Method, apparatus and system for channel access in an unauthorized band

Abstract

The present invention relates to a method, apparatus, and system for channel access in an unauthorized band. Specifically, the present invention relates to a method, apparatus, and system thereof, the method comprising the steps of: receiving uplink scheduling information; and when the terminal stops uplink transmission during uplink transmission being performed according to the uplink scheduling information, in order to resume uplink transmission, if the channel sensed by the terminal is continuously unoccupied after the terminal stops uplink transmission, perform a type-II LBT, and if the channel sensed by the terminal is continuously occupied after the terminal stops uplink transmission, perform a type-I LBT, wherein the type-I channel access includes performing a random backoff after channel sensing, and the type-II channel access includes only performing channel sensing.

Description

[0001] This application is a divisional application of the patent application with the application number 201780057852.6 (PCT / KR2017 / 007967), the international filing date of July 24, 2017, and the invention title of "Method, Apparatus, and System for Channel Access in Unlicensed Bands", which was filed with the Chinese Patent Office on March 20, 2019. Technical Field

[0002] The present invention relates to a wireless communication system. Specifically, the present invention relates to a method, device, and system for performing channel access in an unlicensed band. Background Art

[0003] In recent years, with the explosive growth of mobile services due to the popularity of smart devices, it has been difficult to handle the increasing data usage for providing cellular communication services only through conventional licensed spectrum or LTE licensed bands.

[0004] In this context, a solution to the spectrum shortage problem has been designed by using unlicensed (alternatively, unauthorised, unlicensed, or not necessarily authorised) spectrum or LTE unlicensed bands (e.g., 2.4 GHz band, 5 GHz band, etc.) to provide cellular communication services.

[0005] However, different from the licensed band where a communication service provider secures the exclusive right to use a frequency through a process such as auction, in the unlicensed band, multiple communication facilities can be used simultaneously without restriction when only complying with a predetermined level of adjacent band protection rules. Therefore, when using the unlicensed band in cellular communication services, it is difficult to ensure the level of communication quality provided in the licensed band, and interference problems may occur with common wireless communication devices (e.g., wireless LAN devices) using the unlicensed band.

[0006] Therefore, it is necessary to prioritize research on coexistence schemes for conventional unlicensed band devices and schemes for efficient sharing of radio channels in order to solve the LTE technology in the unlicensed band. That is, it is necessary to develop a robust coexistence mechanism (RCM) to prevent devices using LTE technology in the unlicensed band from affecting conventional unlicensed band devices. Summary of the Invention

[0007] Technical Problem

[0008] The present invention has been dedicated to providing a method for efficiently transmitting signals in a wireless communication system (specifically, a cellular wireless communication system and its devices). Further, the present invention has been dedicated to providing a method for efficiently transmitting signals in a specific frequency band (e.g., an unlicensed band) and its devices.

[0009] The technical objectives expected to be achieved in the present invention are not limited to the foregoing objectives, and those skilled in the art will clearly understand other technical objectives not described above from the following disclosure.

[0010] Technical solution

[0011] A first embodiment of the present invention provides a method for a user equipment to perform uplink transmission in a specific cell in a wireless communication system, including: receiving uplink scheduling information; and when the user equipment has stopped uplink transmission during the execution of uplink transmission according to the uplink scheduling information, in order to resume uplink transmission, when the channel sensed by the user equipment is continuously idle after the uplink transmission has stopped, performing a second type of channel access; and when the channel sensed by the user equipment is not continuously idle after the uplink transmission has stopped, performing a first type of channel access, where the first type of channel access includes performing a random backoff after channel sensing, and the second type of channel access only includes performing channel sensing.

[0012] A second embodiment of the present invention provides a user equipment used in a wireless communication system, including: a wireless communication module; a processor, where the processor receives uplink scheduling information, and when the user equipment has stopped uplink transmission during the execution of uplink transmission according to the uplink scheduling information, in order to resume uplink transmission, when the channel sensed by the user equipment is continuously idle after the uplink transmission has stopped, performing a second type of channel access; and when the channel sensed by the user equipment is not continuously idle after the uplink transmission has stopped, performing a first type of channel access, where the first type of channel access includes performing a random backoff after channel sensing, and the second type of channel access only includes performing channel sensing.

[0013] In the first and second embodiments, the uplink transmission may include transmission on multiple subframes, and the user equipment stopping the uplink transmission during the execution of the uplink transmission may include discarding the uplink transmission in subframes other than the last subframe of the multiple subframes.

[0014] In the first and second embodiments, the wireless communication system may include a wireless communication system based on the 3rd Generation Partnership Project (3GPP), and the first type of channel access may include Category-4 Listen Before Talk (LBT), and the second type of channel access may include Category-2 LBT.

[0015] In the first and second embodiments, the first type of channel access may include performing a random backoff using a variable-size contention window (CW), and the second type of channel access may include performing channel sensing for a duration of 25 us without random backoff.

[0016] In the first and second embodiments, the specific cell may be an unlicensed cell.

[0017] A third embodiment of the present invention provides a method for a user equipment to perform uplink transmission in multiple carriers in a wireless communication system, including: receiving uplink scheduling information indicating a first type of channel access for a first set of carriers; receiving uplink scheduling information indicating a second type of channel access for a second set of carriers; performing the first type of channel access only for a specific carrier among the first set of carriers and performing the second type of channel access for the remaining carriers; and performing the second type of channel access indicated by the uplink scheduling information for the second set of carriers, wherein when the first type of channel access fails in the specific carrier, the uplink transmission is discarded only in the first set of carriers among the carriers where the second type of channel access is performed.

[0018] A fourth embodiment of the present invention provides a method for a user equipment to perform uplink transmission in multiple carriers in a wireless communication system, including: receiving uplink scheduling information indicating a first type of channel access for a first set of carriers; performing the first type of channel access only for a specific carrier among the first set of carriers and performing the second type of channel access for the remaining carriers; and adjusting the contention window size (CWS) for each carrier, wherein the reception response information for the uplink transmission on the specific carrier transmitted by performing the first type of channel access is reflected in the CWS adjustment of the user equipment, while the reception response information for the uplink transmission on the remaining carriers among the first set of carriers where the first type of channel access is not performed is not reflected in the CWS adjustment of the user equipment.

[0019] Advantageous Effects

[0020] According to an exemplary embodiment of the present invention, a method for efficiently transmitting signals in a wireless communication system (specifically, a cellular wireless communication system and its devices) is provided. Further, a method for efficiently transmitting signals in a specific frequency band (e.g., unlicensed band) and its devices is provided.

[0021] The effects obtained in the present invention are not limited to the foregoing effects, and those skilled in the art will clearly understand other effects not described above from the following disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] To assist in understanding the present invention, the accompanying drawings, which are included as part of the detailed description, provide embodiments of the present invention and describe the technical problems of the present invention together with the detailed description.

[0023] Figure 1Illustrates the physical channels used in a 3rd Generation Partnership Project (3GPP) system and a general signal transmission method using the physical channels.

[0024] Figure 2 Illustrates an example of a radio frame structure used in a wireless communication system.

[0025] Figure 3 Illustrates an example of a downlink (DL) / uplink (UL) time slot structure used in a wireless communication system.

[0026] Figure 4 Illustrates the structure of a downlink subframe.

[0027] Figure 5 Illustrates the structure of an uplink subframe.

[0028] Figure 6 Is a schematic diagram for describing single-carrier communication and multi-carrier communication.

[0029] Figure 7 Illustrates an example of applying cross-carrier scheduling technology.

[0030] Figure 8 Illustrates the DL / UL hybrid automatic repeat request (HARQ) process in a single-cell scenario.

[0031] Figure 9 Illustrates a licensed-assisted access (LAA) service environment.

[0032] Figure 10 Illustrates the layout scenario of user equipment and a base station in an LAA service environment.

[0033] Figure 11 Illustrates a communication scheme operating in an unlicensed band in the prior art.

[0034] Figure 12 and 13 Illustrates the listen-before-talk (LBT) process for DL transmission.

[0035] Figure 14 Illustrates DL transmission in an unlicensed band.

[0036] Figures 15 to 17 Illustrates the DL transmission process according to an unlicensed band.

[0037] Figures 18 to 22 Illustrates the UL transmission process in an unlicensed band.

[0038] Figures 23 to 27 Illustrates UL multi-carrier transmission according to the present invention.

[0039] Figures 28 to 29It is a diagram for explaining a method of recovering transmission when some transmissions are discarded during multi-subframe transmission.

[0040] Figure 30 The figure illustrates the configurations of a user equipment and a base station according to an exemplary embodiment of the present invention. Detailed implementation manners

[0041] By considering the functions in the present invention, the terms used in this specification are preferably the commonly used general terms that are widely used currently. However, according to the intention, habit, and emergence of new technologies of those skilled in the art, the terms can be changed. Further, in specific cases, there are terms arbitrarily selected by the applicant, and in such cases, their meanings will be described in the corresponding description part of the present invention. Therefore, the present invention aims to show that the terms used in this specification should be analyzed, and this analysis is not only based on the name of the term, but also based on the substantial meaning of the term and the content throughout this specification.

[0042] Throughout this specification and the following claims, when an element is described as "coupled" to another element, the element can be "directly coupled" to the other element or "electrically coupled" to the other element through a third element. Further, unless explicitly described to the contrary, the words "comprise" and variations (such as "comprises" or "comprising") will be understood to mean including the stated element, but not excluding any other element. Also, in some exemplary embodiments, the limitations such as "equal to or greater than" or "equal to or less than" based on a specific threshold can be appropriately replaced with "greater than" or "less than" respectively.

[0043] The following techniques can be used in various wireless access systems, such as Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier FDMA (SC-FDMA), etc. CDMA can be implemented by radio technologies such as Universal Terrestrial Radio Access (UTRA) or CDMA 2000. TDMA can be implemented by radio technologies such as Global System for Mobile Communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA can be implemented by radio technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA), etc. UTRA is part of the Universal Mobile Telecommunications System (UMTS). The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is part of the Evolved UMTS (E-UMTS) that uses Evolved UMTS Terrestrial Radio Access (E-UTRA), and LTE-Advanced (LTE-A) is an evolved version of 3GPP LTE. 3GPP LTE / LTE-A is described mainly for the sake of clear description, but the technical spirit of the present invention is not limited thereto.

[0044] Figure 1 Illustrates the physical channels used in the 3GPP system and the general signal transmission method using the physical channels. The user equipment receives information from the base station through the downlink (DL), and the user equipment transmits information to the base station through the uplink (UL). The information transmitted / received between the base station and the user equipment includes data and various control information, and various physical channels exist according to the type / purpose of the information transmitted / received between the base station and the user equipment.

[0045] When the power of the user equipment is turned on or the user equipment enters the cell in a new way, the user equipment performs an initial cell search operation (S301) including synchronizing with the base station, etc. For this purpose, the user equipment receives the Primary Synchronization Channel (P-SCH) and the Secondary Synchronization Channel (S-SCH) from the base station to synchronize with the base station and obtain information including the cell ID, etc. Thereafter, the user equipment receives the Physical Broadcast Channel from the base station to obtain the in-cell broadcast information. The user equipment receives the Downlink Reference Signal (DL RS) in the initial cell search step to verify the downlink channel state.

[0046] The user equipment that has completed the initial cell search receives the Physical Downlink Control Channel (PDCCH) and the Physical Downlink Shared Channel (PDSCH) according to the information loaded on the PDCCH to obtain more detailed system information (S302).

[0047] When there is no radio resource for initial access to a base station or signal transmission, a user equipment may perform a random access procedure (RACH procedure) for the base station (S303 to S306). To this end, the user equipment may transmit a preamble through a physical random access channel (PRACH) (S303), and receive a response message for the preamble through a PDCCH and a corresponding PDSCH (S304). In the case of contention-based RACH, a contention resolution procedure may also be performed.

[0048] Thereafter, the user equipment may receive a PDCCH / PDSCH (S307), and transmit a physical uplink shared channel (PUSCH) / physical uplink control channel (PUCCH) (S308) as a general procedure. The user equipment receives downlink control information (DCI) through a PDCCH. The DCI includes control information for the user equipment (such as resource allocation information), and the format varies according to the purpose of use. The control information transmitted from the user equipment to the base station is designated as uplink control information (UCI). The UCI includes an acknowledgement / negative acknowledgement (ACK / NACK), a channel quality indicator (CQI), a precoding matrix index (PMI), a rank indicator (RI), etc. The UCI may be transmitted through a PUSCH and / or a PUCCH.

[0049] Figure 2 FIG. illustrates an example of a radio frame structure used in a wireless communication system. Figure 2 (a) FIG. illustrates a frame structure for frequency division duplex (FDD), and Figure 2 (b) FIG. illustrates a frame structure for time division duplex (TDD).

[0050] Referring to Figure 2 , the frame structure may have a length of 10 ms (307,200 Ts) and may be composed of 10 subframes (SFs). Ts represents a sampling time and is expressed as Ts = 1 / (2048 * 15 kHz). Each subframe may have a length of 1 ms and may be composed of 2 time slots. Each time slot has a length of 0.5 ms. The time for transmitting one subframe is defined as a transmission time interval (TTI). The time resources may be distinguished by a radio frame number / index, a subframe number / index #0 to #9, and a time slot number / index #0 to #19.

[0051] The radio frame can be configured in different ways according to the duplex mode. In the FDD mode, the downlink transmission and the uplink transmission are separated by frequency, and the radio frame includes only one of the downlink subframes and the uplink subframes for a specific frequency band. In the TDD mode, the downlink transmission and the uplink transmission are separated by time, and the radio frame includes both the downlink subframes and the uplink subframes for a specific frequency band.

[0052] Figure 3 The figure shows the structure of the downlink / uplink time slot.

[0053] Refer to Figure 3 , the time slot includes multiple Orthogonal Frequency Division Multiplexing (OFDM) symbols in the time domain and multiple Resource Blocks (RBs) in the frequency domain. The OFDM symbol also means a symbol period. According to the multiple access scheme, the OFDM symbol can be called an OFDMA symbol, a Single-Carrier Frequency Division Multiple Access (SC-FDMA) symbol, etc. The number of OFDM symbols included in a time slot can be variously modified according to the length of the Cyclic Prefix (CP). For example, in the case of the standard CP, a time slot includes 7 OFDM symbols, and in the case of the extended CP, a time slot includes 6 OFDM symbols. The RB is defined as N DL / UL symb (e.g., 7) consecutive OFDM symbols in the time domain and N RB sc (e.g., 12) consecutive subcarriers in the frequency domain. The resource composed of one OFDM symbol and one subcarrier is called a Resource Element (RE) or a tone. An RB is composed of N DL / UL symb *N RB sc resource elements.

