KR20210144596A - Method and apparatus for communication between terminal and satellite in non terrestrial network - Google Patents

Abstract

Disclosed are a method and apparatus for communication between a terminal and a satellite in a non-terrestrial network. An operating method of a terminal includes the steps of: performing a beam scan operation to receive reference signals of satellites; selecting one reference signal that satisfies a preset criterion from among the reference signals received by the beam scan operation; identifying a first satellite that has transmitted the one reference signal from among the satellites; transmitting a paging signal to the first satellite; and receiving data from the first satellite.

Description

Method and apparatus for communication between a terminal and a satellite in a non-terrestrial network

The present invention relates to a communication technology in a non-terrestrial network, and more particularly, to a technology for broadband communication between a terminal and a satellite.

For processing of rapidly increasing wireless data, a frequency band (eg, a frequency band of 6 GHz or more) higher than a frequency band (eg, a frequency band of 6 GHz or less) of long term evolution (LTE) (or LTE-A) A communication network (eg, a new radio (NR) communication network) using The NR communication network may support a frequency band of 6 GHz or higher as well as a frequency band of 6 GHz or less, and may support various communication services and scenarios compared to an LTE communication network. For example, a usage scenario of the NR communication network may include enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communication (URLLC), massive Machine Type Communication (mMTC), and the like.

The NR communication network may provide a communication service to terminals located in terrestrial. Recently, as well as on the ground, the demand for communication services for airplanes, drones, satellites, etc. located in non-terrestrial is increasing, and for this purpose, non-terrestrial network (NTN) ) are being discussed. Non-terrestrial networks may be implemented based on NR technology. For example, in a non-terrestrial network, communication between a satellite and a communication node located on the ground or a communication node located on the non-ground (eg, an airplane, a drone, etc.) may be performed based on the NR technology. In a non-terrestrial network, a satellite may perform the function of a base station in an NR communication network.

Meanwhile, a satellite constellation may be operated using a low transmission delay characteristic of a low earth orbit (LEO) satellite. By operating a cluster satellite, communication coverage may be expanded, and thus, an entire space information technology communication (ITC) service may be provided. Based on the above-mentioned characteristics, global companies (eg, OneWeb, Space-X, Telesat) are developing technologies for providing Internet service based on (ultra) small swarm satellites. According to statistics, of the 2614 small satellites scheduled to be launched by 2026, more than 50% may be communication satellites. Huawei has announced plans for 6G service using LEO satellites. Based on this, the role of LEO small satellites in the field of communications could be important.

Satellite communication technology is being developed to provide global services, but information on network configuration, transmission protocol, and technology of the satellite vehicle is not fully disclosed. The reason is that a transmission standard for broadband communication based on LEO satellites using high frequencies above the K band has not been developed. The DVB standard was mainly used for broadband communication based on geostationary earth orbit (GEO) satellites, and there were attempts to apply the DVB standard to LEO satellite-based broadband communication, but the world standard technology for LEO satellite communication is still being prepared.

In particular, in LEO satellite communication using a high frequency of K band or higher, the terminal may be a very small apparatus terminal (VAST) having a phased array antenna, not a handheld terminal such as a mobile phone. The VAST may have a form independent of the mobile communication terminal. Given the size and/or weight of the VAST, personal portable use of the VAST may not be appropriate. Therefore, technologies for accessing the LEO satellite network as well as the terrestrial network using the portable terminal are required.

An object of the present invention for solving the above problems is to provide a method and apparatus for communication between a terminal and a low earth orbit (LEO) satellite in a non-terrestrial network.

In order to achieve the above object, a method of operating a terminal in a non-terrestrial network according to a first embodiment of the present invention includes: performing a beam scan operation to receive reference signals transmitted by satellite payloads for initial access; Selecting one reference signal that satisfies a preset criterion from among reference signals received by a beam scan operation, identifying a first satellite that has transmitted the one reference signal from among the satellites, the first satellite transmitting a paging signal to a , and receiving data from the first satellite.

Here, the method of operating the terminal may further include performing communication with a second satellite among the satellites when the communication between the terminal and the first satellite is performed for more than a preset time.

Here, the communicating with the second satellite may include transmitting the paging signal to the second satellite without performing the beam scan operation.

