Channel access method for transmitting in unlicensed bands and device using the same

Abstract

To provide a base station of a wireless communication system.SOLUTION: The base station of wireless communication includes a communication module and a processor. The processor is configured to receive a grant for scheduling a plurality of uplink transmissions from the base station, and, when the terminal attempts a first fixed duration-based channel access for a first transmission being one of the uplink transmissions and fails in the first fixed duration-based channel access, attempt a second fixed duration-based channel access for a second transmission being a transmission following the first transmission.SELECTED DRAWING: Figure 20

Description

[Technical Field]

[0001] The present invention relates to a new wireless communication system, and more particularly to a channel access method and an apparatus using the same in a wireless communication system operating in an unlicensed band. [Background technology]

[0002] Since the commercialization of 4G (4th generation) communication systems, efforts have been made to develop new 5G (5th generation) communication systems to meet the increasing demand for wireless data traffic. 5G communication systems are also called communication systems beyond 4G networks, post-LTE systems, or new radio (NR) systems. To achieve high data transmission rates, 5G communication systems include systems operating using ultra-high frequency (mmWave) bands above 6 GHz. Furthermore, to ensure coverage, communication systems operating using frequency bands below 6 GHz are also being considered for implementation in base stations and terminals.

[0003] The 3GPP (registered trademark, hereinafter the same) (3rd generation partnership project) NR system improves network spectral efficiency, allowing carriers to provide more data and voice services within a given bandwidth. Therefore, the 3GPP NR system is designed to meet the demand for high-speed data and media transmission in addition to high-capacity voice support. The advantages of the NR system include high throughput, low latency, support for frequency division duplex (FDD) and time division duplex (TDD) on the same platform, an improved end-user experience, and low operating costs due to a simple architecture.

[0004] For more efficient data processing, dynamic TDD in the NR system can use a scheme of varying the number of orthogonal frequency division multiplexing (OFDM) symbols available for uplink and downlink use according to the data traffic direction of users in the cell. For example, if the downlink traffic of a cell is greater than the uplink traffic, the base station can allocate a relatively large number of downlink OFDM symbols to a slot (or subframe). Information about the slot configuration needs to be transmitted to the terminal.

[0005] To mitigate the path loss of radio waves in the ultra-high frequency band and increase the transmission distance of radio waves, technologies being discussed for 5G communication systems include beamforming, massive MIMO, full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, hybrid beamforming that combines analog beamforming and digital beamforming, and large scale antenna technology. In addition, to improve the system's network, technological developments are being made in the 5G communication system regarding advanced small cells, improved small cells, cloud radio access networks (cloud RAN), ultra-dense networks, device to device communication (D2D), vehicle to everything communication (V2X), wireless backhaul, non-terrestrial network communication (NTN), moving networks, cooperative communication, coordinated multi-points (CoMP), and interference cancellation.Other advanced coding modulation (ACM) methods being developed for 5G systems include hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC), as well as advanced access technologies such as filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA).

[0006] Meanwhile, the Internet, a human-centered network where humans generate and consume information, is evolving into the IoT (Internet of Things) network, which exchanges and processes information among distributed components such as objects. IoE (Internet of Everything) technology, which combines big data processing technology through connections with cloud servers, is also emerging. To realize the IoT, technological elements such as sensing technology, wired and wireless communication and network infrastructure, service interface technology, and security technology are required. Recently, research has focused on sensor networks, machine-to-machine (M2M), and machine-type communication (MTC) technologies for connecting objects. In an IoT environment, intelligent IT (internet technology) services are provided that collect and analyze data generated by connected objects and create new value in human life. Through the integration and convergence of traditional IT technology and various industries, the IoT is being applied to areas such as smart homes, smart buildings, smart cities, smart or connected cars, smart grids, healthcare, smart home appliances, and advanced medical services.

[0007] Therefore, various attempts are being made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine-to-machine, and MTC are being implemented using 5G communication technologies such as beamforming, MIMO, and array antennas. The application of cloud radio access networks (cloud RAN), the big data processing technology mentioned above, is also an example of the fusion of 5G and IoT technologies. Generally, mobile communication systems were developed to provide voice services while ensuring user activity.

[0008] However, the mobile communication system has gradually expanded its service area from voice to data services, and has now developed to the extent that it can provide high-speed data services. However, due to resource shortages in currently provided mobile communication systems and users' demands for higher speed services, a more advanced mobile communication system is required.

[0009] In recent years, as mobile traffic has increased rapidly with the proliferation of smart devices, existing licensed frequency spectrums or licensed frequency bands have become unable to withstand the increasing data usage for providing cellular communication services.

[0010] In this situation, the use of unlicensed frequency spectrum or unlicensed frequency bands (e.g., 2.4 GHz band, 5 GHz band, 6 GHz band, bands above 52.6 GHz, etc.) to provide cellular communication services is being discussed as a solution to the spectrum shortage problem.

[0011] Unlike licensed bands, where telecommunications carriers secure exclusive frequency usage rights through procedures such as auctions, unlicensed bands can be used simultaneously by an unlimited number of communication devices, provided that they comply with certain levels of adjacent band protection regulations. As a result, when unlicensed bands are used for cellular communication services, it is difficult to guarantee the same level of communication quality as that provided in licensed bands, and interference problems may occur with wireless communication devices (e.g., wireless LAN devices) that already use unlicensed bands.

[0012] To use LTE and NR technologies in unlicensed bands, research must be conducted on coexistence methods with existing unlicensed band devices and methods for efficiently sharing radio channels with other wireless communication devices. In other words, a robust coexistence mechanism (RCM) must be developed to prevent devices using LTE and NR technologies in unlicensed bands from affecting existing unlicensed band devices. Summary of the Invention [Problem to be solved by the invention]

[0013] It is an object of one embodiment of the present invention to provide a channel access method for transmission in a wireless communication system operating in an unlicensed spectrum and an apparatus using the same. [Means for solving the problem]

[0014] According to an embodiment of the present invention, a terminal that wirelessly communicates with a base station in an unlicensed band includes a communication module and a processor that controls the communication module. The processor receives a grant from the base station to schedule multiple uplink transmissions, and the terminal attempts first fixed-duration-based channel access for a first transmission, which is one of the multiple uplink transmissions, and, if the first fixed-duration-based channel access fails, attempts second fixed-duration-based channel access for a second transmission, which is a transmission subsequent to the first transmission. The first fixed-duration-based channel access is channel access in which, if a channel is sensed to be idle within the first fixed duration, the terminal that performs the first fixed-duration-based channel access is allowed to transmit immediately after the first fixed duration. The second fixed-duration-based channel access is channel access in which, if a channel is sensed to be idle during the second fixed duration, the terminal that performs the second fixed-duration-based channel access is allowed to transmit immediately after the second fixed duration.

[0015] The first fixed duration may be shorter than the second fixed duration.

[0016] The first fixed duration may be 16 us and the second fixed duration may be 25 us.

[0017] The grant may indicate a fixed duration-based channel access as a channel access type and may indicate a channel access priority to be used to access the channel on which the multiple uplink transmissions are carried.

[0018] The grant may indicate the first fixed duration based channel access as a channel access type.

[0019] The grant may include one or more grants that schedule the multiple uplink transmissions, the multiple uplink transmissions being consecutive in time with no gaps.

[0020] A base station for wirelessly communicating with a terminal in an unlicensed band according to an embodiment of the present invention includes a communication module and a processor for controlling the communication module. When a duration of a transmission from the terminal is less than a maximum channel occupancy time and a gap between the transmission from the terminal and a transmission to the terminal is not greater than a first fixed duration, the processor transmits to the terminal within the maximum channel occupancy time without sensing immediately after the gap on the channel on which the transmission from the terminal was performed. In this case, the first fixed duration is 16 us.

[0021] If a gap between the transmission of the terminal and a transmission to the terminal is not greater than a first fixed duration, the processor transmits to the terminal immediately after the gap without sensing within a pre-specified duration, and the pre-specified duration may be a constraint applied to the transmission of the base station separately from the maximum channel occupancy time.

[0022] The processor may attempt first fixed duration-based channel access on a channel on which the transmission of the terminal is performed when a gap between the transmission of the terminal and a transmission to the terminal is equal to a first fixed duration. The first fixed duration-based channel access may be channel access in which, when a channel is sensed to be idle within the first fixed duration, a base station performing the first fixed duration-based channel access is allowed to perform transmission immediately after the first fixed duration.

[0023] If the gap between the transmission of the terminal and the transmission to the terminal is not greater than a second fixed duration, the processor attempts second fixed-duration-based channel access on the channel on which the transmission of the terminal was made. The second fixed-duration-based channel access may be channel access in which, if the channel is sensed to be idle during the second fixed duration, the base station performing the second fixed-duration-based channel access is allowed to transmit immediately after the second fixed duration. In this case, the second fixed duration may be 25 us.

[0024] The channel occupation, including the transmission of the terminal and the transmission of the base station to the terminal, may be initiated by the base station.

[0025] The channel occupation, including the transmission of the terminal and the transmission of the base station to the terminal, may be initiated by the terminal.

[0026] A method for operating a terminal that wirelessly communicates with a base station in an unlicensed band according to an embodiment of the present invention may include receiving, from the base station, a grant for scheduling a plurality of uplink transmissions; attempting, by the terminal, first fixed duration-based channel access for a first transmission that is one of the plurality of uplink transmissions; and, if the first fixed duration-based channel access fails, attempting second fixed duration-based channel access for a second transmission that is a transmission subsequent to the first transmission. In this case, the first fixed duration-based channel access may be channel access in which, if a channel is sensed to be idle within a first fixed duration, the terminal that performs the first fixed duration-based channel access is allowed to transmit immediately after the first fixed duration, and the second fixed duration-based channel access may be channel access in which, if a channel is sensed to be idle during a second fixed duration, the terminal that performs the second fixed duration-based channel access is allowed to transmit immediately after the second fixed duration.

[0027] The first fixed duration may be shorter than the second fixed duration.

[0028] The first fixed duration may be 16 us and the second fixed duration may be 25 us.

[0029] The grant may indicate a fixed duration-based channel access as a channel access type and may indicate a channel access priority to be used to access the channel on which the multiple uplink transmissions are carried.

[0030] The grant may indicate the first fixed duration based channel access as a channel access type.

[0031] The grant may include one or more grants that schedule the multiple uplink transmissions, the multiple uplink transmissions being consecutive in time with no gaps.

[0032] According to an embodiment of the present invention, a method for operating a base station for wirelessly communicating with a terminal in an unlicensed band includes, when a duration of a transmission of the terminal is less than a maximum channel occupancy time and a gap between the transmission of the terminal and a transmission to the terminal is not greater than a first fixed duration, transmitting to the terminal within the maximum channel occupancy time without sensing immediately after the gap on a channel on which the transmission of the terminal is performed, wherein the first fixed duration is 16 us.

[0033] The method may further include, when a gap between the transmission of the terminal and a transmission to the terminal is not greater than a first fixed duration, immediately transmitting to the terminal after the gap without sensing within a pre-specified duration, wherein the pre-specified duration may be a constraint applied to the transmission of the base station separately from the maximum channel occupancy time.

[0034] The method may further include attempting first fixed duration-based channel access on a channel on which the transmission of the terminal is performed when a gap between the transmission of the terminal and a transmission to the terminal is equal to a first fixed duration. In this case, the first fixed duration-based channel access may be channel access in which, when a channel is sensed to be idle within the first fixed duration, a base station performing the first fixed duration-based channel access is allowed to perform transmission immediately after the first fixed duration.

[0035] The method may further include attempting second fixed duration-based channel access on the channel on which the transmission of the terminal is performed when a gap between the transmission of the terminal and a transmission to the terminal is not greater than a second fixed duration. In this case, the second fixed duration-based channel access may be channel access in which, if the channel is sensed to be idle during the second fixed duration, the base station performing the second fixed duration-based channel access is allowed to perform transmission immediately after the second fixed duration. In addition, the second fixed duration may be 25 us.

[0036] The channel occupation, including the transmission of the terminal and the transmission of the base station to the terminal, may be initiated by the base station.

[0037] The channel occupation, including the transmission of the terminal and the transmission of the base station to the terminal, may be initiated by the terminal. [Effects of the Invention]

[0038] One embodiment of the present invention provides a channel access method for transmitting in a wireless communication system operating in an unlicensed spectrum and an apparatus using the same.

[0039] The effects obtained from the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those having ordinary skill in the art to which the present invention pertains from the following description. [Brief explanation of the drawings]

[0040] [Figure 1] FIG. 1 is a diagram illustrating an example of a radio frame structure used in a wireless communication system. [Figure 2] 1 is a diagram illustrating an example of a downlink (DL) / uplink (UL) slot structure in a wireless communication system. [Figure 3]1 is a diagram illustrating physical channels used in a 3GPP system (e.g., NR) and a general signal transmission method using the physical channels. [Figure 4] FIG. 1 illustrates an SS / PBCH block for initial cell access in a 3GPP NR system. [Figure 5] FIG. 1 illustrates a procedure for control information and control channel transmission in a 3GPP NR system. [Figure 6] A diagram showing a CORESET in which PDCCH is transmitted in a 3GPP NR system. [Figure 7] A diagram showing a method for setting a PDCCH search space in a 3GPP NR system. [Figure 8] FIG. 8 is a conceptual diagram illustrating carrier aggregation. [Figure 9] FIG. 1 is a diagram for explaining terminal carrier communication and multi-carrier communication. [Figure 10] A diagram showing an example in which a cross-carrier scheduling technique is applied. [Figure 11] 1 is a diagram illustrating a code block group (CBG) configuration and its time-frequency resource mapping according to an embodiment of the present invention; [Figure 12] 1 is a diagram illustrating a process in which a base station performs TB-based transmission or CBG-based transmission according to an embodiment of the present invention, and a terminal transmits HARQ-ACK in response thereto. [Figure 13] FIG. 1 is a diagram illustrating an NR-U (NR-Unlicensed) service environment. [Figure 14] FIG. 1 is a diagram illustrating an example of a deployment scenario of a terminal and a base station in an NR-U service environment. [Figure 15] 1 is a diagram illustrating an existing communication system (e.g., wireless LAN) that operates in an unlicensed band. [Figure 16] FIG. 1 is a diagram illustrating a channel access process based on Category 4 LBT according to an embodiment of the present invention. [Figure 17]FIG. 1 illustrates an embodiment of a method for adjusting a contention window size (CWS) based on HARQ-ACK feedback. [Figure 18] 2A and 2B are block diagrams showing the configurations of a terminal and a base station according to an embodiment of the present invention. [Figure 19] FIG. 10 is a diagram showing that in an embodiment of the present invention, if the duration of the initiating node's transmission within the channel occupation initiated by the initiating node does not exceed the MCOT of the channel occupation, the responding node transmits within the COT initiated by the initiating node. [Figure 20] FIG. 10 is a diagram illustrating the operation of a terminal in an embodiment of the present invention when downlink transmission cannot occupy MCOT within the channel occupation initiated by the base station and the terminal's transmission is scheduled or configured by the base station. DETAILED DESCRIPTION OF THE INVENTION

[0041] The terms used in this specification are generally used as widely as possible, taking into consideration the functions of the present invention. However, these may vary depending on the intentions of those skilled in the art, practice, or the emergence of new technologies. In addition, in certain cases, the applicant may arbitrarily select terms. In such cases, the meaning of the terms will be described in the description of the relevant invention. Therefore, it is clear that the terms used in this specification should be analyzed based on the substantive meaning of the terms and the overall content of this specification, rather than simply the names of the terms.

