Hybrid automatic repeat request technique in non-terrestrial network

Abstract

A method by which a first communication node communicates with a second communication node through a link in a wireless communication system may comprise the steps of: transmitting a primary redundant version of transmission data; and when retransmission of the transmission data is required, transmitting a secondary RV for the transmission data. One of the first and second communication nodes may be a non-terrestrial node. At least one of the primary RV and the secondary RV may be selected from among a plurality of RV candidates on the basis of a condition of the link. The condition may vary according to the movement of the non-terrestrial node.

Description

Hybrid automatic retransmission request technique in non-terrestrial networks

[0001] The present disclosure relates to Hybrid Automatic Repeat Request (HARQ) technology, and more particularly, to HARQ technology in a Non-Terrestrial Network (NTN).

[0002] Communication networks (e.g., 5G, 6G, etc.) can provide communication services to terminals located on the ground. Demand for communication services for not only terrestrial but also non-terrestrial devices such as aircraft, drones, and satellites is increasing, and NTN technologies are being discussed to meet these needs. NTN can be implemented based on 5G, 6G, etc. communication technologies. In NTN, satellites can function as base stations in communication networks (e.g., 5G, 6G, etc.).

[0003] Meanwhile, research on NTN has been ongoing, but there are still areas for improvement, such as increasing coverage and capacity.

[0004] Enhanced NTN transmission technologies (e.g., HARQ technologies for coverage and capacity enhancement in NTN environments) are provided.

[0005] One aspect of the present disclosure provides a method for a first communication node to communicate with a second communication node through a link in a wireless communication system, the method comprising: transmitting a primary redundancy version (RV) of transport data; and transmitting a secondary RV of the transport data when retransmission of the transport data is required.

[0006] In some embodiments, one of the first and second communication nodes may be a non-terrestrial node. In some embodiments, the other of the first and second communication nodes may be a terrestrial node.

[0007] In some embodiments, at least one of the first RV and the second RV may be selected from among a plurality of RV candidates based on a condition of the link.

[0008] In some embodiments, the condition may vary depending on the movement of the non-terrestrial node. In some embodiments, the condition may be based on at least one of the round trip time of the link and the elevation angle of the non-terrestrial node. In some embodiments, the condition may be determined based on the elapsed time since the non-terrestrial node becomes capable of providing service to the terrestrial node.

[0009] In some embodiments, the method may further include a step of selecting one of a plurality of RV combination candidates, each candidate including a primary RV and a secondary RV, based on the condition. In this case, the primary and secondary RVs for the transmission data may be included in the selected RV combination candidate.

[0010] In some embodiments, the method may further include a step of selecting one of a plurality of primary RV candidates based on the condition. In this case, the primary RV for the transmission data may be the selected primary RV candidate.

[0011] In some embodiments, the step of transmitting the secondary RV may include the step of receiving transmission result information of the primary RV from the second communication node; and the step of transmitting the secondary RV based on the received transmission result information. In some embodiments, the transmission result information may include information indicating whether retransmission is necessary and information used to select the second RV.

[0012] In some embodiments, the step of transmitting the primary RV may include the step of transmitting the primary RV based on information about the primary RV received from the second communication node, and the step of transmitting the secondary RV may include the step of transmitting the secondary RV based on information about the secondary RV received from the second communication node.

[0013] Another aspect of the present disclosure provides a method for a second communication node to communicate with a first communication node through a link in a wireless communication system, the method comprising: receiving a first RV for transmission data from the first communication node; transmitting a response to the first RV based on a decoding result of the received first RV; and, when receiving a second RV for the transmission data, combining and decoding the received first RV and the received second RV.

[0014] In some embodiments, one of the first and second communication nodes may be a non-terrestrial node. In some embodiments, the other of the first and second communication nodes may be a terrestrial node.

[0015] In some embodiments, at least one of the first RV and the second RV may be selected from among a plurality of RV candidates based on a condition of the link.

[0016] In some embodiments, the condition may vary depending on the movement of the non-terrestrial node. In some embodiments, the condition may be based on at least one of the round trip time of the link and the elevation angle of the non-terrestrial node. In some embodiments, the condition may be determined based on the elapsed time since the non-terrestrial node becomes capable of providing service to the terrestrial node.

[0017] In some embodiments, the method may further include the step of transmitting information about a plurality of RV combination candidates, each candidate including a primary RV and a secondary RV. In this case, the primary and secondary RVs may be included in the candidates selected by the first communication node from among the plurality of RV combination candidates.

[0018] In some embodiments, the method may further include the step of transmitting information about candidates for the primary RV to the first communication node. In this case, the primary RV may be a candidate selected by the first communication node from among the candidates for the primary RV.

[0019] In some embodiments, the response to the primary RV may include information indicating whether retransmission is necessary and information used to select the secondary RV.

[0020] In some embodiments, the method may further include the steps of allocating resources for transmission of the primary RV to the first communication node; and the steps of allocating resources for transmission of the secondary RV to the first communication node. In one example, the resources for transmission of the primary RV and the resources for transmission of the secondary RV may be allocated using semi-persistent scheduling. In another example, the resources for transmission of the primary RV may be allocated using semi-persistent scheduling, and the resources for transmission of the secondary RV may be allocated using dynamic scheduling.

[0021] Another aspect of the present disclosure provides a device for a first communication node communicating with a second communication node through a link in a wireless communication system, the device comprising: a transceiver; and a processor connected to the transceiver, the processor performing an operation of transmitting a first RV for transmission data; and an operation of transmitting a second RV for the transmission data when retransmission of the transmission data is required.

