Method and apparatus for transmitting data in non-terrestrial network

Abstract

The present invention relates to a method of a base station in an NTN, and may comprise the steps of: allocating RSs corresponding to each of a first satellite and a second satellite; controlling to send data and RS corresponding to each satellite to the UE through the first satellite and the second satellite; receiving an RS measurement report message from the UE; and determining, based on the received RS measurement report message, a transmission mode from among a single transmission mode in which data is transmitted through one of the first satellite and the second satellite, and a diversity transmission mode in which data is transmitted through both the first satellite and the second satellite.

Description

Technical Field

[0001] The present invention relates to data transmission technology in non-terrestrial networks, and more particularly, to diversity transmission technology. Background Art

[0002] Communication networks (e.g., 5G communication networks, 6G communication networks, etc.) are being developed to provide enhanced communication services compared to existing communication networks (e.g., long term evolution (LTE), LTE-Advanced (LTE-A), etc.). 5G communication networks (e.g., New Radio (NR) communication networks) can support not only frequency bands of 6 GHz or below, but also frequency bands of 6 GHz or above. That is, the 5G communication network can support the frequency range FR1 band and / or FR2 band. Compared with the LTE communication network, the 5G communication network can support a wide variety of communication services and scenarios. For example, the usage scenarios of the 5G communication network may include enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communication (URLLC), massive Machine Type Communication (mMTC), etc.

[0003] Compared with 5G communication networks, 6G communication networks can support a wide variety of communication services and scenarios. 6G communication networks can meet the requirements of ultra-performance, ultra-bandwidth, ultra-space, ultra-precision, ultra-intelligence and / or ultra-reliability. 6G communication networks can support various broadbands and can be applied to various usage scenarios (e.g., terrestrial communication, non-terrestrial communication, sidelink communication, etc.).

[0004] A communication network (e.g., a 5G communication network, a 6G communication network, etc.) can provide communication services to terminals located on the ground. Recently, the demand for communication services not only for the ground but also for non-ground aircraft, drones, and satellites has been increasing, and for this purpose, the technology of non-terrestrial networks (NTN) has been discussed. The non-terrestrial network can be implemented based on 5G communication technology, 6G communication technology, etc. For example, in a non-terrestrial network, communication between a satellite and a ground communication node or a non-terrestrial communication node (e.g., an aircraft, a drone, etc.) can be performed based on 5G communication technology, 6G communication technology, etc. In NTN, a satellite can perform the function of a base station in a communication network (e.g., a 5G communication network, a 6G communication network, etc.).

[0005] On the other hand, in NTN, the long distance between the satellite and the terminal and the significant Doppler shift caused by high-speed movement may degrade the link quality. To overcome this, research on coverage enhancement (CovEnh) has been actively discussed in 3GPP standard meetings since Rel-17. The performance improvements that can be achieved by transmitting and receiving using a single satellite are limited, and these limitations become more apparent, especially when the elevation angle is low or in urban / suburban areas with many high-rise buildings. Low Earth Orbit (LEO) satellite systems such as Starlink and OneWeb are designed or planned to use hundreds to thousands of satellites to provide global services. In this case, a specific service area can be served by multiple satellites, thereby increasing the feasibility of implementing diversity technology by utilizing the transmission and reception of multiple satellites. However, due to the differences in transmission delays and Doppler shift values ​​between links via different satellites, it is considered challenging to directly apply the multi-TRP transmission technology developed for the terrestrial network (TN) to satellite diversity in the NTN environment.

[0006] When supporting terminals with antennas with lower antenna gain (e.g., handheld terminals), or when the link budget is low, it is necessary to utilize the diversity transmission technology of multiple satellites to enhance performance. In the NTN environment, each link via different satellites may experience significant differences in transmission delay and Doppler shift values. Therefore, it is difficult to directly apply the multi-TRP transmission technology developed for TN. Accordingly, for satellite diversity transmission in the NTN environment, it is necessary to develop a new satellite diversity transmission technology that takes the NTN environment into consideration. Summary of the invention

[0007] Technical issues

[0008] The present invention is directed to providing a method and apparatus for diversity transmission in a non-terrestrial network.

[0009] Technical Solution

[0010] The method of a base station according to the present invention for achieving the above-mentioned purpose may include: allocating a reference signal (RS) corresponding to each of a first satellite and a second satellite; controlling the first satellite and the second satellite to send the RS and data corresponding to each satellite to a user equipment (UE); receiving an RS measurement report message from the UE; determining a transmission mode in a single transmission mode of transmitting data via one of the first satellite and the second satellite or a diversity transmission mode of transmitting data via both the first satellite and the second satellite based on the received RS measurement report message; and transmitting data to the UE based on the determined transmission mode, wherein the RS measurement report message includes: a first time delay and a first Doppler shift based on the first RS received through a first link of the first satellite, and a second time delay and a second Doppler shift based on the second RS received through a second link of the second satellite.

[0011] When the difference between the first time delay and the second time delay is smaller than a predetermined first threshold, and the difference between the first Doppler frequency shift and the second Doppler frequency shift is smaller than a predetermined second threshold, the diversity transmission mode may be determined.

[0012] When the difference between the first time delay and the second time delay is greater than or equal to a predetermined first threshold, or when the difference between the first Doppler shift and the second Doppler shift is greater than or equal to a predetermined second threshold, a single transmission mode may be determined.

[0013] The RS measurement report message may be received via a serving satellite among the first satellite and the second satellite.

[0014] The RS measurement report message may consist of a first RS measurement report message received via a first link and a second RS measurement report message received via a second link, wherein the first RS measurement report message may include a first time delay and a first Doppler frequency shift, and the second RS measurement report message may include a second time delay and a second Doppler frequency shift.

[0015] When a diversity transmission request is received from the UE, allocation of RSs corresponding to each of the first satellite and the second satellite may be performed.

[0016] The method may further include: receiving a diversity transmission request from the UE; when the transmission mode determined based on the RS measurement report message is a single transmission mode, compensating for a first time delay so that a difference between the first time delay and a second time delay becomes smaller than a predetermined first threshold; compensating for a first Doppler frequency shift so that a difference between the first Doppler frequency shift and the second Doppler frequency shift becomes smaller than a predetermined second threshold; and determining a diversity transmission mode by applying the compensation value.

[0017] The first link having the first time delay may be a longer time delay than the second link.

[0018] A base station according to an exemplary embodiment of the present invention may include at least one processor, wherein the at least one processor causes the base station to execute: allocating a reference signal (RS) corresponding to each of a first satellite and a second satellite; controlling the first satellite and the second satellite to send the RS and data corresponding to each satellite to a user equipment (UE); receiving an RS measurement report message from the UE; determining a transmission mode in a single transmission mode of transmitting data via one of the first satellite and the second satellite or a diversity transmission mode of transmitting data via both the first satellite and the second satellite based on the received RS measurement report message; and transmitting data to the UE based on the determined transmission mode, wherein the RS measurement report message includes: a first time delay and a first Doppler shift based on the first RS received through a first link of the first satellite, and a second time delay and a second Doppler shift based on the second RS received through a second link of the second satellite.

[0019] When the difference between the first time delay and the second time delay is smaller than a predetermined first threshold, and the difference between the first Doppler frequency shift and the second Doppler frequency shift is smaller than a predetermined second threshold, the diversity transmission mode may be determined.

[0020] When the difference between the first time delay and the second time delay is greater than or equal to a predetermined first threshold, or when the difference between the first Doppler shift and the second Doppler shift is greater than or equal to a predetermined second threshold, a single transmission mode may be determined.

[0021] The RS measurement report message may be received via a serving satellite among the first satellite and the second satellite.

[0022] The RS measurement report message may consist of a first RS measurement report message received via a first link and a second RS measurement report message received via a second link, wherein the first RS measurement report message may include a first time delay and a first Doppler frequency shift, and the second RS measurement report message may include a second time delay and a second Doppler frequency shift.

[0023] The at least one processor may further cause the base station to perform: when a diversity transmission request is received from the UE, allocating an RS corresponding to each of the first satellite and the second satellite.

[0024] The at least one processor may further cause the base station to perform: receiving a diversity transmission request from the UE; when the transmission mode determined based on the RS measurement report message is a single transmission mode, compensating for the first time delay so that the difference between the first time delay and the second time delay becomes less than a predetermined first threshold; compensating for the first Doppler frequency shift so that the difference between the first Doppler frequency shift and the second Doppler frequency shift becomes less than a predetermined second threshold; and determining the diversity transmission mode by applying the compensation value.

[0025] A first link having a first time delay may have a longer time delay than a second link.

[0026] Beneficial effects

[0027] According to the present invention, the NTN base station or NTN UE can determine the transmission delay and Doppler shift degree of each link through different satellites by measuring or estimating them using reference signals. Based on the differences in transmission delay and Doppler shift between the identified links, the diversity transmission mode or the single transmission mode can be determined. In addition, according to the present invention, when it is necessary to perform the single transmission mode, the system can compensate for the differences in transmission delay and Doppler shift between the links in response to a request from the UE, thereby operating in the diversity transmission mode. Accordingly, the data transmission efficiency in the NTN can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1a is a conceptual diagram illustrating a first exemplary embodiment of a non-terrestrial network.

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

[0030] Figure 2a is a conceptual diagram illustrating a third exemplary embodiment of a non-terrestrial network.

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

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

[0033] Figure 3 is a block diagram illustrating a first exemplary embodiment of communication nodes constituting a non-terrestrial network.

[0034] Figure 4 is a block diagram illustrating a first exemplary embodiment of a communication node performing communications.

[0035] Figure 5a is a block diagram illustrating a first exemplary implementation of a transmit path.

[0036] Figure 5b is a block diagram illustrating a first exemplary implementation of a receive path.

[0037] Figure 6a is a conceptual diagram illustrating a first exemplary embodiment of a protocol stack of a user plane in a non-terrestrial network based on a transparent payload.

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

[0039] Figure 7a is a conceptual diagram illustrating a first exemplary embodiment of a protocol stack for a user plane in a non-terrestrial network based on a regenerative payload.

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

[0041] Figures 8a to 8c is a conceptual diagram showing three operating schemes of TRP.

[0042] Figure 9a is a conceptual diagram showing a comb-6 mode with three TRPs as a DL-PRS mode in a 3GPP TN, Figure 9b is a conceptual diagram showing the comb-4 mode which is a UL-PRS mode in 3GPP TN.

[0043] Fig.10a is a schematic diagram showing the constellation of Starlink, Fig.10b is a schematic diagram showing Alaska gateway antennas deployed in a OneNet system.

[0044] Fig.11 is a conceptual diagram showing diversity signal transmission using two transparent satellites in an NTN environment.

[0045] Fig.12 is a sequence diagram illustrating a measurement-based switching operation between satellite diversity transmission mode and single transmission mode in NTN.

[0046] Fig.13 is a flowchart illustrating an operation of a base station in determining a transmission mode according to a first exemplary embodiment of the present invention.

[0047] Fig.14 is a sequence diagram illustrating a measurement-based switching operation between satellite diversity transmission mode and single transmission mode in NTN.

[0048] Fig.15 is a flow chart showing a switching operation between a JT mode and a non-JT mode in an NTN.

[0049] Fig.16 is a sequence diagram illustrating a method of performing a pre-compensation based satellite diversity transmission mode in NTN.

[0050] Fig.17 is a flowchart illustrating an operation of a base station in determining a transmission mode according to a fourth exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0051] Although the present invention is capable of various modifications and alternative forms, specific embodiments thereof are shown by way of example in the accompanying drawings and will be described in detail herein. However, it should be understood that it is not intended to limit the present invention to the specific forms disclosed, but on the contrary, the present invention covers all modifications, equivalent forms and alternative forms falling within the spirit and scope of the present invention. Throughout the description of the figures, the same reference numerals refer to the same elements.