[0054] The resources of the time slot can be represented as a resource grid composed of N DL / UL RB *N RB sc subcarriers and N DL / UL symb OFDM symbols. Each RE in the resource grid is uniquely defined by the index pair (k, 1) of each time sequence. K represents the index given from 0 to N DL / UL RB *N RB sc -1 in the frequency domain, and 1 represents the index given from 0 to N DL / UL symb -1 in the time domain. Here, N DL RB represents the number of Resource Blocks (RBs) in the downlink time slot, and N ULRB Indicates the number of RBs in the UL time slot. N DL RB and N UL RB depend on the DL transmission bandwidth and the UL transmission bandwidth respectively. N DL symb Indicates the number of symbols in the downlink time slot, and N UL symb Indicates the number of symbols in the UL time slot. N RB sc Indicates the number of subcarriers that make up one RB. A resource grid is set for each antenna port.

[0055] Figure 4 Illustrates the structure of the downlink subframe.

[0056] Referring to Figure 4 , the subframe can be composed of 14 OFDM symbols. According to the subframe setting, the first 1 to 3 (alternatively, 2 to 4) OFDM symbols are used as the control region, and the remaining 13 to 11 (alternatively, 12 to 10) OFDM symbols are used as the data region. R1 to R4 represent the reference signals for antenna ports 0 to 3. The control channels allocated to the control region include the Physical Control Format Indicator Channel (PCFICH), the Physical Hybrid ARQ Indicator Channel (PHICH), the Physical Downlink Control Channel (PDCCH), etc. The data channels allocated to the data region include the PDSCH, etc. When the Enhanced PDCCH (EPDCCH) is set, the PDSCH and the EPDCCH are multiplexed in the data region by Frequency Division Multiplexing (FDM).

[0057] The PDCCH, which is a physical downlink control channel, is allocated to the first n OFDM symbols of the subframe, where n is represented by the PCFICH as an integer of 1 (alternatively, 2) or greater. The PDCCH announces to each user equipment or group of user equipments information associated with the resource allocation of the Paging Channel (PCH) and the Downlink Shared Channel (DL-SCH) as transmission channels, uplink scheduling grants, HARQ information, etc. The data (i.e., transport blocks) of the PCH and the DL-SCH are transmitted through the PDSCH. Except for specific control information or specific service data, each of the base station and the user equipment usually transmits and receives data through the PDSCH.

[0058] Transmit information indicating which user equipment (one or more user equipments) the PDSCH data is to be transmitted to, information indicating how the user equipment receives the PDSCH data and decodes the PDSCH data, etc., and include this information in the PDCCH / EPDCCH. For example, assume that the PDCCH / EPDCCH is CRC masked using a radio network temporary identifier (RNTI) called "A" and information about data transmitted using a radio resource called "B" (e.g., frequency position) and a DCI format called "C" (i.e., transmission format information (e.g., transport block size, modulation scheme, coding information, etc.) is transmitted through a specific subframe). In this case, the user equipment in the cell monitors the PDCCH / EPDCCH by using its RNTI information, and when one or more user equipments with the "A" RNTI are provided, the user equipment receives the PDCCH / EPDCCH and receives the PDSCH represented by "B" and "C" through the information about the received PDCCH / EPDCCH.

[0059] Figure 5 Illustrate the structure of an uplink subframe.

[0060] Refer to Figure 5 , the subframe can be divided into a control region and a data region in the frequency domain. The PUCCH is allocated to the control region, and the PUCCH carries UCI. The PUSCH is allocated to the data region, and the PUSCH carries user data.

[0061] The PUCCH can be used to transmit the following control information.

[0062] - Scheduling Request (SR): Information used to request UL-SCH resources. The SR is transmitted by using an on-off keying (OOK) scheme.

[0063] - HARQ-ACK: Response to the PDCCH and / or response to the downlink data packet (e.g., codeword) on the PDSCH. A codeword is an encoded format of a transport block. The HARQ-ACK indicates whether the PDCCH and PDSCH are successfully received. The HARQ-ACK response includes a positive ACK (simply, ACK), a negative ACK (NACK), a discontinuous transmission (DTX), or NACK / DTX. DTX means that the user equipment loses the PDCCH (alternatively, a semi-persistent scheduling (SPS) PDSCH) and NACK / DTX refers to the case of NACK or DTX. The HARQ-ACK is used in combination with HARQ-ACK / NACK and ACK / NACK.

[0064] - Channel State Information (CSI): Feedback information about the downlink channel. Feedback information related to Multiple-Input Multiple-Output (MIMO) includes RI and PMI.

[0065] Table 1 shows the relationship between PUCCH formats and UCI.

[0066] [Table 1]

[0067]

[0068]

[0069] In the following, carrier aggregation will be described. Carrier aggregation means that a wireless communication system uses multiple frequency blocks as one larger logical frequency band in order to use a wider frequency band. When the entire system band is extended through carrier aggregation, the frequency bands used for communicating with each user equipment are defined by Component Carriers (CCs).

[0070] Figure 6 is a schematic diagram for describing single-carrier communication and multi-carrier communication. Figure 6 (a) illustrates the subframe structure of a single carrier, and Figure 6 (b) illustrates the subframe structure of multi-carriers of carrier aggregation.

[0071] Referring to Figure 6 (a), in a single-carrier system, the base station and the user equipment perform data communication through one corresponding DL band and one UL band. The DL / UL band is divided into multiple orthogonal subcarriers, and each frequency band operates at one carrier frequency. In FDD, the DL and UL bands operate at different carrier frequencies respectively, and in TDD, the DL and UL bands operate at the same carrier frequency. The carrier frequency refers to the center frequency of the frequency band.

[0072] Referring to Figure 6 (b), carrier aggregation is distinguished from an OFDM system that performs DL / UL communication in a baseband divided into multiple subcarriers using one carrier frequency, because carrier aggregation performs DL / UL communication using multiple carrier frequencies. Referring to Figure 6 (b), three 20 MHz CCs are aggregated in each of UL and DL to support a bandwidth of 60 MHz. The CCs can be adjacent to each other or non-adjacent to each other in the frequency domain. For convenience, Figure 6(b) This illustrates the case where the bandwidth of the UL CC and the bandwidth of the DL CC are the same and symmetric to each other, but the bandwidths of the respective CCs can be determined independently. Further, asymmetric carrier aggregation where the number of UL CCs and the number of DL CCs are different from each other is also available. The (multiple) DL / UL CCs are independently allocated / configured for each user equipment, and the (multiple) DL / UL CCs allocated / configured for the user equipment are designated as the (multiple) serving UL / DL CCs of the corresponding user equipment.

[0073] The base station can activate some or all of the serving CCs of the user equipment or deactivate some CCs. When the base station allocates the (multiple) CCs to the user equipment, if the CC allocation to the user equipment is completely reconfigured or if the user equipment does not perform a handover, at least one specific CC among the (multiple) CCs configured for the corresponding user equipment is not deactivated. The specific CC that is always activated is called the primary CC (PCC), and the CCs that the base station can arbitrarily activate / deactivate are called secondary CCs (SCCs). The PCC and SCCs can be distinguished based on control information. For example, specific control information can be set to be sent / received only through a specific CC, and the specific CC can be called the PCC, and the remaining (multiple) CCs can be called the (multiple) SCCs. The PUCCH is transmitted only on the PCC.

[0074] In 3GPP, the concept of a cell is used to manage radio resources. A cell is defined as a combination of DL resources and UL resources, that is, a combination of DL CCs and UL CCs. A cell can be configured by only DL resources or a combination of DL resources and DL resources. When carrier aggregation is supported, the link between the carrier frequency of the DL resources (alternatively, DL CCs) and the carrier frequency of the UL resources (alternatively, UL CCs) can be indicated by system information. For example, the combination of DL resources and UL resources can be indicated by a link in System Information Block Type 2 (SIB2). The carrier frequency refers to the center frequency of each cell or CC. The cell corresponding to the PCC is called the primary cell (PCell), and the cell corresponding to the SCC is called the secondary cell (SCell). The carrier corresponding to the PCell is the DL PCC in the downlink, and the carrier corresponding to the PCell is the UL PCC in the uplink. Similarly, the carrier corresponding to the SCell is the DL SCC in the downlink, and the carrier corresponding to the SCell is the UL SCC in the uplink. Depending on the user equipment capabilities, the (multiple) serving cells can consist of the PCell and zero or more SCells. For a user equipment in the RRC_CONNECTED state that does not have any configuration for carrier aggregation or does not support carrier aggregation, there is only one serving cell consisting of only the PCell.

[0075] Figure 7 FIG. illustrates an example of applying cross-carrier scheduling. When cross-carrier scheduling is configured, the control channel transmitted through the first CC can schedule the data channel transmitted through the first CC or the second CC by using the Carrier Indicator Field (CIF). The CIF is included in the DCI. In other words, the scheduling cell is configured, and the DL grant / UL grant scheduling transmitted in the PDCCH region of the scheduling cell schedules the PDSCH / PUSCH of the scheduled cell. That is, the search space for multiple component carriers exists in the PDCCH region of the scheduling cell. The PCell can basically be the scheduling cell, and a specific SCell can be designated as the scheduling cell by the upper layer.

[0076] In Figure 7 , it is assumed that three DL CCs are aggregated. In this article, DL component carrier #0 is assumed to be the DL PCC (alternatively, the PCell), and DL component carrier #1 and DL component carrier #2 are assumed to be DL SCCs (alternatively, SCell). Further, it is assumed that the DL PCC is set to monitor the PDCCH of the CC. When CIF is disabled, according to the LTE PDCCH rules (non-cross-carrier scheduling and self-carrier scheduling), the corresponding DL CC can transmit only the PDCCH that schedules its PDSCH without CIF. On the contrary, when CIF is enabled by UL-specific (alternatively, UL group-specific or cell-specific) upper layer signaling, a specific CC (e.g., DLPCC) can transmit the PDCCH that schedules the PDSCH of DL CC A and the PDCCH that schedules the PDSCH of another CC by using CIF (cross-carrier scheduling). On the contrary, in another DL CC, no PDCCH is transmitted.

[0077] Figure 8 FIG. illustrates the DL / UL HARQ process in the case of a single cell. Figure 8 (a) FIG. illustrates the DL HARQ process, and Figure 8 (b) FIG. illustrates the UL HARQ process. In the case of the DL HARQ process, ACK / NACK (A / N) for (i) the PDSCH scheduled by the PDCCH, (ii) the PDSCH without a corresponding PDCCH (i.e., SPS PDSCH), and (iii) the PDCCH indicating SPS release is fed back. In the case of the UL HARQ process, ACK / NACK (A / N) for (i) the PUSCH scheduled by the PDCCH and (ii) the PUSCH without a corresponding PDCCH (i.e., SPS PUSCH) is fed back. The PDCCH includes the EPDCCH.

[0078] Referring to Figure 8(a), The user equipment receives a PDCCH (alternatively, an EPDCCH) in subframe #n-k (S802) and receives a PDSCH indicated by the PDCCH in the same subframe (S804). The PDCCH transmits scheduling information (i.e., DL grant), and the PDSCH transmits one or more (e.g., two) transport blocks (TBs) (alternatively, codewords (CWs)) according to the transmission mode. Subsequently, the user equipment may transmit ACK / NACK for the PDSCH (i.e., the transport block) in subframe #n (S806). 1-bit ACK / NACK may be transmitted in response to a single transport block, and 2-bit ACK / NACK may be transmitted in response to two transport blocks. ACK / NACK is basically transmitted via the PUCCH, but when transmitting the PUSCH in subframe #n, ACK / NACK may be transmitted via the PUSCH. K represents the time interval between the DL subframe and the UL subframe. In FDD, k = 4, and in TDD, k may be given by the Downlink Association Setting Index (DASI). ACK / NACK refers to HARQ-ACK. The HARQ-ACK response includes ACK, NACK, DTX, and NACK / DTX.

[0079] Reference Figure 8 (b), The user equipment receives a PDCCH (alternatively, an EPDCCH) in subframe #n-k1 (S812) and transmits a PUSCH indicated by the PDCCH in subframe #n (S814). The PDCCH transmits scheduling information (i.e., UL grant), and the PUSCH transmits one or more (e.g., two) transport blocks (TBs) (alternatively, codewords (CWs)) according to the transmission mode. Thereafter, the user equipment receives reception response information for the PUSCH (i.e., the transport block) in subframe #n+k2 via the PHICH or the UL grant (S816). The UL grant includes a new data indicator (NDI) for each TB. Additionally, according to the handover, the NDI indicates a new data transmission or indicates a retransmission of the TB of the previous PUSCH. For example, if the NDI value is switched with respect to the NDI value of the previous UL grant, the NDI indicates a new data transmission, otherwise the NDI indicates a retransmission of the TB of the previous PUSCH. k1 / k2 represents the time interval between the DL subframe and the UL subframe. In FDD, k1 = k2 = 4, and in TDD, k1 / k2 depends on the TDD UL-DL configuration.

[0080] When multiple cells are configured for the user equipment, ACK / NACK information may be transmitted by using PUCCH format 3 or a channel selection scheme based on PUCCH format 1b.

[0081] Configure ACK / NACK payloads in PUCCH format 3 for each cell, and then concatenate the ACK / NACK payloads in PUCCH format 3 according to the cell index order. Regardless of the actual data transmission in each cell, configure the ACK / NACK payloads for all cells configured for the user equipment. Each bit in the ACK / NACK payload indicates the HARQ-ACK feedback of the corresponding transport block (alternatively, codeword). The HARQ / ACK feedback indicates ACK or NACK, and treats DTX as NACK. NACK and DTX have the same HARQ-ACK feedback value. If necessary, the base station can distinguish between NACK and DTX by using the information about the control channel that the base station is to transmit to the user equipment.

[0082] When aggregating two cells, the channel selection scheme based on PUCCH format 1b can be set for transmitting ACK / NACK. In the channel selection scheme based on PUCCH format 1b, the ACK / NACK responses for multiple transport blocks (alternatively, codewords) are identified by a combination of PUCCH resource index and bit values.

[0083] Table 2 shows the mapping between HARQ-ACK(j) of each cell and the transport block (TB) in the channel selection scheme based on PUCCH format 1b. When A = 2 to 4, Tables 3 to 5 show the mappings of ACK, NACK, DTX, and NACK / DTX respectively. The user equipment selects one PUCCH resource corresponding to the HARQ-ACK set from A PUCCH resources and transmits the 2-bit value corresponding to the HARQ-ACK set by using the selected PUCCH resource. Transmit DTX one by one and transmit it as NACK / DTX. When transmitting NACK / DTX, if necessary, the base station can distinguish between NACK and DTX by using the information about the control channel that the base station is to transmit to the user equipment.

[0084] [Table 2]

[0085]

[0086] [Table 3]

[0087]

[0088]

[0089] [Table 4]

[0090]

[0091] [Table 5]

[0092]

[0093] Example: CWS adjustment scheme for random backoff of unauthorized bands

[0094] Figure 9 Illustrate an authorized Licensed-Assisted Access (LAA) service environment.

