KR20220140349A - Apparatus and method for transmitting downlink control information in non-terrestrial network system - Google Patents

Abstract

The present invention relates to an apparatus and method for transmitting downlink control information in a non-terrestrial network system. A wireless communication system (100) includes a plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) and a plurality of user equipment (130-1, 130-2, 130-3, 130-4, 130-5, 130-6). Each of a first base station (110-1), a second base station (110-2), and a third base station (110-3) may form a macro cell. Each of a fourth base station (120-1) and a fifth base station (120-2) may form a small cell.

Description

Apparatus and method for transmitting downlink control information in a non-terrestrial network

The present invention relates to a wireless communication system, and more particularly, to an apparatus and method for transmitting downlink control information in a non-terrestrial network.

3GPP paved the way for commercial application of 5G by completing the first global 5G New Radio (NR) standard in Release (Rel)-15. In addition, NR-based Non-Terrestrial Network (NTN) is being considered as one of the evolutionary stages of NR for the activation of 5G and expansion of the ecosystem. Due to its wide service coverage capabilities and reduced vulnerability of space/air platforms to physical attacks and natural disasters, NTN provides services in areas where terrestrial 5G networks are not serviced (isolated or remote areas, on board aircraft or ships) and areas with poor service ( Suburbs or rural areas) can provide 5G services in a cost-effective manner. It also provides continuity of service to passengers on board M2M and IoT devices or mobile platforms (aircraft, ship, high-speed train, bus, etc.) Enables 5G service support. Together, it can support the availability of 5G networks by providing efficient multicast/broadcast resources for data delivery to the network edge or user terminals. These benefits can be provided through a standalone NTN or an integrated network of ground and non-terrestrial, and are expected to have an impact in transport, public safety, media and entertainment, eHealth, energy, agriculture, finance, and automotive sectors. .

The NR-based NTN standardization study of the 3GPP RAN Working Group (WG) started with approval as a Rel-15 study item (SI) for RAN plenary and RAN1 at the RAN plenary meeting RAN#75 in March 2017. The purpose of this SI is to develop a channel model of NTN and study NTN scenario and the influence of NR accordingly, and it is summarized in Technical Report (TR) TR 38.811. Based on this, it was proposed as a Rel-16 item for standard issues requiring NTN standardization, and was approved as Rel-16 SI at the RAN#80 meeting in June 2018.

An object of the present invention is to provide an apparatus and method for transmitting downlink control information in a non-terrestrial network in a non-terrestrial network system.

Apparatus and method for transmitting downlink control information in a non-terrestrial network

More efficient data transmission/reception is possible in the network cell included in the non-terrestrial network system. In addition, it is possible to perform more efficient HARQ operation.

1 is a conceptual diagram illustrating a wireless communication system according to an embodiment of the present invention.
2 is an exemplary diagram illustrating an NR system to which a data transmission method according to an embodiment of the present invention can be applied.
3 is a diagram for explaining a resource grid supported by a radio access technology to which this embodiment can be applied.
4 is a diagram for explaining a bandwidth part supported by a radio access technology to which the present embodiment can be applied.
5 is a diagram exemplarily illustrating a synchronization signal block in a radio access technology to which the present embodiment can be applied.
6 is a diagram for explaining a random access procedure in a radio access technology to which this embodiment can be applied.
7 is a diagram for explaining various forms of a non-terrestrial network structure to which an embodiment can be applied.
8 is a diagram for explaining a HARQ processing period for setting the number of HARQ processes.
9 shows a portion of DCI according to an example.
10 is an operation flowchart of a base station and a terminal for transmitting and receiving DCI according to an example.
11 is an RRC message including a HARQ-FeedbackEnabled field according to an example.
12 shows an example in which a transport block is repeatedly transmitted from a base station in HARQ-disable mode.
13 is an operation flowchart of a base station and a terminal transmitting and receiving signals in HARQ disable mode according to an example.
14 is a block diagram of a terminal and a base station exchanging DCI according to an example.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements.

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

When a component is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but it is understood that other components may exist in between. it should be On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that the other element does not exist in the middle.

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

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

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a conceptual diagram illustrating a wireless communication system according to an embodiment of the present invention.

Referring to FIG. 1 , a wireless communication system 100 includes a plurality of communication nodes 110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3. , 130-4, 130-5, 130-6).

Each of the plurality of communication nodes may support at least one communication protocol. For example, each of the plurality of communication nodes is a CDMA (Code Division Multiple Access) based communication protocol, WCDMA (Wideband CDMA) based communication protocol, TDMA (Time Division Multiple Access) based communication protocol, FDMA (Frequency Division Multiple) Access) based communication protocol, OFDM(Orthogonal Frequency Division Multiplexing) based communication protocol, OFDMA(Orthogonal Frequency Division Multiple Access) based communication protocol, SC(Single Carrier)-FDMA based communication protocol, NOMA(Non-Orthogonal Multiplexing) Access)-based communication protocol, SDMA (space division multiple access)-based communication protocol, etc. may be supported.

The wireless communication system 100 includes a plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 and a plurality of user equipments 130-1, 130-2, 130-3, 130-4, 130-5, 130-6).

Each of the first base station 110-1, the second base station 110-2, and the third base station 110-3 may form a macro cell. Each of the fourth base station 120-1 and the fifth base station 120-2 may form a small cell. The fourth base station 120-1, the third terminal 130-3, and the fourth terminal 130-4 may belong to the coverage of the first base station 110-1. The second terminal 130-2, the fourth terminal 130-4, and the fifth terminal 130-5 may belong to the coverage of the second base station 110-2. The fifth base station 120-2, the fourth terminal 130-4, the fifth terminal 130-5, and the sixth terminal 130-6 may belong to the coverage of the third base station 110-3. . The first terminal 130-1 may belong to the coverage of the fourth base station 120-1. The sixth terminal 130-6 may belong to the coverage of the fifth base station 120-2.