[0052] It will be understood that, although the terms first, second, etc. can be used herein to describe each element, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, without departing from the scope of the present invention, the first element can be referred to as the second element and similarly, the second element can be referred to as the first element. As used in this article, the term "and / or" includes any combination and all combinations of one or more related enumeration items.

[0053] In the present invention, “at least one of A and B” may mean “at least one of A or B” or “at least one of a combination of one or more of A and B”. Furthermore, in an exemplary embodiment of the present invention, “one or more of A and B” may mean “one or more of A or B” or “one or more of a combination of one or more of A and B”.

[0054] In the present invention, "(re)transmission" may mean "transmission", "retransmission" or "transmission and retransmission", "(re)configuration" may mean "configuration", "reconfiguration" or "configuration and reconfiguration", "(re)connection" may mean "connection", "reconnection" or "connection and reconnection", and "(re)access" may mean "access", "reaccess" or "access and reaccess".

[0055] It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there can be intervening elements. Conversely, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements.

[0056] The terms used in this article are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in this article, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. It will be further understood that when the terms "include" and / or "comprising" are used in this article, it is explained that there are described features, numerical values, steps, operations, elements, components or combinations thereof, but does not exclude the presence or addition of one or more other features, numerical values, steps, operations, elements, components and / or combinations thereof.

[0057] Unless otherwise defined, all terms (including technical and scientific terms) used in this article have the same meaning as those commonly understood by ordinary technicians in the field to which the present invention belongs. It will be further understood that terms (for example, terms defined in commonly used dictionaries) should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted as an idealized or overly formal meaning unless explicitly defined as such in this article.

[0058] Hereinafter, the exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In order to promote overall understanding when describing the present invention, the same components in the accompanying drawings are represented by the same reference numerals, and repeated descriptions thereof will be omitted. In addition to the exemplary embodiments clearly described in the present invention, operations can also be performed according to the combination of the exemplary embodiments, the expansion of the exemplary embodiments and / or the modification of the exemplary embodiments. The execution of some operations can be omitted, and the execution order of the operations can be changed.

[0059] Even when describing a method performed at a first communication node among communication nodes (e.g., transmission or reception of a signal), the corresponding second communication node may perform a method corresponding to the method performed at the first communication node (e.g., reception or transmission of a signal). That is, when describing the operation of a user equipment (UE), a base station corresponding to the UE may perform an operation corresponding to the operation of the UE. Conversely, when describing the operation of a base station, a UE corresponding to the base station may perform an operation corresponding to the operation of the base station. In a non-terrestrial network (NTN) (e.g., a payload-based NTN), the operation of a base station may refer to the operation of a satellite, and the operation of a satellite may refer to the operation of a base station.

[0060] A base station may refer to a node B, an evolved node B (eNodeB), a next generation node B (gNodeB), a gNB, a device, an apparatus, a node, a communication node, a base transceiver station (BTS), a radio remote head (RRH), a transmission reception point (TRP), a radio unit (RU), a roadside unit (RSU), a radio transceiver, an access point, an access node, etc. A UE may refer to a terminal, a device, an apparatus, a node, a communication node, an end node, an access terminal, a mobile terminal, a station, a subscriber station, a mobile station, a portable subscriber station, an on-board unit (OBU), etc.

[0061] In the present invention, signaling may be at least one of higher layer signaling, medium access control (MAC) signaling, or physical (PHY) signaling. A message for higher layer signaling may be referred to as a "higher layer message" or a "higher layer signaling message". A message for MAC signaling may be referred to as a "MAC message" or a "MAC signaling message". A message for PHY signaling may be referred to as a "PHY message" or a "PHY signaling message". Higher layer signaling may refer to the sending and receiving operations of system information (e.g., master information block (MIB), system information block (SIB)) and / or RRC messages. MAC signaling may refer to the sending and receiving operations of a MAC control element (CE). PHY signaling may refer to the sending and receiving operations of control information (e.g., downlink control information (DCI), uplink control information (UCI), and sidelink control information (SCI)).

[0062] In the present invention, “configure an operation (e.g., send an operation)” may mean “send configuration information (e.g., information element or parameter) of an operation and / or information indicating the execution of an operation with a signal”. “Configure an information element (e.g., parameter)” may mean “send a corresponding information element with a signal”. In the present invention, “signal and / or channel” may mean signal, channel, or “signal and channel”, and “signal” may be used to mean “signal and / or channel”.

[0063] The communication system may include at least one of a terrestrial network, a non-terrestrial network, a 4G communication network (e.g., a long term evolution (LTE) communication network), a 5G communication network (e.g., a new radio (NR) communication network), or a 6G communication network. Each of the 4G communication network, the 5G communication network, and the 6G communication network may include a terrestrial network and / or a non-terrestrial network. The non-terrestrial network may operate based on at least one communication technology of the LTE communication technology, the 5G communication technology, or the 6G communication technology. The non-terrestrial network may provide communication services in various frequency bands.

[0064] The communication network to which the exemplary embodiment is applied is not limited to the content described below, and the exemplary embodiment can be applied to various communication networks (e.g., 4G communication network, 5G communication network and / or 6G communication network). Here, the communication network can be used in the same sense as the communication system.

[0065] Figure 1a is a conceptual diagram illustrating a first exemplary embodiment of a non-terrestrial network.

[0066] like Figure 1a As shown, the non-terrestrial network (NTN) may include a satellite 110, a communication node 120, a gateway 130, a data network 140, etc. A unit including the satellite 110 and the gateway 130 may correspond to a remote radio unit (RRU). Figure 1a The NTN shown may be a transparent payload-based NTN. Satellite 110 may be a low earth orbit (LEO) satellite, a medium earth orbit (MEO) satellite, a geostationary earth orbit (GEO) satellite, a high elliptical orbit (HEO) satellite, or an unmanned aircraft system (UAS) platform. The UAS platform may include a high altitude platform station (HAPS). The non-GEO satellite may be a LEO satellite and / or a MEO satellite.

[0067] The communication node 120 may include a communication node located at a ground location (e.g., a user equipment (UE) or a terminal) and a communication node located in a non-ground space (e.g., an aircraft, a drone). A service link may be established between the satellite 110 and the communication node 120, and the service link may be a radio link. The satellite 110 may provide communication services to the communication node 120 using one or more beams. The shape of the coverage area of ​​the beam of the satellite 110 may be elliptical or circular.

[0068] In non-terrestrial networks, the following three types of service links can be supported.

[0069] - Earth-fixed: The service link may be provided by a beam that always continuously covers the same geographical area (eg, a geosynchronous orbit (GSO) satellite).

[0070] - quasi-earth-fixed: the service link may be provided by a beam covering one geographical area during a defined period and by a beam covering another geographical area during another period (e.g. a non-GSO (NGSO) satellite forming a steerable beam).

[0071] - Earth-moving: The service link may be provided by a beam moving over the surface of the Earth (eg, a NGSO satellite forming a fixed or non-steerable beam).

[0072] The communication node 120 may perform communication (e.g., downlink communication and uplink communication) with the satellite 110 using 4G communication technology, 5G communication technology, and / or 6G communication technology. Communication between the satellite 110 and the communication node 120 may be performed using an NR-Uu interface and / or a 6G-Uu interface. When supporting dual connectivity (DC), the communication node 120 may be connected to other base stations (e.g., base stations supporting 4G, 5G, and / or 6G functions) and the satellite 110, and perform DC operations based on technologies defined in 4G, 5G, and / or 6G technical specifications.

[0073] The gateway 130 may be located at a ground location, and a feeder link may be established between the satellite 110 and the gateway 130. The feeder link may be a radio link. The gateway 130 may be referred to as a "non-terrestrial network (NTN) gateway". The communication between the satellite 110 and the gateway 130 may be performed based on an NR-Uu interface, a 6G-Uu interface, or a satellite radio interface (SRI). The gateway 130 may be connected to the data network 140. There may be a "core network" between the gateway 130 and the data network 140. In this case, the gateway 130 may be connected to the core network, and the core network may be connected to the data network 140. The core network may support 4G communication technology, 5G communication technology, and / or 6G communication technology. For example, the core network may include an access and mobility management function (AMF), a user plane function (UPF), a session management function (SMF), and the like. Communication between the gateway 130 and the core network may be performed based on an NG-C / U interface or a 6G-C / U interface.

[0074] like Figure 1b As shown in the exemplary embodiment of FIG. 1 , in a transparent payload-based NTN, a “core network” may exist between the gateway 130 and the data network 140 .

[0075] Figure 1b is a conceptual diagram illustrating a second exemplary embodiment of a non-terrestrial network.

[0076] like Figure 1b As shown, the gateway can be connected to the base station, the base station can be connected to the core network, and the core network can be connected to the data network. Each of the base station and the core network can support 4G communication technology, 5G communication technology and / or 6G communication technology. The communication between the gateway and the base station can be performed based on the NR-Uu interface or the 6G-Uu interface, and the communication between the base station and the core network (e.g., AMF, UPF, SMF, etc.) can be performed based on the NG-C / U interface or the 6G-C / U interface.

[0077] Figure 2a is a conceptual diagram illustrating a third exemplary embodiment of a non-terrestrial network.

[0078] like Figure 2a As shown, the non-terrestrial network may include a first satellite 211, a second satellite 212, a communication node 220, a gateway 230, a data network 240, and the like. Figure 2aThe NTN shown may be an NTN based on a regenerated payload. For example, each of satellite 211 and satellite 212 may perform a regeneration operation (e.g., demodulation, decoding, re-encoding, re-modulation, and / or filtering operation) on a payload received from another entity (e.g., communication node 220 or gateway 230) and transmit the regenerated payload.

[0079] Each of satellite 211 and satellite 212 can be a LEO satellite, a MEO satellite, a GEO satellite, a HEO satellite or a UAS platform. The UAS platform can include a HAPS. Satellite 211 can be connected to satellite 212, and an inter-satellite link (ISL) can be established between satellite 211 and satellite 212. ISL can operate in an RF band or an optical band. ISL can be optionally established. Communication node 220 can include a ground communication node (e.g., UE or terminal) and a non-ground communication node (e.g., an aircraft or a drone). A service link (e.g., a radio link) can be established between satellite 211 and communication node 220. Satellite 211 can provide communication services to communication node 220 using one or more beams.

[0080] The communication node 220 can perform communication (e.g., downlink communication or uplink communication) with the satellite 211 using 4G communication technology, 5G communication technology, and / or 6G communication technology. The communication between the satellite 211 and the communication node 220 can be performed using the NR-Uu interface or the 6G-Uu interface. When DC is supported, the communication node 220 can be connected to other base stations (e.g., base stations supporting 4G, 5G, and / or 6G functions) and the satellite 211, and can perform DC operations based on the technologies defined in the 4G, 5G, and / or 6G technical specifications.

[0081] The gateway 230 may be located at a ground location, a feeder link may be established between the satellite 211 and the gateway 230, and a feeder link may be established between the satellite 212 and the gateway 230. The feeder link may be a radio link. When an ISL is not established between the satellite 211 and the satellite 212, a feeder link between the satellite 211 and the gateway 230 may be established compulsorily. The communication between each of the satellite 211 and the satellite 212 and the gateway 230 may be performed based on an NR-Uu interface, a 6G-Uu interface, or an SRI. The gateway 230 may be connected to a data network 240.

[0082] like Figure 2b and Figure 2c As shown in the exemplary embodiment of FIG. 2 , a “core network” may exist between gateway 230 and data network 240 .

[0083] Figure 2bis a conceptual diagram showing a fourth exemplary embodiment of a non-terrestrial network, Figure 2c is a conceptual diagram illustrating a fifth exemplary embodiment of a non-terrestrial network.

