How to perform cell reselection in a wireless communication system

Abstract

A method for a terminal to perform cell reselection based on a non-terrestrial network (NTN) in a wireless communication system may be provided, wherein the method for performing cell reselection may include the steps of: acquiring cell reselection condition information from a base station; moving from a first cell to a second cell based on mobility of the terminal; and acquiring measurement-related information for cell reselection from the second cell; and performing an NTN cell search if a specific condition for cell reselection is met based on the cell reselection condition information.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for measuring neighboring cells for cell reselection in a wireless communication system.

[0002] The present invention relates to a method for performing cell reselection based on non-terrestrial networks (NTN). [Background technology]

[0003] The International Telecommunication Union (ITU) is developing the International Mobile Telecommunication (IMT) framework and standards, and recently discussions for fifth-generation (5G) communications have been underway through a program called "IMT for 2020 and beyond."

[0004] To meet the requirements set out in "IMT for 2020 and beyond," the 3GPP (registered trademark) 3rd Generation Partnership Project (NR) New Radio (NR) system is currently discussing the support of various numerologies for time-frequency resource unit standards, taking into account various scenarios, service requirements, potential system compatibility, etc.

[0005] In addition, in new communication systems, discussions are underway on how to support seamless communication services at the service level for mobile terminals (e.g., vehicles / trains / ship-type terminals / personally owned smartphones) using not only terrestrial networks (TR) but also non-terrestrial networks (NON). Below, we will explain how to measure neighboring cells and perform cell reselection taking into account the mobility of terminals between NTN and TN. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a method and apparatus for performing cell reselection in a wireless communication system.

[0007] The present invention relates to a method for performing cell reselection in an NTN environment.

[0008] The present invention relates to a method for determining specific conditions for performing NTN cell reselection in an NTN environment.

[0009] The present invention relates to a method for determining specific conditions for performing TN cell reselection in an NTN environment. [Means for solving the problem]

[0010] According to one embodiment, a method for a terminal performing cell reselection based on a non-terrestrial network (NTN) in a wireless communication system may be provided, wherein the method for performing cell reselection may include the steps of: acquiring cell reselection condition information from a base station; moving from a first cell to a second cell based on mobility of the terminal; and acquiring measurement-related information for cell reselection from the second cell; and performing an NTN cell search if a specific condition for cell reselection is met based on the cell reselection condition information.

[0011] Furthermore, according to an embodiment, the cell reselection condition information may be set based on at least one of a tracking area code (TAC) list, a RAN (RAN area code) list, and a cell ID.

[0012] Furthermore, according to one embodiment, cell reselection condition information can be delivered to the terminal through a radio resource control (RRC) message.

[0013] Further, according to one embodiment, A method for a terminal to perform cell reselection based on non-terrestrial networks (NTN) in a wireless communication system, the method including the steps of: acquiring reference location information and distance threshold information for each of at least one or more cells from a base station; deriving distance condition information based on the reference location information and the distance threshold information for each of the at least one or more cells; and performing a TN cell search based on the current location of the terminal and the distance condition information.

[0014] Furthermore, according to one embodiment, the reference location information and distance threshold information for each of the at least one or more cells may be included in the frequency information configured for each of the at least one or more cells.

[0015] Furthermore, according to one embodiment, at least one of the cells may be a TN cell or an NTN cell.

[0016] The above briefly summarized features of the present disclosure are merely exemplary embodiments of the following detailed description of the present disclosure and are not intended to limit the scope of the present disclosure. [Effects of the Invention]

[0017] SUMMARY OF THE INVENTION The present disclosure provides a method and apparatus for performing cell reselection in a wireless communication system.

[0018] According to the present disclosure, a method for performing cell reselection in an NTN environment can be provided.

[0019] According to the present disclosure, a method for determining specific conditions for performing NTN cell reselection in an NTN environment can be provided.

[0020] According to the present disclosure, a method for determining specific conditions for performing TN cell reselection in an NTN environment can be provided.

[0021] The effects obtained by the present disclosure are not limited to the effects described above, and other effects not mentioned will be clearly understood by those having ordinary skill in the art to which the present disclosure pertains from the following description. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram for explaining an NR frame structure to which the present disclosure can be applied. [Figure 2] FIG. 2 is a diagram illustrating an NR resource structure to which the present disclosure may be applied. [Figure 3] FIG. 3 is a diagram illustrating an NTN including transparent satellites to which the present disclosure may be applied. [Figure 4] FIG. 4 is a diagram illustrating an NTN including regenerative satellites without inter-satellite links (ISLs) to which the present disclosure may be applied. [Figure 5] FIG. 5 is a diagram illustrating an NTN including a regenerative satellite with an ISL to which the present disclosure can be applied. [Figure 6] FIG. 6 is a diagram illustrating a user plane (UP) protocol stack structure in an NTN including a transparent satellite to which the present disclosure can be applied. [Figure 7] FIG. 7 is a diagram illustrating a control plane (CP) protocol stack structure in an NTN including a transparent satellite to which the present disclosure can be applied. [Figure 8] FIG. 8 is a diagram illustrating a timing advance calculation method to which the present disclosure can be applied. [Figure 9] FIG. 9 is a diagram illustrating an earth fixed cell scenario to which the present disclosure may be applied. [Figure 10] FIG. 10 is a diagram illustrating an earth moving cell scenario to which the present disclosure may be applied. [Figure 11] FIG. 11 is a diagram illustrating a method for mapping PCI to satellite beams to which the present disclosure may be applied. [Figure 12] FIG. 12 is a diagram showing a method in which a satellite to which the present disclosure is applicable covers multiple TAs (tracking areas). [Figure 13] FIG. 13 is a diagram illustrating a method for measuring a TN cell in an NTN environment that is applicable to the present disclosure. [Figure 14] FIG. 14 is a diagram showing an overlapping environment of a TN cell and an NTN cell applicable to the present disclosure. [Figure 15] FIG. 15 is a diagram showing an environment in which a TN cell and an NTN cell are superimposed, which is applicable to the present disclosure. [Figure 16] FIG. 16 illustrates a method for performing TAC list-based measurements applicable to the present disclosure. [Figure 17] FIG. 17 illustrates a TAC list-based NTN cell measurement signaling procedure applicable to the present disclosure. [Figure 18] FIG. 18 illustrates a method for performing a cell list-based measurement procedure applicable to the present disclosure. [Figure 19] Figure 19 illustrates a cell list based NTN cell measurement signaling procedure applicable to the present disclosure. Figure 19 illustrates a new timer to which the present disclosure can be applied. [Figure 20] FIG. 20 is a diagram illustrating a method for performing measurements based on RAC (RAN area code) applicable to the present disclosure. [Figure 21] FIG. 21 is a diagram illustrating a method for performing measurements based on RAC (RAN area code) applicable to the present disclosure. [Figure 22] FIG. 22 illustrates a RAC list-based NTN cell measurement signaling procedure applicable to the present disclosure. [Figure 23] FIG. 23 illustrates a method for performing measurements based on TAC, cell and / or RAC lists applicable to the present disclosure. [Figure 24] FIG. 24 illustrates an NTN cell measurement signaling procedure based on TAC, cell, and / or RAC lists applicable to the present disclosure. [Figure 25]FIG. 25 is a diagram showing an SSB configuration applicable to the present disclosure. [Figure 26] FIG. 26 is a diagram illustrating an SMTC window configuration configured in a network for specific frequency measurements applicable to the present disclosure. [Figure 27] 27 is a diagram illustrating a method for performing a cell search based on a reference location of a neighboring TN cell applicable to the present disclosure. Referring to FIG. 27, the terminal [Figure 28] 28 is a diagram showing a TN cell configuration applicable to the present disclosure. As described above, information about TN neighboring cells and information for cell reselection may be associated with each other. As an example, [Figure 29] FIG. 29 is a diagram showing the reference position of an NTN cell applicable to the present disclosure. [Figure 30] FIG. 30 is a flowchart illustrating a method for performing a conditional NTN cell search applicable to the present disclosure. [Figure 31] FIG. 31 is a flowchart illustrating a method for performing a conditional TN cell search to which the present disclosure may be applied. [Figure 32] FIG. 32 is a diagram showing the configuration of an apparatus to which the present disclosure can be applied. BEST MODE FOR CARRYING OUT THE INVENTION

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present disclosure will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily implement the present disclosure. However, the present disclosure may be embodied in various different forms and is not limited to the embodiments described herein.

[0024] In describing embodiments of the present disclosure, if it is determined that a detailed description of a known configuration or function would obscure the gist of the present disclosure, the detailed description will be omitted. In addition, in the drawings, parts that are not related to the description of the present disclosure will be omitted, and similar parts will be designated by similar reference numerals.

[0025] In this disclosure, when a component is said to be "coupled," "coupled," or "connected" to another component, this refers not only to a direct connection, but also to an indirect connection where there is another component between them. Furthermore, when a component is said to "include" or "have" another component, this does not exclude the other component, but means that the component may further include the other component, unless otherwise specified.

[0026] In this disclosure, terms such as first and second are used only to distinguish one component from another, and do not limit the order or importance of the components unless otherwise specified. Therefore, within the scope of this disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

[0027] In this disclosure, components that are distinguished from one another are used to clearly describe the characteristics of each component and do not necessarily mean that the components are separate. That is, multiple components may be integrated into a single hardware or software unit, or a single component may be distributed into multiple hardware or software units. Therefore, even if not otherwise specified, such integrated or distributed embodiments are also included within the scope of this disclosure.

[0028] In this disclosure, the components described in various embodiments are not necessarily essential components, and some may be optional components. Therefore, an embodiment consisting of a subset of the components described in one embodiment is also included in the scope of this disclosure. Note that an embodiment including other components in addition to the components described in various embodiments is also included in the scope of this disclosure.

[0029] The present disclosure describes a wireless communication network, and operations performed in the wireless communication network may be performed in a process of controlling the network and transmitting or receiving signals by a system (e.g., a base station) that manages the wireless communication network, or in a process of transmitting or receiving signals by a terminal coupled to the wireless network.

[0030] It is apparent that various operations performed for communication with a terminal in a network consisting of multiple network nodes including a base station may be performed by the base station or other network nodes other than the base station. The term "base station (BS)" may be replaced with terms such as fixed station, Node B, eNodeB (eNB), ng-eNB, gNodeB (gNB), access point (AP), etc. Furthermore, the term "terminal" may be replaced with terms such as user equipment (UE), mobile station (MS), mobile subscriber station (MSS), subscriber station (SS), non-AP station (non-AP STA), etc.

[0031] In this disclosure, transmitting or receiving a channel includes transmitting or receiving information or signals through the channel. For example, transmitting a control channel means transmitting control information or signals through the control channel. Similarly, transmitting a data channel means transmitting data information or signals through the data channel.

[0032] In the following description, the term NR (New Radio) system is used to distinguish the system to which various examples of the present disclosure are applied from existing systems, but the scope of the present disclosure is not limited by these terms.

[0033] The NR system supports various subcarrier spacings (SCS) taking into account various scenarios, service requirements, and potential system compatibility. The NR system can also support the transmission of physical signals / channels through multiple beams to overcome adverse channel conditions such as high path loss, phase noise, and frequency offset that occur at high carrier frequencies. This allows the NR system to support applications such as enhanced Mobile Broadband (eMBB), massive Machine Type Communications (mMTC) / ultra Machine Type Communications (uMTC), and Ultra Reliable and Low Latency Communications (URLLC).

[0034] Hereinafter, 5G mobile communication technology may be defined to include not only the NR system but also the existing LTE-A (Long Term Evolution-Advanced) and LTE (Long Term Evolution) systems. That is, 5G communication may include not only the newly defined NR system but also technologies that operate in consideration of backward compatibility with previous systems. Therefore, the 5G mobile communication described below may include technologies that operate based on the NR system and technologies that operate based on previous systems (e.g., LTE-A, LTE), and is not limited to a specific system.

[0035] First, a brief description will be given of the physical resource structure of the NR system to which the present invention is applied.

[0036] FIG. 1 is a diagram for explaining an NR frame structure to which the present disclosure can be applied.

[0037] The basic unit of time domain in NR is T c =1 / (Δf max N f ) and Δf max =480 10 3 and N f = 4096, whereas the time domain base unit in LTE is Ts = 1 / (Δf ref N f,ref ) and Δf ref =15 10 3 and N f,ref = 2048. The constant for the multiple relationship between the base unit of NR time and the base unit of LTE time is κ = T s / T c =64.

[0038] Referring to FIG. 1, the time structure of a frame for downlink / uplink (DL / UL) transmission is T f =(Δf max N f / 100)·T s = 10 ms, where one frame is T sf =(Δf max N f / 1000)·T s The number of consecutive OFDM symbols in each subframe is N subframe,u symb =N slot symb N subframe,u slot Alternatively, each frame may be divided into two half frames of the same size, with half frame 1 consisting of subframes 0-4 and half frame 2 consisting of subframes 5-9.

[0039] N TA denotes the timing advance (TA) between the downlink (DL) and the uplink (UL), where the transmission timing of the uplink transmission frame i is determined based on the downlink reception timing at the terminal according to the following Equation 1:

[0040]

number

[0041] FIG. 2 is a diagram illustrating an NR resource structure to which the present disclosure may be applied.

[0042] The resource elements (REs) in the resource grid can be indexed by each subcarrier spacing, where one resource grid can be generated for each antenna port and each subcarrier spacing, and uplink and downlink transmission and reception can be performed based on the resource grid.

[0043] In the frequency domain, one resource block (RB) consists of 12 REs, and an index (n PRB ) can be configured. The index for the RB can be used within a specific frequency band or system bandwidth. The index for the RB can be defined as in Equation 2 below. Here, N RB sc denotes the number of subcarriers per RB, and k denotes the subcarrier index.

[0044]

number

[0045] New pneumatics for NR systems that support multiple SCSs can operate in frequency ranges or carriers such as below 3 GHz, 3 GHz-6 GHz, 6 GHz-52.6 GHz, or above 52.6 GHz, solving the problem of not being able to use wide bandwidths in frequency ranges or carriers such as 700 MHz or 2 GHz.

[0046] Table 1 below shows examples of pneumoradio supported by the NR system.

[0047] [Table 1]

[0048] Referring to Table 1, the neural network parameters can be defined based on the subcarrier spacing (SCS), cyclic prefix (CP) length, and number of OFDM symbols per slot used in an Orthogonal Frequency Division Multiplexing (OFDM) system. These values ​​can be provided to the UE through upper layer parameters DL-BWP-mu and DL-BWP-cp for the downlink and through upper layer parameters UL-BWP-mu and UL-BWP-cp for the uplink.

[0049] In Table 1, when the subcarrier spacing setting index (u) is 2, the subcarrier spacing (Δf) is 60 kHz, and normal CP and extended CP can be applied. In other cases, only normal CP can be applied.

[0050] A normal slot can be defined as a basic time unit used to transmit one piece of data and control information in an NR system. The length of a normal slot can be basically set to 14 OFDM symbols. Furthermore, unlike a slot, a subframe has an absolute time length corresponding to 1 ms in an NR system and can be used as a reference time for the length of other time intervals. Here, for coexistence or backward compatibility between LTE and NR systems, a time interval similar to an LTE subframe may be required in the NR standard.

[0051] For example, in LTE, data may be transmitted based on a transmission time interval (TTI), which is a unit of time, and the TTI may be set in units of one or more subframes. Here, in LTE, one subframe may be set to 1 ms and may include 14 OFDM symbols (or 12 OFDM symbols).

