Method and device for performing handover on basis of non-terrestrial networks in wireless communication system

Abstract

A wireless communication system may include: as a step in which a wireless user device in NTN coverage receives a handover command from a source base station, a step in which one or more wireless user devices in the NTN coverage receive the handover command and check whether a handover condition is satisfied on the basis of the handover command; and a step of performing random access to a target base station in a RACH resource allocated on the basis of a wireless user device identifier, when the handover condition is satisfied.

Description

Method and device for performing handover based on a non-terrestrial network in a wireless communication system

[0001] The present invention relates to a method for performing handover based on non-terrestrial networks (NTNs) in a wireless communication system. Specifically, the present invention relates to a method for reducing signaling overhead that occurs when multiple terminals simultaneously perform handovers due to feeder link switching or satellite movement in an NTN environment.

[0002]

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

[0004] To meet the requirements presented in "IMT for 2020 and beyond," the 3rd Generation Partnership Project (3GPP) NR (New Radio) system is being discussed to support various numerologies based on time-frequency resource units, taking into account various scenarios, service requirements, and potential system compatibility.

[0005] In addition, in new communication systems, discussions are underway on how to support uninterrupted communication services at the service level for mobile terminals (e.g., vehicle / train / ship-type terminals / personally-carried smartphones) by using non-terrestrial networks (NTN) as well as terrestrial networks (TN).

[0006]

[0007] The present invention can provide a method and device for performing handover in an NTN environment of a wireless communication system.

[0008] The present invention relates to a method and apparatus for simultaneously performing handover for multiple terminals according to feeder link switch or satellite movement in an NTN environment of a wireless communication system.

[0009] The present invention relates to a method and apparatus for performing common handover in an NTN environment of a wireless communication system.

[0010] The present invention relates to a method and apparatus for performing common handover and terminal identifier-based handover in an NTN environment of a wireless communication system.

[0011]

[0012] In one embodiment, a method may include a step of receiving a handover command from a source base station by a wireless user device within non-terrestrial networks (NTN) coverage, the step of determining whether one or more wireless user devices within the NTN coverage receive the handover command and satisfy a handover condition based on the handover command, and a step of performing a random access to a target base station on a random access channel (RACH) resource allocated based on a wireless user device identifier if the handover condition is satisfied.

[0013] Also, according to one embodiment, in a wireless user device, a memory storing instructions for the wireless device, when executed by a wireless transceiver, one or more processors, and one or more processes, the operation of the wireless device may be: receiving a handover command from a source base station within non-terrestrial networks (NTN) coverage, wherein one or more wireless user devices within the NTN coverage receive the handover command, determine whether a handover condition is satisfied based on the handover command, and if the handover condition is satisfied, perform a random access to a target base station on a random access channel (RACH) resource allocated based on a wireless user device identifier.

[0014] Additionally, the following may be commonly applied:

[0015] According to one embodiment, the handover command includes common target base station information that is common to one or more wireless user devices, and the wireless user devices can determine handover conditions based on the common target base station information.

[0016] Additionally, according to one embodiment, the handover condition may be determined based on at least one of the signal strength of the source base station, the signal strength of the target base station, the distance between the source base station and the terminal, the distance between the target base station and the terminal, and the time confirmed by the terminal.

[0017] Additionally, according to one embodiment, the RACH resources allocated to each of the one or more wireless user devices based on the wireless user device identifier may be temporally distinct resources.

[0018] Additionally, according to one embodiment, each of the one or more wireless user devices may perform random access at different times based on RACH resources allocated to each of the one or more wireless user devices based on a wireless user device identifier.

[0019]

[0020] According to the present disclosure, a method for performing handover in an NTN environment of a wireless communication system can be provided.

[0021] According to the present disclosure, a method for simultaneously performing handover for multiple terminals according to feeder link switch or satellite movement in an NTN environment of a wireless communication system can be provided.

[0022] According to the present disclosure, a method for performing common handover in an NTN environment of a wireless communication system can be provided.

[0023] According to the present disclosure, a method for performing common handover and terminal identifier-based handover in an NTN environment of a wireless communication system can be provided.

[0024] The present disclosure is not limited to the effects described above, and other effects not mentioned will be clearly understood by those skilled in the art to which the present disclosure pertains from the description below.

[0025]

[0026] FIG. 1 is a drawing for explaining an NR frame structure to which the present disclosure can be applied.

[0027] FIG. 2 is a diagram showing an NR resource structure to which the present disclosure can be applied.

[0028] FIG. 3 is a diagram illustrating an NTN including a transparent satellite to which the present disclosure can be applied.

[0029] FIG. 4 is a diagram illustrating an NTN including a regenerative satellite without inter-satellite links (ISLs) to which the present disclosure may be applied.

[0030] FIG. 5 is a diagram illustrating an NTN including a regenerative satellite having an ISL to which the present disclosure can be applied.

[0031] 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.

[0032] 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.

[0033] FIG. 8 is a diagram illustrating a transparent payload-based NTN structure to which the present disclosure can be applied.

[0034] FIG. 9 is a diagram illustrating a regenerative payload-based NTN structure to which the present disclosure can be applied.

[0035] Fig. 10 is a drawing showing an NTN structure to which the present disclosure can be applied.

[0036] FIG. 11 is a diagram illustrating a method for providing a service based on NTN and TN integration applicable to the present disclosure.

[0037] FIG. 12 is a diagram illustrating a method for providing a service based on NTN and TN integration applicable to the present disclosure.

[0038] FIG. 13 is a diagram illustrating a method for performing cell reselection based on a reference position applicable to the present disclosure.

[0039] Figure 14 is a drawing showing an SMTC applicable to the present disclosure.

[0040] Figure 15 is a diagram showing the received signal strength according to distance in TN and NTN applicable to the present disclosure.

[0041] FIG. 16 is a diagram illustrating satellite switching operations in an Earth-fixed cell scenario applicable to the present disclosure.

[0042] FIG. 17 is a diagram illustrating a signaling procedure for common handover applicable to the present disclosure.

[0043] FIG. 18 is a diagram illustrating a terminal identifier-based random access attempt procedure applicable to the present disclosure.

[0044] FIG. 19 is a flowchart illustrating a common handover and terminal identifier-based RACH procedure applicable to the present disclosure.

[0045] FIG. 20 is a flowchart illustrating a method for allocating terminal identifier-based RACH resources applicable to the present disclosure.

[0046] Figure 21 is a drawing showing a device configuration to which the present disclosure can be applied.

[0047]

[0048] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present disclosure. However, the present disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0049] In describing embodiments of the present disclosure, detailed descriptions of known configurations or functions will be omitted if they are deemed to obscure the gist of the present disclosure. Furthermore, portions of the drawings that are irrelevant to the description of the present disclosure have been omitted, and similar portions are designated with similar reference numerals.

[0050] In the present disclosure, when a component is said to be "connected," "coupled," or "connected" to another component, this may include not only a direct connection, but also an indirect connection in which another component exists in between. Furthermore, when a component is said to "include" or "have" another component, unless otherwise specifically stated, this does not exclude the other component, but rather implies that the other component may be included.

[0051] In this disclosure, terms such as first, second, etc. are used solely to distinguish one component from another, and do not limit the order or importance of components unless specifically stated otherwise. Accordingly, 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.

[0052] In this disclosure, distinct components are used to clearly illustrate their respective characteristics, and do not necessarily imply that the components are separated. 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 specifically mentioned, such integrated or distributed embodiments are also included within the scope of this disclosure.

[0053] In the present disclosure, the components described in various embodiments are not necessarily essential components, and some may be optional components. Therefore, embodiments comprising a subset of the components described in one embodiment are also within the scope of the present disclosure. Furthermore, embodiments including other components in addition to the components described in various embodiments are also within the scope of the present disclosure.

[0054] 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 a signal in a system (e.g., a base station) that manages the wireless communication network, or in a process of transmitting or receiving a signal in a terminal connected to the wireless network.

[0055] It is self-evident that various operations performed for communication with terminals in a network consisting of multiple network nodes including a base station can be performed by the base station or other network nodes other than the base station. 'Base station (BS)' can be replaced by terms such as fixed station, Node B, eNodeB (eNB), ng-eNB, gNodeB (gNB), and access point (AP). In addition, 'terminal' can be replaced by terms such as UE (User Equipment), MS (Mobile Station), MSS (Mobile Subscriber Station), SS (Subscriber Station), and non-AP station (non-AP STA).

[0056] In the present disclosure, transmitting or receiving a channel means transmitting or receiving information or a signal through the channel. For example, transmitting a control channel means transmitting control information or a signal through the control channel. Similarly, transmitting a data channel means transmitting data information or a signal through the data channel.

