Method and device for hybrid automatic repeat request feedback transmission considering handover in non-terrestrial network

Abstract

A method performed by a terminal comprises the steps of: transmitting, to a first base station, first UL data having a first RV corresponding to a first transmission in a HARQ procedure for UL data; receiving first HARQ feedback information about the first UL data from the first base station; when the first HARQ feedback information includes a NACK, transmitting, to the first base station, at least one piece of second UL data having at least one second RV in the HARQ procedure for the UL; performing an HO procedure of an LEO satellite on the basis of location information about the terminal and movement information about the base station; and transmitting, to the second base station, at least one piece of third UL data having at least one remaining RV in the HARQ procedure for UL.

Description

Hybrid automatic repetitive request feedback transmission method and device considering handover in non-terrestrial networks

[0001] The present disclosure relates to a hybrid automatic repeat request (HARQ) transmission technology in a communication system, and more specifically, to a HARQ transmission technology that considers handover in a non-terrestrial network based on a regenerative payload.

[0002] To handle the rapidly increasing volume of wireless data, communication networks (e.g., new radio (NR) communication networks) that use frequency bands higher than the frequency bands of LTE (long term evolution) (or LTE-A) (e.g., frequency bands below 6 GHz) (e.g., frequency bands below 6 GHz) are being considered. NR communication networks can support frequency bands above 6 GHz as well as frequency bands below 6 GHz, and can support a wider variety of communication services and scenarios compared to LTE communication networks. For example, usage scenarios for NR communication networks may include eMBB (enhanced Mobile BroadBand), URLLC (Ultra Reliable Low Latency Communication), mMTC (massive Machine Type Communication), etc.

[0003] NR communication networks can provide communication services to terminals located on the ground (terrestrial). Recently, there has been an increasing demand for communication services for aircraft, drones, satellites, etc., located not only on the ground but also in non-terrestrial areas, and to meet this demand, technologies for non-terrestrial networks (NTNs) are being discussed. Non-terrestrial networks can 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 between a communication node located in a non-terrestrial area (e.g., an aircraft, a drone, etc.) can be performed based on NR technology. In a non-terrestrial network, a satellite can perform the function of a base station in an NR communication network.

[0004] Satellite orbits around the Earth can be classified into geostationary, medium, and low orbits. Geostationary satellites move at the same speed as the Earth's rotation at an altitude of 36,000 km, appearing to be "stationary" from Earth's perspective. Medium orbit satellites operate at altitudes between 2,000 and less than 36,000 km. While geostationary satellites complete one orbit around the Earth in 24 hours, low orbit satellites complete one orbit in just 1 hour and 30 minutes. If all base station functions are mounted on a low orbit satellite, frequent handovers may occur because the satellite moves at very high speeds. Therefore, technology may be required to prevent a decrease in data transmission rates and data delays.

[0005] The objective of the present disclosure to solve the above-mentioned problems is to provide a hybrid automatic repetitive request transmission method and apparatus that considers handover in a non-terrestrial network.

[0006] A method of a terminal according to embodiments of the present disclosure for achieving the above objective comprises: transmitting to a first base station first UL data having a first redundancy version (RV) corresponding to the first transmission in a hybrid automatic repeat request (HARQ) procedure for uplink (UL) data; receiving first HARQ feedback information for the first UL data from the first base station; if the first HARQ feedback information includes a negative acknowledgment (NACK), transmitting to the first base station at least one second UL data having at least one second RV in the HARQ procedure for the UL; and performing a handover (HO) procedure for an LEO satellite based on location information of the terminal and movement information of the base station, wherein the movement information of the base station includes movement information of the first base station and movement information of the second base station. and may include the step of transmitting at least one third UL data having at least one residual RV in the HARQ procedure for the above UL to the second base station.

[0007] The first base station is a low earth orbit (LEO) satellite to which the terminal is connected, the second base station is a handover (HO) candidate LEO satellite, and the first base station and the second base station can be connected via an inter-satellite link (ISL).

[0008] Prior to the HO procedure above, the method may further include the step of receiving at least one second HARQ feedback information from the first base station, which includes a NACK for at least one second UL data.

[0009] At least one of the received RV information or HARQ information is transmitted from the first base station to the second base station via ISL, the received RV information includes the first RV and the at least one second RV, and the HARQ information may include information related to the HARQ procedure for the UL data.

[0010] A method of a second base station according to embodiments of the present disclosure for achieving the above objective may include: receiving received RV information and HARQ information related to the HARQ procedure, wherein the received data includes at least one data having at least one redundancy version (RV) received based on a hybrid automatic repeat request (HARQ) procedure for uplink (UL) data transmitted by a terminal to the first base station; performing a handover (HO) procedure for the terminal communicating with the first base station from the first base station; and receiving at least one UL data including at least one residual RV in the HARQ procedure for the UL data from the terminal.

[0011] The first base station is a low earth orbit (LEO) satellite to which the terminal is connected, the second base station is a handover (HO) candidate LEO satellite, and the first base station and the second base station can be connected via an inter-satellite link (ISL).

[0012] The method may further include the step of transmitting a first HARQ feedback information to the terminal, which includes an acknowledgment (ACK) or a negative acknowledgment (NACK) for at least one UL data based on the received RV information and the HARQ information.

[0013] The above received RV information and the above HARQ information are received from the first base station through ISL, and at least one UL data having at least one RV included in the RV information can be transmitted from the terminal to the first base station.

[0014] At least one HARQ feedback information for at least one UL data having at least one RV included in the received RV information is transmitted by the first base station to the terminal, and the at least one HARQ feedback information may include a NACK.

[0015] A terminal according to embodiments of the present disclosure for achieving the above objective comprises at least one processor, wherein the at least one processor comprises: transmitting to a first base station first UL data having a redundancy version (RV) corresponding to a first transmission in a hybrid automatic repeat request (HARQ) procedure for uplink (UL) data; receiving first HARQ feedback information for the first UL data from the first base station; and, if the first HARQ feedback information includes a NACK, transmitting from the first base station at least one second UL data including at least one second RV in the HARQ procedure for the UL; and performing a handover (HO) procedure for an LEO satellite based on location information of the terminal and movement information of the base station, wherein the movement information of the base station includes movement information of the first base station and movement information of the second base station. And in the HARQ procedure for the above UL, it may cause at least one third UL data having at least one residual RV to be transmitted to the second base station.

[0016] The first base station is a low earth orbit (LEO) satellite to which the terminal is connected, the second base station is a handover (HO) candidate LEO satellite, and the first base station and the second base station can be connected via an inter-satellite link (ISL).

[0017] The above at least one processor may further cause the terminal to receive at least one second HARQ feedback information, including a NACK for the at least one second UL data, from the first base station before the HO procedure is performed.

[0018] At least one of the received RV information or HARQ information is transmitted from the first base station to the second base station via ISL, the received RV information includes the first RV and the at least one second RV, and the HARQ information may include information related to the HARQ procedure for the UL data.

[0019] According to the present disclosure, HARQ feedback can be efficiently transmitted in a non-ground network based on a low-orbit satellite, and the long HARQ process caused by long propagation delay can be effectively performed. Accordingly, the waste of communication resources and unnecessary transmissions can be reduced, and problems such as reduced data transmission rates and data delays can be minimized.

[0020] FIG. 1 is a conceptual diagram illustrating a first embodiment of a non-ground network.

[0021] FIG. 2 is a conceptual diagram illustrating a second embodiment of a non-ground network.

[0022] FIG. 3 is a block diagram illustrating a first embodiment of an entity constituting a non-ground network.

[0023] FIG. 4 is a conceptual diagram illustrating the reach range of a ground terminal signal according to embodiments of the present disclosure.

[0024] FIG. 5 is a conceptual diagram illustrating the configuration of redundancy versions for a hybrid automatic recurrence request according to embodiments of the present disclosure.

[0025] FIG. 6 is a conceptual diagram illustrating, over time, a hybrid automatic iterative request process for the movement of an LEO satellite and uplink transmission of a ground terminal according to embodiments of the present disclosure.

[0026] FIG. 7 is a conceptual diagram illustrating the distance to a ground terminal due to the movement of LEO satellites according to embodiments of the present disclosure.

[0027] FIG. 8 is a flowchart illustrated to explain a first method for efficiently managing a handover process according to embodiments of the present disclosure.

[0028] FIG. 9 is a flowchart illustrated to explain a second method for efficiently managing a handover process according to embodiments of the present disclosure.

[0029] FIG. 10 is a conceptual diagram illustrating a HARQ process using the transmission of residual redundancy versions between low-orbit satellites according to embodiments of the present disclosure.

[0030] FIG. 11 is a conceptual diagram illustrating a HARQ procedure using the transmission of residual redundancy version information and HARQ information related to a hybrid automatic request procedure between low-orbit satellites for downlink data according to embodiments of the present disclosure.

[0031] FIG. 12 is a conceptual diagram illustrating a HARQ procedure using the transmission of HARQ information related to a hybrid automatic request procedure and reception redundancy version information between low-orbit satellites for uplink data according to embodiments of the present disclosure.

[0032] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the invention to specific embodiments, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0033] Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component. The term "and / or" includes a combination of a plurality of related described items or any of a plurality of related described items.

[0034] When it is stated that one component is "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to that other component, there may also be other components in between. On the other hand, when it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0035] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0036] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0037] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the attached drawings. In order to facilitate an overall understanding of the present invention, the same reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted.

[0038] A communication network to which embodiments according to the present invention are applied will be described. The communication system may include a non-terrestrial network (NTN), a 4G communication network (e.g., a long-term evolution (LTE) communication network), and / or a 5G communication network (e.g., a new radio (NR) communication network). The 4G communication network and the 5G communication network may be classified as terrestrial networks.