[0052] Furthermore, non-slots can be defined in NR. A non-slot may refer to a slot having a number of symbols at least one smaller than that of a normal slot. For example, when providing low latency, such as in a URLLC service, the latency can be reduced by using a non-slot having a number of symbols smaller than that of a normal slot. Here, the number of OFDM symbols included in a non-slot can be determined taking into account the frequency range. For example, in a frequency range of 6 GHz or higher, a non-slot having a length of one OFDM symbol can be considered. As a further example, the number of OFDM symbols defining a non-slot can include at least two OFDM symbols. Here, the range of the number of OFDM symbols included in a non-slot can be set as the length of a mini-slot up to a predetermined length (e.g., the normal slot length minus 1). However, as a non-slot standard, the number of OFDM symbols may be limited to, but not limited to, 2, 4, or 7 symbols.

[0053] For example, in unlicensed bands below 6 GHz, subcarrier spacing where u is 1 and 2 can be used, and in unlicensed bands above 6 GHz, subcarrier spacing where u is 3 and 4 can be used. For example, when u is 4, it can be used for SSB (Synchronization Signal Block).

[0054] [Table 2]

[0055] Table 2 shows the number of OFDM symbols per slot (N) for normal CP, depending on the subcarrier spacing setting (u). slot symb ), number of slots per frame (N frame,u slot ), the number of slots per subframe (N subframe,u slot) Table 2 shows the above values ​​based on a normal slot having 14 OFDM symbols.

[0056] [Table 3]

[0057] Table 3 shows the number of slots per frame and the number of slots per subframe when extended CP is applied (i.e., when u is 2 and the subcarrier spacing is 60 kHz), based on a normal slot with 12 OFDM symbols per slot.

[0058] As mentioned above, one subframe may correspond to 1 ms on the time axis. Furthermore, one slot may correspond to 14 symbols on the time axis. For example, one slot may correspond to 7 symbols on the time axis. Therefore, the number of slots and symbols that can be considered within 10 ms, which corresponds to one radio frame, can be set differently. Table 4 shows the number of slots and symbols according to each SCS. In Table 4, the 480 kHz SCS may not be considered, but is not limited to these examples.

[0059] [Table 4]

[0060] For example, in an existing wireless communication system, communication can be performed based on a terrestrial network consisting of a terminal located on the ground and a base station located on the ground. The terminal can connect to the network wirelessly. Here, when the terminal moves, the terminal can continuously receive the same service through another base station in the terrestrial network. After connecting to the network, the terminal can connect to a specific service server through another wired or internet network. Furthermore, the terminal can receive a service that connects with another terminal via wired or wireless communication through the network.

[0061] However, new wireless communication systems can support terminal communications not only through terrestrial networks but also through non-terrestrial networks (NTNs). Here, NTNs can refer to networks or portions of networks that use airborne or spaceborne mobile objects equipped with base stations or relay devices. For example, NTNs can support terminal-to-terminal communications services based on satellites equipped with communications capabilities in low Earth orbit (LEO) and geostationary Earth orbit (GEO). For another example, NTNs can support terminal-to-terminal communications services based on aircraft equipped with communications capabilities within unmanned aerial systems (UAS), but this is not a limitation.

[0062] In the following description, terrestrial networks (TN) will be distinguished from non-terrestrial networks (NTN). That is, in existing communication systems, only terrestrial networks exist, so there is no need to distinguish between them. However, in the following description, NTN and TN will be distinguished as communication systems that enable terminal-to-terminal communication based on NTN, and a method for supporting terminal-to-terminal communication services based on NTN will also be described.

[0063] As an example, but not limited to, wireless communication services between terrestrial base stations and wireless terminals or between mobile base stations are described as mobile services. Furthermore, communication between mobile terrestrial base stations and at least one or more space base stations may be mobile satellite services. Furthermore, wireless communication services between mobile terrestrial base stations and space base stations, or between mobile terrestrial base stations via at least one or more space base stations, may also be mobile satellite services.

[0064] The following describes a method for performing communications based on a wireless communication system that supports both mobile services and mobile satellite services. For example, NTN-related technologies have been introduced specifically for satellite communications. However, NTN can also be introduced in TN communication systems (e.g., 5G systems) to operate like TN. Here, a terminal can simultaneously support NTN and TN. For terminals that simultaneously support NTN and TN, a wireless communication system may require specific technology for NTN in addition to the radio access technologies (RATs) LTE (long-term evolution) and NR (new radio). A method for achieving this is described below. For example, the following may be definitions of the terms related to NTN and TN.

[0065] Non-terrestrial networks (NTN): A network or part of a network using airborne or spaceborne mobile vehicles equipped with base stations or relay devices for communication

[0066] NTN Gateway: A terrestrial base station or gateway located on the ground and equipped with sufficient radio connectivity to connect to a satellite. In general, an NTN gateway can be a transport network layer node (TNL).

[0067] Feeder link: Radio link between the NTN Gateway and the satellite

[0068] Geostationary Earth orbit (GEO): A circular orbit 35,786 km above the Earth's equator that coincides with the Earth's rotation. An object or satellite in this orbit revolves around the Earth at the same period as the Earth's rotation. Therefore, when observed from Earth, it appears to be in a fixed, motionless position.

[0069] Low Earth Orbit (LEO): Orbits between 300km and 1500km above the ground

[0070] Medium Earth Orbit (MEO): Orbits between LEO and GEO

[0071] Unmanned Aircraft Systems (UAS): Generally, the system operates within a range of 8km to 50km above the ground and may include High Altitude Platforms (HAPs).Unmanned aerial systems may include at least one of Tethered UAS (TUA), Lighter Than Air UAS (LTA), and Heavier Than Air UAS (HTA) systems.

[0072] Minimum Elevation angle: The minimum angle required for a ground terminal to point towards an airborne satellite or UAS base station.

[0073] Mobile Services: Wireless communication services between terrestrial base stations and wireless terminals or between mobile base stations

[0074] Mobile Satellite Services: It may be a wireless communication service between a mobile terrestrial base station and one or more space base stations, or between a mobile terrestrial base station and a space base station, or between mobile terrestrial base stations through one or more space base stations.

[0075] Non-Geostationary Satellites: These may be satellites in LEO and MEO orbits, which orbit the Earth with a period between about 1.5 hours and 10 hours.

[0076] On Board Processing: Digital processing of uplink RF signals onboard satellites or non-terrestrial equipment

[0077] Transparent payload: This can mean changing the carrier frequency of an uplink RF signal, filtering and amplifying it before transmitting it over the downlink.

[0078] Regenerative payload: The uplink RF signal is modified and amplified before transmission over the downlink, and the signal modification may include digital processing such as decoding, demodulation, remodulation, re-encoding, and filtering.

[0079] Onboard NTN base station (On board NTN gNB): It can refer to an onboard satellite in which a base station (gNB) is implemented in a regenerative payload structure.

[0080] On-ground NTN base station (On ground NTN gNB): A terrestrial base station (gNB) realized with a transparent payload structure

[0081] One-way latency: The time it takes to travel from a wireless terminal to a shared data network or from the shared data network to a wireless terminal in a wireless communication system.

[0082] Round Trip Delay (RTD): This may be the time it takes for a signal to travel from a wireless terminal to an NTN gateway, or from an NTN gateway to a wireless terminal, and then return. At this time, the returning signal may have a different form or message than the signal.

[0083] Satellite: It may be a spaceborne vehicle equipped with a wireless communication transceiver capable of supporting a transparent payload or a regenerative payload, and may generally be located in a LEO, MEO, or GEO orbit.

[0084] Satellite beam: The beam generated by the onboard satellite antenna

[0085] Service link: Radio link between satellite and terminal (UE)

[0086] User Connectivity: Capability to set up and maintain data / voice / video transmission between the network and the terminal

[0087] User Throughput: Data transmission rate provided to the device

[0088] FIG. 3 is a diagram illustrating an NTN including transparent satellites to which the present disclosure may be applied.

[0089] Referring to Figure 3, the terminals included in the NTN may include terrestrial network terminals. For example, the NTN and TN terminals may include manned or unmanned vehicles such as ships, trains, buses, or airplanes, and are not limited to a specific form. Referring to Figure 3, transparent satellite payloads generated through a network including transparent satellites may be realized in a manner corresponding to an RF repeater.

[0090] More specifically, a network including transparent satellites can perform frequency switching and amplification on received radio signals in both uplink and downlink directions, and transmit the radio signals. Thus, the satellites can perform the function of relaying the NR-Uu radio interface, which includes both feeder links and service links, as described below.

[0091] As another example, referring to FIG. 3, a feeder link satellite radio interface (SRI) may be included in the NR-Uu interface. That is, the satellite may not be the end of the NR-Uu interface. Here, the NTN gateway may support all functions necessary to transmit signals defined in the NR-Uu interface. As an example, other transparent satellites may be connected to the same terrestrial base station. That is, a configuration in which multiple transparent satellites are connected to one terrestrial base station may also be possible. The base station may be an eNB or a gNB, but is not limited to a specific form.

[0092] FIG. 4 is a diagram illustrating an NTN including regenerative satellites without inter-satellite links (ISLs) to which the present disclosure may be applied.

[0093] Referring to FIG. 4, the NTN may include a regenerative satellite. Here, the regenerative satellite may mean that a base station function is included within the satellite. For example, a regenerative satellite payload generated through a network including the regenerative satellite may be realized in a manner that regenerates a signal received from the ground.

[0094] More specifically, the regenerating satellite can receive signals from the ground based on the NR-Uu radio interface on the service link between the terminal and the satellite. As another example, the regenerating satellite can receive signals from the ground through an SRI (Satellite Radio Interface) on the feeder link between the NTN gateway. Here, the SRI (Satellite Radio Interface) can be defined as the transport layer between the satellite and the NTN gateway. The transport layer can refer to the transport layer among the layers defined as the OSI 7 layer. That is, based on the regenerating satellite, the signals from the ground can be transformed based on digital processing such as, but not limited to, decoding, demodulation, remodulation, re-encoding, and filtering.

[0095] FIG. 5 is a diagram illustrating an NTN including a regenerative satellite with an ISL to which the present disclosure can be applied.

[0096] Referring to Figure 5, the ISL can be defined in the transport layer. As another example, the ISL can be defined as a radio interface or a visible light interface, and is not limited to a specific embodiment. Here, the NTN gateway can support all functions of the transport protocol. Furthermore, each regenerative satellite can be a base station, and multiple regenerative satellites can be connected to the same 5G core network on the ground.

[0097] Figure 6 is a diagram showing a user plane (UP) protocol stack structure in an NTN including a transparent satellite to which the present disclosure can be applied, and Figure 7 is a diagram showing a control plane (CP) protocol stack structure in an NTN including a transparent satellite to which the present disclosure can be applied.

[0098] The NR Uu interface may be an interface defined as a protocol for wireless connection between a terminal and a base station in an NR system. In this case, the NR Uu interface may include a user plane defined as a protocol for user data transmission, including the NTN. Furthermore, the NR Uu interface may include a control plane defined as a protocol for transmitting signaling including radio resource control information, including the NTN. For example, the medium access control (MAC) layer may be configured based on a radio link control (RLC), a packet data convergence protocol (PDCP), a service data adaptation protocol (SDAP), and a radio resource control (RAC), and protocols for each layer may be defined based on the NR among 3GPP RAN-related standards, but are not limited thereto.

[0099] As an example, Figure 6 shows a UP protocol stack structure based on a transparent satellite. That is, the satellite and NTN gateway can transmit only frequency switching and amplification of the received wireless signal. Furthermore, Figure 7 shows a CP protocol stack structure based on a transparent satellite. That is, the satellite and NTN gateway can transmit only frequency switching and amplification of the received wireless signal.

[0100] Based on the above, a wireless communication system supporting terminal-to-terminal communication in an NTN and a TN can be considered. Here, as an example, an NTN may have a longer round trip time (RTT) between a terminal and a base station than an existing TN. Therefore, from the perspective of UP, the terminal needs to store data transmitted through each of the uplink and downlink in a buffer for a longer period of time due to the increased RTT. That is, the terminal needs to store more data in a buffer. Therefore, the terminal may require a larger memory capacity than conventional terminals, which will be described later.

[0101] FIG. 8 illustrates a timing advance calculation method to which the present disclosure can be applied. As mentioned above, because satellites included in an NTN are located in the sky, the signal round trip time (RTT) can be long. For example, a LEO satellite can be located 300 km to 1,200 km above the sky, while a GEO satellite can be located 36,000 km or more above the equator. Therefore, propagation delays in an NTN can be significantly larger than in a TN. However, because an NTN is located in the sky, cell coverage can be greater than in a terrestrial network.

[0102] That is, since the RTT and cell coverage of an NTN may differ from those of a TN, it is necessary to newly define a method for obtaining time synchronization for uplink transmission in an NTN. As an example, Figure 8 shows a method for calculating the TA value generated depending on the satellite payload type.

[0103] More specifically, Figure 8(a) may be a method for calculating the TA value when the satellite payload type is a regenerated payload, and Figure 8(b) may be a method for calculating the TA value when the satellite payload type is a transparent payload.

[0104] Here, for initial connection and continuous maintenance of the timing advance (TA) value, it is possible to consider the case where the terminal knows the satellite's orbital force, i.e., orbital information (ephemeris), and the terminal's location. Here, satellite orbital information may refer to the distance between each satellite and the receiver and the location information of each satellite. As an example, the terminal may learn the TA value itself and then apply it (hereinafter referred to as option 1). As another example, the terminal may receive instructions for TA compensation and correction from the network (hereinafter referred to as option 2).

[0105] For example, referring to FIG. 8(a), if the satellite payload type is a regenerative payload, the satellite can directly function as a base station. In this case, the terminal can calculate a TA value required for uplink transmission including a physical random access channel (PRACH). The terminal can calculate a common TA value Tcom and a terminal-specific TA value TUEx. For example, the common TA value Tcom may be a TA value required for all terminals due to the large cell coverage and long round-trip time (RTT) of the NTN. That is, since the NTN is located in the sky and is relatively longer than the distance between terminals, a common TA value Tcom that takes into account the long round-trip time (RTT) in the cell coverage may be required. In addition, the terminal-specific TA value TUEx may be a value that occurs due to the different positions of each terminal within the cell coverage. If the terminal knows the satellite's position at a specific time in advance through satellite orbital information (ephemeris) that it has stored in advance or received from NTN, and if the terminal knows its position through a function such as GNSS, the terminal can calculate the distance between the satellite and the terminal at a specific time, so it can learn the TA value itself and then correct the TA value, thereby determining the TA value.

[0106] As described above, the terminal can perform uplink timing alignment between the terminals received from the base station with overall TA compensation.

[0107] As another example, the terminal may perform timing alignment of downlink and uplink frames on the network side. When the satellite payload type is a transparent payload, as shown in FIG. 8(b), the satellite may filter and amplify the radio signal and transmit it to the NTN gateway. That is, the satellite may operate like an RF repeater. In this case, the NTN gateway may need to be changed based on the satellite's continuous movement. The common TA value Tcom in FIG. 8(b) may be determined based on the sum of the distance D01 between the reference point and the satellite and the distance D02 between the satellite and the NTN gateway. The feeder link may change as the NTN gateway changes based on the satellite's movement. That is, the distance between the satellite and the NTN gateway may change based on the changed feeder link. Therefore, the generated common TA value may change, and the terminal may need to update it. Furthermore, when the network sets an offset between the downlink frame timing and the uplink frame timing, it is necessary to further consider the case where the TA value generated by the feeder link is not corrected in the overall TA compensation method. Furthermore, if a terminal can only calculate a different TA value TUEx for each terminal, the terminal needs to identify one reference point for each beam or cell and transmit information about this to other terminals. If the network sets an offset between downlink frame timing and uplink frame timing, the network needs to manage the offset information regardless of the satellite payload type. Here, as an example, the network can provide a value for TA correction to each terminal, and the present invention is not limited to the above-mentioned embodiment.