[0057] In the following description, the term NR (New Radio) system is used for the purpose of distinguishing the system to which various examples of the present disclosure are applied from existing systems; however, the scope of the present disclosure is not limited by this term.

[0058] NR systems support a variety of subcarrier spacings (SCS) to accommodate diverse scenarios, service requirements, and potential system compatibility. Furthermore, NR systems can support the transmission of physical signals / channels across multiple beams to overcome challenging channel conditions, such as high path loss, phase noise, and frequency offsets that occur at high carrier frequencies. This enables NR systems 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).

[0059] Hereinafter, 5G mobile communication technology can be defined to include not only the NR system, but also the existing LTE-A (Long Term Evolution-Advanced) system and LTE (Long Term Evolution) system. 5G mobile communication may include technology that operates in consideration of backward compatibility with previous systems as well as the newly defined NR system. Therefore, the 5G mobile communication below may include technology that operates based on the NR system and technology that operates based on previous systems (e.g., LTE-A, LTE), and is not limited to a specific system.

[0060] First, we would like to briefly explain the physical resource structure of the NR system to which the present invention is applied.

[0061] FIG. 1 is a drawing for explaining an NR frame structure to which the present disclosure can be applied.

[0062] In NR, the basic unit of time domain is It can be, , and N can be 4096. Meanwhile, in LTE, the basic unit of the time domain is It can be, And, =2048. The constant for the multiplication relationship between the NR time base unit and the LTE time base unit is k= can be defined as

[0063] Referring to Figure 1, the time structure of a frame for downlink / uplink (DL / UL) transmission is can have. Here, one frame is It consists of 10 subframes corresponding to time. The number of consecutive OFDM symbols in each subframe is = It can be. In addition, each frame is divided into two half frames of the same size, half frame 1 can be composed of sub frames 0-4, and half frame 2 can be composed of sub frames 5-9.

[0064] represents the timing advance (TA) between the downlink (DL) and uplink (UL). Here, the transmission timing of the uplink transmission frame i is determined based on the downlink reception timing at the terminal, based on the following mathematical expression 1.

[0065] [Mathematical Formula 1]

[0066]

[0067] Here, It may be a TA offset value that occurs due to differences in duplex mode, etc. In FDD (Frequency Division Duplex), has a value of 0, but in TDD (Time Division Duplex), it takes into account the margin for DL-UL switching time. It can be defined as a fixed value. For example, in TDD (Time Division Duplex) of FR1 (Frequency Range 1), which is a frequency below 6 GHz, is 39936 or 25600 It could be 39936 is 20.327μs, and 25600 is 13.030μs. Also, at FR2 (Frequency Range 2), which is a millimeter wave (mmWave) frequency, is 13792 It could be. At this time, 13792 is 7.020 μs.

[0068] FIG. 2 is a diagram showing an NR resource structure to which the present disclosure can be applied.

[0069] Resource elements (REs) within a resource grid can be indexed according to each subcarrier spacing. Here, one resource grid can be created for each antenna port and each subcarrier spacing. Uplink and downlink transmission and reception can be performed based on the corresponding resource grid.

[0070] In the frequency domain, one Resource Block (RB) consists of 12 REs, and each of the 12 REs can be configured with an index (nPRB) for one RB. The index for an RB can be utilized within a specific frequency band or system bandwidth. The index for an RB can be defined as in the following mathematical expression 2. Here, represents the number of subcarriers per RB, and k represents the subcarrier index.

[0071] [Equation 2]

[0072]

[0073]

[0074] Different numerologies can be configured to meet the diverse services and requirements of NR systems. For example, while LTE / LTE-A systems can support a single subcarrier spacing (SCS), NR systems can support multiple SCSs.

[0075] A new numerology for NR systems supporting multiple SCSs can operate in frequency ranges or carriers such as below 3GHz, 3GHz-6GHz, 6GHZ-52.6GHz or above 52.6GHz to address the issue of not being able to use wide bandwidth in frequency ranges or carriers such as 700MHz or 2GHz.

[0076] Table 1 below shows examples of numerologies supported by the NR system.

[0077] [Table 1]

[0078]

[0079] Referring to Table 1 above, the numeral can be defined based on the subcarrier spacing (SCS), cyclic prefix (CP) length, and number of OFDM symbols per slot used in the Orthogonal Frequency Division Multiplexing (OFDM) system. The above values ​​can be provided to the terminal through the upper layer parameters DL-BWP-mu and DL-BWP-cp for the downlink, and through the upper layer parameters UL-BWP-mu and UL-BWP-cp for the uplink.

[0080] In Table 1 above, 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. For other numerology indices, only normal CP can be applied.

[0081] A normal slot can be defined as the basic time unit used to transmit a single piece of data and control information in an NR system. The length of a normal slot can be set to the number of OFDM symbols, which is 14 by default. Furthermore, unlike slots, a subframe has an absolute time length equivalent 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.

[0082] For example, in LTE, data can be transmitted based on a unit of time called a Transmission Time Interval (TTI), which can be set to one or more subframes. Here, one subframe can be set to 1ms and can contain 14 OFDM symbols (or 12 OFDM symbols).

[0083] In addition, a non-slot can be defined in NR. A non-slot can mean a slot having a number that is at least one symbol smaller than a normal slot. For example, in the case of providing low latency such as URLLC service, latency can be reduced through a non-slot having a number of symbols smaller than a normal slot. Here, the number of OFDM symbols included in a non-slot can be determined by considering the frequency range. For example, a non-slot with a length of 1 OFDM symbol can be considered in a frequency range of 6 GHz or higher. As an additional example, the number of OFDM symbols defining a non-slot can include at least 2 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 - 1). However, as a specification of a non-slot, the number of OFDM symbols may be limited to 2, 4, or 7 symbols, but is not limited thereto.

[0084] Additionally, for example, in unlicensed bands below 6 GHz, subcarrier spacing where u equals 1 and 2 may be used, and in unlicensed bands above 6 GHz, subcarrier spacing where u equals 3 and 4 may be used. For example, when u equals 4, it may be used for SSB (Synchronization Signal Block).

[0085] [Table 2]

[0086]

[0087] Table 2 shows the number of OFDM symbols per slot for normal CP, by subcarrier spacing setting (u). ), number of slots per frame ( ), number of slots per subframe ( ) is shown. Table 2 shows the above-described values ​​based on a normal slot having 14 OFDM symbols.

[0088] [Table 3]

[0089]

[0090] Table 3 shows the number of slots per frame and the number of slots per subframe based on normal slots with 12 OFDM symbols per slot when extended CP is applied (i.e., when u is 2 and the subcarrier spacing is 60 kHz).

[0091] As mentioned above, one subframe may correspond to 1ms on the time axis. Additionally, one slot may correspond to 14 symbols on the time axis. For example, one slot may correspond to 7 symbols on the time axis. Accordingly, the number of slots and symbols that can be considered within 10ms corresponding to one radio frame may be set differently. Table 4 may show the number of slots and symbols according to each SCS. In Table 4, the 480kHz SCS may not be considered, but is not limited to these examples.

[0092] [Table 4]

[0093]

[0094]

[0095] Furthermore, for example, in existing wireless communication systems, communication could be performed based on a terrestrial network comprised of ground-based terminals and ground-based base stations. Terminals could access the network wirelessly. Here, when moving, the terminal could continuously receive the same service through other base stations within the terrestrial network. After connecting to the network, the terminal could access a specific service server through other wired or Internet networks. Furthermore, the terminal could receive services that connected it to other terminals through wired or wireless communication via the network.

[0096] However, new wireless communication systems can support terminal communication not only through terrestrial networks but also through non-terrestrial networks (NTN). Here, NTN can refer to a network or a part of a network that utilizes a mobile device floating in the air or space equipped with a base station or relay equipment. For example, NTN can support terminal-to-terminal communication services based on satellites equipped with communication capabilities in LEO (Low Earth Orbit) and GEO (Geostationary Earth orbit). As another example, NTN can support terminal-to-terminal communication services based on aircraft equipped with communication capabilities within Unmanned Aircraft Systems (UAS), but is not limited thereto.

[0097] Below, we distinguish between terrestrial networks (TN) and non-terrestrial networks (NTN). In existing communication systems, only terrestrial networks existed, so this distinction was not necessary. In contrast, below, we distinguish between NTN and TN as communication systems that enable terminal-to-terminal communication based on NTN, and describe methods for supporting terminal-to-terminal communication services based on these distinctions.