[0039] Non-terrestrial networks may operate based on LTE technology and / or NR technology. Non-terrestrial networks may support communication in frequency bands above 6 GHz as well as in frequency bands below 6 GHz. 4G communication networks may support communication in frequency bands below 6 GHz. 5G communication networks may support communication in frequency bands above 6 GHz as well as in frequency bands below 6 GHz. The communication networks to which the embodiments according to the present invention are applied are not limited to those described below, and the embodiments according to the present invention may be applied to various communication networks (e.g., 4G communication networks and / or 5G communication networks). Here, the term "communication network" may be used interchangeably with "communication system."

[0040] FIG. 1 is a conceptual diagram illustrating a first embodiment of a non-ground network.

[0041] Referring to FIG. 1, the non-ground network may include a satellite (110), a communication node (120), a gateway (130), a data network (140), etc. The non-ground network illustrated in FIG. 1 may be a non-ground network based on a transparent payload. 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).

[0042] The communication node (120) may include a communication node located on the ground (e.g., UE (user equipment), terminal) and a communication node located off the ground (e.g., airplane, 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 refer to a user link. The satellite (110) may provide communication services to the communication node (120) using one or more beams. The shape of the receiving range (footprint) of the satellite (110) beam may be elliptical.

[0043] A communication node (120) can communicate with a satellite (110) (e.g., downlink communication, uplink communication) using LTE technology and / or NR technology. Communication between the satellite (110) and the communication node (120) can be performed using an NR-Uu interface. If dual connectivity (DC) is supported, the communication node (120) can be connected to the satellite (110) as well as other base stations (e.g., base stations supporting LTE and / or NR functions), and can perform DC operations based on technology defined in LTE and / or NR specifications.

[0044] 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 a 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), etc. Communication between the gateway (130) and the core network may be performed based on an NG-C / U interface.

[0045] 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 the core network may support NR technology. Communication between the gateway (130) and the base station may be performed based on an NR-Uu interface, and communication between the base station and the core network (e.g., AMF, UPF, SMF) may be performed based on an NG-C / U interface.

[0046] FIG. 2 is a conceptual diagram illustrating a second embodiment of a non-ground network.

[0047] Referring to FIG. 2, the non-ground network may include satellite #1 (211), satellite #2 (212), a communication node (220), a gateway (230), a data network (1240), etc. The non-ground network illustrated in FIG. 2 may be a regenerative payload-based non-ground network. For example, each of satellites #1-2 (211, 212) may perform a regenerative operation (e.g., demodulation, decoding, re-coding, re-modulation, and / or filtering) on ​​a payload received from other entities constituting the non-ground network (e.g., communication node (220), gateway (230)), and may transmit the regenerative payload.

[0048] Each of satellites #1-2 (211, 212) may be a LEO satellite, MEO satellite, GEO satellite, HEO satellite, or UAS platform. A UAS platform may include a HAPS. Satellite #1 (211) may be connected to satellite #2 (212), and an inter-satellite link (ISL) may be established between satellite #1 (211) and satellite #2 (212). The ISL may operate in a radio frequency (RF) band or an optical band. The ISL may be established optionally. Communication nodes (220) may include communication nodes located on the ground (e.g., UE, terminal) and communication nodes located off the ground (e.g., airplane, drone). A service link (e.g., wireless link) may be established between satellite #1 (211) and the communication node (220). A service link may mean a user link. Satellite #1 (211) can provide communication services to a communication node (220) using one or more beams.

[0049] The communication node (220) can communicate with satellite #1 (211) (e.g., downlink communication, uplink communication) using LTE technology and / or NR technology. Communication between satellite #1 (211) and the communication node (220) can be performed using an NR-Uu interface. If DC is supported, the communication node (220) can be connected to satellite #1 (211) as well as other base stations (e.g., base stations supporting LTE and / or NR functions) and can perform DC operations based on technology defined in the LTE and / or NR specifications.

[0050] The gateway (230) may be located on the ground, and a feeder link may be established between satellite #1 (211) and the gateway (230), and a feeder link may be established between satellite #2 (212) and the gateway (230). The feeder link may be a wireless link. If an ISL is not established between satellite #1 (211) and satellite #2 (212), a feeder link between satellite #1 (211) and the gateway (230) may be established mandatorily.

[0051] Communication between each of satellites #1-2 (211, 2122) and the gateway (230) can be performed based on an NR-Uu interface or SRI. The gateway (230) can be connected to a data network (240). A "core network" may exist between the gateway (230) and the data network (240). In this case, the gateway (230) can be connected to the core network, and the core network can be connected to the data network (240). The core network may support NR technology. For example, the core network may include an access and mobility function (AMF), a user plane function (UPF), a session management function (SMF), etc. Communication between the gateway (230) and the core network can be performed based on an NG-C / U interface.

[0052] 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 the core network may support NR technology. Communication between the gateway (230) and the base station may be performed based on an NR-Uu interface, and communication between the base station and the core network (e.g., AMF, UPF, SMF) may be performed based on an NG-C / U interface.

[0053] Meanwhile, entities constituting the non-terrestrial network shown in FIGS. 1 and 2 (e.g., satellite, communication node, gateway, etc.) can be configured as follows.

[0054] FIG. 3 is a block diagram illustrating a first embodiment of an entity constituting a non-ground network.

[0055] Referring to FIG. 3, the communication node (300) may include at least one processor (310), a memory (320), and a transceiver (330) that is connected to a network to perform communication. Additionally, the communication node (300) may further include an input interface device (340), an output interface device (350), a storage device (360), etc. Each component included in the communication node (300) may be connected by a bus (370) to communicate with one another.

[0056] However, each component included in the communication node (300) may be connected via individual interfaces or individual buses centered around the processor (310), rather than via a common bus (370). For example, the processor (310) may be connected via a dedicated interface to at least one of the memory (320), the transmission / reception device (330), the input interface device (340), the output interface device (350), and the storage device (360).

[0057] The processor (310) can 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 composed of at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory (320) may be composed of at least one of read-only memory (ROM) and random access memory (RAM).

[0058] Meanwhile, NTN reference scenarios can be defined as shown in Table 1 below.

[0059] NTN shown in Fig. 1, NTNGEO shown in Fig. 2, Scenario A, BLEO (Adjustable Beam) Scenario C1, Scenario D1, LEO (Beam Moving with Satellite) Scenario C2, Scenario D2

[0060] In the non-ground network shown in FIG. 1, if the satellite (110) is a GEO satellite (e.g., a GEO satellite that supports transparent functions), this may be referred to as “Scenario A”. In the non-ground network shown in FIG. 2, if satellite #1-2 (211, 212) is a GEO satellite (e.g., a GEO that supports regenerative functions), this may be referred to as “Scenario B”.

[0061] In the non-ground network illustrated in FIG. 1, if the satellite (110) is a LEO satellite having steerable beams, this may be referred to as "Scenario C1". In the non-ground network illustrated in FIG. 1, if the satellite (110) is a LEO satellite having beams that move with the satellite, this may be referred to as "Scenario C2". In the non-ground network illustrated in FIG. 2, if satellite #1-2 (211, 212) is a LEO satellite having steerable beams, this may be referred to as "Scenario D1". In the non-ground network illustrated in FIG. 2, if satellite #1-2 (211, 212) is a LEO satellite having beams that move with the satellite, this may be referred to as "Scenario D2".

[0062] The parameters for the NTN reference scenarios defined in Table 1 can be defined as shown in Table 2 below.

[0063] Scenarios A and B Scenarios C and D Elevation 35,786 km 600 km 1,200 km Spectrum (Service Link) < 6 GHz (e.g., 2 GHz) > 6 GHz (e.g., DL 20 GHz, UL 30 GHz) Maximum Channel Bandwidth Capacity (Service Link) 30 MHz for band < 6 GHz 1 GHz for band > 6 GHz Maximum Distance between Satellite and Communication Node (e.g., UE) at Minimum Elevation Angle 40,581 km 1,932 km (600 km Altitude) 3,131 km (1,200 km Altitude) Maximum RTD (Round Trip Delay) (Propagation Delay Only) Scenario A: 541.46 ms (Service and Feeder Links) Scenario B: 270.73 ms (Service Link Only) Scenario C: (Transparent Payload: Service and Feeder Links) - 25.77 ms (600 km Altitude) - 41.77ms (1200km altitude) Scenario D: (Regeneration Payload: Service Link Only) - 12.89ms (600km altitude) - 20.89ms (1200km altitude) Max differential delay within a single cell 10.3ms 3.12ms (600km altitude) 3.18ms (1200km altitude) Service Link NR feeder link defined by 3GPP 3GPP or non-3GPP defined radio interface

[0064] In addition, in the NTN reference scenarios defined in Table 1, the delay constraint can be defined as shown in Table 3 below.

[0065] Scenario A Scenario B Scenario C1-2 Scenario D1-2 Satellite Altitude 35,786 km 600 km Maximum RTD at radio interface between base station and UE 541.75 ms (Worst case) 270.57 ms 28.41 ms 12.88 ms Minimum RTD at radio interface between base station and UE 477.14 ms 238.57 ms 8 ms 4 ms

[0066] Next, communication methods between a terminal and an LEO satellite in a communication system will be described. Even when a method performed at a first communication node among the communication nodes (e.g., transmission or reception of a signal) is described, 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 the operation of a terminal is described, the corresponding base station may perform an operation corresponding to the operation of the terminal. Conversely, when the operation of a base station is described, the corresponding terminal may perform an operation corresponding to the operation of the base station.

[0067] In a non-ground network, a satellite constellation can provide communication services. A satellite constellation may be referred to as a satellite constellation. A satellite constellation may consist of multiple small satellites (e.g., small LEO satellites). Small satellites may refer to Cube satellites or CubeSats. A non-ground network may include satellites (110, 211, 212), communication nodes (120, 220), gateways (130, 230), and / or ground control units. Gateways may be used for control, network operation, and / or backhauling. Ground control units may be used for telemetry, tracking, and / or command transmission of the satellites. Ground control units may be included in the gateway. Alternatively, ground control units may exist separately from the gateway.