[0022] In some embodiments, one of the first and second communication nodes may be a non-terrestrial node. In some embodiments, the other of the first and second communication nodes may be a terrestrial node. For example, the first communication node may be a User Equipment (UE) that is the terrestrial node, and the second communication node may be a base station located on a satellite that is a non-terrestrial node. In another example, the first communication node may be a base station located on a satellite that is a non-terrestrial node, and the second communication node may be a UE that is the terrestrial node.

[0023] In some embodiments, at least one of the first RV and the second RV may be selected from among a plurality of RV candidates based on a condition of the link.

[0024] In some embodiments, the condition may vary depending on the movement of the non-ground node.

[0025] Another aspect of the present disclosure provides a device for a second communication node communicating with a first communication node through a link in a wireless communication system, the device comprising: a transceiver; and a processor connected to the transceiver, wherein the processor performs an operation of receiving a first RV for transmission data from the first communication node; an operation of transmitting a response to the first RV based on a decoding result of the received first RV; and an operation of decoding the received first RV and the received second RV by combining them when receiving a second RV for the transmission data.

[0026] In some embodiments, one of the first and second communication nodes may be a non-terrestrial node. In some embodiments, the other of the first and second communication nodes may be a terrestrial node. For example, the first communication node may be a UE, which is a terrestrial node, and the second communication node may be a base station located on a satellite, which is a non-terrestrial node. In another example, the first communication node may be a base station located on a satellite, which is a non-terrestrial node, and the second communication node may be a UE, which is a terrestrial node.

[0027] In some embodiments, at least one of the first RV and the second RV may be selected from among a plurality of RV candidates based on a condition of the link.

[0028] In some embodiments, the condition may vary depending on the movement of the non-ground node.

[0029] Another aspect of the present disclosure provides a non-transitory recording medium storing instructions readable by a processor of an electronic device, the instructions causing the processor to perform embodiments of the present disclosure.

[0030] This Summary is provided to introduce a selection of concepts in a simplified form that are further explained in the Detailed Description below. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all of the problems mentioned in any portion of this specification. In addition to the exemplary aspects, embodiments, and features described above, additional aspects, embodiments, and features will become apparent by reference to the following Detailed Description and Drawings.

[0031] Some embodiments of the present disclosure may have the following advantages. However, this does not mean that all embodiments must include all of the advantages, and thus the scope of the present invention should not be construed as being limited thereby.

[0032] According to some embodiments, enhanced NTN transmission techniques (e.g., HARQ techniques for coverage and capacity enhancement in NTN environments) may be provided.

[0033] Figure 1 is a conceptual diagram illustrating a non-terrestrial network.

[0034] Figure 2 is a conceptual diagram illustrating a non-terrestrial network including a core network.

[0035] Figure 3 is a block diagram illustrating the internal configuration of a communication node.

[0036] Figure 4 is a block diagram illustrating communication between communication nodes.

[0037] Figures 5a and 5b are conceptual diagrams illustrating a user plane protocol stack and a control plane protocol stack, respectively, in a non-terrestrial network based on regenerative payload.

[0038] Figure 6 is a conceptual diagram illustrating the operation of HARQ.

[0039] Figure 7 is a conceptual diagram illustrating a redundancy version (RV) used in HARQ.

[0040] Figure 8 is a conceptual diagram for explaining the elevation angle of a satellite.

[0041] Figure 9 is a table showing the relationship between the elevation angle of a satellite, the distance between a terminal and a satellite, and the one-way propagation time in a LEO system having an altitude of 600 km.

[0042] Figure 10 is a flowchart illustrating some embodiments of HARQ for NTN.

[0043] Figures 11a to 11c are conceptual diagrams illustrating retransmission patterns for cases where the elevation angle is high, the elevation angle is low, and the elevation angle is very low, respectively.

[0044] Figure 12 is a table for explaining an embodiment of a HARQ response.

[0045] The description of the present invention is merely an example for structural and functional explanation, and therefore, the scope of the present invention should not be construed as being limited by the embodiments described in the text. That is, since the embodiments can be modified in various ways and can take various forms, the scope of the present invention should be understood to include equivalents that can realize the technical idea. In addition, the purposes or effects presented in the present invention do not mean that a specific embodiment must include all of them or only such effects, and therefore, the scope of the present invention should not be construed as being limited thereby.

[0046] Meanwhile, the meanings of the terms described in this disclosure should be understood as follows.

[0047] Terms such as "first" and "second" are intended to distinguish one component from another, and the scope of the rights should not be limited by these terms. For example, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component.

[0048] When a component is said to be "connected" to another component, it should be understood that while it may be directly connected to that other component, there may also be other components intervening. Conversely, when a component is said to be "directly connected" to another component, it should be understood that there are no other intervening components. Similarly, other expressions describing relationships between components, such as "between" and "directly between," or "adjacent to" and "directly adjacent to," should be interpreted similarly.

[0049] Singular expressions should be understood to include plural expressions unless the context clearly indicates otherwise, and terms such as "comprises" or "have" should be understood to specify the presence of a feature, number, step, operation, component, part or combination thereof, but not to exclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0050] For each step, the identifiers (e.g., a, b, c, etc.) are used for convenience of explanation and do not describe the order of the steps. The steps may occur in a different order than stated unless the context clearly dictates a specific order. That is, the steps may occur in the same order as stated, may be performed substantially simultaneously, or may be performed in the opposite order.