[0042] Throughout this specification, when a component is said to be "connected" to another component, this includes not only "directly connected" but also "electrically connected" through other components in between. Furthermore, when a component is said to "comprise" a specific component, this does not mean excluding the other component, but also means including the other component, unless otherwise specified to the contrary. In addition, limitations such as "more than" or "less than" based on a specific threshold may be appropriately replaced with "more than" or "less than," respectively, depending on the embodiment.

[0043] The following technologies are used in various wireless access systems, such as CDMA (code division multiple access), FDMA (frequency division multiple access), TDMA (time division multiple access), OFDMA (orthogonal frequency division multiple access), and SC-FDMA (single carrier frequency division multiple access). CDMA is implemented in radio technologies such as UTRA (Universal Terrestrial Radio Access) and CDMA2000. TDMA is implemented in radio technologies such as GSM (Global System for Mobile communications), GPRS (General Packet Radio Service), and EDGE (Enhanced Data Rates for GSM Evolution). OFDMA is implemented in radio technologies such as IEEE802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE802-20, and E-UTRA (Evolved UTRA). UTRA is part of UMTS (Universal Mobile Telecommunications System). 3GPP LTE (Long term evolution) is a part of E-UMTS (Evolved UMTS) that uses E-UTRA, and LTE-A (Advanced) is an evolved version of 3GPP LTE. 3GPP NR is a system designed separately from LTE / LTE-A and is a system for supporting eMBB (enhanced Mobile Broadband), URLLC (Ultra-Reliable and Low Latency Communication), and mMTC (massive Machine Type Communication) services, which are requirements of IMT-2020. For clarity of explanation, the following description will focus on 3GPP NR, but the technical concept of the present invention is not limited thereto.

[0044] Unless otherwise specified herein, the base station may include a next generation node B (gNB) defined in 3GPP NR. Also, unless otherwise specified, the terminal may include a user equipment (UE). Hereinafter, to facilitate understanding of the description, each content will be described as a separate embodiment, but each embodiment may be used in combination with each other. In this disclosure, "configuring" a terminal may mean configuration by a base station. Specifically, the base station may transmit a channel or a signal to the terminal to configure the operation of the terminal or parameter values ​​used in the wireless communication system.

[0045] FIG. 1 is a diagram illustrating an example of a radio frame structure used in a radio communication system.

[0046] Referring to FIG. 1, a radio frame used in a 3GPP NR system has a length of 10 ms (ΔfmaxNf / 100)*Tc). Each radio frame consists of 10 equally sized subframes (SF). Here, Δfmax=480*103 Hz, Nf=4096, Tc=1 / (Δfref*Nf,ref), Δfref=15*103 Hz, and Nf,ref=2048. The 10 subframes in a frame are numbered 0 to 9. Each subframe has a length of 1 ms and consists of one or more slots depending on the subcarrier spacing. More specifically, the subcarrier spacing that can be used in a 3GPP NR system is 15*2 μkHz. μ is the subcarrier spacing configuration factor and has values ​​from 0 to 4. That is, 15 kHz, 30 kHz, 60 kHz, 120 kHz, or 240 kHz is used as the subcarrier spacing. A 1 ms long subframe consists of 2μ slots, each of which is 2-μms long. The 2μ slots in one subframe are numbered from 0 to 2μ-1. The slots in one radio frame are numbered from 0 to 10*2μ-1. Time resources are divided by at least one of the radio frame number (also called radio frame index), subframe number (also called subframe index), and slot number (or slot index).

[0047] 2 is a diagram illustrating an example of a downlink (DL) / uplink (UL) slot structure in a wireless communication system, particularly illustrating a resource grid structure of a 3GPP NR system.

[0048] There is one resource grid per antenna port. Referring to FIG. 2, a slot includes multiple OFDM symbols in the time domain and multiple resource blocks (RBs) in the frequency domain. An OFDM symbol also refers to one symbol interval. Unless otherwise specified, an OFDM symbol is simply referred to as a symbol. Hereinafter, the term "symbol" includes OFDM symbols, SC-FDMA symbols, DFTs-OFDM symbols, etc. Referring to FIG. 2, a signal transmitted from each slot is represented by a resource grid consisting of Nsize, μgrid, x*NRBSC subcarriers, and Nslotsymb OFDM symbols. Here, x=DL for the downlink resource grid and x=UL for the uplink resource grid. Nsize, μgrid, and x denote the number of resource blocks (RBs) according to the subcarrier spacing factor μ (x is DL or UL), and Nslotsymb denotes the number of OFDM symbols in a slot. NRBSC is the number of subcarriers constituting one RB, and NRBSC=12. Depending on the multiple access method, the OFDM symbol is called a cyclic prefix OFDM (CP-OFDM) symbol or a discrete Fourier transform spread OFDM (DFT-S-OFDM) symbol.

[0049] The number of OFDM symbols included in one slot may vary depending on the length of the cyclic prefix (CP). For example, a normal CP includes 14 OFDM symbols, while an extended CP includes 12 OFDM symbols. In a specific embodiment, the extended CP is used only with a subcarrier spacing of 60 kHz. For convenience of explanation, FIG. 2 illustrates a case where one slot consists of 14 OFDM symbols. However, the present invention is equally applicable to slots having other numbers of OFDM symbols. Referring to FIG. 2, each OFDM symbol includes Nsize, μgrid, and x*NRBSC subcarriers in the frequency domain. Subcarriers are classified into data subcarriers for transmitting data, reference signal subcarriers for transmitting reference signals, and guard bands. The carrier frequency is also called the center frequency (fc).

[0050] One RB is defined by NRBSC (e.g., 12) consecutive subcarriers in the frequency domain. Incidentally, a resource consisting of one OFDM symbol and one subcarrier is called a resource element (RE) or tone. Therefore, one RB consists of Nslotsymb*NRBSC resource elements. Each resource element in the resource grid is uniquely defined by an index pair (k, l) within one slot. k is an index ranging from 0 to Nsize, μgrid, x*NRBSC-1 in the frequency domain, and l is an index ranging from 0 to Nslotsymb-1 in the time domain.

[0051] In order for a terminal to receive a signal from a base station or transmit a base station signal, the time / frequency synchronization of the terminal must be aligned with the time / frequency synchronization of the base station, because if the base station and the terminal are not synchronized, the terminal cannot determine the time and frequency parameters required to demodulate DL signals and transmit UL signals at the correct time.

[0052] Each symbol in a radio frame operating in time division duplex (TDD) or unpaired spectrum consists of at least one of a downlink symbol (DL symbol), an uplink symbol (UL symbol), or a flexible symbol. A radio frame operating on a downlink carrier in frequency division duplex (FDD) or paired spectrum consists of downlink symbols or flexible symbols, and a radio frame operating on an uplink carrier consists of uplink symbols or flexible symbols. A downlink symbol allows downlink transmission but not uplink transmission, and an uplink symbol allows uplink transmission but not downlink transmission. Whether a flexible symbol is used for downlink or uplink is determined depending on the signal.

[0053] Information about the type of each symbol, i.e., information indicating any one of downlink symbols, uplink symbols, and flexible symbols, is formed by a cell-specific (or common) RRC signal. The information about each symbol type is additionally formed by a UE-specific (or dedicated) RRC signal. The base station uses the cell-specific RRC signal to notify i) the period of the cell-specific slot configuration, ii) the number of slots having only downlink symbols from the beginning of the period of the cell-specific slot configuration, iii) the number of downlink symbols from the first symbol in the slot immediately following the slot having only downlink symbols, iv) the number of slots having only uplink symbols from the end of the period of the cell-specific slot configuration, and v) the number of uplink symbols from the last symbol in the slot immediately preceding the slot having only uplink symbols. Here, symbols that are not configured as either uplink or downlink symbols are flexible symbols.

[0054] If the information regarding the symbol type consists of the UE-specific RRC signal, the base station signals whether the flexible symbol is a downlink symbol or an uplink symbol using the cell-specific RRC signal. At this time, the UE-specific RRC signal cannot change a downlink symbol or an uplink symbol consisting of the cell-specific RRC signal to another symbol type. The specific UE RRC signal signals, for each slot, the number of downlink symbols among the Nslotsymb symbols of the slot and the number of uplink symbols among the Nslotsymb symbols of the slot. At this time, the downlink symbols of the slot are continuously configured from the first symbol to the i-th symbol of the slot. Also, the uplink symbols of the slot are continuously configured from the j-th symbol to the last symbol of the slot (where i < j). In a slot, a symbol that is not configured as either an uplink symbol or a downlink symbol is a flexible symbol.

[0055] The type of symbol configured by the RRC signal as described above can be called a semi-static DL / UL configuration. In the semi-static DL / UL configuration configured by the RRC signal previously, the flexible symbol may be indicated as a downlink symbol, an uplink symbol, or a flexible symbol by the dynamic SFI (slot format information) transmitted on the physical downlink control channel (PDCCH). At this time, a downlink symbol or an uplink symbol configured by the RRC signal is not changed to another symbol type. Table 1 exemplifies the dynamic SFI that the base station can indicate to the UE.

[0056]

Table 1

[0057] In Table 1, D represents a downlink symbol, U represents an uplink symbol, and X represents a flexible symbol. As shown in Table 1, up to two DL / UL switchings may be allowed within one slot.

[0058] FIG. 3 is a diagram illustrating physical channels used in a 3GPP system (for example, NR) and a general signal transmission method using the physical channels.

[0059] When a terminal is powered on or newly enters a cell, the terminal performs an initial cell search (S101). Specifically, the terminal synchronizes with a base station during the initial cell search. To do this, the terminal receives a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) from the base station to synchronize with the base station and acquire information such as a cell index. Next, the terminal receives a physical broadcast channel from the base station to acquire broadcast information within the cell.

[0060] After completing the initial cell search, the terminal receives a physical downlink shared channel (PDSCH) via a physical downlink control channel (PDCCH) and information carried on the PDCCH to acquire more detailed system information than that acquired through the initial cell search (S102). Here, the system information transmitted to the terminal is cell-common system information for the terminal to operate correctly in a physical layer in Radio Resource Control (RRC), and is called remaining system information or system information block (SIB) 1.

[0061] When a terminal first connects to a base station or when there are no radio resources for signal transmission (when the terminal is in RRC_IDLE mode), the terminal can perform a random access procedure with the base station (steps S103 to S106). First, the terminal transmits a preamble on a physical random access channel (PRACH) (S103) and can receive a response message for the preamble from the base station on a PDCCH and a corresponding PDSCH (S104). If the terminal receives a valid random access response message, the terminal transmits data including its own identifier, etc. to the base station on a physical uplink shared channel (PUSCH) indicated by an uplink grant transmitted from the base station on the PDCCH (S105). Next, the terminal waits for reception of a PDCCH as instructed by the base station to resolve collisions. If the terminal successfully receives the PDCCH with its own identifier (S106), the random access procedure ends. During the random access procedure, the terminal can acquire terminal-specific system information required for the terminal to operate correctly in the physical layer of the RRC layer. If the terminal acquires the terminal-specific system information in the RRC layer, the terminal enters the RRC connected mode (RRC_CONNECTED mode).

[0062] The RRC layer is used to generate and manage messages for control between a terminal and a radio access network (RAN). Furthermore, the base station and terminal can broadcast cell system information required for all terminals in the cell, manage paging message transmission, manage mobility and handover, report terminal measurements and related control, and manage and store terminal capabilities at the RRC layer. Generally, the update of signals transmitted at the RRC layer (hereinafter referred to as RRC signals) is longer than the transmission / reception period (i.e., transmission time interval, TTI) at the physical layer, so that the RRC configuration can be maintained unchanged for a long period.

[0063] After the above procedures, the UE receives a PDCCH / PDSCH (S107) and transmits a physical uplink shared channel (PUSCH) / physical uplink control channel (PUCCH) (S108) as a general uplink / downlink signal transmission procedure. In particular, the UE receives downlink control information (DCI) via the PDCCH. The DCI includes control information such as resource allocation information for the UE. The format of the DCI may vary depending on the purpose of use. The uplink control information (UCI) transmitted by the UE to the base station via the uplink includes a downlink / uplink ACK / NACK signal, a channel quality indicator (CQI), a precoding matrix index (PMI), a rank indicator (RI), etc. Here, the CQI, PMI, and RI are included in channel state information (CSI). In the case of a 3GPP NR system, the UE transmits control information such as the above-mentioned HARQ-ACK and CSI via the PUSCH and / or PUCCH.

[0064] FIG. 4 is a diagram illustrating an SS / PBCH block for initial cell access in a 3GPP NR system.

[0065] When a terminal is powered on or attempts to access a new cell, it acquires time and frequency synchronization with the cell and performs an initial cell search process. During the cell search process, the terminal detects the cell's physical cell identity (NcellID). To do this, the terminal receives synchronization signals, such as a primary synchronization signal (PSS) and a secondary synchronization signal (SSS), from the base station to synchronize with the base station. At this time, the terminal obtains information such as a cell identity (ID).