[0068] The link through which the gateway transmits signals to a terminal (e.g., a communication node) via the satellite may be a forward link (e.g., a downlink). The link through which the terminal transmits signals to the gateway via the satellite may be a reverse link (e.g., an uplink). The satellite can enable "connections between users" and / or "connections between users and the gateway" by extending the terrestrial network. The satellite can provide optimal performance by using multi-beam antennas and digital relay. The gateway can manage the network's access and backhaul. If an ISL is not established between the satellites, multiple gateways may be required to cover a global area. The gateway can be connected to a 5G terrestrial network.

[0069] The ground control unit can perform monitoring, testing, and / or configuration update operations regarding the status of the satellite's subsystems. The aforementioned control operations may be necessary for satellite maintenance and / or orbit maintenance. The terminal can connect with the satellite and track LEO satellites. The terminal can efficiently utilize frequency resources by using a phased array antenna with high-gain characteristics and / or digital processing technology.

[0070] The satellite may support phased array antenna technology that directly radiates N multibeams over a service area and / or software-defined digital repeater technology that complements the transmission specifications of the satellite constellation. Here, N may be a natural number. The aforementioned technology may imply a high level of flexibility. The satellite can support surging demand without increasing the scale of the satellite constellation. The satellite may support full beam hopping capabilities on both forward links and / or return links (e.g., reverse links). The satellite may provide independent links to terminals and support the operation of gateway links on the ground using different capacities. To support the aforementioned operations, a multibeam satellite array scheme may be used in which each of the multibeams can be steered independently in multiple directions.

[0071] Multibeam antennas and digital processors can flexibly change coverage, power, and allocated frequencies to provide a high level of resource allocation flexibility in time and / or space. High-frequency reuse methods can be utilized. When ultra-high-capacity processing technology is used, high bit rates can be provided, and implementation can be achieved at a low cost.

[0072] In communication systems (e.g., NR communication systems), a hybrid automatic repeat request (HARQ) method may be used to improve data reliability. In the HARQ method, the transmitter can transmit data processed using channel coding or forward error correction (FEC). The receiver can perform decoding of the data and then transmit the decoding result to the transmitter using an ACK / NACK signal. If the transmitter receives a NACK signal from the receiver indicating a decoding failure, the transmitter can retransmit the data. The receiver can perform decoding by combining the retransmitted data with the previously received data.

[0073] HARQ methods can be classified into chase combining (CC) methods and incremental redundancy (IR) methods. In the chase combining method, the transmitter can retransmit all or part of a previously transmitted signal. The receiver can perform decoding by combining the signals received over multiple transmissions. In the incremental redundancy method, the transmitter can transmit additional redundancy information each time it retransmits, combined with the channel encoding scheme. The receiver can perform decoding by combining the previously received information with the redundancy information.

[0074] Although HARQ is not efficient in terms of data transmission rates, it is an essential technology for reliable data transmission even in poor channel conditions. HARQ is being adopted in various wireless communication systems. In NTN, which extends 5G NR technology or subsequent technologies to satellite communication environments, HARQ is also a necessary technology when considering the low signal-to-noise ratio (SNR).

[0075] In the case of NTN, there can be significant propagation delay between LEO satellites located hundreds of kilometers above and ground terminals, and the final transmission of HARQ may take a long time. In other words, there may be a disadvantage in that it takes a long time for the transmission of all redundancy versions (RVs) to be completed. However, considering the robustness of data transmission, HARQ technology cannot be excluded.

[0076] When all base station functions are mounted on an LEO satellite, frequent handovers (HO) may occur because the LEO moves at a very high speed. Depending on the location of the ground terminal and the LEO satellite, situations may frequently arise where an HO must occur before the entire HARQ process is completed. Such frequent abnormal HARQ behavior can occur because the time required for the entire HARQ process increases due to frequent HOs and significant propagation delays in the NTN. In a terrestrial network, such frequent abnormal HARQ behavior may not occur.

[0077] In the case of regenerative payload-based NTNs that equip LEO satellites with base station functions, long propagation delays may occur. It may take a long time to receive HACK feedback (e.g., ACK or NACK) for a transmitted signal. If the maximum number of HARQ transmissions is large, transmission delays may be prolonged, and HO may occur during this time. As a result, a situation may arise where the LEO satellite serving as the base station changes.

[0078] In the present disclosure, a method for applying HARQ in consideration of frequent HOs caused by the rapid movement speed of an LEO satellite in a regenerated payload-based NTN where the base station (e.g., gNB) function is mounted on an LEO satellite (hereinafter referred to as the "HARQ method considering HOs") will be described. A ground terminal may be located at the coverage boundary of two LEO satellites. A long time may be required until all HARQ processes are completed, and the frequency of situations where an HO must occur in the middle may increase as shown in FIG. 4. All HARQ processes may include the process from retransmission and receiving HARQ feedback (e.g., ACK / NACK) until the final transmission is successful.

[0079] FIG. 4 is a conceptual diagram illustrating the reach range of a ground terminal signal according to embodiments of the present disclosure.

[0080] Referring to FIG. 4, the communication system (400) may include LEO satellite #0 (410), LEO satellite #1 (420), and a ground terminal (430). LEO satellite #0 (410) and LEO satellite #1 (420) may include a base station (e.g., gNB). At a first time point, LEO satellite #0 (410) may be located within the reach of the ground terminal signal, and LEO satellite #1 (420) may be located at the boundary of the reach of the ground terminal signal. Due to the movement of LEO satellite #0 (410) and LEO satellite #1 (420), at a second time point, LEO satellite #0 (410) may be located at the boundary of the reach of the ground terminal signal, and LEO satellite #1 (420) may be located within the reach of the ground terminal signal. At the first point in time, it can be assumed that the ground terminal (430) transmits uplink (UL) data to the second LEO satellite (420). The second point in time may be a point in time after the first point in time.

[0081] At the first time point, the ground terminal (430) may be connected to LEO satellite #0 (410) located within the reach of the ground terminal signal, and the ground terminal (430) may not be connected to LEO satellite #1 (420) located at the boundary of the reach of the ground terminal signal. The ground terminal (430) may transmit UL data to the connected LEO satellite #0 (410), and LEO satellite #0 (410) may receive UL data from the ground terminal (430). At the second time point, LEO satellite #0 (410) may be located at the boundary of the reach of the ground terminal signal due to movement.

[0082] When a ground terminal (430) transmits UL data to LEO satellite #0 (410), the ground terminal (430) can configure a redundancy version (RV) of the channel-encoded data for HARQ according to various puncturing patterns as shown in FIG. 5.

[0083] FIG. 5 is a conceptual diagram illustrating the configuration of redundancy versions for a hybrid automatic recurrence request according to embodiments of the present disclosure.

[0084] Referring to FIG. 5, a communication system (e.g., a 5G communication system) may support a HARQ IR method (500). In the communication system, if a receiver (e.g., LEO satellite #0 (410) in FIG. 4) fails to decode a specific packet after only one reception, the receiver may request a transmission (e.g., a ground terminal (430) in FIG. 4) to retransmit the specific packet. If the transmission uses low-density parity check (LDPC) encoding, the HARQ IR method may be applied to the specific packet, and the receiver may receive the retransmitted packet up to four times. In the HARQ IR method, after a circular buffer is created, some bits within the circular buffer may be transmitted by changing the starting point of the transmitted packet according to the RV for each transmission. The first transmission can correspond to RV0, the second transmission can correspond to RV2, the third transmission can correspond to RV3, and the fourth transmission can correspond to RV4.

[0085] In the HARQ IR method, the transmitter may first transmit RV0, which contains systematic bits and some redundancy bits. When the transmitter receives a NACK from the receiver, it may transmit RV2, which contains the redundancy bits, to the receiver. The receiver may perform decoding using RV0 and RV2. If the receiver performs decoding using RV0 and RV2, the decoding probability may be increased. If decoding continues to fail at the receiver after the transmission of RV2, the transmitter may sequentially transmit RV3 and RV1.

[0086] The HARQ process for LEO satellite movement and UL transmission can be represented over time as shown in Fig. 6.

[0087] FIG. 6 is a conceptual diagram illustrating, over time, a hybrid automatic iterative request process for the movement of an LEO satellite and uplink transmission of a ground terminal according to embodiments of the present disclosure.

[0088] Referring to FIG. 6, the communication system (600) may include an LEO satellite and a ground terminal. The LEO satellite may be LEO satellite #0 (410) or LEO satellite #1 (420) as shown in FIG. 4, and the ground terminal may be the ground terminal (430) as shown in FIG. 4. The LEO satellite may be located within the reach of the ground terminal signal between time t0 and time t4. After time t4, the LEO satellite may move out of the reach of the ground terminal signal, and the LEO satellite may not receive the RV of the HARQ (e.g., RV3) from the ground terminal. It may be assumed that the ground terminal has formed a circular buffer containing the RV(s) by performing channel encoding (e.g., LDPC encoding) for the UL data.

[0089] At time t1, a ground terminal can transmit data containing RV0 to an LEO satellite. The LEO satellite may fail to channel decode (e.g., LDPC decoding) the data containing RV0 received from the ground terminal. The LEO satellite may transmit HARQ feedback information to the ground terminal, including a NACK indicating a failure in channel decoding for the data containing RV0. The ground terminal may receive HARQ feedback information from the LEO satellite, including a NACK indicating a failure in channel decoding for the data containing RV0.