Here, the one reference signal may be a reference signal having the greatest reception strength among the received reference signals.

Here, the confirming of the first satellite may include confirming the satellite power of the first satellite based on the one reference signal.

Here, the paging signal may include information on the orientation direction between the terminal and the first satellite determined based on the one reference signal.

According to the satellite and the terminal proposed in the present invention, satellite communication can be efficiently performed. In particular, in a non-terrestrial network, communication speed can be improved, and an access procedure between a terminal and a satellite can be performed quickly. In addition, a terminal supporting satellite communication may be miniaturized. Accordingly, the performance of the non-terrestrial network can be improved.

1 is a conceptual diagram illustrating a first embodiment of a non-terrestrial network.
2 is a conceptual diagram illustrating a second embodiment of a non-terrestrial network.
3 is a block diagram illustrating a first embodiment of entities constituting a non-terrestrial network.
4 is a block diagram illustrating a first embodiment of a satellite in a non-terrestrial network;
5 is a conceptual diagram illustrating a first embodiment of an antenna mounted on a satellite in a non-terrestrial network.
6 is a block diagram illustrating a first embodiment of a digital signal processor mounted on a satellite in a non-terrestrial network.
7 is a conceptual diagram illustrating a first embodiment of satellite deployment in a beam scan area of a terminal in a non-terrestrial network.
8 is a flowchart illustrating a first embodiment of an initial access procedure between a terminal and a satellite in a non-terrestrial network.
9 is a conceptual diagram illustrating a time required for an initial access procedure in a non-terrestrial network.
10 is a conceptual diagram illustrating a first embodiment of a beam shape of a terminal in a non-terrestrial network.
11 is a conceptual diagram illustrating a first embodiment of a terminal in a non-terrestrial network.
12 is a flowchart illustrating a first embodiment of a communication method between a terminal and a satellite in a non-terrestrial network.
13 is a conceptual diagram illustrating a first embodiment of a satellite tracking method in a non-terrestrial network.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component. and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being “connected” or “connected” to another component, it is understood that the other component may be directly connected or connected to the other component, but other components may exist in between. it should be On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that no other element is present in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In describing the present invention, in order to facilitate the overall understanding, the same reference numerals are used for the same components in the drawings, and duplicate descriptions of the same components are omitted.

A communication network to which embodiments according to the present invention are applied will be described. The communication system is a non-terrestrial network (NTN), a 4G communication network (eg, a long-term evolution (LTE) communication network), and/or a 5G communication network (eg, a new radio (NR) communication network). ) communication network). A 4G communication network and a 5G communication network may be classified as a terrestrial network.

The non-terrestrial network may operate based on LTE technology and/or NR technology. The non-terrestrial network may support communication in a frequency band of 6 GHz or higher as well as a frequency band of 6 GHz or less. A 4G communication network can support communication in a frequency band of 6 GHz or less. The 5G communication network can support communication not only in frequency bands below 6 GHz, but also in frequency bands above 6 GHz. A communication network to which embodiments according to the present invention are applied is not limited to the content described below, and embodiments according to the present invention may be applied to various communication networks (eg, 4G communication network and/or 5G communication network). . Here, a communication network may be used in the same sense as a communication system.

1 is a conceptual diagram illustrating a first embodiment of a non-terrestrial network.

Referring to FIG. 1 , the non-terrestrial network may include a satellite 110 , a communication node 120 , a gateway 130 , a data network 140 , and the like. The non-terrestrial network shown in FIG. 1 may be a transparent payload-based non-terrestrial network. The 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 communication node 120 may include a communication node located on the ground (eg, user equipment (UE), a terminal) and a communication node located on a non-ground (eg, an airplane, 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 service link may mean a user link. Satellite 110 may provide communication services to communication node 120 using one or more beams. The shape of the footprint of the beam of the satellite 110 may be elliptical.

The communication node 120 may perform communication (eg, downlink communication, uplink communication) with the satellite 110 using LTE technology and/or NR technology. Communication between the satellite 110 and the communication node 120 may be performed using an NR-Uu interface. If DC (dual connectivity) is supported, the communication node 120 may be connected to the satellite 110 as well as other base stations (eg, base stations supporting LTE and/or NR functions), and LTE and/or NR DC operation may be performed based on the technology defined in the standard.