Here, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 is a NodeB, an evolved NodeB, and a next generation Node B (NodeB). B, gNB), BTS (Base Transceiver Station), wireless base station (radio base station), wireless transceiver (radio transceiver), access point (access point), access node (node), road side unit (RSU), DU (Digital Unit), CDU (Cloud Digital Unit), RRH (Radio Remote Head), RU (Radio Unit), TP (Transmission Point), TRP (transmission and reception point), to be referred to as a relay node (relay node), etc. can Each of the plurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5, 130-6 is a terminal, an access terminal, a mobile terminal, It may be referred to as a station, a subscriber station, a mobile station, a portable subscriber station, a node, a device, and the like.

A plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6) Each may support cellular communication (eg, long term evolution (LTE), advanced (LTE-A), New Radio (NR), etc. defined in the 3rd generation partnership project (3GPP) standard). Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may operate in different frequency bands or may operate in the same frequency band. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to each other through an ideal backhaul or a non-ideal backhaul, and the ideal backhaul Alternatively, information may be exchanged with each other through a non-ideal backhaul. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to a core network (not shown) through an ideal backhaul or a non-ideal backhaul. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits a signal received from the core network to the corresponding terminals 130-1, 130-2, 130-3, 130 -4, 130-5, 130-6), and the signal received from the corresponding terminal (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) is transmitted to the core network can be sent to

Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may support OFDM-based downlink transmission. In addition, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may support OFDM or DFT-Spread-OFDM-based uplink transmission. In addition, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits multiple input multiple output (MIMO) (eg, single user (SU)-MIMO, MU (Multi User)-MIMO, massive MIMO, etc.), Coordinated Multipoint (CoMP) transmission, carrier aggregation transmission, transmission in an unlicensed band, direct device to device, D2D) communication (or proximity services (ProSe)) may be supported, etc. Here, each of the plurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5, 130-6 Base stations 110-1, 110-2, 110-3, 120-1, 120-2 and corresponding operations and/or base stations 110-1, 110-2, 110-3, 120-1, 120-2 ) can perform operations supported by .

For example, the second base station 110-2 may transmit a signal to the fourth terminal 130-4 based on the SU-MIMO method, and the fourth terminal 130-4 may transmit a signal based on the SU-MIMO method. A signal may be received from the second base station 110 - 2 . Alternatively, the second base station 110-2 may transmit a signal to the fourth terminal 130-4 and the fifth terminal 130-5 based on the MU-MIMO scheme, and the fourth terminal 130-4. and each of the fifth terminals 130 - 5 may receive a signal from the second base station 110 - 2 by the MU-MIMO method. Each of the first base station 110-1, the second base station 110-2, and the third base station 110-3 may transmit a signal to the fourth terminal 130-4 based on the CoMP method, and the fourth The terminal 130-4 may receive signals from the first base station 110-1, the second base station 110-2, and the third base station 110-3 by the CoMP method. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 includes the terminals 130-1, 130-2, 130-3, 130-4, 130-5, 130-6) and a signal may be transmitted/received based on the CA method.

Each of the first base station 110-1, the second base station 110-2, and the third base station 110-3 coordinates D2D communication between the fourth terminal 130-4 and the fifth terminal 130-5. (coordination), each of the fourth terminal 130-4 and the fifth terminal 130-5 is D2D communication by the coordination of each of the second base station 110-2 and the third base station 110-3 can be performed.

Hereinafter, even when a method (eg, transmission or reception of a signal) performed in a first communication node among communication nodes is described, a second communication node corresponding thereto corresponds to the method performed in the first communication node. A method (eg, receiving or transmitting a signal) may be performed. That is, when the operation of the terminal is described, the corresponding base station may perform the operation corresponding to the operation of the terminal. Conversely, when the operation of the base station is described, the corresponding terminal may perform the operation corresponding to the operation of the base station.

Also, hereinafter, downlink (DL) means communication from a base station to a terminal, and uplink (UL: uplink) means communication from a terminal to a base station. In the downlink, the transmitter may be a part of the base station, and the receiver may be a part of the terminal. In the uplink, the transmitter may be a part of the terminal, and the receiver may be a part of the base station.

Recently, as the spread of smartphones and Internet of Things (IoT) terminals is rapidly spreading, the amount of information exchanged through a communication network is increasing. Accordingly, in the next-generation wireless access technology, an environment (eg, enhanced mobile broadband communication) that provides a faster service to more users than the existing communication system (or the existing radio access technology) )) needs to be considered. To this end, design of a communication system in consideration of MTC (Machine Type Communication) providing a service by connecting a plurality of devices and objects is being discussed. In addition, the design of a communication system (eg, URLLC (Ultra-Reliable and Low Latency Communication)) considering a service and/or a terminal sensitive to communication reliability and/or latency is being discussed

Hereinafter, for convenience of description, in this specification, the next-generation radio access technology is referred to as a New Radio Access Technology (RAT), and a wireless communication system to which the New RAT is applied is referred to as a New Radio (NR) system. In the present specification, NR-related frequencies, frames, subframes, resources, resource blocks, regions, bands, subbands, control channels, data channels, synchronization signals, various reference signals, various signals or various messages are past or present. It can be interpreted in various meanings used or used in the future.

2 is an exemplary diagram illustrating an NR system to which a data transmission method according to an embodiment of the present invention can be applied.

NR, a next-generation wireless communication technology that is being standardized in 3GPP, provides an improved data rate compared to LTE, and is a radio access technology that can satisfy various QoS requirements required for each segmented and detailed usage scenario. . In particular, enhancement Mobile BroadBand (eMBB), massive MTC (mMTC), and Ultra Reliable and Low Latency Communications (URLLC) have been defined as representative usage scenarios of NR. As a method for satisfying the requirements for each scenario, a frame structure that is flexible compared to LTE is provided. The frame structure of NR supports a frame structure based on multiple subcarriers. The basic subcarrier spacing (SubCarrier Spacing, SCS) becomes 15 kHz, and 15 kHz*2^n (n=0, 1, 2, 3, 4) supports a total of 5 types of SCS.