[0066] The synchronization signal (SS) will be described in more detail with reference to Figure 4(a). The synchronization signal is divided into a PSS and an SSS. The PSS is used to obtain time-domain synchronization and / or frequency-domain synchronization, such as OFDM symbol synchronization and slot synchronization. The SSS is used to obtain frame synchronization and a cell group ID. Referring to Figure 4(a) and Table 1, an SS / PBCH block consists of 20 consecutive RBs (=240 subcarriers) on the frequency axis and 4 consecutive OFDM symbols on the time axis. In this case, in the SS / PBCH block, the PSS is transmitted in the first OFDM symbol, and the SSS is transmitted in the third OFDM symbol via subcarriers 56 to 182. Here, the lowest subcarrier index in the SS / PBCH block starts from 0. In the first OFDM symbol in which the PSS is transmitted, the base station does not transmit signals via the remaining subcarriers, i.e., subcarriers 0 to 55 and 183 to 239. In addition, in the third OFDM symbol in which the SSS is transmitted, the base station does not transmit signals through subcarriers 48 to 55 and 183 to 191. The base station transmits a physical broadcast channel (PBCH) through the remaining REs in the SS / PBCH block excluding the signals.

[0067] [Table 2]

[0068] The SS groups a total of 1008 unique physical layer cell IDs (physical layer cell IDs) into 336 physical layer cell ID groups, each containing three unique identifiers, through the combination of three PSSs and SSSs. Specifically, each physical layer cell ID is part of only one physical layer cell ID group. Thus, the physical layer cell ID NcellID = 3N(1)ID + N(2)ID is uniquely defined by an index N(1)ID ranging from 0 to 335 indicating a physical layer cell ID group and an index N(2)ID ranging from 0 to 2 indicating a physical layer identifier within the physical layer cell ID group. The UE detects the PSS and identifies one of the three unique physical layer identifiers. The UE also detects the SSS and identifies one of the 336 physical layer cell IDs associated with the physical layer identifier. In this case, the PSS sequence dPSS(n) is as follows:

[0069]

number

[0070] where x(i+7)=(x(i+4)+x(i)) mod 2,

[0071] Given that [x(6)x(5)x(4)x(3)x(2)x(1)x(0)]=[1110110].

[0072] Also, the SSS sequence dSSS(n) is as follows:

[0073]

number

[0074] where x0(i+7)=(x0(i+4)+x0(i))mod 2 x1(i+7)=(x1(i+1)+x1(i))mod 2,

[0075] Given that [x0(6)x0(5)x0(4)x0(3)x0(2)x0(1) 0(0)]=[0000001], [x1(6)x1(5)x1(4)x1(3)x1(2)x1(1)x1(0)]=[0000001].

[0076] A 10-ms radio frame is divided into two 5-ms half-frames. Referring to FIG. 4(b), the slots in which SS / PBCH blocks are transmitted within each half-frame are described. The slots in which SS / PBCH blocks are transmitted are either Cases A, B, C, D, or E. In Case A, the subcarrier spacing is 15 kHz, and the start point of the SS / PBCH block is the {2, 8}+14*n symbol. Here, n = 0 or 1 for carrier frequencies below 3 GHz. Also, n = 0, 1, 2, or 3 for carrier frequencies above 3 GHz and below 6 GHz. In Case B, the subcarrier spacing is 30 kHz, and the start point of the SS / PBCH block is the {4, 8, 16, 20}+28*n symbol. Here, n = 0 for carrier frequencies below 3 GHz. Also, n = 0 or 1 for carrier frequencies above 3 GHz and below 6 GHz. In Case C, the subcarrier spacing is 30 kHz and the start of the SS / PBCH block is {2, 8}+14*n symbols, where n=0, 1 for carrier frequencies below 3 GHz. For carrier frequencies above 3 GHz and below 6 GHz, n=0, 1, 2, 3. In Case D, the subcarrier spacing is 120 kHz and the start of the SS / PBCH block is {4, 8, 16, 20}+28*n symbols, where n=0, 1, 2, 3, 5, 6, 7, 8, 10, 11, 12, 13, 15, 16, 17, 18 for carrier frequencies above 6 GHz. In Case E, the subcarrier spacing is 240 kHz and the start of the SS / PBCH block is {8, 12, 16, 20, 32, 36, 40, 44}+56*n symbols. In this case, n=0, 1, 2, 3, 5, 6, 7, 8 for carrier frequencies above 6 GHz.

[0077] 5 is a diagram showing a procedure for transmitting control information and a control channel in a 3GPP NR system. Referring to FIG. 5(a), a base station adds a cyclic redundancy check (CRC) masked (e.g., XORed) with a radio network temporary identifier (RNTI) to control information (e.g., DCI) S202. The base station scrambles the CRC with an RNTI value determined according to the purpose / target of each control information. The common RNTI used by one or more terminals includes at least one of a system information RNTI (SI-RNTI), a paging RNTI (P-RNTI), a random access RNTI (RA-RNTI), and a transmit power control RNTI (TPC-RNTI). The UE-specific RNTI includes at least one of a cell temporary RNTI (C-RNTI), a CS-RNTI, or an MCS-C-RNTI. The base station then performs channel encoding (e.g., polar coding) S204 and rate-matching S206 according to the amount of resource(s) used for PDCCH transmission. The base station then multiplexes DCI(s) based on a CCE (control channel element)-based PDCCH structure S208. The base station then applies additional processes S210, such as scrambling, modulation (e.g., QPSK), and interleaving, to the multiplexed DCI(s) and maps them to resources to be transmitted. A CCE is the basic resource unit for the PDCCH, and one CCE consists of multiple (e.g., six) resource element groups (REGs). One REG consists of multiple (e.g., 12) REs. The number of CCEs used for one PDCCH is defined as the aggregation level. 3GPP NR systems use aggregation levels of 1, 2, 4, 8, or 16.FIG. 5(b) is a diagram relating to CCE aggregation levels and PDCCH multiplexing, showing the types of CCE aggregation levels used for one PDCCH and the CCE(s) transmitted in the control region accordingly.

[0078] FIG. 6 is a diagram showing a CORESET in which a PDCCH is transmitted in a 3GPP NR system.

[0079] A CORESET is a time-frequency resource over which a PDCCH, a control signal for a terminal, is transmitted. A search space, which will be described later, is mapped to one CORESET. Therefore, a terminal does not monitor all frequency bands to receive a PDCCH, but rather monitors a time-frequency region designated as a CORESET and decodes the PDCCH mapped to the CORESET. A base station configures one or more CORESETs for each cell of a terminal. A CORESET consists of up to three consecutive symbols on the time axis. A CORESET also consists of six consecutive PRBs on the frequency axis. In the embodiment of FIG. 5, CORESET#1 consists of consecutive PRBs, and CORESET#2 and CORESET#3 consist of non-consecutive PRBs. A CORESET can be located at any symbol within a slot. For example, in the embodiment of FIG. 5, CORESET#1 starts from the first symbol of the slot, CORESET#2 starts from the fifth symbol of the slot, and CORESET#9 starts from the ninth symbol of the slot.

[0080] FIG. 7 is a diagram illustrating a method for configuring a PDCCH search space in a 3GPP NR system.

[0081] At least one search space exists in each CORESET for transmitting a PDCCH to a terminal. In an embodiment of the present invention, the search space is a set of all time-frequency resources (hereinafter referred to as PDCCH candidates) on which the PDCCH of the terminal is transmitted. The search space includes a common search space that all 3GPP NR terminals should commonly search, and a terminal-specific or UE-specific search space that a specific terminal should search. In the common search space, all terminals in a cell belonging to the same base station monitor a PDCCH that is configured to be commonly searched. In addition, the terminal-specific search space is configured for each terminal so that the PDCCH allocated to each terminal is monitored at a different search space position depending on the terminal. In the case of a terminal-specific search space, the search spaces allocated to terminals may partially overlap due to the limited control region to which the PDCCH is allocated. Monitoring the PDCCH includes blind decoding of PDCCH candidates in the search space. If blind decoding is successful, it is expressed as the PDCCH being (successfully) detected / received, and if blind decoding fails, it is expressed as the PDCCH being undetected / unreceived or not being successfully detected / received.

[0082] For convenience of explanation, a PDCCH scrambled with a group common (GC) RNTI already known by one or more terminals to transmit downlink control information to one or more terminals is referred to as a group common (GC) PDCCH or a common PDCCH. Also, a PDCCH scrambled with a terminal-specific RNTI already known by a specific terminal to transmit uplink scheduling information or downlink scheduling information to one specific terminal is referred to as a terminal-specific PDCCH. The common PDCCH is included in a common search space, and the terminal-specific PDCCH is included in the common search space or the terminal-specific PDCCH.

[0083] A base station notifies each terminal or a group of terminals of information regarding resource allocation of transmission channels, a paging channel (PCH) and a downlink-shared channel (DL-SCH) (i.e., DL Grant) or information regarding resource allocation of a UL-SCH and hybrid automatic repeat request (HARQ) (i.e., UL Grant) via a PDCCH. The base station transmits PCH transport blocks and DL-SCH transport blocks via a PDSCH. The base station transmits data excluding specific control information or specific service data via the PDSCH. In addition, terminals receive data excluding specific control information or specific service data via the PDSCH.

[0084] A base station transmits information on which terminal (one or more terminals) PDSCH data is transmitted to and how the terminal should receive and decode the PDSCH data, by including the information in a PDCCH. For example, assume that DCI transmitted over a specific PDCCH is CRC masked with RNTI "A," and the DCI indicates that the PDSCH is allocated to radio resource "B" (e.g., frequency location), and indicates transmission format information "C" (e.g., transmission block size, modulation scheme, coding information, etc.). A terminal monitors the PDCCH using its own RNTI information. In this case, if there is a terminal that blind decodes the PDCCH using RNTI "A," the terminal receives the PDCCH and receives the PDSCH indicated by "B" and "C" through the received PDCCH information.

[0085] Table 3 shows an example of a PUCCH used in a wireless communication system.

[0086] [Table 3]

[0087] The PUCCH is used to transmit the following uplink control information (UCI):

[0088] - SR (Scheduling Request): Information used to request uplink UL-SCH resources.

[0089] HARQ-ACK: A response to a PDCCH (indicating DL SPS release) and / or a response to an uplink transport block (TB) on a PDSCH. HARQ-ACK indicates whether information transmitted via a PDCCH or a PDSCH has been received. HARQ-ACK responses include a positive ACK (simply referred to as ACK), a negative ACK (hereinafter referred to as NACK), DTX (Discontinuous Transmission), or NACK / DTX. Here, the term HARQ-ACK is used interchangeably with HARQ-ACK / NACK and ACK / NACK. Generally, ACK is represented by a bit value of 1, and NACK is represented by a bit value of 0.

[0090] CSI: Feedback information for the downlink channel. It is generated by the terminal based on the CSI-RS (Reference Signal) transmitted by the base station. MIMO (multiple input multiple output)-related feedback information includes RI and PMI. CSI is divided into CSI part 1 and CSI part 2 according to the information indicated by the CSI.

[0091] In the 3GPP NR system, five PUCCH formats are used to support various service scenarios, various channel environments, and frame structures.

[0092] PUCCH format 0 is a format that transmits 1-bit or 2-bit HARQ-ACK information or SR. PUCCH format 0 is transmitted using one or two OFDM symbols on the time axis and one RB on the frequency axis. If PUCCH format 0 is transmitted using two OFDM symbols, the same sequence is transmitted in two symbols using different RBs. This allows the UE to obtain frequency diversity gain. More specifically, the UE determines a cyclic shift value mcs according to the Mbit-bit UCI (Mbit = 1 or 2), cyclically shifts a 12-length base sequence by the determined mcs value, maps the resulting sequence to one OFDM symbol and 12 REs of one PRB, and transmits it. If the number of cyclic shifts available to the UE is 12 and Mbit = 1, 1-bit UCIs 0 and 1 are represented by sequences corresponding to two cyclic shifts with a cyclic shift value difference of 6. Also, if Mbit=2, then 2-bit UCI 00, 01, 11, 10 is represented by a sequence corresponding to four cyclic shifts with a difference of three between the cyclic shift values.

[0093] PUCCH format 1 carries 1-bit or 2-bit HARQ-ACK information or SR. PUCCH format 1 is transmitted using consecutive OFDM symbols on the time axis and one PRB on the frequency axis. Here, the number of OFDM symbols occupied by PUCCH format 1 is one of 4 to 14. More specifically, UCI with Mbit=1 is modulated using BPSK. The UE modulates UCI with Mbit=2 using quadrature phase shift keying (QPSK). The modulated complex-valued symbol d(0) is multiplied by a sequence of length 12 to obtain a signal. The UE spreads the obtained signal using an orthogonal cover code (OCC) on the time axis to even-numbered OFDM symbols assigned to PUCCH format 1 and transmits it. In PUCCH format 1, the maximum number of different UEs multiplexed in the same RB can be determined depending on the length of the OCC used. In odd-numbered OFDM symbols of PUCCH format 1, a demodulation reference signal (DMRS) is spread by OCC and mapped.

[0094] PUCCH format 2 carries UCI exceeding 2 bits. PUCCH format 2 is transmitted using one or two OFDM symbols on the time axis and one or more RBs on the frequency axis. If PUCCH format 2 is transmitted using two OFDM symbols, the same sequence is transmitted using different RBs across the two OFDM symbols. This allows the UE to obtain frequency diversity gain. More specifically, Mbit UCI (Mbit>2) is bit-level scrambled, QPSK modulated, and mapped to the RBs of one or two OFDM symbols. Here, the number of RBs is one of 1 to 16.

[0095] PUCCH format 3 or PUCCH format 4 transmits UCI exceeding 2 bits. PUCCH format 3 or PUCCH format 4 is transmitted using consecutive OFDM symbols on the time axis and one PRB on the frequency axis. The number of OFDM symbols occupied by PUCCH format 3 or PUCCH format 4 is one of 4 to 14. Specifically, the terminal modulates Mbit-bit UCI (Mbit>2) using π / 2-BPSK (Binary Phase Shift Keying) or QPSK to generate complex symbols d(0) to d(Msymb-1). Here, Msymb=Mbit when π / 2-BPSK is used, and Msymb=Mbit / 2 when QPSK is used. The terminal does not apply block-wise spreading to PUCCH format 3. However, the terminal may apply block-wise spreading to one RB (i.e., 12 subcarriers) using a PreDFT-OCC of length -12 so that PUCCH format 4 has a multiplexing capacity of 2 or 4. The terminal transmit precoding (or DFT-precoding) the spreaded signal, maps it to each RE, and transmits the spreaded signal.