The gateway 130 may be located on the ground, and a feeder link may be established between the satellite 110 and the gateway 130 . The feeder link may be a wireless link. The gateway 130 may be referred to as a “non-terrestrial network (NTN) gateway”. Communication between the satellite 110 and the gateway 130 may be performed based on an NR-Uu interface or a satellite radio interface (SRI). The gateway 130 may be connected to the data network 140 . A “core network” may exist between the gateway 130 and the data network 140 . 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 NR technology. For example, the core network may include an access and mobility management function (AMF), a user plane function (UPF), a session management function (SMF), and the like. Communication between the gateway 130 and the core network may be performed based on the NG-C/U interface.

Alternatively, a base station and a core network may exist between the gateway 130 and the data network 140 . In this case, the gateway 130 may be connected to the base station, the base station may be connected to the core network, and the core network may be connected to the data network 140 . The base station and core network may support NR technology. Communication between the gateway 130 and the base station may be performed based on the NR-Uu interface, and communication between the base station and the core network (eg, AMF, UPF, SMF) may be performed based on the NG-C/U interface. can

2 is a conceptual diagram illustrating a second embodiment of a non-terrestrial network.

Referring to FIG. 2 , the non-terrestrial network may include a satellite #1 211 , a satellite #2 212 communication node 220 , a gateway 230 , a data network 1240 , and the like. The non-terrestrial network shown in FIG. 2 may be a non-terrestrial network based on a regenerative payload. For example, each of satellites #1-2 (211, 212) may include a payload received from another entity (eg, communication node 220, gateway 230) constituting a non-terrestrial network. A regeneration operation (eg, a demodulation operation, a decryption operation, a re-encoding operation, a re-modulation operation, and/or a filtering operation) may be performed on the , and the regenerated payload may be transmitted.

Each of satellites #1-2 (211, 212) may be an LEO satellite, a MEO satellite, a GEO satellite, a HEO satellite, or a UAS platform. The UAS platform may include HAPS. The satellite #1 (211) may be connected to the satellite #2 (212), and an inter-satellite link (ISL) may be established between the satellite #1 (211) and the satellite #2 (212). The ISL may operate at a radio frequency (RF) frequency or an optical band. ISL may be set as optional. The communication node 220 may include a communication node located on the ground (eg, UE, a terminal) and a communication node located on a non-ground (eg, an airplane, a drone). A service link (eg, a radio link) may be established between satellite #1 211 and the communication node 220 . The service link may mean a user link. Satellite #1 211 may provide communication services to communication node 220 using one or more beams.

The communication node 220 may perform communication (eg, downlink communication, uplink communication) with the satellite #1 211 using LTE technology and/or NR technology. Communication between satellite #1 211 and the communication node 220 may be performed using an NR-Uu interface. When DC is supported, the communication node 220 may be connected to satellite #1 211 as well as other base stations (eg, base stations supporting LTE and/or NR functions), and conform to LTE and/or NR standards. A DC operation may be performed based on a defined technique.

The gateway 230 may be located on the ground, and a feeder link may be established between the satellite #1 211 and the gateway 230 , and a feeder link may be established between the satellite #2 212 and the gateway 230 . have. The feeder link may be a wireless link. When the ISL is not established between the satellite #1 (211) and the satellite #2 (212), a feeder link between the satellite #1 (211) and the gateway 230 may be mandatory.

Communication between each of the satellites #1-2 (211, 2122) and the gateway 230 may be performed based on an NR-Uu interface or SRI. The gateway 230 may be connected to the data network 240 . A “core network” may exist between the gateway 230 and the data network 240 . In this case, the gateway 230 may be connected to the core network, and the core network may be connected to the data network 240 . The core network may support NR technology. For example, the core network may include AMF, UPF, SMF, and the like. Communication between the gateway 230 and the core network may be performed based on the NG-C/U interface.

Alternatively, a base station and a core network may exist between the gateway 230 and the data network 240 . In this case, the gateway 230 may be connected to the base station, the base station may be connected to the core network, and the core network may be connected to the data network 240 . The base station and core network may support NR technology. Communication between the gateway 230 and the base station may be performed based on the NR-Uu interface, and communication between the base station and the core network (eg, AMF, UPF, SMF) may be performed based on the NG-C/U interface. can

Meanwhile, entities (eg, satellites, communication nodes, gateways, etc.) constituting the non-terrestrial network shown in FIGS. 1 and 2 may be configured as follows.