[0051] In an embodiment, even if a method (e.g., transmitting or receiving a signal) performed by a first communication node among communication nodes is described, a corresponding second communication node can perform a method (e.g., receiving or transmitting a signal) corresponding to the method performed by the first communication node. For example, if an operation of a UE is described, a corresponding base station can perform an operation corresponding to the operation of the UE. Conversely, if an operation of a base station is described, a corresponding UE can perform an operation corresponding to the operation of the base station. In an NTN, an operation of a base station can mean an operation of a satellite, and an operation of a satellite can mean an operation of a base station.

[0052] A base station may be referred to as a NodeB, an evolved NodeB, a gNodeB (next generation node B), a gNB, a device, an apparatus, a node, a communication node, a BTS (base transceiver station), a RRH (radio remote head), a TRP (transmission reception point), a RU (radio unit), an RSU (road side unit), a radio transceiver, an access point, an access node, etc. A UE may be referred to as a terminal, a device, an apparatus, a node, a communication node, an end node, an access terminal, a mobile terminal, a station, a subscriber station, a mobile station, a portable subscriber station, an OBU (on-broad unit), etc.

[0053] In the present disclosure, signaling may be at least one of upper layer signaling, MAC signaling, or PHY (physical) signaling. A message used for upper layer signaling may be referred to as an "upper layer message" or an "upper layer signaling message." A message used for MAC signaling may be referred to as a "MAC message" or a "MAC signaling message." A message used for PHY signaling may be referred to as a "PHY message" or a "PHY signaling message." Upper layer signaling may refer to a transmission and reception operation of system information (e.g., a master information block (MIB), a system information block (SIB)) and / or an RRC message. MAC signaling may refer to a transmission and reception operation of a MAC control element (CE). PHY signaling may refer to a transmission and reception operation of control information (e.g., downlink control information (DCI), uplink control information (UCI), sidelink control information (SCI)).

[0054] In the present disclosure, “an operation (e.g., a transmission operation) is set” may mean that “setting information for the operation (e.g., an information element, a parameter)” and / or “information instructing the performance of the operation” is signaled. “An information element (e.g., a parameter) is set” may mean that the information element is signaled.

[0055] The communication system may include at least one of a terrestrial network, a non-terrestrial network, a 4G communication network, a 5G communication network, or a 6G communication network. Each of the 4G communication network, the 5G communication network, and the 6G communication network may include a terrestrial network and / or a non-terrestrial network. The non-terrestrial network may operate based on at least one communication technology among LTE communication technology, 5G communication technology, and 6G communication technology. The non-terrestrial network may provide communication services in various frequency bands.

[0056] The communication network to which the embodiment is applied is not limited to what is described below, and the embodiment may be applied to various communication networks (e.g., 4G communication networks, 5G communication networks, and / or 6G communication networks). Here, the communication network may be used in the same sense as the communication system.

[0057] Figure 1 is a conceptual diagram illustrating a non-terrestrial network.

[0058] Referring to FIG. 1, the non-terrestrial network may include a satellite (110), a communication node (120), a gateway (130), a data network (140), etc. 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).

[0059] The non-terrestrial network may be a regenerative payload-based non-terrestrial network. For example, a satellite (110) may perform a regenerative operation (e.g., a demodulation operation, a decoding operation, a re-encoding operation, a re-modulation operation, and / or a filtering operation) on a payload received from another entity constituting the non-terrestrial network (e.g., a communication node (220), a gateway (230)) and transmit the regenerated payload.

[0060] The communication node (120) may include a ground-based communication node (e.g., a UE) and a non-ground-based communication node (e.g., an airplane or drone). A service link may be established between the satellite (110) and the communication node (120), and the service link may be a radio link. The satellite (110) may provide a communication service to the communication node (120) using one or more beams.

[0061] The communication node (120) can perform communication (e.g., downlink communication, uplink communication) with the satellite (110) using 4G communication technology, 5G communication technology, and / or 6G communication technology. Communication between the satellite (110) and the communication node (120) can be performed using an NR-Uu interface and / or a 6G-Uu interface. When DC (dual connectivity) is supported, the communication node (120) can be connected to not only the satellite (110) but also other base stations (e.g., base stations supporting 4G functions, 5G functions, and / or 6G functions), and can perform DC operations based on technologies defined in the 4G standard, the 5G standard, and / or the 6G standard.

[0062] 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 an "NTN gateway." Communication between the satellite (110) and the gateway (130) may be performed based on a NR-Uu interface, a 6G-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), as illustrated in FIG. 2 . 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).

[0063] Figure 2 is a conceptual diagram illustrating a non-terrestrial network including a core network.

[0064] The core network may support 4G communication technology, 5G communication technology, and / or 6G communication technology. For example, the core network may include an access and mobility management function (AMF), a user plane function (UPF), a session management function (SMF), etc. Communication between the gateway (130) and the core network may be performed based on an NG-C / U interface or a 6G-C / U interface.

[0065] The base station function can be performed by a satellite. That is, the base station can be located on the satellite. Payloads can be processed by the base station located on the satellite. Base stations located on different satellites can be connected to the same core network. A single satellite can have one or more base stations.

[0066] Meanwhile, entities (e.g., satellites, base stations, UEs, communication nodes, gateways, etc.) constituting the non-terrestrial network illustrated in FIG. 1 and / or FIG. 2 may be configured as follows. In the present disclosure, entities may be referred to as communication nodes.

[0067] Figure 3 is a block diagram illustrating the internal configuration of a communication node.

[0068] Referring to FIG. 3, a communication node (300) may include at least one processor (310), a memory (320), and a transmission / reception device (330) that is connected to a network and performs communication. In addition, the communication node (300) may further include an input interface device (340), an output interface device (350), a storage device (360), etc.