[0090] At time t2, the ground terminal can transmit data containing RV2 to the LEO satellite. The LEO satellite may fail to channel decode the data containing RV2 received from the ground terminal. The LEO satellite can transmit HARQ feedback information to the ground terminal, including a NACK indicating a failure in channel decoding of the data containing RV2. The ground terminal can receive HARQ feedback information from the LEO satellite, including a NACK indicating a failure in channel decoding of the data containing RV2. The LEO satellite can perform channel decoding of the data containing RV2 using the data containing RV0 received from the ground terminal at time t1 and the data containing RV2 received from the ground terminal at time t2.

[0091] At time t3, the ground terminal can transmit data containing RV3 to the LEO satellite. After time t4, the LEO satellite may move out of the reach of the ground terminal signal. The LEO satellite may not receive the data containing RV3 transmitted by the ground terminal. After time t4, the HARQ procedure between the LEO satellite and the ground terminal may no longer proceed.

[0092] In Fig. 6, the transmission of UL data with RV0 and the transmission of UL data with RV2 may be processes that waste communication resources. The ground terminal and the LEO satellite may determine that the HARQ procedure is abnormal after a certain period of time. There may be a problem in that the ground terminal and the LEO satellite have to wait until the HARQ procedure is completed.

[0093] In this disclosure, a method for efficiently managing HARQ procedures in consideration of handover (HO) will be described. In this case, it may be assumed that the orbit information of LEO satellites is known in advance to the ground terminal or that the LEO satellites broadcast orbit information to the ground terminal. It may be assumed that the ground terminal periodically transmits its own location information.

[0094] A ground terminal may have information on LEO satellites to connect to at a specific point in time and HO candidate LEO satellites that will pass over the ground terminal after a certain period of time. Specifically, the ground terminal can determine whether the LEO satellite currently connected will move out of the ground terminal's communication range after a certain amount of time and whether it can perform the HO process to connect to a new LEO satellite. The location information of the LEO satellites and the location information of the ground terminal can be used in the HO process.

[0095] If the location information of the ground terminal and the orbit information of the LEO satellites are known in advance, the ground terminal can obtain the location information of the LEO satellite currently connected based on the location information of the ground terminal. The ground terminal can obtain the location information of the HO candidate LEO satellite that will pass over the ground terminal as shown in Fig. 7.

[0096] FIG. 7 is a conceptual diagram illustrating the distance to a ground terminal due to the movement of LEO satellites according to embodiments of the present disclosure.

[0097] Referring to FIG. 7, the communication system (700) may include LEO satellite #0, LEO satellite #1, and a ground terminal. LEO satellite #0 may be LEO satellite #0 (410) as illustrated in FIG. 4, and LEO satellite #1 may be LEO satellite #1 (420) as illustrated in FIG. 4. The ground terminal may be the ground terminal (430) as illustrated in FIG. 4. LEO satellite #0 may be located within the reach of the ground terminal signal at time t and may be the LEO satellite that the ground terminal is connected to. LEO satellite #1 may be located outside the reach of the ground terminal signal at time t and may be the HO candidate LEO satellite of the ground terminal. After time t, it can be assumed that LEO satellite #0 moves away from the ground terminal and LEO satellite #1 moves closer to the ground terminal. At time t+T, LEO satellite #0 may be out of the reach of the ground terminal signal, and LEO satellite #1 may be within the reach of the ground terminal signal. At time t, the distance between LEO satellite #0 and the ground terminal can be expressed by the function D0(t). The distance between LEO satellite #1 and the ground terminal can be expressed by the function D1(t). At time t+T, the distance between LEO satellite #0 and the ground terminal can be expressed by the function D0(t+T). The distance between LEO satellite #1 and the ground terminal can be expressed by the function D1(t+T). T can be a natural number greater than or equal to 1.

[0098] At time t, LEO satellite #0 may be the LEO satellite connected to by the ground terminal and may be located within the reach of the ground terminal signal. The distance between LEO satellite #0 and the ground terminal can be represented as D0(t). LEO satellite #1 may be an HO candidate LEO satellite and may be located outside the reach of the ground terminal signal. The distance between LEO satellite #1 and the ground terminal can be represented as D1(t).

[0099] At time t+T, LEO satellite #0 may be located outside the range of the ground terminal signal. The connection between LEO satellite #0 and the ground terminal may be disconnected (or unconnected). LEO satellite #1 may be located within the range of the ground terminal signal. The connection between LEO satellite #1 and the ground terminal may be connected.

[0100] In the first method (hereinafter, the first HARQ transmission method) for efficiently managing a HARQ process by considering HO in the present disclosure, data transmission using HARQ may be performed at time t. In the first HARQ transmission method, data transmission using HARQ may be allowed only when the maximum time of the HARQ process is less than the remaining connection time T. In other words, if the maximum time of the HARQ process is greater than the remaining connection time T, HARQ may be deactivated.

[0101] FIG. 8 is a flowchart illustrated to explain a first method for efficiently managing a handover process according to embodiments of the present disclosure.

[0102] Referring to FIG. 8, the communication system may include LEO satellite #0, LEO satellite #1, and a ground terminal. LEO satellite #0, LEO satellite #1, and the ground terminal may be the LEO satellite #0, LEO satellite #1, and the ground terminal illustrated in FIG. 7. LEO satellite #0, LEO satellite #1, and the ground terminal may be configured identically or similarly to the communication node illustrated in FIG. 3. The ground terminal may acquire LEO satellite distance information including the distance between LEO satellite #0 and LEO satellite #1 and the ground terminal, respectively. The ground terminal may acquire LEO satellite received signal strength information by performing a measurement operation for each of the plurality of LEO satellites. The ground terminal may estimate the HO time based on the LEO satellite distance information and the LEO satellite received signal strength information. The ground terminal may determine whether to disable HARQ for UL data based on the estimated HO time. If the ground terminal determines that HARQ for UL data is to be disabled, the ground terminal may disable HARQ transmission for UL data. At time t, LEO satellite #0 can be assumed to be the LEO satellite connected to the ground terminal, and LEO satellite #1 can be assumed to be the HO candidate LEO satellite. In explaining Fig. 8, content that overlaps with that explained with reference to Figs. 1 through 7 may be omitted.

[0103] In step S810, the ground terminal can obtain LEO satellite distance information including the distance between LEO satellite #0 and LEO satellite #1 and the ground terminal, respectively. The ground terminal can obtain LEO satellite received signal strength information by performing a measurement operation for LEO satellite #0 and LEO satellite #1, respectively.

[0104] LEO satellite distance information may include the distance between the ground terminal and LEO satellite #0 and the distance between the ground terminal and LEO satellite #1. As previously mentioned, at time t, the distance between the ground terminal and LEO satellite #0 can be expressed as D0(t), and the distance between the ground terminal and LEO satellite #1 can be expressed as D1(t).

[0105] A ground terminal can acquire LEO satellite received signal strength information by performing a measurement operation on the reference signal (RS) of LEO satellite #0 and LEO satellite #1. The RS of LEO satellite #0 and LEO satellite #1 may include a synchronization signal (SS) for the downlink, a channel state information reference signal (CSI-RS), a demodulation reference signal (DM-RS), etc. The LEO satellite received signal strength information may include reference signal received power (RSRP), reference signal received quality (RSRQ), received signal strength indicator (RSSI), signal-to-noise ratio (SNR), etc.

[0106] In step S820, the ground terminal can estimate the HO time to LEO satellite #1 based on the LEO satellite distance information and LEO satellite received signal strength information obtained in step S810.

[0107] The ground terminal can perform an HO at the point when the distance between LEO satellite #0 and the ground terminal becomes smaller than the distance between LEO satellite #1 and the ground terminal. At this time, the received signal strength of LEO satellite #1 obtained by the ground terminal performing a measurement operation on LEO satellite #1 may be greater than a set received signal strength threshold. LEO satellite #1 may be a candidate LEO satellite as previously mentioned. At time t, the distance between LEO satellite #0 and the ground terminal can be represented by the function D0(t), and the distance between LEO satellite #0 and the ground terminal can be represented by the function D1(t).

[0108] In step S830, the ground terminal can determine whether to disable HARQ based on the HO time estimated in step S820. If the ground terminal determines that HARQ is to be disabled, the ground terminal can perform step S840 to disable HARQ. If the ground terminal determines that HARQ is not to be disabled, the ground terminal can perform step S850 to enable HARQ.

[0109] In step S840, the ground terminal can perform HARQ deactivation.

[0110] In step S850, the ground terminal can perform HARQ activation.

[0111] In one embodiment, if D1(t+T) = D0(t+T) is satisfied, the time value of T can be expressed as the remaining connection time.

[0112] When a ground terminal performs UL data transmission using HARQ at time t, the ground terminal can determine whether the maximum time of the HARQ process is greater than the remaining time (T). If the ground terminal determines that the maximum time of the HARQ process is greater than the remaining time (T), the ground terminal can disable HARQ. If the ground terminal determines that the maximum time of the HARQ process is less than the remaining time (T), the ground terminal can enable HARQ. The maximum time of the HARQ process may refer to the maximum number of times RVs are transmitted (e.g., 'max_HARQ_Tx') and the total time considering the reception of ACK / NACK after each RV transmission.

[0113] In the first HARQ transmission method described above, steps S810 through S850 have been described individually, but this is not intended to limit the order in which the steps are performed, and if necessary, each step may be performed simultaneously, in a different order, or combined.