[0098] For example, wireless communication services between ground base stations and wireless terminals or between mobile base stations are described as mobile services, but are not limited thereto. Furthermore, communications between mobile ground base stations and at least one space base station may be considered mobile satellite services. Furthermore, wireless communication services between mobile ground base stations and space base stations, or between mobile ground base stations via at least one space base station, may also be considered mobile satellite services, but are not limited thereto.

[0099] The following describes a method for performing communication based on a wireless communication system that supports both mobile services and mobile satellite services. For example, while NTN technologies have been introduced specifically for satellite communications, NTN can also be introduced in TN communication systems (e.g., 5G systems) to operate alongside TN. Here, terminals can support both NTN and TN simultaneously. For terminals that support both NTN and TN simultaneously, wireless communication systems may require specific NTN technologies in addition to long-term evolution (LTE) and new radio (NR) systems, which are radio access technologies (RATs). The following describes a method for achieving this. For example, the following may be definitions of each term related to NTN and TN.

[0100]

[0101] Non-terrestrial networks (NTN):

[0102] A network or part of a network that utilizes airborne or space-based mobile devices carrying base stations or relay equipment for communications.

[0103]

[0104] NTN Gateway (NTN-gateway):

[0105] A ground station or gateway located on the Earth's surface and equipped with sufficient wireless access equipment to connect to satellites. Typically, an NTN gateway may be a transport network layer node (TNL).

[0106]

[0107] Feeder link:

[0108] Wireless link between NTN gateway and satellite

[0109]

[0110] Geostationary Earth orbit (GEO):

[0111] A circular orbit 35,786 km above the Earth's equator, aligned with the direction of Earth's rotation. Objects or satellites in this orbit revolve with the same period as the Earth's rotation. Therefore, when observed from Earth, they appear to be stationary and motionless.

[0112]

[0113] Low Earth Orbit (LEO):

[0114] Orbits between 300 and 1500 km above the Earth

[0115]

[0116] Medium Earth Orbit (MEO):

[0117] Orbits that exist between LEO and GEO

[0118]

[0119] Unmanned Aircraft Systems (UAS):

[0120] Systems typically operate between 8 and 50 km above ground level and may include high-altitude platforms (HAPs). Unmanned aerial systems may include at least one of the following systems: Tethered UAS (TUA), Lighter Than Air UAS (LTA), and Heavier Than Air UAS (HTA).

[0121]

[0122] Minimum Elevation angle:

[0123] Minimum angle required for a ground terminal to face a satellite or UAS base station in the air

[0124]

[0125] Mobile Services:

[0126] Wireless communication services between ground base stations and wireless terminals or between mobile base stations

[0127]

[0128] Mobile Satellite Services:

[0129] It may be a wireless communication service between mobile ground base stations and one or more space base stations, or between mobile ground base stations and space base stations, or between mobile ground base stations via one or more space base stations.

[0130]

[0131] Non-Geostationary Satellites:

[0132] Satellites in LEO and MEO orbits may be satellites that orbit the Earth with a period of approximately 1.5 to 10 hours.

[0133]

[0134] On Board Processing:

[0135] Digital processing of uplink RF signals mounted on satellite or non-terrestrial equipment

[0136]

[0137] Transparent payload:

[0138] This may mean changing the carrier frequency of the uplink RF signal and filtering and amplifying it before transmitting it via the downlink.

[0139]

[0140] Regenerative payload:

[0141] Modification and amplification of an uplink RF signal before transmission via the downlink. The signal modification may include digital processing such as decoding, demodulation, re-modulation, re-encoding, and filtering.

[0142]

[0143] Onboard NTN gNB:

[0144] It may refer to an onboard satellite with a base station (gNB) implemented in a regenerative payload structure.

[0145]

[0146] On ground NTN gNB:

[0147] A ground base station (GNB) implemented in a transparent payload structure.

[0148]

[0149] One-way latency:

[0150] The time it takes for a wireless terminal to reach a public data network or from a public data network to a wireless terminal in a wireless communication system.

[0151]

[0152] Round Trip Delay (RTD):

[0153] It may be the time it takes for any signal to reach a wireless terminal from the NTN gateway or from the NTN gateway to the wireless terminal and then return. At this time, the returning signal may be a signal containing a different form or message than the arbitrary signal.

[0154]

[0155] Satellite:

[0156] It can be a space vehicle equipped with a radio communication transceiver capable of supporting transparent payloads or regenerative payloads, and can typically be located in LEO, MEO, or GEO orbits.

[0157]

[0158] Satellite beam:

[0159] The beam generated by the antenna of the onboard satellite

[0160]

[0161] Service link:

[0162] Wireless link between satellite and terminal (UE)

[0163]

[0164] User Connectivity:

[0165] The ability to establish and maintain data / voice / video transmission between the network and the terminal.

[0166]

[0167] User Throughput:

[0168] Data transmission rate provided to the terminal

[0169]

[0170] FIG. 3 is a diagram illustrating an NTN including a transparent satellite to which the present disclosure can be applied.

[0171] Referring to FIG. 3, terminals included in the NTN may include terrestrial network terminals. For example, terminals in the NTN and TN may include manned or unmanned vehicles, such as ships, trains, buses, or airplanes, and may not be limited to a specific form. Referring to FIG. 3, a transparent satellite payload generated through a network including transparent satellites may be implemented in a manner corresponding to an RF repeater.

[0172] More specifically, a network including transparent satellites can perform frequency conversion and amplification for radio signals received in both uplink and downlink directions, and transmit the radio signals. Accordingly, the satellites can relay the NR-Uu radio interface, which includes both feeder links and service links, as described below.

[0173] As another example, referring to FIG. 3, a Satellite Radio Interface (SRI) over a feeder link may be included in the NR-Uu interface. That is, the satellite may not be the end point of the NR-Uu interface. Here, the NTN gateway may support all functions necessary to transmit signals defined in the NR-Uu interface. For example, other transparent satellites may be connected to the same base station on the ground. That is, a configuration in which multiple transparent satellites are connected to a single ground base station may also be possible. The base station may be an eNB or a gNB, but may not be limited to a specific form.

[0174] FIG. 4 is a diagram illustrating an NTN including a regenerative satellite without inter-satellite links (ISLs) to which the present disclosure may be applied.

[0175] Referring to Figure 4, the NTN may include a regenerative satellite. Here, a regenerative satellite may mean a satellite that includes a base station function. For example, a regenerative satellite payload generated through a network including a regenerative satellite may be implemented by regenerating a signal received from the ground.

[0176] More specifically, the regenerative 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 regenerative satellite can receive signals from the ground through the SRI (Satellite Radio Interface) on the feeder link between the NTN gateways. Here, the SRI (Satellite Radio Interface) can be defined in the transport layer between the satellite and the NTN gateway. The transport layer can mean the transport layer among the layers defined by the OSI 7 layer. That is, based on the regenerative satellite, the signal from the ground can be transformed based on digital processing such as decoding, demodulation, re-modulation, re-encoding, and filtering, but is not limited thereto.

[0177] FIG. 5 is a diagram illustrating an NTN including a regenerative satellite having an ISL to which the present disclosure can be applied.

[0178] Referring to Figure 5, ISL can be defined at the transport layer. Alternatively, ISL can be defined as a wireless 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 regeneration satellite can serve as a base station, and multiple regeneration satellites can be connected to the same 5G core network on the ground.

[0179] 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 may be applied. 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 may be applied.

[0180] The NR Uu interface may be an interface defined by protocols for wireless connection between a terminal and a base station in an NR system. At this time, the NR Uu interface may include a user plane defined by protocols for transmitting user data, including NTN. In addition, the NR Uu interface may include a control plane defined by protocols for transmitting signaling including radio resource control information, including NTN. For example, the Medium Access Control (MAC) layer is set based on Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP), Service Data Adaptation Protocol (SDAP), and Radio Resource Control (RRC), and the protocols for each layer may be defined based on NR among 3GPP RAN-related standards, but may not be limited thereto.

[0181] For example, FIG. 6 may be a UP protocol stack structure based on a transparent satellite. That is, only frequency conversion and amplification of transparently received wireless signals may be performed and transmitted at the satellite and NTN gateway. Furthermore, FIG. 7 may be a CP protocol stack structure based on a transparent satellite. That is, only frequency conversion and amplification of transparently received wireless signals may be performed at the satellite and NTN gateway.

[0182] Based on the above, a wireless communication system supporting terminal-to-terminal communication using NTN and TN can be considered. For example, NTN may have a longer roundtrip time (RTT) between the terminal and the base station than conventional TN. Therefore, from a UP perspective, the terminal needs to buffer data to be transmitted via both uplink and downlink for a longer period of time due to the increased RTT. In other words, the terminal needs to store more data in the buffer. Consequently, the terminal may require a larger memory capacity than conventional systems, which will be discussed later.