[0108] As another example, a method (Option 2) in which the network instructs TA compensation and correction can be considered. In this case, a common TA value can be generated based on a common element for propagation delay shared by all terminals located within the coverage of a satellite beam or cell. The network can transmit a common TA value to terminals for each satellite beam or cell based on a broadcast method. The common TA value can be calculated by the network assuming at least one reference position for each satellite beam or cell. In addition, the TA value TUEx for each terminal can be determined based on the random access procedure defined in an existing communication system (e.g., Release 15 or Release 16 in an existing NR system). In this case, for example, when a long TA value or a TA value in negative number form is applied, a new field may be required in the random access message. For example, if the network provides a timing change rate to the terminal, the terminal can support TA value correction based on the timing change rate.

[0109] FIG. 9 is a diagram illustrating an earth fixed cell scenario to which the present disclosure may be applied.

[0110] Referring to FIG. 9, a fixed cell may be a cell in which the position where a signal is transmitted by a satellite is fixed. For example, since a satellite moves over time, it is necessary to change its antenna and beam so that service coverage is fixed to a specific position in order to maintain the fixed cell. In this case, as an example, in FIG. 9, satellite 1 (910) can maintain the fixed cell by changing its antenna and beam between T1 and T3. Here, after a specific time T4 has passed, satellite 1 can no longer service the location, so satellite 2 (920) can provide service at the location to maintain service continuity. In this case, the beam or cell of satellite 2 (920), which serves the same location as satellite 1 (910) served at the previous time (T1 to T3) after time T4, can maintain the characteristics of the beam or cell of satellite 1 (910), and is not limited to the above-described embodiment.

[0111] As a more specific example, when a service is provided by satellite 1 (910) and satellite 2 (920), at least one of a physical cell ID (PCI) value and system information can be maintained to be the same. That is, as a cell with fixed service coverage, it can be set based on a satellite that can change the antenna and beam angle among satellites in LEO and MEO orbits, excluding GEO.

[0112] 10 is a diagram illustrating an earth moving cell scenario to which the present disclosure can be applied. As an example, a cell in which service coverage moves may be an earth moving cell.

[0113] For example, referring to Figure 10, satellite 1 (1010), satellite 2 (1020), and satellite 3 (1030) can each provide service to cells having different PCIs. In this case, the antenna and beam by which the satellite transmits signals to the ground are fixed, and the form in which the service coverage moves as the satellite moves over time can be called an Earth moving cell. Earth moving cells can be established based on satellites in LEO and MEO orbits, excluding GEO, that have fixed antenna and beam angles. Here, these satellites have the advantages of being cheaper and having a lower failure rate than satellites that can adjust the antenna and beam angles.

[0114] Additionally, FIG. 11 is a diagram illustrating a method for mapping PCI to satellite beams to which the present disclosure may be applied.

[0115] For example, a PCI may refer to an index that can logically distinguish a cell. That is, beams having the same PCI value may be included in the same cell. For example, referring to FIG. 11(a), a PCI may be assigned to multiple satellite beams. Conversely, referring to FIG. 11(b), one PCI may be assigned to each satellite beam in one satellite. For example, a satellite beam may be configured with one or more SSB (Synchronization Signal Block, SS / PBCH block) beams. One cell (or PCI) may be configured with up to L SSB beams. Here, L may be 4, 8, 64, or 256 depending on the size of the frequency band and / or subcarrier band, but is not limited to the above embodiment. That is, L may use one or more SSB indexes for each PCI, similar to a terrestrial network (TN), which is an existing communication system (NR system). This allows SSBs transmitted through different beams to be distinguished, and the SSB index may be mapped to a logically defined antenna port or a physically separated beam.

[0116] For example, a terminal connectable to an NTN may be a terminal that supports a Global Navigation Satellite System (GNSS) function. However, terminals connectable to an NTN may also include terminals that do not support GNSS. As another example, an NTN may support a terminal that supports a GNSS function but does not acquire location information through GNSS, and is not limited to the above-described embodiment.

[0117] As described above, a terminal can communicate through an NTN. For example, a terminal can receive services based on a 5G / B5G NTN-based non-terrestrial network. This allows the terminal to escape the regional, environmental, spatial, and economic constraints of wireless access services (e.g., LTE, NR, WiFi, etc.) based on the installation of terrestrial network equipment. For example, based on the above, advanced wireless access technologies provided on terrestrial networks may be applicable to non-terrestrial network platforms (e.g., satellites and UAVs). This allows various wireless access service products and technologies to be provided along with advanced network technologies.

[0118] The NTN platform can function as a kind of mirror, carrying the functions of relaying NR signals in space or at high altitudes, or as a base station (gNB, eNB). As an example, the NG-RAN-based NTN architecture can realize its functions using the "Transparent payload-based NTN" and "Regenerative payload-based NTN" structures, as mentioned above.

[0119] Furthermore, as an example, NTN technology can be utilized as an extended network structure and technology of the 5GIAB (Integrated Access and Backhaul) architecture to provide wider coverage and more wireless connectivity services. The integration of NTN with terrestrial networks can ensure service continuity and scalability of 5G systems.

[0120] As a specific example, an integrated NTN / TN network can provide significant benefits in terms of 5G target performance (e.g., user-experienced data transmission speed and reliability) in urban and suburban areas. As another example, an integrated NTN / TN network can ensure connectivity not only in highly dense areas (e.g., concert venues, sports stadiums, shopping centers, etc.) but also for fast-moving objects such as airplanes, high-speed trains, vehicles, and ships. As another example, an integrated NTN / TN network can use data transmission services simultaneously from the NTN network and the TN network through its multi-connection function. In this case, it is possible to selectively utilize better networks depending on the traffic characteristics and traffic load, thereby achieving both the efficiency and economy of 5G wireless transmission services.

[0121] A terminal on general flat ground can simultaneously connect to the NTN network and the TN network to use wireless data services. Furthermore, the terminal can simultaneously connect to one or more NTN platforms (e.g., two or more LEO / GEO satellites) to provide wireless data connection services for harsh environments or regions that are difficult to support with the TN network. This allows the terminal to be used in conjunction with various services. In particular, the integrated NTN network and TN network improves the reliability of autonomous driving services and enables efficient network operation, and is not limited to the above-mentioned embodiments.

[0122] For example, LTE mobile communication-based V2X technology or standard technology based on the IEEE 802.11p standard may have similar service limitations. LTE V2X standards can be provided to meet the requirements defined by C-ITS (e.g., a time delay of approximately 100 ms, reliability of approximately 90%, and generation of messages of tens to hundreds of bytes approximately 10 times per second). Therefore, new V2X services requiring low latency, high reliability, high data traffic capacity, and improved positioning may be required. Based on the above, standardization of 5G wireless access technology (e.g., New Radio (NR)) is currently underway. For example, various numerologies, frame structures, and corresponding L2 / L3 protocol structures are being standardized to more flexibly meet the requirements of new services than LTE. Based on the above, sidelink wireless access technology can be introduced based on 5G mobile communication technology to support improved V2X services such as autonomous driving and remote driving, and the NTN network can be utilized for this purpose.

[0123] As another example, NTN networks can be used to support IoT services in harsh environments and areas not covered by terrestrial networks. For example, IoT equipment may often need to perform wireless communication with minimal power consumption in harsh channel environments (e.g., mountains, deserts, or oceans) depending on its intended use. Previously proposed cellular-based technologies may primarily be intended to provide mobile broadband (MBB) services. Therefore, they may be less efficient in providing IoT services in terms of radio resource utilization and power control, and may not be able to support flexible operation. Furthermore, as an example, existing non-cellular-based IoT technologies may have limitations in providing various IoT services due to limited mobility support and coverage. Taking the above into consideration, NTN networks can be applied, thereby improving services.

[0124] Furthermore, for example, applying 5G mobile communication-based sidelink technology through the NTN network can provide users with wider coverage and mobility through a more efficient wireless communication method than current Bluetooth / Wi-Fi-based wearable devices. Furthermore, it can differentiate from existing communication standards in applications (e.g., wearable multimedia services) that require high data transmission speeds and mobility support using wearable devices.

[0125] As another example, the NTN network can improve public safety communication networks and expand disaster communication coverage. For example, the high reliability and low latency technology of 5G mobile communication systems can be used through the NTN network to provide public services such as disaster response. For example, by utilizing mobile base stations such as drones that support 5G mobile communications, mobile broadband services can be supported even in deserts and high mountain areas. In other words, when the NTN network is applied to public services, it can cover a variety of regions, thereby expanding disaster communication coverage.

[0126] 12 is a diagram illustrating a method in which a satellite to which the present disclosure can be applied covers multiple tracking areas (TAs). A terminal can register with a network through a registration procedure. A terminal that is registered with the network (e.g., 5GMM-REGISTERED) can transmit a registration request message to an access and mobility management function (AMF) for periodic registration updates according to its mobility.

[0127] Specifically, if the UE's current tracking area identifier (TAI) is not in the tracking area list received from the AMF where the UE previously registered (i.e., if the UE moves to a tracking area code (TAC) that is not in the registration area where the UE previously registered), the UE may transmit a registration request message to the AMF for a mobility registration update. Here, the TAI may refer to an identifier including the PLMN (MCC + MNC) and the TAC. As another example, if the UE receives a configuration update command, the UE may transmit a registration request message to the AMF for a mobility registration update. As another example, if the UE requests new local area data network (LADN) information, the UE may transmit a registration request message to the AMF for a mobility registration update. Here, the local area data network (LADN) may refer to a specific area if a specific service is provided only in that area. For example, the UE may perform a data network connection through a PDU session only to a specific TA that represents the geographical information of the area.

[0128] As another example, when a timer (for example, T3512) expires in a terminal in an RRC idle state and a periodic registration update procedure occurs, the terminal may transmit a registration request message to the AMF for a mobility registration update. That is, the terminal may perform a mobility registration update based on various conditions and is not limited to the above-mentioned cases.

[0129] Referring to FIG. 12, a case in which a terminal performs communication based on an NTN can be considered. An NTN satellite 1210 can be connected to a base station 1230 through an NTN gateway 1220, as described above. For example, the NTN satellite 1210 can serve a wider coverage area than a TN. Therefore, the NTN satellite 1210 can cover multiple TAs. As a specific example, based on NTN communication, an NTN cell (e.g., satellite NG-RAN) can have TACs corresponding to the area served by the satellite (e.g., TA 1, TA 2, TA 3, TA 4, ..., TA 58, TA 59, TA 60). Here, the NTN cell can broadcast multiple TACs for the area served by the NTN cell through system information. When a terminal receives multiple TAC information through system information, the terminal's non-access stratum (NAS) layer can select one TAI. Here, the TAI can be composed of a PLMN and a TAC.

[0130] When a UE is camped in an NTN cell, the UE can receive multiple TACs from a lower layer. The UE can configure multiple TAIs through multiple TACs and the current PLMN. The UE can select one of the multiple configured TAIs. Specifically, if only one TAI is included in the UE's current registration area, the UE can select the TAI. On the other hand, if multiple TAIs are included in the UE's current registration area, the UE can select a TAI based on tracking area information included in the service area information. Here, the tracking area information can include allowed tracking area information and non-allowed tracking area information. The UE can select a TAI that is included in the allowed tracking area but not in the non-allowed tracking area. For example, if multiple TAIs are included in the allowed tracking area but not in the non-allowed tracking area, the UE can select one TAI according to a preset method (e.g., LADn service area information). That is, the UE can select one of the multiple TAIs configured in the UE based on certain conditions.

[0131] On the other hand, if all TAIs are not included in the terminal's current registration area, the terminal may select a TAI that is not included in a list of TAIs forbidden from network connection (e.g., 5GS forbidden tracking areas for roaming, 5GS forbidden tracking areas for provision of service). Also, for example, if there are multiple TAIs, the terminal may select one of the multiple TAIs based on certain conditions. The terminal may consider the selected TAI to be the current TAI.

[0132] Here, a case can be considered in which a lower layer of the UE transmits multiple TACs to the NAS layer, in which case the UE can perform a TAI selection operation based on at least one of a change in tracking area information (e.g., allowed tracking area, non-allowed tracking area) and a change in network prohibition information (e.g., 5GS forbidden tracking areas for roaming, 5GS forbidden tracking areas for provision of service).

[0133] The following describes how a terminal measures neighboring cells for cell reselection in an NTN system.

[0134] For example, frequency bands for NTN communications can be defined in a wireless communication system (e.g., 3GPP NR) as FR1 (450 MHz-6 GHz), FR2 (24.25 GHz-52.6 GHz), FR2x (52.6 GHz-71 GHz), FR3 (7.125 GHz, 24.25 GHz), and FR4 (52.6 GHz-114.25 GHz). Here, multiple operating band configurations within the bands can indicate at least one of uplink, downlink, bandwidth, and duplex mode. For example, the NTN system can use the S-band regions of 1980-2010 MHz and 2170-2200 MHz. These bands can overlap with bands of existing wireless communication systems (e.g., 3GPP NR).

[0135] As a specific example, if bands 1 and 65 of a wireless communication system (e.g., 3GPP NR) in FR1 use adjacent or the same frequency region as the NTN band, a cross-border issue may occur.

[0136] Referring to Table 5, NTN operating bands can overlap with TN frequency bands. As an example, NTN bands can completely overlap with TN bands operating with FDD in the 65 band (uplink operating band 1920-2010 MHz, downlink operating band 2110-2200 MHz). Furthermore, NTN bands can partially overlap with TN bands operating with FDD in the 24 band (uplink operating band 1626.5-1660.5 MHz, downlink operating band 1525-1559 MHz). Therefore, operators must coordinate the use of frequency bands by TNs and NTNs in the same geographic location.

[0137] [Table 5]

[0138] Further, as an example, the following information can be taken into consideration in order for the terminal to perform neighbor cell measurements for cell reselection:

[0139] PLMN(Public land mobile network) Selection

[0140] The terminal can check available radio frequency (RF) bands according to its capabilities to search for available PLMNs and closed access groups (CAGs) within the NR band. The terminal can search for the cell with the strongest signal strength and check system information to determine whether each carrier includes any PLMNs and which CAGs are associated with it.