[0114] The first HARQ transmission method can be easily applied when the sizes of the satellite cells or satellite beams are identical or similar. If the sizes of the satellite cells or satellite beams are different, in the first HARQ transmission method, an HO from LEO satellite #0 to LEO satellite #1 may not occur at the point when D0() becomes smaller than D1(). The first HARQ transmission method may have a problem in that data transmission using HARQ cannot be determined solely by the distance between the ground terminal and the LEO satellite. As mentioned above, D0() can represent the distance between LEO satellite #0 and the ground terminal. D1() can represent the distance between LEO satellite #1 and the ground terminal. At time t, LEO satellite #1 may be an LEO satellite located within the reach of the ground terminal signal and may be a terminal connected to the ground terminal. LEO satellite #0 may be an LEO satellite located outside the reach of the ground terminal signal and may be a candidate LEO satellite for HO of the ground terminal.

[0115] In order to solve the aforementioned problems, a second method for efficiently managing the HARQ process by considering HO in the present disclosure (hereinafter, the second HARQ transmission method) will be described.

[0116] FIG. 9 is a flowchart illustrated to explain a second method for efficiently managing a handover process according to embodiments of the present disclosure.

[0117] Referring to FIG. 9, a communication system (e.g., a 5G communication system) may include an LEO satellite and a ground terminal. The LEO satellite may be LEO satellite #0 as illustrated in FIG. 7. The ground terminal may be the ground terminal as illustrated in FIG. 7. The ground terminal may determine whether to disable HARQ based on additional information provided (or received) from the LEO satellite to determine whether to disable HARQ. As previously mentioned, it may be assumed that the orbit information of the LEO satellite is known to the ground terminal in advance or that the LEO satellite broadcasts orbit information to the ground terminal. It may be assumed that the ground terminal transmits its own location information to the LEO satellite.

[0118] In step S910, the LEO satellite may provide (or transmit) additional information to the ground terminal to determine whether to disable HARQ. The ground terminal may receive (or receive) additional information from the LEO satellite to determine whether to disable HARQ.

[0119] In the second HARQ transmission method, a base station (e.g., LEO satellite) may transmit additional information necessary to determine HARQ deactivation (hereinafter referred to as 'HARQ deactivation determination information') to a terminal (e.g., ground terminal) through at least one of physical layer signaling, MAC (medium access control) layer signaling, RRC (radio resource control) signaling, or SI (system information) signaling.

[0120] HARQ disable decision information may include at least one of cell boundary area information or cell boundary time information. The cell boundary area information may include serving cell boundary area information or target cell boundary area information. If the cell is defined in a circular shape, the cell boundary area information may include a reference position and a threshold value. The cell boundary area information may be provided in a polygonal or elliptical shape. If the cell is a moving cell, the cell boundary area information may further include epoch time information for the cell boundary area information. The cell boundary time information may include at least one of the service time of the serving cell or the service time of the target cell. The epoch time information may include an epoch time value.

[0121] If the signaling overhead associated with the transmission of HARQ disable judgment information is large, the HO boundary area / time information provided to perform handover in NTN may be used as is for the HARQ disable judgment.

[0122] For example, the reference location and threshold of the serving / target cell in the fixed beam provided through the SIB can be used as cell boundary area information.

[0123] As another example, cell boundary area information may include reference position, threshold, and epoch time information of the serving / target cell in the moving beam provided through the SIB.

[0124] As previously mentioned, the HARQ disable decision information may include at least one of cell boundary region information or cell boundary time information. For example, t-Service provided through SIB may be used as cell boundary time information.

[0125] In step S920, the ground terminal may determine whether to disable HARQ based on additional information provided (or received) in step S910 for determining whether to disable HARQ. If the ground terminal determines that HARQ is disabled based on the additional information for determining whether to disable HARQ, the ground terminal may perform step S930. If the ground terminal determines that HARQ is not disabled based on the additional information for determining whether to disable HARQ, the ground terminal may perform step S940.

[0126] In step S930, the ground terminal can perform HARQ deactivation.

[0127] In step S940, the ground terminal can perform HARQ activation.

[0128] In the second HARQ transmission method described above, steps S910 through S940 have been described individually, but this is not intended to limit the order in which the steps are performed, and if necessary, each step may be performed simultaneously, in a different order, or combined.

[0129] As described above, when cell boundary area information and / or cell boundary time information is provided (or transmitted) from the base station to the terminal, the terminal can determine the time from the current location to the cell boundary area as the remaining time T value. If the maximum time of the HARQ process is greater than the remaining time T, the HARQ process may be disabled. The base station may refer to a LEO satellite, and the terminal may refer to a ground terminal.

[0130] In describing FIGS. 7 through 9, the HARQ operation may be performed only on LEO Satellite #0 among LEO Satellite #0 and LEO Satellite #1. If the HARQ process for DL ​​data transmission occurs on LEO Satellite #0, it may be considered that LEO Satellite #1 takes over and performs the HARQ process for DL ​​data transmission from LEO Satellite #0. In an LEO-based NTN, as shown in FIG. 10, LEO satellites can be connected via an inter-satellite link (ISL) to transmit and receive signal(s).

[0131] FIG. 10 is a conceptual diagram illustrating a HARQ process using the transmission of residual redundancy versions between low-orbit satellites according to embodiments of the present disclosure.

[0132] Referring to FIG. 10, the communication system (1000) may include LEO satellite #0, LEO satellite #1, and a ground terminal. At time t, LEO satellite #0 may be the LEO satellite connected to the ground terminal, and LEO satellite #1 may be the HO candidate LEO satellite of the ground terminal. At time t+T, LEO satellite #0 may transmit (or send) residual information, received RV information, and / or HARQ-related information to LEO satellite #1 via ISL. Residual RV information may include RV(s) that LEO satellite #0 failed to transmit to the ground terminal during HARQ transmission for the downlink. Received RV information may include RV(s) that LEO satellite #0 received from the ground terminal during HARQ transmission for the uplink. After time t, LEO satellite #0 may move away from the ground terminal and LEO satellite #1 may move closer to the ground terminal. It can be assumed that LEO satellite #1 is close to the HO point at time t+T. In explaining Fig. 10, content that overlaps with what has been explained with reference to Figs. 1 through 9 may be omitted.

[0133] At time t, LEO satellite #0 may be located within the reach of the ground terminal signal, and the ground terminal may be LEO satellite #0. LEO satellite #1 may be located at the boundary of the reach of the ground terminal signal and may be a candidate LEO satellite for HO of the ground terminal.

[0134] At time t+T, LEO satellite #0 may be close to the HO point, and LEO satellite #1 may be located within the reach of the ground terminal signal. LEO satellite #0 may transmit residual RV information, received RV information, and / or HARQ-related information to LEO satellite #1 via ISL. Remaining RV information may include RV(s) that LEO satellite #0 failed to transmit to the ground terminal during HARQ transmission for the downlink. Received RV information may include RV(s) that LEO satellite #0 received from the ground terminal during HARQ transmission for the uplink.

[0135] The HARQ process for a downlink or uplink can be performed as shown in FIGS. 11 and FIGS. 12.

[0136] First, the HARQ process using the transmission of residual RV(s) and HARQ-related information between LEO satellites for the downlink will be explained.

[0137] FIG. 11 is a conceptual diagram illustrating a HARQ procedure using the transmission of residual redundancy version information and HARQ information related to a hybrid automatic request procedure between low-orbit satellites for downlink data according to embodiments of the present disclosure.

[0138] Referring to FIG. 11, a communication system (e.g., a 5G communication system) may include LEO satellite #0, LEO satellite #1, and a ground terminal. In a HARQ procedure for downlink (DL) data, data having a first RV (e.g., RV0 in FIG. 5) corresponding to the first transmission and data having a second RV (e.g., RV2 in FIG. 5) corresponding to the second transmission may be transmitted from LEO satellite #0 to the ground terminal. In a HARQ procedure for DL ​​data, data having a third RV (e.g., RV3 in FIG. 5) corresponding to the third transmission and data having a fourth RV (e.g., RV1) corresponding to the fourth transmission may be transmitted from LEO satellite #1 to the ground terminal. When LEO satellite #1 determines that it is approaching an HO point, LEO satellite #0 may transmit remaining RV information for the downlink and / or HARQ information related to the HARQ procedure to LEO satellite #1 via ISL. In FIG. 11, the residual RV information may include data having RVs (e.g., RV0 and RV3 in FIG. 5) that LEO satellite #0 failed to transmit to the ground terminal during the HARQ procedure for DL ​​data. Transmission of data having the first RV may correspond to initial transmission. Transmission of data having the second to fourth RVs may correspond to retransmission.

[0139] Referring to FIG. 11, LEO satellite #0, LEO satellite #1, and the ground terminal may be the LEO satellite #0, LEO satellite #1, and the ground terminal illustrated in FIG. 10. LEO satellite #0, LEO satellite #1, and the ground terminal may be configured identically or similarly to the communication node illustrated in FIG. 3. It may be assumed that LEO satellite #0 and LEO satellite #1 are connected via ISL to transmit and receive signal(s). In describing FIG. 11, details that overlap with those described with reference to FIG. 1 through FIG. 10 may be omitted.

[0140] In step S1110, LEO satellite #0 can transmit data having a first RV corresponding to the first transmission in the HARQ procedure for DL ​​data to a ground terminal. The ground terminal can receive data having a first RV corresponding to the first transmission in the HARQ procedure for DL ​​data from LEO satellite #0.

[0141] A ground terminal can perform channel decoding (e.g., LDPC decoding) on ​​data having a first RV received from LEO satellite #0 and determine whether the channel decoding of the data having the first RV is successful or unsuccessful. If the ground terminal determines that the channel decoding of the data having the first RV received from LEO satellite #0 has failed, the ground terminal may perform step S1120. The first RV may correspond to RV0 in FIG. 5, which includes systematic bits and some redundancy bits.

[0142] In step S1120, the ground terminal may transmit a NACK to LEO satellite #0 indicating that channel decoding for data having the first RV has failed in the HARQ procedure for DL ​​data. LEO satellite #0 may receive HAREQ feedback information from the ground terminal including a NACK indicating that channel decoding for data having the first RV has failed in the HARQ procedure for DL ​​data.