[0095] Refer to Figure 9 , a service environment can be provided to a user, in which the Long-Term Evolution (LTE) technology (11) in a conventional licensed band where active discussions have been carried out and LTE-Unlicensed (LTE-U) or LAA as the LTE technology (12) in an unlicensed band can be connected to each other. For example, the LTE technology (11) in the licensed band and the LTE technology (12) in the unlicensed band in the LAA environment can be integrated by using technologies (such as, carrier aggregation, etc.), which can help to expand the network capacity. Further, in an asymmetric traffic structure where the downlink data volume is greater than the uplink data volume, LAA can provide an optimized LTE service according to various requirements or environments. For convenience, the LTE technology in the authorized (alternatively, authorized or permitted) band is referred to as LTE-Licensed (LTE-L), and the LTE technology in the unlicensed (alternatively, unauthorized, unlicensed, not necessarily authorized) band is referred to as LTE-Unlicensed (LTE-U) or LAA.

[0096] Figure 10 Illustrate the layout scenarios of user equipment and base stations in the LAA service environment. The frequency band targeted by the LAA service environment has a short radio communication reach distance due to high-frequency characteristics. Considering this, the layout scenarios of user equipment and base stations in an environment where conventional LTE-L service and LAA service coexist can be an overlapping model and a co-location model.

[0097] In the overlapping model, the macro base station can perform wireless communication with X UE and X' UE in the macro area (32) by using an authorized carrier and is connected to multiple Remote Radio Heads (RRHs) through the X2 interface. Each RRH can perform wireless communication with X UE or X' UE in a predetermined area (31) by using an unlicensed carrier. The frequency bands of the macro base station and the RRH are different from each other and do not interfere with each other, but it is necessary to quickly exchange data between the macro base station and the RRH through the X2 interface in order to use the LAA service as an auxiliary downlink channel for the LTE-L service through carrier aggregation.

[0098] In a co-located model, a pico / femto base station can perform wireless communication with a Y UE by using an authorized carrier and an unauthorized carrier. However, the use of LTE-L service and LAA service by the pico / femto base station for downlink transmission may be limited. Depending on the frequency band, transmission power, etc., the coverage range (33) of the LTE-L service and the coverage range (34) of the LAA service may be different.

[0099] When performing LTE communication in an unauthorized band, a conventional device (e.g., a wireless LAN (Wi-Fi) device) that performs communication in the corresponding unauthorized band may not demodulate an LTE-U message or data, and determines the LTE-U message or data as a kind of energy for performing interference avoidance operations through an energy detection technique. That is, when the energy corresponding to the LTE-U message or data is less than -62 dBm or a specific energy detection (ED) threshold, the wireless LAN device can perform communication by ignoring the corresponding message or data. Therefore, the user equipment performing LTE communication in the unauthorized band may be frequently interfered with by the wireless LAN device.

[0100] Therefore, it is necessary to allocate or reserve a specific frequency band within a specific time to effectively implement the LTE-U technology / service. However, since peripheral devices performing communication through the unauthorized band attempt to access based on the energy detection technique, there is a problem of difficulty in performing efficient LTE-U services. Therefore, it is necessary to prioritize research on coexistence schemes for conventional unauthorized band devices and schemes for efficiently sharing radio channels in order to solve the LTE-U technology. That is, it is necessary to develop a robust coexistence mechanism in which the LTE-U device does not affect the conventional unauthorized band device.

[0101] Figure 11 Illustrates a communication scheme (e.g., wireless LAN) operating in an unauthorized band in the prior art. Since most devices operating in the unauthorized band operate based on listen before talk (LBT), a clear channel assessment (CCA) technique that senses the channel for idleness before data transmission is performed.

[0102] Refer to Figure 11 , a wireless LAN device (e.g., an AP or STA) checks whether the channel is busy by performing carrier sensing before transmitting data. When a radio signal with a predetermined intensity or greater intensity is sensed in the channel for transmitting data, it is determined that the corresponding channel is busy, and the wireless LAN device delays accessing the corresponding channel. This process is called clear channel assessment, and the signal level used to determine whether a signal is sensed is called the CCA threshold. Meanwhile, when no radio signal is sensed in the corresponding channel or a radio signal with an intensity less than the CCA threshold is sensed, it is determined that the channel is idle.

[0103] When it is determined that the channel is idle, a terminal having data to transmit performs a backoff process after a delay period (e.g., Arbitration Inter Frame Space (AIFS), PCF Inter Frame Space (PIFS), etc.). The delay period refers to the minimum time that the terminal needs to wait after the channel becomes idle. The backoff process allows the terminal to further standby for a predetermined time after the delay period. For example, during the period when the channel is in an idle state, the terminal stands by while reducing the time slot time for the time slot corresponding to the random number assigned to the terminal in the contention window (CW), and the terminal that has completely exhausted the time slot time can attempt to access the corresponding channel.

[0104] When the terminal successfully accesses the channel, the terminal can transmit data through the channel. When the data is successfully transmitted, the CW size (CWS) is reset to the initial value (CWmin). On the contrary, when the data is not successfully transmitted, the CWS is doubled. Therefore, the terminal is assigned a new random number within a range twice as large as the previous random number range to perform the backoff process in the next CW. In the wireless LAN, only ACK is defined as the response information received for data transmission. Therefore, when ACK is received for data transmission, the CWS is reset to the initial value, and when no feedback information is received for data transmission, the CWS is doubled.

[0105] As described above, since most of the communications in the unlicensed band in the prior art are operated based on LBT, LTE also considers LBT in LAA to coexist with conventional devices. Specifically, in LTE, the channel access methods on the unlicensed band can be classified into the following 4 categories according to the presence / application scheme of LBT.

[0106] ● Category 1 (cat-1): No LBT

[0107] - The LBT process performed by the Tx entity is not executed.

[0108] ● Category 2 (cat-2): LBT without random backoff

[0109] - Determine the time interval (e.g., 25 us) for sensing the channel in the idle state before the Tx entity performs transmission on the channel. Random backoff is not performed. This can be referred to as type 2 channel access.

[0110] ● Category 3 (cat-3): LBT with random backoff having a fixed-size CW

[0111] - The LBT method that performs random backoff by using a fixed-size CW. The Tx entity has a random number N in the CW, and the CW size is defined by the minimum / maximum value. The CW size is fixed. The random number N is used to determine the time interval for sensing the channel in the idle state before the Tx entity performs transmission on the channel.

[0112] ● Category 4 (cat-4): LBT with random backoff of CWs of variable size

[0113] - An LBT method that performs random backoff by using CWs of variable size. The Tx entity has a random number N in the CW, and the CW size is defined by the minimum / maximum value of N. The Tx entity can change the CW size when generating the random number N. The random number N is used to determine the time interval for which the Tx entity needs to sense the channel in the idle state before performing a transmission on the channel. This can be referred to as type 1 channel access.

[0114] Figure 12 and Figure 13 illustrates the DL transmission process based on category 4 LBT. Category 4 LBT can be used to ensure fair channel access using Wi-Fi. Referring to Figure 12 and Figure 13 the LBT process includes an initial CCA (ICCA) and an extended CCA (ECCA). In ICCA, no random backoff is performed, and in ECCA, random backoff is performed by using CWs of variable size. ICCA is applicable when the channel is idle when signal transmission is required, and ECCA is applicable when the channel is busy when signal transmission is required or when DL transmission has just been performed. Although the following description is based on DL transmission, it is also applicable to UL transmission. In the case of UL transmission, the base station is replaced by the user equipment in the following description.

[0115] Referring to Figure 12 the downlink transmission process based on category 4 LBT, i.e., type 1 channel access can be performed as follows.

[0116] Initial CCA

[0117] - S1202: The base station verifies that the channel is idle.

[0118] - S1204: The base station verifies whether signal transmission is required. When signal transmission is not required, the process returns to S1202, and when signal transmission is required, the process continues to S1206.

[0119] - S1206: The base station verifies that the channel is idle during the ICCA delay period (B icca) Whether it is idle. The ICCA delay period is configurable. As an example of an implementation, the ICCA delay period can consist of an interval of 16 μs and n consecutive CCA time slots. In this article, n can be a positive integer, and one CCA time slot interval can be 9 μs. According to the QoS level, the number of CCA time slots can be configured in different ways. By considering the delay period of Wi-Fi (e.g., DIFS or AIFS), the ICCA delay period can be set to an appropriate value. For example, the ICCA delay period can be 34 μs. When the channel is idle during the ICCA delay period, the base station can perform a signal transmission process (S1208). When it is determined that the channel is busy during the ICCA delay period, the process continues to S1212 (ECCA).

[0120] -S1208: The base station can perform a signal transmission process. When the signal transmission is not performed, the process continues to S1202 (ICCA), and when the signal transmission is performed, the process continues to S1210. Even when the backoff count N reaches 0 in S1218 and S1208 is executed, when the signal transmission is not performed, the process continues to S1202 (ICCA), and when the signal transmission is performed, the process continues to S1210.

[0121] -S1210: When additional signal transmission is not required, the process continues to S1202 (ICCA), and when additional signal transmission is required, the process continues to S1212 (ECCA).

[0122] Extended CCA

[0123] -S1212: The base station generates a random number N in the CW. N is used as a count during the backoff process, and N is generated from [0, q - 1]. The CW can consist of q ECCA time slots, and the ECCA time slot size can be 9 μs or 10 μs. In S1214, the CW size (CWS) can be defined as q and can be variable. Thereafter, the base station continues to S1216.

[0124] -S1214: The base station can update the CWS. The CWS q can be updated to a value between X and Y. The X and Y values are configurable parameters. The CWS update / adjustment (dynamic backoff) can be performed whenever N is generated, and the CWS update / adjustment (semi-static backoff) can be performed semi-statically at a predetermined time interval. The CWS can be updated / adjusted based on exponential backoff or binary backoff. That is, the CWS can be updated / adjusted in the form of the square of 2 or a multiple of 2. In combination with PDSCH transmission, the CWS can be updated / adjusted based on the feedback / report of the user equipment (e.g., HARQ ACK / NACK) or based on base station sensing.

[0125] -S1216: The base station verifies whether the channel is idle within the ECCA delay period (D ecca ). The ECCA delay period is configurable. As an example of an implementation, the ECCA delay period can consist of an interval of 16 μs and n consecutive CCA time slots. Herein, n can be a positive integer, and one CCA time slot interval can be 9 μs. According to the QoS level, the number of CCA time slots can be configured in different ways. By considering the delay period of Wi-Fi (e.g., DIFS or AIFS), the ECCA delay period can be set to an appropriate value. For example, the ECCA delay period can be 34 μs. When the channel is idle within the ECCA delay period, the base station proceeds to S1218. When it is determined that the channel is busy during the ECCA delay period, the base station repeats S1216.

[0126] -S1218: The base station verifies whether N is 0. When N is 0, the base station can perform the signal transmission process (S1208). In this case, (N = 0), the base station may not perform the transmission immediately and performs a CCA check within at least one time slot to continue the ECCA process. When N is not 0 (i.e., N > 0), the process proceeds to S1220.

[0127] -S1220: The base station senses the channel during one ECCA time slot interval (T). The ECCA time slot size can be 9 μs or 10 μs, and the actual sensing time can be at least 4 μs.

[0128] -S1222: When it is determined that the channel is idle, the process proceeds to S1224. When it is determined that the channel is busy, the process returns to S1216. That is, after the channel becomes idle, an ECCA delay period is applied again, and N is not counted during the ECCA delay period.

[0129] -S1224: Subtract 1 from N (ECCA decrement count)

[0130] Figure 13 Substantially the same / similar to the Figure 12 transmission process, and according to the implementation solution, different from the Figure 12 . Therefore, the detailed problem can be described with reference to the Figure 12 content.

[0131] -S1302: The base station verifies whether signal transmission is required. When signal transmission is not required, S1302 is repeated, and when signal transmission is required, the process proceeds to S1304.

[0132] -S1304: The base station verifies whether the time slot is idle. When the time slot is idle, the process continues to S1306, and when the time slot is busy, the process continues to S1312 (ECCA). The time slot can correspond to the Figure 12 CCA time slot in.

[0133] -S1306: The base station verifies whether the channel is idle within the delay period (D). D can correspond to the Figure 12 ICCA delay period in. When the channel is idle within the delay period, the base station can perform the signal transmission process (S1308). When it is determined that the channel is busy during the delay period, the process continues to S1304.

[0134] -S1308: If necessary, the base station can perform the signal transmission process.

[0135] -S1310: When the signal transmission is not performed, the process continues to S1302 (ICCA), and when the signal transmission is performed, the process continues to S1312 (ECCA). Even when the backoff count N reaches 0 in S1318 and S1308 is performed, when the signal transmission is not performed, the process continues to S1302 (ICCA), and when the signal transmission is performed, the process continues to S1312 (ECCA).

[0136] Extended CCA

[0137] -S1312: The base station generates a random number N in the CW. N is used as a count during the backoff process, and N is generated from [0, q - 1]. In S1314, the CW size (CWS) can be defined as q and can be variable. Thereafter, the base station continues to S1316.

[0138] -S1314: The base station can update the CWS. The CWS q can be updated to a value between X and Y. The X and Y values are configurable parameters. The CWS update / adjustment (dynamic backoff) can be performed whenever N is generated, and the CWS update / adjustment (semi-static backoff) can be performed semi-statically at a predetermined time interval. The CWS can be updated / adjusted based on exponential backoff or binary backoff. That is, the CWS can be updated / adjusted in the form of the square of 2 or a multiple of 2. In combination with PDSCH transmission, the CWS can be updated / adjusted based on the feedback / report of the user equipment (e.g., HARQ ACK / NACK) or based on base station sensing.

[0139] -S1316: The base station verifies whether the channel is idle within the delay period (D). D can correspond to the Figure 12corresponds to the ECCA delay period in. The D in S1306 and the D in S1316 can be the same as each other. When the channel is idle during the delay period, the base station continues to S1318. When it is determined that the channel is busy during the delay period, the base station repeats S1316.

[0140] -S1318: The base station verifies whether N is 0. When N is 0, the base station can perform the signal transmission process (S1308). In this case, (N = 0), the base station may not perform the transmission immediately and perform a CCA check during at least one time slot to continue the ECCA process. When N is not 0 (i.e., N>0), the process continues to S1320.

[0141] -S1320: The base station selects one of the operations of subtracting 1 from N and the operation of not decreasing N (self-delay). The self-delay operation can be performed according to the implementation / selection of the base station, and in the self-delay, the base station does not perform energy detection sensing and does not even perform ECCA decrement counting.

[0142] -S1322: The base station can select one of the operation of not performing energy detection sensing and the energy detection operation. When the energy detection sensing is not performed, the process continues to S1324. When the energy detection operation is performed, if the energy level is equal to or less than the energy detection threshold (i.e., idle), the process continues to S1324. If the energy level is greater than the energy detection threshold (i.e., busy), the process returns to S1316. That is, after the channel is idle, a delay period is applied again, and N is not counted during the delay period.

[0143] -S1324: The process continues to S1318.