3 is a block diagram illustrating a first embodiment of entities constituting a non-terrestrial network.

Referring to FIG. 3 , 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 , and the like. Each of the components included in the communication node 300 may be connected by a bus 370 to communicate with each other.

However, each of the components included in the communication node 300 may not be connected to the common bus 370 but to the processor 310 through an individual interface or an individual bus. 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. .

The processor 310 may execute a program command stored in at least one of the memory 320 and the storage device 360 . The processor 310 may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present invention are performed. Each of the memory 320 and the storage device 360 may be configured of at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 320 may include at least one of a read only memory (ROM) and a random access memory (RAM).

Meanwhile, NTN reference scenarios may be defined as shown in Table 1 below.

When the satellite 110 in the non-terrestrial network shown in FIG. 1 is a GEO satellite (eg, a GEO satellite supporting a transparent function), this may be referred to as “scenario A”. If satellites #1-2 (211, 212) in the non-terrestrial network shown in FIG. 2 are GEO satellites (eg, GEO supporting regenerative function), this may be referred to as “scenario B”. have.

When the satellite 110 in the non-terrestrial network shown in FIG. 1 is an LEO satellite with steerable beams, it may be referred to as “scenario C1”. If the satellite 110 in the non-terrestrial network shown in FIG. 1 is an LEO satellite with beams move with satellite, this may be referred to as “scenario C2”. In the non-terrestrial network shown in FIG. 2 , when satellites #1-2 ( 211 , 212 ) are LEO satellites with tunable beams, this may be referred to as “scenario D1”. When satellites #1-2 (211, 212) in the non-terrestrial network shown in FIG. 2 are LEO satellites having beams moving together with the satellite, this may be referred to as “scenario D2”.

Parameters for NTN reference scenarios defined in Table 1 may be defined as shown in Table 2 below.

In addition, in the NTN reference scenarios defined in Table 1, a delay constraint may be defined as shown in Table 3 below.

Next, communication methods between a terminal and an LEO satellite in a communication system will be described. Even when a method (eg, transmission or reception of a signal) performed in a first communication node among communication nodes is described, a corresponding second communication node is a method (eg, a method corresponding to the method performed in the first communication node) For example, reception or transmission of a signal) may be performed. That is, when the operation of the terminal is described, the corresponding base station may perform the operation corresponding to the operation of the terminal. Conversely, when the operation of the base station is described, the corresponding terminal may perform the operation corresponding to the operation of the base station.

In a non-terrestrial network, a swarm satellite may provide communication services. A constellation satellite may be referred to as a satellite constellation. A swarm satellite may consist of a plurality of small satellites (eg, small LEO satellites). The small satellite may mean a cube satellite or a cubesat. The non-terrestrial network may include satellites 110 , 211 , 212 , communication nodes 120 , 220 , gateways 130 , 230 , and/or ground control devices. A gateway may be used for control, network operation, and/or backhauling. Ground control devices may be used for telemetry, tracking, and/or command transmission of satellites. The ground control device may be included in the gateway. Alternatively, the ground control device may exist separately from the gateway.

A link through which the gateway transmits a signal to a terminal (eg, a communication node) via a satellite may be a forward link (eg, a downlink). The link through which the terminal transmits a signal to the gateway through the satellite may be a reverse link (eg, uplink). Satellites may enable “connections between users” and/or “connections between users and gateways” by extending terrestrial networks. Satellites can provide optimal performance by using multi-beam antennas and digital relays. The gateway may manage access and backhaul of the network. If ISL between satellites is not established, a plurality of gateways may be required to cover a global area. The gateway may be associated with a 5G terrestrial network.

The ground control device may perform a monitoring operation, a test operation, and/or a configuration update operation on the status of a subsystem of the satellite. The above-described control operation may be necessary for maintenance of the satellite and/or maintaining the orbit of the satellite. The terminal may be connected to the satellite and may track the LEO satellite. The UE can efficiently use frequency resources by using a phased array antenna and/or digital processing technology having high gain characteristics.