[0069] For example, as illustrated in FIG. 2, each component included in the communication node (300) may be connected to each other by a bus (370) to communicate with each other. As another example, each component included in the communication node (300) may be connected to each other through individual interfaces or individual buses centered around the processor (310), rather than a common bus (370). For example, the processor (310) may be connected to at least one of a memory (320), a transceiver (330), an input interface device (340), an output interface device (350), or a storage device (360) through a dedicated interface.

[0070] The processor (310) can execute program commands stored in at least one of the memory (320) and the storage device (360). The processor (310) may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor in which the methods according to the embodiments are performed. Each of the memory (320) and the storage device (360) may be configured with at least one of a volatile storage medium or a non-volatile storage medium. For example, the memory (320) may be configured with at least one of a read-only memory (ROM) or a random access memory (RAM).

[0071] Meanwhile, communication nodes performing communication in a communication network (e.g., a non-terrestrial network) may be configured as follows. The communication node illustrated in FIG. 4 may be a specific embodiment of the communication node illustrated in FIG. 3.

[0072] Figure 4 is a block diagram illustrating communication between communication nodes.

[0073] Referring to FIG. 4, each of the first communication node (400a) and the second communication node (400b) may be a base station or a UE. The first communication node (400a) may transmit a signal to the second communication node (400b). The transmission processor (411) included in the first communication node (400a) may receive data (e.g., a data unit) from a data source (410). The transmission processor (411) may receive control information from a controller (416). The control information may include at least one of system information, RRC configuration information (e.g., information configured by RRC signaling), MAC control information (e.g., MAC CE), or PHY control information (e.g., DCI, SCI).

[0074] The transmitting processor (411) may perform a processing operation on data (e.g., an encoding operation, a symbol mapping operation, etc.) to generate data symbol(s). The transmitting processor (411) may perform a processing operation on control information (e.g., an encoding operation, a symbol mapping operation, etc.) to generate control symbol(s). In addition, the transmitting processor (411) may generate synchronization / reference symbol(s) for a synchronization signal and / or a reference signal.

[0075] The Tx MIMO processor (412) may perform spatial processing operations (e.g., precoding operations) on data symbol(s), control symbol(s), and / or synchronization / reference symbol(s). An output (e.g., a symbol stream) of the Tx MIMO processor (412) may be provided to modulators (MODs) included in the transceivers (413a to 413t). The modulators (MODs) may perform processing operations on the symbol streams to generate modulation symbols, and may perform additional processing operations (e.g., analog conversion operations, amplification operations, filtering operations, upconversion operations) on the modulation symbols to generate signals. The signals generated by the modulators (MODs) of the transceivers (413a to 413t) may be transmitted via the antennas (414a to 414t).

[0076] Signals transmitted by the first communication node (400a) may be received by antennas (464a to 464r) of the second communication node (400b). Signals received by the antennas (464a to 464r) may be provided to demodulators (DEMODs) included in transceivers (463a to 463r). The demodulator (DEMOD) may perform a processing operation (e.g., a filtering operation, an amplification operation, a downconversion operation, a digital conversion operation) on the signal to obtain samples. The demodulator (DEMOD) may perform an additional processing operation on the samples to obtain symbols. The MIMO detector (462) may perform a MIMO detection operation on the symbols. The receiving processor (461) may perform a processing operation (e.g., a deinterleaving operation, a decoding operation) on the symbols. The output of the receiving processor (461) may be provided to a data sink (460) and a controller (466). For example, data may be provided to the data sink (460) and control information may be provided to the controller (466).

[0077] The second communication node (400b) can transmit a signal to the first communication node (400a) using the same principle as the signal transmission operation of the first communication node (400a) described above. The first communication node (400a) can receive and process a signal transmitted from the second communication node (400b) using the same principle as the signal reception operation of the second communication node (400b) described above.

[0078] Memories (415 and 465) can store data, control information, and / or program code. Scheduler (417) can perform scheduling operations for communication. Processors (411, 412, 419, 461, 468, 469) and controllers (416, 466) illustrated in FIG. 4 may be the processor (310) illustrated in FIG. 3 and may be used to perform the methods described in the present disclosure.

[0079] Meanwhile, the first communication node (400a) and the second communication node (400b) can perform HARQ-based data transmission.

[0080] Figures 5a and 5b are conceptual diagrams illustrating a user plane protocol stack and a control plane protocol stack, respectively, in a non-terrestrial network based on regenerative payload.

[0081] Referring to FIGS. 5A and 5B , user data and control data (e.g., control information) may be transmitted and received through an interface between a UE and a satellite (e.g., a base station). User data may refer to a user protocol data unit (PDU). The protocol stack of the satellite radio interface (SRI) may be used to transmit and receive user data and / or control data between the satellite and the gateway. User data may be transmitted and received through a GTP (GPRS (general packet radio service) tunneling protocol)-U tunnel between the satellite and the core network.

[0082] Meanwhile, in a non-terrestrial network, a base station can transmit system information (e.g., SIB19) containing satellite assistance information for NTN access. A UE can receive system information (e.g., SIB19) from the base station, check the satellite assistance information included in the system information, and perform communication (e.g., non-terrestrial communication) based on the satellite assistance information.

[0083] In some embodiments, communication nodes (e.g., UEs, satellite base stations) may utilize ephemeris data. For example, communication nodes may use ephemeris data to determine the location of a satellite base station, estimate elevation angles, round trip times (RTT), etc., or determine a redundancy version (RV) used for HARQ retransmissions.