Referring to Figure 2, the NG-RAN (Next Generation-Radio Access Network) is a control plane (RRC) protocol termination for the NG-RAN user plane (SDAP / PDCP / RLC / MAC / PHY) and UE (User Equipment) It consists of gNBs that provide Here, NG-C represents a control plane interface used for the NG2 reference point between the NG-RAN and the 5GC (5 Generation Core). NG-U represents the user plane interface used for the NG3 reference point between NG-RAN and 5GC.

gNBs are interconnected through the Xn interface, and connected to the 5GC through the NG interface. More specifically, the gNB is connected to an Access and Mobility Management Function (AMF) through the NG-C interface and to a User Plane Function (UPF) through the NG-U interface.

In the NR system of FIG. 2, multiple numerologies may be supported. Here, the numerology may be defined by a subcarrier spacing and a cyclic prefix (CP) overhead. In this case, a plurality of subcarrier intervals may be derived by scaling the basic subcarrier interval by an integer. Also, although it is assumed that very low subcarrier spacing is not used at very high carrier frequencies, the numerology used can be selected independently of the frequency band.

In addition, in the NR system, various frame structures according to a number of numerologies may be supported.

<NR Waveform, Pneumologic and Frame Structure>

In NR, a CP-OFDM waveform using a cyclic prefix is used for downlink transmission, and CP-OFDM or DFT-S-OFDM is used for uplink transmission. OFDM technology is easy to combine with MIMO (Multiple Input Multiple Output), and has advantages of using a low-complexity receiver with high frequency efficiency.

On the other hand, in NR, since the requirements for data rate, delay rate, coverage, etc. are different for each of the three scenarios described above, it is necessary to efficiently satisfy the requirements for each scenario through the frequency band constituting an arbitrary NR system. . To this end, a technique for efficiently multiplexing a plurality of different numerology-based radio resources has been proposed.

Specifically, the NR transmission numerology is determined based on sub-carrier spacing and cyclic prefix (CP), and the μ value is used as an exponential value of 2 based on 15 kHz as shown in Table 1 below. is changed to

μ subcarrier spacing
(kHz) Cyclic prefix Supported for data Supported for synch 0 15 Normal Yes Yes One 30 Normal Yes Yes 2 60 Normal, Extended Yes No 3 120 Normal Yes Yes 4 240 Normal No Yes

As shown in Table 1 above, NR pneumatology can be divided into five types according to the subcarrier spacing. This is different from the fact that the subcarrier interval of LTE, one of the 4G communication technologies, is fixed at 15 kHz. Specifically, subcarrier intervals used for data transmission in NR are 15, 30, 60, and 120 kHz, and subcarrier intervals used for synchronization signal transmission are 15, 30, 120 and 240 kHz. In addition, the extended CP is applied only to the 60 kHz subcarrier interval. On the other hand, as for the frame structure in NR, a frame having a length of 10 ms is defined, which is composed of 10 subframes having the same length of 1 ms. One frame can be divided into half frames of 5 ms, and each half frame includes 5 subframes. In the case of a 15 kHz subcarrier interval, one subframe consists of one slot, and each slot consists of 14 OFDM symbols.

<NR Physical Resources>

In relation to a physical resource in NR, an antenna port, a resource grid, a resource element, a resource block, a bandwidth part, etc. are considered do.

An antenna port is defined such that a channel on which a symbol on an antenna port is carried can be inferred from a channel on which another symbol on the same antenna port is carried. When the large-scale property of a channel carrying a symbol on one antenna port can be inferred from a channel carrying a symbol on another antenna port, the two antenna ports are QC/QCL (quasi co-located or QC/QCL) quasi co-location). Here, the wide range characteristic includes one or more of a delay spread, a Doppler spread, a Doppler shift, an average delay, and a spatial Rx parameter.

3 is a diagram for explaining a resource grid supported by a radio access technology to which this embodiment can be applied.

Referring to FIG. 3 , in the resource grid, since the NR supports a plurality of numerologies on the same carrier, a resource grid may exist according to each numerology. In addition, the resource grid may exist according to an antenna port, a subcarrier interval, and a transmission direction.

A resource block consists of 12 subcarriers, and is defined only in the frequency domain. In addition, a resource element is composed of one OFDM symbol and one subcarrier. Accordingly, as in FIG. 3 , the size of one resource block may vary according to the subcarrier interval. In addition, NR defines "Point A" serving as a common reference point for a resource block grid, a common resource block, a physical resource block, and the like.

4 is a diagram for explaining a bandwidth part supported by a radio access technology to which the present embodiment can be applied.

In NR, unlike LTE in which the carrier bandwidth is fixed at 20 MHz, the maximum carrier bandwidth is set from 50 MHz to 400 MHz for each subcarrier interval. Therefore, it is not assumed that all terminals use all of these carrier bandwidths. Accordingly, in NR, as shown in FIG. 4 , a bandwidth part (BWP) may be designated within the carrier bandwidth and used by the terminal. In addition, the bandwidth part is associated with one neurology and is composed of a subset of continuous common resource blocks, and may be dynamically activated according to time. A maximum of four bandwidth parts are configured in the terminal, respectively, in uplink and downlink, and data is transmitted/received using the bandwidth part activated at a given time.

In the case of a paired spectrum, the uplink and downlink bandwidth parts are set independently, and in the case of an unpaired spectrum, to prevent unnecessary frequency re-tunning between downlink and uplink operations For this purpose, the downlink and uplink bandwidth parts are set in pairs to share a center frequency.

<NR Initial Connection>

In NR, the terminal accesses the base station and performs a cell search and random access procedure in order to perform communication.

Cell search is a procedure in which the UE synchronizes the cell of the corresponding base station using a synchronization signal block (SSB) transmitted by the base station, obtains a physical layer cell ID, and obtains system information.

5 is a diagram exemplarily illustrating a synchronization signal block in a radio access technology to which the present embodiment can be applied.