[0143] The transmission of data having the first RV may be the first transmission in the HARQ procedure for DL ​​data transmitted by LEO satellite #0 to the ground terminal in step S1110. The ground terminal may transmit HARQ feedback information to LEO satellite #0, including a NACK indicating that channel decoding for the data having the first RV received from LEO satellite #0 in step S1110 has failed. LEO satellite #0 may receive HARQ feedback information from the ground terminal, including a NACK indicating that channel decoding for the data having the first RV received in step S1110 has failed. LEO satellite #0 may perform step S1130 to transmit data having the second RV corresponding to the second transmission in the HARQ procedure for DL ​​to the ground terminal.

[0144] In step S1130, LEO satellite #0 can transmit data having a second RV corresponding to the second transmission in the HARQ procedure for DL ​​data to a ground terminal. The ground terminal can receive data having a second RV corresponding to the second transmission in the HARQ procedure for DL ​​data from LEO satellite #0.

[0145] The ground terminal can perform channel decoding on data having a second RV received from LEO satellite #0 and determine whether the channel coding of the data having the second RV is successful or unsuccessful. If the ground terminal determines that the channel decoding of the data having a second RV received from LEO satellite #0 has failed, the ground terminal can perform step S1140. The second RV may correspond to RV2 containing redundancy bits in FIG. 5.

[0146] In step S1140, the ground terminal may transmit HARQ feedback information to LEO satellite #0, including a NACK indicating that channel decoding for the second RV failed in the HARQ procedure for the DL data. LEO satellite #0 may receive HARQ feedback information from the ground terminal, including a NACK indicating that channel decoding for the data having the second RV failed.

[0147] The transmission of data having the second RV may be the second transmission in the HARQ procedure for the DL data transmitted by LEO satellite #0 to the ground terminal in step S1130. The ground terminal may transmit HARQ feedback information to LEO satellite #0, including a NACK indicating that channel decoding for the data having the second RV received from LEO satellite #0 in step S1130 has failed. LEO satellite #0 may receive HARQ feedback information from the ground terminal, including a NACK indicating that channel decoding for the data having the second RV received in step S1130 has failed.

[0148] LEO satellite #0 can determine whether the ground terminal is close to the time of the HO to LEO satellite #1. If LEO satellite #0 determines that the ground terminal is close to the time of the HO to LEO satellite #1, LEO satellite #0 can perform step S1150.

[0149] In step S1150, LEO satellite #0 may transmit residual RV information, including data having a third RV and data having a fourth RV corresponding to the residual RVs in the HARQ procedure for DL ​​data, and / or HARQ information related to the HARQ procedure for DL ​​data to LEO satellite #1.

[0150] The third RV and the fourth RV may correspond to RV3 and RV4 in FIG. 5, which include some redundancy bits and some systomic bits.

[0151] LEO satellite #0 can transmit residual RV information to LEO satellite #1, which includes data having a third RV and data having a fourth RV corresponding to the residual RVs in the HARQ procedure for DL ​​data. LEO satellite #1 can receive residual RV information from LEO satellite #0, which includes data having a third RV and data having a fourth RV corresponding to the residual RVs in the HARQ procedure for DL ​​data (S1151). Next, LEO satellite #0 can transmit HARQ information related to the HARQ procedure for DL ​​data to LEO satellite #1. LEO satellite #1 can receive HARQ information related to the HARQ procedure for DL ​​data from LEO satellite #0 (S1155).

[0152] HARQ information may include a new data indicator (NDI), RV information, transport block size (TBS), and / or HARQ process ID.

[0153] In step S1150 of Fig. 11, the remaining RV information and HARQ information are sequentially transmitted to LEO satellite #1, but are not limited thereto.

[0154] In one embodiment, LEO satellite #0 may transmit a message (e.g., an RRC message) containing remaining RV information and HARQ information to LEO satellite #1. LEO satellite #1 may receive a message (e.g., an RRC message) containing remaining RV information and HARQ information from LEO satellite #0.

[0155] It may include a step of performing an HO procedure based on the location information of the terminal and the movement information of the LEO satellite, and the movement information of the LEO satellite may include the movement path of LEO satellite #0 and the movement path of LEO satellite #0.

[0156] Movement information of LEO satellites may refer to the orbital information of LEO satellites. As mentioned earlier, the orbital information of LEO satellites may be known to the ground terminal in advance, or the LEO satellites may broadcast the orbital information to the ground terminal. The terminal may periodically transmit its location information to the LEO satellite(s).

[0157] For example, the HO may be a conditional HO. In a conditional HO, the condition for performing the HO may be set based on the terminal's location information and the movement information of the LEO satellite.

[0158] If the HO procedure from LEO satellite #0 to LEO satellite #1 is successfully completed, LEO satellite #1 and the ground terminal can perform steps S1160 to S1190.

[0159] In step S1160, LEO satellite #1 can transmit data having a third RV corresponding to the third transmission in the HARQ procedure for DL ​​data to a ground terminal. The ground terminal can receive data having a third RV3 corresponding to the third transmission in the HARQ procedure for DL ​​data from LEO satellite #1.

[0160] A ground terminal can perform channel decoding on data having a third RV received from LEO satellite #1 and determine whether the channel decoding of the data having the third RV is successful or unsuccessful. If the ground terminal determines that the channel decoding of the data having the third RV received from LEO satellite #1 has failed, the ground terminal can perform step S1170. The third RV may correspond to RV3 in FIG. 5, which includes some redundancy bits and some systomic bits.

[0161] In step S1170, the ground terminal may transmit HARQ feedback information to LEO satellite #1, which includes a NACK indicating that channel decoding for data having a third RV has failed in the HARQ procedure for DL ​​data. LEO satellite #1 may receive HARQ feedback information from the ground terminal, which includes a NACK indicating that channel decoding for data having a third RV has failed.

[0162] Data having a third RV may be the third transmission in the HARQ procedure for DL ​​data transmitted by LEO Satellite #1 to the ground terminal in step S1160. The ground terminal may transmit HARQ feedback information to LEO Satellite #1, including a NACK indicating that channel decoding for the data having a third RV received from LEO Satellite #1 in step S1160 has failed. LEO Satellite #1 may receive HARQ feedback information from the ground terminal, including a NACK indicating that channel decoding for the data having a third RV received in step S1160 has failed. LEO Satellite #1 may perform step S1180 to transmit DL data having a fourth RV, corresponding to the fourth transmission in the HARQ procedure for DL, to the ground terminal.

[0163] In step S1180, LEO satellite #1 can transmit data having a fourth RV corresponding to the fourth transmission in the HARQ procedure for DL ​​data to a ground terminal. The ground terminal can receive data having a fourth RV corresponding to the fourth transmission in the HARQ procedure for DL ​​data from LEO satellite #1.

[0164] The ground terminal can perform channel decoding on data having a fourth RV received from LEO satellite #1 and determine whether the channel decoding of the data having the fourth RV is successful or not. If the ground terminal determines that the channel decoding of the data having a fourth RV received from LEO satellite #1 is successful, the ground terminal can perform step S1190. As previously mentioned, the fourth RV may correspond to RV0 in FIG. 5, which includes some redundancy bits and some systemic bits.

[0165] In step S1190, the ground terminal may transmit HARQ feedback information to LEO satellite #1, including an ACK indicating that channel decoding for data having the fourth RV in the HARQ procedure for DL ​​data was successful. LEO satellite #1 may receive HARQ feedback information from the ground terminal, including an ACK indicating that channel decoding for data having the fourth RV in the HARQ procedure for DL ​​data was successful. LEO satellite #1 may determine that the HARQ procedure for DL ​​data was successfully performed.

[0166] Data having the fourth RV may be the fourth transmission in the HARQ procedure for UL data transmitted by LEO satellite #1 to the ground terminal in step S1180. The ground terminal may transmit HARQ feedback information to LEO satellite #1, including an ACK indicating that channel decoding of the data having the fourth RV received from LEO satellite #1 in step S1180 was successful. LEO satellite #1 may receive HARQ feedback information from the ground terminal, including an ACK indicating that channel decoding of the data having the fourth RV received in step S1180 was successful.

[0167] In FIG. 11, in the HARQ procedure for DL ​​data, data having a first RV corresponding to the first transmission and data having a second RV corresponding to the second transmission can be transmitted from LEO satellite #0 to a ground terminal. In the HARQ procedure for DL ​​data, data having a third RV corresponding to the third transmission and data having a fourth RV corresponding to the fourth transmission can be transmitted from LEO satellite #1 to a ground terminal.

[0168] In FIG. 11, steps S1110 to S1155 may be performed prior to the HO procedure.

[0169] In FIG. 11, after the HO procedure is performed, steps S1160 to S1190 may be performed.

[0170] In Fig. 11, the HO procedure can be performed prior to step S1160.

[0171] As illustrated in FIG. 11, a HARQ procedure for DL ​​data can be performed on the handovered LEO satellite (e.g., LEO #1 in FIG. 11) after the handover. After the handover, the handovered LEO satellite can transmit the remaining RV(s) (e.g., RV3 and RV1 in FIG. 11) in the HARQ procedure for DL ​​data to a ground terminal. The remaining RV(s) in the HARQ procedure for DL ​​data may include information indicating that a transmission delay may occur.

[0172] In FIG. 11, steps S1110 through S1190 are described individually, but this is not intended to limit the order in which the steps are performed, and if necessary, each step may be performed simultaneously, in a different order, or combined.

[0173] Next, a HARQ procedure utilizing the transmission of residual RV(s) and HARQ-related information between LEO satellites for the uplink will be described.

[0174] FIG. 12 is a conceptual diagram illustrating a HARQ procedure using the transmission of HARQ information related to a hybrid automatic request procedure and reception redundancy version information between low-orbit satellites for uplink data according to embodiments of the present disclosure.