[0084] For example, ephemeris data can be loaded onto the UE in advance (e.g., during manufacturing or SIM card issuance). In another example, the UE can be included in a SIB transmitted by a base station (e.g., a satellite base station or a terrestrial base station) and transmitted to the UE. In another example, the base station can transmit detailed parameters related to ephemeris data to the UE through a dedicated RRC message during initial connection or handover. For example, the base station can unicast neighboring satellite information only to necessary UEs. In another example, considering the point in time when orbit prediction error increases, the validity time of the UE's stored value can be designated and the latest value can be transmitted to the UE through a SIB or RRC.

[0085] Ephemeris data can be a set of information that describes the orbital path of a satellite over time (e.g., the satellite's position and velocity). For example, ephemeris data can include orbital parameters. For example, the satellite's orbit can be mathematically defined through Keplerian elements such as the orbital semi-major axis, eccentricity, and inclination. As another example, ephemeris data can include information that directly specifies the satellite's state in terms of position (x, y, z) and velocity (vx, vy, vz) vectors in the Earth-Centered, Earth-Fixed (ECEF) coordinate system using a state vector at a specific reference point in time. Ephemeris data can be expressed in the Two-Line Element (TLE) format and can be combined with a standardized propagation model such as Simplified General Propagation (SGP4) to calculate the satellite's position and velocity at a specific point in time.

[0086] In some embodiments, the UE may combine its location information with ephemeris data to compute its own uplink timing advance (TA) value or pre-compensate its own uplink signal frequency.

[0087] In some embodiments, the UE can predict the future trajectories of satellites using ephemeris data. This enables intelligent, long-term cell selection, proactively determining and selecting satellites that will provide stable service for a longer period of time, even if the current signal is slightly weaker.

[0088] In some embodiments, the UE and satellite base station can utilize ephemeris data to perform a conditional handover (CHO). For example, the handover can be triggered based on a location-based condition (when the UE reaches a specific geographic coordinate), a time-based condition (when a specific preset time arrives), a time-of-flight (TA)-based condition, or an elevation-based condition.

[0089] Figure 6 is a conceptual diagram illustrating the operation of HARQ.

[0090] Figure 7 is a conceptual diagram illustrating RV used in HARQ.

[0091] When transmission (or retransmission) is performed, the original data bit stream (i.e., the transmission data) can be channel-coded with a forward error correction (Forward Error Correction) code such as LDPC. A Cyclic Redundancy Check (CRC) code can be inserted into the original data bit stream before channel coding. The encoded bits can be converted into a set of output bits for transmission through puncturing or rate matching. As illustrated in Fig. 7, which bits are actually transmitted is determined by the RV, and different sets of bits can be transmitted when different RVs are used. The process of selecting bits to be transmitted in different RVs can be performed using a circular buffer as illustrated in Fig. 7 and an interleaving pattern defined for each RV. As a result, each RV (RV0, RV1, RV2, RV3) provides a different portion of the rate-matched output, which can increase the probability of successful decoding at the receiving end. Each RV (RV0, RV1, RV2, RV3) can be configured by reading some of the bits stored in the circular buffer during the rate matching process, as illustrated in FIG. 7.

[0092] In a HARQ-based data transmission procedure, a first communication node (610) can transmit an RV (RV0) for transport data, and a second communication node (610) can decode the received RV and transmit a HARQ response (e.g., ACK or NACK). In addition, if retransmission is required, the first communication node (610) can transmit the next round RV (RV1, RV2, or RV3) for the transport data, and the second communication node (610) can perform decoding by combining (e.g., soft combining) the received current round RV and the previously received and stored previous round RV, and transmit a HARQ response.

[0093] Figure 6 illustrates Case 1 (Pass at the Single Reception) that succeeds at the first reception and Case 2 (Pass with Retransmission) that succeeds after retransmission.

[0094] In Example 1, the base station (610) can transmit PDSCH data encoded with the first RV (RV0) to the UE (620) via the PDSCH. After receiving and decoding the data, the UE (620) can determine whether an error has occurred. Methods for determining whether an error has occurred include, but are not limited to, a CRC-based error check, and a determination based on soft information (e.g., LLR in LDPC) obtained through FEC decoding. If it is determined that no error has occurred, the UE (620) can transmit an ACK message notifying successful reception to the base station (610) via the PUCCH or PUSCH. Since the transmission was successful with one RV transmission in Example 1, retransmission is not necessary, and the UE (620) does not need to store the data in the HARQ buffer and can transmit the decoded data to the upper layer.

[0095] In Example 2, the base station (610) can transmit PDSCH data encoded with the first RV (RV0) to the UE (620) via the PDSCH. The UE (620) can determine whether an error has occurred after receiving and decoding the data. If an error is detected, the UE (620) can transmit a NACK message to the base station (610) notifying a reception failure. The base station (610) receiving the NACK can perform a first retransmission. For example, the base station (610) can retransmit the data with a different RV (RV1) to increase the probability of successful decoding. Similarly, the UE (620) can receive the retransmitted data, combine it with the previously received RV (RV0), decode it, and then determine whether an error has occurred. If an error is detected, the UE (620) can transmit another NACK message notifying a second reception failure. The base station (610) then transmits a second retransmission, and the UE (610) receives it, decodes it by combining it with existing data, and can then determine whether an error has occurred. If no error has occurred, the UE (620) can transmit an ACK message notifying successful reception to the base station (610) via the PUCCH or PUSCH, and forward the decoded data to the upper layer.