Referring to FIG. 5, the SSB consists of a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS) occupying 1 symbol and 127 subcarriers, respectively, and a PBCH spanning 3 OFDM symbols and 240 subcarriers. .

The terminal receives the SSB by monitoring the SSB in the time and frequency domains.

SSB can be transmitted up to 64 times in 5ms. A plurality of SSBs are transmitted using different transmission beams within 5 ms, and the UE performs detection on the assumption that SSBs are transmitted every 20 ms when viewed based on one specific beam used for transmission. The number of beams that can be used for SSB transmission within 5 ms time may increase as the frequency band increases. For example, up to 4 SSB beams can be transmitted in 3 GHz or less, and SSB can be transmitted using up to 8 different beams in a frequency band of 3 to 6 GHz and up to 64 different beams in a frequency band of 6 GHz or more.

Two SSBs are included in one slot, and the start symbol and the number of repetitions within the slot are determined according to the subcarrier interval as follows.

On the other hand, the SSB is not transmitted at the center frequency of the carrier bandwidth, unlike the SS of the conventional LTE. That is, the SSB may be transmitted in a place other than the center of the system band, and a plurality of SSBs may be transmitted in the frequency domain when broadband operation is supported. Accordingly, the UE monitors the SSB using a synchronization raster that is a candidate frequency location for monitoring the SSB. The carrier raster and synchronization raster, which are the center frequency location information of the channel for initial access, are newly defined in NR, and the synchronization raster has a wider frequency interval than the carrier raster, so that it can support fast SSB search of the terminal. can

The UE may acquire the MIB through the PBCH of the SSB. MIB (Master Information Block) includes minimum information for the terminal to receive the remaining system information (RMSI, Remaining Minimum System Information) broadcast by the network. In addition, the PBCH includes information on the position of the first DM-RS symbol in the time domain, information for the UE to monitor SIB1 (eg, SIB1 neurology information, information related to SIB1 CORESET, search space information, PDCCH related parameter information), offset information between the common resource block and the SSB (the position of the absolute SSB in the carrier is transmitted through SIB1), and the like. Here, the SIB1 neurology information is equally applied to some messages used in the random access procedure for accessing the base station after the UE completes the cell search procedure. For example, the neurology information of SIB1 may be applied to at least one of messages 1 to 4 for the random access procedure.

The aforementioned RMSI may mean System Information Block 1 (SIB1), and SIB1 is periodically broadcast (eg, 160 ms) in the cell. SIB1 includes information necessary for the UE to perform an initial random access procedure, and is periodically transmitted through the PDSCH. In order for the UE to receive SIB1, it must receive neurology information used for SIB1 transmission and CORESET (Control Resource Set) information used for scheduling SIB1 through the PBCH. The UE checks scheduling information for SIB1 by using SI-RNTI in CORESET, and acquires SIB1 on PDSCH according to the scheduling information. SIBs other than SIB1 may be transmitted periodically or may be transmitted according to the request of the UE.

6 is a diagram for explaining a random access procedure in a radio access technology to which this embodiment can be applied.

Referring to FIG. 6 , upon completion of cell search, the terminal transmits a random access preamble for random access to the base station. The random access preamble is transmitted through the PRACH. Specifically, the random access preamble is transmitted to the base station through a PRACH consisting of continuous radio resources in a specific slot that is periodically repeated. In general, when the UE initially accesses the cell, a contention-based random access procedure is performed, and when random access is performed for beam failure recovery (BFR), a contention-free random access procedure is performed.

The terminal receives a random access response to the transmitted random access preamble. The random access response may include a random access preamble identifier (ID), a UL Grant (uplink radio resource), a Temporary Cell - Radio Network Temporary Identifier (TC-RNTI), and a Time Advance Command (TAC). Since one random access response may include random access response information for one or more UEs, the random access preamble identifier may be included to inform which UE the included UL Grant, TC-RNTI, and TAC are valid. The random access preamble identifier may be an identifier for the random access preamble received by the base station. The TAC may be included as information for the UE to adjust uplink synchronization. The random access response may be indicated by a random access identifier on the PDCCH, that is, RA-RNTI (Random Access - Radio Network Temporary Identifier).

Upon receiving the valid random access response, the terminal processes information included in the random access response and performs scheduled transmission to the base station. For example, the UE applies the TAC and stores the TC-RNTI. In addition, data stored in the buffer of the terminal or newly generated data is transmitted to the base station by using the UL grant. In this case, information for identifying the terminal should be included.

Non-Terrestrial Network

A non-terrestrial network refers to a network or a segment of a network using airborne vehicles such as a High Altitude Platform (HAPS) or a spaceborne vehicle such as a satellite. According to NTN defined in 3GPP, an artificial satellite is a network node that is connected to a terminal through wireless communication and provides a wireless access service to the terminal. In one aspect, a satellite in NTN may be configured to perform the same or similar functions and operations as a base station in a terrestrial network. In this case, from the viewpoint of the terminal, the artificial satellite may be recognized as another base station. In that respect, the artificial satellite introduced herein may be a concept included in the base station in a broad sense. That is, a person skilled in the art can obviously derive an embodiment in which the base station is replaced with a satellite from the embodiments depicting the base station or describing the function of the base station. Accordingly, even if such embodiments are not explicitly disclosed herein, such embodiments fall within the scope of the present specification and the spirit of the present invention.

3GPP is developing a technology for supporting NR operation in a non-terrestrial network using the aforementioned satellite or air transport vehicle. However, in the non-terrestrial network, the distance between the base station and the terminal is longer than in the terrestrial network using the terrestrial base station. This can result in very large round trip delays (RTDs). For example, in the NTN scenario using Geostationary Earth Orbiting (GEO) located at an altitude of 35,768 km, the RTD is 544.751 ms, and in the NTN scenario using HAPS located at an altitude of 229 km, the RTD is known to be 3.053 ms. In addition, the RTD in the NTN scenario using the LEO (Low Earth Orbiting) satellite system can appear up to 25.76ms. As such, in order to perform a communication operation to which the NR protocol is applied in a non-terrestrial network, a technology for supporting the base station and the terminal to perform the NR operation is required even under such propagation delay.