[0096] In this case, the number of RBs occupied by PUCCH format 2, PUCCH format 3, or PUCCH format 4 is determined according to the length of UCI transmitted by the terminal and the maximum code rate. If the terminal uses PUCCH format 2, the terminal transmits both HARQ-ACK information and CSI information via the PUCCH. If the number of RBs that the terminal can transmit is greater than the maximum number of RBs that PUCCH format 2, PUCCH format 3, or PUCCH format 4 can use, the terminal does not transmit some UCI information and transmits only the remaining UCI information according to the priority of the UCI information.

[0097] PUCCH format 1, PUCCH format 3, or PUCCH format 4 is configured via RRC signaling to indicate frequency hopping within a slot. When frequency hopping is configured, the index of the RB to be frequency hopped is configured via RRC signaling. If PUCCH format 1, PUCCH format 3, or PUCCH format 4 is transmitted over N OFDM symbols on the time axis, the first hop has floor(N / 2) OFDM symbols, and the second hop has ceil(N / 2) OFDM symbols.

[0098] PUCCH format 1, PUCCH format 3, or PUCCH format 4 is configured to be repeatedly transmitted in multiple slots. In this case, the number K of slots in which the PUCCH is repeatedly transmitted is configured by an RRC signal. The repeatedly transmitted PUCCH should start from the same OFDM symbol position in each slot and have the same length. If the RRC signal indicates that any one of the OFDM symbols in a slot in which the UE should transmit the PUCCH is a DL symbol, the UE does not transmit the PUCCH from that slot but postpones its transmission to the next slot.

[0099] Meanwhile, in a 3GPP NR system, a terminal transmits and receives using a bandwidth smaller than or equal to the bandwidth of a carrier (or cell). To this end, the terminal is configured with a bandwidth part (BWP) consisting of a continuous portion of the carrier bandwidth. A terminal operating according to TDD or using an unpaired spectrum is configured with up to four DL / UL BWP pairs per carrier (or cell). The terminal also activates one DL / UL BWP pair. A terminal operating according to FDD or using a paired spectrum is configured with up to four DL BWPs per downlink carrier (or cell) and up to four UL BWPs per uplink carrier (or cell). The terminal activates one DL BWP and one UL BWP for each carrier (or cell). The terminal may not receive or transmit from time-frequency resources other than the activated BWP. An activated BWP is called an active BWP.

[0100] The base station refers to the activated BWP among the BWPs configured for the UE as a DCI. The BWP indicated in the DCI is activated, and the other configured BWP(s) are deactivated. In a carrier (or cell) operating in TDD, the base station includes a bandwidth part indicator (BPI) indicating the activated BWP in the DCI scheduling the PDSCH or PUSCH to change the DL / UL BWP pair of the UE. The UE receives the DCI scheduling the PDSCH or PUSCH and identifies the activated DL / UL BWP pair based on the BPI. In a downlink carrier (or cell) operating in FDD, the base station includes a BPI indicating the activated BWP in the DCI scheduling the PDSCH to change the DL BWP of the UE. In an uplink carrier (or cell) operating in FDD, the base station includes a BPI indicating the activated BWP in the DCI scheduling the PDSCH to change the UE's UL BWP.

[0101] FIG. 8 is a conceptual diagram illustrating carrier aggregation.

[0102] Carrier aggregation refers to a method in which a mobile station uses multiple frequency blocks or (logical) cells consisting of uplink resources (or component carriers) and / or downlink resources (or component carriers) in one large logical frequency band so that the wireless communication system can use a wider frequency band. For convenience of explanation, the term "component carrier" will be used hereinafter.

[0103] Referring to Figure 8, in an example of a 3GPP NR system, the entire system band includes up to 16 component carriers, each of which has a bandwidth of up to 400 MHz. A component carrier includes one or more physically contiguous subcarriers. While Figure 8 shows each component carrier having the same bandwidth, this is merely an example, and each component carrier may have a different bandwidth. Furthermore, although each component carrier is shown adjacent to each other on the frequency axis, this is shown only as a logical concept, and each component carrier may be physically adjacent to each other or separated from each other.

[0104] A different center frequency is used for each component carrier. Also, a common center frequency is used for physically adjacent component carriers. In the embodiment of Fig. 8, if it is assumed that all component carriers are physically adjacent, center frequency A is used for all component carriers. Also, if it is assumed that the component carriers are not physically adjacent, center frequency A and center frequency B are used for each component carrier.

[0105] When the entire system band is expanded by carrier aggregation, the frequency band used for communication with each terminal is defined in component carrier units. Terminal A uses the entire system band of 100 MHz and communicates using all five component carriers. Terminals B1 to B5 only use a 20 MHz bandwidth and communicate using one component carrier. Terminals C1 and C2 only use a 40 MHz bandwidth and each communicate using two component carriers. The two component carriers may or may not be logically / physically adjacent. The example in Figure 8 shows a case where terminal C1 uses two non-adjacent component carriers and terminal C2 uses two adjacent component carriers.

[0106] 9A and 9B are diagrams for explaining single-carrier communication and multi-carrier communication, in particular, FIG. 9A shows a subframe structure of a single carrier, and FIG. 9B shows a subframe structure of a multi-carrier.

[0107] Referring to FIG. 9(a), in an FDD mode, a typical wireless communication system transmits or receives data through one DL band and one corresponding UL band. In another specific embodiment, in a TDD mode, the wireless communication system divides a radio frame into uplink time units and downlink time units in the time domain, and transmits or receives data through the uplink / downlink time units. Referring to FIG. 9(b), three 20 MHz component carriers (CCs) are aggregated in each of the UL and DL to support a 60 MHz bandwidth. The CCs may be adjacent or non-adjacent to each other in the frequency domain. For convenience, FIG. 9(b) illustrates a case where the bandwidths of the UL CC and the DL CC are the same and symmetrical, but the bandwidths of each CC may be determined independently. Also, asymmetric carrier aggregation, in which the number of UL CCs and the number of DL CCs are different, is possible. The DL / UL CC allocated / configured to a specific terminal via RRC is referred to as the serving DL / UL CC of the specific terminal.

[0108] A base station communicates with a terminal by activating some or all of the serving CCs of the terminal or deactivating some of the CCs. The base station may change the activated / deactivated CCs or the number of activated / deactivated CCs. When a base station allocates CCs available to a terminal in a cell-specific or terminal-specific manner, at least one of the allocated CCs may not be deactivated unless the CC allocation for the terminal is completely reconfigured or the terminal performs a handover. A CC that is not deactivated by the terminal is called a primary CC (PCC) or PCell (primary cell), and a CC that the base station can activate / deactivate freely is called a secondary CC (SCC) or SCell (secondary cell).

[0109] Meanwhile, 3GPP NR uses the concept of a cell to manage radio resources. A cell is defined as a combination of downlink and uplink resources, i.e., a combination of DL CC and UL CC. A cell may consist of only DL resources or a combination of DL and UL resources. If carrier aggregation is supported, the linkage between the carrier frequency of DL resources (or DL ​​CC) and the carrier frequency of UL resources (or UL CC) is indicated by system information. Carrier frequency refers to the center frequency of each cell or CC. A cell corresponding to a PCC is called a PCell, and a cell corresponding to an SCC is called an SCell. The carrier corresponding to a PCell in the downlink is a DL PCC, and the carrier corresponding to a PCell in the uplink is a UL PCC. Similarly, the carrier corresponding to an SCell in the downlink is a DL SCC, and the carrier corresponding to an SCell in the uplink is a UL SCC. Depending on the terminal capacity, a serving cell(s) may consist of one PCell and zero or more SCells. For a UE in RRC_CONNECTED state but not configured with carrier aggregation or not supporting carrier aggregation, there is only one serving cell consisting of only a PCell.

[0110] As described above, the term "cell" used in carrier aggregation is different from the term "cell" referring to a certain geographical area where communication services are provided by one base station or one antenna group. However, in order to distinguish between a cell referring to a certain geographical area and a cell of carrier aggregation, in the present invention, a cell of carrier aggregation is referred to as a CC, and a cell of a geographical area is referred to as a cell.

[0111] 10 is a diagram illustrating an example in which a cross-carrier scheduling technique is applied. When cross-carrier scheduling is configured, a control channel transmitted over a first CC schedules a data channel transmitted over a first or second CC using a carrier indicator field (CIF). The CIF is included in the DCI. In other words, a scheduling cell is configured, and a DL grant / UL grant transmitted from the PDCCH region of the scheduling cell schedules the PDSCH / PUSCH of a scheduled cell. That is, the PDCCH region of the scheduling cell is the search space for multiple component carriers. The PCell is basically the scheduling cell, and a specific SCell is designated as the scheduling cell by a higher layer.

[0112] In the embodiment of Figure 10, it is assumed that three DL CCs are merged. Here, it is assumed that DL component carrier #0 is a DL PCC (or PCell), and DL component carrier #1 and DL component carrier #2 are DL SCCs (or SCells). It is also assumed that the DL PCCs are configured as PDCCH monitoring CCs. If cross-carrier scheduling is not configured by terminal-specific (or terminal-group-specific, or cell-specific) higher layer signaling, the CIF is disabled, and each DL CC transmits only a PDCCH that schedules its own PDSCH without a CIF according to the NR PDCCH rules (non-cross-carrier scheduling, self-carrier scheduling). On the other hand, if cross-carrier scheduling is configured by UE-specific (or UE-group-specific, or cell-specific) higher layer signaling, the CIF is enabled, and a specific CC (e.g., DL PCC) uses the CIF to transmit not only a PDCCH that schedules the PDSCH of DL CC A but also a PDCCH that schedules the PDSCH of another CC (cross-carrier scheduling). On the other hand, no PDCCH is transmitted on other DL CCs. Therefore, depending on whether cross-carrier scheduling is configured for the UE, the UE either monitors a PDCCH that does not include a CIF to receive a self-carrier scheduled PDSCH, or monitors a PDCCH that includes a CIF to receive a cross-carrier scheduled PDSCH.

[0113] 9 and 10 illustrate the subframe structure of the 3GPP LTE-A system, the same or similar structure can also be applied to the 3GPP NR system, however, in the 3GPP NR system, the subframes in FIG. 9 and 10 may be replaced with slots.

[0114] 11 shows a code block group (CBG) configuration and its time-frequency resource mapping according to an embodiment of the present invention. More specifically, FIG. 11(a) shows an embodiment of a CBG configuration included in one transport block (TB), and FIG. 11(b) shows the time-frequency resource mapping of the CBG configuration.

[0115] A maximum supportable length is defined for a channel code. For example, the maximum supportable length of a turbo code used in 3GPP LTE(-A) is 6144 bits. However, the length of a transport block (TB) transmitted on a PDSCH may be longer than 6144 bits. If the length of a TB is longer than the maximum supportable length, the TB may be divided into code blocks (CBs) with a maximum length of 6144 bits. Each CB is a unit for channel coding. Furthermore, several CBs may be grouped together to form one CBG for efficient retransmission. A terminal and a base station require information on how the CBG is configured.

[0116] The CBGs and CBs within the TB may be configured according to various embodiments. According to one embodiment, the number of available CBGs may be determined to a fixed value or may be configured by RRC configuration information between the base station and the terminal. In this case, the number of CBs may be determined according to the length of the TB, and the CBGs may be configured according to the determined number information. According to another embodiment, the number of CBs that may be included in one CBG may be determined to a fixed value or may be configured according to RRC configuration information between the base station and the terminal. In this case, when the number of CBs is determined according to the length of the TB, the number of CBGs may be configured according to the CB number information per CBG.

[0117] Referring to the embodiment of FIG. 11(a), one TB may be divided into eight CBs. The eight CBs may be further grouped into four CBGs. Such a mapping relationship between CBs and CBGs (or CBG configuration) may be statically configured between the base station and the terminal, or semi-statically configured using RRC configuration information. According to another embodiment, the mapping relationship may be configured by dynamic signaling. When the terminal receives a PDCCH transmitted from the base station, the terminal can directly or indirectly identify the CB and CBG mapping relationship (or CBG configuration) using explicit information and / or implicit information. One CBG may include only one CB or may include all CBs constituting one TB. For reference, the method proposed in the embodiments of the present invention is applicable regardless of the CB and CBG configuration.

[0118] Referring to FIG. 11(b), CBGs constituting one TB are mapped to the scheduled time-frequency resources of the PDSCH. According to one embodiment, each CBG may be first allocated to the frequency axis and then extended to the time axis. When a PDSCH consisting of one TB including four CBGs is allocated to seven OFDM symbols, CBG0 may be transmitted over the first and second OFDM symbols, CBG1 may be transmitted over the second, third, and fourth OFDM symbols, CBG2 may be transmitted over the fourth, fifth, and sixth OFDM symbols, and CBG3 may be transmitted over the sixth and seventh OFDM symbols. Such a time-frequency mapping relationship between the CBGs and the PDSCH may be determined between the base station and the terminal. However, the mapping relationship shown in FIG. 11(b) is merely an example for explaining the present invention, and the method proposed in this embodiment of the present invention is applicable regardless of the time-frequency mapping relationship of the CBGs.

[0119] FIG. 12 shows a process in which a base station performs TB-based transmission or CBG-based transmission and a terminal transmits a HARQ-ACK in response thereto. Referring to FIG. 12, the base station can configure a transmission scheme suitable for the terminal, either TB-based transmission or CBG-based transmission. The terminal can transmit HARQ-ACK information bits according to the transmission scheme configured by the base station on a PUCCH or a PUSCH. The base station can configure a PDCCH to schedule a PDSCH to be transmitted to the terminal. The PDCCH can schedule TB-based transmission and / or CBG-based transmission. For example, one TB or two TBs can be scheduled in the PDCCH. If one TB is scheduled, the terminal must feed back a one-bit HARQ-ACK. If two TBs are scheduled, the terminal must feed back a two-bit HARQ-ACK for each of the two TBs. To eliminate ambiguity between the base station and the terminal, a predetermined order may exist between each information bit of the two-bit HARQ-ACK and the two TBs. For reference, when the MIMO transmission rank or layer is low, one TB may be transmitted with one PDSCH, and when the MIMO transmission rank or layer is high, two TBs may be transmitted with one PDSCH.