[0084] like Figure 2b and Figure 2c As shown, the gateway can be connected to the core network, and the core network can be connected to the data network. The core network can support 4G communication technology, 5G communication technology and / or 6G communication technology. For example, the core network may include AMF, UPF, SMF, etc. The communication between the gateway and the core network can be performed based on the NG-C / U interface or the 6G-C / U interface. The functions of the base station can be performed through the satellite. That is, the base station can be located on the satellite. The payload can be processed by the base station located on the satellite. Base stations located on different satellites can be connected to the same core network. A satellite can have one or more base stations. In Figure 2b In non-terrestrial networks, it may not be possible to establish ISLs between satellites. Figure 2c In non-terrestrial networks, ISLs between satellites can be established.

[0085] On the other hand, the composition Figure 1a , Figure 1b , Figure 2a , Figure 2b and / or Figure 2c The entities of the non-terrestrial network shown (eg, satellite, base station, UE, communication node, gateway, etc.) may be configured as follows: In the present invention, the entity may be referred to as a communication node.

[0086] Figure 3 is a block diagram illustrating a first exemplary embodiment of communication nodes constituting a non-terrestrial network.

[0087] like Figure 3 As shown, the communication node 300 may include at least one processor 310, a memory 320, and a transceiver 330 connected to a network to perform communication. In addition, the communication node 300 may further include an input interface device 340, an output interface device 350, a storage device 360, etc. The components included in the communication node 300 may be connected through a bus 370 to communicate with each other.

[0088] However, each component included in the communication node 300 may be connected to the processor 310 through a separate interface or a separate bus instead of the common bus 370. For example, the processor 310 may be connected to at least one of the memory 320, the transceiver 330, the input interface device 340, the output interface device 350, and the storage device 360 ​​through a dedicated interface.

[0089] The processor 310 may execute at least one instruction stored in at least one of the memory 320 and the storage device 360. The processor 310 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which the method according to the exemplary embodiment of the present invention is executed. Each of the memory 320 and the storage device 360 ​​may be configured as at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 320 may be configured with at least one of a read-only memory (ROM) and a random access memory (RAM).

[0090] On the other hand, a communication node that performs communication in a communication network (eg, a non-terrestrial network) may be configured as follows. Figure 4 The communication nodes shown may be Figure 3 A specific exemplary embodiment of a communication node is shown.

[0091] Figure 4 is a block diagram illustrating a first exemplary embodiment of a communication node performing communications.

[0092] like Figure 4 As shown, each of the first communication node 400a and the second communication node 400b can be a base station or a UE. The first communication node 400a can send a signal to the second communication node 400b. The transmission processor 411 included in the first communication node 400a can receive data (e.g., data unit) from the data source 410. The transmission processor 411 can receive control information from the controller 416. The control information may include at least one of system information, RRC configuration information (e.g., information configured by RRC signaling), MAC control information (e.g., MAC CE) or PHY control information (e.g., DCI, SCI).

[0093] The transmit processor 411 may generate data symbols by performing processing operations on data (e.g., encoding operations, symbol mapping operations, etc.). The transmit processor 411 may generate control symbols by performing processing operations on control information (e.g., encoding operations, symbol mapping operations, etc.). In addition, the transmit processor 411 may generate synchronization / reference symbols for synchronization signals and / or reference signals.

[0094] The Tx MIMO processor 412 may perform spatial processing operations (e.g., precoding operations) on data symbols, control symbols, and / or synchronization / reference symbols. The output (e.g., symbol stream) of the Tx MIMO processor 412 may be provided to a modulator (MOD) included in the transceiver 413a to the transceiver 413t. The modulator may generate modulation symbols by performing processing operations on the symbol stream, and may generate signals by performing additional processing operations (e.g., analog conversion operations, amplification operations, filtering operations, up-conversion operations, etc.) on the modulation symbols. The signals generated by the modulators of the transceivers 413a to the transceivers 413t may be transmitted through the antennas 414a to the antennas 414t.

[0095] The signal transmitted by the first communication node 400a can be received at the antenna 464a to the antenna 464r of the second communication node 400b. The signal received at the antenna 464a to the antenna 464r can be provided to the demodulator (DEMOD) included in the transceiver 463a to the transceiver 463r. The demodulator (DEMOD) can obtain samples by performing processing operations (e.g., filtering operations, amplification operations, down-conversion operations, digital conversion operations, etc.) on the signal. The demodulator can perform additional processing operations on the samples to obtain symbols. The MIMO detector 462 can perform MIMO detection operations on the symbols. The receiving processor 461 can perform processing operations (e.g., deinterleaving operations, decoding operations, etc.) on the symbols. The output of the receiving processor 461 can be provided to the data sink 460 and the controller 466. For example, data can be provided to the data sink 460, and control information can be provided to the controller 466.

[0096] On the other hand, the second communication node 400b can send a signal to the first communication node 400a. The transmission processor 468 included in the second communication node 400b can receive data (e.g., data unit) from the data source 467, and perform processing operations on the data to generate data symbols. The transmission processor 468 can receive control information from the controller 466, and perform processing operations on the control information to generate control symbols. In addition, the transmission processor 468 can generate reference symbols by performing processing operations on reference signals.

[0097] The Tx MIMO processor 469 may perform spatial processing operations (e.g., precoding operations) on data symbols, control symbols, and / or reference symbols. The output (e.g., symbol stream) of the Tx MIMO processor 469 may be provided to a modulator (MOD) included in the transceiver 463a to the transceiver 463t. The modulator may generate modulation symbols by performing processing operations on the symbol stream, and may generate signals by performing additional processing operations (e.g., analog conversion operations, amplification operations, filtering operations, up-conversion operations) on the modulation symbols. The signals generated by the modulators of the transceivers 463a to the transceivers 463t may be transmitted via the antennas 464a to the antennas 464t.

[0098] The signal transmitted by the second communication node 400b may be received at the antenna 414a to the antenna 414r of the first communication node 400a. The signal received at the antenna 414a to the antenna 414r may be provided to a demodulator (DEMOD) included in the transceiver 413a to the transceiver 413r. The demodulator may obtain samples by performing a processing operation (e.g., a filtering operation, an amplification operation, a down-conversion operation, a digital conversion operation) on the signal. The demodulator may perform additional processing operations on the samples to obtain symbols. The MIMO detector 420 may perform a MIMO detection operation on the symbols. The receiving processor 419 may perform a processing operation (e.g., a deinterleaving operation, a decoding operation, etc.) on the symbols. The output of the receiving processor 419 may be provided to the data sink. 418 and controller 416. For example, data may be provided to data sink 418 and control information may be provided to controller 416.

[0099] Memory 415 and storage 465 may store data, control information and / or program codes. Scheduler 417 may perform scheduling operations for communications. Figure 4 The processors 411, 412, 419, 461, 468, 469 and the controllers 416 and 466 shown may be Figure 3 The processor 310 shown may be used to execute the methods described in the present invention.

[0100] Figure 5a is a block diagram illustrating a first exemplary embodiment of a transmit path, Figure 5b is a block diagram illustrating a first exemplary implementation of a receive path.

[0101] like Figure 5a and Figure 5bAs shown, the transmission path 510 can be implemented in a communication node that transmits a signal, and the receiving path 520 can be implemented in a communication node that receives a signal. The transmission path 510 may include a channel coding and modulation block 511, a serial-to-parallel (S to P) block 512, an N-point inverse fast Fourier transform (IFFT) block 513, a parallel-to-serial (P to S) block 514, a cyclic prefix (CP) adding block 515 and an up-converter (UC) 516. The receiving path 520 may include a down-converter (DC) 521, a CP deletion block 522, an S to P block 523, an N-point FFT block 524, a P to S block 525 and a channel decoding and demodulation block 526. Here, N may be a natural number.

[0102] In the transmission path 510, the information bits may be input to the channel coding and modulation block 511. The channel coding and modulation block 511 may perform coding operations (e.g., low-density parity check (LDPC) coding operations, polar coding operations, etc.) and modulation operations (e.g., quadrature phase shift keying (OPSK), quadrature amplitude modulation (QAM), etc.) on the information bits. The output of the channel coding and modulation block 511 may be a modulation symbol sequence.

[0103] The S to P block 512 may convert the frequency domain modulation symbols into parallel symbol streams to generate N parallel symbol streams. N may be an IFFT size or an FFT size. The N-point IFFT block 513 may generate a time domain signal by performing an IFFT operation on the N parallel symbol streams. The P to S block 514 may convert the output (e.g., parallel signals) of the N-point IFFT block 513 into a serial signal to generate a serial signal.

[0104] The CP adding block 515 may insert a CP into the signal. The UC 516 may up-convert the frequency of the output of the CP adding block 515 to a radio frequency (RF) frequency. In addition, the output of the CP adding block 515 may be filtered in baseband before up-conversion.

[0105] The signal transmitted from the transmission path 510 may be input to the reception path 520. The operation in the reception path 520 may be an operation opposite to the operation in the transmission path 510. The DC 521 may down-convert the frequency of the received signal to the baseband frequency. The CP removal block 522 may remove the CP from the signal. The output of the CP removal block 522 may be a serial signal. The S to P block 523 may convert the serial signal into a parallel signal. The N-point FFT block 524 may generate N parallel signals by performing an FFT algorithm. The P to S block 525 may convert the parallel signal into a modulation symbol sequence. The channel decoding and demodulation block 526 may perform a demodulation operation on the modulation symbol, and may recover the data by performing a decoding operation on the result of the demodulation operation.

[0106] exist Figure 5a and Figure 5b In the present invention, discrete Fourier transform (DFT) and inverse DFT (IDFT) can be used to replace FFT and IFFT. Figure 5a and Figure 5b Each of the blocks (eg, components) in the embodiment may be implemented by at least one of hardware, software, or firmware. Figure 5a and Figure 5b Some blocks in the can be implemented by software, and other blocks can be implemented by hardware or a combination of hardware and software. Figure 5a and Figure 5b In the , a block can be subdivided into multiple blocks, multiple blocks can be integrated into one block, some blocks can be omitted, and blocks that support other functions can be added.

[0107] On the other hand, the NTN reference scenario may be defined as shown in Table 1 below.

[0108] [Table 1]

[0109] NTN shown in Figure 1 NTN shown in Figure 2 GEO Scenario A Scenario B LEO (Steering Beam) Scenario C1 Scenario D1 LEO (beam that moves with the satellite) Scenario C2 Scene D2

[0110] when Figure 1a and / or Figure 1b When the satellite 110 in the NTN shown is a GEO satellite (e.g., a GEO satellite supporting transparency functionality), this may be referred to as "Scenario A". Figure 2a , Figure 2b and / or Figure 2c When satellite 211 and satellite 212 in the illustrated NTN are GEO satellites (eg, GEOs supporting regeneration functionality), this may be referred to as "scenario B."

[0111] when Figure 1a and / or Figure 1bWhen the satellite 110 in the NTN shown is a LEO satellite with a steerable beam, this may be referred to as "Scenario C1". Figure 1a and / or Figure 1b When the satellite 110 in the NTN shown is a LEO satellite with a beam that moves with the satellite, this may be referred to as "Scenario C2". Figure 2a , Figure 2b and / or Figure 2c When satellite 211 and satellite 212 in the NTN shown are LEO satellites with steerable beams, this may be referred to as "Scenario D1". Figure 2a , Figure 2b and / or Figure 2c When satellite 211 and satellite 212 in the NTN shown are LEO satellites with beams that move with the satellites, this may be referred to as “scenario D2.” Parameters for the NTN reference scenario defined in Table 1 may be defined as shown in Table 2 below.

[0112] [Table 2]

[0113]

[0114] In addition, in the scenario defined in Table 1, the delay constraint may be defined as shown in Table 3 below.

[0115] [Table 3]

[0116]

[0117] Figure 6a is a conceptual diagram showing a first exemplary embodiment of a protocol stack for a user plane in a non-terrestrial network based on a transparent payload, Figure 6b is a conceptual diagram illustrating a first exemplary embodiment of a protocol stack of a control plane in a non-terrestrial network based on a transparent payload.