7 is a diagram for explaining various forms of a non-terrestrial network structure to which an embodiment can be applied.

Referring to FIG. 7 , the non-terrestrial network may be designed in a structure in which a terminal performs wireless communication using a device located in the sky. For example, the non-terrestrial network may be implemented in a structure in which a satellite or air transport device is positioned between a terminal and a base station (gNB) to relay communication, such as in the 710 structure. As another example, the non-terrestrial network may be implemented in a structure in which a satellite or air transport device performs some or all of the functions of a base station (gNB) to perform communication with a terminal, such as a 720 structure. As another example, the non-terrestrial network may be implemented as a structure in which a satellite or air transport device is positioned between a relay node and a base station (gNB) to relay communication, such as in the 730 structure. As another example, the non-terrestrial network may be implemented in a structure in which a satellite or air transport device performs some or all of the functions of a base station (gNB) to perform communication with a relay node, such as in the 740 structure.

Accordingly, in this specification, a configuration for performing communication with a terminal in connection with a core network is described as a network node or a base station, but this may refer to the aforementioned airborne vehicles or spaceborne vehicles. If necessary, a network node or a base station may refer to the same device, or may be used to distinguish different devices according to a non-terrestrial network structure.

That is, the network node or base station refers to an apparatus for transmitting and receiving data to and from a terminal in a non-terrestrial network structure, and controlling an access procedure and data transmission/reception procedure of the terminal. Accordingly, when the airborne vehicles or the spaceborne vehicle apparatus performs some or all of the functions of the base station, the network node or the base station may refer to an airborne vehicle or a spaceborne vehicle apparatus. Alternatively, when airborne vehicles or spaceborne vehicles perform a role of relaying signals of separate terrestrial base stations, the network node or base station may refer to a terrestrial base station.

Each embodiment provided below may be applied to an NR terminal through an NR base station or may be applied to an LTE terminal through an LTE base station. In addition, each embodiment provided below can be applied to an LTE terminal that connects to an eLTE base station connected through a 5G system (or 5G Core Network), and EN-DC (E-UTRA NR) that provides LTE and NR wireless connection at the same time Dual Connectivity) terminals or NE-DC (NR E-UTRA Dual Connectivity) terminals may be applied.

HARQ operation in non-terrestrial networks

In NR, HARQ retransmission scheme is applied to improve data reliability. In the case of synchronous HARQ, the retransmission time is systematically promised. Therefore, the uplink grant message sent from the base station to the terminal needs only to be transmitted during initial transmission, and subsequent retransmission is performed by the ACK/NACK signal. In the case of asynchronous HARQ, since the retransmission time is not promised to each other, the base station must send a retransmission request message to the terminal. In addition, in the case of non-adaptive HARQ, the frequency resource or MCS for retransmission is the same as the previous transmission, and in the case of adaptive HARQ, the frequency resource or MCS for retransmission may be different from the previous transmission. For example, in the case of the asynchronous adaptive HARQ scheme, since the frequency resource or MCS for retransmission varies for each transmission time, the retransmission request message may include UE ID, RB allocation information, HARQ process ID/number, RV, and NDI information. .

For NR, asynchronous (Asynchronous) adaptive (Adaptive) HARQ is supported in downlink transmission. The base station may provide the HARQ-ACK feedback timing to the terminal dynamically in DCI or semi-statically in the RRC configuration. According to the 3GPP TS 38.321 MAC specification, the MAC entity includes one HARQ entity for each serving cell, and each HARQ entity maintains 16 downlink HARQ processes. Each HARQ process is associated with a HARQ process identifier (HARQ process identifier). HARQ functions to ensure delivery between the UE and the base station in the physical layer. According to the TS 38.321 MAC standard, the HARQ operation (HARQ Operation/HARQ Procedure) for this is as follows. First, in downlink transmission, uplink feedback (HARQ feedback) is performed in response to downlink transmission/retransmission on PUCCH or PUSCH. Next, in uplink transmission, uplink HARQ retransmission may be triggered without waiting for feedback on previous transmission.

In addition, NR supports asynchronous (Asynchronous) adaptive (Adaptive) HARQ in uplink transmission. The base station schedules uplink transmission and retransmission using the uplink grant on DCI. The MAC entity includes one HARQ entity for each serving cell, and each HARQ entity maintains 16 uplink HARQ processes.

HARQ feedback (feedback) includes downlink HARQ feedback and uplink HARQ feedback. Downlink HARQ feedback is an operation in which the base station transmits downlink data or transport block to the terminal and then the terminal transmits ACK/NACK to the base station (refer to FIG. 8). In the uplink HARQ feedback, the terminal transmits uplink data or transport block is an operation in which the base station transmits ACK/NACK to the terminal after transmitting Since the downlink HARQ feedback is HARQ feedback for a physical downlink shared channel (PDSCH) that is downlink data, it may be referred to as PDSCH-to-HARQ feedback.

HARQ feedback may be operated in either a “enabled” mode or a “disabled” mode. Hereinafter, information for setting the HARQ feedback to the usable mode or the unusable mode is referred to as a HARQ feedback enabled/disabled indicator.

The subject for setting the HARQ feedback to the usable mode or the unusable mode may be a base station, and may be a terminal in a special situation such as sidelink communication. When the base station sets the HARQ feedback to the usable mode or the unusable mode, the base station may transmit a HARQ feedback enabled/disabled indicator to the terminal. In this case, the HARQ feedback enabled/disabled indicator may be transmitted while being included in downlink control information (DCI) generated in the physical layer of the base station. Alternatively, the HARQ feedback enabled/disabled indicator may be transmitted while being included in an RRC message generated in an upper layer of the base station. Alternatively, the HARQ feedback enabled/disabled indicator may be transmitted while being included in a MAC message generated in the MAC layer of the base station.