[0144] LBT scheme for uplink transmission

[0145] As a method for performing LBT used by a terminal in the transmission of uplink traffic corresponding to an uplink grant, the LBT scheme performed when sending an uplink grant can be executed, or when sending uplink traffic within the maximum channel occupancy time (MCOT) ensured when sending an uplink grant, a single interval LBT such as 16us, 25us, 34us, or 43us (hereinafter referred to as type 2 channel access) can be executed, so as to achieve fast channel access for uplink data transmission.

[0146] Alternatively, as a method for performing LBT for a terminal to use in the transmission of uplink traffic corresponding to an uplink grant, an LBT scheme performed when transmitting the uplink grant may be executed, or cat-4 LBT (hereinafter, may be referred to as type 1 channel access) may be executed when transmitting uplink traffic outside the MCOT ensured when transmitting the uplink grant.

[0147] Alternatively, the base station may signal to the terminal whether to perform type 2 channel access capable of fast channel access, or perform type 1 channel access in which random backoff is performed as LBT for uplink traffic. For example, the base station may notify the terminal of type 1 channel access or type 2 channel access through the uplink grant. In this case, type 1 channel access represents Cat-4 LBT, and type 2 channel access represents Cat-2 LBT or 25us LBT.

[0148] CWS adjustment for DL transmission

[0149] Figure 14 An example of the base station performing DL transmission in an unlicensed band is illustrated. The base station may aggregate one or more cells in an authorized band (for convenience, an LTE-L cell, or an LAA cell) and one or more cells in an unlicensed band (for convenience, an LTE-U cell). In Figure 14 , a case where one LTE-L cell and one LTE-U cell are aggregated to communicate with a user equipment is assumed. The LTE-L cell may be a PCell, and the LTE-U cell may be an SCell. In the LTE-L cell, the base station may only use frequency resources and perform operations according to LTE in the prior art. Therefore, all radio frames may be composed of regular subframes (rSFs) with a length of 1 ms (see Figure 2 ), and DL transmission (e.g., PDCCH and PDSCH) may be performed in each subframe (see Figure 1 ). Meanwhile, in the LTE-U cell, DL transmission is performed based on LBT for coexistence with conventional devices (e.g., Wi-Fi devices). Further, it is necessary to allocate or reserve a specific frequency band within a specific time to effectively implement LTE-U technology / services. Therefore, in the LTE-U cell, DL transmission may be performed through a set of one or more consecutive subframes (DL transmission bursts) after LBT. Depending on the LBT situation, the DL transmission burst may start with a regular subframe (rSF) or a partial subframe (pSF). The pSF may be a part of the subframe and may include the second time slot of the subframe. Further, the DL transmission burst may end with an rSF or a pSF.

[0150] In the following, a method for adaptively adjusting the CWS for channel access in an unlicensed band will be described. The CWS can be adjusted based on user equipment (UE) feedback, and the UE feedback for CWS adjustment can include HARQ-ACK responses and CQI / PMI / RI. More specifically, a method for adaptively controlling the CWS based on HARQ-ACK responses will be described. The HARQ-ACK responses include ACK, NACK, and DTX.

[0151] As a reference, as described with reference to Figure 11 Even in Wi-Fi, the CWS is adjusted based on ACK. When ACK is feedback, the CWS is reset to the minimum value (CWmin), and when ACK is not feedback, the CWS is increased. However, since Wi-Fi is an end-to-end (1:1) system while a cellular system (e.g., LTE) is a multiple access system, the Wi-Fi method cannot be efficiently applied, and a CWS adjustment method considering multiple access is required.

[0152] First, terms are defined as follows.

[0153] - HARQ-ACK feedback value set (HARQ-ACK feedback set): This set refers to the (multiple) HARQ-ACK feedback values used to update / adjust the CWS. The HARQ-ACK feedback set corresponds to the (multiple) HARQ-ACK feedback values that are decoded and available when determining the CWS. The HARQ-ACK feedback set includes the (multiple) HARQ-ACK feedback values for one or more DL (channel) transmissions (e.g., PDSCH) on an unlicensed band (e.g., an LTE-U cell). The HARQ-ACK feedback set can include the (multiple) HARQ-ACK feedback values for DL (channel) transmissions (e.g., PDSCH), e.g., multiple HARQ-ACK feedback values feedback from multiple user equipments. The HARQ-ACK feedback value can represent the reception response information of a transport block or PDSCH, and represents ACK, NACK, DTX, and NACK / DTX. Depending on the context, the HARQ-ACK feedback value can be used interchangeably with HARQ-ACK value / bit / response / information, etc.

[0154] - Reference window: This reference window refers to the time interval during which DL transmissions (e.g., PDSCH) corresponding to the HARQ / ACK feedback set are performed in an unlicensed band (e.g., an LTE-U cell). The reference window can be defined in units of SF. The reference window will be described / proposed in more detail below.

[0155] In LTE, according to the HARQ-ACK feedback scheme or PUCCH format, the HARQ-ACK value can represent only ACK and NACK, or further represent DTX. For example, when PUCCH format 3 is configured as the HARQ-ACK feedback method, the HARQ-ACK value can represent only ACK and NACK. In contrast, when the channel selection scheme using PUCCH format 1b is configured as the HARQ-ACK feedback method, the HARQ-ACK value can represent ACK, NACK, DTX, and NACK / DTX.

[0156] Therefore, the cases of configuring only ACK and NACK as the HARQ-ACK response and the case of further configuring DTX as the HARQ-ACK response are described separately. The basic problems are common to each other.

[0157] Case 1: The case of only considering ACK and NACK as HARQ-ACK responses

[0158] The following method can be regarded as a method of adjusting the CWS based on the HARQ-ACK feedback set. Options 1 to 3 and alternatives 1 to 3 can be combined.

[0159] - Option 1: If all HARQ-ACK feedback values in the reference window are determined to be NACK, the CWS is increased, and if not (i.e., if there is at least one ACK), the CWS can be reset to the minimum value.

[0160] - Option 2: If at least one of the HARQ-ACK feedback values in the reference window is determined to be NACK, the CWS is increased, and if not (i.e., if all values are ACK), the CWS can be reset to the minimum value.

[0161] - Option 3: If NACK is determined to be at least Z% (0 < Z < 100) among the HARQ-ACK feedback values in the reference window, the CWS is increased, and if not, the CWS can be reset to the minimum value. As an example, Z can be 50 or 80. That is, if the ratio of NACK in the HARQ-ACK feedback (hereinafter referred to as Y%) is equal to or greater than the reference value, the CWS is increased, and when the ratio of NACK is less than the reference value, the CWS can be reset to the minimum value. Depending on the unit, the reference value can be 0 < reference value < 1 or 0% < reference value < 100%. Similarly, if ACK is determined to be less than P% (X = 100 - Z) of the values in the reference window of the HARQ-ACK feedback, the CWS is increased, and if not, the CWS can be reset to the minimum value. As an example, P can be 20 or 50.

[0162] When the CWS increases, the CWS can be doubled, increase exponentially between the minimum CW_min and the maximum CW_max, or increase to the maximum value.

[0163] In addition, when at least one of the following conditions is satisfied, the CWS can be reset to CW_min.

[0164] - Alternative 1: The case where the maximum CWS (CW_max) is used for K consecutive ECCAs. Here, K is fixed to one of 1, 2, and 3 or K can be selected by the base station within {1, …, 8}.

[0165] - Alternative 2: There is no case of DL transmission performed by the base station for at least T time periods. T is a predetermined value or a configurable value.

[0166] - Alternative 3: The case where the maximum HARQ retransmission is used in K consecutive ECCAs. Here, K is fixed to one of 1, 2, and 3 or K can be selected by the base station within {1, …, 8}.

[0167] The reference window can be: (1) a single subframe, (2) multiple (e.g., two) subframes, or (3) all subframes in which HARQ-ACK feedback is available in the last DL transmission burst (i.e., the latest DL transmission burst on the unlicensed band).

[0168] Here, (1) a single subframe can be the first or last subframe of the last DL transmission burst. A single subframe can be a regular subframe rSF or a partial subframe pSF. However, in a partial subframe, the number of user equipments served by the base station is limited. Therefore, when the first or last subframe of the last DL transmission burst is a partial subframe, the base station can define the HARQ-ACK feedback set based on the HARQ-ACK feedback values of the (multiple) user equipments corresponding to the regular subframe and efficiently adjust the CWS according to channel conflict or interference. For example, when the first subframe or the last subframe of the last DL transmission burst is a partial subframe, the reference window can be multiple subframes.

[0169] Here, (2) multiple subframes can be the first multiple subframes or the last multiple subframes in the last DL transmission burst. For example, when the number of multiple subframes is 2, the multiple subframes can be the first two subframes of the last DL transmission burst, i.e., (the first subframe) partial subframe or regular subframe, and (the second subframe) regular subframe. Further, the multiple subframes can be the last two subframes, i.e., (the first subframe) regular subframe, and (the second subframe) partial subframe or regular subframe.

[0170] Case 2-1: The case of also considering DTX as a HARQ-ACK response

[0171] In the following, a method for adjusting the CWS by treating ACK, NACK, and DTX as HARQ-ACK responses transmitted from a user equipment will be described. In self-carrier scheduling, that is, in the case where the DL transmission (e.g., PDSCH) of a carrier in an unlicensed band is performed through a control channel (e.g., (E)PDCCH) transmitted on the same unlicensed-band carrier, the HARQ feedback that can be transmitted by the user equipment regarding the DL transmission of the unlicensed band may include ACK, NACK, DTX, and NACK / DTX. In this document, since DTX corresponds to a case where the DL transmission is not successful due to a hidden node or the like in the unlicensed-band carrier, DTX can be used together with NACK for CWS adjustment. Further, DTX is one of the methods, that is, a case where even if the base station transmits a control channel (e.g., (E)PDCCH) including scheduling information to the user equipment, the user equipment notifies the base station that the user equipment may not decode the corresponding control channel. DTX can be determined only by the HARQ-ACK feedback value or by considering the HARQ-ACK feedback value and the actual scheduling situation. For convenience, a self-carrier scheduling operation is assumed.

[0172] The following method can be regarded as a method for adjusting the CWS based on a HARQ-ACK feedback set. Methods A-1 to A-4 and methods B-1 to B-3 can be combined.

[0173] - Method A-1: When all HARQ-ACK feedback values in the reference window are NACK, all HARQ-ACK feedback values are determined to be DTX, or all HARQ-ACK feedback values are NACK / DTX, the CWS increases, and if not (i.e., if there is at least one ACK), the CWS can be reset to the minimum value.

[0174] - Method A-2: If at least one of the HARQ-ACK feedback values in the reference window is determined to be NACK, DTX, or NACK / DTX, the CWS increases, and if not (i.e., if all values are ACK), the CWS can be reset to the minimum value.

[0175] - Method A-3: If NACK or DTX is determined to be at least Z% (0 < Z < 100) in the HARQ-ACK feedback value of the reference window, the CWS is increased, and if not, the CWS can be reset to the minimum value. As an example, Z can be 50 or 80. In this document, at least Z% of NACK or DTX means increasing either NACK or DTX (i.e., the sum of NACK, DTX, and NACK / DTX) to become at least Z%. That is, NACK / DTX and DTX can be regarded as the same as NACK. Therefore, if the ratio of NACK or DTX in the HARQ-ACK feedback (hereinafter referred to as Y%) is equal to or greater than the reference value, the CWS is increased, and when the ratio of NACK or DTX is less than the reference value, the CWS can be reset to the minimum value. Depending on the unit, the reference value can be 0 < reference value < 1 or 0% < reference value < 100%. Similarly, if ACK is determined to be less than P% (X = 100 - Z) in the HARQ-ACK feedback value of the reference window, the CWS is increased, and if not, the CWS can be reset to the minimum value. As an example, P can be 20 or 50.

[0176] - Method A-4: In the case where all HARQ-ACK feedback values in the reference window are determined to be DTX, considering that all control channels PDCCH / EPDCCH are not received by the user equipment or the decoding of PDCCH and EPDCCH is unsuccessful due to interference from other nodes, the base station increases the CWS, and if not (i.e., in the case where not all HARQ-ACK feedback values are determined to be DTX), the CWS can be adjusted according to Method A-1 to A-3.

[0177] When the CWS is increased, the CWS can be doubled, increased exponentially between the minimum value CW_min and the maximum value CW_max, or increased to the maximum value.

[0178] In addition, when at least one of the following conditions is met, the CWS can be reset to CW_min.

[0179] - Method B-1: The maximum value CWS (CW_max) is used for the case of K consecutive ECCAs. In this document, K is fixed to one of 1, 2, and 3 or K can be selected by the base station within {1,..., 8}.

[0180] - Method B-2: There is no case where DL transmission is performed by the base station for at least T time periods. T is a predetermined value or a configurable value.

[0181] - Method B-3: The case of using maximum HARQ retransmission within K consecutive ECCAs. In this document, K is fixed to one of 1, 2, and 3 or K can be selected by the base station within {1, …, 8}.

[0182] The reference window can be: (1) a single subframe, (2) multiple (e.g., two) subframes, or (3) all subframes in which HARQ-ACK feedback is available in the last DL transmission burst (i.e., the latest DL transmission burst on the unlicensed band). Details can refer to the content described in Case 1.

[0183] Case 2-2: The case of also considering DTX as a HARQ-ACK response

[0184] In the following, another example of a method for adjusting the CWS by treating ACK, NACK, and DTX as HARQ-ACK responses transmitted from the user equipment will be described. In the case of self-carrier scheduling, that is, in the case where the DL transmission (e.g., PDSCH) of the carrier in the unlicensed band is performed through a control channel (e.g., (E)PDCCH) transmitted on the same unlicensed band carrier, the HARQ feedback that can be transmitted by the user equipment for the DL transmission in the unlicensed band can include ACK, NACK, DTX, and NACK / DTX. In this document, since DTX corresponds to the case where the DL transmission is unsuccessful due to a hidden node or the like in the unlicensed band carrier, DTX can be used together with NACK for CWS adjustment. Further, the DTX disclosed in this document is one of the methods, that is, even if the base station transmits a control channel (e.g., (E)PDCCH) including scheduling information to the user equipment, the user equipment notifies the base station that the user equipment does not decode the corresponding control channel. DTX can be determined only by the HARQ-ACK feedback value or by considering the HARQ-ACK feedback value and the actual scheduling situation. For convenience, self-carrier scheduling operations are assumed.

[0185] The following method can be regarded as a method for adjusting the CWS based on the HARQ-ACK feedback set. Method C-1 and C-2 and Method D-1 to D-3 can be combined.