[0183] FIGS. 8 to 10 are drawings showing NTN structures to which the present disclosure can be applied.

[0184] In wireless communication systems (e.g., 5G, B5G, 6G), services can be provided based on non-terrestrial networks. NTN can provide advanced wireless access technologies that are free from the limitations of wireless access services (e.g., LTE, NR, WiFi, etc.) that rely on terrestrial network equipment. For example, NTN can be freer from regional, environmental, spatial, and economic limitations than terrestrial networks. Furthermore, advanced wireless access technologies can be applied to non-terrestrial network platforms (e.g., satellites, unmanned aerial vehicles (UAVs), etc.), allowing for the provision of creative and diverse wireless access service products and technologies alongside advanced network technologies.

[0185] The NTN platform can be positioned in space or at high altitudes and can be equipped with base station (e.g., gNB) functions. For example, the NTN architecture can consider a transparent payload-based NTN and a regenerative payload-based NTN. A transparent payload-based NTN can be a structure in which the NTN platform performs the function of transmitting a signal from an NTN gateway to an NTN terminal, and a satellite can relay and transmit a signal between the NTN terminal and the NTN gateway. In other words, a transparent payload-based NTN can be a relay-based operation that relays and transmits a signal. On the other hand, a regenerative payload-based NTN can have an onboard function that can generate a signal in relation to a signal being received or a signal to be transmitted. In other words, a regenerative payload-based NTN can generate a new signal after signal processing without relaying a signal. This may apply if the NTN is equipped with a terrestrial network base station function, and a radio interface can be configured between the NTN platform and the core network (e.g., 5GC). For example, the radio interface is an NG interface, and 5G wireless access and network technologies can be used in the NTN network, but this embodiment is not limited thereto.

[0186] When communicating using the transparent payload-based NTN method, the network can utilize the NTN, similar to a relay node, to transmit signals to the NTN terminal via a Uu link. Conversely, when communicating using the regenerative payload-based NTN method, the network transmits signals to the NTN, and the NTN utilizes the terrestrial network's base station function to process and regenerate the signals received from the network and transmit them to the NTN terminal.

[0187] Additionally, as an example, NTN can be utilized as an extended network structure and technology with an integrated access and backhaul (IAB) architecture. As described above, NTN can enable communications over a wider coverage area and be utilized for more wireless access services, and may not be limited to a specific form.

[0188] Here, referring to FIG. 8, in a transparent payload-based NTN, a terminal (810), a satellite (820), and an NTN gateway (830) can be connected via a Uu link. That is, the satellite (820) can only perform a relay role. On the other hand, referring to FIG. 9, in a regenerative payload-based NTN, a terminal (910) and a satellite (920) can be connected via a Uu link, and a satellite (920) and an NTN gateway can be connected via a satellite radio interface (SRI). That is, the satellite (920) can perform the function of a base station of a terrestrial network, regenerate signals after signal processing, and transmit them.

[0189] Also, referring to FIG. 10, relay nodes (1021, 1022) between terminals (1011, 1012) and satellites (1031, 1032) may be considered. Here, terminals (1011, 1012) and relay nodes (1021, 1022) may be connected via Uu links, and relay nodes (1021, 1022) and satellites (1031, 1032) may also be connected via Uu links. If the satellite is a transparent payload-based satellite (1031), the satellite (1031) and the NTN gateway (1041) may also be connected via Uu links. On the other hand, if the satellite is a regenerative payload-based satellite (1032), the satellite (1032) and the NTN gateway (1042) may be connected based on an SRI interface, as described above.

[0190] FIG. 11 and FIG. 12 are diagrams illustrating a method for providing a service based on NTN and TN integration applicable to the present disclosure.

[0191] The integration of NTN and terrestrial networks (TN) can improve service continuity and scalability in wireless communication systems. For example, integrated NTN and TN networks can enhance target performance, such as user experience, data transmission rate, and reliability. Furthermore, integrated NTN and TN networks can ensure seamless communication services in densely populated areas (e.g., concert halls, sports stadiums, shopping centers, etc.). Furthermore, integrated NTN and TN networks can ensure connectivity for airplanes, high-speed trains, vehicles, ships, and other communication-enabled devices.

[0192] Here, referring to FIG. 11, the terminal (1110) can receive data transmission services simultaneously from both the NTN and the TN based on the multi-connection function. That is, the terminal (1110) can perform communication using the existing TN base station (1120), and can further perform communication using the NTN satellite (1130) and NTN gateway (1140). The terminal (1110) can select a network by considering the characteristics of the traffic and the traffic loading, thereby improving the efficiency of the wireless transmission service.

[0193] For example, in FIG. 11, the terminal (1110) may be a method for performing communication based on a transparent payload-based NTN. On the other hand, in FIG. 12, the terminal (1210) may be a method for performing communication based on a regenerative payload-based NTN. In a transparent payload-based NTN, the satellite (1130) may only perform the function of relaying and transmitting a signal. On the other hand, in a regenerative payload-based NTN, the satellite (1230) may receive and process a signal, and then generate and transmit a new signal, as described above.

[0194] In an integrated NTN and TN network, terminals can utilize wireless data services that connect to both NTN and TN simultaneously. As another example, a terminal can simultaneously connect to one or more NTN platforms (e.g., two or more LEO / GEO satellites) to provide wireless data access services for environments and regions with limited communication support. This allows for the interconnected utilization of various services.

[0195] As a specific example, the NTN and TN integrated network can improve the reliability of autonomous driving services and enable efficient network operation. Here, vehicle communication services based on existing wireless communication systems (e.g., LTE)-based V2X (vehicle to everything) technology or other communication systems (e.g., IEEE 802.11p) may have limitations in service reliability. For example, V2X technology based on existing wireless communication systems and vehicle communication technology based on other communication systems can provide services based on requirements defined in C-ITS (cooperative-intelligent transport systems) (e.g., time delay of approximately 100 ms, reliability of approximately 90%, and generation of messages of tens to hundreds of bytes in size approximately 10 times per second). Here, new V2X services that require lower latency, higher reliability, more data traffic, and improved positioning may be needed, and the NTN and TN integrated network can be utilized for this.

[0196] For example, current wireless communication systems (e.g., 5G) can provide various numerologies, frame structures, and corresponding L2 / L3 protocol structures to respond more flexibly to the requirements of diverse and new services in the future than existing wireless communication systems. In addition, current wireless communication systems have introduced sidelink wireless access technology, which can support enhanced V2X services such as autonomous driving and remote driving. As another example, integrated NTN and TN networks can support Internet of Things (IoT) services in areas that cannot be covered by TN due to harsh environments. For example, IoT devices can perform wireless communication using minimal power in harsh channel environments (e.g., underground spaces and deep spaces inside buildings) depending on the purpose of use. Here, existing cellular-based wireless communication systems are mainly aimed at providing MBB (mobile broadband) services, so they may be inefficient in providing IoT services in terms of radio resource utilization and power control. Additionally, existing non-cellular IoT technologies may have limited mobility support and coverage, which may pose many limitations in providing IoT services.

[0197] For example, IoT services delivered via cellular-based wireless communication systems can offer more efficient wireless communication services than existing Bluetooth / Wi-Fi-based wearable devices. Cellular-based wireless communication systems can offer wide coverage and support for mobile devices, enabling more efficient IoT services. Furthermore, they can offer differentiation in applications requiring high data rates and mobility support (e.g., wearable multimedia services) utilizing wearable devices.

[0198] As another example, integrated NTN and TN networks can improve public safety communications networks and expand disaster communications coverage. For example, mobile base stations (e.g., drones) supporting wireless communication systems can be used to support mobile broadband services in areas where TN communications are difficult to provide (e.g., deserts, high mountains, etc.). In other words, applying the aforementioned features of integrated NTN and TN networks to public services can expand disaster communications coverage by covering a wider range of areas, and is not limited to a specific form.

[0199] FIG. 13 is a diagram illustrating a method for performing cell reselection based on a reference position applicable to the present disclosure.

[0200] FIG. 13 may be a distance-based neighbor cell measurement method for cell reselection in a satellite having an Earth-fixed beam. For example, a satellite provides a service at a fixed location for a specific period of time, and may provide a method for an RRC idle state terminal (1330) to efficiently perform cell reselection in an NTN environment with similar signal strength. As a specific example, the terminal (1320) may perform measurement based on the distance between a reference location and the terminal (1320) as a condition for performing measurement on an adjacent cell. Here, the terminal (1320) may determine the distance between the reference location and the terminal through reference location information provided by a satellite (Sat 1, 1310) connected to the terminal through system information. If the distance between the reference location and the terminal exceeds a distance threshold, the terminal (1320) may recognize that the terminal is located on the outskirts of the current cell, and accordingly, may perform measurement on an adjacent cell to perform reselection on an appropriate cell. For example, the distance threshold may be set based on the signal strength distribution within a specific area where the satellite is fixed and the mobility pattern of the terminal (1320). Based on the above-described configuration, the terminal (1320) in an NTN environment can perform transitions to adjacent cells more quickly and accurately.