In a communication environment with a large HARQ RTT delay such as NTN, HARQ feedback may cause communication delay. For example, if the terminal fails to receive downlink data and has to wait for retransmission of downlink data after transmitting a NACK to the base station, it is not possible to decode the data until the retransmission of the data, which causes inconvenience to the user. can Therefore, in NTN, HARQ feedback may be set to unavailable mode.

If the HARQ feedback is set to the unavailable mode, the receiving side does not request retransmission even if data reception fails, and the transmitting side does not perform retransmission even if data transmission fails. In this case, in preparation for a situation in which the channel environment deteriorates, the transmitting side may operate in a mode in which the same data is continuously transmitted to the receiving side.

On the other hand, when the HARQ feedback is set to the unavailable mode, at least some of the HARQ-related procedures and signaling already defined in the NR communication system may be unnecessary or may need to be changed. For example, HARQ-related signaling includes a new data indicator (NDI) field included in DCI, a redundancy version (RV) field, and transmit power control (TPC) for a scheduled PUCCH. field, PDSCH-to-HARQ feedback timing indicator field, and the like. When HARQ feedback is set to an unusable mode (HARQ disabled), the above HARQ related signaling may be used for purposes other than the original purpose. Hereinafter, a case in which the PDSCH-to-HARQ feedback timing indicator field is used for another purpose in the HARQ disabled state will be exemplarily described, but this may be equally applied to the NCI, RV, and TPC fields. That is, in the following embodiments, the PDSCH-to-HARQ feedback timing indicator field may be replaced with the NDI field, the RV field, and the TPC field, and such replaced embodiments are also included in the embodiment of the present invention.

9 shows a portion of DCI according to an example.

Referring to FIG. 9 , the DCI for scheduling the PDSCH according to the present embodiment may have a CRC scrambled by TC-RNTI or C-RNTI, for example in format 1_0 or 1_1. DCI may include a HARQ process number field of at least 4 bits and a PDSCH-to-HARQ feedback timing indicator field of at least 3 bits.

The NR communication system is designed to be flexible rather than fixed in HARQ feedback timing, and the gap between the slot in which the PDSCH is transmitted and the slot in which the HARQ feedback regarding the PDSCH is transmitted is determined by the PDSCH-to-HARQ feedback timing indicator. .

As an example, in the case of DCI format 1_0, the PDSCH-to-HARQ feedback timing indicator field indicates one of {1, 2, 3, 4, 5, 6, 7, 8} values, and the HARQ feedback timing is {1, 2, 3, 4, 5, 6, 7, 8}.

As another example, in the case of DCI format 1_1, the HARQ feedback timing is determined by a combination of the PDSCH-to-HARQ feedback timing indicator field and dl_dataToUL-ACK information provided by higher layer signaling.

However, if the HARQ feedback is set to the unavailable mode, since the HARQ feedback does not occur, the 3-bit PDSCH-to-HARQ feedback timing indicator field is not used and may be unnecessary waste. Nevertheless, since the DCI format should be fixed, the 3-bit PDSCH-to-HARQ feedback timing indicator field should be maintained as it is, but may be defined to be used for another purpose.

For example, when the UE receives DCI including the PDSCH-to-HARQ feedback timing indicator field in a state in which the HARQ feedback is set to the unavailable mode, the UE sets the PDSCH-to-HARQ feedback timing indicator field as the first indication, PDSCH-to. - It is recognized that the second instruction is included, not the HARQ feedback timing, and a procedure or operation according to the second instruction can be performed.

As an example, the second instruction may include additional instructions specifically required for NTN communication compared to NR communication.

As another example, the second indication may include trigger information for changing the HARQ feedback to the usable mode.

As another example, the second instruction may include information capable of directly or indirectly estimating propagation delay and Doppler effect occurring in the NTN environment. And this second instruction may be used as a variable for determining the signal strength of the terminal.

For example, the second indication may be type information (LEO, GEO, etc.) of the base station (satellite), satellite position, altitude, speed information, etc., and a common (or average) stored by the base station (satellite). It may be delay time information or reference delay time information, or at least one combination thereof. In this case, each piece of information is divided into a plurality of ranges, and the second instruction may be configured in a form indicating any one of the plurality of ranges. For example, if the second instruction of 3 bits includes reference delay time information, the reference delay time has 8 ranges, such as 1~10mm (first range), 10~20mm (second range), ?? , and a total of 8 values of the 3-bit second indication may correspond to the 8 ranges in a 1:1 ratio.

As another example, the second instruction may include information for supporting forward error correction (FEC). This is to compensate for errors caused by the absence of HARQ feedback.

As another example, the second instruction may include information about beam per cell information (one/multi) or polarization mode of the base station (satellite). Neighboring cells in an NTN network may use different polarization modes for interference mitigation. These are right hand circular polarization (RHCP) and left hand circular polarization (LHCP). Accordingly, the base station (satellite) needs to transmit information about the polarization mode for NTN to the terminal, and in this case, the second instruction may be used as information about the polarization mode.

10 is an operation flowchart of a base station and a terminal for transmitting and receiving DCI according to an example.

Referring to FIG. 10, the base station sets the HARQ feedback to the unavailable mode (S1010). The mode setting of the HARQ feedback may be made in units of logical channels that process transport blocks. For example, the base station may set the first logical channel to the HARQ feedback unavailable mode and set the second logical channel to the HARQ feedback enabled mode.

The base station transmits an RRC message to the terminal to inform the terminal that the HARQ feedback is set to the unavailable mode (S1020). The RRC message is, for example, as shown in FIG. 11, and includes a HARQ-FeedbackEnabled field indicating an enable mode or a disabled mode of HARQ feedback.

The UE receives the RRC message and confirms that the HARQ feedback is set to the unavailable mode (S1030). When the HARQ feedback is in the unavailable mode, the UE interprets the PDSCH-to-HARQ feedback timing field included in the DCI transmitted from the base station later as the second indication, not the first indication.