[0175] Referring to FIG. 12, a communication system (e.g., a 5G communication system) may include LEO satellite #0, LEO satellite #1, and a ground terminal. In a HARQ procedure for uplink (UL) data, data having a first RV (e.g., RV0 in FIG. 5) corresponding to the first transmission and data having a second RV (e.g., RV2 in FIG. 5) corresponding to the second transmission may be transmitted from the ground terminal to LEO satellite #0. In a HARQ procedure for UL data, data having a third RV (e.g., RV3 in FIG. 5) corresponding to the third transmission and data having a fourth RV (e.g., RV1 in FIG. 5) corresponding to the fourth transmission may be transmitted from the ground terminal to LEO satellite #1. When LEO satellite #1 approaches an HO point, LEO satellite #0 may transmit received RV information for UL data and / or HARQ information related to the HARQ procedure to LEO satellite #1 via ISL. In FIG. 12, the received RV information may include data having RVs (e.g., RV0 and RV3 in FIG. 5) received by LEO satellite #0 from a ground terminal in a HARQ procedure for UL data. Transmission of data having the first RV may correspond to an initial transmission. Transmission of data having the second to fourth RVs may correspond to a retransmission.

[0176] Referring to FIG. 12, LEO satellite #0, LEO satellite #1, and the ground terminal may be the LEO satellite #0, LEO satellite #1, and the ground terminal illustrated in FIG. 10. LEO satellite #0, LEO satellite #1, and the ground terminal may be configured identically or similarly to the communication node illustrated in FIG. 3. It may be assumed that LEO satellite #0 and LEO satellite #1 are connected via ISL to transmit and receive signal(s). In describing FIG. 12, details that overlap with those described with reference to FIG. 1 through 11 may be omitted.

[0177] In step S1210, the ground terminal can transmit data having a first RV corresponding to the first transmission in the HARQ procedure for UL data to LEO satellite #0. LEO satellite #0 can receive data having a first RV corresponding to the first transmission in the HARQ procedure for DL ​​data from the ground terminal.

[0178] LEO satellite #0 can perform channel decoding (e.g., LDPC decoding) on ​​data having a first RV received from a ground terminal and determine whether the channel decoding of the data having the first RV is successful or failed. If LEO satellite #0 determines that the channel decoding of the data having the first RV received from the ground terminal has failed, the LEO satellite may perform step S1220. As previously mentioned, the first RV may correspond to RV0 in FIG. 5, which includes systematic bits and some redundancy bits.

[0179] In step S1220, LEO satellite #0 may transmit HARQ feedback information to a ground terminal, including a NACK indicating that channel decoding for data having a first RV has failed in the HARQ procedure for UL data. The ground terminal may receive HARQ feedback information from LEO satellite #0, including a NACK indicating that channel decoding for data having a first RV has failed in the HARQ procedure for UL data.

[0180] Data transmission having the first RV may be the first transmission in the HARQ procedure for UL data transmitted by the ground terminal to LEO satellite #0 in step S1210. LEO satellite #0 may transmit HARQ feedback information to the ground terminal, including a NACK indicating that channel decoding for the data having the first RV received from the ground terminal in step S1210 has failed. The ground terminal may receive HARQ feedback information from LEO satellite #0, including a NACK indicating that channel decoding for the data having the first RV received in step S1210 has failed. The ground terminal may perform step S1230 to transmit data having the second RV corresponding to the second transmission in the HARQ procedure for UL data to LEO satellite #0.

[0181] In step S1230, the ground terminal can transmit data having a second RV corresponding to the second transmission in the HARQ procedure for UL data to LEO satellite #0. LEO satellite #0 can receive UL data having a second RV corresponding to the second transmission in the HARQ procedure for UL data from the ground terminal.

[0182] LEO satellite #0 can perform channel decoding on data having a second RV received from a ground terminal and determine whether the channel decoding for the second RV is successful or unsuccessful. If LEO satellite #0 determines that channel decoding has failed on data having a second RV received from a ground terminal, LEO satellite #0 can perform step S1240. As mentioned above, the second RV may correspond to RV2 containing redundancy bits in FIG. 5.

[0183] In step S1240, LEO satellite #0 may transmit HARQ feedback information to a ground terminal, including a NACK indicating that decoding for data having a second RV has failed in the HARQ procedure for UL data. The ground terminal may receive HARQ feedback information from LEO satellite #0, including a NACK indicating that channel decoding for data having a second RV has failed.

[0184] The transmission of data having the second RV may be the second transmission in the HARQ procedure for the UL data transmitted by the ground terminal to LEO satellite #0 in step S1230. LEO satellite #0 may transmit HARQ feedback information to the ground terminal, including a NACK indicating that channel decoding for the data having the second RV received from the ground terminal in step S1230 has failed. The ground terminal may receive HARQ feedback information, including a NACK indicating that channel decoding for the data having the second RV received from LEO satellite #0 in step S1230 has failed.

[0185] LEO satellite #0 can determine whether the ground terminal is close to the time of the HO to LEO satellite #1. If LEO satellite #0 determines that the ground terminal is close to the time of the HO to LEO satellite #1, LEO satellite #0 can perform step S1250.

[0186] In step S1250, LEO satellite #0 may transmit to LEO satellite #1 received RV information including data having a first RV and data having a second RV received from a ground terminal in a HARQ procedure for UL data, and / or HARQ information related to the HARQ procedure for UL data.

[0187] LEO Satellite #0 can transmit received RV information, including data having a first RV and data having a second RV, received from a ground terminal in a HARQ procedure for UL data, to LEO Satellite #1. LEO Satellite #1 can receive received RV information, including data having a first RV and data having a second RV, received from a ground terminal in a HARQ procedure for UL data, from LEO Satellite #0 (S1251). Next, LEO Satellite #0 can transmit HARQ information related to the HARQ procedure for UL data to LEO Satellite #1. LEO Satellite #1 can receive HARQ information related to the HARQ procedure for UL data from LEO Satellite #0 (S1252).

[0188] As mentioned above, HARQ information may include NDI, RV information, TBS, and / or HARQ process ID.

[0189] In step S1250 of FIG. 12, LEO satellite #0 is depicted as sequentially transmitting received RV information and HARQ-related information to LEO satellite #1, but is not limited thereto.

[0190] In one embodiment, LEO satellite #0 may transmit a message (e.g., an RRC message) containing received RV information and HARQ information to LEO satellite #1. LEO satellite #1 may receive a message (e.g., an RRC message) containing received RV information and HARQ information from LEO satellite #0.

[0191] It may include a step of performing an HO procedure based on the location information of the terminal and the movement information of the LEO satellite, and the movement information of the LEO satellite may include the movement path of LEO satellite #0 and the movement path of LEO satellite #0.

[0192] Movement information of LEO satellites may refer to the orbital information of LEO satellites. As mentioned earlier, the orbital information of LEO satellites may be known to the ground terminal in advance, or the LEO satellites may broadcast the orbital information to the ground terminal. The terminal may periodically transmit its location information to the LEO satellite(s).

[0193] For example, the HO may be a conditional HO. In a conditional HO, the condition for performing the HO may be set based on the terminal's location information and the movement information of the LEO satellite.

[0194] In step S1250 of FIG. 12, LEO satellite #0 is depicted as transmitting received RV information to LEO satellite #1, which includes data having RV(s) (e.g., RV3 and RV1) received during HARQ transmission for the uplink, but is not limited thereto. LEO satellite #0 may transmit RV decoding information for the RV(s) received during HARQ transmission for the uplink to LEO satellite #1. LEO satellite #1 may receive RV decoding information for the RV(s) received during HARQ transmission for the uplink from LEO satellite #0. The RV decoding information may include log-likelihood ratio (LLR) values ​​obtained by performing channel decoding on data having RV(s) received in a HARQ procedure for UL data.

[0195] If the HO procedure from LEO satellite #0 to LEO satellite #1 is successfully completed, the ground terminal and LEO satellite #1 can perform steps S1260 to S1290.

[0196] In step S1260, the ground terminal can transmit data having a third RV3 corresponding to the third transmission in the HARQ procedure for UL data to LEO satellite #1. LEO satellite #1 can receive data from the ground terminal having a third RV corresponding to the third transmission in the HARQ procedure for UL data.

[0197] LEO satellite #1 can perform channel decoding (e.g., LDPC decoding) on ​​data having a third RV received from a ground terminal and determine whether the channel decoding of the data having the third RV is successful or unsuccessful. If LEO satellite #1 determines that the channel decoding of the data having the third RV received from the ground terminal has failed, LEO satellite #1 can perform step S1270. As previously mentioned. The third RV may correspond to RV3 in FIG. 5, which includes some redundancy bits and some systematic bits.

[0198] In step S1270, LEO satellite #1 may transmit HARQ feedback information to a ground terminal, including a NACK indicating that channel decoding for data having a third RV failed in the HARQ procedure for UL data. The ground terminal may receive HARQ feedback information from LEO satellite #1, including a NACK indicating that channel decoding for data having a third RV failed.

[0199] Data having a third RV may be the third transmission in the HARQ procedure for UL data transmitted by the ground terminal to LEO satellite #1 in step S1260. LEO satellite #1 may transmit HARQ feedback information to the ground terminal, including a NACK indicating that channel decoding for the data having a third RV received from the ground terminal in step S1260 has failed. The ground terminal may receive HARQ feedback information from LEO satellite #1, including a NACK indicating that channel decoding for the data having a third RV received in step S1260 has failed. The ground terminal may perform step S1280 to transmit data having a fourth RV corresponding to the fourth transmission in the HARQ procedure for UL data to LEO satellite #1.