[0186] - Method C-1: In the case where there is DTX in the HARQ-ACK feedback value of the reference window, according to Method A-3, when calculating Y% as the HARQ-ACK feedback based on NACK or DTX, the weight can be applied to DTX. In the case where the base station can distinguish NACK and DTX, and in the case where the user equipment feeds back DTX even when the base station transmits PDSCH related to the control channels PDCCH / EPDCCH, the base station can know that the corresponding user equipment does not accept the control channels PDCCH / EPDCCH. In this case, the base station can identify the probability of interference or hidden nodes occurring in the corresponding channel. Therefore, when receiving DTX from the user equipment, the base station can calculate Y% by applying the weight to DTX in order to more actively solve the problems generated by interference or hidden nodes on the channel. Further, when NACK / DTX is included in the HARQ-ACK feedback value within the reference window, the base station can regard NACK / DTX as NACK. In contrast, when the user equipment feeds back NACK / DTX to the base station, it is meaningful for the user equipment to notify the base station that the HARQ-ACK feedback value can be DTX. Therefore, when feeding back NACK / DTX from the user equipment, the base station can calculate Y% by applying the weight to NACK / DTX in the HARQ-ACK feedback set. The values regarded as HARQ-ACK feedback can be ACK, NACK, NACK / DTX, and DTX. As described herein, Y% for adjusting the CWS can be calculated by considering different weights for NACK, NACK / DTX, and DTX in addition to ACK.

[0187] Formula 1 represents an example of Method C-1. This method can be similarly represented by another formula and is not limited by the following formula.

[0188] [Formula 1]

[0189] Y% = {W_A * Pr(A) + W_B * Pr(B) + W_C * Pr(C)} * 100,

[0190] In this document, Pr(A) represents the probability of NACK in the reference window, that is, Pr(A) = the number of NACKs / the total number of available HARQ-ACK feedbacks in the reference window. In this document, Pr(B) represents the probability of NACK / DTX in the reference window, that is, Pr(B) = the number of NACK / DTXs / the total number of available HARQ-ACK feedbacks in the reference window. In this document, Pr(C) represents the probability of DTX in the reference window, that is, Pr(C) = the number of DTXs / the total number of available HARQ-ACK feedbacks in the reference window. W_A refers to the weight of NACK, W_B refers to the weight of NACK / DTX, and W_C refers to the weight of DTX.

[0191] First, W_A = W_B = W_C is the case where the same weights in the HARQ-ACK feedback set are used to calculate NACK, NACK / DTX, and DTX when calculating Y%. W_A < W_B = W_C is the case where larger weights than the weight of NACK are used to calculate NACK / DTX and DTX, and the same weights in the HARQ-ACK feedback set are used to calculate NACK / DTX and DTX when calculating Y%. W_A = W_B < W_C is the case where the same weights are used to calculate NACK and NACK / DTX, and a larger weight in the HARQ-ACK feedback set is used to calculate DTX when calculating Y%. W_A < W_B = W_C is the case where a weight larger than NACK is used to calculate NACK / DTX, and a weight larger than NACK / DTX in the HARQ-ACK feedback set is used to calculate DTX when calculating Y%.

[0192] - When the calculated Y% is at least Z%, the CWS increases, and if not, the CWS can be reset to the minimum value. In this document, Z% is a reference value that can be set in the base station (for example, 0 < Z < 100). For example, Z can be 50 or 80.

[0193] - Method C-2: When there is at least one DTX feedback in the reference window, the CWS can increase. This method is a method that overrides Option-3 or Method A-3. If not (i.e., no DTX), the CWS can be adjusted according to Option-3 or Method A-3. Since DTX indicates that the user equipment does not receive the control channel PDCCH / EPDCCH on the unauthorized band due to interference or hidden nodes in the same channel, the base station can increase the CWS as a method to solve the problem.

[0194] When the CWS increases, the CWS can be doubled, increased exponentially between the minimum CW_min and the maximum CW_max, or increased to the maximum value.

[0195] In addition, CWS can be reset to CW_min when at least one of the following conditions is satisfied.

[0196] - Method D-1: The maximum CWS (CW_max) is used for the case of K consecutive ECCAs. Here, K is fixed to one of 1, 2, and 3 or K can be selected by the base station within {1, …, 8}.

[0197] - Method D-2: There is no case of DL transmission performed by the base station for at least T periods. T is a predetermined value or a value that can be set.

[0198] - Method D-3: The case where the maximum HARQ retransmission is used in K consecutive ECCAs. Here, K is fixed to one of 1, 2, and 3 or K can be selected by the base station within {1, …, 8}.

[0199] The reference window can be: (1) a single subframe, (2) multiple (e.g., two) subframes, or (3) all subframes in which HARQ-ACK feedback is available in the last DL transmission burst (i.e., the latest DL transmission burst on the unlicensed band). For details, refer to the content described in Case 1.

[0200] According to whether the scheduling cell is an LTE-L cell or an LTE-U cell in cross-carrier scheduling, Case 2-1 and Case 2-2 can be applied in different ways as described below.

[0201] - In the case of cross-carrier where the DL transmission in the unlicensed carrier is scheduled from different unlicensed bands (i.e., unlicensed carrier, unlicensed band cell, and LTE-U cell), CWS can be adjusted by using the same method as in self-carrier scheduling. The reason is that since the control channel (e.g., PDCCH / EPDCCH) is transmitted in the unlicensed carrier, the base station can perform in the same way as in the case of self-carrier scheduling based on the (multiple) HARQ-ACK responses (ACK, NACK, DTX, and NACK / DTX).

[0202] - In the case of cross-carrier scheduling where DL transmissions transmitted in an unlicensed carrier are scheduled from an authorized band (i.e., an authorized carrier, an authorized band cell, and an LTE-L cell), the PDCCH / EPDCCH, which is the control channel for scheduling the DL transmission, is transmitted in the authorized band. In this case, since DTX feedback is used to determine the decoding situation of the user equipment for the control channel transmitted in the authorized band, it cannot help to adaptively adjust the CWS for channel access in the unlicensed band. Therefore, in cross-carrier scheduling from the authorized band, the method of adjusting the CWS considering DTX is set not to be used, and the CWS can be adjusted by considering only ACK and NACK as the (multiple) HARQ-ACK responses for DL transmissions (e.g., PDSCH) in the unlicensed band. Alternatively, the CWS can be adjusted by considering only ACK, NACK, and NACK / DTX as the (multiple) HARQ-ACK responses for DL transmissions (e.g., PDSCH) in the unlicensed band. For example, DTX, which is the HARQ-ARQ response due to cross-carrier scheduling from the authorized band, can be excluded during the application of Case 1, 2-1, and 2-2. Specifically, in Option 3 and Method A-3, DTX of the HARQ-ARQ due to cross-carrier scheduling from the authorized band can be excluded when calculating Z%. That is, in the HARQ-ACK feedback set, only ACK and NACK are selected to calculate Z%, or only ACK, NACK, and NACK / DTX are selected to calculate Z%. In addition, the following two methods can be used by the base station to calculate Z% without including DTX in Option 3 and Method A-3.

[0203] - First, when determining Z%, DTX indicating a control channel reception failure at the user equipment for control channel transmission on the authorized cell is not included in the overall HARQ-ACK value and is not included in the ratio of NACK.

[0204] - Second, when determining Z%, DTX indicating a control channel reception failure at the user equipment for control channel transmission on the authorized cell is included in the overall HARQ-ACK value but is not included in the ratio of NACK.

[0205] - As described above, if DL transmissions sent on an unlicensed carrier are cross-carrier scheduled from an authorized frequency band (i.e., an authorized carrier, an authorized frequency band cell, and an LTE-L cell), DTX, as the HARQ-ACK response from the cross-carrier scheduling of the authorized frequency band, can be excluded from the processes of Case 1, 2-1, and 2-2. Specifically, when calculating Z% in Option 3 and Method A-3, DTX, as the HARQ-ACK response from the cross-carrier scheduling of the authorized frequency band, can be excluded. In addition, the following two methods can be used by the base station to exclude DTX and calculate Z% in Option 3 and Method A-3.

[0206] - First, when determining Z%, DTX indicating reception of a control channel failure at the user equipment for control channel transmission on the authorized cell is not included in the overall HARQ-ACK value and is not included in the ratio of NACK.

[0207] - Second, DTX indicating reception of a control channel failure at the user equipment for control channel transmission on the authorized cell is included in the overall HARQ-ACK value but is not included in the ratio of NACK.

[0208] However, when performing HARQ-ACK feedback using a channel selection scheme based on PUCCH format 1b (i.e., PUCCH format 1b with channel selection), even if the user equipment does not perform transmission, the base station can determine the HARQ-ACK response based on no transmission. Specifically, the base station can determine the HARQ-ACK response corresponding to no transmission based on the HARQ-ACK response values in Tables 3 to 5 defined for A = 2 to 4. For example, when A = 2, if the user equipment does not perform transmission, the base station can determine based on Table 3 that the HARQ-ACK response corresponding to no transmission is [HARQ-ACK(0), HARQ-ACK(1)] = [DTX, NACK / DTX].

[0209] - If a DL transmission sent on an unlicensed carrier is cross-carrier scheduled from an authorized band (i.e., an authorized carrier, an authorized band cell, and an LTE-L cell), and the user equipment is configured to send HARQ-ACK responses using a channel selection scheme based on PUCCH format 1b in cases other than (i) the case where there is no transmission from the user equipment and (ii) the case where the base station fails to detect a HARQ-ACK response, then when calculating Z% to adjust the CWS, the NACK / DTX state and any state as the HARQ-ACK response can be regarded as NACK. That is, if there is a clear HARQ-ACK response, the NACK / DTX state and any state can be regarded as NACK when calculating Z%. On the other hand, in cases of (i) no transmission from the user equipment or (ii) the base station failing to detect a HARQ-ACK response, the HARQ-ACK response determined by the base station as DTX can be excluded when calculating Z%. In this case, as a method of configuring the DTX to be excluded when calculating Z%, the following two methods are possible.

[0210] - First, since the corresponding DTX may not reflect the channel state of the unlicensed cell, when determining Z%, DTX is not included in the overall HARQ-ACK value and is not included in the ratio of NACK.

[0211] - Second, the corresponding DTX is included in the overall HARQ-ACK value but not in the ratio of NACKs.

[0212] In contrast, in the case of no transmission from the user equipment or (ii) when the base station fails to detect a HARQ response, the HARQ-ACK response determined by the base station as NACK / DTX when calculating Z% can be considered a NACK. This can be a method for allowing the base station to perform CWS adjustment by assuming the possibility of a NACK for DL transmission on an unlicensed carrier. In contrast, in the case of (i) the user equipment indicating NACK / DTX with no transmission or (ii) the base station not detecting a HARQ-ACK response, the HARQ-ACK response determined by the base station as NACK / DTX when calculating Z% is considered DTX rather than NACK so that NACK / DTX is not included in Z%. Thus, the NACK / DTX state can be ignored. Specifically, since it may not be determined whether (i) and (ii) are due to an error in PDCCH / EPDCCH transmission in the licensed carrier or due to the case where the base station does not perform PUCCH detection, because the channel state of the channel on which the PUCCH is transmitted on the licensed carrier is not in a good state, while the NACK for the PDSCH transmitted through the unlicensed carrier by the user equipment is transmitted through the PUCCH on the licensed carrier. Therefore, when calculating Z%, the corresponding NACK / DTX state can be regarded as DTX so that it can be not regarded as NACK when calculating Z%. That is, the NACK / DTX state can be ignored so as not to be included in Z%. Here, the following two methods can be used for the base station to ignore the NACK / DTX determination of Z% without including NACK / DTX.

[0213] - First, since the DTX indicating the failure to receive the control channel at the user equipment for the control channel transmission on the licensed cell may not reflect the channel state of the unlicensed cell, NACK / DTX can be configured not to be included in the overall HARQ-ACK value and not in the ratio of NACKs when determining Z%.

[0214] - Second, since the DTX indicating the failure to receive the control channel at the user equipment for the control channel transmission on the licensed cell may not be able to reflect the channel state of the unlicensed cell, NACK / DTX can be configured to be included in the overall HARQ-ACK value but not in the ratio of NACKs.

[0215] Meanwhile, when determining that a part of the HARQ-ACK is DTX and another part of the HARQ-ACK is determined to be NACK / DTX during the process of detecting HARQ-ACK for no transmission, DTX as a part of the HARQ-ACK can be equivalently reflected in the calculation of Z% as NACK / DTX. For example, if NACK / DTX is regarded as NACK to be reflected in Z%, DTX can also be determined as NACK to be reflected in Z% of the NACK. On the other hand, if NACK / DTX is not reflected in Z%, DTX can be regarded as DTX not being reflected in Z%. Here, the following two methods can be used to set the base station not to reflect DTX when determining Z%.

[0216] - First, since DTX indicating the reception of the control channel fails at the user equipment for the control channel transmission on the authorized cell does not reflect the channel state of the unauthorized cell, DTX is not included in the entire HARQ-ACK value and not included in the ratio of NACK when determining Z%.

[0217] - Second, DTX indicating the reception of the control channel fails at the user equipment for the control channel transmission on the authorized cell is included in the entire HARQ-ACK value, but not included in the ratio of NACK.

[0218] Figures 15 to 17 Illustrate the signal transmission process. Figure 15 Illustrate the method for adjusting the CWS according to Case 1, and Figure 16 and Figure 17 Illustrate the reference window for generating the HARQ-ACK feedback set. Case 2-1 and 2-2 can be similarly executed.

[0219] Refer to Figure 15, the base station can transmit the nth DL transmission burst in the unlicensed band (e.g., an LTE-U cell) (S1502), and then, when additional DL transmission is required, transmit the (n + 1)th DL transmission burst based on ECCA (S1512). Specifically, when the channel in the unlicensed band is idle during the ECCA delay period, the base station also performs random backoff in the CW (S1510). The base station can generate a random number N in the CW (e.g., [0, q - 1]) (S1508) and perform backoff as long as the time slot corresponds to the random number N (S1510). Here, the CWS is adaptively changed based on the HARQ-ACK feedback value from the user equipment (S1506). The HARQ-ACK feedback value used to adjust the CWS includes the HARQ-ACK feedback value of the latest DL transmission burst (the nth DL transmission burst). The HARQ-ACK feedback value used to adjust the CWS includes the HARQ-ACK feedback value of the DL transmission on the reference window in the DL transmission burst (S1504).

[0220] When applying Scenario 1, the CWS can be adjusted as follows based on the HARQ-ACK feedback value. Scenarios 2-1 and 2-2 can be applied similarly.

[0221] - Option 1: When all HARQ-ACK feedback values of the reference window are NACK, the CWS increases, and if not, the CWS is reset to the minimum value.

[0222] - Option 2: When at least one of the HARQ-ACK feedback values of the reference window is NACK, the CWS increases, and if not, the CWS is reset to the minimum value.

[0223] - Option 3: When the NACK among the HARQ-ACK feedback values of the reference window is at least Z% (0 < Z < 100), the CWS increases, and when the NACK is not at least Z%, the CWS is reset to the minimum value.

[0224] When the CWS increases, the CWS can be doubled, increased exponentially between the minimum value (CW_min) and the maximum value (CW_max), or increased to the maximum value.

