, The source satellite forms a first quasi-Earth fixed cell, and the target satellite forms a second quasi-Earth fixed cell, The PCI (physical cell identifier) ​​of the first quasi-terrestrial fixed cell and the PCI of the second quasi-terrestrial fixed cell are the same, The frequency of the first SSB (synchronization signal block) transmitted by the source satellite and the frequency of the second SSB transmitted by the target satellite are the same. Terminal method.

4. In claim 1, The step of performing communication with the above target satellite is: A step of interrupting the communication service of the source satellite based on the satellite switching; A step of connecting to the target satellite based on the target satellite-related information; and Based on the target satellite-related information, communication is performed through the target satellite and the service link of the target satellite. Terminal method.

5. In claim 1, The step of performing communication with the above target satellite is: A step of connecting to the target satellite based on the target satellite related information; A step in which communication is interrupted on the service link of the source satellite after connecting to the target satellite; and A step of performing communication through the target satellite and the service link of the target satellite based on the target satellite-related information, Terminal method.

6. In claim 1, The terminal determines the uplink TA (timing advance) of the target satellite based on the target satellite-related information, and applies the determined uplink TA to the communication with the target satellite. Terminal method.

7. In claim 1, The target satellite related information includes at least one of an epoch time, uplink timing advance information, ephemeris information, uplink synchronization validity period, cell-specific scheduling offset, network scheduling offset, timing advance report information, downlink polarization information, or uplink polarization information in non-terrestrial network configuration information for the target satellite. Terminal method.

8. In claim 1, The above target satellite-related information includes the time when the communication service of the source satellite is interrupted, The terminal does not empty the uplink HARQ (hybrid automatic repeat request) buffer and holds it when the communication service is interrupted at the time when the communication service of the source satellite is interrupted, and resumes the uplink HARQ operation to the target satellite when the step of performing communication with the target satellite starts. Terminal method.

9. In claim 1, The target satellite-related information is included in the SIB (system information block) that the terminal obtains from the source satellite. Terminal method.

10. In claim 1, If the target satellite-related information is included in the non-terrestrial network-related SIB, the terminal performs the satellite switching, and if the target satellite-related information is not included in the non-terrestrial network-related SIB, the terminal does not perform the satellite switching. Terminal method.

11. As a method of base station, A step of providing target satellite-related information to a terminal through a source satellite connected to the base station; A step of performing satellite switching from the source satellite to the target satellite at a time when the provision of communication service of the source satellite is interrupted; and A step of providing a communication service to the terminal through the target satellite after performing the above satellite switching is included. The base station provides the communication service to the terminal through the target satellite without performing a random access procedure between the target satellite and the terminal. Base station method.

12. In claim 11, The above target satellite related information is included in the SIB (system information block) transmitted to the terminal. Base station method.

13. In claim 11, The target satellite related information includes at least one of an epoch time, uplink timing advance information, ephemeris information, uplink synchronization validity period, cell-specific scheduling offset, network scheduling offset, timing advance report information, downlink polarization information, or uplink polarization information in non-terrestrial network configuration information for the target satellite. Base station method.

14. In claim 11, Instructing the terminal to perform the satellite switching by including the target satellite-related information in the non-terrestrial network-related SIB, and instructing the terminal not to perform the satellite switching by not including the target satellite-related information in the non-terrestrial network-related SIB. Base station method.

15. As a terminal, Includes a processor, The above processor is the terminal, Obtain target satellite related information from source satellite; Perform satellite switching from the source satellite to the target satellite based on the target satellite related information; and Causing communication with the target satellite based on the target satellite related information after performing the above satellite switching, Terminal.

16. In claim 15, In the step of performing communication with the target satellite based on the target satellite related information after performing the above satellite switching, the processor causes the terminal to, Connecting to the target satellite without random access based on the target satellite-related information; and Causing communication with the target satellite based on the target satellite-related information, Terminal.

17. In claim 15, In the step of performing communication with the target satellite based on the target satellite related information after performing the above satellite switching, the processor causes the terminal to, Based on the above satellite switching, the communication service of the source satellite is interrupted; Connected to the target satellite based on the target satellite related information; and Causing communication to be performed through the target satellite and the service link of the target satellite based on the target satellite-related information. Terminal.

18. In claim 15, The above target satellite-related information includes the time when the communication service of the source satellite is interrupted, The processor causes the terminal to hold an uplink HARQ (hybrid automatic repeat request) buffer without emptying it when the communication service is interrupted at the time when the communication service of the source satellite is interrupted, and to resume an uplink HARQ operation to the target satellite when a step of performing communication with the target satellite begins. Terminal.

19. In claim 15, The target satellite-related information is included in the SIB (system information block) that the terminal obtains from the source satellite. Terminal.

20. In claim 15, If the target satellite-related information is included in the non-terrestrial network-related SIB, the processor causes the terminal to perform the satellite switching, and if the target satellite-related information is not included in the non-terrestrial network-related SIB, the processor causes the terminal not to perform the satellite switching. Terminal.

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