[0096] Meanwhile, methods for increasing coverage and capacity in NTN environments are continuously being discussed. In a transparent NTN environment, the RTT from terminal to satellite to GW can exceed the delay required for VoIP (i.e., 20 msec). In this case, HARQ-based transmission techniques may be unsuitable, so blind repetition techniques have been proposed to increase coverage of VoIP services. This is because voice services on mobile devices require high performance due to low antenna gain and low transmit power. However, this method assumes a worst-case scenario regardless of channel conditions and repeats transmission a predefined fixed number of times, which inevitably increases resource consumption.

[0097] Figure 8 is a conceptual diagram for explaining the elevation angle of a satellite.

[0098] Figure 9 is a table showing the relationship between the elevation angle of a satellite, the distance between a terminal and a satellite, and the one-way propagation time in a LEO system having an altitude of 600 km.

[0099] Typically, when the LEO system's altitude is 600 km, the round-trip time can range from 4 msec to 11.52 msec as the service elevation angle varies from 90 to 20 degrees. Therefore, VoIP services can also utilize at least one HARQ feedback and retransmission. Therefore, several embodiments for service coverage enhancement and capacity-efficient HARQ in this regenerative payload-based NTN environment are disclosed.

[0100] Figure 10 is a flowchart illustrating some embodiments of HARQ for NTN.

[0101] The operation according to FIG. 10 may be performed by a first communication node (1001) or a second communication node (1002). This operation may be performed by a communication node implemented with a structure (e.g., including a transceiver and a processor) as illustrated in FIGS. 3 and 4.

[0102] Referring to FIG. 10, in a wireless communication system, a first communication node (1001) may establish a link with a second communication node (1002) (S1010). One of the first and second communication nodes (1001, 1002) may be a non-terrestrial node (e.g., a satellite-based base station). The other of the first and second communication nodes may be a terrestrial node (e.g., a UE). For example, the first communication node (1001) may be a UE, and the second communication node (1002) may be a satellite-based base station. In another example, the first communication node (1001) may be a satellite-based base station, and the second communication node (1002) may be a UE. In the following description, some embodiments will be described assuming that the first communication node (1001) is a UE and the second communication node (1002) is a satellite-based base station. However, it will be readily understood by those skilled in the art that the same principles can be implemented and described in the opposite case (i.e., when the first communication node is a satellite-based base station and the second communication node is a UE), or when a terrestrial node other than a UE is used, or when a non-terrestrial node other than a satellite-based base station (e.g., a UAV-based base station) is used.

[0103] The first communication node (1001) can transmit the first RV for transport data (S1020). To this end, the first communication node (1001) performs encoding (S1012) and first RV determination (S1015) for the transport data, and then selects an encoded bit string corresponding to the determined first RV from among the encoding results, and transmits the selected encoded bit string by loading it onto modulation symbols (e.g., OFDM symbols).

[0104] The second communication node (1002) receives and decodes the first RV from the first communication node (1001), and can transmit a response (i.e., HARQ feedback) to the first RV based on the decoding result (i.e., the result of checking whether an error occurred after channel decoding) (S1030).

[0105] If retransmission of the transmission data is required (S1032), the first communication node (1001) may transmit a secondary RV for the transmission data (S1040). For example, the first communication node (1001) may receive a response to the primary RV and determine whether retransmission is required.

[0106] The second communication node (1002) receives a secondary RV from the first communication node (1001), combines it with the previously stored primary RV, performs decoding on the combined result, and then transmits a response to the secondary RV based on the decoding result (i.e., the result of checking whether an error occurred after channel decoding) (S1050).

[0107] If a second retransmission of the transmission data is required (S1052), the first communication node (1001) can transmit a third RV for the transmission data (S1060).

[0108] The second communication node (1002) can receive the third RV from the first communication node (1001), combine it with the previously stored first and second RVs, perform decoding on the combined result, and then transmit a response to the third RV based on the decoding result (i.e., the result of checking whether an error occurred after channel decoding).

[0109] In the embodiments illustrated in FIG. 10, for convenience, the first and second RV transmissions are mainly illustrated, but it can be seen from the description of the present disclosure that more rounds of RV transmission are also expandable.

[0110] At least one of the 1st to Kth (natural number) order RVs can be selected from among multiple RV candidates based on the conditions of the link (S1015, S1035). Detailed examples related to RV selection are described below.

[0111] The conditions of the above link may change depending on the movement of the non-terrestrial node (e.g., satellite-based base station). For example, the conditions may be based on at least one of the round-trip time of the link and the elevation angle of the non-terrestrial node. The conditions may be determined based on the elapsed time since the non-terrestrial node becomes capable of providing service to the terrestrial node. For example, a timer may be started from the time the non-terrestrial node becomes capable of providing service to the terrestrial node, and the relative position (e.g., elevation angle or round-trip time) of the non-terrestrial node may be estimated based on the timer value.

[0112] When the second communication node (1002) receives the second RV for the transmission data, it can combine and decode the received first RV and the received second RV, and transmit a response to the second RV based on the decoding result (i.e., the result of checking whether an error occurred after channel decoding) (S1050).

[0113] The second communication node (1002) may allocate resources for transmission of the first RV to the first communication node (1001) before S1020, and may allocate resources for transmission of the second RV to the first communication node (1001) before S1040. For example, the second communication node (1002) may perform resource allocation for transmission of the first and second RVs according to semi-persistent scheduling. As another example, the second communication node (1002) may perform resource allocation for transmission of the first RV according to semi-persistent scheduling, and may perform resource allocation for transmission of the second RV according to dynamic scheduling.

[0114] Figures 11a to 11c are conceptual diagrams illustrating retransmission patterns (i.e., RV combinations) for high elevation angles, low elevation angles, and very low elevation angles, respectively.