A satellite may support a phased array antenna technology that directly radiates N multiple beams to a service area and/or a software-defined digital repeater technology that supplements the transmission standard of a cluster satellite. Here, N may be a natural number. The above-described technology may mean a high level of flexibility. Even without increasing the size of the swarm satellites, the satellites can support surging demand. A satellite may support full beam hopping functionality in both the forward link and/or the return link (eg, reverse link). The satellite may provide an independent link to the terminal and may support the gateway's link running on the ground using different capacities. In order to support the above-described operation, a multi-beam satellite array method capable of independently steering each of the multi-beams in several directions may be used.

The multi-beam antenna and digital processor may flexibly change coverage, power, and allocated frequency to provide a high level of resource allocation flexibility in time and/or space. A high frequency reuse scheme may be used. When ultra-high-capacity processing technology is used, a high bit rate may be provided, and implementation may be possible at a low cost.

4 is a block diagram illustrating a first embodiment of a satellite in a non-terrestrial network;

Referring to FIG. 4 , the satellite may include a repeater 410 , a user link antenna 420 , and a feeder link antenna 430 . In addition, the satellite may further include a wide beam antenna. The user link antenna 420 may be referred to as a user link payload antenna. The user link antenna 420 may be connected to a terminal, and the feeder link antenna 430 may be connected to a gateway. The repeater 410 may support "connection between user link and user link" and/or "connection between user link and feeder link". The repeater 410 may perform a function (eg, a signal processing function) of a base station (eg, gNB) if necessary.

LEO satellites can move in orbit. Therefore, a reconfigurable satellite antenna may be required to match the satellite beam with the communication traffic space in which the terminal is located within the service area. The hopping function of the reconfiguration beam may support a complete handover to a terminal (eg, a mobile device). By adjusting the antenna gain, high power can be provided to hotspots (eg, airports) where high communication capacity is required. A planar antenna can be easily mounted on a satellite, and the physical number of antennas can be reduced by using a beamforming network suitable for multiple beams. To implement a communication service, a user link antenna connected to a terminal, a feeder link antenna communicating with a gateway, an ISL antenna for communication between satellites, and/or RS for transmitting and receiving a reference signal (eg, a reference signal) A (reference signal) antenna may be used.

The user link payload antenna 420 may be a phased array antenna, and may be classified into a multi-beam receiving antenna and a multi-beam transmitting antenna. Each of the multi-beam receive antenna and the multi-beam transmit antenna belonging to the user link antenna 420 may support 8 beams. The feeder link antenna 430 may be a phased array antenna, and may be classified into a multi-beam receiving antenna and a multi-beam transmitting antenna. Each of the multi-beam receive antenna and the multi-beam transmit antenna belonging to the feeder link antenna 430 may support two beams. The ISL antenna may constitute an RF link or an optical communication link.

5 is a conceptual diagram illustrating a first embodiment of an antenna mounted on a satellite in a non-terrestrial network.

Referring to FIG. 5 , the user link antenna may support N beams. Here, N may be a natural number. The user link antenna may include 3169 radiation elements, a splitter, a beamforming module, and the like.

6 is a block diagram illustrating a first embodiment of a digital signal processor mounted on a satellite in a non-terrestrial network.

Referring to FIG. 6 , the digital signal processor includes an analog to digital converter (ADC) 610 , an analysis filter bank 620 , a digital processing unit 630 , a switching unit 640 , and a synthesis filter bank (synthesis). filter bank) 650 , and/or a digital to analog converter (DAC) 660 . ADC 610 may be a high-speed ADC. A filter bank can be used to separate the signal of a channel into subchannels. The digital processing unit 630 may support multiple input multiple output (MIMO). The switching unit 640 may support switching between subchannels. The digital signal processor may support a signal reproduction processing operation. The digital signal processor may be included in the repeater 410 illustrated in FIG. 4 .

The digital signal processor may support all wireless interfaces and/or core network functions. A digital signal processor may digitize a waveform of a signal so as to be independent of evolution of a wireless interface, and a digital channelizer that does not perform demodulation and decoding operations may be applied to a digital signal processor. In addition, the digital signal processor may support a digital beamforming operation, single-channel duplication-based broadcasting, or multiple casting. Some of the digital signal processors can separate the user link and the feeder link. Therefore, a reproduction processing method advantageous for delay can be applied to a digital signal processor.