[0120] The UE can transmit a 1-bit TB-based HARQ-ACK for each TB to inform the base station of whether each TB has been successfully received. To generate a HARQ-ACK for one TB, the UE can check for a reception error of the TB using the TB-CRC. If the TB-CRC for the TB is successfully checked, the UE generates an ACK for the HARQ-ACK for the TB. However, if a TB-CRC error occurs for the TB, the UE generates a NACK for the HARQ-ACK for the TB. The UE transmits the TB-based HARQ-ACK thus generated to the base station. The base station retransmits the TB for which a NACK has been returned from the UE among the TB-based HARQ-ACKs received from the UE.

[0121] Furthermore, the UE may transmit a 1-bit CBG-based HARQ-ACK for each CBG to inform the base station of whether each CBG has been successfully received. To generate a HARQ-ACK for one CBG, the UE may decode all CBs included in the CBG and check for reception errors for each CB using the CB-CRC. If the UE successfully receives all CBs constituting one CBG (i.e., if all CB-CRCs are successfully checked), the UE generates an ACK for the HARQ-ACK for the CBG. However, if the UE does not successfully receive at least one of the CBs constituting one CBG (i.e., if at least one CB-CRC error occurs), the UE generates a NACK for the HARQ-ACK for the CBG. The UE transmits the generated CBG-based HARQ-ACK to the base station. The base station retransmits the CBGs for which a NACK has been returned from the UE among the CBG-based HARQ-ACKs received from the UE. According to an embodiment, the CB configuration of the retransmitted CBG may be the same as the CB configuration of the previously transmitted CBG. The length of the CBG-based HARQ-ACK information bits transmitted by the UE to the base station may be determined based on the number of CBGs transmitted in the PDSCH or the maximum number of CBGs configured in the RRC signal.

[0122] On the other hand, even if the UE successfully receives all CBGs included in the TB, a TB-CRC error for the TB may occur. In this case, the UE may perform CBG-based HARQ-ACK flipping to request retransmission for the TB. That is, even if all CBGs included in the TB are successfully received, the UE may generate all CBG-based HARQ-ACK information bits as NACK. A base station that receives CBG-based HARQ-ACK feedback in which all HARQ-ACK information bits are NACK retransmits all CBGs of the TB.

[0123] According to an embodiment of the present invention, CBG-based HARQ-ACK feedback may be used for successful TB transmission. The base station may instruct the terminal to transmit the CBG-based HARQ-ACK. At this time, a retransmission method using the CBG-based HARQ-ACK may be used. The CBG-based HARQ-ACK may be transmitted on a PUCCH. Furthermore, if UCI is configured to be transmitted on a PUSCH, the CBG-based HARQ-ACK may be transmitted on the PUSCH. Configuration of HARQ-ACK resources in the PUCCH may be configured by an RRC signal. Furthermore, the HARQ-ACK resource to be actually transmitted may be indicated via a PDCCH that schedules a PDSCH to be transmitted based on the CBG. The terminal may transmit a HARQ-ACK indicating whether the transmitted CBG has been successfully received or not via one PUCCH resource indicated by the PDCCH among the PUCCH resources configured by the RRC signal.

[0124] The base station can identify whether the terminal has successfully received the CBG transmitted to the terminal by using the CBG-based HARQ-ACK feedback of the terminal. That is, the base station can recognize the CBGs that the terminal has successfully received and the CBGs that the terminal has failed to receive by using the HARQ-ACK for each CBG received from the terminal. The base station can perform CBG retransmission based on the received CBG-based HARQ-ACK. More specifically, the base station can collectively retransmit only CBGs for which unsuccessful reception of HARQ-ACK has been responded in one TB. In this case, CBGs for which successful reception of HARQ-ACK has been responded are excluded from retransmission. The base station can schedule the CBGs to be retransmitted in one PDSCH and transmit them to the terminal.

[0125] <Communication methods in unlicensed spectrum>

[0126] FIG. 13 illustrates an example of an NR-U (NR-Unlicensed) service environment.

[0127] Referring to Figure 13, a service environment in which NR technology 11 in a licensed spectrum and NR-U, which is NR technology 12 in an unlicensed spectrum, are integrated may be provided to users. For example, in an NR-U environment, NR technology 11 in a licensed spectrum and NR technology 12 in an unlicensed spectrum may be integrated using techniques such as carrier aggregation, which can contribute to network capacity expansion. Also, in an asymmetric traffic structure in which downlink data is relatively larger than uplink data, NR-U can provide NR services optimized according to various requirements or environments. For convenience, NR technology in a licensed spectrum is referred to as NR-L (NR-Licensed), and NR technology in an unlicensed spectrum is referred to as NR-U (NR-Unlicensed).

[0128] Figure 14 shows an example of a deployment scenario of a terminal and a base station in an NR-U service environment. The frequency band targeted by the NR-U service environment has high-frequency characteristics, so the wireless communication reach distance is not long. Considering this, in an environment where existing NR-L services and NR-U services coexist, the deployment scenario of a terminal and a base station may be an overlay model or a co-located model.

[0129] In the overlay model, a macro base station performs wireless communication with X and X' terminals in a macro region 32 using a licensed band carrier, and may be connected to multiple RRHs (Radio Remote Heads) via an X2 interface. Each RRH can perform wireless communication with X or X' terminals in a certain region 31 using an unlicensed band carrier. Since the frequency bands of the macro base station and the RRHs are different from each other, there is no mutual interference. However, in order to use the NR-U service as a supplementary downlink channel for the NR-L service using carrier aggregation, fast data exchange is required between the macro base station and the RRHs via the X2 interface.

[0130] In the co-located model, the pico / femto base station can simultaneously use licensed and unlicensed band carriers to perform wireless communication with the Y terminal. However, the pico / femto base station may only use both the NR-L service and the NR-U service during downlink transmission. The coverage 33 of the NR-L service and the coverage 34 of the NR-U service may differ from each other depending on the frequency band, transmission power, etc.

[0131] When NR communication is performed in an unlicensed band, existing equipment (e.g., wireless LAN (Wi-Fi) equipment) communicating in the unlicensed band cannot demodulate the NR-U message or data. Therefore, the existing equipment can interpret the NR-U message or data as a type of energy and perform interference avoidance operations using an energy detection (or detection) technique. That is, if the energy corresponding to the NR-U message or data is less than -62 dBm or a specific ED (Energy Detection) threshold, the WLAN equipment can ignore the message or data and communicate. Therefore, terminals performing NR communication in an unlicensed band can frequently be interfered with by WLAN equipment.

[0132] Therefore, to effectively implement NR-U technology / services, it is necessary to allocate or reserve specific frequency bands at specific times. However, peripheral devices communicating in unlicensed bands attempt to connect based on energy detection methods, making efficient NR-U services difficult. Therefore, for NR-U technology to take hold, prior research must be conducted into coexistence methods with existing unlicensed band devices and methods for efficiently sharing radio channels. In other words, a robust coexistence mechanism must be developed that does not affect NR-U devices on existing unlicensed band devices.

[0133] Figure 15 shows an existing communication system (e.g., wireless LAN) that operates in unlicensed bands. Devices that operate in unlicensed bands usually operate on a Listen-Before-Talk (LBT) basis, and perform Clear Channel Assessment (CCA) to sense the channel before transmitting data.

[0134] Referring to Figure 15, a WLAN device (e.g., AP, STA) performs carrier sensing before transmitting data to check whether a channel is busy. If a wireless signal of a certain strength or higher is detected from a channel to which data is to be transmitted, the channel is determined to be busy, and the WLAN device delays access to the channel. This process is called clear channel assessment, and the signal level that determines whether a signal is detected is called a CCA threshold. On the other hand, if no wireless signal is detected from the channel or a wireless signal of a strength lower than the CCA threshold is detected, the channel is determined to be idle.

[0135] If a channel is determined to be idle, a terminal with data to transmit performs a backoff procedure after a defer duration (e.g., Arbitration InterFrame Space (AIFS), PCF IFS (PIFS), etc.). The defer duration refers to the minimum time a terminal must wait after a channel becomes idle. The backoff procedure allows a terminal to wait any additional time after the defer deadline. For example, a terminal waits by decreasing a slot time equal to a random number assigned to the terminal within a contention window (CW) while the channel is idle, and a terminal that has exhausted all slot times can attempt to access the channel.

[0136] Once a terminal successfully accesses a channel, it can transmit data over the channel. If data transmission is successful, the contention window size (CWS) is reset to its initial value (CWmin). On the other hand, if data transmission fails, the CWS is doubled. As a result, the terminal is assigned a new random number within a range twice the previous random number range and performs a backoff procedure in the next CW. In WLANs, only ACK is defined as reception response information for data transmission. Therefore, if an ACK is received for data transmission, the CWS is reset to its initial value, and if no feedback information is received for data transmission, the CWS is doubled.

[0137] As mentioned above, since existing communications in unlicensed bands mostly operate on the LBT basis, channel access in the NR-U system also performs LBT for coexistence with existing devices. Specifically, channel access methods in unlicensed bands in NR can be divided into the following four categories depending on whether or not LBT is used / applied.

[0138] ●Category 1: No LBT

[0139] - The Tx entity does not perform the LBT procedure for transmission.

[0140] Category 2: LBT without random backoff

[0141] The Tx entity senses whether the channel is idle during a first interval without random backoff in order to transmit. That is, the Tx entity can transmit on the channel immediately after sensing the channel as idle during the first interval. The first interval is an interval of a pre-configured length immediately before the Tx entity transmits. According to one embodiment, the first interval may be 25 us long, but the present invention is not limited thereto.

[0142] Category 3: LBT with random backoff using a fixed-size CW

[0143] - The Tx entity obtains a random number within a fixed-size CW, sets it as the initial value of a backoff counter (or backoff timer) N, and performs backoff using the set backoff counter N. That is, in the backoff procedure, the Tx entity decrements the backoff counter by 1 each time the channel is sensed as idle during a pre-set slot period. Here, the pre-set slot period may be 9 us, but the present invention is not limited to this. The backoff counter N is decremented by 1 from its initial value, and when the value of the backoff counter N reaches 0, the Tx entity can transmit. Meanwhile, to perform backoff, the Tx entity decrements the second interval (i.e., the defer period T d ) to determine whether the channel is idle. According to an embodiment of the present invention, the Tx entity can sense (or determine) whether the channel is idle during the second interval based on whether the channel is idle during at least a portion (e.g., one slot) of the second interval. The second interval may be set based on the channel access priority class of the Tx entity and may consist of a 16 us period and m consecutive slot periods, where m is a value set by the channel access priority class. If the channel is sensed as idle during the second interval, the Tx entity performs channel sensing to decrease the backoff counter. On the other hand, if the channel is sensed as occupied during the backoff procedure, the backoff procedure is aborted. After aborting the backoff procedure, the Tx entity can resume backoff if the channel is sensed as idle during an additional second interval. In this way, the Tx entity can transmit if the channel is idle for N slot periods of the backoff counter in addition to the second interval. At this time, the initial value of the backoff counter N is obtained within a CW of fixed size.

[0144] Category 4: LBT with random backoff using variable-size CW

[0145] - The Tx entity obtains a random number within a variable-size CW, sets it as the initial value of a backoff counter (or backoff timer) N, and performs backoff using the set backoff counter N. More specifically, the Tx entity can adjust the size of the CW based on HARQ-ACK information for a previous transmission, and the initial value of the backoff counter N is obtained within a CW of the adjusted size. The specific process by which the Tx entity performs backoff is as described in Category 3. The Tx entity can transmit if the channel is idle during the second interval plus the slot period of the backoff counter N. In this case, the initial value of the backoff counter N is obtained within a variable-size CW.

[0146] In the above Categories 1 to 4, the Tx entity may be a base station or a terminal. According to the embodiments of the present invention, the first type channel access may refer to the channel access of Category 4, and the second type channel access may refer to the channel access of Category 2.

[0147] FIG. 16 illustrates a channel access process based on Category 4 LBT according to an embodiment of the present invention.

[0148] To perform channel access, the Tx entity first waits for a defer period T d According to an embodiment of the present invention, the defer period T d The channel sensing for the defer period T d For example, the defer period T d The channel sensing for the defer period T dThe Tx entity may perform channel sensing during one slot period within the defer period T d It is checked whether the channel is idle by channel sensing for the channel (S304). d If the channel is sensed as idle for the defer period T, the Tx entity proceeds to step S306. d If the channel is not sensed as idle for the defer period T (i.e., sensed as occupied), the Tx entity returns to step S302. d The steps S302 to S304 are repeated until the device is sensed as being in an idle state. d may be set based on the channel access priority class of the Tx entity and consists of a period of 16us and m consecutive slot periods, where m is the value set by the channel access priority class.

[0149] Next, the Tx entity obtains a random number within a predetermined CW and sets it as the initial value of a backoff counter (or backoff timer) N (S306), and proceeds to step S308. The initial value of the backoff counter N is randomly selected from a range of values ​​from 0 to CW. The Tx entity performs a backoff procedure using the set backoff counter N. That is, the Tx entity performs the backoff procedure by repeating steps S308 to S316 until the value of the backoff counter N reaches 0. Meanwhile, in FIG. 16, when the channel is in a deferred period T d Although step S306 is performed after the channel is sensed as being in an idle state, the present invention is not limited thereto. That is, step S306 may be performed independently of steps S302 to S304, or may be performed before steps S302 to S304. When step S306 is performed before steps S302 to S304, the channel is set to the defer period T by steps S302 to S304. d If the Tx entity senses the Tx channel as idle, the Tx entity proceeds to step S308.

[0150] In step S308, the Tx entity determines whether the value of the backoff counter N is 0. If the value of the backoff counter N is 0, the Tx entity proceeds to step S320 and transmits. If the value of the backoff counter N is not 0, the Tx entity proceeds to step S310. In step S310, the Tx entity decrements the value of the backoff counter N by 1. According to one embodiment, the Tx entity may selectively decrement the value of the backoff counter by 1 during the channel sensing process for each slot. At this time, step S310 may be skipped at least once depending on the Tx entity's selection. Next, the Tx entity performs channel sensing for an additional slot period (S312). The Tx entity determines whether the channel is idle through channel sensing for the additional slot period (S314). If the channel is sensed as idle for the additional slot period, the Tx entity returns to step S308. In this manner, the Tx entity can decrement the backoff counter by 1 each time the channel is sensed as idle during a pre-set slot period, where the pre-set slot period may be 9 us, but the present invention is not limited thereto.