[0141] Cell re-selection and measurement information

[0142] For example, system information block 2 (SIB2) may include common information related to intra / inter-frequency and inter-RAT for cell reselection of a terminal. The intra / inter-frequency and inter-RAT information for cell reselection may include at least one of a parameter (nrofSS-BlocksToaverage) related to measuring the average value of signal strengths of several SSBs as signal strength, a threshold value for SSB signal strength (absThreshSS-BlocksConsolidation), a range (rangeToBestCell) of the cell-ranking criterion R for final cell reselection, a scaling factor (Q-Hyst), and mobility state parameters (MobilityStateParameters) for estimating the movement / velocity state of the terminal. Furthermore, SIB2 may include at least one of general information for inter-frequency and inter-RAT reselection (cellReselectionServingFreqInfo), signal strength threshold for measurement trigger (s-NonIntraSearchP), signal quality threshold (s-NonIntraSearchQ), signal strength threshold for cell reselection to an inter-frequency or inter-RAT of equal or lower priority (threshServingLowP), signal quality threshold (threshServingLowQ), and priority (cellReselectionPriority, cellReselectionSubPriority).Furthermore, SIB2 may include at least one of information for intra-frequency cell reselection (intraFreqCellReselectionInfo), minimum signal strength (q-RxLevMin, q-RxLevMinSUL), minimum signal quality (q-QualMin) for signal strength calculation of adjacent intra-frequency cells in the cell selection criteria (S-Criterion) procedure, signal strength threshold (s-IntraSearchP), signal quality threshold (s-IntraSearchQ) for measurement trigger, time for reselection (t-ReselectionNR), band list (frequencyBandList) to apply cell reselection parameters, SMTC, and SSB to be measured within the SMTC duration (ssb-ToMeasure).

[0143] Inter-frequency measurement procedure

[0144] For example, SIB4 includes information about neighboring cells associated with inter-frequency cell reselection. The information is a cell reselection parameter for one frequency and may be applied only within a specific cell as cell-specific information. Furthermore, for example, SIB4 includes an inter-frequency information list (interFreqCarrierFreqList), which may include information about up to eight frequencies.

[0145] Each frequency information can indicate the downlink carrier frequency with the ARFCN (dl-CarrierFreq) value. If multiple bands are included, SIB4 contains the band list (frequencyBandList), the parameter for measuring the average signal strength of the number of SSBs (nrofSS-BlocksToaverage), the SSB signal strength threshold (absThreshSS-BlocksConsolidation), SMTC, SSB subcarrier spacing (ssbSubcarrierSpacing), and SMTC. SSB to be measured within the duration (ssb-ToMeasure), instruction on whether to derive the SSB index of the neighboring cell from the serving cell (deriveSSB-IndexFromCell), information indicating the specific slot and symbol for measuring the SSB signal strength within the SMTC window (ss-RSSI-Measurement), minimum signal strength (q-RxLevMin, q-RxLevMinSUL) for calculating the signal strength of neighboring inter-frequency cells in the cell selection criteria (S-Criterion) procedure, minimum signal quality (q-QualMin), time for reselection (t-ReselectionNR), and inter-frequency by priority. The cell reselection parameter may include at least one of a signal strength threshold (threshX-HighP, threshX-LowP), a signal quality threshold (threshX-HighQ, threshX-LowQ), a priority (cellReselectionPriority, cellReselectionSubPriority), a frequency-dependent signal strength offset (q-OffsetFreq) used in the cell R-criterion ranking procedure, a neighbor cell information list (InterFreqNeighCellList), and an excluded neighbor cell information list (interFreqExcludedCell).Here, the neighbor cell information list may include at least one of one or more PCIs (physCellId), a signal strength offset (q-OffsetCell) used in the cell R-criterion ranking procedure, and minimum signal strength (q-RxLevMinOffsetCell) and minimum signal quality (q-QualMinOffsetCell) information for signal strength calculation in the cell selection S-criterion procedure. The neighbor cell information list may also specify an allowed cell list (intraFreqAllowedCellList) and an excluded cell list (IntraFreqExcludedCellList) as a PCI range. Here, the PCI range may indicate a start PCI and a range (4, 8, 12, 16, ..., 1008).

[0146] Intra-frequency measurement procedure

[0147] SIB3 can include information about neighbor cells associated with intra-frequency cell reselection. The neighbor cell information list (IntraFreqNeighCellList) can include at least one of one or more PCIs (physCellId), a signal strength offset (q-OffsetCell) used in the cell R-criterion ranking procedure, and minimum signal strength (q-RxLevMinOffsetCell) and minimum signal quality (q-QualMinOffsetCell) information for signal strength calculation in the cell selection S-criterion (S-Criterion) procedure. Additionally, the allowed cell list (intraFreqAllowedCellList) and excluded cell list (IntraFreqExcludedCellList) in the neighbor cell information list can be specified as a PCI range. Here, the PCI range can indicate a start PCI and a range (4, 8, 12, 16, ..., 1008).

[0148] Measurement rules for cell re-selection

[0149] In an existing wireless communication system (e.g., NR), an RRC idle / inactive UE may not perform inter-frequency measurement if the signal strength of the serving cell is above a threshold. Conversely, an RRC idle / inactive UE may always perform inter-frequency measurement if the signal strength of the serving cell is below a threshold. Further, as an example, the UE may always measure an inter-frequency having a higher priority than the current NR frequency. Conversely, if the UE has the same or lower priority as the current NR frequency, the UE may not need to measure the inter-frequency if the signal strength of the serving cell is above a certain threshold, but may always perform inter-frequency measurement if the signal strength is below the threshold.

[0150] SMTC(SSB based measurement timing configuration)

[0151] For example, in existing wireless communication systems (e.g., LTE), a cell-specific reference signal (CRS) was periodically transmitted to allow a terminal to measure the signal strength of a serving / neighboring cell. However, in current wireless communication systems (e.g., NR), the concept of always-on-signal (e.g., CRS) may not be applied to reduce overhead and interference with neighboring cells. Therefore, in current wireless communication systems, a terminal needs to measure the signal strength (RSRP, RSRQ) of a serving cell and neighboring cells in order to handover to a cell with stronger signal strength or add a new carrier. Therefore, in current wireless communication systems (e.g., NR), a terminal can measure signal strength through an SS / PBCH block (SSB) including a synchronization signal (SS) and a physical broadcast channel (PBCH) used for downlink synchronization.

[0152] Specifically, the number of SSBs may vary depending on the frequency operating band. For example, in the FR1 band below 3 GHz, four SSBs may be configured in one burst. Furthermore, in the FR1 band from 3 to 6 GHz, eight SSBs may be configured in one burst. Furthermore, in the FR1 band from 6 GHz and above, 64 SSBs may be configured in one burst. The period of the SSB burst set may be 5, 10, 20, 40, 80, or 160 ms, and may be periodically transmitted from the cell. However, to reduce terminal power consumption, it is not necessary to measure signal strength every SSB period. Here, as an example, an SMTC window may be applied so that the terminal can check signal strength for SSB measurement. That is, the terminal may periodically measure SSB signal strength every SMTC window to reduce terminal power consumption.

[0153] Here, the network can configure the SMTC window for the terminal through an RRC message. Specifically, the network can transmit ssbFrequency (NR-ARFCN), SSB SCS (ssbSubcarrierSpacing), and SMTC information in MeasObjectNR through the RRC message. The network can configure the time unit periodicity and offset information (periodicityAndOffset) and duration indicating the window size in SMTC through the RRC message. As another example, the network can provide specific frequency information (ARFCN) and SMTC information in system information together to the terminal. The terminal can determine which band to check at what time based on the frequency information (ARFCN) and time information (SMTC).

[0154] For example, in an NTN environment with large propagation delay, multiple SMTC configurations may be possible because multiple cells cannot all be included in the SMTC window. In addition, the UE can perform signal strength measurements for the serving cell and neighboring cells even in an RRC connected / inactive / idle environment. Based on the above, a method for the UE to measure neighboring cells for cell reselection will be described below.

[0155] A technology for providing service continuity taking into account mobility between NTNs and TNs and between NTNs may be needed. For example, a method for providing service continuity by performing measurements based on mobility between NTNs and TNs and between NTNs may be needed.

[0156] More specifically, a method for reducing power consumption of an RRC idle / inactive UE will be described below. As an example, the UE may operate based on one of an RRC connected state, an RRC idle state, and an RRC inactive state. Here, if the RRC of the UE is logically connected to the RRC of the core network, it may be in an RRC connected state. Conversely, if the RRC of the UE is not connected to the RRC of the core network, it may be in an RRC idle state. However, transitioning from the RRC idle state to the RRC connected state may require a lot of signaling. In consideration of the above, an RRC inactive state may exist. In the RRC inactive state, the UE can be considered to be in a connected state from the perspective of the core network. That is, the core network can maintain both the user plane and control plane of the UE in an active state. Therefore, paging can be initiated by the RAN in the RRC inactive state.

[0157] Below, we will describe a method for reducing the power consumption of a terminal. In particular, since a terminal is not in a state where it transmits data in an RRC idle / inactive state, it is necessary to minimize power consumption. In existing wireless communication systems (e.g., Rel-17), a terminal can preferentially select / camp on a terrestrial networks (TN) cell in relation to an NTN cell and a TN cell. Therefore, the terminal needs to constantly measure the signal strength of neighboring TN cells, which may result in constant power consumption. Below, we will describe a method for performing a conditional cell search taking the above points into consideration.

[0158] FIG. 13 is a diagram illustrating a method for measuring TN cells in an NTN environment applicable to the present disclosure. Referring to FIG. 13, NTN cell coverage can be determined based on an NTN satellite 1310. Here, TN cells may exist within the NTN cell coverage. Specifically, for terminals 1, 2, and 3 (1321, 1322, 1323), there may not be any TN cells with sufficient signal strength. Therefore, terminals 1, 2, and 3 (1321, 1322, 1323) are camped on NTN cells and can always perform cell search for the TN frequency domain to camp on TN cells. On the other hand, as terminals within the NTN cell coverage, there may be TN cells with sufficient signal strength for terminals 4, 5, 6, and 7 (1324, 1325, 1326, 1327). Therefore, terminals 4, 5, 6, and 7 (1324, 1325, 1326, 1327) can camp on TN cells. Here, terminals 1, 2, and 3 (1321, 1322, 1323) camped on NTN cells are camped on NTN cells, but perform measurements on TN cells and search for TN cells, which may result in increased power consumption, and a solution to reduce this may be needed.

[0159] In addition, terminals 4, 5, 6, and 7 (1324, 1325, 1326, 1327) camped in the TN cell may also consume power by continuously performing measurements on the NTN cell, and a solution to reduce this may be needed.

[0160] In the following, considering the above points, a method (method 1) for performing a conditional NTN cell search (frequency measurement) and a method (method 2) for performing a conditional TN cell search (frequency measurement) will be described. Here, methods 1 and 2 are not mutually exclusive. However, for the sake of convenience, each method is described separately, and it is obvious that each method can be applied depending on the situation of the terminal.

[0161] Method 1 (Conditional NTN cell search (frequency measurement))

[0162] The UE may perform measurements for cell reselection of inter-frequency and inter-RAT frequencies indicated through system information. Here, conditions for performing measurements for cell reselection of inter-RAT frequencies and inter-RAT frequencies may be as shown in Table 6 below. That is, the UE may determine whether to perform measurements based on whether the priority of the inter-frequency or inter-RAT frequency is higher than the current frequency and whether the signal strength and signal quality of the serving cell are greater than a threshold. In particular, the UE may consider a case where the priority of the inter-frequency or inter-RAT frequency is lower than the current frequency but the signal strength and signal quality of the serving cell are greater than a threshold. In this case, the UE may not perform measurements for inter-frequency or inter-RAT if the reference position between the UE and the UE is smaller than a distance threshold set based on the system information, and may perform measurements for inter-frequency or inter-RAT if the reference position between the UE and the UE is greater than the distance threshold. On the other hand, if there is no distance threshold set based on system information, the terminal does not always need to perform measurements on inter-frequency or inter-RAT frequencies.

[0163] Furthermore, if the inter-frequency or inter-RAT frequency has a lower priority than the current frequency, but the signal strength and signal quality of the serving cell are lower than a threshold, the terminal can perform measurements on the inter-frequency or inter-RAT.

[0164] Also, as an example, if a t-service of the serving cell exists in the system information (e.g., SIB19), the UE may perform intra / inter-frequency and inter-RAT measurements before the t-service regardless of the conditions in Table 6 below. Here, the t-service may refer to the absolute time (epoch time) at which a fixed cell provides coverage. As another example, the UE may always perform measurements on high-priority intra / inter-frequency and inter-RAT frequencies regardless of the conditions in Table 6.

[0165] [Table 6]

[0166] FIG. 14 is a diagram showing an overlapping environment of a TN cell and an NTN cell applicable to the present disclosure. Referring to FIG. 14, an NTN cell A based on a satellite 1410 can overlap with a TN cell. Here, the coverage of the NTN cell A in FIG. 14(b) may be wider than the coverage of the NTN cell A in FIG. 14(a). However, this is merely an example for convenience of explanation, and multiple cells may exist in an area that can be served by a satellite, and is not limited to a specific embodiment.

[0167] As an example, the coverage of the NTN cell in Figures 14(a) and 14(b) may be an urban area where TN cells are densely present and a suburban / mountainous area where TN cells are rare or absent. As another example, Figures 14(a) and 14(b) may be a land area where TN cells are densely present and an ocean area where TN cells are rare or absent, but this is not limited to a specific embodiment. Here, a registration area (RA) may be an area that the network can configure taking into account the mobility and services of the terminal. An RA can be configured for a terminal through multiple TACs. Therefore, the terminal can move within the RA and camp on a TN or NTN cell without a registration update procedure.

[0168] Here, as an example, in Figures 14(a) and 14(b), the UE is camped on a TN cell and may be located at the coverage edge (TN cell edge) where the signal strength or signal quality of the serving cell, the TN cell, is lower than a certain value. Here, the UE may perform a procedure to measure and search for an NTN cell. However, in a situation where there are many neighboring TN cells around the UE, the UE may need to camp on a TN cell rather than an NTN cell. Therefore, the measurement and search for an NTN cell in the UE may be an unnecessary procedure.

[0169] As a more specific example, in Figures 14(a) and 14(b), a terminal located on the edge of TN cells 2 and 3 (TN Cell 2, 3) needs to prioritize camping on adjacent TN cells. Therefore, NTN cell measurement and search may be unnecessary procedures for a terminal located on the edge of a cell. Also, as an example, even in an area where service coverage of NTN cell A does not exist as in Figure 14(a), the terminal may not need to perform NTN cell measurement and search procedures. Also, even if the service coverage of NTN cell A covers an area where TN cells are densely packed as in Figure 14(b), NTN cell measurement and search may be unnecessary because the terminal must camp on a TN cell with a higher priority. On the other hand, since there are no adjacent TN cells for a terminal camping on TN cell 6 (TN Cell 6), NTN cell measurement and search may be necessary, and cell search conditions taking the above-mentioned situation into consideration may be necessary.

[0170] 15 is a diagram illustrating an environment in which TN cells and NTN cells overlap, which is applicable to the present disclosure. Referring to FIG. 15, NTN cells can overlap with TN cells based on satellite 1510.

[0171] Here, when a terminal camps on a TN cell, the TN frequency can be configured to have a high priority and the NTN frequency can be configured to have a low priority. That is, since the TN cell provides high QoS, the terminal can be configured to prioritize camping on the TN cell. In this case, if the signal strength (Srxlev) and signal quality (Squal) of the TN cell, which is the serving cell, are lower than the signal strength threshold (s-IntraStraphP) and signal quality threshold (s-IntraSterQ), the terminal can always measure the inter-frequency or inter-RAT frequency with a lower priority. This can be as shown in Table 6.