[0118] like Figure 6a and Figure 6b As shown, user data can be sent and received between the UE and the core network (e.g., UPF), and control data (e.g., control information) can be sent and received between the UE and the core network (e.g., AMF). Each of the user data and the control data can be sent and received via a satellite and / or a gateway. Figure 6a The protocol stack of the user plane shown can be applied identically or similarly to a 6G communication network. Figure 6b The control plane protocol stack shown can be applied identically or similarly to a 6G communication network.

[0119] Figure 7a is a conceptual diagram illustrating a first exemplary embodiment of a protocol stack for a user plane in a non-terrestrial network based on a regenerative payload, Figure 7bis a conceptual diagram illustrating a first exemplary embodiment of a protocol stack for a control plane in a non-terrestrial network based on a regenerative payload.

[0120] like Figure 7a and Figure 7b As shown, each of user data and control data (e.g., control information) can be sent and received through an interface between a UE and a satellite (e.g., a base station). User data can refer to a user protocol data unit (PDU). A protocol stack of a satellite radio interface (SRI) can be used to send and receive user data and / or control data between a satellite and a gateway. User data can be sent and received between a satellite and a core network through a general packet radio service (GPRS) tunneling protocol (GTP)-U tunnel.

[0121] On the other hand, in a non-terrestrial network, the base station may transmit system information (e.g., SIB19) including satellite assistance information for NTN access. The UE may receive the system information (e.g., SIB19) from the base station, identify the satellite assistance information included in the system information, and perform communication (e.g., non-terrestrial communication) based on the satellite assistance information. SIB19 may include the information elements defined in Table 4 below.

[0122] [Table 4]

[0123]

[0124]

[0125] The NTN-Config defined in Table 4 may include the information elements defined in Table 5 below.

[0126] [Table 5]

[0127]

[0128] The EphemerisInfo defined in Table 5 may include the information elements defined in the following Table 6.

[0129] [Table 6]

[0130]

[0131]

[0132] On the other hand, diversity-based coverage enhancement was proposed at the 3GPP RAN1 109-e meeting in May 2022. The proposal mentioned the following points.

[0133] Frequency hopping is already supported in legacy NR releases and can continue to be used to provide frequency domain diversity in NR NTN. In previous discussions, it has been mentioned that diversity using different satellites or different carriers is related to the specific characteristics of NTN. However, this scenario is somewhat complex and considering the limited TUs, it is not preferred to study this type of diversity in Release 18.

[0134] ● Polarization-based diversity can also be considered. Polarization can support data transmission during the initial access process and the RRC connected state. During the initial access process, SSBs with different polarization modes can be used. In the RRC connected state, different polarization modes can be used at least in different time domain resources to achieve diversity gain.

[0135] Hereinafter, a signal transmission method in a multiple transmitting and receiving point (multi-TRP) operation in a terrestrial network (TN) is described.

[0136] In TN, multiple TRPs enable a base station to communicate with a terminal using one or more TRPs. In this case, a TRP can correspond to a cell, a remote radio head, or a relay node. In 3GPP, the following three operation schemes are being considered.

[0137] Figures 8a to 8c is a conceptual diagram showing three operating schemes of TRP.

[0138] like Figure 8a As shown, a first TRP 811, a second TRP 812, and a user equipment (UE) 821 are shown. The first TRP 811 and the second TRP 812 can each send a physical downlink shared channel (PDSCH) 831 and 832 to the UE 821. At this time, a physical downlink control channel (PDCCH) 841 carrying control information of the PDSCH can be sent only through one specific TRP. Figure 8a The example in FIG. 8 shows a case where the first TRP 811 sends a PDCCH to a UE 821. As is well known, the PDCCH can carry downlink control information (DCI).

[0139] exist Figure 8a In this case, if a radio link problem occurs in the first TRP 811 and reception of the PDCCH fails, communication via the second TRP 812 may also be affected.

[0140] Figure 8b Shows something like Figure 8a The first TRP 811, the second TRP 812, and the UE 821. The first TRP 811 may send DCI to the UE 821 through the PDCCH 841, and send data based on the DCI to the UE 821 through the PDSCH 831. The second TRP 812 may also send DCI to the UE 821 through the PDCCH 842, and send data based on the DCI to the UE 821 through the PDSCH 832.

[0141] Figure 8b It indicates that TRP 811 and TRP 812 send PDSCH 831 and PDSCH 832 and PDCCH 841 and PDCCH 842 to UE 821 respectively. Figure 8b In this case, even if a radio link problem occurs in one of the TRPs, communication can be maintained via another TRP.

[0142] Figure 8c Shows something like Figure 8a The first TRP 811, the second TRP 812 and the UE 821. Figure 8c In this case, the first TRP 811 and the second TRP 812 can jointly process downlink (DL) signals and uplink (UL) signals. Figure 8c The example in may correspond to a scenario similar to the coordinated multi-point (CoMP) defined in 3GPP.

[0143] Figure 8c A situation is shown in which the first TRP 811 and the second TRP 812 perform collaborative transmission to UE 821 using PDSCH 831 and PDSCH 832.

[0144] like Figures 8a to 8c As shown, in a TN using this transmission scheme, data transmission and reception can be performed through multiple links. Although the distances between TRPs located at different locations and the UE are different, considering that the propagation speed is the speed of light and the absolute distance between the TRP and the UE in a typical TN cell deployment is within a few kilometers, the difference in transmission delay between the two links can be much smaller than the OFDM symbol duration. Therefore, the UE can receive signals from multiple TRPs almost simultaneously.

[0145] exist Figure 8a and 8b In the case of , UE 821 can use two receiving modules to receive signals from two satellites and perform diversity signal processing. Figure 8cIn the case of CoMP, UE 821 can use a single receiving module to process the signal in a manner similar to CoMP.

[0146] Hereinafter, a positioning reference signal (PRS) in a TN is described.

[0147] In TN, PRS is defined for positioning purposes. In RRC idle / inactive state, the UE can request the positioning system information block through on-demand system information request using random access message 1 or message 3. In addition, in RRC connected mode, the UE can request the positioning system information block using on-demand connected mode.

[0148] Figure 9a is a conceptual diagram showing a comb-6 mode with three TRPs as a DL-PRS mode in a 3GPP TN, Figure 9b is a conceptual diagram showing the comb-4 mode which is a UL-PRS mode in 3GPP TN.

[0149] Figure 9a represents an example of DL-PRS in downlink, Figure 9b An example of UL-SRS in uplink is shown. The information that can be obtained through PRS measurement is as follows.

[0150] -Received signal time difference (RSTD) of the DL PRS of each beam at the UE

[0151] -UE Rx-Tx time difference

[0152] -Multi-cell round trip time (multi-RTT)

[0153] -Downlink angle of departure (DL-AoD)

[0154] -Uplink angle of arrival (UL-AoA)

[0155] Hereinafter, a low earth orbit (LEO) satellite system having a mega constellation is described.

[0156] Representative LEO satellite systems include Starlink and OneWeb. These two systems use or plan to use hundreds to thousands of satellites to provide global service coverage. The OneWeb system currently consists of 720 satellites and will eventually include 900 satellites at an altitude of 1200km. It includes 18 polar orbits, each with 40 satellites. OneWeb plans to establish 50 to 70 gateway sites around the world, which will include approximately 500 or more gateway antennas. Accordingly, a single gateway site can have up to ten 2.4-meter antennas.

[0157] As of March 2020, Starlink, operated by SpaceX, has deployed 362 satellites into orbit and plans to deploy a total of 12,000 satellites. Starlink has three orbital altitudes, and the number of satellites corresponding to each altitude is as follows.

[0158] (1) 1,600 satellites at an altitude of 550 km

[0159] (2) 2800 satellites at 1150 km altitude in Ku and Ka bands

[0160] (3) 7,500 satellites at 340 km altitude in the V band

[0161] To operate such a large number of satellites and provide broadband data transmission of more than 600Mbps, hundreds of ground stations and approximately 3,500 gateway antennas are required.

[0162] Fig.10a is a schematic diagram showing the constellation of Starlink, Fig.10b is a schematic diagram showing an Alaska gateway antenna deployed in a OneNet system.

[0163] In the case of Starlink, Fig.10a As shown, or in the OneWeb system, such as combined Fig.10b As described, when a particular service area is served by multiple satellites, a diversity effect can be achieved. In addition, a single gateway can be configured to establish connections with multiple satellites.

[0164] In NTN, the link quality is reduced due to the long distance between the satellite and the terminal (e.g., UE) and the significant Doppler shift caused by high-speed movement. Therefore, since Release 17, 3GPP has been actively discussing coverage enhancement (CovEnh) research to solve this problem. When only a single satellite is used to perform transmission and reception, the performance improvement is limited. In particular, these limitations become more apparent when the elevation angle is low or in urban / suburban areas with a high density of high-rise buildings. LEO satellite systems such as Starlink and OneWeb utilize or plan to utilize hundreds to thousands of satellites to provide global service coverage. In this case, a specific service area can be served by multiple satellites. Therefore, the feasibility of implementing diversity technology by transmitting and receiving via multiple satellites is high. However, due to the differences in transmission delay and Doppler shift between links via different satellites, it is considered challenging to directly apply the multi-TRP transmission technology developed for TN to satellite diversity in NTN.

[0165] When supporting terminals using antennas with low antenna gain, such as handheld terminals (e.g., UE), or when the link budget is low, a diversity transmission scheme utilizing multiple satellites is needed as a performance enhancement measure. In particular, in an NTN environment, the transmission delays and Doppler shifts experienced by multiple links via different satellites may have significant differences.

[0166] Due to these large differences in transmission delay and Doppler shift, it is difficult to directly apply the multi-TRP transmission technology developed for TN. Therefore, in order to realize satellite diversity transmission in the NTN environment, a new satellite diversity transmission scheme that takes into account the NTN environment needs to be developed. In particular, considering the complexity of the terminal, the signals received from multiple links need to be time-controlled so that they are received at appropriate time intervals. In addition, since the satellites participating in the diversity have different Doppler shift values, Doppler shift pre-compensation needs to be performed for each link.

[0167] Fig.11 is a conceptual diagram showing diversity signal transmission using two transparent satellites in an NTN environment.

[0168] like Fig.11 As shown, UE 1101, a first satellite 1111, a second satellite 1112 and a gateway 1131 are shown. Here, the gateway 1131 can be directly connected to the base station ( Fig.111131), configured as a single system with a base station, or connected to a base station via other networks. In the present invention, as described below, the operation of the gateway 1131 can be understood as the operation of the base station. In other words, the gateway 1131 can be a device connected to the satellite 1111 and the satellite 1112, and the actual control of the signal transmission and reception with the satellite 1111 and the satellite 1112 can be performed by the base station. However, in order to distinguish between the base station in the TN and the base station connected to the gateway 1131, Fig.11 The base station is described as the gateway 1131. Generally, a base station constituting a TN in a mobile communication system will be referred to as a "TN base station".

[0169] UE 1101 may receive signals from a TN base station or from at least one satellite in the NTN. In addition, UE 1101 may send signals to a TN base station or receive signals from at least one satellite in the NTN. Since the present invention describes the NTN environment, the case where UE 1101 communicates with the TN is omitted.

[0170] As described above, the first satellite 1111 may have a feeder link 1141 with a gateway 1131 located on the ground, and the second satellite 1112 may also have a feeder link 1142 with the gateway 1131 located on the ground.

[0171] The first satellite 1111 and the second satellite 1112 may be satellites capable of transmitting signals overlapping a specific area 1120 on the ground. In other words, Fig.11 The illustrated multi-NTN communication area 1120 may be an area capable of simultaneously communicating with the first satellite 1111 and the second satellite 1112. In the following description, an area capable of receiving signals from two or more satellites is referred to as a "multi-NTN communication area".