[0225] Referring to Figure 16 and Figure 17 , the reference window can be composed of the starting subframe ( Figure 16 ) and the last subframe ( Figure 17)When the reference window is located at the start position of the DL transmission burst, the reference window can be composed of (i) one normal subframe and (ii) one partial subframe and one normal subframe. Further, when the reference window is located at the end position of the DL transmission burst, the reference window can be composed of (i) one normal subframe and (ii) one normal subframe and one sub-subframe.

[0226] This method assumes that the HARQ-ACK response sent from the user equipment is sent via PUCCH or PUSCH on the PCell of the authorized band.

[0227] Next, when the user equipment is configured to send ACK, NACK, NACK / DTX, and DTX values as HARQ-ACK responses for the PDSCH transmitted via DL on the UL of the unlicensed carrier, a method for performing CW size update / adjustment for the transmission in the base station will be described.

[0228] The case of sending HARQ-ACK for the PDSCH transmitted via DL on the LAA SCell only via the UL on the unlicensed carrier or the LAA SCell will be described.

[0229] - In method 100, in the case where HARQ-ACK for PDSCH transmitted on DL via an unlicensed carrier or LAA SCell is only transmitted on UL via the unlicensed carrier or LAA SCell, if at least one ACK is fed back as the HARQ-ACK transmitted on UL via the LAA SCell, the base station may reset the CW size for DL PDSCH transmission on the LAA SCell, otherwise the CW size may be increased (e.g., doubled). That is, when the base station successfully decodes the PUCCH or PUSCH including the HARQ-ACK sent from the user equipment on the LAA SCell and detects at least one ACK for the PDSCH sent from the base station from the user equipment, the base station may reset the CW size. In this case, the base station determines that the channel of the medium between the base station and the user equipment is idle to reset each CWp (e.g., p = {1, 2, 3, 4}) that can be set differently according to the channel access priority to CWmin. Additionally, when the user equipment sends feedback using NACK because the user equipment fails to decode the PDSCH and the base station detects or determines NACK, NACK / DTX, or DTX, the base station may double the CW. Alternatively, even in the case where NACK, NACK / DTX, or DTX is detected at the base station, which may occur due to the transmission of the PUCCH or PUSCH including the HARQ-ACK sent from the user equipment on the unlicensed carrier, the base station may double the CW. In this case, the base station may determine that the channel of the medium between the base station and the user equipment is busy, and may double CWp (e.g., p = {1, 2, 3, 4}) set differently according to the type of channel access priority. Furthermore, if the LBT using the CW_max value is repeatedly set to K times (e.g., K = {1,..., 8}) after doubling the CW size, CWp may be set to the CW_min value. The value of K may be specified by the base station as a value in {1,..., 8}.

[0230] When the number of unlicensed carriers increases, it may not be possible to transmit HARQ-ACK values only through UL on a specific single unlicensed carrier. In this case, HARQ-ACK transmission can be performed through UL in units of groups, in which the transmission of HARQ-ACK responses is possible and is set by RRC. At the same time, when there is not much DL PDSCH transmission on the unlicensed carrier, the HARQ-ACK response can be sent only through UL on a single LAA SCell. When HARQ-ACK transmission is performed through UL of a group unit, the unlicensed carrier (e.g., LAA SCell index) on which the transmission of HARQ-ACK depends on channel availability based on channel access within the group can be configured to vary dynamically in units of subframes, or can be configured as a single semi-static unlicensed carrier (e.g., LAA SCell). The base station that receives feedback on HARQ-ACK based on a group can update / adjust the CWp and group_index by managing the CWp and group_index (group index) of the DL PDSCH to be sent to the user equipment based on the group. Based on the feedback of HARQ-ACK for the DL PDSCH on the LAA SCELL configured as a group, the CW size can be reset or doubled.

[0231] The case where the HARQ-ACK feedback of the PDSCH transmitted on the unlicensed carrier or LAA SCell is divided into the HARQ-ACK feedback transmitted through the PUCCH or PUSCH on the licensed carrier and the HARQ-ACK feedback transmitted through the PUCCH or PUSCH on the unlicensed carrier will be described.

[0232] - In method 110, the HARQ-ACK feedback for the PDSCH transmitted on an unlicensed carrier or LAA SCell is divided into the HARQ-ACK feedback transmitted on the licensed carrier via PUCCH or PUSCH and the HARQ-ACK feedback transmitted on the unlicensed carrier via PUCCH or PUSCH. In this case, based on Z% of NACK (e.g., 80 or 50, which can be a natural number set by the base station), if the feedback determined to be NACK is Z% or greater, the CW size is updated / adjusted to double the CW according to the CW size of the HARQ-ACK feedback transmitted via UL on the licensed carrier, otherwise the CW size is updated / adjusted to reset the CW size. When transmitting the HARQ-ACK feedback on the licensed carrier in the HARQ-ACK feedback of the PDSCH transmitted on the LAA cell, methods A-1, A-2, A-3, A-4, B-1, B-2, B-3 and their combinations can be used to adjust / update the CW size of the LAA SCell for transmitting the PDSCH corresponding to the HARQ-ACK transmitted on the licensed carrier. If the LBT using the CW_max value is repeatedly set to K times (e.g., K = {1,..., 8}) after doubling the CW size, the CWp can be set to the CW_min value. The value K can be specified by the base station as a value in {1,..., 8}.

[0233] In the case of CW size update / adjustment according to the HARQ-ACK feedback transmitted via UL on the unlicensed carrier, the group of HARQ-ACK corresponding to the PDSCH transmitted via DL on the LAA SCell is transmitted only via UL on the unlicensed carrier, or the LAA SCell can be limited to the LAA SCell for transmitting the PDSCH corresponding to the HARQ-ACK transmitted on the unlicensed carrier. Therefore, the same method as in method 100 can be applied to perform CW size update / adjustment on the PDSCH transmitted on the LAA SCell. If the LBT using the CW_max value is repeatedly set to K times (e.g., K = {1,..., 8}) after doubling the CW size, the CWp can be set to the CW_min value. The value K can be specified by the base station as a value in {1,..., 8}.

[0234] Unlike the method of updating / adjusting the CW size according to whether the cell that independently sends HARQ-ACK is an unlicensed cell (e.g., LAA SCell) or a licensed cell, by referring to the HARQ-ACK feedback on the licensed carrier and the HARQ-ACK feedback on the unlicensed carrier, a method of managing the CW size of LBT for DL PDSCH transmission on the unlicensed carrier or LAA SCell can also be considered. When the conditions of Method 100 and Method 110, which are a hybrid method of Method 100 and Method 110, are met, that is, when the case where the ACK as the feedback value sent on the unlicensed carrier through UL is detected by the base station (i.e., Condition - 110) and the case where the feedback regarded as NACK is not equal to or greater than Z% (i.e., Condition - 110) are both satisfied, the CW size can be reset. However, when neither of the two conditions is met, the CW size may be doubled. Alternatively, since Condition - 100 considers UL transmission on the unlicensed carrier, it is determined that the channel state of the unlicensed carrier can be better reflected, so that the CW size can be reset or doubled according to whether Condition - 100 is met. In contrast, Condition - 110, which is designed to better reflect the channel state of all UEs, is considered to better reflect the channel state of the unlicensed carrier among all UEs, so that a method of resetting or doubling the CW size according to whether Condition - 110 is met can be considered. If the LBT that will use the CW_max value after doubling the CW size is repeated K times (e.g., K = {1,..., 8}), then CWp can be set to the CW_min value. The value of K can be specified by the base station as one value in {1,..., 8}.

[0235] In the LTE system up to the existing Release 13, if simultaneous transmission of PUSCH and PUCCH is set in the user equipment, the simultaneous transmission of PUSCH and PUCCH can be performed in the same carrier or different carriers. However, if simultaneous transmission of PUSCH and PUCCH is not configured in the user equipment, in the case where PUSCH transmission is not scheduled in the corresponding subframe, the transmission of UCI such as HARQ-ACK and CSI is performed on the PUCCH, and in the case where PUSCH transmission is scheduled in the corresponding subframe, the transmission of UCI such as HARQ-ACK and CSI sent through the PUCCH is piggybacked on the PUSCH. When carrier aggregation is performed, this also applies to different carriers.

[0236] In this case, when performing carrier aggregation, in the case where the aggregated carriers consist of different licensed carriers and unlicensed carriers, it is assumed that a set of cells on which PUCCH transmission is possible consists of licensed carriers and unlicensed carriers. In this case, if simultaneous transmission of PUSCH and PUCCH is configured in the user equipment, HARQ-ACK and CSI, which are user equipment feedbacks for DL transmission on the licensed carrier, can be sent via the PUCCH on the licensed carrier, but HARQ-ACK cannot be sent via the scheduled PUSCH on the unlicensed carrier, and CSI (e.g., periodic CSI or aperiodic CSI) can be sent to the scheduled PUSCH on the unlicensed carrier. Additionally, if HARQ-ACK and CSI, which are user equipment feedbacks for DL transmission on the unlicensed carrier, are sent via the PUCCH on the licensed carrier, or if the PUSCH on the unlicensed carrier is scheduled, transmission via the corresponding PUSCH is possible.

[0237] However, if simultaneous transmission of PUSCH and PUCCH is not configured in the user equipment, HARQ-ACK and CSI can be sent via the PUCCH on the licensed carrier as feedback from the user equipment for DL transmission from the licensed carrier, but HARQ-ACK cannot be sent via the scheduled PUSCH on the unlicensed carrier, and CSI (e.g., periodic CSI or aperiodic CSI) can be sent via the scheduled PUSCH on the unlicensed carrier. According to the method used in the existing LTE system, if the PUSCH is not scheduled in the corresponding subframe, HARQ-ACK and CSI are sent via the PUCCH on the licensed carrier as user equipment feedbacks for DL transmission on the licensed carrier and the unlicensed carrier, and if the PUSCH is scheduled in the corresponding subframe on the licensed carrier or the unlicensed carrier, only the scheduled PUSCH is used to carry HARQ-ACK and CSI as user equipment feedbacks for DL transmission on the licensed carrier and the unlicensed carrier and sent. However, since HARQ-ACK, which is user equipment feedback for DL transmission sent on the licensed carrier, is configured not to be sent on the unlicensed carrier, if the PUSCH is scheduled on the unlicensed carrier, the HARQ-ACK response, which is user equipment feedback for DL transmission sent on the licensed carrier, cannot be sent via the predetermined PUSCH on the unlicensed carrier. Therefore, the following options can be considered to address the corresponding situation.

[0238] - Option 1. In the case where the configuration of carrier aggregation (CA) consists of an authorized carrier and an unauthorized carrier, as a set of cells on which the transmission of PUCCH is possible, it consists of an authorized carrier and an unauthorized carrier, and if the simultaneous transmission of PUSCH and PUCCH is not configured in the user equipment, in the subframes where the transmission of PUCCH can be performed, the user equipment does not expect to transmit the PUSCH to be scheduled on the unauthorized carrier of the user equipment, and the user equipment only assumes the transmission of PUCCH, so that the HARQ-ACK and CSI as the user equipment feedback for DL transmission on the authorized carrier and the unauthorized carrier are sent via PUCCH on the authorized carrier.

[0239] - Option 2. In the case where the configuration of CA consists of an authorized carrier and an unauthorized carrier, as a set of cells on which PUCCH can be sent, it consists of an authorized carrier and an unauthorized carrier, and if the simultaneous transmission of PUSCH and PUCCH is not configured in the user equipment, for the subframes where the transmission of PUCCH can be performed, as the feedback of the user equipment for DL transmission on the authorized carrier to be sent by the user equipment, only when the HARQ-ACK response is the subframe to be sent, the user equipment does not expect the PUSCH transmission to be scheduled on the unauthorized carrier from the base station. Additionally, the user equipment only assumes the transmission of PUCCH, so that the HARQ-ACK and CSI as the user equipment feedback for DL transmission on the authorized carrier and the unauthorized carrier are sent via PUCCH on the authorized carrier. Since the HARQ-ACK response for DL transmission only on the authorized carrier may not be sent to the PUSCH on the unauthorized carrier, the CSI can be sent to the PUSCH on the unauthorized carrier. Therefore, this method can be applied only when the UCI type to be carried is the HARQ-ACK response for DL transmission on the authorized carrier.

[0240] - Option 3. In the case where CA consists of an authorized carrier and an unauthorized carrier, as a set of cells on which PUCCH can be sent, and the simultaneous transmission of PUSCH and PUCCH is not configured in the user equipment, for the subframes where PUCCH transmission is possible, if the PUSCH transmission from the base station is scheduled on the unauthorized carrier, the user equipment configures the HARQ-ACK and CSI as the user equipment feedback for DL transmission on the authorized carrier and the unauthorized carrier to be sent via PUSCH on the unauthorized carrier by using the conventional UCI multiplexing method.

[0241] - Option 4. In the case where CA consists of an authorized carrier and an unauthorized carrier, as a set of cells on which PUCCH can be transmitted, and the simultaneous transmission of PUSCH and PUCCH is not configured in the user equipment, for subframes where PUCCH transmission is possible, if PUSCH transmission is scheduled by the base station on the unauthorized carrier, the user equipment discards the scheduled PUSCH on the unauthorized carrier, and by assuming transmission only through PUCCH, the user equipment configures HARQ-ACK and CSI as the user equipment feedback for DL transmission on the authorized carrier and on the unauthorized carrier to be sent on the authorized carrier through PUCCH.

[0242] - Option 5. In the case where CA consists of an authorized carrier and an unauthorized carrier, as a set of cells on which PUCCH can be transmitted, and the simultaneous transmission of PUSCH and PUCCH is not configured in the user equipment, for subframes where PUCCH transmission is possible, if PUSCH transmission is scheduled by the base station on the unauthorized carrier, the user equipment discards the scheduled PUSCH only when the subframe is a HARQ-ACK response as the user equipment feedback for DL transmission on the authorized carrier to be sent by the user equipment. Additionally, by assuming transmission only through PUCCH, the user equipment configures HARQ-ACK and CSI as the user equipment feedback for DL transmission on the authorized carrier and on the unauthorized carrier to be sent on the authorized carrier through PUCCH. Since the HARQ-ACK response for DL transmission only on the authorized carrier may not be sent on the unauthorized carrier through PUSCH, CSI can be sent on the unauthorized carrier through PUSCH. Therefore, only when the UCI type to be carried is the HARQ-ACK response for DL transmission on the authorized carrier, the scheduled PUSCH on the unauthorized carrier can be discarded by applying the corresponding method.

[0243] <Exclusion method for calculating the NACK rate for PUSCH transmission drop when adjusting the CWS>

[0244] In Options 4 to 5, the base station can schedule PUSCH, but the user equipment can discard PUSCH. If CWS adjustment is performed based on the PUSCH reception at the base station in ULLBT, then in the cases of Options 4 to 5, since the base station can identify the PUSCH discard from the user equipment according to the combination of configuration information, for the PUSCH discard of the user equipment, during CWS adjustment, the corresponding PUSCH discard may not indicate conflict handling or interference situation on the unauthorized carrier. Therefore, the discarded PUSCH can be configured not to be used for calculating the NACK ratio for CWS adjustment or not to be used for calculating Z% of the NACK for DL CWS adjustment.