[0115] When the elevation angle is high, only the systematic part of the encoding result can be sent as the first RV, as illustrated in Fig. 11a. When the elevation angle is high, the channel condition is generally good, such as a high probability of Line of Sight. Therefore, in the initial transmission, a packet (i.e., the systematic code sequence of the encoding result) can be sent, and in the retransmission, multiple RVs (i.e., N=4 RVs) can be sent as the second RV. In this case, the number of RVs to be transmitted in the retransmission (i.e., N) can be predefined and transmitted through signaling.

[0116] When the elevation angle is low, the channel condition may generally be poor. Therefore, as illustrated in Fig. 11b, in the initial transmission (i.e., the first RV transmission), a packet (i.e., a systematic code sequence among the encoding results) and N1-1 (=3) RVs (RV1, RV2, RV3) may be transmitted, and in the retransmission (i.e., the second RV transmission), N2 (=4) RVs (RV0, RV1, RV2, RV3) may be transmitted. In this case, the values ​​of N1 and N2 may be predefined and transmitted through signaling.

[0117] The case of Fig. 11a corresponds to N1=1 and N2=4.

[0118] When the elevation angle is very low, the channel conditions can generally be very poor. Therefore, as illustrated in Figure 11c, the maximum number of packets or RVs can be transmitted in the initial transmission.

[0119] Referring back to FIG. 10, in one embodiment of selecting the first and second RVs, the first communication node (1001) may select one from among a plurality of RV combination candidates based on the conditions before S1020. Each of the RV combination candidates may include 1st to Kth (natural number)th RVs. For example, when RV combination candidate 1, RV combination candidate 2, and RV combination candidate 3 are the RV combinations illustrated in FIG. 11a, FIG. 11b, and FIG. 11c, the values ​​of K, N1, and N2 of RV combination candidate 1 may be K=2, N1=1, N2=4, the values ​​of K, N1, and N2 of RV combination candidate 2 may be K=2, N1=4, N2=4, and the values ​​of K, N1, and N2 of RV combination candidate 2 may be K=1, N1=8. That is, different RV combination candidates may have different RVs of the maximum degree (K) or a specific degree. Each RV combination candidate may include RVs of the 1st to Kth (natural number) degrees. In this case, the first communication node (1001) may perform 1st RV transmission (S1020) using the 1st RV included in the selected RV combination candidate, and may perform 2nd RV transmission (S1040) using the 2nd RV included in the selected RV combination candidate. For example, the plurality of RV combination candidates may be preset in the first communication node (1001) and used for future combination candidate selection. For another example, information on the plurality of RV combination candidates may be received from the second communication node (1002) and used for future combination candidate selection. The second communication node (1002) may transmit information on the plurality of RV combination candidates through RRC signaling.

[0120] In another embodiment of selecting a primary RV, the first communication node (1001) may select one of a plurality of primary RV candidates based on the above conditions prior to S1020. In this case, the first communication node (1001) may perform primary RV transmission (S1020) using the selected primary RV candidate. For example, the plurality of primary RV candidates may be preset in the first communication node (1001) and used for selecting a primary RV candidate in the future. In another example, information about the plurality of primary RV candidates may be received from the second communication node (1002) and used for selecting a primary RV candidate in the future. The second communication node (1002) may transmit information about the plurality of primary RV candidates via RRC signaling.

[0121] In another embodiment of selecting a secondary RV, the first communication node (1001) may receive transmission result information of the primary RV from the second communication node (S1030) and transmit the secondary RV based on the received transmission result information (S1040). The transmission result information of the primary RV may include whether retransmission is necessary and information used to select the secondary RV (e.g., an identifier for the secondary RV). That is, in this case, the selection of the secondary RV may be performed by the second communication node (1002), as illustrated in FIGS. 11A and 11B . For example, the response to the primary RV may include a plurality of bits, and the plurality of bit values ​​may indicate whether retransmission is necessary and information used to select the secondary RV. FIG. 12 is a table for explaining an embodiment of an HARQ response. As illustrated in Fig. 12, a method of allocating multiple bits to a HARQ response can improve coverage and prevent resource waste due to retransmission. For example, as illustrated in bit values ​​01, 10, and 11 of Fig. 12, it is possible to instruct to transmit N (= 2, 4, 8) RVs during retransmission. For example, as illustrated in Figs. 11a and 11b, a second communication node (1002) can select a secondary RV, generate and transmit a NACK and an HARQ response specifying the selected secondary RV. The number of RVs to retransmit (i.e., N) during retransmission can be selected from the perspectives of signal quality and optimal use of resources. This is because only one retransmission is allowed, and a larger N value increases the probability of successful reception, but may also increase the possibility of resource waste. Methods for predicting signal quality include, but are not limited to, techniques utilizing the scaling of the logarithm of the likelihood ratio (LLR) of Turbo channel coding, the parity check satisfaction rate of LDPC codes, reception SINR, RSRQ, AI / ML techniques, etc.

[0122] In another embodiment of selecting the first and second RVs, the first communication node (1001) may receive information about the first RV (e.g., an identifier for the first RV) from the second communication node (1002) before S1020, and perform first RV transmission (S1010) according to the received information about the first RV. In addition, the first communication node (1001) may receive information about the second RV (e.g., an identifier for the second RV) from the second communication node (1002) before S1050, and perform second RV transmission (S1050) according to the received information about the second RV. The second communication node (1002) may transmit information about the plurality of first or second RV candidates through RRC signaling.

[0123] The operations of the method according to the present disclosure can be implemented as a computer-readable program or code on a computer-readable recording medium. A computer-readable recording medium includes any type of recording device that stores information readable by a computer system. Furthermore, a computer-readable recording medium can be distributed across network-connected computer systems, allowing the computer-readable program or code to be stored and executed in a distributed manner.