[0172] For example, when a terminal is located at the edge of a cell, the signal strength and signal quality of the serving cell may be lower than the signal strength threshold and signal quality threshold. In the above situation, if the signal strength and signal quality of the serving cell of a terminal camped on a TN cell become weak, the terminal may be forced to perform measurements on the NTN cell with lower priority. Referring to FIG. 15, NTN Cell A can serve a wider area in FIG. 15(b) than in FIG. 15(a). However, this is merely an example for convenience of explanation, and multiple cells may exist in an area that can be served by a satellite. For example, the TACs of areas where TN cells are densely packed or exist in FIG. 15(a) and FIG. 15(b) may be TAC10 to TAC26. For example, FIG. 15(a) and FIG. 15(b) may represent an urban area where TN cells are densely packed and a suburban / mountainous area where TN cells are rare or absent. As another example, Figures 15(a) and 15(b) may represent a land area where TN cells are densely located or present, and an ocean area where TN cells are rare or absent, but are not limited to a specific embodiment. Here, the UE performs initial access through a TN cell and can receive a registration area (RA) configuration from the AMF. The RA is an area that the network can configure taking into account the mobility and services of the UE, and may be configured for the UE through multiple TACs. Therefore, the UE can move within the RA and camp on a TN or NTN cell without a registration update procedure.

[0173] Referring to Figures 15(a) and 15(b), a case can be considered in which a UE is camped on a TN cell having TAC21 and the signal strength or signal quality of the serving TN cell is lower than a certain value. The UE may perform a procedure for measuring and searching for an NTN cell in the above-mentioned situation, but it may be unnecessary for the UE to perform an NTN cell measurement and search procedure when there are many neighboring TN cells around the UE. Also, as an example, even in a location where there is no service coverage of NTN cell A as shown in Figure 15(a), it may be unnecessary to perform a procedure for measuring and searching for an NTN cell. Also, even if the service coverage of NTN cell A covers an area where TN cells are densely packed due to the service coverage of NTN cell A as shown in Figure 15(b), the UE must camp on a TN cell with a higher priority, so measurement and search for the NTN cell may be unnecessary.

[0174] That is, as described above, when a terminal that does not need NTN frequency measurement performs NTN frequency measurement, the terminal may continuously consume power, so a method for reducing this may be necessary. To this end, a terminal camped on a TN cell may conditionally perform NTN cell measurement and search based on information that can estimate the terminal's location or a specific location (e.g., TAC / Cell / RAC).

[0175] Specifically, FIG. 16 illustrates a method for performing TAC list-based measurement applicable to the present disclosure. Referring to FIG. 16, the coverage of NTN cell A can be determined based on a satellite 1610. Here, an RRC dormant terminal 1620 may be assigned a registration area (RA) by the AMF after performing an initial connection. The RA is an area to which the terminal 1620 can move without performing a registration update and may include multiple TACs. As a specific example, if the terminal 1620 is assigned an RA having TACs A, B, and C, the RRC dormant terminal 1620 can move to a cell having TACs A, B, and C without a registration update procedure by the AMF. On the other hand, if the terminal 1620 moves to a cell having TAC D, the terminal 1620 may be assigned a new RA after performing a registration update procedure by the AMF.

[0176] Referring to FIG. 16, when an NTN cell and a TN cell overlap, a TAC can be configured based on the NTN cell and the TN cell. A TAC may refer to a geographically fixed location. Each base station cell may have a specific TAC identifier. As a specific example, the terminal 1620 may be assigned an RA (TACs 3 to 26) including all TACs shown in FIG. 16 by the AMF. However, this is merely an example for convenience of explanation and is not limited to the above-described embodiment. The terminal 1620 can move within an RA without a registration update procedure in the AMF and can camp on a cell having one TAC within the RA. As an example, if the terminal 1620 is in the TAC21 area, the terminal 1620 can camp on a TN cell having TAC21. Here, if the terminal moves to TAC7, the terminal can camp on an NTN cell because there is no TN cell with a sufficiently strong signal strength. In this case, the NTN cell A can serve a wider area than the TN cell. Therefore, the NTN cell can transmit multiple TACs to the terminal 1620 through system information. The terminal can select one TAC belonging to the RA from among multiple TACs acquired through system information and derive the TAI.

[0177] Here, an RRC idle UE can receive the configuration of cell reselection parameters for camping through an RRC message (e.g., RRC Release, SIB2, 3, 4). That is, if the UE 1620 receives the configuration of cell reselection parameters for the NTN cell after transitioning to the RRC idle state at TAC21, the UE can continuously perform a search for the NTN cell within the RA. Since the NTN cell exists within the RA in the network, the cell reselection parameters for the NTN cell may be configured as an RRC message. However, since the UE 1620 cannot camp on the NTN cell in other areas that do not have TACs 4 to 11 served by NTN cell A, performing a cell search may increase unnecessary power consumption.

[0178] Furthermore, since TN cells support higher QoS than NTN cells, a UE 1620 camped on a TN cell may not need to camp on an NTN cell through cell reselection. On the other hand, if the signal strength of the serving cell of the UE 1620 camped on a TN cell is insufficient and the UE 1620 is in an area where it can receive the SSB of the NTN cell, it may need to search for an NTN cell. Specifically, if the signal strength of the UE 1620 camped on a TN cell with TAC 10 is insufficient at the edge of the cell, the UE 1620 may need to search for NTN cell A. Considering the above situation, the UE 1620 can reduce power consumption by searching for an NTN cell with a specific TAC.

[0179] Referring to FIG. 16, the network can include TACs 4 to 10 served by NTN cell A or TACs capable of detecting SSBs of NTN cell A in the TAC list for NTN cell search. In this case, the network can configure NTN cell reselection parameters and configure them in the UE 1620 through an RRC message. As an example, the UE 1620 located in TAC 21 can receive NTN cell reselection parameters and TAC list configuration through an RRC message (e.g., system information, RRC release) in the TN cell. The UE 1620 can recognize that TAC 21 is not located in the TAC list. Therefore, the UE 1620 can only search for the TN cell for which the configuration is accepted, without performing NTN cell search. Also, if the UE moves to TAC 22 due to movement, the UE 1620 can be in a state of camping on the TN cell having TAC 22 because it is only performing a search for the TN cell. On the other hand, if the terminal moves to a TAC region (e.g., TAC10) indicated by the TAC list and is camped in a TN cell having TAC10, the terminal 1620 can perform an NTN cell search based on the NTN cell reselection parameters configured. Also, even though the terminal 1620 has moved to a TAC region indicated by the TAC list, the TN cell must be prioritized because it supports higher QoS. Therefore, the terminal 1620 camped in a TN cell must perform an NTN cell search taking into account a procedure for checking not only the TAC list but also the signal strength of the serving cell.

[0180] FIG. 17 illustrates a TAC list-based NTN cell measurement signaling procedure applicable to the present disclosure. Referring to FIG. 17, a terminal 1710 may receive an RRC message from TN Cell A 1720 in an RRC connected / inactive / idle state (S100). At this time, the terminal 1710 may acquire and configure specific conditions for cell reselection (TAC list) and parameters (e.g., CellReselection) including frequency information, SMTC, and other information in the RRC message. The terminal 1710 may then transition to an RRC dormant state (S105). For example, the terminal 1710 may transition to an RRC dormant state after a period of time has elapsed or by receiving an RRC release message. Here, the RRC dormant terminal 1710 is camped on TN Cell A 1720 (S110) and may perform frequency measurement based on the configured parameters. Specifically, the terminal 1710 may perform frequency measurement for intra / inter frequencies using parameters (e.g., cell reselection) including frequency information, SMTC, and other information. The terminal 1710 may then need to perform cell reselection to a new cell based on the terminal's mobility (S115). As an example, the terminal 1710 may select TN Cell B 1730 through a cell reselection procedure. The terminal 1710 may receive an RRC message (e.g., system information) from TN Cell B 1730 and receive parameters including TAC#F associated with TN Cell B 1730 (S120). At this time, TAC#F may not be included in the TAC list. Therefore, the terminal 1710 camped on TN Cell B 1730 may not need to perform NTN cell measurement and search (S125). The terminal 1710 may then reselect a new cell based on the terminal's mobility (S130). The terminal 1710 may select TN Cell C 1740 through a cell reselection procedure. The terminal 1710 may then receive an RRC message (e.g., system information) from TN Cell C 1740 and receive parameters having TAC#B associated with TN Cell C.For example, TAC#B may be included in the TAC list. Therefore, the terminal 1710 camped on TN cell C 1740 (S140) can perform NTN cell measurement and search. That is, the terminal 1710 checks the signal strength and signal quality of the serving cell, TN cell C (1740), and if the signal strength and signal quality are lower than a specific value, it can perform NTN cell measurement and search (S145).

[0181] As another example, the terminal 1710 can perform measurements and searches for NTN cells based on the TAC list without a procedure for checking the signal strength and signal quality of the serving cell, TN cell C 1740.

[0182] Here, the TAC list may include one or more TACs expressed as 24-bit strings. For example, in FIG. 17, the TAC list may include TAC#B and TAC#C, each of which has a 24-bit string, but this is merely an example and is not limited to the above-described embodiment.

[0183] In addition, the TAC may be configured differently depending on the PLMN (MCC+MNC). As another example, a UE in an RRC dormant / inactive state may have multiple PLMNs to which it can camp. Here, the RA may also be configured with multiple TACs for each PLMN. Therefore, the network may configure a TAC list for each PLMN, or configure a TAI in the UE. Here, since the TAI is configured with the PLMN and the TAC, multiple TAIs may be configured based on the TAC list. Note that the TAC list is merely an example and is not limited to the above-mentioned names.

[0184] FIG. 18 is a diagram illustrating a method for performing a cell list-based measurement procedure applicable to the present disclosure. Referring to FIG. 18, NTN cell A coverage can be determined based on satellite 1810. Here, after an RRC dormant UE performs an initial connection, it may be assigned a registration area (RA) to a mobile area without performing a registration update from AMF. The RA may include multiple TACs. As a specific example, if a UE is assigned an RA with TACs A, B, and C, the RRC dormant UE may move to a cell with TACs A, B, and C without a registration update procedure from AMF. On the other hand, if UE 1620 moves to a cell with TAC D, UE 1820 may be assigned a new RA after performing a registration update procedure from AMF.

[0185] Referring to FIG. 18, the NTN cell and the TN cell may overlap. In this case, the TAC may refer to a geographically fixed location. Therefore, each base station cell may have a specific TAC identifier. The UE may be assigned an RA (TACs 3 to 18) including all TACs in FIG. 18 by the AMF, but this is merely an example and is not limited to the above-described embodiment. That is, the UE can move within an RA without a registration update procedure in the AMF and can camp on a cell having one TAC within the RA. For example, when the UE is in the TAC18 area, it can camp on TN cell 3 having TAC 18. Also, when the UE moves to TAC 7, there is no TN cell with a sufficiently strong signal strength, so it can camp on the NTN cell. Here, since NTN cell A serves a wider area than the TN cell, multiple TACs can be transmitted to the UE through system information. The UE can select one TAC belonging to the RA from the multiple TACs received through the system information and derive the TAI. Here, as an example, an RRC idle state UE may receive the configuration of cell reselection parameters for camping through an RRC message (e.g., RRC Release, SIB2, 3, 4). That is, if a UE that has transitioned to the RRC idle state receives the configuration of cell reselection parameters for the NTN cell from TN cell 3 at TAC 18, the UE can continuously perform a search for the NTN cell within the RA. Here, since the NTN cell exists within the RA, the network may configure the cell reselection parameters for the NTN cell as an RRC message. However, since the UE cannot camp on the NTN cell in areas other than TACs 4, 5, 6, 7, 8, 10, and 11 served by NTN cell A, performing a cell search may increase unnecessary power consumption. Furthermore, since TN cells support higher QoS than NTN cells, a UE camped on a TN cell may not need to camp on the NTN cell through cell reselection. However, based on Table 6 above, a terminal camped in a TN cell may need to search for an NTN cell in an area where the signal strength of the serving cell is insufficient and the SSB of the NTN cell can be confirmed.As a specific example, if a terminal camped in TN cell 5 having TAC 10 does not have sufficient signal strength at the edge of the cell, the terminal may need to perform a cell search for NTN cell A. Therefore, the power consumption of an RRC idle terminal can be reduced through a procedure in which the terminal searches for NTN cells in a specific cell.

[0186] More specifically, for NTN cell search, the network may include cells 5 (1821) and 6 (1822) in the cell list, which have a TAC served by NTN cell A and can detect the SSB of NTN cell A. The network may set NTN cell reselection parameters including the cell list and configure them in the terminal through an RRC message. For example, a terminal located in TAC 18 may receive the configuration of NTN cell reselection parameters and a cell list (TN cells 5 and 6) through an RRC message (e.g., system information, RRC release) in TN cell 3. If the terminal is camped on TN cell 3, which is not located in the cell list in TAC 18, the terminal may not perform NTN cell search and may only perform the TN cell search for which the configuration is accepted. On the other hand, if the terminal moves to TAC 15 due to the terminal's mobility, the terminal may be camped on TN cell 8 having TAC 15 because it is only performing a search for TN cells. On the other hand, if the terminal is camped on a TN cell (e.g., TN cell 5, 6, 1821, 1822) indicated in the cell list according to the terminal's mobility, the terminal can perform an NTN cell search based on the configured NTN cell reselection parameters. For example, even if the terminal is camped on a TN cell indicated in the cell list, the TN cell should be prioritized because it supports higher QoS. Therefore, a terminal camped on a TN cell should perform an NTN cell search by considering not only the cell list check but also the procedure for checking the signal strength of the serving cell.

[0187] FIG. 19 illustrates a cell list-based NTN cell measurement signaling procedure applicable to the present disclosure. Referring to FIG. 19, a terminal 1910 may receive an RRC message from a TN cell A 1920 in an RRC connected / inactive / idle state (S200). At this time, the terminal may acquire and configure specific conditions for cell reselection (cell list) and parameters (e.g., CellReselection) including frequency information, SMTC, and other information in the RRC message. The terminal 1910 may then transition to an RRC dormant state (S205). For example, the terminal 1910 may transition to an RRC dormant state after a period of time has elapsed or by receiving an RRC release message. Here, the RRC dormant state terminal 1910 is camped on the TN cell A 1920 (S210) and can perform frequency measurement based on the configured parameters. Specifically, the terminal 1910 can perform intra- / inter-frequency frequency measurement according to parameters (e.g., CellReselection) including frequency information, SMTC, and other information. Thereafter, the terminal 1910 may need to perform cell reselection to a new cell based on the terminal's mobility (S215). As an example, the terminal 1910 may select TN Cell B (TN Cell B, 1930) through a cell reselection procedure. The terminal 1910 may receive an RRC message (e.g., system information) from TN Cell B 1930 and receive parameters including a TAC#F and cell ID (Cell B) associated with TN Cell B 1930 (S220). At this time, Cell B may not be included in the cell list. Therefore, the terminal 1910 camped on TN Cell B 1930 may not need to perform NTN cell measurement and search (S225). Thereafter, the terminal 1910 may reselect a new cell based on the terminal's mobility (S230). The terminal 1910 may select TN Cell C (TN Cell C) 1940 through a cell reselection procedure. Thereafter, the terminal 1910 may receive an RRC message (eg, system information) of the TNCell C 1940 to receive parameters including the TAC#B associated with the TNCell C and the cell ID (Cell C).As an example, cell C may be included in the cell list. Therefore, the terminal 1910 camped on TN cell C 1940 (S240) can perform NTN cell measurement and search. That is, the terminal 1910 checks the signal strength and signal quality of the serving cell, TN cell C 1940, and if they are lower than a specific value, can perform NTN cell measurement and search (S245). As another example, the terminal 1910 can perform measurement and search for the NTN cell without the procedure of checking the signal strength and signal quality of the serving cell, TN cell C 1940.