The setting of a method for the terminal to access the satellite may be determined in consideration of a new radio (NR) access method (ie, a 5G access method). In this case, the terminal may access a plurality of satellites. A terminal that does not support a global navigation satellite system (GNSS) function may also access the satellite(s). The satellite may include a small antenna for transmission of a reference signal and reception of a call signal of the terminal. The small antenna can have a wide beam width and can be mounted on the satellite independently of the user link antenna. The reference signal transmitted by the satellite may include an identifier (ID) of the satellite, location information, time information, and/or movement trajectory information. The terminal may determine the position of the satellite based on the reference signal received from the satellite.

The access procedure between the terminal and the satellite may be performed as follows. The terminal may access the satellite using the NR access method. Each of the satellites may have M cells, and the number of simultaneously transmittable beams in each of the satellites may be N. Here, each of M and N may be a positive integer. When M and N are the same, one beam transmission may be possible in one cell. The number of beams per downlink cell that can be generated by an antenna mounted on a satellite (hereinafter, referred to as a “satellite antenna”) may be determined based on the number of antenna array elements. For example, the number of beams per downlink cell that can be generated by the satellite antenna may be 200. The number of beams per uplink cell that can be generated by an antenna mounted in the terminal (hereinafter, referred to as "terminal antenna") may be determined based on the number of antenna array elements, and the like. For example, the number of beams per uplink cell that can be generated by the terminal antenna may be 100.

The round-trip delay time may be the maximum round-trip delay time between the terminal and the satellite. At low orbital altitudes (eg, 600 km), the round trip delay may be 25.77 milliseconds (milliseconds). "When the subcarrier spacing (SCS) is 120 kHz, two synchronization signal blocks (SSBs) are allocated in one slot, and the transmission period of the SSB is 20 ms", the beam sweeping procedure can be completed within 5 ms have.

7 is a conceptual diagram illustrating a first embodiment of satellite deployment in a beam scan area of a terminal in a non-terrestrial network.

Referring to FIG. 7 , the terminal may perform a beam sweeping operation within a beam scan area. The beam sweeping operation may refer to a beam scanning operation. That is, the terminal may receive a signal (eg, SSB, reference signal) from the satellite(s) located within the beam scan area. A plurality of satellites may be located within the beam scan area.

8 is a flowchart illustrating a first embodiment of an initial access procedure between a terminal and a satellite in a non-terrestrial network.

Referring to FIG. 8 , a UE may access a satellite by performing a 4-step random access procedure or a 2-step random access procedure. The satellite may transmit the SSB (S810). One SSB may be mapped to one beam, and the SSB may be transmitted based on a time division multiplexing (TDM) scheme. The SSB may be transmitted based on a beam sweeping scheme. In this case, the SSB may be transmitted using 200 beams.

The UE may perform the SSB reception operation based on the beam sweeping method. For example, the terminal may receive 200 beams (eg, SSB) in each of the reception beams. The reception beam may mean a reception direction. The UE may check the SSB index and measure the reference signal received power (RSRP) of the SSB. The UE may synchronize with the satellite based on the SSB having the largest RSRP. In addition, the terminal may receive system information (eg, a master information block (MIB)) from the satellite.

The satellite may transmit system information (eg, system information block (SIB)) including random access channel (RACH) configuration information (eg, RACH resource allocation information) (S820). System information may be transmitted through a physical downlink shared channel (PDSCH). The terminal may receive system information from the satellite and may check RACH configuration information included in the system information.

The UE may transmit a random access (RA) preamble to the satellite in the RACH occasion mapped to the SSB having the largest RSRP (S830). The RA preamble may mean Msg1. The satellite may receive the RA preamble from the terminal and may transmit a random access response (RAR) to the terminal in response to the RA preamble (S840). RAR may mean Msg2.

The terminal may receive the RAR from the satellite. When the RAR is received, the UE may transmit Msg3 (eg, a radio resource control (RRC) connection request message) to the satellite (S850). The satellite may receive Msg3 from the terminal. When Msg3 is received, the satellite may transmit Msg4 (eg, an RRC connection setup message) to the terminal (S860). The terminal may receive Msg4 from the satellite. When Msg4 is received, the terminal may transmit an RRC connection complete message to the satellite (S870). The satellite may receive an RRC connection complete message from the base station. When the above-described operation is completed, the terminal may be connected (eg, connected) to the satellite.