[0172] Fig.11 The example in FIG. 1 shows a case where a UE 1101 located on the ground is located in a multi-NTN communication area 1120. Therefore, the UE 1101 located in the multi-NTN communication area 1120 can transmit and receive signals with the first satellite 1111 through a service link 1151 between the first satellite 1111 and the UE 1101. In addition, the UE 1101 located in the multi-NTN communication area 1120 can transmit and receive signals with the second satellite 1112 through a service link 1152 between the second satellite 1112 and the UE 1101. Here, the signal may include data, control information, a reference signal, and the like.

[0173] exist Fig.11 In the embodiment, considering the transparent satellite, the first satellite 1111 and the second satellite 1112 can form a satellite diversity transmission and reception environment. However, it should be noted that Fig.11Satellites 1111 and 1112 in the embodiment are not limited to transparent satellites. In other words, the same scheme can be applied even when satellites 1111 and 1112 are non-transparent satellites. However, for ease of description, the following description assumes that satellites 1111 and 1112 are transparent satellites.

[0174] The transparent satellite can be used as a simple repeater and can perform operations such as frequency filtering, frequency conversion, and signal amplification. Gateway 1131 can establish and use feeder links with both satellite 1111 and satellite 1112 at the same time, such as Fig.11 Although for ease of description, Fig.11 Only a single UE is shown in FIG. 1 , but it is obvious to those skilled in the art that a plurality of UEs may be located in the multi-NTN communication area 1120. The UE located in the multi-NTN communication area 1120 may perform diversity reception using signals transmitted from two or more satellites.

[0175] In order to describe diversity reception, the first link and the second link are distinguished and described separately.

[0176] The link between the gateway 1131, the first satellite 1111, and the UE 1101 may be referred to as a first link, and the link between the gateway 1131, the second satellite 1112, and the UE 1101 may be referred to as a second link. The first link and the second link may be distinguishable at least at a reference signal level, and the gateway 1131 may control transmission by using a different antenna / Tx module for each satellite.

[0177] The first link and the second link may have different propagation path distances and Doppler shift values. The gateway 1131 may perform timing control and Doppler shift pre-compensation for each link individually.

[0178] In TN multi-TRP transmission, such as Figures 8a to 8c As described above, the difference in transmission delay between links is less than the OFDM symbol duration, and the difference in Doppler shift between links is negligible. Therefore, no separate processing for the difference in delay and Doppler shift between links is proposed.

[0179] However, in an NTN environment, additional operations are required to consider the difference in transmission delay and Doppler shift between the two links. In this case, when the diversity transmission uses the same resources and polarization, cooperative transmission such as CoMP (e.g., joint transmission (JT)) can be applied. When different resources or polarizations are used, non-JT diversity reception using different streams for each link can also be applied. In both cases, appropriate timing control and Doppler shift pre-compensation need to be performed to reduce the complexity of UE 1101 and ensure diversity gain.

[0180] Accordingly, the present invention provides a scheme for switching transmission modes between satellite diversity and single transmission in an NTN environment, and a scheme for link-specific timing control and Doppler shift pre-compensation for satellite diversity.

[0181] First exemplary embodiment: Method for switching between diversity transmission mode and single transmission mode based on measurements

[0182] A first exemplary embodiment of the present invention provides a method for switching between a satellite diversity transmission mode of a downlink (DL) in an NTN environment and a satellite single transmission mode of the DL based on measurement information such as time delay (transmission delay) and Doppler shift. Hereinafter, the satellite diversity mode refers to a technique for obtaining a diversity gain by transmitting a signal via two or more satellites. Since the following description relates to a diversity mode in an NTN environment, the diversity mode may refer to a satellite diversity mode.

[0183] In this case, the first exemplary embodiment of the present invention relates to a case where it is determined whether to perform a diversity transmission mode or a single transmission mode based on measurements and reports of the UE. In the following description, a link may refer to a link between a satellite and a terminal and / or a link between a satellite and a gateway. In addition, it should be noted that a gateway may be used independently, or the gateway may be directly connected to a base station or indirectly connected to a base station via other networks.

[0184] According to the first exemplary embodiment of the present invention, when the difference in time delay and Doppler shift between two links in the NTN environment is within a certain level, a diversity transmission mode for performing joint transmission (JT) can be applied. When the difference exceeds a certain level, a single transmission mode can be applied. When the base station does not have a function for link-specific timing and Doppler shift pre-compensation, the first exemplary embodiment of the present invention can be used.

[0185] Fig.12 is a sequence diagram illustrating a measurement-based switching operation between satellite diversity transmission mode and single transmission mode in NTN.

[0186] Fig.12 Entities (eg, UE 1101, first satellite 1111, and second satellite 1112) use Fig.11 However, the base station 1121 can be directly connected to Fig.11 The gateway 1131 shown may be configured as a single system, or may be connected to the gateway 1131 via other networks. Fig.12 The base station 1121 described in the above may refer to a base station connected to Fig.11 The base station of the gateway 1131 is shown.

[0187] Fig.12 The satellite diversity transmission mode using two satellites, i.e., by using two links of the first satellite 1111 and the second satellite 1112 is described. However, it should be noted that when three or more satellites form a multi-NTN communication area, such as Fig.11 As described in , three or more satellites may also be utilized.

[0188] In step S1200 , UE 1101 may send a diversity transmission request message to base station 1121 . Fig.12 The case where UE 1101 sends a diversity request message to base station 1121 is shown, but it is also possible that base station 1121 sends a diversity transmission request message to UE 1101. Accordingly, base station 1121 can receive a diversity transmission request message from UE 1101.

[0189] On the other hand, as described above, when UE 1101 is located in a multi-NTN communication area, the transmission of the diversity transmission request message may occur. In addition, the diversity transmission request message may be transmitted to base station 1121 via first satellite 1111 or via second satellite 1112. In other words, the diversity transmission request message may be a message transmitted when UE 1101 is in a single transmission mode. In this case, the satellite used by UE 1101 to transmit the diversity transmission request message may be a serving satellite.

[0190] In another example, when UE 1101 is currently in diversity transmission mode but intends to maintain diversity transmission mode, a diversity transmission request message may also be sent. In this case, the diversity transmission request message may be sent via the first satellite 1111 and / or the second satellite 1112. In other words, the diversity transmission request message may be sent via a single satellite or via two satellites.

[0191] The criteria for determining whether UE 1101 is located in a multi-NTN communication area may be whether a signal is received from two or more satellites, and / or the location information of UE 1101 and the location information of satellite 1111 and satellite 1112 derived from the ephemeris information. When UE 1101 is located in a multi-NTN communication area, UE 1101 may determine that diversity transmission is possible. In another example, even when UE 1101 is located in a multi-NTN communication area, a diversity transmission request may be selectively made based on the quality of the received signal and / or service requirements. For example, when the quality of the received signal is good, UE 1101 may not need diversity transmission. In another example, when a relatively low-speed data service that is not sensitive to delay is provided, it may not be necessary to send a diversity transmission request message. Accordingly, UE 1101 may determine whether it is necessary to send a diversity transmission request message to base station 1121 by utilizing various types of information. Fig.12 It shows a situation where a diversity transmission request message needs to be sent based on at least one of the above criteria.

[0192] The diversity transmission request message according to the present invention can be sent dynamically in the form of event triggering. In other words, the diversity transmission request message can be sent at any time when the event is triggered. In another example, according to the present invention, the diversity transmission request message can indicate the request or release of diversity transmission in a semi-static manner at a predetermined period. In this case, the request period can be determined based on the position of UE 1101, ephemeris information and the moving speed of the satellite.

[0193] In step S1202, base station 1121 may allocate reference signals (RS) to be transmitted via satellite 1111 and satellite 1112 based on the received diversity transmission request message. Fig.12 The first satellite 1111 and the second satellite 1112 are shown as an example, and thus the RSs may be classified into a first RS transmitted via the first satellite 1111 and a second RS transmitted via the second satellite 1112. In this case, the first RS and the second RS may utilize the PRS defined in the TN. In addition, the first RS and the second RS may be different RSs to allow identification of the corresponding satellites.

[0194] The first RS and the second RS may be sent periodically. In another example, the first RS and the second RS may be sent upon request. If the first RS and the second RS are sent periodically, the transmission period of each of the first RS and the second RS may be changed using a predefined value or through signaling.

[0195] In step S1204a and step S1206a, the base station 1121 may transmit data including the first RS and the second RS to the first satellite 1111 and the second satellite 1112, respectively. In this case, the base station 1121 may transmit data including the first RS through a first feeder link established with the first satellite 1111 via the gateway 1131. Fig.12 Similarly, the base station 1121 can send data including the second RS through a second feeder link established with the second satellite 1112 via the gateway 1131, which is Fig.12 Not shown in FIG.

[0196] In step S1204b, the first satellite 1111 may transmit data including the first RS received from the base station 1121 to the UE 1101 through the service link. In step S1206b, the second satellite 1112 may transmit data including the second RS received from the base station 1121 to the UE 1101 through the service link. Accordingly, in steps S1204b and S1206b, the UE 1101 may receive the first RS and the second RS from the first satellite 1111 and the second satellite 1112, respectively.

[0197] Fig.12 The case where step S1204a and step S1206a are performed sequentially is shown. However, when actual transmission occurs through the feeder link, step S1204a and step S1206a may be performed simultaneously. In another example, in step S1204b and step S1206b, base station 1121 may change or adjust the transmission timing of the RS to be transmitted via satellite 1111 and satellite 1112 so that UE 1101 receives them simultaneously or sequentially.

[0198] In step S1208, UE 1101 may measure RSs received from first satellite 1111 and second satellite 1112 and obtain measurement information. Here, the measurement information may include a time delay (or a change in time delay) between transmission and reception of each link and a Doppler shift (or a change in Doppler shift) of each link.

[0199] In other words, UE 1101 can measure the time delay (or change in time delay) and Doppler shift (or change in Doppler shift) between transmission and reception by using the first RS received via the first satellite 1111. The measurement information may be measurement information of the first link. Similarly, UE 1101 can measure the time delay (or change in time delay) and Doppler shift (or change in Doppler shift value) between transmission and reception by using the second RS received via the second satellite 1112. The measurement information may be measurement information of the second link.

[0200] In step S1210, UE 1101 may send a reference signal measurement report message to base station 1121. The reference signal measurement report message may include measurement information of the first link and measurement information of the second link, as described above. UE 1101 may send a reference signal measurement report message periodically or based on a specific request. For example, when receiving a request message for a reference signal measurement report from base station 1121, UE 1101 may send a reference signal measurement report message to base station 1121. In another example, UE 1101 may send a reference signal measurement report message to base station 1121 at a preconfigured period.

[0201] In addition, when UE 1101 has only one link, for example, when a single satellite is currently serving, UE 1101 can send a reference signal measurement report message through a link formed with a single serving satellite. In another example, when UE 1101 is served by two satellites, a single link or two links can be used to send a reference signal measurement report message. In this case, when two links are used, the reference signal measurement report message sent through the two links may include the same information or different information. When the reference signal measurement report message includes the same information, the message may include measurement information of both the first link and the second link. On the other hand, when the reference signal measurement report message includes different information, the message may be sent separately for the corresponding link. For example, the measurement information of the first link may be sent via the first satellite 1111 corresponding to the first link, and the measurement information of the second link may be sent via the second satellite 1112 corresponding to the second link.

[0202] Accordingly, in step S1210, the base station 1121 may receive the reference signal measurement report message through a single link or two links.

[0203] In step S1220, base station 1121 may determine the transmission mode based on the received reference signal measurement report message. Fig.13 The operation of determining the transmission mode is further described in.

[0204] In step S1230, base station 1121 may transmit data to UE 1101 according to the determined mode. For example, when the determined mode is the diversity mode, base station 1121 may transmit data to UE 1101 via first satellite 1111 and second satellite 1112. On the other hand, when the determined mode is the single transmission mode, base station 1121 may transmit data to UE 1101 via the serving satellite.