[0188] Here, cell ID may refer to a cell identity. In this case, the cell ID may be composed of a 36-bit string and may be composed of a gNB ID and a cell identifier. Here, the gNB ID may be composed of 22 or 32 bits. Therefore, the cell identifier can be expressed in 14 or 4 bits. For example, if the gNB ID is divided into 22 bits, an operator can allocate 4,194,305 IDs for macro cells or small cells. Here, for example, a 14-bit cell identifier can be allocated considering 250 DUs per CU and 12 cells per DU in a CU-DU structure. Therefore, in FIG. 19, the cell list may include a 36-bit string including the gNB ID and cell identifier for cell C. In addition, the cell ID may be configured to differ depending on the PLMN (MCC+MNC). For example, a UE in an RRC idle / inactive state may camp on multiple PLMNs. Here, the RA may also be configured with multiple TACs for each PLMN. The network can configure a cell list for each PLMN, or configure an NCGI (NR Cell Global Indefinite) in the terminal. Here, since the NCGI is composed of a PLMN and a cell ID, multiple NCGIs can be configured based on the cell list. Also, the cell list is merely an example and is not limited to this name.

[0189] 20 and 21 are diagrams illustrating a method for performing measurements based on RAC (RAN area code) applicable to the present disclosure.

[0190] Referring to FIG. 20, a cell ID (or cell identifier) ​​is a parameter for distinguishing cells, and an independent value can be assigned to each cell within a PLMN. The UE can confirm PLMN information and the associated Tracking Area Code (TAC), RAN-Area Code (RAC), and cell ID from a PLMN identifier information list (PLMN-IDIntentifoList) in system information (e.g., SIB1). Here, the TAC and cell ID are as described above. Furthermore, the RAC may refer to a parameter for dividing a specific RAN area into up to 255 areas within one TAC. That is, the TN cell can transmit the TAC in which it is located and the RAC information associated with the TAC to the UE. The UE can determine whether to perform a mobility update to the network based on the received information. For example, the mobility update may be the registration update described above. As another example, the mobility update may be a RAN-based notification area update (RNAU) procedure performed by a UE in an RRC inactive state. For example, if an RRC inactive state UE is removed from the RNA (RAN-notification area) cell list, the RRC inactive state UE needs to accept the configuration of a new RNA cell list and can therefore perform the RNAU procedure. That is, the RRC inactive state UE can perform the RNAU procedure based on the mobility of the UE.

[0191] For example, referring to FIG. 20, an RAC may be configured within a TAC. That is, multiple RACs may be configured within each TAC. Furthermore, each TN cell may have one or more unique TACs and RACs. As a specific example, TN cell 1 (2010) may have TAC#A and RACs 1, 2, 3, and 4. TN cell 2 (2020) may have TAC#A and RACs 7, 8, 9, and 10, and TN cell 4 (2040) may have TAC#C and RAC 1. That is, each cell may have a TAC and RAC depending on the location of service coverage. Here, each cell may inform a terminal of its own TAC and RAC through system information. The terminal may check the TAC and RAC that a cell has through the system information.

[0192] Further, referring to FIG. 21, the coverage of NTN cell A can be determined based on satellite 2110. After an RRC idle terminal performs initial connection, it may be assigned an RA (Registration Area) in a movable area without performing a registration update from AMF. Here, the RA includes multiple TACs. As a specific example, if a terminal is assigned an RA having TACs A, B, and C, the RRC idle terminal can move to a cell having TACs A, B, and C without a registration update procedure from AMF. On the other hand, if the terminal moves to a cell having TAC D, the terminal may be assigned a new RA after performing a registration update procedure from AMF.

[0193] As an example, the UE may be assigned an RA (TAC A, B, C, D, E, F, G) including all TACs in FIG. 21 from the AMF, but this is only an example and is not limited to the above-described embodiment. That is, the UE can move within the RA without a registration update procedure in the AMF and can camp on a cell having one TAC within the RA.

[0194] For example, when the UE is in the TAC#B area, it can camp on TN cell 6 having TAC#B in the vicinity of the UE. If the UE then moves to TAC#D based on the UE's mobility, the UE can camp on NTN cell because there is no TN cell with a sufficiently strong signal strength. Here, NTN cell A serves a wider area than the TN cell, so multiple TACs can be transmitted to the UE through system information. The UE can derive the TAI by selecting one TAC belonging to the RA from the multiple TACs included in the system information.

[0195] Furthermore, an RRC idle UE can receive the configuration of cell reselection parameters for camping through an RRC message (e.g., RRC Release, SIB2, 3, 4). That is, if a UE that transitioned to the RRC idle state at TAC#B receives the configuration of cell reselection parameters for the NTN cell from TN cell 6, the UE must continuously search for the NTN cell within the RA. Here, since the NTN cell exists within the RA, the network may configure the cell reselection parameters for the NTN cell using an RRC message. However, since the UE cannot camp on the NTN cell in areas other than TAC#A, D, E, F, and G served by NTN cell A, performing a cell search may increase unnecessary power consumption. Furthermore, since TN cells support higher QoS than NTN cells, a UE camped on a TN cell may not need to camp on the NTN cell through cell reselection.

[0196] Therefore, based on Table 6, if a terminal camped on a TN cell has insufficient signal strength of the serving cell and can perform SSB of the NTN cell, NTN cell search may be necessary. As a specific example, if a terminal camped on TN cell 3 having TAC#A and RAC3, 4, 5, and 6 or TN cell 4 having TAC#C and RAC1 has insufficient signal strength at the cell boundary, the terminal may perform cell search for NTN cell A. Therefore, the power consumption of an RRC idle terminal can be reduced through the procedure in which the terminal searches for an NTN cell in a specific cell.

[0197] More specifically, for NTN cell search, the network may include in the RAC list a combination list of TAC#A, RAC3, 4, 5, 6, and TAC#C, RAC1, which can detect the SSB of NTN cell A served by NTN cell A. Then, the network may set NTN cell reselection parameters and configure them in the UE through an RRC message. As an example, a UE located in TAC#B may receive the configuration of NTN cell reselection parameters and RAC list (TAC#A, RAC3, 4, 5, 6, and / or TAC#C, RAC1) through an RRC message (e.g., system information, RRC Release) in TN cell 6. Since the UE is camped on TN cell 6 having a TAC and RAC that are not configured in the RAC list in TAC#B, it may not perform NTN cell search and may only perform TN cell search for the accepted configuration. Also, if the UE moves to TAC#C based on the UE's mobility, the UE may be camped on TN cell 5 having TAC#C because it is only performing a search for TN cells. Here, the TAC and RAC combination of TN cell 5 may not be configured in the RAC list. Therefore, the UE does not need to perform NTN cell search. On the other hand, if the UE is camped on a TN cell (e.g., TN cell 1, 3, 4) having a TAC and RAC combination indicated in the RAC list according to the UE's movement, the UE can perform NTN cell search based on the configured NTN cell reselection parameters. Also, even if the UE is camped on a TN cell having a TAC and RAC combination indicated in the RAC list, the TN cell can be prioritized because it supports higher QoS. Therefore, a UE camped on a TN cell needs to perform NTN cell search through a procedure of checking the RAC list and also the signal strength of the serving cell.

[0198] FIG. 22 illustrates an RAC list-based NTN cell measurement signaling procedure applicable to the present disclosure. Referring to FIG. 22, a terminal 2210 may receive an RRC message from a TN cell A 2220 in an RRC connected / inactive / idle state (S300). At this time, the terminal may acquire and configure specific conditions for cell reselection (RAC list) and parameters (e.g., CellReselection) including frequency information, SMTC, and other information in the RRC message. The terminal 2210 may then transition to an RRC dormant state (S305). For example, the terminal 2210 may transition to an RRC dormant state after a period of time has elapsed or by receiving an RRC release message. Here, the RRC dormant state terminal 2210 is camped on the TN cell A 2220 (S310) and may perform frequency measurement based on the configured parameters. Specifically, the terminal 2210 may perform intra- / inter-frequency frequency measurement according to parameters (e.g., CellReselection) including frequency information, SMTC, and other information. Thereafter, the terminal 2210 may need to perform cell reselection to a new cell based on the terminal's mobility (S315). As an example, the terminal 2210 may select TN Cell B 2230 through a cell reselection procedure. The terminal 2210 may receive an RRC message (e.g., system information) from TN Cell B 2230 and receive parameters including TAC#B and RAC#10 associated with TN Cell B 2230 (S320). At this time, TAC#B and RAC#10 may not be included in the RAC list. Therefore, the terminal 2210 camped on TN Cell B 2230 may not need to perform NTN cell measurement and search (S325). Thereafter, the terminal 2210 may reselect a new cell based on the terminal's mobility (S330). The terminal 2210 may select TN Cell C 2240 through a cell reselection procedure. Thereafter, the terminal 2210 may receive an RRC message (eg, system information) of the TNCell C 2240 to receive parameters including the TAC#B and RAC#1 associated with the TNCell C.As an example, cells TAC#B and RAC#1 may be included in the RAC list. Therefore, the terminal 2210 camped on T C cell C2240 (S340) can perform NTN cell measurement and search. That is, the terminal 2210 checks the signal strength and signal quality of the serving cell T C cell C2240, and if they are lower than a specific value, it can perform NTN cell measurement and search (S345). As another example, the terminal 2210 can perform measurement and search for the NTN cell without checking the signal strength and signal quality of the serving cell T C cell C2240.

[0199] Here, the RAC list may include one or more TACs expressed as a 24-bit string. Furthermore, each TAC may include one or more RACs (integer). Here, the TAC and RAC may be configured differently depending on the PLMN (MCC+MNC). As an example, a UE in an RRC dormant / inactive state may have multiple PLMNs to camp on. An RA may be configured with multiple TACs per PLMN. The network may configure an RAC list for each PLMN, or may configure an RAC according to a TAI in the UE. Here, since a TAI is configured with a PLMN and a TAC, multiple combinations of TAIs and RACs may be configured in the RAC list. Note that the RAC list is merely an example and is not limited to the above names.

[0200] 23 illustrates a method for performing measurements based on a TAC, a cell, and / or a RAC list applicable to the present disclosure. As an example, when there are multiple cells in one TAC, the network may provide the TAC, the cell, and / or the RAC list to the terminal for NTN cell measurements to reduce power consumption.

[0201] As an example, a terminal that has received the configuration of the TAC list (e.g., TACs 10 and 11) of FIG. 16 described above can measure the NTN cell according to the signal strength of the serving cell while camping on TN cells 5, 6, 9, and 10 having TAC 10 or 11. Here, when the terminal camps on TN cells 9 and 10, the terminal may not need to measure the NTN cell because adjacent TN cells 5 or 6 exist. Therefore, the network may configure at least one of one or more combinations of TAC, cell, and RAC list in the terminal for NTN cell measurement. As a specific example, the combination may be a TAC and a cell list, or a RAC and a cell list, but this is merely an example and is not limited to the above-described embodiment.

[0202] FIG. 24 illustrates an NTN cell measurement signaling procedure based on at least one of a TAC, a cell, and an RAC list applicable to the present disclosure. Referring to FIG. 24, a terminal 2410 may receive an RRC message from a TN cell A 2420 in an RRC connected / inactive / idle state (S400). At this time, the RRC message may include specific conditions for cell reselection (RAC list) and parameters (e.g., cellreselection) including frequency information, SMTC, and other information. The terminal 2410 may then transition to an RRC dormant state (S405). For example, the terminal 2410 may transition to an RRC dormant state after a period of time has elapsed or by receiving an RRC release message. Here, the RRC dormant terminal 2410 is camped on the TN cell A 2420 (S410) and may perform frequency measurement based on parameters received from the configuration. Specifically, the terminal 2410 may perform frequency measurement for intra / inter frequencies according to parameters (e.g., CellReselection) including frequency information, SMTC, and other information. Thereafter, the terminal 2410 may need to perform cell reselection to a new cell based on the terminal's mobility (S415). As an example, the terminal 2410 may select TN Cell B (TN Cell B, 2430) through a cell reselection ranking procedure. The terminal 2410 may receive an RRC message (e.g., system information) from TN Cell B 2430 and receive parameters including TAC#B and Cell ID(cell B) associated with TN Cell B 2430 (S420). At this time, TAC#B may be included in the TAC list, but Cell ID(cell B) may not be included in the cell list. Therefore, the terminal 2410 camped on TN Cell B 2430 may not need to perform NTN cell measurement and search (S425). Thereafter, the terminal 2410 may reselect a new cell based on the terminal's mobility (S430). The terminal 2410 may select a TN Cell C (TN Cell C, 2440) through a cell reselection ranking procedure.Thereafter, the terminal 2410 may receive an RRC message (e.g., system information) from TNCell C 2440 and receive parameters including a TAC#B and a cell ID (cell C) associated with TNCell C. As an example, cell TAC#B and cell ID (cell C) may be included in the TAC list and cell list. Thus, the terminal 2410 camped on TNCell C 2440 (S440) may perform NTN cell measurement and search. That is, the terminal 2410 checks the signal strength and signal quality of the serving cell, TNCell C 2440, and if they are lower than a specific value, performs NTN cell measurement and search (S445). As another example, the terminal 2410 may perform measurement and search for the NTN cell without checking the signal strength and signal quality of the serving cell, TNCell C 2440. While FIG. 24 describes an embodiment based on a combination of a TAC list and a cell list, a combination of an RAC and a cell list is also possible and is not limited to a specific embodiment.

[0203] Here, as an example, the TAC, RAC, and cell ID may be configured differently depending on the PLMN (MCC+MNC). Also, a UE in an RRC idle / inactive state may be able to camp on multiple PLMNs. Therefore, the RA may also be configured with multiple TACs for each PLMN. The network may configure at least one of a TAC, a cell, and an RAC list for each PLMN. As another example, the network may configure at least one of a TAI, an NCGI, and an RAC combination for each PLMN in the UE. Here, the TAI is configured from the PLMN and the TAC, and the NCGI is configured from the PLMN and the Cell ID. Therefore, a combination of a TAC and a cell list, or an RAC and multiple TAIs, NCGIs, and RACs in the cell list may be configured. Also, as an example, the TAC and cell list and the RAC and cell list are merely examples and are not limited to these names.

[0204] Figure 25 is a diagram illustrating an SSB configuration applicable to the present disclosure. Referring to Figure 25, a cell can provide SSB configuration information to a terminal through system information (e.g., SIB1). Figure 25 illustrates a case where the subcarrier spacing (SCS) is 15 kHz, the frequency band is 3 to 6 GHz, and the maximum number of SSBs available in SIB1 between 3 and 6 GHz is eight. Note that in Figure 25, the inOneGroup indicating the SSB to be used for actual transmission among the eight SSBs may be (1 1 1 1 1 1 0 1), but this is merely an example and is not limited to the above-described embodiment. Here, the symbol position of the SSB may be predefined for a specific subcarrier spacing and frequency band. As an example, the SSB starting symbol of candidate SSBs in Figure 25 can be determined according to Equation 3 below, and the SSB can be transmitted at symbol indexes 2, 8, 16, 22, 30, 36, 44, and 50 based on Equation 3.