[0245] The representation of an unlicensed carrier in the present disclosure may be the same as the representation of an LAA SCell.

[0246] CWS adjustment for UL transmission

[0247] A method for adjusting the CWS of the UL LBT of a user equipment will be described.

[0248] When the base station manages the user equipment-specific CWS of each user equipment, or each user equipment enables the base station to identify the CWS of each user equipment, the base station may update / adjust the CWS of each user equipment based on the UL transmission sent from the user equipment. Meanwhile, in the case of the power limitation of the user equipment, depending on the priorities of the channels of the licensed carrier and the unlicensed carrier, the PUSCH transmission may be discarded on the unlicensed carrier. However, since it may be difficult for the base station to identify the power limitation state of the user equipment, it may not be recognized whether the channel discarded due to the power limitation is sent by the user equipment. The base station expects the user equipment to send the scheduled channel and expects UL reception at the corresponding reception timing. Therefore, when the UL transmission is discarded in the user equipment, the base station may determine the reception response for the UL transmission as NACK and use NACK as the information for updating the CWS of the using device. However, due to the power limitation state of the user equipment, the discarded UL transmission may not be useful information for determining whether the channel between the user equipment and the base station is busy or idle. Therefore, when the base station performs CWS update / adjustment for each user equipment, the CWS update / adjustment may be performed considering whether the base station receives the PUSCH sent by the user equipment. For example, when the user equipment sends PUSCH and the base station successfully decodes the PUSCH, the base station may reset the CWS of the corresponding user equipment to the minimum value (i.e., CWmin) by determining that the response to the PUSCH transmission is ACK. In this case, the user equipment determines that the channel between the user equipment and the base station is idle, such that the user equipment may reset each CWp (e.g., p = {1, 2, 3, 4}), which may be set to the minimum value differently according to the channel access priority category (i.e., (CWmin, p)). Meanwhile, when the base station fails to decode the corresponding PUSCH, the base station may double the CWS of the corresponding user equipment by determining that the response to the PUSCH transmission is NACK. In this case, the user equipment determines that the channel between the user equipment and the base station is busy, such that the user equipment doubles the CWp (e.g., p = {1, 2, 3, 4}) set differently according to the channel access priority category. Additionally, if the base station performs energy detection for the PUSCH transmission by detecting the UL DM-RS, or if the PUSCH is scheduled using the SRS, the energy detection of the SRS may be performed to determine whether the PUSCH is sent.

[0249] When the base station manages the CWS of each user equipment according to the PUSCH decoding result, the base station can use the new data indicator (NDI) included in the UL grant to enable each user equipment to perform CWS update / adjustment. The NDI is 1-bit information indicating the initial transmission / retransmission of the PUSCH based on whether it is switched based on the NDI value of the previous UL grant. For example, if the NDI value of the current UL grant is equal to the NDI value of the previous UL grant, the current UL grant indicates a retransmission of the PUSCH (i.e., the decoding of the previous PUSCH failed). Additionally, if the NDI value of the current UL grant is switched differently from the previous value, the current UL grant indicates the initial transmission of the PUSCH (i.e., the decoding of the previous PUSCH was successful). Specifically, when switching the NDI on the UL grant received from the base station in the nth subframe, such that the transmission of the PUSCH scheduled for the corresponding user equipment in the (n + 4)th subframe indicates new data, when receiving the UL grant, the CWp of the corresponding user equipment can be reset, i.e., the current CWp can be set to the CW_min,p value. In contrast, when the NDI received on the UL grant received from the base station in the nth subframe does not indicate new data (i.e., when the NDI in the (n - 4)th UL subframe was not switched to indicate a retransmission of the PUSCH), it can perform LBT for the transmission of the PUSCH in the (n + 4)th subframe by doubling the current CWS (when receiving the UL grant). Additionally, if the LBT using the CW_max value is repeatedly set to K times (e.g., K = {1,..., 8}) by retransmission, the CWp can be set to the CW_min value. The value of K can be specified by the base station as one value in {1,..., 8}.

[0250] Next, when the base station only manages the CWS for base station transmission and each user equipment manages its own CWS without information on the CWS of the user equipment, each user equipment can perform CWS update / adjustment using the new data indicator (NDI) information included in the UL grant sent from the base station. For example, when switching the NDI on the UL grant received from the base station in the nth subframe such that the transmission of the PUSCH scheduled for the corresponding user equipment in the (n + 4)th subframe indicates new data, when receiving the UL grant, the CWp of the corresponding user equipment can be reset, that is, the current CWp can be set to the CW_min,p value. In contrast, when the NDI received on the UL grant received from the base station in the nth subframe does not indicate new data (i.e., when the NDI in the (n - 4)th UL subframe has not been switched to indicate retransmission of the PUSCH), it can perform LBT for transmitting the PUSCH in the (n + 4)th subframe by doubling the current CWS (when receiving the UL grant). Additionally, if the LBT using the CW_max value is repeatedly set to K times (e.g., K = {1,..., 8}) by retransmission, the CWp can be set to the CW_min value. The value of K can be specified by the base station as one value in {1,..., 8}.

[0251] If the user equipment adjusts the CWS according to the switching of the NDI included in the UL grant, it can consider updating / adjusting the CWS depending on whether the UL transmission on the reference subframe has been successfully decoded to quickly adjust the CWS according to the UL channel state. Here, the reference subframe can be defined as follows.

[0252] - The reference subframe is defined as the start transmission subframe of the most recent UL transmission burst for which it is desired to use the Cat-4 LBT procedure, and it refers to the subframe in which the transmission of the UL DMRS or SRS from the user equipment is detected by the base station and the PUSCH is decoded.

[0253] - The reference subframe can be defined as the start transmission subframe of the most recent UL transmission burst for which it is desired to use the Cat-4 LBT procedure.

[0254] - The reference subframe can be defined as the first subframe of the reference scheduling burst in which the base station successfully decodes at least one transport block on the LAA SCell. The reference scheduling burst refers to the most recent consecutive UL subframes scheduled for the corresponding user equipment. The reference scheduling burst is the UL subframe expected to initiate UL transmission after Cat-4 LBT, and it refers to the UL subframe expected to complete transmission at least four subframes before rather than the subframe in which the CWS adjustment transmission information (e.g., NDI) is sent.

[0255] - A reference subframe can be defined as the (starting) subframe of the most recent UL transmission burst successfully transmitted by the user equipment.

[0256] - After the user equipment executes Cat-4, the reference subframe can be defined as the (starting) subframe of the most recent UL transmission burst successfully transmitted.

[0257] When the base station successfully decodes the reference subframe (e.g., PUSCH), the CWS can be reset by the user equipment. Additionally, when the base station fails to successfully decode the reference subframe (e.g., PUSCH), the CWS can be increased by the user equipment. When the CWS is defined for each channel access priority class, the CWSp can be reset or increased to the next higher allowed CWSp value for each channel access priority class. p is the channel access priority class (e.g., p = {1, 2, 3, 4}).

[0258] When the PUSCH carries multiple transport blocks (TBs) in the reference subframe (i.e., UL SU-MIMO) and at least one TB in the reference subframe is successfully decoded, the CWS for each channel access priority class is successfully decoded, and otherwise, the CWS can be increased to the next higher allowed CWS value for each channel access priority. The success / failure of the user equipment's transmission relative to the reference subframe can be determined by referring to the NDI value sent by the base station in the UL grant. The NDI is set for each TB. Therefore, if the NDI of at least one TB that is switched for the reference subframe is switched, the CWS can be reset for each channel access priority class, otherwise (i.e., there is no switched NDI), for each channel access priority class, the CWS can be increased to the next higher allowed CWS value. In other words, if any NDI is switched in a subsequent UL grant after the reference subframe and is associated with the reference subframe (e.g., only one of the two NDIs is switched), the CWS can be reset to the minimum value, and if there is no switched NDI, the CWS can be increased. It can be determined whether the UL grant is associated with the reference subframe of the previous UL transmission burst (or the uplink transmission (e.g., PUSCH)) based on whether the HARQ process ID of the reference subframe is the same as the HARQ process ID of the subframe scheduled by the UL grant. Since asynchronous HARQ can be applied to UL transmissions on the LAA SCell, it can be determined whether the UL grant is associated with the reference subframe of the previous UL transmission burst based on whether the HARQ process ID in the UL grant is the same as the HARQ of the process ID used to schedule the reference subframe. At the same time, when the LBT using the CW_max value is repeated K times (e.g., K = {1,..., 8}) by retransmission, only the CWp of the repeated channel access priority can be set to the CW_min value. The value of K can be specified by the base station as one value in {1,..., 8}.

[0259] Meanwhile, the base station may signal to the user equipment or indicate the position of the reference subframe within the reference scheduling burst that the user equipment may use to update the CWS. For example, when the information indicating cat-4 LBT as the LBT type to be performed by the user equipment in UL transmission is implicitly or explicitly signaled to the user equipment via UL grant, the information regarding the position of the reference subframe may be included in the corresponding UL grant. Even if no reference subframe is detected in the base station, the base station may send the user equipment the information regarding the position of the reference subframe.

[0260] For example, the number of bits may be determined according to the number of subframes scheduled for multi-subframe scheduling to notify the position of the reference subframe in the reference scheduling burst via a bitmap. As another example, the position of the reference subframe may be indicated, including the case where the reference subframe is not detected via a bitmap, regardless of the number of subframes scheduled for multi-subframe scheduling (e.g., 0000: no reference subframe, 1000: first subframe, 0100: second subframe, 0010: third subframe, 0001: fourth subframe). In contrast, assuming that the maximum number of subframes that can be multi-subframe scheduled is four, the position of the reference subframe may be specified by two bits. As another example, five states (e.g., no reference subframe, 1st subframe, 2nd subframe, 3rd subframe, and 4th subframe), including the case where no reference subframe is detected, may be signaled by 3 bits.

[0261] When the user equipment receives the position of the reference subframe from the base station, the user equipment may perform UL transmission (e.g., PUSCH) in the subframe (e.g., the first UL subframe of four consecutive UL subframes) before the reference subframe (e.g., the second UL subframe of four consecutive UL subframes) in the reference scheduling burst. In this case, even though the user equipment has transmitted earlier, the base station may not receive the UL transmission in the reference subframe. Therefore, the user equipment may determine that a conflict has occurred in the base station reception for UL transmission, and the user equipment may increase the CWS (e.g., double) for each channel access priority class (or LBT priority class).

[0262] When the user equipment receives the position of the reference subframe from the base station, the user equipment may perform UL transmission (e.g., PUSCH) in the subframe (e.g., the third UL subframe of four consecutive UL subframes) after the reference subframe (e.g., the second UL subframe of four consecutive UL subframes) in the reference scheduling burst. In this case, the user equipment may maintain the CWS for each channel access priority class (or LBT priority class) without change. That is, the base station considers that the UL transmission is received in the reference subframe, even though the user equipment sends it later, and may maintain the CWS by considering it has nothing to do with the conflict in the base station reception for UL transmission.

[0263] When the user equipment receives the position of the reference subframe from the base station, the user equipment may perform UL transmission (e.g., PUSCH) in the same subframe in the reference scheduling burst (e.g., the first UL subframe of four consecutive UL subframes). In this case, since the user equipment performs UL transmission in the reference subframe and the base station successfully decodes at least one transport block for the UL transmission of the reference subframe, the user equipment may determine that the base station has successfully received the UL transmission. Therefore, the user equipment may reset the CWS for each channel access priority class (or LBT priority class) to the minimum value.

[0264] Meanwhile, if the user equipment is configured to reset the CWS based on the NDI for the reference subframe or increase it to the next higher allowed level in cat-4 LBT, since asynchronous HARQ is applied to UL transmission in the LAA SCell, rather than synchronous HARQ, it is not ensured that a UL grant for retransmission (e.g., PUSCH) of the UL transmission that can be referenced for transmission in subframe n is sent in subframe (n + 4). Therefore, when no UL grant is received in subframe (n + 4), there is ambiguity regarding whether the user equipment should reset the CWS or increase it to the next level to use the CWS for cat-4 LBT. To solve this problem, if the NDI of at least one TB based on the most recently received UL grant NDI is switched, the user equipment resets the CWS for each channel access priority class to CW_min, and otherwise, increases the CWS to the CWS value of the next higher allowed level for each channel access priority class. Additionally, when the LBT using the CW_max value is repeatedly set to K times (e.g., K = {1,..., 8}) by retransmission, only the CWp of the repeated channel access priority may be set to the CW_min value. The value of K may be specified by the base station as one value in {1,..., 8}.

[0265] Therefore, as described above, the base station may not distinguish the following three cases where the user equipment fails to send PUSCH. Therefore, a method for classifying the following three cases according to the corresponding method and a method for adjusting the CWS will be described.

[0266] - First, the case where PUSCH cannot be sent due to not receiving a UL grant,

[0267] - Second, the case where LBT fails before PUSCH transmission and PUSCH may not be sent

[0268] - Third, the case where LBT is successful before PUSCH transmission but PUSCH may not be sent (e.g., UL power limit case)

[0269] First, as an example of a method for distinguishing between the first and second cases, if the LAA SCell is configured to receive cross-carrier scheduling from a cell of an authorized carrier, the (E)PDCCH and PDSCH including the UL grant for signal transmission of the UL PUSCH on the LAA SCell can be simultaneously transmitted in the downlink. In this case, when the base station detects an explicit HARQ-ACK feedback (including the cases of receiving "ACK, NACK" or "ACK, NACK, NACK / DTX" or at least ACK or NACK) as the feedback on the PDSCH rather than the transmission on the authorized carrier or the non-authorized carrier, since it can be seen that the (E)PDCCH scheduling the PDSCH is considered successful in the user equipment, the base station can determine that the user equipment has successfully received the UL grant. Therefore, in the first case, that is, since the UL grant is not received and the PUSCH may not be transmitted, the PUSCH can be excluded from the event to adjust the CWS (e.g., increase the CWS) for performing UL LBT for the next PUSCH transmission. When the (E)PDCCH including the UL grant is transmitted from a cell of the authorized carrier, since the first case may not be conducive to notifying the status of the channel conflict for transmitting the UL PUSCH on the LAA SCell, the base station can exclude adjusting the CWS of the uplink transmission of the user equipment. That is, when the base station may not receive (or detect) the PUSCH at the transmission timing of the PUSCH determined by receiving the UL grant, the base station can determine that the PUSCH is not transmitted due to the failure of the PUSCH LBT and increase the CWS of the corresponding user equipment (e.g., double).