[0205] Fig.13 is a flowchart illustrating an operation of a base station in determining a transmission mode according to a first exemplary embodiment of the present invention.

[0206] The base station 1121 may receive a reference signal measurement report message from the UE 1101, such as Fig.12 . Base station 1121 may obtain the measurement information of the first link and the measurement information of the second link included in the reference signal measurement report message. Each of the measurement information of the first link and the measurement information of the second link may include the time delay between transmission and reception of each link (or the change in time delay) and the Doppler shift (or the change in Doppler shift) of each link, as described above. Accordingly, base station 1121 may obtain the time delay between transmission and reception of each link (or the change in time delay) and the Doppler shift (or the change in Doppler shift) of each link.

[0207] In step S1310, the base station 1121 may calculate the difference in the time delay between the two links. For example, the difference between the time delay of the first link and the time delay of the second link may be calculated. In this case, the difference between the two values ​​(i.e., the time delay difference) may be taken as an absolute value. In addition, the base station 1121 may calculate the difference in the Doppler shift between the two links. For example, the difference between the Doppler shift of the first link and the Doppler shift of the second link may be calculated. In this case, the difference between the two values ​​(i.e., the Doppler shift difference) may also be taken as an absolute value.

[0208] In step S1312, the base station 1121 may check whether the time delay difference is less than a preconfigured first threshold. In addition, the base station 1121 may check whether the Doppler shift difference is less than a preconfigured second threshold. Here, the first threshold and the second threshold may be thresholds for determining whether diversity transmission can be performed.

[0209] If the check result of step S1312 indicates that the time delay difference is greater than or equal to the preconfigured first threshold or the Doppler shift difference is greater than or equal to the preconfigured second threshold, the base station 1121 may proceed to step S1314. On the other hand, if the check result of step S1312 indicates that the time delay difference is less than the preconfigured first threshold and the Doppler shift difference is less than the preconfigured second threshold, the base station 1121 may proceed to step S1316.

[0210] In step S1314, since the time delay difference is greater than or equal to the preconfigured first threshold or the Doppler shift difference is greater than or equal to the preconfigured second threshold, base station 1121 may determine that diversity transmission is not possible. Accordingly, base station 1121 may determine that a single transmission mode needs to be implemented.

[0211] When proceeding to step S1316, since the time delay difference is less than the preconfigured first threshold and the Doppler shift difference is less than the preconfigured second threshold, the base station 1121 can check the current mode. If the current mode is the single transmission mode, the base station 1121 can proceed to step S1318, and if the current mode is the diversity transmission mode, the base station 1121 can proceed to step S1320.

[0212] In step S1318, since the previously checked condition indicates that diversity transmission can be performed and the current transmission mode is the single transmission mode, the base station 1121 may determine to switch to the diversity transmission mode.

[0213] In step S1320, since the previously checked condition indicates that diversity transmission can be performed and the current transmission mode is the diversity transmission mode, the base station 1121 may determine to maintain the diversity transmission mode.

[0214] exist Fig.12 and Fig.13 In the process described above, if the current transmission mode is the diversity transmission mode, in addition to executing the diversity transmission request Fig.12 In addition to step S1200, other processes may be repeated periodically. In other words, the base station 1121 may determine whether to maintain the diversity transmission mode or switch to the single transmission mode at a preconfigured period. Accordingly, the base station 1121 and the UE 1101 may maintain the current mode (e.g., maintain the single transmission mode or maintain the diversity transmission mode) or switch to another mode (e.g., switch from the single transmission mode to the diversity transmission mode or switch from the diversity transmission mode to the single transmission mode).

[0215] Fig.12 and Fig.13 The operation of sending information about the determined mode, such as maintaining the diversity transmission mode, switching to the diversity transmission mode, maintaining the single transmission mode, or switching to the single transmission mode, is not shown. However, it will be appreciated by those skilled in the art that the base station 1121 may send such mode information to the UE 1101. In addition, the mode information may be sent via downlink control information (DCI), MAC-CE, or RRC message.

[0216] Second exemplary embodiment: Method for switching between satellite diversity mode and single transmission mode in DL transmission

[0217] A second exemplary embodiment of the present invention provides a method for switching between a satellite diversity transmission mode and a single transmission mode in an NTN environment. Hereinafter, the satellite diversity mode may refer to a technique for obtaining a diversity gain by transmitting a signal via two or more satellites. Since the following description relates to a diversity mode in an NTN environment, the diversity mode may refer to a satellite diversity mode.

[0218] A second exemplary embodiment of the present invention provides a method in which, when the time delay and Doppler shift can be estimated based on the ephemeris information and the position information of the UE, the base station can determine whether to perform a diversity transmission mode or a single transmission mode. To implement this method, the present invention assumes that the UE periodically sends its position information to the base station. Accordingly, the base station can periodically receive the position information from the UE. In addition, the base station can have a priori knowledge of the satellite ephemeris, calculate and derive the position information of the satellite, or receive the satellite position information from each satellite.

[0219] The operation according to the second exemplary embodiment of the present invention also follows the same principle described in the first exemplary embodiment, wherein when the difference in time delay and the difference in Doppler shift between two links in the NTN environment are within a certain level, a diversity transmission mode involving joint transmission (JT) is applied, and when (one or more) differences exceed a certain level, a single transmission mode is applied. The second exemplary embodiment of the present invention can also be used when the base station does not have a function for link-specific timing and Doppler shift pre-compensation.

[0220] Fig.14 is a sequence diagram illustrating a measurement-based switching operation between satellite diversity transmission mode and single transmission mode in NTN.

[0221] Fig.14 The entities in Fig.12 However, it should be noted that the operation of each entity (eg, UE 1101, first satellite 1111, second satellite 1112, and base station 1121) follows the operation described below.

[0222] Fig.14 The base station 1121 shown can be directly connected to Fig.11 The gateway 1131 shown may be configured as a single system, or may be connected to the gateway 1131 via other networks. Fig.14 The base station 1121 described in the above may refer to a base station connected to Fig.11 The base station of the gateway 1131 is shown.

[0223] Fig.14 The satellite diversity mode using two satellites, i.e., two links using the first satellite 1111 and the second satellite 1112 is described. However, it should be noted that when three or more satellites form a multi-NTN communication area, such as Fig.11 As described in , three or more satellites may also be utilized.

[0224] In step S1400 , UE 1101 may send a diversity transmission request message to base station 1121 . Fig.14The case where UE 1101 sends a diversity request message to base station 1121 is shown, but it is also possible that base station 1121 sends a diversity transmission request message to UE 1101. Accordingly, base station 1121 can receive a diversity transmission request message from UE 1101.

[0225] On the other hand, as described above, when UE 1101 is located in a multi-NTN communication area, the transmission of the diversity transmission request message may occur. In addition, the diversity transmission request message may be transmitted to base station 1121 via first satellite 1111 or via second satellite 1112. In other words, the diversity transmission request message may be a message transmitted when UE 1101 is in a single transmission mode. In this case, the satellite used by UE 1101 to transmit the diversity transmission request message may be a serving satellite.

[0226] In another example, when UE 1101 is currently in diversity transmission mode but intends to maintain diversity transmission mode, a diversity transmission request message may also be sent. In this case, the diversity transmission request message may be sent via the first satellite 1111 and / or the second satellite 1112. In other words, the diversity transmission request message may be sent via a single satellite or via two satellites.

[0227] The criteria for determining whether UE 1101 is located in a multi-NTN communication area may be whether a signal is received from two or more satellites, and / or the location information of UE 1101 and the location information of satellite 1111 and satellite 1112 derived from ephemeris information. When UE 1101 is located in a multi-NTN communication area, UE 1101 may determine that diversity transmission is possible. In another example, even when UE 1101 is located in a multi-NTN communication area, a diversity transmission request may be selectively made based on the quality of the received signal and / or service requirements. For example, when the quality of the received signal is good, UE 1101 may not need diversity transmission. In another example, when a relatively low-speed data service that is not sensitive to delay is provided, it may not be necessary to send a diversity transmission request message. Accordingly, UE 1101 may determine whether it is necessary to send a diversity transmission request message to base station 1121 by utilizing various types of information. Fig.14 It shows a situation where a diversity transmission request message needs to be sent based on at least one of the above criteria.

[0228] The diversity transmission request message according to the present invention can be sent dynamically in the form of event triggering. In other words, the diversity transmission request message can be sent at any time when the event is triggered. In another example, according to the present invention, the diversity transmission request message can indicate the request or release of diversity transmission in a semi-static manner at a predetermined period. In this case, the request period can be determined based on the position of UE 1101, ephemeris information and the moving speed of the satellite.

[0229] In step S1402, base station 1121 may estimate time delay and Doppler shift based on the ephemeris information of satellite 1111 and satellite 1112 and the location information of UE. Here, the ephemeris information of satellite 1111 and satellite 1112 may include information of a specific orbit and location on the earth, such as Fig.10a As shown. In other words, the ephemeris information of satellite 1111 and satellite 1112 may include information about the latitude, longitude, and altitude of satellite 1111 and satellite 1112. In addition, the location information of UE 1101 may be based on the location information periodically reported by UE 1101 to base station 1121, as described above. In this case, when UE 1101 is served by a single serving satellite, UE 1101 may send location information to base station 1121 via the serving satellite. If UE 1101 is served by two or more satellites in a diversity transmission mode, UE 1101 may send location information to base station 1121 using either or both of the two satellites.

[0230] In step S1404, the base station 1121 may determine the transmission mode based on the estimated time delay and Doppler shift. The operation for determining the transmission mode may be as follows: Fig.13 In addition, after determining the transmission mode, the base station 1121 can set the timer value to a pre-configured time value. Here, since the UE's location information and the satellite's ephemeris information are constantly changing, the timer can be used as a mechanism to update the information.

[0231] However, the difference in time delay calculated based on the measurement value reported by UE 1101 is Fig.13 Different, in Fig.14 In , the difference can be calculated based on the estimated time delay. Similarly, although in Fig.13 The difference between the measured Doppler shifts is calculated in the case of Fig.14 In this case, the difference in Doppler shift can be obtained from the estimated Doppler shift.

[0232] In step S1406, base station 1121 may transmit data to UE 1101 according to the determined mode. For example, when the determined mode is the diversity mode, base station 1121 may transmit data to UE 1101 via first satellite 1111 and second satellite 1112. On the other hand, when the determined mode is the single transmission mode, base station 1121 may transmit data to UE 1101 via the serving satellite.

[0233] In step S1408, the base station 1121 may check whether the value of the timer reaches zero. If the check result of step S1408 indicates that the value of the timer is zero, the base station 1121 may proceed to step S1402. On the other hand, if the check result of step S1408 indicates that the value of the timer is not zero, the base station 1121 may proceed to step S1410 to reduce the value of the timer. Here, the timer may use a fixed value. In another example, the setting value of the timer may be changed dynamically according to the situation.

[0234] exist Fig.14 In the example of , the timer can be set to a time value for repeatedly executing the steps after step S1402. Accordingly, instead of using a timer, steps S1408 and S1410 can be replaced by steps for checking whether a predefined time (or time period) has passed. If the steps are modified to check whether a predefined time has passed, the next check time can be set before proceeding to step S1402. In addition, even when a timer is used, if the value of the timer reaches zero, the timer can be reset. When UE 1101 is in active communication, the method using a timer or a predefined time (or time period) can be applied. In other words, when UE 1101 is in an inactive mode or an idle mode, these operations may not be performed.

[0235] Third exemplary embodiment: Downlink transmission mode switching method between satellite diversity mode and single transmission mode Law

[0236] The third exemplary embodiment of the present invention described below provides a method for switching between a satellite diversity transmission mode and a single transmission mode in an NTN environment. Hereinafter, the satellite diversity mode may refer to a technique for obtaining a diversity gain by transmitting a signal via two or more satellites. Since the following description relates to a diversity mode in an NTN environment, the diversity mode may refer to a satellite diversity mode.