9 is a conceptual diagram illustrating a time required for an initial access procedure in a non-terrestrial network.

Referring to FIG. 9 , the time required for the initial access procedure may be as follows.

(1) RTT/2 (12.89 ms) + beam sweeping operation for 200 beams (13 ms) = 25.89 ms

(2) RTT/2 (12.89 ms) + 20Х100 beams (2000 ms) = 2012.89 ms

In (2), the UE may simultaneously apply receive beams (eg, four receive beams). In this case, the time of (2) may be "RTT/2 (12.89 ms) + 20Х100/4 beams (500 ms) = 512.89 ms".

Alternatively, the access procedure between the terminal and the satellite may be performed as follows. The terminal may use an array antenna, and a sub-array may be configured for direction detection. A satellite may transmit SSB using one beam in coverage (eg, sector). In this case, the terminal may estimate the beam direction of the satellite by performing a direction finding algorithm on the SSB or the reference signal. The terminal may convert the estimated beam direction into a direction based on Earth surface coordinates, and inform the satellite of the converted direction information through a physical random access channel (PRACH), and an access procedure according to the PRACH can be performed. The terminal connected to the satellite may form four reception beams according to a preset time interval, and may track the beam direction of the satellite to minimize a reception power difference between the reception beams. According to the above-described operation, the time required for the initial access procedure may be "12.89 ms, which is half of the round trip time (RTT) + time to perform the direction finding algorithm + a".

The terminal can access the Internet in a very easy way and can always point to the satellite. To support this operation, the terminal may track a moving satellite using a satellite array antenna. In order for the mobile terminal to easily track the satellite, the sensor(s) may be mounted on the terminal to predict the direction of the terminal.

10 is a conceptual diagram illustrating a first embodiment of a beam shape of a terminal in a non-terrestrial network.

Referring to FIG. 10 , a satellite tracking operation may be performed through various direction detection sensor(s) mounted in the terminal. The direction of the terminal may be predicted through a magnetic north sensor and/or a tilt sensor mounted in the terminal. A micro electro mechanical systems (MEMS) sensor capable of miniaturization (eg, a gyroscope, an accelerometer, a magnetometer) may be used, and an algorithm for increasing accuracy may be applied.

11 is a conceptual diagram illustrating a first embodiment of a terminal in a non-terrestrial network.

Referring to FIG. 11 , the terminal may maintain stability to track constantly moving and changing satellites (eg, cluster satellites). The terminal may have high reliability. In order to lower the cost of the terminals, millions of terminals can be mass-produced. The terminal may include a satellite antenna, a phone for driving an application, and a battery. The terminal may have a foldable shape and may be a portable terminal.

Meanwhile, the terminal may be directly connected to the satellite. The UE may not support the GNSS function. Also, the terminal may not be mounted on a fast moving object. The terminal may generate a beam having a wide width for reception of a reference signal transmitted from a satellite and/or transmission of a paging signal. The reference signal of the satellite may include information (eg, satellite power) necessary for the terminal to estimate the position of the corresponding satellite. For example, the reference signal may include an ID of a satellite, location information, time information, and/or movement trajectory information.

12 is a flowchart illustrating a first embodiment of a communication method between a terminal and a satellite in a non-terrestrial network.

Referring to FIG. 12 , a satellite (eg, a base station) may transmit a reference signal (eg, a downlink signal) (S1210). The reference signal may be transmitted through terminal coverage. For example, a satellite may transmit a reference signal for full terminal coverage using one or more beams. The reference signal may be transmitted using a TDM method or a frequency division multiplexing (FDM) method according to the number of satellites and/or the number of beams. Since the antenna of the terminal has a high gain, the beam width of the antenna of the terminal may be narrow. Accordingly, the terminal can find a satellite transmitting a reference signal using a beam having a narrow width. The UE may identify 3 to 6 satellites in a region of -40 degrees to +40 degrees. "When the terminal's antenna diameter is 20 cm and the terminal's antenna beam width is about 8 degrees", the terminal may receive reference signals from 3 to 6 satellites by performing 10Х10 beam scan operations. The beam scan operation may be performed using each of the beams of the terminal. When the execution time of one beam scan operation is 10 ms, the terminal may receive about 4 satellite signals (eg, a reference signal) in 1 second. The terminal may select one reference signal (eg, a reference signal having the greatest reception strength) that satisfies a preset criterion from among the received reference signals, and may identify a satellite that has transmitted the selected reference signal. The preset criterion may be a received signal strength, a received signal quality, and the like. The terminal may determine the satellite power (eg, the direction, elevation, and/or azimuth of the satellite from the viewpoint of the coordinates of the terminal) based on the selected reference signal. That is, the terminal may identify the satellite based on the received reference signal.