[0201]

[0202] Additionally, in a wireless communication system, a terminal may perform measurements and report to the network based on a measurement and reporting configuration provided by the network. The network may provide configuration information for performing measurements and reporting measurement results to a terminal in an RRC connection state. For example, the network may provide configuration information for measurement and reporting to the terminal in an environment that includes different frequency bands (e.g., NR frequency bands and E-UTRA frequency bands) or different radio access technologies (hereinafter, "RATs"), and is not limited to a specific form.

[0203] In a wireless communication system, a terminal may perform measurement based on at least one of a synchronization signal block (SSB)-based measurement and a channel state information-reference signal (CSI-RS)-based measurement for handover, and report the measurement result to a network.

[0204] The network transmits CSI-RS to the terminal, and the terminal can obtain channel state information (CSI) through measurement and report it to the network. The network can use CSI to perform link adaptation, such as scheduling, physical resource block (PRB) allocation, and modulation scheme determination.

[0205] The network can transmit CSI-RS to terminals in an RRC connection state. For example, the network can provide CSI-RS with a narrow beam to terminals located at the cell edge in a high frequency band, thereby ensuring a high signal-to-interference plus noise ratio (SINR) and measurement accuracy. The CSI-RS can be configured by the network and provided to terminals in an RRC connection state, and the terminals can decode the CSI-RS.

[0206] On the other hand, SSB can be blind decoded based on a wide beam. For example, SSB can propagate signals in multiple directions, which can alleviate system congestion. However, there may be limitations in providing a better signal-to-noise ratio (SNR) and more accurate measurements than CSI-RS with a narrow beam. For example, a CSI-RS measurement configuration to support beam mobility can be configured through the "csi-measConfig" information element (IE). In addition, a CSI-RS measurement configuration to support cell mobility can be configured through the "measConfig" information element, and may not be limited to a specific format.

[0207] In addition, the terminal can perform measurement on a reference signal (RS) acquired from the network, and transmit a measurement report to the network when a reporting condition is satisfied. Here, the measurement object may be a component for a specific measurement task and may be set within a measurement identifier (MeasID). For example, the measurement identifier may include at least one of the "ssbFrequency", "ssbSubcarrierSpacing", and SMTC (Slot Measurement Timing Configuration) parameters. In addition, the measurement identifier may further include other parameters and is not limited to a specific form. Here, the above-described parameters may be as shown in Table 5 below.

[0208] That is, "ssbFrequency" may be the frequency of the SSB block associated with the measurement object, and "ssbSubcarrierSpacing" may represent the subcarrier spacing of the SSB block. For example, the subcarrier spacing of the SSB block may be set to 15 kHz or 30 kHz below 6 GHz, and to 120 kHz or 240 kHz above 6 GHz. In addition, SMTC may set the interval of the SSB burst (slot measurement timing configuration), which may be set to one of 5, 10, 20, 40, 80, and 160 ms. The SMTC window may be a period in which the terminal measures the SSB signal strength, and may include the timing and period of the SSB. For example, the SMTC may be adaptively configured considering the channel condition and the power consumption of the terminal. The SMTC window may be set to a specific period so as to efficiently measure the signal strength of the terminal, but may not be limited to a specific form.

[0209] [Table 5]

[0210]

[0211]

[0212] FIG. 14 is a diagram illustrating an SMTC applicable to the present disclosure. Referring to FIG. 14, the SSB burst set periodicity of cell 1 (1410) and cell 2 (1420) may be set to one of 5, 10, 20, 40, 80, and 160 ms. For example, cell 1 (1410) may have a longer SSB burst periodicity than cell 2 (1420), but this is merely an example for convenience of explanation and may not be limited thereto. In addition, the SSB burst set of each cell may be determined based on the number of SSBs actually transmitted.

[0213] The SMTC window periodicity may be set to be greater than the SSB burst period. The network may set the SMTC window periodicity according to the channel condition to reduce the power consumption of the terminal. As a specific example, the SMTC window periodicity of cell 1 (1410) may be set to be greater than the SSB burst period of cell 1 (1410). The terminal may measure the SSB signal strength of cell 1 (1410) within the SMTC window interval at each SMTC window period according to the SMTC configuration. As another example, the SMTC window periodicity of cell 2 (1420) may be set to be the same as the SSB burst period of cell 2 (1420). The terminal may measure the SSB signal strength of cell 2 (1420) within the SMTC window interval at each SMTC window period according to the SMTC configuration. However, FIG. 14 is an operation for convenience of explanation and may not be limited thereto.

[0214]

[0215] In wireless communication systems, geostationary orbit (GSO) and non-geostationary orbit (NGSO) network scenarios can be applied based on transparent payloads. Furthermore, terminals capable of global navigation satellite system (GNSS) operation and a certain level of power (e.g., 3GPP power class 3) can be used in wireless communication systems. Furthermore, wireless communication systems can support operation in frequency bands above 10 GHz to enhance NTN functionality. Furthermore, wireless communication systems can support optimized operation for handsets, such as smartphones, to enhance NTN functionality. Furthermore, NTN environments can experience significant propagation delays and may involve moving satellites. In wireless communication systems, considering the aforementioned environments, support for methods for determining terminal location within the network can be considered to meet regulatory requirements such as mobility, improved service continuity, and emergency call and public warning systems.

[0216] FIG. 15 is a diagram illustrating the received signal strength according to distance in TN and NTN applicable to the present disclosure. Referring to FIG. 15, in a TN environment, a transmission signal may be generated from a base station (1511) located on the ground. Therefore, the received signal strength of a terminal (near-UE, 1521) located close to the coverage center may be greater than that of a terminal (far-UE, 1522) located far from the coverage center. On the other hand, in an NTN environment, the transmission signal may be generated from a satellite located high above, so the distance between the terminals may be large. Therefore, the difference between the received signal strength of a terminal (near-UE, 1523) located close to the coverage center and that of a terminal (far-UE, 1524) located far from the coverage center may not be large. Considering the above, when a terminal performs a cell reselection procedure in an NTN environment, there may be limitations in performing the cell reselection procedure based on the received signal strength as in a terrestrial network. For example, because the difference in received signal strength within satellite coverage may not be significant, the terminal may not perform measurements for cell reselection. Consequently, there may be insufficient time for neighboring cell SSB search, signal strength measurements, and camping.

[0217] In addition, in NTN, the cell to which a terminal is connected may change according to satellite movement and feeder link switch regardless of whether the terminal moves. As described above, since the change in received signal strength may not be large in the NTN environment, cell reselection in an Earth-fixed beam (or Earth-fixed cell) in the NTN environment may be performed based on the distance and time between the terminal and the reference location. As a specific example, cell reselection may be performed based on time in an Earth-fixed cell. The network transmits information on the time (t-service) at which the satellite services the corresponding coverage through system information, and the terminal may perform cell reselection before the time (t-service) at which the coverage is serviced based on the time information. If information on the time (t-service) at which the coverage is serviced is included in the system information, the terminal may regard the cell as an Earth-fixed cell. On the other hand, if the time (t-service) for servicing the corresponding coverage is not included in the system information, the terminal may regard the corresponding cell as an earth-moving cell. As another example, cell reselection may be performed based on the distance between the terminal and a reference location in an earth-fixed cell. When a distance-based cell reselection method is performed, the network may transmit system information including the reference location of the serving cell and a distance threshold to the terminal. Based on the system information, the terminal may perform measurements for cell reselection when the distance between the terminal and the reference location becomes greater than the threshold.

[0218] In addition, as an example, a method for reducing signaling overhead may be applied when a handover occurs in an NTN environment in a wireless communication system. The following describes a method for commonly transmitting a handover command to a terminal through an RRC (radio resource control) message and a method for instructing the start of a handover through DCI (downlink control information) when a handover occurs in an NTN environment. As an example, Table 6 below may be, but is not limited to, considerations in a wireless communication system to improve NTN-TN and NTN-NTN mobility and service continuity.