[0151] If the channel is not sensed as idle (i.e., sensed as occupied) for an additional slot period in step S314, the Tx entity proceeds to step S316. In step S316, the Tx entity determines whether the channel is to be idle for an additional deferred period T d According to an embodiment of the present invention, the channel sensing in step S316 may be performed in slot units. That is, the Tx entity may check whether the channel is idle in the additional defer period T d Check whether the channel is sensed as idle for all slot periods of T d If an occupied slot is detected within the additional defer period T, the Tx entity immediately restarts step S316. dIf the channel is sensed as idle for the entire slot period, the Tx entity returns to step S308.

[0152] On the other hand, if the value of the backoff counter N is confirmed as 0 in step S308, the Tx entity performs transmission (S320). The Tx entity receives HARQ-ACK feedback corresponding to the transmission (S322). The Tx entity can determine whether the previous transmission was successful based on the received HARQ-ACK feedback. Next, the Tx entity adjusts the CW size for the next transmission based on the received HARQ-ACK feedback (S324).

[0153] Thus, the Tx entity can transmit the data for a deferred period T d After sensing the channel as idle for N additional slot periods, transmission can occur if the channel is idle. As mentioned above, the Tx entity may be a base station or a terminal, and the channel access process of FIG. 16 may be used for downlink transmission of the base station and / or uplink transmission of the terminal.

[0154] Hereinafter, a method for adaptively adjusting CWS when accessing a channel in an unlicensed band will be proposed. CWS may be adjusted based on UE (User Equipment) feedback, and the UE feedback used for CWS adjustment may include HARQ-ACK feedback, CQI / PMI / RI. In the present invention, a method for adaptively adjusting CWS based on HARQ-ACK feedback is proposed. HARQ-ACK feedback includes at least one of ACK, NACK, DTX, and NACK / DTX.

[0155] As mentioned above, in WLAN systems, CWS is also adjusted based on ACK. When ACK feedback is received, CWS is reset to the minimum value (CWmin), and when ACK feedback is not received, CWS increases. However, in cellular systems, a CWS adjustment method that takes multiple connections into account is required.

[0156] First, for the purpose of explaining the present invention, the following terms are defined.

[0157] - Set of HARQ-ACK feedback values ​​(i.e., HARQ-ACK feedback set): refers to HARQ-ACK feedback values ​​used for CWS update / adjustment. The HARQ-ACK feedback set corresponds to the HARQ-ACK feedback values ​​decoded and available at the time the CWS is determined. The HARQ-ACK feedback set includes HARQ-ACK feedback values ​​for one or more DL (channel) transmissions (e.g., PDSCH) on an unlicensed band carrier (e.g., Scell, NR-U cell). The HARQ-ACK feedback set may include HARQ-ACK feedback values ​​for DL ​​(channel) transmissions (e.g., PDSCH), for example, multiple HARQ-ACK feedback values ​​fed back from multiple UEs. The HARQ-ACK feedback value indicates acknowledgement information for a code block group (CBG) or a transmission block (TB) and may indicate any one of ACK, NACK, DTX, or NACK / DTX. In this context, the term HARQ-ACK feedback value may be used interchangeably with terms such as HARQ-ACK value, HARQ-ACK information bit, and HARQ-ACK response.

[0158] Reference window: A time interval during which DL transmission (e.g., PDSCH) corresponding to a HARQ-ACK feedback set is performed in an unlicensed carrier (e.g., an Scell, an NR-U cell). The reference window may be defined in slot or subframe units depending on the embodiment. The reference window may refer to one or more specific slots (or subframes). According to an embodiment of the present invention, the specific slot (or reference slot) may include the starting slot of the last DL transmission burst in which at least some HARQ-ACK feedback is expected to be available.

[0159] FIG. 17 illustrates an embodiment of a method for adjusting a contention window size (CWS) based on HARQ-ACK feedback. In the embodiment of FIG. 17, the Tx entity may be a base station and the Rx entity may be a terminal, but the present invention is not limited thereto. Also, the embodiment of FIG. 17 assumes a channel access procedure for DL ​​transmission of the base station, but at least some of the configuration may be applied to a channel access procedure for UL transmission of the terminal.

[0160] Referring to Figure 17, after a Tx entity transmits an n-th DL transmission burst on an unlicensed band carrier (e.g., an Scell, an NR-U cell) (S402), if an additional DL transmission is required, the Tx entity can transmit an (n+1)-th DL transmission burst based on LBT channel access (S412). Here, a transmission burst represents a transmission using one or more adjacent slots (or subframes). Figure 17 illustrates a channel access procedure and a CWS coordination method based on the above-described first type channel access (i.e., Category 4 channel access).

[0161] First, the Tx entity receives HARQ-ACK feedback corresponding to a PDSCH transmission on an unlicensed band carrier (e.g., an Scell, an NR-U cell) (S404). The HARQ-ACK feedback used for CWS adjustment includes HARQ-ACK feedback corresponding to the last DL transmission burst (i.e., the nth DL transmission burst) on the unlicensed band carrier. More specifically, the HARQ-ACK feedback used for CWS adjustment includes HARQ-ACK feedback corresponding to a PDSCH transmission on a reference window within the last DL transmission burst. The reference window may represent one or more specific slots (or subframes). According to an embodiment of the present invention, the specific slot (or reference slot) includes the starting slot of the last DL transmission burst for which at least a portion of the HARQ-ACK feedback is expected to be available.

[0162] When HARQ-ACK feedback is received, a HARQ-ACK value is obtained for each transport block (TB). The HARQ-ACK feedback includes at least one of a TB-based HARQ-ACK bit sequence and a CBG-based HARQ-ACK. If the HARQ-ACK feedback is a TB-based HARQ-ACK bit sequence, one HARQ-ACK information bit is obtained for each TB. On the other hand, if the HARQ-ACK feedback is a CBG-based HARQ-ACK bit sequence, N HARQ-ACK information bits are obtained for each TB, where N is the maximum number of CBGs per TB configured in the Rx entity for PDSCH transmission. According to an embodiment of the present invention, for CWS determination, a HARQ-ACK value for each TB may be determined according to the HARQ-ACK information bit for each TB in the HARQ-ACK feedback. More specifically, if the HARQ-ACK feedback is a TB-based HARQ-ACK bit sequence, one HARQ-ACK information bit for the TB is determined as the HARQ-ACK value. However, if the HARQ-ACK feedback is a CBG-based HARQ-ACK bit sequence, one HARQ-ACK value may be determined based on N HARQ-ACK information bits corresponding to the CBG included in the TB.

[0163] Next, the Tx entity adjusts the CWS based on the HARQ-ACK value determined in step S404 (S406). That is, the Tx entity determines the CWS based on the HARQ-ACK value determined by the HARQ-ACK information bit for each TB in the HARQ-ACK feedback. More specifically, the CWS may be adjusted based on the ratio of NACKs in the HARQ-ACK value. First, variables may be defined as follows:

[0164] - p: Priority class value

[0165] - CW_min_p: Already configured CWS minimum value for priority class p

[0166] - CW_max_p: Maximum configured CWS value for priority class p

[0167] - CW_p: CWS for transmission of priority class p. CW_p is set to one of multiple CWS values ​​between CW_min_p and CW_max_p included in the allowed CWS set of priority class p.

[0168] According to an embodiment of the present invention, the CWS may be determined by the following steps:

[0169] Step A-1) For all priority classes p, CW_p is set to CW_min_p, where p includes {1, 2, 3, 4}.

[0170] Step A-2) If the ratio of NACKs in the HARQ-ACK values ​​for PDSCH transmissions of reference window k is equal to or greater than Z%, increase CW_p to the next highest allowed value for all priority classes p (and remain in step A-2). Otherwise, proceed to step A-1. Here, Z is a pre-defined integer in the range 0<=Z<=100, and according to one embodiment, it may be set to any one of the values ​​{30, 50, 70, 80, 100}.

[0171] where reference window k includes the starting slot (or subframe) of the last transmission by the Tx entity and is the slot (or subframe) in which at least some HARQ-ACK feedback is expected to be possible. If CW_p=CW_max_p, then the next highest allowed value for CW_p adjustment is CW_max_p.

[0172] Next, the Tx entity selects a random number within the CWS determined in step S406 and sets it as the initial value of a backoff counter N (S408). The Tx entity performs backoff using the set backoff counter N (S410). That is, the Tx entity may decrement the backoff counter by 1 for each slot period during which the channel is sensed as idle. When the value of the backoff counter reaches 0, the Tx entity may transmit the (n+1)th DL transmission burst on the channel (S412).

[0173] Meanwhile, in the above-mentioned CWS adjustment process, it is necessary to determine whether DTX or NACK / DTX is also considered in addition to ACK and NACK in the HARQ-ACK feedback. According to an embodiment of the present invention, whether DTX or NACK / DTX is also considered in the CWS adjustment process may be determined depending on whether transmission in the unlicensed band is based on self-carrier scheduling or cross-carrier scheduling.

[0174] During self-carrier scheduling, DL transmission (e.g., PDSCH) on an unlicensed band carrier is scheduled by a control channel (e.g., (E)PDCCH) transmitted on the same unlicensed band carrier. Here, DTX indicates a case where DL transmission fails due to a hidden node on the unlicensed band carrier, and may be used together with NACK for CWS adjustment. DTX is also a method by which a terminal notifies a base station when the terminal fails to decode a control channel (e.g., (E)PDCCH) including scheduling information transmitted from the base station to the terminal. DTX may be determined solely by the HARQ-ACK feedback value, or may be determined taking into consideration the HARQ-ACK feedback value and the actual scheduling situation. According to an embodiment of the present invention, DTX and NACK / DTX may be counted as NACK for CWS adjustment in a self-carrier scheduling situation. That is, if the combined ratio of NACK, DTX, and NACK / DTX in the HARQ-ACK value for PDSCH transmissions in reference window k is equal to or greater than Z%, CWS is increased to the next highest allowed value, otherwise CWS is reset to the minimum value.

[0175] During cross-carrier scheduling, DL transmission (e.g., PDSCH) on an unlicensed band carrier may be scheduled on a control channel (e.g., (E)PDCCH) transmitted on a licensed band carrier. In this case, DTX feedback is used to determine the UE's decoding status for the control channel transmitted on the licensed band carrier, and is therefore not useful for adaptively adjusting CWS for channel access in the unlicensed band. Therefore, according to an embodiment of the present invention, DTX may be ignored for CWS determination in a cross-carrier scheduling situation from a licensed band. That is, for CWS adjustment, the NACK ratio may be calculated by considering only ACK and NACK among HARQ-ACK values, or the NACK ratio may be calculated by considering only ACK, NACK, and NACK / DTX. Therefore, DTX may be excluded when calculating the NACK ratio.

[0176] 18 is a block diagram illustrating the configuration of a terminal and a base station according to an embodiment of the present invention. In an embodiment of the present invention, the terminal may be implemented as any of various types of wireless communication devices or computing devices that ensure portability and mobility. The terminal may be referred to as a UE, a station (STA), a mobile subscriber (MS), etc. In addition, in an embodiment of the present invention, the base station controls and manages cells (e.g., macrocells, femtocells, picocells, etc.) corresponding to a service area, and performs functions such as signal transmission, channel assignment, channel monitoring, self-diagnosis, and relaying. The base station may be referred to as a next generation NodeB (gNB) or an access point (AP), etc.

[0177] As shown, a terminal 100 according to one embodiment of the present invention includes a processor 110 , a communication module 120 , a memory 130 , a user interface unit 140 , and a display unit 150 .

[0178] First, the processor 110 executes various commands or programs to process data within the terminal 100. The processor 110 also controls the overall operation of the terminal 100, including each unit, and controls the transmission and reception of data between the units. Here, the processor 110 is configured to perform operations according to the embodiments described in the present invention. For example, the processor 110 may receive slot configuration information, determine the slot configuration based on the information, and perform communication according to the determined slot configuration.

[0179] Next, the communication module 120 is an integrated module that performs wireless communication using a wireless communication network and wireless LAN access using a wireless LAN. To this end, the communication module 120 includes multiple network interface cards (NICs) such as cellular communication interface cards 121 and 122 and an unlicensed band communication interface card 123, either built-in or external. Although the communication module 120 is shown as an integrated module in the drawings, the network interface cards may be independently arranged depending on the circuit configuration or application, unlike the drawings.

[0180] The cellular communication interface card 121 transmits and receives wireless signals to and from at least one of the base station 200, an external device, and a server via a mobile communication network, and provides cellular communication services in a first frequency band based on instructions from the processor 110. According to one embodiment, the cellular communication interface card 121 includes at least one NIC module that utilizes a frequency band below 6 GHz. The at least one NIC module of the cellular communication interface card 121 independently performs cellular communication with at least one of the base station 200, the external device, and the server in accordance with a cellular communication standard or protocol for the frequency band below 6 GHz supported by the NIC module.

[0181] The cellular communication interface card 122 transmits and receives wireless signals to and from at least one of the base station 200, an external device, and a server using a mobile communication network, and provides cellular communication services in the second frequency band based on instructions from the processor 110. According to one embodiment, the cellular communication interface card 122 includes at least one NIC module that uses a frequency band above 6 GHz. The at least one NIC module of the cellular communication interface card 122 independently performs cellular communication with at least one of the base station 200, the external device, and the server in accordance with the cellular communication standard or protocol for the frequency band above 6 GHz that the NIC module supports.

[0182] The unlicensed band communication interface card 123 transmits and receives wireless signals to and from at least one of the base station 200, an external device, and a server via the third frequency band, which is an unlicensed band, and provides unlicensed band communication services based on instructions from the processor 110. The unlicensed band communication interface card 123 includes at least one NIC module that utilizes the unlicensed band. For example, the unlicensed band may be 2.4 GHz, 5 GHz, 6 GHz, 7 GHz, or 52.6 GHz or higher. The at least one NIC module of the unlicensed band communication interface card 123 independently or dependently performs cellular communication with at least one of the base station 200, the external device, and the server according to the unlicensed band communication standard or protocol of the frequency band supported by the NIC module.