[0237] In a third exemplary embodiment of the present invention, when the time delay difference and the Doppler shift difference between two links in the diversity transmission mode are less than the corresponding threshold value, the joint transmission (JT) mode can be applied. On the contrary, when the time delay difference and the Doppler shift difference between two links are greater than the corresponding threshold value, the non-joint transmission (non-JT) mode can be applied.

[0238] When using JT mode and non-JT mode, you can Fig.13 The corresponding parts described in are modified as in the third exemplary embodiment of the present invention.

[0239] Fig.15 is a flow chart showing a switching operation between a JT mode and a non-JT mode in an NTN.

[0240] In step S1510, the base station 1121 may calculate the difference of the measured time delay or calculate the difference of the estimated time delay. Here, the difference of the measured time delay may be obtained as follows: the base station 1121 may control the reference signal to be sent to the UE 1101 via the first satellite 1111 and the second satellite 1112, and receive the reference signal measurement report from the UE 1101. In other words, the difference of the measured time delay may be obtained as follows: the base station 1121 may control the reference signal to be sent to the UE 1101 via the first satellite 1111 and the second satellite 1112, and receive the reference signal measurement report from the UE 1101. Fig.12 The measured time delay is obtained by performing steps S1220 to S1210 described in the specification.

[0241] In addition, the time delay estimated by step S1402 may be used to calculate the difference in the estimated time delay, such as Fig.14 described.

[0242] In step S1510, the base station 1121 may also calculate the difference of the measured Doppler frequency shift or the difference of the estimated Doppler frequency shift. Fig.12 The difference of the measured Doppler shift can be obtained by performing steps S1220 to S1210 described in the above, as described above. On the other hand, the difference of the estimated Doppler shift can be estimated by step S1402, such as Fig.14 described.

[0243] In step S1512, the base station 1121 may check whether the calculated (or estimated) time difference and the calculated (or estimated) Doppler frequency shift difference meet the first condition. Fig.15 However, it should be noted that the following description is also applicable when the estimated time difference value and the estimated Doppler shift difference value are used.

[0244] Here, the first condition may use a threshold value for determining a single transmission mode. Fig.12 and Fig.13 As described in, the base station 1121 can check whether the calculated time delay difference is less than a first threshold and whether the calculated Doppler shift difference is less than a second threshold. If either of the two values ​​is equal to or greater than the corresponding threshold, a single transmission mode may need to be performed.

[0245] For example, step S1512 of checking whether the first condition is satisfied may be a step of checking whether the condition for the single transmission mode is satisfied. If the checking result of step S1512 indicates that the condition for the single transmission mode is satisfied, the base station 1121 may proceed to step S1514. On the other hand, if the checking result of step S1512 indicates that the condition for the single transmission mode is not satisfied, the base station 1121 may proceed to step S1520.

[0246] In step S1514, the base station 1121 may determine that a single transmission mode needs to be implemented. In other words, the base station 1121 may determine a mode of providing services to the UE 1101 via only one satellite.

[0247] In step S1520, the base station 1121 may check whether the second condition is satisfied. Here, the second condition may be a condition group for determining whether the JT mode is possible. When the calculated time delay difference is within a third threshold value less than the first threshold value, and the calculated Doppler shift difference is within a fourth threshold value less than the second threshold value, the JT mode may be possible. Here, the first threshold value may be expressed as δ T2 , the second threshold can be expressed as δ F2 , the third threshold can be expressed as δ T , the fourth threshold can be expressed as δ F Then, satisfying the above-mentioned first condition may correspond to satisfying any one of Equation 1 or Equation 2 below.

[0248] [Equation 1]

[0249] The calculated time delay difference ≥ δ T2

[0250] [Equation 2]

[0251] The calculated Doppler shift difference ≥ δ F2

[0252] On the other hand, satisfying the second condition may correspond to satisfying Equation 3 and Equation 4 simultaneously.

[0253] [Equation 3]

[0254] The calculated time delay difference <δ T

[0255] [Equation 4]

[0256] The calculated Doppler shift difference <δ F

[0257] Accordingly, the base station 1121 may check whether Equation 3 and Equation 4 are satisfied. If the check result of step S1520 indicates that the second condition is satisfied, the base station 1121 may proceed to step S1530. If the check result of step S1520 indicates that the second condition is not satisfied, the base station 1121 may proceed to step S1522.

[0258] In step S1522, base station 1121 may determine that the non-JT mode needs to be performed. In other words, base station 1121 may transmit different data via each of satellite 1111 and satellite 1112, or may perform data transmission using only one satellite.

[0259] In step S1530, the base station 1121 may check whether the current mode is the non-JT mode. If the current mode is the non-JT mode, the base station 1121 may proceed to step S1532. If the current mode is the JT mode, the base station 1121 may proceed to step S1534.

[0260] In step S1532, the base station 1121 may switch the current mode to the JT mode. In other words, the mode switching may be performed.

[0261] In step S1534, since the current mode is the JT mode and the JT mode can be executed, the base station 1121 can maintain the JT mode.

[0262] Above Fig.15 Can replace Fig.12 and / or Fig.14 The transmission mode determination step. Fig.12 The transmission mode determination step is modified to Fig.15 The form described in can be omitted Fig.12 or replace it with a "joint transmission request message". Fig.14 The transmission mode determination step is modified to Fig.15 can be omitted Fig.14 or replace it with a "joint transmission request message".

[0263] Fourth exemplary embodiment: Timing and Doppler shift pre-compensation method for satellite diversity mode

[0264] The fourth exemplary embodiment of the present invention described below provides a method for pre-compensating the timing and Doppler shift of a satellite diversity transmission mode in an NTN environment. Hereinafter, the satellite diversity mode may refer to a technique for obtaining a diversity gain by transmitting a signal via two or more satellites. Since the following description relates to a diversity mode in an NTN environment, the diversity mode may refer to a satellite diversity mode.

[0265] When the time delay difference and Doppler shift difference between two links (e.g., a link via a first satellite and a link via a second satellite) in an NTN environment are below a certain level, the diversity in the JT scheme described in the third exemplary embodiment can be applied. However, in the third exemplary embodiment, the JT diversity method is applied only when the second condition is met (which means that the time delay difference and the Doppler shift difference are within a predetermined range). In contrast, in a fourth exemplary embodiment of the present invention, a method for applying a diversity transmission mode by pre-compensation is provided even when at least one of the conditions of equations 3 and 4 is not met. Therefore, this method can be used when the base station has a pre-compensation function that allows time delay (or timing) and Doppler shift compensation to be performed for each individual link.

[0266] Fig.16 is a sequence diagram illustrating a method of performing a pre-compensation based satellite diversity transmission mode in NTN.

[0267] Fig.16 The entities in Fig.12 and Fig.14 However, it should be noted that the operation of each entity (eg, UE 1101, first satellite 1111, second satellite 1112, and base station 1121) follows the operation described below.

[0268] Fig.16 The base station 1121 shown can be directly connected to Fig.11 The gateway 1131 shown may be configured as a single system, or may be connected to the gateway 1131 via other networks. Fig.16 The base station 1121 described in the above may refer to a base station connected to Fig.11 The base station of the gateway 1131 is shown.

[0269] Fig.16 The satellite diversity mode using two satellites, i.e., two links using the first satellite 1111 and the second satellite 1112 is described. However, it should be noted that when three or more satellites form a multi-NTN communication area, such as Fig.11 As described in , three or more satellites may also be utilized.

[0270] although Fig.16 Although not shown in the figure, the base station 1121 can instruct the UE 1101 to report the location information at a pre-configured period. Accordingly, the UE 1101 can report the location information to the base station 1121 via the serving satellite at a pre-configured period. In the following description, it should be noted that the process of the UE 1101 reporting the location information at a pre-configured period is not shown in the figure. Fig.16 Shown in.

[0271] In step S1600 , UE 1101 may send a diversity transmission request message to base station 1121 . Fig.16 FIG. 1 shows a case where UE 1101 sends a diversity request message to base station 1121. However, it is also possible that base station 1121 sends a diversity request message to UE 1101. Accordingly, base station 1121 can receive a diversity request message from UE 1101. In addition, since the diversity request message in step S1600 is the same as Fig.12 and Fig.14 The messages described in are the same, so repeated descriptions are omitted.

[0272] In step S1602, base station 1121 may allocate reference signals (RS) to be transmitted via satellite 1111 and satellite 1112 to corresponding satellites based on the received diversity transmission request message. Step S1602 may correspond to Fig.12 Therefore, repeated description is omitted.

[0273] In step S1604a and step S1606a, base station 1121 may transmit data including a first reference signal and a second reference signal via first satellite 1111 and second satellite 1112, respectively. Step S1604a and step S1606a may correspond to Fig.12 Step S1204a and step S1206a described in . In addition, step S1604b and step S1606b may correspond to Fig.12 Step S1204b and step S1206b described in .

[0274] In step S1608, UE 1101 may measure the reference signals received from first satellite 1111 and second satellite 1112, and may obtain measurement information. Here, the measurement information may include the time delay (or the change in the time delay) between transmission and reception of each link and the Doppler shift (or the change in the Doppler shift) of each link. Step S1608 may correspond to Fig.12 Step S1208 described in .

[0275] In step S1610, UE 1101 may send a reference signal measurement report message to base station 1121. The reference signal measurement report message may include measurement information of the first link and measurement information of the second link, as described above. Step S1610 may correspond to Fig.12 Accordingly, in step S1610, the base station 1121 may receive the reference signal measurement report message via one link or two links.

[0276] In step S1620, the base station 1121 may determine the transmission mode based on the received reference signal measurement report message. Fig.17 An operation for determining a transmission mode is described.

[0277] In step S1622, the base station 1121 may calculate and apply a timing advance (TA) value. At this time, the TA value may correspond to a TA value via the corresponding satellite 1111 and the satellite 1112. In addition, the base station 1121 may calculate and apply a Doppler pre-compensation (DPC). Step S1622 will be described as an example.

[0278] The difference in time delay between the first satellite 1111 and the second satellite 1112 may be greater than a first threshold value set for the diversity transmission mode. In this case, based on the TA value, the time delay difference may be compensated so that the difference becomes less than the first threshold value. At this time, the time delay compensation may adjust the time delay of the link with a larger time delay. Conversely, the time delay compensation may adjust the time delay of the link with a smaller time delay. Through the time delay compensation, the time delay difference between the first link via the first satellite 1111 and the second link via the second satellite 1112 may be compensated to be within the first threshold value applicable to the diversity transmission mode.

[0279] In addition, the difference in Doppler shift between the first satellite 1111 and the second satellite 1112 may be greater than a predetermined second threshold. In this case, based on the measured (or estimated) Doppler shift, DPC may be performed for the satellite with the larger Doppler shift. If the Doppler shift of the first satellite 1111 is large, DPC may be performed for the first link via the first satellite 1111 so that the difference in Doppler shift between the first link and the second link is compensated to be within the second threshold.

[0280] In step S1630, the base station 1121 may utilize the determined mode to transmit data to the UE 1101. For example, if the determined mode is the diversity mode, the base station 1121 may transmit data to the UE 1101 via the first satellite 1111 and the second satellite 1112. On the other hand, if the determined mode is the single transmission mode, the base station 1121 may transmit data to the UE 1101 via the serving satellite.

[0281] Fig.17 is a flowchart illustrating an operation of a base station in determining a transmission mode according to a fourth exemplary embodiment of the present invention.

[0282] Base station 1121 may receive a reference signal measurement report message from UE 1101, such as Fig.16Alternatively, base station 1121 may estimate the time delay (or change in time delay) between transmission and reception of each link and the Doppler shift (or change in Doppler shift) of each link, as described in Fig.14 In the following description, the description is based on the state that the base station 1121 receives the time delay (or change in the time delay) between the transmission and reception of each link and the Doppler shift (or change in the Doppler shift) of each link from the reference signal, as shown in FIG. Fig.16 However, it should be noted that estimated values ​​can also be used, such as Fig.14 In step S1402.