[0219] [Table 6]

[0220]

[0221]

[0222] In an NTN environment, an earth-fixed cell may have a fixed cell location on the ground regardless of satellite movement, while an earth-moving cell may have a cell location that continuously changes depending on satellite movement. For example, a terminal may need to perform a handover based on the movement of an NTN cell or feeder link switching, which may result in signaling overhead between the network and the terminal. As a specific example, feeder link switching may be performed in an earth-fixed cell / earth-moving cell based on satellite movement. Based on feeder link switching, the terminal may need to disconnect from the existing gateway and connect to a new gateway. Here, since feeder link switching may be applied to all terminals within an NTN cell, all terminals within the NTN cell may need to disconnect from the existing gateway and connect to a new gateway. Therefore, the network needs to issue a handover command to all terminals connected to the NTN cell. In the above-described environment, the network may require a lot of signaling because it must issue a handover command to all terminals within the NTN coverage, which may result in different handover successes for each terminal. Specifically, the base station may need to perform DL assignment to issue a handover command equal to the number of terminals within the NTN coverage. A terminal that has received a handover command from the base station may attempt a random access channel (RACH) procedure toward the target base station. Here, signaling may be required for the handover command instruction, and terminals that have received a handover command instruction within the NTN cell may attempt the RACH procedure simultaneously. In the above-described situation, the possibility of handover failure may increase, and a RACH resource shortage may occur.That is, in the above-described situation, a handover command from the serving cell base station and a RACH operation of the terminal to the target cell can occur with the two signaling overheads in Table 7 below.

[0223] [Table 7]

[0224]

[0225]

[0226] For example, considering the first signaling overhead, a common handover operation can be applied to terminals within an NTN cell, thereby reducing signaling overhead. Specifically, terminals within NTN coverage can receive target cell information and a handover command transmitted by the serving cell base station through a single signaling, thereby reducing signaling overhead compared to the conventional method of transmitting a handover command to each terminal.

[0227] Additionally, as an example, a terminal identifier-based RACH operation may be performed to reduce the secondary signaling overhead. Based on the common handover described above, terminals within NTN coverage are required to perform the RACH procedure for uplink synchronization to the target cell. Here, if multiple terminals within NTN coverage perform the RACH procedure simultaneously, the terminals' random access attempts to the target cell may fail due to limited RACH resources, resulting in signaling overhead. Therefore, a method of dividing the RACH procedure into time / preamble resources according to a specific terminal identifier may be considered, thereby reducing the failure probability of the RACH procedure.

[0228]

[0229] Below, a common handover method for reducing signaling overhead in an NTN system is described. For example, a terminal may receive an RRC message containing target cell information from a source base station (or source cell) for a common handover. The terminal may check handover conditions based on the RRC message and perform random access to the target base station (or target cell). In addition, a method for successfully performing a RACH procedure in an NTN system may be provided. Specifically, the terminal may receive an RRC message containing target cell information from the source base station (or source cell). The terminal may check handover conditions based on the RRC message and attempt random access to the target base station (or target cell) based on information and an identifier in the RRC message. A specific method for this is described below.

[0230] When a common handover is performed to reduce signaling overhead in an NTN system, the source base station (or source cell) may provide RRC configuration information of the target base station (or target cell) to the terminal. Here, the RRC configuration information may be serving cell configuration common information, but may not be limited thereto. The source base station (or source cell) may provide information about the target base station (or target cell) to terminals within NTN coverage through an RRC message, and may instruct a common handover based on the information. That is, the source base station (or source cell) may commonly provide information about the target base station (or target cell) to terminals so that multiple terminals within NTN coverage can hand over to the target base station (or target cell).

[0231] As a specific example, a source base station (or source cell) may provide information on a target base station (or target cell) to one or more terminals via an RRC message (e.g., system information, RRC reconfiguration, etc.). In the following, information commonly provided to one or more terminals is referred to as common target base station (or target cell) information. However, this is only for convenience of explanation and may be used with other names and is not limited to a specific form. When one or more terminals satisfy a handover condition, one or more terminals may attempt a handover to the target base station (or target cell) based on the common target base station (or target cell) information. The handover attempt may mean performing a RACH procedure to the target base station (or target cell). For example, the handover condition may be one of the items in Table 8 below, but may not be limited to the embodiment. That is, the handover condition can be satisfied based on at least one of the signal strength (e.g., RSRP (Reference Signals Received Power), RSRQ (Reference Signals Received Quality), SINR (Signal to Interference plus Noise Ratio)) of the source base station (or source cell), the signal strength (e.g., RSRP, RSRQ, SINR) of the target base station (or target cell), the distance between the source base station (or source cell), the target base station (or target cell), and the terminal, and the time confirmed by the terminal, and when the handover condition is satisfied, one or more terminals can attempt handover based on common target base station (or target cell) information.

[0232] [Table 8]

[0233]

[0234]

[0235] Below, based on the above, a method for one or more terminals within NTN coverage to perform a common handover is described. In addition, a method for performing a terminal identifier-based RACH procedure to prevent collisions when one or more terminals within NTN coverage simultaneously perform a RACH procedure through a common handover is described.

[0236] FIG. 16 is a diagram illustrating a satellite switching operation in an Earth-fixed cell scenario applicable to the present disclosure. Referring to FIG. 16(a), in the Earth-fixed cell scenario, a service in a specific area may be provided by switching from a satellite (1611) that suspends service to a satellite (1612) that starts service due to the movement of satellites (1611, 1612). In FIG. 16(a), satellite 1 (1611) may suspend service in area X (area X) due to the movement of the satellite, and satellite 2 (1612) may provide service in area X thereafter as an approaching satellite. However, this is merely an example for convenience of explanation and may not be limited to the embodiment. As an example, satellite 1 (Satellite 1, 1611) and satellite 2 (Satellite 2, 1612) may have feeder links connected to the same NTN gateway and base station. Here, satellite 1 (1611) can stop providing service in a specific area depending on the movement of the satellite, and satellite 2 (1612) can start providing service in a specific area depending on the movement of the satellite.

[0237] As another example, referring to FIG. 16(b), in an Earth-fixed scenario, feeder link switching may occur due to satellite movement. Specifically, satellite 1 (1613) may be servicing a specific area (area X) through an existing NTN gateway (1621) and a base station (1631) (old gNB and old NTN gateway), but may move away from the existing NTN gateway (1621) and base station (1631) and provide service through a new NTN gateway (1622) and a new base station (1632) (new gNB and new NTN gateway). However, this is just one example and may not be limited thereto.

[0238] In the scenarios of Fig. 16(a) and Fig. 16(b), all terminals within a specific area (area X) that is NTN coverage need to perform a handover to a new base station / cell. Here, one or more terminals within NTN coverage can perform a common handover. As another example, one or more terminals within NTN coverage can perform a terminal identifier-based RACH operation.

[0239] FIG. 17 is a diagram illustrating a signaling procedure for a common handover applicable to the present disclosure. Referring to FIG. 17, when a source base station (or source cell, 1720) determines a handover for terminals within a specific area (i.e., NTN coverage), the source base station (or source cell, 1720) may request a handover to a target base station (or target cell, 1730). The target base station (or target cell, 1730) may respond by including common target base station (or target cell) information in a handover command after approving the handover request. Thereafter, the source base station (or source cell, 1720) may transmit a handover command to one or more terminals within the coverage via an RRC message to the terminal (1710). Here, the common target base station (or target cell) information may be included in the handover command or transmitted together with the RRC message. One or more terminals can receive a handover command and continuously check the handover conditions set by the source base station (or source cell). Here, if the handover conditions are satisfied, one or more terminals can perform a RACH procedure to the target base station (or target cell). Information for the RACH procedure can be included in the common target base station (or target cell) information. Here, since the NTN system performs communication via satellite, uplink synchronization considering the propagation delay to the satellite may be required. Taking the above-described point into account, the uplink synchronization can consider the feeder link delay and the service link delay. For example, the common target base station (or target cell) information can include NTN-specific information (e.g., NTN-config), and the NTN-specific information can include synchronization parameters for performing uplink synchronization.As a specific example, the synchronization parameters for performing uplink synchronization may include at least one of epochTime, NTN-UlSyncValidityDuration, kmac, TA-Info, NTN-polarizationDL, NTN-polarizationUL, ephemerisInfo, and TA-Report information. Here, TA-Common, TA-CommonDrift, and TA-CommonDriftVariant may be further included in the TA information. As an example, feeder link delay information for a target base station (or target cell) may be indicated based on the above-described parameters in the TA information. Through the three parameters of the TA information (TA common, TA common drift, TA common drift variant), the terminal may calculate a one-way propagation delay at time (t), which may be expressed by the following mathematical expression 3.