[0183] The memory 130 stores control programs and various data used by the terminal 100. The control programs include predetermined programs required for the terminal 100 to perform wireless communication with at least one of the base station 200, an external device, and a server.

[0184] Next, the user interface 140 includes various types of input / output means provided in the terminal 100. That is, the user interface unit 140 receives user input using various input means, and the processor 110 controls the terminal 100 based on the received user input. Also, the user interface 140 performs output based on instructions from the processor 110 using various output means.

[0185] The display unit 150 then outputs various images to a display screen, and displays various display objects such as a user interface based on the content or control instructions of the processor 110.

[0186] The base station 200 according to the embodiment of the present invention also includes a processor 210 , a communication module 220 , and a memory 230 .

[0187] First, the processor 210 executes various instructions or programs to process data within the base station 200. The processor 210 also controls the overall operation of the base station 200, including each unit, and controls the transmission and reception of data between the units. Here, the processor 210 is configured to perform operations according to the embodiments described herein. For example, the processor 210 may signal slot configuration information and perform communication according to the signaled slot configuration.

[0188] Next, the communication module 220 is an integrated module that performs wireless communication using a wireless communication network and wireless LAN access using a wireless LAN. To this end, the communication module 220 includes multiple network interface cards, such as cellular communication interface cards 221 and 222 and an unlicensed band communication interface card 223, either built-in or externally mounted. Although the communication module 220 is shown as an integrated module in the drawings, the network interface cards may be independently arranged depending on the circuit configuration or application, unlike the drawings.

[0189] The cellular communication interface card 221 transmits and receives wireless signals to and from at least one of the terminal 100, the external device, and the server using a mobile communication network, and provides cellular communication services in the first frequency band based on instructions from the processor 210. According to one embodiment, the cellular communication interface card 221 includes at least one NIC module that uses a frequency band below 6 GHz. The at least one NIC module of the cellular communication interface card 221 independently performs cellular communication with at least one of the terminal 100, the external device, and the server according to a cellular communication standard or protocol for the frequency band below 6 GHz supported by the NIC module.

[0190] The cellular communication interface card 222 transmits and receives wireless signals to and from at least one of the terminal 100, an external device, and a server using a mobile communication network, and provides cellular communication services in the second frequency band based on instructions from the processor 210. According to one embodiment, the cellular communication interface card 222 includes at least one NIC module that uses a frequency band above 6 GHz. The at least one NIC module of the cellular communication interface card 222 independently performs cellular communication with at least one of the terminal 100, the external device, and the server according to a cellular communication standard or protocol for the 6 GHz or higher frequency band supported by the NIC module.

[0191] The unlicensed band communication interface card 223 transmits and receives wireless signals to and from at least one of the terminal 100, an external device, and a server using the third frequency band, which is an unlicensed band, and provides unlicensed band communication services based on instructions from the processor 210. The unlicensed band communication interface card 223 includes at least one NIC module that uses the unlicensed band. For example, the unlicensed band may be 2.4 GHz, 5 GHz, 6 GHz, 7 GHz, or 52.6 GHz or higher. The at least one NIC module of the unlicensed band communication interface card 223 independently or dependently performs cellular communication with at least one of the terminal 100, an external device, and a server according to the unlicensed band communication standard or protocol of the frequency band supported by the NIC module.

[0192] The terminal 100 and base station 200 shown in Figure 18 are block diagrams according to one embodiment of the present invention, and the separate blocks indicate logically distinct device elements. Therefore, the above-described device elements may be mounted on one chip or multiple chips depending on the device design. In addition, some components of the terminal 100, such as the user interface 140 and display unit 150, may be selectively provided in the terminal 100. In addition, the user interface 140 and display unit 150 may be additionally provided in the base station 200 as needed.

[0193] A channel access procedure performed in an unlicensed band by a wireless communication device according to an embodiment of the present invention will be described with reference to FIG. 19. Specifically, an LBT procedure used when a wireless communication device according to an embodiment of the present invention performs channel access in an unlicensed band will be described. In particular, a channel access in which the wireless communication device performs transmission based on a channel sensing result within a time interval of a pre-specified duration may be set for the wireless communication device. In this case, if the wireless communication device fails to access the channel, an operation method of the wireless communication device will be described. The pre-specified duration mentioned above may be 16 us.

[0194] For ease of explanation, a wireless communication device that is a wireless endpoint initiating channel occupancy is referred to as an initiating node. Furthermore, a wireless communication device that is a wireless endpoint communicating with the initiating node is referred to as a responding node. The initiating node may be a base station, and the responding node may be a mobile station. Alternatively, the initiating node may be a mobile station, and the responding node may be a base station. When the initiating node attempts to transmit data, the initiating node may perform channel access based on a channel access priority class determined according to the type of data. At this time, parameters used for channel access may be determined according to the type of data. The parameters used for channel access may include at least one of a minimum CW value, a maximum CW value, a maximum channel occupancy time (MCOT), which is the maximum duration for occupying a channel in one channel occupancy, and the number of sensing slots (mp). Specifically, the initiating node may perform the above-described Category 4 LBT based on a channel access priority class determined according to the type of data.

[0195] Table 4 below shows an example of parameter values ​​used for channel access based on channel access priority classes. Specifically, Table 4 shows parameter values ​​used for channel access for each channel access priority class for downlink transmission in the LTE LAA system.

[0196] When the downlink channel transmitted by the wireless communication device includes data traffic, the defer duration may be set based on the channel access priority class of the traffic included in the downlink channel. f ) one or more (m p ) slot section (T sl ) can be included. In this case, the slot interval (T slThe duration of the initial interval may be 9 us. sl ) is included in the defer period. p ) may be set based on the channel access priority class as described above. Specifically, the number of slot periods included in the defer period (m p ) may be set as shown in Table 4.

[0197] [Table 4]

[0198] In addition, the wireless communication device can set the range of the CW value according to the channel access priority class. min,p <=CW<=CW max,p The CW value can be set to satisfy the following. min,p ) and maximum value (CW max,p ) may be determined by the channel access priority class. Specifically, the minimum value of CW (CW min,p ) and maximum value (CW max,p ) may be determined as shown in Table 4. The wireless communication device determines the minimum value of CW (CW min,p ) and maximum value (CW max,p ) can be set. When a wireless communication device accesses a channel, the wireless communication device can adjust the value of CW as previously described with reference to FIGS. 15 to 17. In addition, in the unlicensed band, MCOT(T mcot,p) may be determined according to the channel access priority of the data included in the transmission, as described above. Specifically, the MCOT may be determined as shown in Table 4. As a result, the wireless communication device may not be allowed to transmit continuously in the unlicensed band for a time exceeding the MCOT. This is because the unlicensed band is a frequency band that various wireless communication devices use according to certain rules. In Table 4, when the value of the channel access priority class is p=3 or p=4 and there is no wireless communication device that uses the unlicensed band for a long term according to the regulations and uses other technology, the wireless communication device mcot,p = 10 ms. Otherwise, the wireless communication device mcot,p =8ms.

[0199] Table 5 shows parameter values ​​used for channel access by channel access priority class for uplink transmission used in the LTE LAA system.

[0200] [Table 5]

[0201] As shown in Table 5, the MCOT value of 6 ms may be increased to 8 ms if a transmission includes one or more gaps. A gap refers to the time from when transmission is interrupted on a carrier until transmission resumes on that carrier. In this case, the minimum duration of a gap is 100 us. The maximum duration of a transmission before a gap is 6 ms. The duration of a gap is not included in the channel occupancy time. When the channel access priority class value is 3 or 4 and it is guaranteed that no other wireless access technologies are used on the carrier where channel access is performed, the MCOT value may be 10 ms. In this case, other wireless access technologies may include Wi-Fi. In other cases, the MCOT value may be determined as described in Note 1 of Table 5.

[0202] The COT represents the time that a wireless communication device occupies a channel. The MCOT, as described above, represents the maximum time that an initiating node can continuously occupy a channel on any one carrier in the unlicensed band. However, as described above, gaps, which are periods when no transmission is performed, may be included between multiple transmissions. When gaps are included, the value of the MCOT may be applied differently.

[0203] 19 shows that in an embodiment of the present invention, the responding node transmits within the channel occupation initiated by the initiating node if the duration of the initiating node's transmission within the channel occupation initiated by the initiating node does not exceed the MCOT of the channel occupation. In other words, after the initiating node completes transmission on one of the channels, the responding node transmits on that channel. This transmission by the initiating node and the responding node on one channel can be expressed as sharing the channel occupation.

[0204] If the duration of the initiating node's transmission is less than the duration of the MCOT, the responding node can transmit within the channel occupancy initiated by the initiating node. Such a case is shown in Figure 19, where the gap between the initiating node's transmission and the responding node's transmission is assumed to be 16 us. In this case, how the responding node accesses the channel can become an issue.

[0205] In an embodiment of the present invention, if the duration of the gap is not greater than the first duration, the responding node can immediately transmit after the gap without sensing. Specifically, the responding node can perform the above-described Category 1 channel access. The first duration may be 16 us, which is also applicable to the embodiments described below. In such an embodiment, a further constraint may be applied to the duration of the responding node's transmission in addition to the MCOT. In a specific embodiment, the responding node can transmit within a pre-specified duration. In this case, the pre-specified duration may be a constraint applied to the responding node's transmission apart from the MCOT. Specifically, the pre-specified duration may be 584 us.

[0206] In an embodiment of the present invention, when the duration of the gap is the same as the first duration, the responding node may perform first fixed duration-based channel access for transmission following the gap. The first fixed duration-based channel access is channel access in which, if the channel is sensed to be idle within the first fixed duration, the wireless communication device performing the first fixed duration-based channel access is allowed to transmit immediately after the first fixed duration. Specifically, in the first fixed duration-based channel access, the wireless communication device senses the channel within the first fixed duration, and transmits on the channel if the channel is sensed to be idle within the fixed duration. The first fixed duration-based channel access may be the above-mentioned Category 2 LBT. In such an embodiment, the initiating node may implicitly or explicitly instruct the responding node to use the first fixed duration-based channel access. For example, the base station, which is the initiating node, may use a grant to instruct the responding node to use the first fixed duration-based channel access.

[0207] In an embodiment of the present invention, if the initiating node initiates a channel occupation and the scheduled transmissions are consecutive or the gap between granted transmissions is not greater than the second fixed duration, the node performing the second transmission may perform second fixed duration-based channel access. The second fixed duration-based channel access is a channel access in which, if the channel is idle during the second fixed duration, the wireless communication device performing second fixed duration-based channel access is allowed to transmit immediately after the second fixed duration. Specifically, in the second fixed duration-based channel access, the wireless communication device performs channel sensing during the second fixed duration, and transmits on the channel if it senses that the channel is idle during the fixed duration. The second fixed duration may be greater than the first fixed duration. Specifically, the second fixed duration may be 25 us, which is also applicable to the embodiments described below. Furthermore, even if an uplink transmission is not followed by a downlink transmission within the same channel occupation, the terminal may perform the second fixed duration-based channel access for the uplink transmission after the uplink transmission. Also, even if a downlink transmission is not followed by an uplink transmission within the same channel occupation, the terminal may perform the second fixed duration-based channel access for the uplink transmission. Furthermore, if the gap between an uplink transmission and a subsequent downlink transmission within the same channel occupation is greater than 16 us but not greater than 25 us, the base station may perform the second fixed duration-based channel access for the downlink transmission.

[0208] An example will be described that is applied when the gap is not larger than the first fixed duration, which may be 16 us as described above.

[0209] If the gap is not larger than the first fixed duration, a responding node that transmits following the gap can either transmit immediately without sensing or perform first fixed duration-based channel access to transmit. In this case, the responding node can either transmit immediately without sensing or perform first fixed duration-based channel access to transmit, depending on whether the transmission following the gap includes data traffic that can be classified as traffic or data traffic that determines a channel access priority class. Specifically, when the responding node transmits HARQ-ACK feedback for data traffic transmitted from the initiating node, the responding node can transmit immediately without sensing.

[0210] In yet another specific embodiment, when the responding node transmits uplink control information (UCI) for the data traffic transmitted from the initiating node, the responding node can immediately transmit without sensing.

[0211] In yet another specific embodiment, when the responding node transmits the SRS, the responding node can transmit immediately without sensing.

[0212] In yet another specific embodiment, when the responding node transmits a physical random access channel (PRACH), the responding node can transmit immediately without sensing.

[0213] In the above-described embodiment, if the responding node performs a transmission including data traffic immediately after the gap, the responding node may perform first fixed duration-based channel access. Specifically, if the data traffic is scheduled or configured by the initiating node, the responding node may perform first fixed duration-based channel access. If the data traffic can be classified as traffic or the channel access priority class of the data traffic can be determined, the responding node may perform first fixed duration-based channel access.

[0214] In the above embodiment, the responding node immediately transmitting without sensing may mean that the initiating node performs the above-mentioned Category 4 channel access. As mentioned above, the first fixed duration-based channel access may be Category 2 LBT.

[0215] Within a COT initiated by the initiating node, the initiating node may transmit after the responding node transmits. In this case, within a COT initiated by the initiating node, the gap between the initiating node's transmission following the responding node's transmission may not be greater than the first fixed duration. Depending on whether the transmission after the gap includes data traffic that can be classified as traffic or data traffic that determines a channel access priority class, the initiating node may transmit immediately without sensing or may perform first fixed duration-based channel access for transmission.

[0216] Specifically, when the initiating node transmits only control information for scheduling data to be transmitted by the responding node, the initiating node can immediately transmit without sensing. In this case, the control information may be at least one of PDCCH only, group common signaling, paging, reference signal only, tracking reference signal (TRS), RACH message 4, or handover command.

[0217] In yet another specific embodiment, when the initiating node transmits only broadcasting information, the initiating node can immediately transmit without sensing. In this case, the broadcasting information may be at least one of a discovery reference signal (DRS), an SS / PBCH block, a Type0-PDCCH, or remaining system information (RMSI).

[0218] In the above-described embodiment, when the initiating node performs a transmission including data traffic immediately after the gap, the initiating node may perform the first fixed duration-based channel access. Specifically, when the data traffic is scheduled for or configured for the responding node, the initiating node may perform the first fixed duration-based channel access. When the data traffic can be classified into traffic or the channel access priority class of the data traffic can be determined, the initiating node may perform the first fixed duration-based channel access.