[0205]

number

[0206] For example, the SSBs actually transmitted by the network may vary depending on the environment. Therefore, the network can inform the terminal of the actual SSB transmission through SIB1 in a bitmap format (e.g., inOneGroup). In FIG. 25, inOneGroup is set to (1 1 1 1 1 1 0 1), so SSBs 2510, 2520, 2530, 2540, 2550, 2560, and 2570, excluding SSB #6, out of the eight SSBs, can be transmitted. For example, if the frequency band is 3 GHz or less, the maximum number of SSBs may be four, and the SSB starting symbol of the candidate SSBs may be expressed as in Equation 4 below, and SSBs can be transmitted at symbols 2, 8, 16, and 22.

[0207]

number

[0208] As another example, the maximum number of SSBs in FR2 may be 64. In this case, SIB1 may include groupPresence, which divides the 64 SSBs into eight groups and indicates in which group the SSB is to be transmitted. As a specific example, if groupPresence is (1 0 0 0 0 0 0 1) and inOneGroup is set to (1 1 0 0 0 0 0 0), the indices of the SSBs actually transmitted may be 0, 1, 56, and 57. Here, an SSB burst set is configured within 5 ms and can be repeatedly transmitted with a specific period.

[0209] FIG. 26 is a diagram illustrating an SMTC window configuration configured by a network for specific frequency measurements applicable to the present disclosure. Referring to FIG. 26, the network can configure SMTC windows for neighboring cell 1 (2610) and neighboring cell 2 (2620) in a terminal. That is, the network can instruct the terminal to perform measurements for a specific time period at specific periods in the time domain so that the terminal can measure the SSBs of neighboring cell 1 (2610) and neighboring cell 2 (2610), and can provide such configuration information. Here, the terminal can set the SMTC window periodicity to be longer than the SSB period in consideration of power consumption. As an example, the network can set the SMTC window configuration to the SSB period of neighboring cell 2 (2620) so that the terminal can measure the SSB of neighboring cell 2 (2620). Furthermore, the network can set the SMTC window configuration to be longer than the SSB period of neighboring cell 1 (2610) so that the terminal can measure the SSB of neighboring cell 1 (2610).

[0210] Here, the terminal can perform an operation for SSB search in an SMTC window duration based on the step-size of the GSCN in the NR-ARFCN indicating a specific frequency band for the above-mentioned intra / inter frequency measurement.

[0211] For example, if TN frequency information is configured in a terminal for cell reselection in an NTN cell, the terminal may perform SSB measurements for each configured SMTC window configuration, which may result in sustained power consumption. In consideration of the above, a procedure may be required to not perform measurements depending on specific conditions (TAC list and / or cell list and / or RAC list).

[0212] For example, since TN cells can satisfy higher QoS than NTN cells, the UE can always prioritize TN cells. That is, when an NTN cell configures a UE to measure a TN cell, the NTN cell can always be set with a high TN priority, and the UE always measures the configured TN cell, so a conditional TN cell measurement and search procedure needs to be added. Conversely, when a UE is camped on a TN cell, the UE can perform measurement on an NTN cell with a lower priority if the signal strength of the serving cell becomes low. Here, since a UE camped on a TN cell may not need to measure an NTN cell, a conditional NTN cell measurement and search procedure needs to be added to reduce UE power consumption. As an example, the UE can measure the NTN frequency according to the above-mentioned specific conditions (at least one combination of the TAC list, cell list, and RAC list), and the procedure for this will be described below. When inter-frequency information is configured in the UE based on an RRC message (e.g., system information, RRC release), the UE can perform measurement according to a specific condition (at least one combination of the TAC list, cell list, and RAC list).

[0213] For example, Table 7 may be a table showing how the UE performs measurements. More specifically, if the priority of the inter-frequency or inter-RAT frequency is the same as or lower than the current frequency and the signal strength and signal quality of the serving cell are lower than a specific value, the UE may perform measurements taking into account the above-mentioned specific conditions (a combination of at least one of the TAC list, the cell list, and the RAC list), which may be as shown in Table 7 below.

[0214] As another example, if the priority of the inter-frequency or inter-RAT frequency is the same as or lower than the current frequency, the terminal may perform measurements taking into account the above-mentioned specific conditions (at least any combination of the TAC list, cell list, and RAC list).

[0215] [Table 7]

[0216] Here, the specific condition (at least any combination of the TAC list, the cell list, and the RAC list) may be configured commonly for all NTN frequency bands in the RRC message. As another example, the specific condition (at least any combination of the TAC list, the cell list, and the RAC list) may be configured only for a specific NTN frequency band, and is not limited to a specific embodiment.

[0217] As a specific example, if the above-mentioned specific conditions (at least one combination of the TAC list, cell list, and RAC list) for all NTN frequencies are configured using one common parameter in an RRC message, the common parameter may be configured using at least one of SIB2, SIB3, and SIB4. If the above-mentioned specific conditions (at least one combination of the TAC list, cell list, and RAC list) are satisfied, the UE may perform measurements for all NTN frequencies, as shown in Table 7 above. As another example, if the above-mentioned specific conditions (at least one combination of the TAC list, cell list, and RAC list) are configured only for a specific NTN frequency band, the network may configure the above-mentioned specific conditions (at least one combination of the TAC list, cell list, and RAC list) for each specific NTN frequency. The UE may perform measurements only on NTN frequencies that satisfy the above-mentioned specific conditions (at least one combination of the TAC list, cell list, and RAC list). Here, the NTN frequency may refer to a specific frequency band and is not limited to a specific embodiment.

[0218] As another example, the conditions under which the UE performs measurements for intra-frequency cell reselection indicated through system information may be as shown in Table 8. That is, the UE may compare the signal strength and signal quality of the serving cell with specific values.

[0219] [Table 8]

[0220] Here, the UE may perform NTN frequency measurement according to the above-mentioned specific conditions (at least one combination of the TAC list, cell list, and RAC list). As an example, when the UE receives and configures intra-frequency information through an RRC message (e.g., system information, RRC release), the UE may perform measurement after checking the above-mentioned specific conditions (at least one combination of the TAC list, cell list, and RAC list), which may be as shown in Table 9 below.

[0221] [Table 9]

[0222] Further, as an example, if a T-service of the serving cell exists in the system information (e.g., SIB19), the UE may perform intra-frequency measurement before the T-service regardless of the conditions in Table 9 below. Here, the T-service may refer to the absolute time (epoch time) at which a fixed cell provides coverage. As another example, the UE may always perform measurement on high-priority intra-frequencies regardless of the conditions in Table 9.

[0223] As described above, in order for the UE to conditionally perform measurements on NTN cells, the TN / NTN can be indicated as a parameter in the existing system information, or the above-mentioned specific conditions for measurement (at least one combination of the TAC list, cell list, and RAC list) can be added. That is, the TN / NTN can be indicated in addition to the inter / intra frequency information priority, SMTC, NR-ARFCN (Absolute radio frequency channel number), band list, and other information for cell reselection as existing system information, or the above-mentioned specific conditions for measurement (at least one combination of the TAC list, cell list, and RAC list) can be added. That is, the above-mentioned specific conditions (at least one combination of the TAC list, cell list, and RAC list) can be included in the parameter configuration for cell reselection. Here, the above-mentioned specific conditions (at least one combination of the TAC list, cell list, and RAC list) can be configured as one common parameter for all bands for NTN frequency measurement, or as specific parameters for a specific NTN frequency band, as described above.

[0224] 2. Conditional TN cell search (frequency measurement)

[0225] As an example, in relation to a conditional TN cell search, a method for performing a cell search based on the reference location of a neighboring TN cell (hereinafter referred to as method 2-1) and a method for performing a cell search based on the reference location of a neighboring NTN cell (hereinafter referred to as method 2-2) can be considered. Here, method 2-1 and method 2-2 can be applied independently in an NTN system. As another example, method 2-1 can be applied preferentially, and method 2-2 can be applied when it is difficult to apply method 2-1, but this is not limited to a specific embodiment. For convenience of explanation, the following description will be based on method 2-1 and method 2-2, respectively. However, each method can be applied in a correlated or complementary manner, and is not limited to a specific embodiment.

[0226] Method 2-1 (Neighbor TN cell reference location based cell search)

[0227] FIG. 27 is a diagram illustrating a method for performing a cell search based on a reference location of a neighboring TN cell applicable to the present disclosure. Referring to FIG. 27, a terminal may perform measurements on TN frequencies based on a reference point (or reference location). Here, a terminal in an RRC idle / inactive state may perform measurements on TN frequencies based on a certain condition to reduce power consumption. As an example, the network may configure a specific point where a TN cell is located as a reference location in the terminal through one or more RRC messages (e.g., system information, RRC release, RRC reconfiguration). As an example, the reference location may be the specific point where a TN cell is located. As another example, the reference location may be set to a specific location that is preset based on the TN cell, and is not limited to a specific embodiment.

[0228] Here, the terminal can check whether its location information is valid. If the terminal's location information is valid, the terminal can compare the distance between the reference point configured in the network and the terminal with a threshold. At this time, if the distance between the reference point configured in the network and the terminal is less than the threshold, the terminal can perform TN frequency measurement.

[0229] As a specific example, the terminal 2720 in satellite 1 (2710) in FIG. 27 can receive configuration and check the distance to reference location 1 (2730). At this time, if the distance to reference location 1 (2730) is equal to or greater than a threshold, the terminal does not need to perform TN frequency measurement. On the other hand, the terminal 2750 in satellite 22740 can receive configuration of two reference locations (reference locations 1 and 2) 2761 and 2762 from the network. However, this is merely an example for convenience of explanation and is not limited to the above-described embodiment. Here, if the terminal 2750's location is valid, it can check the distance to the reference location. Then, the terminal 2750 can determine whether to perform measurement on the TN frequency based on the threshold. In consideration of the above, the NTN cell can provide the terminal with information (e.g., reference location, distance threshold, associated frequency index) that assists TN cell measurement.

[0230] As a specific example, NTN-specific system information (e.g., SIB19) may include information that assists the above-mentioned TN cell measurement. As another example, the information that assists the above-mentioned TN cell measurement may be included in existing system information and is not limited to a specific embodiment. The UE can check information about TN neighbor cells through the system information received from the serving cell, and can therefore determine whether to perform TN-frequency measurement.

[0231] Here, information about TN neighboring cells may be associated with information for cell reselection. For example, when a reference point for a neighboring cell is provided to a terminal as system information, the terminal may determine the frequency band in which the terminal performs measurement and the associated SMTC window based on the terminal's valid location information, the distance to the reference point, and a threshold value. In consideration of the above, the terminal may associate information about neighboring cells with measurement frequency band information to determine TN frequency measurement.

[0232] FIG. 28 is a diagram illustrating a TN cell configuration applicable to the present disclosure. As described above, information on TN neighbor cells may be associated with information for cell reselection. As an example, referring to FIG. 28, an NTN cell may be configured based on satellite 1 (2810). Here, a terminal 2820 may perform measurements on TN neighbor cells taking into account the reference point (or reference position) of the TN cell. Neighbor cell information for TN cell 1 may include reference location 1 2831 and a distance threshold of TN cell 1 as information for determining measurements. In addition, the neighbor cell information for TN cell 1 may include at least one of the frequency band location (NR-ARFCN) of TN cell 1 and a TN index as information for cell reselection. Here, the information for cell reselection may be associated with frequency information in an RRC message (e.g., system information, RRC release). As a specific example, when NR-ARFCN is designated as "A" in TN cell 1, information for cell reselection may be associated with frequency information (InterFreqCarrierFreqInfo or MeasIdleCarrierNR 1,2) in which NR-ARFCN is set to "A". As another example, when TN index is indicated as "1" in TN cell 1, information for cell reselection may be associated with frequency information (InterFreqCarrierFreqInfo or MeasIdleCarrierNR 1).

[0233] Furthermore, when NR-ARFCN is designated as "B" in TN cell 2, information for cell reselection may be associated with frequency information (InterFreqCarrierFreqInfo or MeasIdleCarrierNR 3) in which NR-ARFCN is set to "B". As another example, when TN index is designated as "2" in TN cell 2, information for cell reselection may be associated with frequency information (InterFreqCarrierFreqInfo or MeasIdleCarrierNR 2, 3).

[0234] More specifically, if the distance between the terminal 2820 and TN cell 1 is smaller than a distance threshold, the terminal 2820 may check frequency information associated with at least one of the NR-ARFCN and the TN index. Then, the terminal 2820 may check SSB at the time / frequency corresponding to the SMTC and NR-ARFCN associated with the checked frequency information. Furthermore, if the distance between the terminal 2820 and TN cell 2 is greater than a distance threshold, the terminal 2820 may not check frequency information associated with the NR-ARFCN and the TN index and perform a procedure of checking SSB at the time / frequency corresponding to the SMTC and NR-ARFCN associated with the frequency information. That is, the terminal 2820 may perform a procedure of checking SSB at the time / frequency corresponding to the SMTC and NR-ARFCN associated with the frequency information only within the distance threshold based on the valid current location of the terminal and reference location information configured for each TN cell.

[0235] Here, the reference location information and distance threshold configured for each TN cell may be configured by being included in the frequency information (InterFreqCarrierFreqInfo or MeasIdleCarrierNR). As an example, frequency information 1 (InterFreqCarrierFreqInfo or MeasIdleCarrierNR1) may include NR-ARFCN and SMTC information. Furthermore, frequency information 1 may further include reference location information and distance threshold information. The terminal 2820 can determine whether to perform a procedure to check SSB in the time / frequency configuration (SMTC, NR-ARFCN) based on the information for determining measurements (reference location information, distance threshold), as described above. Here, the reference location information where the TN cell is located may be as shown in Table 10 below. Here, Table 10 may refer to information displayed in latitude and longitude.

[0236] [Table 10]

[0237] For example, since TN cells can satisfy a higher QoS than NTN cells, the UE can always preferentially select TN cells, as described above. That is, when NTN cells configure the UE to measure TN cells, the priority of TN cells can always be set higher. The UE can always measure TN cells based on the above configuration. However, since the UE must always measure the configured TN cells, power consumption may be continuous. Therefore, the UE can reduce power consumption by measuring TN frequencies according to the above-mentioned specific conditions (distance threshold). Specifically, in the procedure in which the UE measures the TN frequency, the UE may receive an RRC message (e.g., system information, RRC release). At this time, the RRC message may include inter-frequency information. The UE can configure a measurement operation based on the inter-frequency information. Here, an operation to check the above-mentioned specific conditions (distance threshold) may be necessary, which may be as shown in Table 11 below. That is, the terminal can perform measurements based on whether the priority of the inter-frequency or inter-RAT frequency is higher than the priority of the current frequency, whether the signal strength and signal quality of the serving cell are greater than a specific value, and whether the distance between the reference position of the target cell and the terminal is greater than a distance threshold, which may be as shown in Table 11 below.

[0238] [Table 11]

[0239] Also, as an example, the UE may measure the TN frequency according to the above-mentioned specific condition (distance threshold) to reduce power consumption. Specifically, in the procedure in which the UE measures the TN frequency, the UE may receive an RRC message (e.g., system information, RRC release). At this time, the RRC message may include intra-frequency information. The UE may configure a measurement operation based on the intra-frequency information, and here, an operation to check the above-mentioned specific condition (distance threshold) may be necessary, which may be as shown in Table 12 below.

[0240] That is, the terminal can perform measurements based on whether the intra-frequency is associated with an NTN cell or a TN cell, whether the signal strength and signal quality of the serving cell are greater than a specific value, and whether the distance between the reference position of the target cell and the terminal is greater than a distance threshold, which may be as shown in Table 11 below.