[0240] [Equation 3]

[0241]

[0242]

[0243] More specifically, referring to FIG. 17, a handover may be determined by a source base station (or source cell, 1720). For example, the source base station (or source cell, 1720) may decide to hand over terminals within the service coverage when the source base station (or source cell, 1720) must leave the service area due to satellite movement (FIG. 16(a)) or when the source base station (or source cell, 1720) must connect to a new NTN gateway due to the distance from the existing NTN gateway (FIG. 16(b)). Thereafter, the source base station (or source cell, 1720) may transmit a handover request to a target base station (or target cell) through an access management function (AMF, 1740) based on the handover decision. The handover request message may include at least one of identifier information (e.g., UE RAN-NGAP-ID, AMF-NGAP-ID, Target gNB ID), handover type, handover cause, and other information, and is not limited to a specific form.

[0244] The AMF (1740) may transmit at least one of UE security context, UE capabilities, PDU (protocol data unit) session information, source to target transparent container, GUAMI (globally unique AMF identifier), and other information along with the handover request message received from the source base station (or source cell, 1720) to the target base station (or target cell). Thereafter, the target base station (or target cell, 1730) may determine whether to accept or reject the handover request through admission control.

[0245] For example, a target base station (or target cell, 1730) may receive a handover request from an AMF (1740) and determine permission for a terminal to perform a handover based on available resources. Here, if the target base station (or target cell, 1730) can allow all PDU sessions corresponding to a radio bearer, the target base station (or target cell, 1730) may transmit a handover request response message to the AMF (1740). The handover request response message may include identifier information (e.g., UE NGAP-IDs), a list of admitted PDU sessions, and target-to-source transparent container (TargetToSource-TransparentContainer) information, and the handover request response message may be transmitted from the target base station (or target cell, 1730) to the AMF (1740). AMF (1740) can transmit a handover command to the source base station (or source cell, 1720) via a handover request acknowledge message. Thereafter, the source base station (or source cell, 1720) can transmit an RRC message including the handover command received from the target base station (or target cell, 1730) to one or more terminals within NTN coverage. Here, if the RRC message is transmitted as system information, the handover command can be included in the NTN-specific system information when the system information is updated. One or more terminals within NTN coverage can receive the handover command from the target base station (or target cell, 1730) through a system information update procedure. Thereafter, the terminal (1710) can check the handover condition. That is, one or more terminals that have received the handover command can continuously check the handover condition.For example, the handover condition may include at least one of the conditions described above and Table 8, but may not be limited thereto. Here, if the handover condition is satisfied, the terminal may attempt random access to the target base station (or target cell, 1730), and after the random access, may perform data transmission and reception with the new satellite.

[0246]

[0247] As described above, one or more terminals within NTN coverage can attempt random access to the target base station (or target cell) after performing a common handover to reduce signaling overhead, as described above. Here, since the RACH resources of the target base station (or target cell) may be limited, there may be a limit to the simultaneous random access attempts of one or more terminals within NTN coverage. Considering the above, one or more terminals within NTN coverage can attempt random access by distinguishing RACH resources that are time-separated, thereby enabling stable operation of the system. Therefore, terminals within NTN coverage can attempt random access to the target base station (or target cell) using RACH resources that are time-separated based on terminal identifiers.

[0248] As an example, FIG. 18 is a diagram illustrating a terminal identifier-based random access attempt procedure applicable to the present disclosure. A handover may be determined by a source base station (or source cell, 1820). For example, the source base station (or source cell, 1820) may decide to handover terminals within the service coverage when the source base station (or source cell, 1820) must leave the service area due to satellite movement (FIG. 16(a)) or when the source base station (or source cell, 1820) must connect to a new NTN gateway due to a distance from the existing NTN gateway (FIG. 16(b)). Thereafter, the source base station (or source cell, 1820) may transmit a handover request to a target base station (or target cell) through an access management function (AMF, 1840) based on the handover decision. The handover request message may include at least one of identifier information (e.g. UE RAN-NGAP-ID, AMF-NGAP-ID, Target gNB ID), handover type, handover cause, and other information, and is not limited to a specific form.

[0249] The AMF (1840) may transmit at least one of UE security context, UE capabilities, PDU session information, source to target transparent container, GUAMI (globally unique AMF identifier), and other information along with the handover request message received from the source base station (or source cell, 1820) to the target base station (or target cell). Thereafter, the target base station (or target cell, 1830) may determine whether to accept or reject the handover request through admission control.

[0250] For example, a target base station (or target cell, 1830) may receive a handover request from an AMF (1840) and determine permission for a terminal to perform a handover based on available resources. Here, if the target base station (or target cell, 1830) can allow all PDU sessions corresponding to a radio bearer, the target base station (or target cell, 1830) may transmit a handover request response message to the AMF (1840). The handover request response message may include identifier information (e.g., UE NGAP-IDs), a list of admitted PDU sessions, and target-to-source transparent container (TargetToSource-TransparentContainer) information, and the handover request response message may be transmitted from the target base station (or target cell, 1830) to the AMF (1840). The AMF (1840) can transmit a handover command to the source base station (or source cell, 1820) via a handover request acknowledge message. Thereafter, the source base station (or source cell, 1820) can transmit an RRC message including the handover command received from the target base station (or target cell, 1830) to one or more terminals within the NTN coverage. Here, if the RRC message is transmitted as system information, the handover command can be included in the NTN-specific system information when the system information is updated. One or more terminals within the NTN coverage can receive the handover command from the target base station (or target cell, 1830) through the system information update procedure. Thereafter, the terminals (1811, 1812) can check the handover condition. That is, one or more terminals that have received the handover command can continuously check the handover condition.For example, the handover conditions may include, but are not limited to, at least one of the conditions described above and Table 8.

[0251] Here, if the handover condition is satisfied, the terminals (1811, 1812) can attempt random access to the target base station (or target cell, 1830) and perform data transmission and reception with a new satellite after the random access. Here, one or more terminals within the NTN coverage may have different terminal identifiers. For example, in FIG. 18, terminal 1 (1811) and terminal 2 (1812) may have different terminal identifiers. Here, if the terminals (1811, 1812) are instructed to activate a UE ID based RACH procedure, the terminals (1811, 1812) may attempt the RACH procedure to the target base station (or target cell, 1830) through RACH resources at different times based on the terminal identifiers. As a specific example, in FIG. 18, we can consider a case where the identifier of terminal 1 (1811) is 1 and the identifier of terminal 2 (1812) is 2. Here, terminal 1 (1811) can attempt the RACH procedure in the first RACH cycle after the handover condition is satisfied according to the cycle in which the RACH resources are configured. On the other hand, terminal 2 (1812) can attempt the RACH procedure in the second RACH cycle after the handover condition is satisfied. That is, terminal 1 (1811) and terminal 2 (1812) can perform the RACH procedure at different times based on the terminal identifiers, thereby reducing the probability of the terminals failing in random access due to RACH resource shortage. However, FIG. 18 is only one example and may not be limited thereto.

[0252] Also, as an example, each of one or more terminals within NTN coverage can perform a random access procedure through a RACH occasion (RO) associated with each terminal identifier. One or more terminals within NTN coverage can perform a random access procedure in an RO derived from the terminal identifier when the activation of a UE ID-based RACH procedure is instructed. The RO may be an opportunity derived based on the terminal identifier, and different ROs may be determined if the terminal identifiers are different. As another example, it may be possible for multiple ROs to be associated with a terminal identifier, and the present invention is not limited to a specific embodiment. As described above, each of one or more terminals within NTN coverage can perform a random access procedure at different times through the terminal identifier. Thereafter, the terminals (1811, 1812) can perform a connection with a target base station (or target cell, 1830) and perform data transmission and reception through a new satellite.

[0253] FIG. 19 is a flowchart illustrating a common handover and terminal identifier-based RACH procedure applicable to the present disclosure.

[0254] Referring to FIG. 19, a terminal can receive a common handover (S1910). For example, one or more terminals within NTN coverage can receive a common handover command via an RRC message. Thereafter, one or more terminals within NTN coverage can check whether a handover condition is satisfied (S1920). That is, one or more terminals within NTN coverage can continuously check whether a handover condition associated with the common handover is satisfied after receiving the common handover. Thereafter, if the handover condition is satisfied, the terminal can perform a RACH procedure based on a terminal identifier (S1930). Here, one or more terminals within NTN coverage can check whether a terminal identifier-based RACH procedure is activated via a handover command or an RRC message indicating a common handover. Here, when the terminal identifier-based RACH procedure is activated, each of one or more terminals within the NTN coverage can perform the RACH procedure by determining at what point in time based on the terminal identifier whether to perform the RACH procedure to the target base station (or target cell). (S1940) On the other hand, when the terminal identifier-based RACH procedure is not activated, one or more terminals within the NTN coverage can perform the RACH procedure to connect to the target base station (or target cell). (S1950) Thereafter, one or more terminals connected to the target base station (or target cell) can perform data transmission and reception based on the target base station (or target cell).