The base station generates a DCI and transmits it to the terminal (S1040). Here, the DCI generated by the base station is, for example, as shown in FIG. x1. When the HARQ feedback is set to the unavailable mode, the base station may transmit the second indication to the terminal using the PDSCH-to-HARQ feedback timing field included in the DCI. Accordingly, the base station according to the present embodiment generates a DCI including the PDSCH-to-HARQ feedback timing field indicating the second indication. Here, the second instruction is in accordance with the above-described embodiment.

The terminal receives the DCI from the base station and checks the second indication from the PDSCH-to-HARQ feedback timing field included in the DCI (S1050).

As an example, the second instruction is a matter defined specifically for NTN communication compared to NR communication.

As another example, the second indication is trigger information for changing the HARQ feedback to the usable mode.

As another example, the second indication is information that can directly or indirectly estimate propagation delay and Doppler effect occurring in the NTN environment. For example, the second indication may be type information (LEO, GEO, etc.) of the base station (satellite), satellite position, altitude, speed information, etc., and a common (or average) stored by the base station (satellite). It may be delay time information or reference delay time information, or at least one combination thereof.

As another example, the second indication is information for supporting forward error correction (FEC).

As another example, the second indication is information about beam per cell information (one/multi) or polarization mode of the base station (satellite).

The terminal performs an appropriate operation based on the second instruction (S1060).

As an example, when the second instruction is a matter specifically defined for NTN communication versus NR communication, the terminal may perform an operation defined specifically for NTN communication.

As another example, when the second indication is trigger information for changing the HARQ feedback to the usable mode, the UE may perform an operation to change the HARQ feedback to the usable mode.

As another example, when the second instruction is information that can directly or indirectly estimate propagation delay and Doppler effect occurring in the NTN environment, the terminal selects a communication environment optimized for the NTN environment based on the second instruction can be set. For example, when the second indication is shared delay time information, the terminal may perform uplink timing advance based on the common delay time information.

As another example, when the second instruction is information for supporting forward error correction (FEC), the terminal may perform an operation for data transmission failure recovery based on the second instruction. .

As another example, when the second instruction is information about beam per cell information (one/multi) or polarization mode of the base station (satellite), the terminal transmits data with the base station based on information about the polarization mode can transmit and receive.

Meanwhile, as described above, when the HARQ feedback is set to the unavailable mode, the receiving side does not request retransmission even if data reception fails, and the transmitting side does not perform retransmission even if the data transmission fails. In this case, in preparation for a situation in which the channel environment deteriorates, the transmitter may operate in a mode in which the transport block is repeatedly transmitted to the receiver, or in an interlaced transmission mode. The interlace transmission mode is a mode in which the same data is transmitted at regular intervals at the slot level, and may be provided to achieve a diversity gain in an NTN environment in which a residual Doppler shift exists.

Referring back to FIG. 8, when the base station transmits a transport block to the terminal in a mode in which HARQ feedback is available, the terminal feeds back ACK/NACK for this. At this time, if the terminal feeds back a NACK indicating that data transmission has failed in the corresponding transport block to the base station, the terminal retransmits the same transport block to the base station. However, if the HARQ feedback is set to an unavailable mode, the base station repeatedly transmits the same transport block to the terminal on successive slots or through interlace slots as shown in FIG. 12 in case data transmission fails. Blind transmission can be performed. At this time, the base station should inform the terminal in advance of information on the HARQ enable/disable mode, information on the number of times the same transport block is repeated in the HARQ disable mode, and/or information on the interlace transmission interval. In this case, information on the number of times the same transport block is repeated and/or information on an interlace transmission interval may be indicated by the PDSCH-to-HARQ feedback timing indicator field in the DCI of FIG. 9 . Alternatively, information on the number of times the same transport block is repeated and/or information on the interlace transmission interval may be indicated by a combination of the PDSCH-to-HARQ feedback timing indicator field and the time resource allocation information field in the DCI of FIG. 9 . have.

Since the same downlink transport block in FIG. 12 is repeated, blind transmission according to FIG. 12 may be called PDSCH repetition. On the other hand, the same uplink transport block may be repeated, and blind transmission in this case may be referred to as PUSCH repetition. In addition, performing PDSCH repetition or PUSCH repetition on the same transport block may include that one transport block is segmented and transmitted in multiple consecutive slots or subframes, and consecutive slots or subframes It may include transmitting the same transport block in all frames.

12 shows an example in which the same transport block is repeated on successive slots (or subslots), but in the interlaced transmission mode, the same transport block may be repeated at regular intervals (or every n slots).

13 is an operation flowchart of a base station and a terminal transmitting and receiving signals in HARQ disable mode according to an example.

Referring to FIG. 13 , the base station sets the HARQ feedback to the unavailable mode ( S1310 ). The mode setting of the HARQ feedback may be performed in units of HARQ processes or logical channels for processing transport blocks. For example, the base station may set the first HARQ process to the HARQ feedback unavailable mode and set the second HARQ process to the HARQ feedback enabled mode.

The base station transmits an RRC message to the terminal to inform the terminal that the HARQ feedback in the specific HARQ process is set to the unavailable mode (S1320). The RRC message is, for example, as shown in FIG. 11, and includes a HARQ-FeedbackEnabled field indicating an enable mode or a disabled mode of HARQ feedback.

The UE receives the RRC message and confirms that the HARQ feedback is set to the unavailable mode (S1330). As an example, when the HARQ feedback is unavailable mode, the UE determines the number of repetitions based on the PDSCH-to-HARQ feedback timing field included in the DCI transmitted from the base station thereafter. As another example, when the HARQ feedback is unavailable mode, the terminal is based on a combination of at least one of the PDSCH-to-HARQ feedback timing field included in the DCI transmitted later from the base station and the time resource allocation information included in the DCI. Information on the number of repetitions and/or the interlace transmission interval may be determined.