[0219] In the above embodiment, the initiating node immediately transmitting without sensing may mean that the initiating node performs the above-mentioned Category 4 channel access. As mentioned above, the first fixed duration-based channel access may be Category 2 LBT.

[0220] In the above-described embodiments, the initiating node may be a base station and the responding node may be a terminal. That is, in the above-described embodiments, the channel occupation may be initiated by the base station. The initiating node may be a terminal and the responding node may be a base station. That is, in the above-described embodiments, the channel occupation may be initiated by the terminal.

[0221] In the above embodiment, nodes transmitting after the gap can transmit within the MCOT.

[0222] FIG. 20 illustrates the operation of a terminal in an embodiment of the present invention when downlink transmission cannot occupy MCOT in the COT initiated by the base station and the terminal transmission is scheduled or configured by the base station.

[0223] In FIG. 20, the gap between the downlink transmission of the base station and the uplink transmission of the terminal is 16 us. In FIG. 20(a), the downlink transmission includes multiple UL grants that schedule PUSCH transmission on a slot-by-slot basis. The terminal transmits PUSCH in multiple slots based on the multiple UL grants. In FIG. 20(b), the downlink transmission includes one UL grant that schedules PUSCH transmission in multiple slots. The terminal transmits PUSCH in multiple slots based on the UL grant. In FIG. 20, scheduling for uplink transmission may be performed within channel occupancy acquired by the base station, which is the initiating node, or the configuration or scheduling of uplink transmission may be performed before channel occupancy. In such a case, the embodiments described below may also be applied.

[0224] The initiating node may be a base station, and the responding node may be a terminal. When the gap between the initiating node's transmission and the responding node's transmission is a first fixed duration, the base station may implicitly or explicitly instruct the responding node to use the first fixed duration-based channel access. For example, the base station, which is the initiating node, may use an UL grant to instruct the responding node to use the first fixed duration-based channel access. In this case, the terminal senses the channel within the first fixed duration. If the channel is sensed as idle within the first duration, the terminal immediately transmits after the first fixed duration. If the channel is sensed as busy within the first duration, the operation method of the terminal becomes an issue. Specifically, as described above, uplink transmissions may be scheduled or configured for the terminal on multiple slots. In this case, even if the terminal fails to access the channel in the first slot of the multiple slots, channel access for uplink transmission may be required in slots other than the first slot of the multiple slots. The operation method of the terminal in this case will be described. For ease of explanation, the slots in which the UE's uplink transmission is scheduled or configured are denoted as {slot(n), slot(n+1), slot(n+2), ..., slot(n+k-1)}, and the number of slots is denoted as k.

[0225] A terminal may be scheduled or configured with multiple uplink transmissions. The multiple uplink transmissions may be consecutive and without gaps. Specifically, the terminal may receive a grant from a base station to schedule the multiple uplink transmissions. The grant refers to downlink control information (DCI) and may include a DL grant or an UL grant to schedule the uplink transmission. In a specific embodiment, the DL grant or the UL grant may indicate a fixed-duration-based channel access as a channel access type and indicate a channel access priority to be used to access a channel on which the multiple uplink transmissions are performed. In this case, the DL grant or the UL grant may indicate the first fixed-duration-based channel access as a channel access type.

[0226] When a terminal attempts a first fixed duration-based channel access for a first transmission, which is one of a plurality of uplink transmissions, and the first fixed duration-based channel access fails, the terminal may attempt the first fixed duration-based channel access for a second transmission, which is a transmission subsequent to the first transmission. When the terminal succeeds in the first fixed duration-based channel access, the terminal may perform the second transmission. In a specific embodiment, the terminal may perform the first fixed duration-based channel access for uplink transmission for each of the remaining slots (slot(n+1), slot(n+2), ..., slot(n+k-1)) after the first slot (slot(n)) of the plurality of slots.

[0227] In yet another specific embodiment, the UE may perform first fixed duration-based channel access for uplink transmission a predetermined number of times in the remaining slots (slot(n+1), slot(n+2), ..., slot(n+k-1)) after the first slot (slot(n)) of the plurality of slots. In this case, the predetermined number of times may be limited to k-1.

[0228] In yet another specific embodiment, if a terminal attempts first fixed duration-based channel access for a first transmission, which is one of a plurality of uplink transmissions, and fails the first fixed duration-based channel access, the terminal may attempt first fixed duration-based channel access or random backoff-based channel access for a second transmission, which is a transmission subsequent to the first transmission, depending on whether the channel is sensed as idle consecutively. If the terminal fails first fixed duration-based channel access in the first slot (slot(n)) and the channel is sensed as idle consecutively after the terminal's failed channel access, the terminal may attempt first fixed duration-based channel access for the second transmission. In this case, if the terminal succeeds in the first fixed duration-based channel access, the terminal may perform the second transmission. In addition, if the UE fails in the first fixed-duration-based channel access in the first slot (slot(n)) and does not continuously sense that the channel is idle after the failed channel access, the UE may perform random backoff-based channel access for uplink transmission in the remaining slots (slot(n+1), slot(n+2), ..., slot(n+k-1)) after the first slot (slot(n)) among the plurality of slots. If the UE succeeds in the random backoff-based channel access, the UE may perform a second transmission. In this case, if the DCI indicates to the UE the random backoff-based channel access as a channel access method in the first slot (slot(n)) or the remaining slots (slot(n+1), slot(n+2), ..., slot(n+k-1)) after the first slot among the plurality of slots, the UE may perform random backoff-based channel access using the channel access priority class indicated by the DCI.When a channel access method other than random backoff-based channel access is indicated to a terminal in a DCI as a channel access method in all of a plurality of slots (slot(n), slot(n+1), slot(n+2), ..., slot(n+k-1)), the terminal can perform random backoff-based channel access for uplink transmission using the channel access priority class indicated in the scheduling DCI. To this end, when a base station indicates fixed duration-based channel access in a DCI, the base station can indicate a channel access priority class to be used for obtaining access to a channel in the DCI. Specifically, when a base station indicates first fixed duration-based channel access in a DCI, the base station can indicate a channel access priority class to be used for obtaining access to a channel in the DCI.

[0229] In yet another specific embodiment, when a terminal attempts a first fixed duration based channel access for a first transmission, which is one of a plurality of uplink transmissions, and the first fixed duration based channel access fails, the terminal may attempt a second fixed duration based channel access for a second transmission, which is a transmission following the first transmission. When the terminal succeeds in the second fixed duration based channel access, the terminal may perform the second transmission. Specifically, after the terminal fails to access the first fixed duration based channel in the first slot (slot(n)), the terminal may attempt a second fixed duration based channel access in every sensing slot (T sl) can sense whether the channel is idle. If the terminal fails in first fixed duration based channel access in the first slot (slot(n)) and the channel is continuously sensed as idle after the terminal has failed channel access, the terminal can perform second fixed duration based channel access for uplink transmission in the remaining slots (slot(n+1), slot(n+2), ..., slot(n+k-1)) after the first slot (slot(n)) among the plurality of slots. This takes into consideration that the first fixed duration based channel access may be performed when the gap is the first fixed duration period, and the gap between transmissions may become large due to the failed channel access in the first slot (slot(n)). If the UE fails in the first fixed-duration-based channel access in the first slot (slot(n)) and does not continuously sense that the channel is idle after the failed channel access, the UE may perform random backoff-based channel access for uplink transmission in the remaining slots (slot(n+1), slot(n+2), ..., slot(n+k-1)) after the first slot of the plurality of slots. If the UE succeeds in the random backoff-based channel access, the UE may perform a second transmission. In this case, if the DCI indicates to the UE the random backoff-based channel access as a channel access method in the first slot (slot(n)) or the remaining slots (slot(n+1), slot(n+2), ..., slot(n+k-1)) after the first slot, the UE may perform random backoff-based channel access using the channel access priority class indicated by the DCI.When a channel access method other than random backoff-based channel access is indicated to a terminal by DCI as a channel access method in all of a plurality of slots (slot(n), slot(n+1), slot(n+2), ..., slot(n+k-1)), the terminal can perform random backoff-based channel access for uplink transmission using the channel access priority class indicated by the scheduling DCI. To this end, when the base station indicates fixed duration-based channel access by DCI, the base station can indicate a channel access priority class to be used for obtaining access to the channel by the DCI. Specifically, when the base station indicates first fixed duration-based channel access by DCI, the base station can indicate a channel access priority class to be used for obtaining access to the channel by the DCI.

[0230] In yet another specific embodiment, a first fixed duration gap is set between a transmission from the base station and an uplink transmission to be transmitted by the terminal, and the terminal may switch the channel access type to the first fixed duration-based channel access for a first transmission, which is one of multiple uplink transmissions. If the first fixed duration-based channel access fails, the terminal may attempt channel access according to the channel access type indicated by the DCI for a second transmission, which is the transmission following the first transmission. If the terminal succeeds in the channel access, the terminal may perform the second transmission. Specifically, if the terminal fails the first fixed duration-based channel access in the first slot (slot(n)), the terminal may perform channel access for uplink transmission according to the channel access type indicated by the DCI in the remaining slots (slot(n+1), slot(n+2), ..., slot(n+k-1)) following the first slot (slot(n)) among the multiple slots. Furthermore, when multiple grants schedule uplink transmissions in multiple slots, the channel access type for uplink transmission may be indicated for each slot. The UE may perform channel access for uplink transmission in the remaining slots (slot(n+1), slot(n+2), ..., slot(n+k-1)) following the first slot (slot(n)) among the plurality of slots according to the channel access type indicated for each slot. In this embodiment, when the channel access type indicated by the DCI is the first fixed duration-based channel access, the operation of the UE may be the same as the first and second described embodiments. However, when the channel access type indicated by the DCI is not the first fixed duration-based channel access, the operation of the UE differs from the first and second described embodiments.

[0231] In yet another specific embodiment, if the UE fails in the first fixed duration-based channel access in the first slot (slot(n)), the UE may perform random backoff-based channel access for uplink transmission in the remaining slots (slot(n+1), slot(n+2), ..., slot(n+k-1)) after the first slot (slot(n)) among the plurality of slots. This takes into consideration the high possibility that the channel is not idle but is being used by another node using the unlicensed band. Specifically, in this embodiment, if the channel is sensed as being busy rather than idle through the first fixed duration-based channel access, even if the UE subsequently performs the first fixed duration-based channel access or the second fixed duration-based channel access, the channel is likely to be busy rather than idle because it is being used by another node. Therefore, this method is such that the UE performs random backoff-based channel access for transmission in slot(n+1) and the following slots before performing uplink transmission.

[0232] In the above embodiment, the random backoff based channel access may be Category 4 LBT.

[0233] In the case where uplink transmission is scheduled first, the embodiments of the present invention have been described mainly in connection with the case where uplink transmission is scheduled by a scheduling grant. The above-described embodiments can also be applied to the case where resources in time and frequency units are configured by RRC configuration, and the UE performs uplink transmission using the configured resources.

[0234] Although the methods and systems of the present invention have been described in connection with particular embodiments, some or all of their components or operations may be implemented using a computing system having a general-purpose hardware architecture.

[0235] The above description of the present invention is for illustrative purposes only, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. Therefore, the above-described embodiments should be understood to be illustrative in all respects and not restrictive. For example, each component described as a single component may be implemented in a distributed form, and similarly, each component described as a distributed component may be implemented in a combined form.

[0236] The scope of the present invention is indicated by the claims set forth below rather than by the above detailed description, and any modifications or variations derived from the meaning and scope of the claims and their equivalents should be construed as being within the scope of the present invention. [Explanation of symbols]

[0237] 110 processors 121 Cellular communication interface card (first frequency band) 122 Cellular communication interface card (second frequency band) 123 Unlicensed Spectrum Communication Interface Card (Third Frequency Band) 130 memory 140 User Interface 150 display units 210 processors 221 Cellular Communication Interface Card (First Frequency Band) 222 Cellular Communication Interface Card (Second Frequency Band) 223 Unlicensed Spectrum Communication Interface Card (Third Frequency Band) 230 memory

Claims

1. 1. A user equipment (UE) for use in a Third Generation Partnership Project (3GPP) based wireless communication system, comprising: a communication module; and a processor for controlling the communication module; The processor: configured to perform a channel access procedure for a set of consecutive transmissions; If channel access is unsuccessful for an nth transmission in the set of consecutive transmissions according to a first channel access procedure, the first channel access procedure includes sensing the channel within 16 μs before the nth transmission, and the processor is configured to attempt transmission of an (n+1)th transmission in the set of consecutive transmissions according to a second channel access procedure, the second channel access procedure including sensing the channel for a fixed time duration greater than 16 μs before the (n+1)th transmission. UE.

2. 2. The UE of claim 1, wherein the fixed time duration greater than 16 μs comprises 25 μs.

3. The UE of claim 1 or 2, wherein the set of consecutive transmissions comprises consecutive physical shared channel transmissions.

4. The UE of claim 1 , wherein the set of consecutive transmissions is within a channel occupation time (COT).

5. 5. The UE of claim 1, wherein the set of consecutive transmissions is associated with one or more grants.

6. The UE of claim 1 , wherein the first and second channel access procedures do not include a backoff operation.

7. 1. A method for use by a user equipment (UE) in a Third Generation Partnership Project (3GPP) based wireless communication system, comprising: performing a channel access procedure for a set of consecutive transmissions; If channel access is unsuccessful for an nth transmission in the set of consecutive transmissions according to a first channel access procedure, the first channel access procedure includes sensing the channel within 16 μs before the nth transmission, and the UE attempts to transmit an (n+1)th transmission in the set of consecutive transmissions according to a second channel access procedure, the second channel access procedure including sensing the channel for a fixed time duration greater than 16 μs before the (n+1)th transmission. method.

8. The method of claim 7 , wherein the fixed time duration greater than 16 μs comprises 25 μs.

9. The method of claim 7 or 8, wherein the set of consecutive transmissions comprises consecutive physical shared channel transmissions.

10. The method of any one of claims 7 to 9, wherein the set of consecutive transmissions is within a channel occupancy time (COT).

11. The method of claim 7 , wherein the set of consecutive transmissions is associated with one or more grants.

12. 12. The method of claim 7, wherein the first and second channel access procedures do not include a back-off operation.

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