[0255] FIG. 20 is a flowchart illustrating a method for allocating terminal identifier-based RACH resources applicable to the present disclosure.

[0256] Referring to FIG. 20, a wireless user device within non-terrestrial network coverage may receive a handover command from a source base station. Here, one or more wireless user devices may exist within the NTN coverage, and one or more wireless user devices may receive the handover command. (S2010) Thereafter, one or more wireless user devices may determine whether a handover condition is satisfied based on the handover command. (S2020) If the handover condition is satisfied, one or more wireless user devices may perform random access to a target base station on an allocated RACH resource based on a wireless user device identifier. (S2030) Here, the handover command may include common target base station information commonly applied to one or more wireless user devices. One or more wireless user devices may determine a handover condition based on the common target base station information. Additionally, as an example, the handover condition may be determined based on at least one of the signal strength of the source base station, the signal strength of the target base station, the distance between the source base station and the terminal, the distance between the target base station and the terminal, and the time confirmed by the terminal, and may be as shown in Table 8 above.

[0257] Additionally, the RACH resources allocated to each of one or more wireless user devices based on the wireless user device identifier may be temporally distinct resources. Here, each of one or more wireless user devices may perform random access at different times based on the RACH resources allocated to each of one or more wireless user devices based on the wireless user device identifier. For example, the RACH resources may be temporally distinct resources and may not be limited to a specific form.

[0258] Figure 21 is a drawing showing a device configuration to which the present disclosure can be applied.

[0259] Referring to FIG. 21, a first device (2100) and a second device (2150) can communicate with each other. In this case, as an example, the first device (2100) may be a base station device, and the second device (2150) may be a terminal device. In another example, both the first device (2100) and the second device (2150) may be terminal devices. In another example, the first device (2100) and the second device (2150) may be satellite IAB nodes. In other words, the first device (2100) and the second device (2150) may be devices that communicate with each other based on NR-based communication, and are not limited to a specific form.

[0260] The first device (2100) may include a processor (2120), an antenna unit (2112), a transceiver (2114), and a memory (2116). The processor (2120) performs baseband-related signal processing and may include a higher layer processing unit (2121) and a physical layer processing unit (2140). The higher layer processing unit (2121) may process operations of a medium access control (MAC) layer, a radio resource control (RRC) layer, or higher layers. The physical layer processing unit (2140) may process operations of a physical (PHY) layer (e.g., uplink reception signal processing, downlink transmission signal processing). In addition to performing baseband-related signal processing, the processor (2120) may also control the overall operation of the first device (2100). The antenna unit (2112) may include one or more physical antennas, and when it includes multiple antennas, it may support MIMO (Multiple Input Multiple Output) transmission and reception. In addition, beamforming may be supported. The memory (2116) may store information processed by the processor (2120), software related to the operation of the first device (2100), an operating system, applications, etc., and may include components such as a buffer. The processor (2120) of the first device (2100) may be configured to implement the operation of the first device in the embodiments described in the present invention.

[0261] The second device (2150) may include a processor (2170), an antenna unit (2162), a transceiver (2164), and a memory (2166). For example, in the present invention, the second device (2150) may communicate with the first device (2100). The processor (2170) may perform baseband-related signal processing and may include a higher layer processing unit (2180) and a physical layer processing unit (2190). The higher layer processing unit (2180) may process operations of a MAC layer, an RRC layer, or higher layers. The physical layer processing unit (2190) may process operations of a PHY layer (e.g., downlink reception signal processing, uplink transmission signal processing, sidelink signal processing). In addition to performing baseband-related signal processing, the processor (2170) may also control operations of the overall terminal device (2150). The antenna unit (2162) may include one or more physical antennas, and when it includes multiple antennas, it may support MIMO transmission and reception. In addition, it may support beamforming. The memory (2166) may store information processed by the processor (2170), software related to the operation of the second device (2150), an operating system, applications, etc., and may include components such as a buffer. The second device (2150) according to an example of the present invention may be associated with a vehicle. For example, the second device (2150) may be integrated into the vehicle, located in the vehicle, or located on the vehicle. In addition, the second device (2150) according to the present invention may be the vehicle itself. In addition, the second device (2150) according to the present invention may be at least one of a wearable terminal, an AV / VR, an IoT terminal, a robot terminal, and a public safety terminal.The terminal device (2150) to which the present invention is applicable may include any type of communication device that supports interactive services utilizing sidelink for services such as Internet access, service execution, navigation, real-time information, autonomous driving, and safety and risk diagnosis. Furthermore, any type of communication device capable of sidelink operation, such as an AR / VR device or sensor that performs relay operations, may be included.

[0262] Here, the vehicles / terminals to which the present invention is applied may include autonomous vehicles / driving terminals, semi-autonomous vehicles / driving terminals, non-autonomous vehicles / driving terminals, etc. Meanwhile, although the second device (2150) 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 should not be construed as limiting the application of the present invention to the described example. In addition, the second device (2150) according to an example of the present invention may also include various types of communication devices capable of performing cooperation to support interactive services utilizing sidelink. In other words, the second device (2150) may not only directly support interactive services utilizing sidelink, but may also be utilized as a cooperation device to support interactive services utilizing sidelink.

[0263] For example, the first device (2100) may be a source base station or a target base station, and the second device (21650) may be a terminal or a wireless user equipment. For example, the second device (2150) within non-terrestrial network coverage may receive a handover command from the source base station. Here, one or more second devices (2150) may exist within NTN coverage, and one or more second devices (2150) may receive the handover command. Thereafter, one or more second devices (2150) may determine whether a handover condition is satisfied based on the handover command. If the handover condition is satisfied, one or more second devices (2150) may perform a random access to the target base station on the RACH resources allocated based on the wireless user equipment identifier. Here, the handover command may include common target base station information that is commonly applied to one or more second devices (2150). One or more second devices (2150) may determine the handover condition based on the common target base station information. Additionally, as an example, the handover condition may be determined based on at least one of the signal strength of the source base station, the signal strength of the target base station, the distance between the source base station and the terminal, the distance between the target base station and the terminal, and the time confirmed by the terminal, and may be as shown in Table 8 above.

[0264] Additionally, the RACH resources allocated to each of the one or more second devices (2150) based on the wireless user device identifier may be temporally distinct resources. Here, each of the one or more second devices (2150) may perform random access at different times based on the RACH resources allocated to each of the one or more second devices (2150) based on the wireless user device identifier. For example, the RACH resources may be temporally distinct resources and may not be limited to a specific form.

[0265] Additionally, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. In the case of hardware implementation, the embodiments may be implemented by 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 processors, controllers, microcontrollers, microprocessors, etc.

[0266] The scope of the present disclosure includes software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that cause operations according to the methods of various embodiments to be executed on a device or a computer, and a non-transitory computer-readable medium having such software or instructions stored thereon and executable on the device or computer.

[0267] The various embodiments of the present disclosure are not intended to list all possible combinations but rather to illustrate 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.

[0268]

[0269] The following may also apply to other systems:

Claims

1. In terms of method, A step for a wireless user device within the coverage of a non-terrestrial networks (NTN) to receive a handover command from a source base station, wherein one or more wireless user devices within the NTN coverage receive the handover command; A step of checking whether the handover condition is satisfied based on the above handover command; and A method comprising the step of performing random access to a target base station on a random access channel (RACH) resource allocated based on a wireless user equipment identifier when the above handover condition is satisfied.

2. In paragraph 1, A method wherein the handover command includes common target base station information commonly applied to the one or more wireless user devices, and the wireless user device determines the handover condition based on the common target base station information.

3. In paragraph 2, A method in which the above handover condition is determined based on at least one of the signal strength of the source base station, the signal strength of the target base station, the distance between the source base station and the terminal, the distance between the target base station and the terminal, and the time confirmed by the terminal.

4. In paragraph 1, A method wherein RACH resources allocated to each of the one or more wireless user devices based on the wireless user device identifiers are temporally distinct resources.

5. In paragraph 4, A method wherein each of the one or more wireless user devices performs the random access at different times based on the RACH resources allocated to each of the one or more wireless user devices based on the wireless user device identifier.

6. For wireless user devices, wireless transceiver; one or more processors; and A memory that stores instructions for the wireless device when executed by one or more of the above processes; The operation of the above wireless device is: Receiving a handover command from a source base station within non-terrestrial networks (NTN) coverage, wherein one or more wireless user devices within the NTN coverage receive the handover command, Check whether the handover conditions are satisfied based on the above handover command, and A wireless user device that performs random access to a target base station on RACH (random access channel) resources allocated based on a wireless user device identifier when the above handover conditions are satisfied.

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