[0124] Additionally, the computer-readable recording medium may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, etc. The program instructions may include not only machine language codes produced by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc.

[0125] While some aspects of the present disclosure have been described in the context of a device, they may also represent a description of a corresponding method, wherein a block or device may correspond to a method step or feature of a method step. Similarly, aspects described in the context of a method may also be described as a corresponding block or item or 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 or more of the most significant method steps may be performed by such a device.

[0126] 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 in the present disclosure. The field-programmable gate array may operate in conjunction with a microprocessor to perform one of the methods described in the present disclosure. In general, the methods may be performed by any hardware device.

[0127] Although the present disclosure has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the claims below.

Claims

1. In a method for a first communication node to communicate with a second communication node through a link in a wireless communication system, A step of transmitting a first redundancy version (RV) of transport data; and If retransmission of the above transmission data is required, a step of transmitting a secondary RV for the above transmission data is included, One of the first and second communication nodes is a non-terrestrial node, At least one of the first RV and the second RV is selected from among a plurality of RV candidates based on the conditions of the link, The above conditions are changed according to the movement of the above non-ground node.

2. In paragraph 1, The other of the first and second communication nodes is a terrestrial node, A method wherein the above condition is based on at least one of the round trip time of the link and the elevation angle of the non-ground node.

3. In paragraph 2, The above condition is determined based on the time elapsed from the time when the non-terrestrial node becomes capable of providing service to the terrestrial node.

4. In paragraph 1, Further comprising a step of selecting one of a plurality of RV combination candidates based on the above conditions, each candidate including a first RV and a second RV; A method in which the first and second RVs for the above transmission data are included in the selected RV combination candidates.

5. In paragraph 4, Further comprising a step of receiving information about the plurality of RV combination candidates from the second communication node, A method wherein the selecting step comprises selecting one of a plurality of RV combination candidates included in the received information.

6. In paragraph 1, Further comprising a step of selecting one of a plurality of primary RV candidates based on the above conditions, A method wherein the first RV for the above transmission data is the selected first RV candidate.

7. In paragraph 6, Further comprising a step of receiving information about the plurality of primary candidates from the second communication node, A method wherein the selecting step comprises selecting one of a plurality of primary RV candidates included in the received information.

8. In the first paragraph, the step of transmitting the second RV A step of receiving transmission result information of the first RV from the second communication node; and A step of transmitting the second RV based on the received transmission result information is included, A method wherein the above transmission result information includes information on whether retransmission is necessary and information used to select the second RV.

9. In paragraph 1, The step of transmitting the first RV includes the step of transmitting the first RV based on information about the first RV received from the second communication node, A method wherein the step of transmitting the secondary RV comprises a step of transmitting the secondary RV based on information about the secondary RV received from the second communication node.

10. In a wireless communication system, a method for a second communication node to communicate with a first communication node through a link, A step of receiving a first RV for transmission data from the first communication node; A step of transmitting a response to the first RV based on the decoding result of the received first RV; and When receiving a secondary RV for the above transmission data, a step of decoding by combining the received primary RV and the received secondary RV, One of the first and second communication nodes is a non-terrestrial node, At least one of the first RV and the second RV is selected from among a plurality of RV candidates based on the conditions of the link, The above conditions are changed according to the movement of the above non-ground node.

11. In paragraph 10, The other of the first and second communication nodes is a ground node, A method wherein the above condition is based on at least one of the round trip time of the link and the elevation angle of the non-terrestrial node.

12. In paragraph 10, Further comprising the step of transmitting information about a plurality of RV combination candidates, each candidate including a first RV and a second RV, A method in which the first and second RVs are included in the candidates selected by the first communication node among the plurality of RV combination candidates.

13. A method according to claim 12, wherein the step of transmitting information about the plurality of RV combination candidates includes a step of transmitting information about the plurality of RV combination candidates through RRC signaling.

14. In paragraph 10, Further comprising a step of transmitting information about candidates of the first RV to the first communication node, A method in which the above first RV is a candidate selected by the first communication node among the candidates for the above first RV.

15. In paragraph 10, the response to the first RV is A method comprising: determining whether retransmission is necessary and information used to select the second RV.

16. In paragraph 10, A step of allocating resources for transmission of the first RV to the first communication node; and Further comprising a step of allocating resources for transmission of the second RV to the first communication node, The above resource allocation is a method of allocation using semi-persistent scheduling.

17. In paragraph 10, A step of allocating resources for transmission of the first RV to the first communication node; and Further comprising a step of allocating resources for transmission of the second RV to the first communication node, Resources for transmission of the above first RV are allocated using semi-static scheduling, A method of allocating resources for transmission of the above secondary RV using dynamic scheduling.

18. In a device for a first communication node communicating with a second communication node through a link in a wireless communication system, a transceiver; and a processor connected to the transceiver, The above processor performs an operation of transmitting a primary RV for the transmission data; and, if retransmission of the transmission data is required, an operation of transmitting a secondary RV for the transmission data. One of the first and second communication nodes is a non-terrestrial node, At least one of the first RV and the second RV is selected from among a plurality of RV candidates based on the conditions of the link, The above conditions are a device that changes according to the movement of the above non-terrestrial node.

19. In paragraph 18, The other of the first and second communication nodes is a ground node, A device wherein the above condition is based on at least one of the round trip time of the link and the elevation angle of the non-terrestrial node.

20. In paragraph 19, The above first communication node is a user equipment which is the ground node, The above second communication node is a device that is a base station located on a satellite as a non-terrestrial node.

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