Meanwhile, the terminal may perform a satellite tracking operation to receive a signal (eg, a reference signal) from a satellite. The satellite tracking operation may be performed as follows.

13 is a conceptual diagram illustrating a first embodiment of a satellite tracking method in a non-terrestrial network.

Referring to FIG. 13 , the satellite may provide a communication service in user coverage, and the user coverage may be changed according to the movement of the satellite. The terminal may identify a satellite by performing a satellite tracking operation (eg, a beam scan operation) using an individual beam, and may receive a signal (eg, a reference signal, control information, data) from the identified satellite. have.

Referring back to FIG. 12 , the terminal may transmit a paging signal to a satellite identified on the basis of the reference signal ( S1220 ). The terminal may calculate the trajectory, velocity, and/or direction of the satellite (eg, the directed satellite) based on the reference signal. When 3 to 6 reference signals are received, the terminal may determine its own direction using the corresponding reference signals. The satellite may receive a call signal from the terminal. The satellite may receive a call signal of the terminal using a beam having a wide width (hereinafter, referred to as a “broad beam”) or a beam having a narrow width (hereinafter referred to as a “narrow beam”). A narrow beam can have a high gain. When the narrow beam is used by the satellite, the terminal may inform the satellite of the directing direction of the narrow beam. For example, the terminal may determine the orientation direction between the terminal and the satellite based on the reference signal, and may transmit a call signal including information on the orientation direction. This operation may be supported when the terminal knows the relative angle between itself and each satellite.

In order to receive the call signal of the terminal, the antenna for the wide beam may be mounted on the satellite. The satellite may receive the call signal of the terminal by using a high-gain antenna when the orientation angle to the terminal is known. When the call signal of the terminal is received, the satellite may transmit an acknowledgment signal for the call signal to the corresponding terminal. Alternatively, the operation of transmitting the acknowledgment signal may be omitted. The processing operation for the call signal may be performed by a satellite and a gateway connected to the satellite.

Since the satellite knows the direction of the terminal, it can transmit data to the terminal using a high-gain antenna (S1230). In the data transmission procedure, since the satellite knows its movement trajectory, it may perform an operation of changing an antenna direction (eg, a beam direction) or a beam selection operation. The terminal may receive data from the satellite and may transmit a response signal (eg, acknowledgment (ACK)) to the data to the satellite (S1240). The terminal may continuously receive data from the corresponding satellite by directing the antenna to the satellite.

When the communication between the terminal and the satellite is performed for more than a preset time (eg, 2 to 5 minutes), the handover operation between the satellites is required because the terminal is out of the user coverage of the satellite. In this case, the terminal may perform again from step S1220 using information of another satellite already known. That is, the terminal may transmit a call signal to another satellite without performing a separate beam scan operation. A call signal for another satellite may be transmitted based on a result of an already performed beam scan operation.

The methods according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the computer-readable medium may be specially designed and configured for the present invention, or may be known and available to those skilled in the art of computer software.

Examples of computer-readable media include hardware devices specially configured to store and carry out program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine language codes such as those generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as at least one software module to perform the operations of the present invention, and vice versa.

Although it has been described with reference to the above embodiments, it will be understood by those skilled in the art that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention as set forth in the following claims. will be able

Claims (1)

A method of operating a terminal in a non-terrestrial network, comprising:
performing a beam scan operation to receive reference signals of satellites;
selecting one reference signal that satisfies a preset criterion from among the reference signals received by the beam scan operation;
identifying a first satellite that has transmitted the one reference signal from among the satellites;
transmitting a paging signal to the first satellite; and
A method of operating a terminal comprising the step of receiving data from the first satellite.

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