The base station generates a DCI and transmits it to the terminal (S1340). Here, the DCI generated by the base station is, for example, as shown in FIG. 9 . When the HARQ feedback is set to the unavailable mode, the base station uses the PDSCH-to-HARQ feedback timing field and/or time resource allocation information included in the DCI to transmit the number of repetitions of the transport block (=k) and/or interlace transmission Information on the interval may be transmitted to the terminal. As an example, the base station according to the present embodiment generates a DCI including a PDSCH-to-HARQ feedback timing field indicating the number of repetitions (=k) of the transport block.

In this case, the PDSCH-to-HARQ feedback timing field may have a size of 3 bits, and the value of k, which is the number of repetitions of the transport block, may be set to 8 times or less, which is the maximum size that can be indicated by 3 bits.

For example, when the number of repeated transmissions of the transport block is 1, the PDSCH-to-HARQ feedback timing field may indicate 0, and when the number of repeated transmissions of the transport block is 2, the PDSCH-to-HARQ feedback timing field is 1 can be indicated.

The terminal receives the DCI from the base station, and checks the number of transmission block repetitions and/or the interlace transmission interval of the base station from the PDSCH-to-HARQ feedback timing field included in the DCI (S1350).

The base station performs physical downlink shared channel (PDSCH) repetition or interlace transmission corresponding to k times for the transport block (S1360). Here, the PDSCH repetition may be per slot, per subslot, or per subframe.

In this case, the base station may transmit the PDSCH including the same transport block to the terminal based on the value of the PDSCH-to-HARQ feedback timing field included in the DCI.

At this time, the terminal receives the PDSCH in which the same transport block is repeated k times based on the value of the PDSCH-to-HARQ feedback timing field included in the DCI received from the base station.

14 is a block diagram of a terminal and a base station exchanging DCI according to an example.

Referring to FIG. 14 , the base station 1500 includes a processor 1510 , a memory 1520 , and a transceiver 1530 . The terminal 1400 includes a processor 1410 , a memory 1420 , and a transceiver 1430 .

First, the processor 1510 of the base station 1500 may set the HARQ feedback to an enable or disable mode. In this embodiment, processor 1510 sets HARQ feedback to disabled mode. The mode setting of the HARQ feedback may be made in units of logical channels that process transport blocks. For example, the processor 1510 may set the first logical channel to the HARQ feedback disabled mode and set the second logical channel to the HARQ feedback enabled mode.

The processor 1510 generates an RRC message for informing the terminal that the HARQ feedback is set to the unavailable mode, and transmits it to the terminal 1400 through the transceiver 1530 . The RRC message is, for example, as shown in FIG. x3, and includes a HARQ-FeedbackEnabled field indicating an enabled mode or a disabled mode of HARQ feedback.

The transceiver 1430 of the terminal 1400 receives the RRC message, and the processor 1410 confirms that the HARQ feedback is set to the unavailable mode. When the HARQ feedback is in the unavailable mode, the processor 1410 interprets the PDSCH-to-HARQ feedback timing field included in the DCI transmitted from the base station 1500 later as the second indication, not the first indication.

The processor 1510 of the base station 1500 generates a DCI and transmits it to the terminal 1400 through the transceiver 1530 . Here, the DCI generated by the processor 1510 of the base station 1500 is, for example, as shown in FIG. 9 . When the HARQ feedback is set to the unavailable mode, the processor 1210 of the base station 1200 may transmit the second indication to the terminal using the PDSCH-to-HARQ feedback timing field included in the DCI. Accordingly, the processor 1510 of the base station 1500 according to the present embodiment generates a DCI including the PDSCH-to-HARQ feedback timing field indicating the second indication. Here, the second instruction is in accordance with the above-described embodiment.

The transceiver 1430 of the terminal 1400 receives the DCI from the base station 1500 , and the processor 1410 checks the second indication from the PDSCH-to-HARQ feedback timing field included in the DCI.

As an example, the second instruction is a matter defined specifically for NTN communication compared to NR communication.

As another example, the second indication is trigger information for changing the HARQ feedback to the usable mode.

As another example, the second indication is information that can directly or indirectly estimate propagation delay and Doppler effect occurring in the NTN environment. For example, the second indication may be type information (LEO, GEO, etc.) of the base station (satellite), satellite position, altitude, speed information, etc., and the common (or average) stored by the base station (satellite). It may be delay time information or reference delay time information, or at least one combination thereof.

As another example, the second indication is information for supporting forward error correction (FEC).

As another example, the second indication is information about beam per cell information (one/multi) or polarization mode of the base station (satellite).

As another example, the second indication is information about the number of repetitions of a transport block transmitted from the base station to the terminal.

As another example, the second indication is information about the number of repetitions of a transport block transmitted from the base station to the terminal.

The processor 1410 of the terminal 1400 performs an appropriate operation based on the second instruction.

As an example, when the second instruction is a matter specifically defined for NTN communication versus NR communication, the processor 1410 may perform an operation defined specifically for NTN communication.

As another example, when the second indication is trigger information for changing the HARQ feedback to the usable mode, the processor 1410 may perform an operation to change the HARQ feedback to the usable mode.

As another example, when the second instruction is information that can directly or indirectly estimate propagation delay and Doppler effect occurring in the NTN environment, the terminal selects a communication environment optimized for the NTN environment based on the second instruction can be set. For example, when the second indication is shared delay time information, the processor 1410 may perform uplink timing advance based on the common delay time information.

As another example, when the second instruction is information for supporting forward error correction (FEC), the processor 1410 performs an operation for recovering data transmission failure based on the second instruction. can do.

As another example, when the second instruction is information about beam per cell information (one/multi) or polarization mode of the base station (satellite), the processor 1410 is based on the information about the polarization mode, the base station Data can be transmitted and received with 1500 .

In the exemplary system described above, methods that can be implemented according to the features of the present invention described above have been described on the basis of a flowchart. For convenience, the methods have been described as a series of steps or blocks, however, the claimed features of the invention are not limited to the order of steps or blocks, and some steps may occur in a different order or concurrently with other steps as described above. In addition, those skilled in the art will understand that the steps shown in the flowchart are not exhaustive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the present invention.

Claims (1)

Apparatus and method for transmitting downlink control information in a non-terrestrial network

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