[0241] [Table 12]

[0242] Method 2-2 (Neighbor NTN cell reference location based cell search)

[0243] 29 is a diagram showing a reference position of an NTN cell applicable to the present disclosure. As an example, for convenience of explanation, reference location information is described in FIG. 29 based on being set in an area where a TN cell is located, but is not limited thereto. As an example, the reference position may be set at the edge of the TN cell. As another example, the reference position may be the reference position of an adjacent NTN cell.

[0244] Referring to FIG. 29, multiple NTN cells can be configured based on satellite 1 (2910). Here, the neighbor cell reference location may not be derived based on the TN cell, but may be derived based on the NTN neighbor cell. As a specific example, there may be a case where the reference location of the TN cell cannot be set for security reasons. In the above-mentioned situation, cell search can be performed based on the reference location of the NTN cell. As an example, in FIG. 29, cells A, B, C, D, E, F, and G may be NTN cells based on a fixed beam (earth fixed beam) by satellite 1 (2910). Here, each NTN cell can provide reference location information to the terminal 2920. The terminal 2920 can control measurements based on the reference location information received from each NTN cell.

[0245] As an example, if the terminal 2920 is camped on cell B, the terminal 2920 can acquire the reference position 2931 of cell B through system information. As another example, if the terminal 2920 is camped on cell G, the terminal 2920 can acquire the reference position 2931 of cell G through system information. Here, it can be considered that the TN cell is located in an overlapping position with cells B, C, and D. In this case, the network can provide the terminal with the reference positions of neighboring cells to control measurements on the TN cell.

[0246] As a specific example, when the UE 2920 is camped on cell B, cell B may provide the UE with the reference location of cell B (Reference location of NTN cell B, 2931) and the reference locations of neighboring cells (Reference location of NTN cell C and / or Reference location of NTN cell D, 2932, 2933) via an RRC message. The UE may determine measurements for TN cells based on the distance from at least one of the reference location 2931 of cell B, which is the serving cell, and the reference locations 2932, 2933 of the neighboring cells. More specifically, the UE may check whether the reference location of cell B, which is the serving cell, is greater than a specific threshold. The UE may also check whether the distance from the reference location of the neighboring cell is greater than a threshold. That is, the UE may determine whether to perform TN cell measurements based on information obtained by comparing the reference location of the serving cell with a threshold and information obtained by comparing the reference locations of the neighboring cells with a threshold.

[0247] For example, since TN cells can satisfy a higher QoS than NTN cells, the UE can always preferentially select TN cells, as described above. That is, when NTN cells configure the UE to measure TN cells, the priority of TN cells can always be set higher. The UE can always measure TN cells based on the above configuration. However, since the UE must always measure the configured TN cells, power consumption may be continuous. Therefore, the UE can reduce power consumption by measuring TN frequencies according to the above-mentioned specific conditions (distance threshold). Specifically, in the procedure in which the UE measures the TN frequency, the UE may receive an RRC message (e.g., system information, RRC release). At this time, the RRC message may include inter-frequency information. The UE can configure a measurement operation based on the inter-frequency information, and an operation to check the above-mentioned specific conditions (distance threshold) may be necessary, which may be as shown in Table 13 below.

[0248] [Table 13]

[0249] Also, as an example, the UE can reduce power consumption by measuring the TN frequency according to the above-mentioned specific condition (distance threshold). Specifically, in the procedure in which the UE measures the TN frequency, the UE can receive an RRC message (e.g., system information, RRC release). At this time, the RRC message can include intra-frequency information. The UE can configure a measurement operation based on the intra-frequency information. Here, an operation to check the above-mentioned specific condition (distance threshold) may be necessary, which may be as shown in Table 14 below.

[0250] [Table 14]

[0251] FIG. 30 is a flowchart illustrating a method for performing a conditional NTN cell search applicable to the present disclosure.

[0252] Referring to FIG. 30, the UE may acquire condition information for cell reselection through an RRC message (S3010). Here, the condition information for cell reselection may be set based on at least one of a TAC list, a RAC list, and a cell list. Here, for example, the UE may receive the RRC message and transition to an idle state. Thereafter, the UE may move from the first cell where it is camped to a second cell based on the UE's mobility (S3020). At this time, the UE may receive an RRC message including measurement-related information for cell reselection from the second cell (S3030). For example, the measurement-related information for cell reselection may include at least one of a TAC list, a RAC list, and a cell ID. Then, the UE determines whether a specific condition is met based on the measurement-related information for cell reselection received from the second cell (S3040). Here, the specific condition may be a condition for determining whether NTN cell measurement and search are necessary based on at least one of the TAC list, the RAC list, and the cell ID list, as described above. For example, if a specific condition is met based on the information obtained from the second cell described above, an NTN cell search can be performed, as described above (S3050).

[0253] FIG. 31 is a flowchart illustrating a method for performing a conditional TN cell search to which the present disclosure can be applied. Referring to FIG. 31, a terminal may acquire reference location information and distance threshold information for each of at least one or more cells through an RRC message (S3110). Here, the at least one or more cells may be TN cells or NTN cells. As an example, if the cell is a TN cell, the reference location information may be a specific point where the TN cell is located. As another example, the reference location information may be a location determined based on the TN cell, and is not limited to a specific embodiment. If the cell is an NTN cell, the reference location information may be information derived based on the NTN cell. Then, the terminal may derive distance condition information based on the reference location information and distance threshold information for each of at least one or more cells (S3120). Then, the terminal may perform a TN cell search based on the current location and the distance condition information, as described above (S3130).

[0254] FIG. 32 is a diagram showing the configuration of an apparatus to which the present disclosure can be applied.

[0255] 32, a first device 3200 and a second device 3250 may communicate with each other. In this case, as an example, the first device 3200 may be a base station device, and the second device 3250 may be a terminal device. As another example, both the first device 3200 and the second device 3250 may be terminal devices. That is, the first device 3200 and the second device 3250 may be devices that communicate with each other based on NR-based communication.

[0256] As an example, consider a case where the first device 3200 is a base station device and the second device 3250 is a terminal device. In this case, the base station device 3200 may include a processor 3220, an antenna unit 3212, a transceiver 3214, and a memory 3216. The processor 3220 performs baseband-related signal processing and may include an upper layer processing unit 3230 and a physical layer processing unit 3240. The upper layer processing unit 3230 may process operations of a Medium Access Control (MAC) layer, a Radio Resource Control (RRC) layer, or higher layers. The physical layer processing unit 3240 may process operations of a physical (PHY) layer (e.g., uplink receive signal processing, downlink transmit signal processing). In addition to performing baseband-related signal processing, the processor 3220 may control the overall operation of the base station device 3200. The antenna unit 3212 may include one or more physical antennas. If multiple antennas are included, MIMO (Multiple Input Multiple Output) transmission and reception may be supported. The base station device 3200 may also support beamforming. The memory 3216 may store information processed by the processor 3220, software associated with the operation of the base station device 3200, an operating system, applications, etc., and may include components such as a buffer. The processor 3220 of the base station device 3200 may be configured to implement the operation of a base station in the embodiments described herein.

[0257] The terminal device 3250 may include a processor 3270, an antenna unit 3262, a transceiver 3264, and a memory 3266. As an example, the terminal device 3250 of the present invention may communicate with the base station device 3200. As another example, the terminal device 3250 of the present invention may perform sidelink communication with another terminal device. That is, the terminal device 3250 of the present invention refers to a device capable of communicating with at least one of the base station device 3200 and another terminal device, and is not limited to communication with a specific device. The processor 3270 performs baseband-related signal processing and may include an upper layer processing unit 3280 and a physical layer processing unit 3290. The upper layer processing unit 3280 may process operations of the MAC layer, the RRC layer, or higher layers. The physical layer processing unit 3290 may process operations of the PHY layer (e.g., downlink receive signal processing, uplink transmit signal processing, sidelink signal processing). In addition to performing baseband-related signal processing, the processor 3270 may control the overall operation of the terminal device 3250. The antenna unit 3262 may include one or more physical antennas, and when multiple antennas are included, it may support MIMO transmission and reception. It may also support beamforming. The memory 3266 may store information processed by the processor 3270, software associated with the operation of the terminal device 3250, an operating system, applications, etc., and may include components such as a buffer. The terminal device 3250 according to an example of the present invention may be associated with a vehicle. For example, the terminal device 3250 may be incorporated into, located in, or located on the vehicle. The terminal device 3250 according to the present invention may also be the vehicle itself. The terminal device 3250 according to the present invention may be at least one of a wearable terminal, an AV / VR terminal, an IoT terminal, a robot terminal, and a public safety terminal.The terminal device 3250 to which the present invention can be applied may include any of various types of communication devices that support interactive services using a sidelink for services such as Internet connection, service execution, navigation, real-time information, autonomous driving, safety, and risk diagnosis, etc. It may also include any type of communication device that can perform a sidelink operation, such as an AR / VR device, or a sensor that performs a relay operation.

[0258] Here, the vehicle / terminal to which the present invention is applied may include an autonomous vehicle / terminal, a semi-autonomous vehicle / terminal, a non-autonomous vehicle / terminal, etc. Meanwhile, although the terminal device 3250 according to an example of the present invention is described as being associated with a vehicle, one or more of the UEs may not be associated with a vehicle. This is merely an example, and the application of the present invention should not be construed as being limited by the described example. In addition, the terminal device 3250 according to an example of the present invention may also include various types of communication devices capable of cooperating to support interactive services using a sidelink. That is, the terminal device 3250 may be used not only to directly support interactive services using a sidelink, but also as a cooperating device to support interactive services using a sidelink.

[0259] For example, the terminal device 3250 may acquire condition information for cell reselection through an RRC message. Here, the condition information for cell reselection may be set based on at least one of a TAC list, a RAC list, and a cell list. The terminal device 3250 may receive the RRC message and transition to an idle state. Thereafter, the terminal device 3250 may move from the first cell on which it is camped to the second cell based on its mobility. At this time, the terminal device 3250 may receive an RRC message including measurement-related information for cell reselection from the second cell. For example, the measurement-related information for cell reselection may include at least one of a TAC list, a RAC list, and a cell ID. Then, the terminal device 3250 may determine whether a specific condition is met based on the measurement-related information for cell reselection received from the second cell. Here, the specific condition may be a condition for determining whether NTN cell measurement and search are necessary based on at least one of the TAC list, the RAC list, and the cell ID list, as described above. As an example, if certain conditions are met based on the information obtained from the first cell described above, the terminal device 3250 may perform an NTN cell search when camped on the second cell.

[0260] Further, as an example, the terminal device 3250 may acquire reference location information and distance threshold information for each of at least one or more cells through an RRC message. Here, in the case of a TN cell, the reference location information may be a specific point where the TN cell is located. As another example, the reference location information may be a location determined based on the TN cell, and is not limited to a specific embodiment. In the case of an NTN cell, the reference location information may be information derived based on the NTN cell. Then, the terminal device 3250 may derive distance condition information based on the reference location information and distance threshold information for each of at least one or more cells. Then, the terminal device 3250 may perform a TN cell search based on the current location and the distance condition information, as described above.

[0261] Furthermore, various embodiments of the present disclosure may be implemented using hardware, firmware, software, or a combination thereof, etc. In the case of a hardware implementation, the implementation may be using one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), general-purpose processors, controllers, microcontrollers, microprocessors, etc.

[0262] The scope of the present disclosure includes software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that cause the operations of the methods of the various embodiments to be performed on a device or computer, as well as non-transitory computer-readable media on which such software or instructions are stored and which can be executed on a device or computer.

[0263] The various embodiments of the present disclosure do not enumerate all possible combinations, but are intended to describe representative aspects of the present disclosure, and the matters described in the various embodiments may be applied independently or in combination of two or more. [Industrial Applicability]

[0264] The above may also be applied to other systems.

Claims

1. A method by which user equipment (UE) performs cell reselection based on a non-terrestrial network (NTN) within a wireless communication system, The step of receiving information for measuring terrestrial network (TN) cells via an NTN cell, wherein the information for measuring the TN cell is: Reference position information for at least one first TN cell; and A step including distance threshold information for at least one first TN cell; The steps include receiving system information including identifier information for at least one first TN cell, A step of determining first distance condition information based on the reference position information for the first at least one TN cell and the distance threshold information for the first at least one TN cell, A step of determining whether the UE is within coverage for the first at least one TN cell based on the location of the UE and the first distance condition information, A method comprising the step of performing at least one measurement for the frequency of the first at least one TN cell based on the determination that the UE is within the coverage of the first at least one TN cell, wherein the frequency of the first at least one TN cell is determined based on the identifier information for the at least one TN cell.

2. The method according to claim 1, wherein the reference position information for the first at least one TN cell and the distance threshold information for the first at least one TN cell are associated with frequency information configured for the first at least one cell.

3. The system information further includes frequency information for the first at least one TN cell. The method according to claim 1, wherein the identifier information for the first at least one TN is included in the frequency information configured for the measurement of the first at least one TN cell.

4. The steps include receiving information for at least one second TN cell, A step of determining second distance condition information based on reference position information for the second at least one TN cell and distance threshold information for the second at least one TN cell, A step of determining whether the UE is within coverage for the second or at least one TN cell based on the location of the UE and the second distance condition information, The method according to claim 1, comprising the step of skipping a measurement of the frequency of the second at least one TN cell based on the determination that the UE is not within the coverage for the second at least one TN cell, wherein the frequency of the second at least one TN cell is determined based on identifier information of the second at least one TN cell.

5. The skip of the measurement of the frequency of the second or at least one TN cell is: The method according to claim 4, comprising skipping at least one of a new radio inter-frequency measurement or an inter-radio access technology (inter-RAT) measurement.

6. The first at least one TN cell includes a first TN cell and a second TN cell as a TN cell group, and the steps include identifying frequency information for the first TN cell, wherein the frequency information for the first TN cell is related to the TN index of the first TN cell, The method further includes the step of identifying frequency information for the second TN cell included in the TN cell group of the first at least one TN cell, The method according to claim 1, wherein the frequency information for the second TN cell is related to the TN index of the second TN cell.

7. The method according to claim 6, wherein the TN index of the first TN cell included in the TN cell group of the first at least one TN cell relates to the reference position information for the first TN cell and the distance threshold information for the first TN cell.

8. The information for TN cell measurement is: The TN index of the first TN cell included in the TN cell group of the first at least one TN cell; The reference position information for the first TN cell; and TN coverage information for the first TN cell, indicating the distance threshold information for the first TN cell; and The TN index of a second TN cell included in the TN cell group of the first at least one TN cell; The reference position information for the second TN cell; and The method according to claim 6, comprising TN coverage information for the second TN cell indicating the distance threshold information for the second TN cell.

9. The reception of the information for TN cell measurement is: The method according to claim 1, comprising receiving a radio resource control (RRC) message containing the information for TN cell measurement while the UE is camping in the NTN cell.

10. The method according to claim 1, wherein the UE camped in the NTN cell is in an RRC idle state or an RRC inactive state.

11. The method according to claim 1, further comprising the step of camping to a specific cell within the first at least one TN cell based on at least one measurement of the first at least one TN cell with respect to the frequency.

12. The method according to claim 1, The reception of the system information, which includes frequency information for at least one first TN cell, is: The method according to claim 1, comprising receiving a system information block 4 (SIB4) containing information for inter-frequency cell reselection related to the first at least one TN cell.

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