[0283] In step S1710, the base station 1121 may calculate the difference in the time delay between the two links. For example, the base station 1121 may calculate the difference between the time delay of the first link and the time delay of the second link. At this time, the difference between the two values ​​may be taken as an absolute value. In addition, the base station 1121 may calculate the difference in the Doppler shift between the two links. For example, the base station 1121 may calculate the difference between the Doppler shift of the first link and the Doppler shift of the second link. Similarly, the difference between the two values ​​may be taken as an absolute value.

[0284] In step S1712, the base station 1121 may check whether the difference in time delay between the two links (i.e., the delay time difference) is less than a pre-configured first threshold. In addition, the base station 1121 may check whether the difference in Doppler frequency shift between the two links (i.e., the Doppler frequency shift difference) is less than a pre-configured second threshold. Here, the first threshold and the second threshold may be thresholds for performing diversity transmission.

[0285] If the check result of step S1712 indicates that the time delay difference is greater than or equal to the preconfigured first threshold, or the Doppler shift difference is greater than or equal to the preconfigured second threshold, the base station 1121 may proceed to step S1716. On the other hand, if the check result of step S1712 indicates that the time delay difference is less than the preconfigured first threshold, and the Doppler shift difference is less than the preconfigured second threshold, the base station 1121 may proceed to step S1714.

[0286] In step S1714, since the time delay difference is less than the preconfigured first threshold and the Doppler shift difference is less than the preconfigured second threshold, base station 1121 can determine that diversity transmission is possible. Accordingly, base station 1121 can determine that diversity transmission mode needs to be implemented.

[0287] On the other hand, if the check result of step S1712 indicates that the time delay difference is equal to or greater than the preconfigured first threshold, or the Doppler shift difference is equal to or greater than the preconfigured second threshold, the base station 1121 may proceed to step S1716 and check whether a diversity transmission mode is required. In the exemplary embodiment described above, the case where the base station 1121 does not have a compensation capability has been described. However, Fig.16 and Fig.17 The base station 1121 described in may have a compensation capability. Therefore, if the diversity transmission mode is required, the base station 1121 may proceed to step S1714 and determine that the diversity transmission mode needs to be performed.

[0288] On the other hand, if the check result of step S1716 indicates that the diversity transmission mode is not required, the base station 1121 may proceed to step S1720 and maintain the single transmission mode.

[0289] Fig.16 and Fig.17 The exemplary embodiments described in the foregoing may correspond to a case where the base station 1121 has a compensation capability. In addition, even when the base station 1121 has a compensation capability, the operator may turn the compensation capability on or off. Therefore, assuming that the compensation capability of the base station 1121 can be turned on or off, the first to third exemplary embodiments described above may correspond to a state where the base station 1121 has a compensation capability but it is turned off, and the fourth exemplary embodiment may correspond to a state where the compensation capability of the base station 1121 is turned on.

[0290] Fifth exemplary embodiment: Uplink switching method between satellite diversity mode and single transmission mode

[0291] In the fifth exemplary embodiment of the present invention described below, the satellite diversity transmission mode and the single transmission mode in the uplink (UL) under the NTN environment will be described, wherein the uplink satellite diversity transmission mode and the single transmission mode are particularly focused on. The uplink satellite diversity transmission mode may refer to a technique in which a UE transmits a signal via two or more satellites to obtain a diversity gain. Since the following description relates to a diversity mode under the NTN environment, the diversity mode may refer to a satellite diversity mode. However, the distinguishing feature from the previous exemplary embodiment is that the fifth exemplary embodiment focuses on the uplink diversity mode.

[0292] In order to meet the conditions of the fifth exemplary embodiment of the present invention, the UE may need to have two transmission modules, or be configured so that a single internal transmission module can transmit signals to different satellites. When two transmission modules are used, the first transmission module can transmit signals to the first satellite 1111, and the second transmission module can transmit signals to the second satellite 1112. Accordingly, when two transmission modules are used, a first UL link toward the base station 1121 via the first satellite 1111 and a second UL link toward the base station 1121 via the second satellite 1112 can be configured respectively.

[0293] Each of the first UL link and the second UL link can have different time delays and different Doppler shifts, as described above. As described in the first to fourth exemplary embodiments, switching between the UL single transmission mode and the UL diversity transmission mode can be performed based on the time delay difference and the Doppler shift difference. In this case, since each link has a separate transmission module, separate timing and Doppler shift pre-compensation control can be performed. Accordingly, as described in the fourth exemplary embodiment, UE 1101 can compensate for the time delay and perform DPC in advance to enable the uplink diversity transmission mode to be implemented.

[0294] On the other hand, if UE 1101 has a single UL transmission module, timing and Doppler shift pre-compensation control cannot be performed separately for each link. Therefore, in this case, since the diversity gain may deteriorate if the quality of one link is too poor, a pre-compensation scheme using an appropriate intermediate value can be used. For example, if the effect of Doppler shift is linear, pre-compensation can be performed based on the intermediate value, and if the effect is non-linear, an algorithm for determining an appropriate value may be required. Various forms of such algorithms may exist. Therefore, in the present invention, a detailed description of a DPC method for compensating for Doppler shift when the effect of Doppler shift is non-linear is omitted.

[0295] In addition, UE 1101 may know its own position. A satellite may broadcast its own position, or UE 1101 may have information for identifying the position of a satellite in advance. Accordingly, it should be noted that not only the measured values ​​as in the first exemplary embodiment but also the estimated values ​​as described in the second exemplary embodiment may be used.

[0296] The operation of the method according to the exemplary embodiment of the present invention can be implemented as a computer-readable program or code in a computer-readable recording medium. The computer-readable recording medium may include a recording device of all types having data that can be read by a computer system. In addition, the computer-readable recording medium can store and execute programs or codes, which can be distributed in a computer system connected via a network and read by a computer in a distributed manner.

[0297] Computer readable recording media may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM or flash memory. Program instructions may include not only machine language codes created by a compiler, but also high-level language codes that can be executed by a computer using an interpreter.

[0298] Although some aspects of the present invention have been described in the context of a device, these aspects may indicate the corresponding description according to the method, and a block or device may correspond to the step of the method or the feature of the step. Similarly, the aspects described in the context of the method may be represented as the feature of a corresponding block or project or a corresponding device. Some or all steps of the method may be performed by (or using) a hardware device such as a microprocessor, a programmable computer or an electronic circuit. In some embodiments, one or more of the most important steps of the method may be performed by such a device.

[0299] In some exemplary embodiments, a programmable logic device such as a field programmable gate array can be used to perform some or all of the functions of the methods described herein. In some exemplary embodiments, the field programmable gate array can be operated with a microprocessor to perform one of the methods described herein. Typically, the method is preferably performed by a specific hardware device.

[0300] The description of the present invention is merely exemplary in nature, and therefore variant forms that do not deviate from the essence of the present invention are intended to be within the scope of the present invention. Such variant forms should not be considered as departing from the spirit and scope of the present invention. Therefore, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope defined by the appended claims.

Claims

1. A method of a base station, comprising: allocating a reference signal (RS) corresponding to each of the first satellite and the second satellite; controlling the first satellite and the second satellite to transmit the RS and data corresponding to each satellite to a user equipment (UE); receiving an RS measurement report message from a UE; determining, based on the received RS measurement report message, a transmission mode in a single transmission mode in which data is transmitted via one of the first satellite and the second satellite or a diversity transmission mode in which data is transmitted via both the first satellite and the second satellite; as well as transmitting data to the UE based on the determined transmission mode, The RS measurement report message includes: a first time delay and a first Doppler frequency shift based on a first RS received through a first link of a first satellite, and a second time delay and a second Doppler frequency shift based on a second RS received through a second link of a second satellite.

2. The method according to claim 1, wherein: When the difference between the first time delay and the second time delay is smaller than a predetermined first threshold, and the difference between the first Doppler frequency shift and the second Doppler frequency shift is smaller than a predetermined second threshold, the diversity transmission mode is determined.

3. The method according to claim 1, wherein: When the difference between the first time delay and the second time delay is greater than or equal to a predetermined first threshold, or when the difference between the first Doppler shift and the second Doppler shift is greater than or equal to a predetermined second threshold, a single transmission mode is determined.

4. The method according to claim 1, wherein: The RS measurement report message is received via a serving satellite among the first satellite and the second satellite.

5. The method according to claim 1, wherein: The RS measurement report message consists of a first RS measurement report message received through a first link and a second RS measurement report message received through a second link, wherein the first RS measurement report message includes a first time delay and a first Doppler frequency shift, and the second RS measurement report message includes a second time delay and a second Doppler frequency shift.

6. The method according to claim 1, wherein: When a diversity transmission request is received from the UE, allocation of RSs corresponding to each of the first satellite and the second satellite is performed.

7. The method according to claim 1, further comprising: receiving a diversity transmission request from a UE; When the transmission mode determined based on the RS measurement report message is the single transmission mode, compensating the first time delay so that a difference between the first time delay and the second time delay becomes smaller than a predetermined first threshold; compensating the first Doppler frequency shift so that a difference between the first Doppler frequency shift and the second Doppler frequency shift becomes smaller than a predetermined second threshold; as well as The diversity transmission mode is determined by applying the compensation value.

8. The method according to claim 7, wherein: The first link having the first time delay has a longer time delay than the second link.

9. A base station comprising at least one processor, wherein: The at least one processor causes the base station to: allocating a reference signal (RS) corresponding to each of the first satellite and the second satellite; controlling the first satellite and the second satellite to transmit the RS and data corresponding to each satellite to a user equipment (UE); receiving an RS measurement report message from a UE; determining, based on the received RS measurement report message, a transmission mode in a single transmission mode in which data is transmitted via one of the first satellite and the second satellite or a diversity transmission mode in which data is transmitted via both the first satellite and the second satellite; as well as transmitting data to the UE based on the determined transmission mode, The RS measurement report message includes: a first time delay and a first Doppler frequency shift based on a first RS received through a first link of a first satellite, and a second time delay and a second Doppler frequency shift based on a second RS received through a second link of a second satellite.

10. The base station according to claim 9, wherein: When the difference between the first time delay and the second time delay is smaller than a predetermined first threshold, and the difference between the first Doppler frequency shift and the second Doppler frequency shift is smaller than a predetermined second threshold, the diversity transmission mode is determined.

11. The base station according to claim 9, wherein: When the difference between the first time delay and the second time delay is greater than or equal to a predetermined first threshold, or when the difference between the first Doppler shift and the second Doppler shift is greater than or equal to a predetermined second threshold, a single transmission mode is determined.

12. The base station according to claim 9, wherein: The RS measurement report message is received via a serving satellite among the first satellite and the second satellite.

13. The base station according to claim 9, wherein: The RS measurement report message consists of a first RS measurement report message received through a first link and a second RS measurement report message received through a second link, wherein the first RS measurement report message includes a first time delay and a first Doppler frequency shift, and the second RS measurement report message includes a second time delay and a second Doppler frequency shift.

14. The base station according to claim 9, wherein: The at least one processor further causes the base station to perform, when a diversity transmission request is received from the UE, allocating an RS corresponding to each of the first satellite and the second satellite.

15. The base station according to claim 9, wherein: The at least one processor further causes the base station to: receiving a diversity transmission request from a UE; When the transmission mode determined based on the RS measurement report message is the single transmission mode, compensating the first time delay so that a difference between the first time delay and the second time delay becomes smaller than a predetermined first threshold; compensating the first Doppler frequency shift so that a difference between the first Doppler frequency shift and the second Doppler frequency shift becomes smaller than a predetermined second threshold; as well as The diversity transmission mode is determined by applying the compensation value.

16. The base station according to claim 15, wherein: The first link having the first time delay has a longer time delay than the second link.

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