[0200] In step S1280, the ground terminal can transmit data having a fourth RV corresponding to the fourth transmission in the HARQ procedure for UL data to LEO satellite #1. LEO satellite #1 can receive data having a fourth RV corresponding to the fourth transmission in the HARQ procedure for UL data from the ground terminal.

[0201] LEO satellite #1 can perform channel decoding on data having a fourth RV received from a ground terminal and determine whether the channel decoding of the data having a fourth RV is successful or not. If LEO satellite #1 determines that the channel decoding of the data having a fourth RV received from the ground terminal is successful, LEO satellite #1 can perform step S1290. As previously mentioned. The fourth RV may correspond to RV0 in FIG. 5, which includes some redundancy bits and some systemic bits.

[0202] In step S1290, LEO satellite #1 may transmit HARQ feedback information to a ground terminal, including an ACK indicating that channel decoding for data having a fourth RV in the HARQ procedure for UL data was successful. The ground terminal may receive HARQ feedback information from LEO satellite #1, including an ACK indicating that channel decoding for data having a fourth RV in the HARQ procedure for UL data was successful. The ground terminal may determine that the HARQ procedure for UL data was successfully performed.

[0203] Data having the fourth RV may be the fourth transmission in the HARQ procedure for UL data transmitted by the ground terminal to LEO satellite #1 in step S1280. LEO satellite #1 may transmit HARQ feedback information to the ground terminal, including an ACK indicating that channel decoding for the data having the fourth RV received from the ground terminal in step S1280 was successful. The ground terminal may receive HARQ feedback information from LEO satellite #1, including an ACK indicating that channel decoding for the data having the fourth RV received in step S1280 was successful.

[0204] In FIG. 12, in the HARQ procedure for UL data, the UL data having a first RV corresponding to the first transmission and the UL data having a second RV corresponding to the second transmission can be transmitted from the ground terminal to LEO satellite #0. In the HARQ procedure for UL data, the data having a third RV corresponding to the third transmission and the UL data having a fourth RV corresponding to the fourth transmission can be transmitted from the ground terminal to LEO satellite #1.

[0205] It may include a step of performing an HO procedure based on the terminal's location information and the LEO satellite's movement information, and the LEO satellite's movement information may include the movement path of LEO satellite #0 and the movement path of LEO satellite #0.

[0206] In FIG. 12, steps S1210 to S1255 may be performed prior to the HO procedure.

[0207] In FIG. 12, steps S1160 through S1190 may be performed after the HO procedure is performed. As illustrated in FIG. 12, the HARQ procedure for UL data may be performed after the handover between the ground terminal (e.g., the ground terminal in FIG. 12) and the handover LEO satellite (e.g., LEO #1 in FIG. 12). After the handover, the ground terminal may transmit received RV information containing data having received RV(s) (e.g., RV3 and RV1 in FIG. 12) in the HARQ procedure for UL data to the handover LEO satellite.

[0208] In FIG. 12, steps S1210 through S1290 are described individually, but this is not intended to limit the order in which the steps are performed, and if necessary, each step may be performed simultaneously, in a different order, or combined.

[0209] A LEO satellite connected to a ground terminal can transmit residual RV information and HARQ information in a HARQ procedure for DL ​​data to an HO candidate satellite via ISL, as described above. After HO, the HO candidate satellite can transmit data containing residual RV(s) in a HARQ procedure for DL ​​data to the ground terminal based on the residual RV information and / or HARQ information. The ground terminal can receive DL data containing residual RV(s) in a HARQ procedure for DL ​​data from the HO candidate satellite.

[0210] A LEO satellite connected to a ground terminal can transmit received RV information and HARQ information for UL data to an HO candidate satellite via ISL, as described above. After HO, the HO candidate satellite can receive data from the ground terminal that has RV(s) not included in the received RV information in the HARQ procedure for UL data based on the received RV information and / or HARQ information for UL data.

[0211] A LEO satellite connected to a ground terminal can transmit RV information and HARQ information in a HARQ procedure for UL data to an HO candidate satellite via ISL, as described above. After HO, the HO candidate satellite can receive data from the ground terminal that has RV(s) not included in the RV decoding information in the HARQ procedure for UL data, based on RV decoding information and / or HARQ-related information in the HARQ procedure for UL data. The RV decoding information may include at least one LLR value in the data having RV(s) received in the HARQ procedure for UL data.

[0212] The operation of the method according to an embodiment of the present invention can be implemented as a computer-readable program or code on a computer-readable recording medium. A computer-readable recording medium includes all types of recording devices in which information that can be read by a computer system is stored. Additionally, the computer-readable recording medium may be distributed across networked computer systems, allowing computer-readable programs or code to be stored and executed in a distributed manner.

[0213] In addition, computer-readable recording media may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, and flash memory. Program instructions may include machine code, such as that generated by a compiler, as well as high-level language code that can be executed by a computer using an interpreter, etc.

[0214] Some aspects of the invention have been described in the context of a device, but may also be described according to a corresponding method, wherein a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method may also be described according to a corresponding block or item or a feature of a corresponding device. Some or all of the method steps may be performed by (or using) a hardware device, such as, for example, a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, at least one of the most important method steps may be performed by such a device.

[0215] In the embodiments, a programmable logic device (e.g., a field-programmable gate array) may be used to perform some or all of the functions of the methods described herein. In the embodiments, the field-programmable gate array may operate with a microprocessor to perform one of the methods described herein. Generally, it is preferable that the methods be performed by some hardware device.

[0216] Although the present invention has been described with reference to preferred embodiments, those skilled in the art will understand that various modifications and changes can be made to the invention without departing from the spirit and scope of the invention as described in the following claims.

Claims

1. As a method of a terminal, A step of transmitting first UL data having a first redundancy version (RV) corresponding to the first transmission to a first base station in a hybrid automatic repeat request (HARQ) procedure for uplink (UL) data; A step of receiving first HARQ feedback information for the first UL data from the first base station; If the first HARQ feedback information includes a negative acknowledgment (NACK), the step of transmitting at least one second UL data having at least one second RV in the HARQ procedure for the UL to the first base station; A step of performing a handover (HO) procedure for an LEO satellite based on the location information of the terminal and the movement information of the base station - the movement information of the base station includes the movement information of the first base station and the movement information of the second base station - ; and A step comprising transmitting at least one third UL data having at least one residual RV in the HARQ procedure for the above UL to the second base station. Method of the terminal.

2. In Claim 1, The first base station is a low earth orbit (LEO) satellite to which the terminal is connected, and the second base station is a handover (HO) candidate LEO satellite, and The first base station and the second base station are connected via an inter-satellite link (ISL). Method of the terminal.

3. In Claim 1, The method further comprises the step of receiving at least one second HARQ feedback information, including a NACK for at least one second UL data, from the first base station prior to the execution of the above HO procedure. Method of the terminal.

4. In Claim 1, At least one of the received RV information or HARQ information is transmitted by the first base station to the second base station via ISL, the received RV information includes the first RV and the at least one second RV, and the HARQ information includes information related to the HARQ procedure for the UL data. Method of the terminal.

5. As a method of the second base station, A step of receiving received RV information including at least one data having at least one redundancy version (RV) received based on a hybrid automatic repeat request (HARQ) procedure for uplink (UL) data transmitted by a terminal to the first base station, and receiving HARQ information related to the HARQ procedure; A step of performing a handover (HO) procedure from the first base station to the terminal communicating with the first base station; and A method comprising the step of receiving at least one UL data including at least one residual RV in the HARQ procedure for the UL data from the terminal. Method of the first base station.

6. In Claim 5, The first base station is a low earth orbit (LEO) satellite to which the terminal is connected, and the second base station is a handover (HO) candidate LEO satellite, and The first base station and the second base station are connected via an inter-satellite link (ISL). Method of the second base station.

7. In Claim 5, The method further includes the step of transmitting a first HARQ feedback information to the terminal, the first HARQ feedback information including an acknowledgment (ACK) or a negative acknowledgment (NACK) for at least one UL data based on the received RV information and the HARQ information. Method of the second base station.

8. In Claim 5, The above received RV information and the above HARQ information are received from the first base station via ISL, and at least one UL data having at least one RV included in the RV information is transmitted from the terminal to the first base station, Method of the second base station.

9. In Claim 8, At least one HARQ feedback information for at least one UL data having at least one RV included in the received RV information is transmitted by the first base station to the terminal, and the at least one HARQ feedback information includes a NACK. Method of the second base station, 10. As a terminal, It includes at least one processor, The above at least one processor is the terminal: In a hybrid automatic repeat request (HARQ) procedure for uplink (UL) data, first UL data having a redundancy version (RV) corresponding to the first transmission is transmitted to the first base station; Receiving first HARQ feedback information for the first UL data from the first base station; If the first HARQ feedback information includes a NACK, at least one second UL data including at least one second RV in the HARQ procedure for the UL is transmitted from the first base station; Performing a handover (HO) procedure for the LEO satellite based on the location information of the above terminal and the movement information of the base station—the movement information of the above base station includes the movement information of the first base station and the movement information of the second base station—; and Causing to transmit at least one third UL data having at least one residual RV in the HARQ procedure for the above UL to the above second base station, Terminal.

11. In Claim 10, The first base station is a low earth orbit (LEO) satellite to which the terminal is connected, and the second base station is a handover (HO) candidate LEO satellite, and The first base station and the second base station are connected via an inter-satellite link (ISL). Terminal.

12. In Claim 10, The above at least one processor is the terminal, Further causing receiving at least one second HARQ feedback information including a NACK for at least one second UL data from the first base station prior to the execution of the above HO procedure, Terminal.

13. In Claim 10, At least one of the received RV information or HARQ information is transmitted by the first base station to the second base station via ISL, the received RV information includes the first RV and the at least one second RV, and the HARQ information includes information related to the HARQ procedure for the UL data. Terminal.

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