[0270] The above can be applied identically to the case where an unlicensed carrier or an LAA SCell is configured for self-carrier scheduling. When an (E)PDCCH and a PDSCH including a UL grant for transmission of a UL PUSCH on the LAA SCell are simultaneously transmitted on the downlink of the LAA SCell, as feedback for the PDSCH, an explicit HARQ-ACK feedback that is not a no-transmission case (including cases where "ACK, NACK" or "ACK, NACK, NACK / DTX" or at least one of ACK or NACK is detected) can be detected by the base station on either the licensed carrier or the unlicensed carrier. In this case, it can be seen that the reception of the (E)PDCCH for scheduling the PDSCH is successful in the user equipment. Additionally, the base station can determine that the user equipment has successfully received the UL grant. Thus, in the first case, i.e., when the PUSCH may not be transmitted because the UL grant is not received on the unlicensed carrier, an adjustment (e.g., CWS increase) for performing UL LBT for the CWS for the next PUSCH transmission can be excluded from the event. That is, when the base station may not receive (or detect) the PUSCH at the transmission timing of the PUSCH determined by receiving the UL grant, the base station can determine that the PUSCH LBT has not been performed due to the failure of the PUSCH and increase the CWS (e.g., double) of the corresponding user equipment.

[0271] Next, an implicit signaling method and an explicit signaling method will be described as methods by which the base station can distinguish between the second and third cases.

[0272] First, as an implicit signaling method, when CA is configured for the power limitation situation of a user equipment, PUSCH on an unlicensed carrier can be discarded according to the transmission priority based on the channel type and channel content in different carriers. The transmission priority can follow the standard up to the priority defined in the existing 3GPP Release-13 (e.g., PRACH > PUCCH > PUSCH with UCI > PUSCH > periodic SRS). Thus, when a channel with a higher priority than the PUSCH on the unlicensed carrier (e.g., PRACH, PUCCH, or PUSCH with UCI) is detected at the transmission timing of the PUSCH according to the UL grant in another carrier, the base station can consider the PUSCH on the unlicensed carrier as discarded due to the power limitation state of the user equipment. In this case, the PUSCH not received on the unlicensed carrier can be excluded from the event to adjust the CWS (e.g., increase the CWS) used to perform UL LBT for transmitting the next PUSCH. That is, although the LBT for the PUSCH has been successful (i.e., the channel is idle), even if the PUSCH is not received (or detected) at the base station at the transmission timing of the PUSCH according to the UL grant, the base station may not double or increase the CWS of the corresponding user equipment (i.e., keep the CWS) because the PUSCH may not be sent due to the power limitation state of the user equipment.

[0273] In addition, in the case of cross-carrier scheduling of PUSCH reception by the user equipment and in the case of self-carrier scheduling of PUSCH reception by the user equipment, the above implicit signaling method can be configured differently. In the case of self-carrier scheduling, when it is determined that the UL grant has been successfully received, the channel state can be considered / regarded as idle at the transmission timing of the PUSCH on the unlicensed carrier. That is, although the PUSCH LBT is successful, considering that the PUSCH cannot be sent due to the power limitation state of the user equipment (i.e., the third case), even if the PUSCH is not received (or detected) at the base station at the transmission timing of the PUSCH according to the UL grant, the CWS of the corresponding user equipment may not be doubled or increased from the previous CWS (i.e., keep the CWS).

[0274] In the case of cross-carrier scheduling, the successful UL grant reception on the licensed carrier may not be considered as a method for determining the channel state at the PUSCH timing on the unlicensed carrier. In this case, since it is difficult for the base station to determine the second case and the third case, the base station arbitrarily determines whether it is the second case or the third case to apply the CWS adjustment method. Alternatively, to configure for obtaining more channel opportunities, even if it is scheduled by the UL grant from the licensed carrier, in the case of not receiving the PUSCH, a method of configuring the CWS to be doubled or increased from the previous value can be considered.

[0275] Next, as an explicit signaling method, information about PUSCH LBT failures on the LAA SCELL or information about whether the PUSCH on the LAA SCell is lost due to power limitations can be included within the PUCCH / PUSCH of the authorized PCell or within the PUCCH / PUSCH of the authorized SCell and sent. Alternatively, information about PUSCH LBT failures on another LAA SCell or information about whether the PUSCH on the LAA SCell is discarded due to power limitations can be included in the PUSCH of the LAA SCell that is set to be sent after successful LBT and sent.

[0276] Figure 18 The figure shows the signal transmission process.

[0277] Reference Figure 18, after receiving a UL grant (e.g., UG#1) from the base station, the user equipment may transmit the nth UL transmission burst (e.g., UTB#1) (S1802). UTB#1 includes one or more, preferably two or more, consecutively scheduled UL subframes, and a PUSCH may be transmitted for each UL subframe. UTB#1 may be transmitted in an unlicensed band (e.g., an LTE-U cell), and may be transmitted based on a Cat-4 LBT procedure (i.e., type 1 channel access). Then, the base station may send a UL grant (e.g., UG#2) to the user equipment (S1804). UG#2 includes scheduling information for the (n + 1)th UL transmission burst (e.g., UTB#2), and UTB#2 includes one or more consecutively scheduled UL subframes. UG#2 includes PUSCH scheduling information for each UL subframe in UTB#2, and each PUSCH scheduling information includes an NDI for each TB. The user equipment may transmit UTB#2 according to UG#2 (S1812). UTB#2 may also be transmitted in an unlicensed band (e.g., an LTE-U cell), and may be transmitted based on a Cat-4 LBT procedure. Specifically, if the channel of the unlicensed band is idle during the ECCA delay period, the user equipment also performs a random backoff within the CWS (S1810). The user equipment generates a random number N equal to or less than the CWS (e.g., [0, q - 1]) (S1808), and performs a backoff using the number of time slots corresponding to the random number N (S1810). In this case, the size of the CW (i.e., CWS) is adaptively changed based on the NDI value of UG#2 (S1806). The NDI value used to adjust the CWS may be related to the UL transmission (i.e., PUSCH) on the reference subframe (i.e., UTB#1) in the most recent UL transmission burst. Specifically, when at least one NDI is switched with respect to the TB transmitted on the reference subframe in UTB#1, the CWS is reset to the minimum value, otherwise the CWS may be increased. For example, if multiple (e.g., two) TBs are transmitted on the reference subframe, and at least one NDI is switched in the UL grant after the reference subframe and associated with the reference subframe (e.g., only one of the two NDIs is switched), the CWS may be reset to the minimum value. Since asynchronous HARQ is applied to UL transmissions in the LAA SCell, in UL transmissions, the HARQ process ID may be used to confirm whether the UL grant is associated with the reference subframe of the previous UL transmission burst. For example, when a UL grant with a HARQ process ID for scheduling the reference subframe is received after the reference subframe (or when the HARQ process ID of the reference subframe is the same as the HARQ process ID of the subframe scheduled by the UL grant), and when at least one NDI value in the UL grant is switched, the CWS may be reset to the minimum value.On the other hand, if a UL grant associated with a reference subframe is not received, or a UL grant associated with a reference subframe is received but the NDI is not switched on all TBs, the CWS can be increased. When the CWS is increased, the CWS can be exponentially doubled or increased or increased to the maximum value between the minimum value (i.e., CW_min) and the maximum value (i.e., CW_max).

[0278] The above method based on multi-subframe scheduling can be similarly applied to the case of single-subframe scheduling.

[0279] Next, a signaling method for adjusting the LBT parameter of the CWS during UL LBT for UL PUSCH transmission performed by a user equipment will be described.

[0280] When the base station notifies the user equipment of the UL LBT parameters, since it may be difficult for the base station to identify the channel access priority class of the traffic sent by the user equipment, notifying the CWS for each channel access priority class may be a large signaling overhead. In addition, when each channel access priority class follows the channel access priority class used in the DL (DL channel access priority class), as shown in Table 6, the range of allowed CWp sizes is large, thus increasing the related signaling overhead.

[0281] [Table 6]

[0282]

[0283] In addition, Table 7 can be used as the LBT parameter for the UL channel access priority class.

[0284] [Table 7]

[0285]

[0286] Note 1: By inserting one or more gaps, the maximum channel occupancy time (MCOT) of 6 ms can be increased to 8 ms, and the minimum duration of the pause caused by the gap should be 100 us. The maximum duration length before including the gap should be 6 ms. The interval duration is not included in the channel occupancy time.

[0287] Note 2: If it is ensured that there is no any other technology (such as Wi-Fi) on the same carrier, the MCOT of LBT priority classes 3 and 4 can be up to 10 ms, otherwise, the MCOT for LBT priority classes 3 and 4 is as specified in Note 1.

[0288] Therefore, in order to notify the base station of the CW size in the LBT parameters that can be notified to the user equipment, a method for reducing the signaling overhead and a method for adjusting the CWS according to the signaling overhead will be described.

[0289] First, since the base station notifies the common value of the CWS regardless of the channel access priority class, the user equipment receiving the common value can perform LBT with the CWS corresponding to the common value according to the common value of the channel access priority to be transmitted. In other words, the base station determines that the CWS is doubled or increased based on the reception of the PUSCH transmitted from the user equipment, and notifies the user equipment of the common value with parameters for LBT regardless of the channel access priority class. The user equipment receiving the common value sets the CWS according to the common value of the LBT of the PUSCH to be transmitted to perform LBT, and transmits the PUSCH according to the success of the LBT. In the case of receiving the common value through UL grant, when the common value is 0, LBT can be performed using the minimum value of the CW size of the channel access priority of the PUSCH to be transmitted, and when the common value is 1, LBT can be performed by setting the minimum value of the CW size to the next level value. Since the common value is applied according to the size of the CWp allowed in each channel access priority, as in the DL, when the maximum CWmax,p value in the channel access priority class is repeatedly set K times, the CWp value can be set to the CWmin,p value in the channel access priority class. Here, K can be selected by the base station from {1, 2,..., 8}. K can be indicated to the user equipment via RRC signaling.

[0290] When using DL channel access priority class 4, 6 is indicated as the common value of the CWS, and in the case where the next PUSCH transmission is expected for a transmission with channel access priority class 1, considering that the maximum CWS is repeated 6 times, according to the condition that if the base station is repeatedly set K times, the CWp value in the channel access priority class should be set to the CWmin,p value, the CWS for the PUSCH of the corresponding channel access priority class can be determined. A method can be considered where when K is configured to 6, CWp can be set to the minimum value of CWS, and if K is configured to 4, it is configured to the maximum value of CWp, and since the common value is greater than the set value K, CWp is configured to the minimum value of CWS.

[0291] In addition, as another method, since the levels of the allowed CWp sizes for UL PUSCH transmission are configured to be the same number of levels (e.g., one of {2, 3, 4, ..., 8 steps}) for each channel access priority class. Additionally, regardless of the channel access priority, the base station notifies the user equipment of the common value of the CWS. Then, the user equipment that receives the common value can perform LBT with backoff using the CWS corresponding to the common value according to the channel access priority class to be transmitted. This can be a method in which the increase or reset of the CWS relative to the adjustment of the CWS for each channel access priority class is controlled to be the same by the common value and the signaling overhead for CWS indication is reduced. In other words, in the case of receiving the common value of the condition for increasing the CWS of each channel access priority class, regardless of the channel access priority class to be transmitted from the user equipment, the CWS is increased to the next higher allowed value. Additionally, even in the case of receiving the common value of the reset condition in the CWS reset or when the reset condition is satisfied by repeating K times, the corresponding CWS of each channel access priority class is reset regardless of the channel access priority class. This can be considered a method for reducing the signaling overhead of the CWS in the LBT parameters transmitted in the UL grant. As an example below, when the channel access priority used in the DL is based on the following method, a method for setting the levels of the allowed CWp sizes to two levels can be used. In the corresponding case, the signaling overhead for indicating the common value of the CWS is sufficient for one bit.

[0292] [Table 8]

[0293] Channel access priority class (p) <![CDATA[Allowed CW p Size]]> 1 {3,7} 2 {7,15} 3 {15,31} 4 {31,63}

[0294] If modified to a more general representation of the allowed CWp size, it can be as follows.

[0295] [Table 9]

[0296] Channel access priority class (p) <![CDATA[Permitted CW p Size]]> 1 {A, B} 2 {C, D} 3 {E, F} 4 {G, H}

[0297] Here, the values of B, C, D, E, F, G, and H can be set to values that satisfy the condition A < B = < C < D = < E < F = < G < H, and the values of B, D, F, and H can be set to the maximum CW size values of the corresponding channel access priority classes. For example, when the maximum allowed CW size uses the value used in the DL, each of B, D, F, and H can have a value of {7, 15, 31, 63, 127, 255, 511, 1023}.

[0298] As another embodiment, if the UL transmission is configured to use a smaller CW size than the DL transmission. For example, when the maximum allowed CW size is configured as {3, 4, 5, 6} or {3, 4, 5, 6, 7}, even with the maximum CWS defined by one of the values in {3, 4, 5, 6} or one of the values in {3, 4, 5, 6, 7}, for each channel access priority class, the allowed CWp size level for UL PUSCH transmission can be set to the same level.

[0299] Table 10 is an example, and a method for setting the allowed CWp size level to two levels can be used.

[0300] [Table 10]

[0301] Channel access priority class (p) <![CDATA[Allowed CW p Size]]> 1,2 {A, B} 3,4 {C, D}

[0302] Here, the B, C, and D values can be set to values that satisfy the condition A < B = < C < D, and the B and D values can be set to the maximum CW size values of the corresponding channel access priority classes. For example, if the maximum allowed CW size is configured as {3, 4, 5, 6} or {3, 4, 5, 6, 7}, then each of B and D can be set to one of {3, 4, 5, 6} or one of {3, 4, 5, 6, 7} as the maximum allowed CW size.

[0303] See Figure 9 , the B, C, D, E, F, G, and H values can be set to values that satisfy the condition A < B = < C < D = < E < F = < G < H, and the B, D, F, and H values can be set to the maximum CW size values of the corresponding channel access priorities. For example, if the maximum allowed CW size is configured as {3, 4, 5, 6} or {3, 4, 5, 6, 7}, then each of B, D, F, and H can be set to one of {3, 4, 5, 6} or one of {3, 4, 5, 6, 7} as the maximum allowed CW size.

[0304] When the base station performs scheduling on the user equipment, as Figures 19 to 20As shown in , and configured for the user equipment to update the reference subframe of the CWS. In this case, the user equipment performs UL LBT for the reference subframe according to the scheduling information sent by the base station in the UL grant. Then, when the LBT is successful, the user equipment performs UL transmission in the UL reference subframe. However, even if the user equipment performs UL transmission, it may happen that the base station fails to detect the UL transmission due to the channel interference condition of the unlicensed band used by the LAA SCell. In this case, due to the transmission failure at the user equipment, or because the user equipment misses the UL grant from the user equipment, the base station may not be able to accurately identify whether the UL transmission of the scheduled UL subframe fails to perform the transmission, or whether the base station cannot detect due to the channel interference in the corresponding subframe. In particular, if the base station still fails to detect the reference subframe even though the reference subframe is sent from the user equipment, the CWS should be increased, but if the base station and the user equipment determine the reference subframe differently, the CWS can be reset even if it is a condition for increasing the CWS. Alternatively, the opposite situation may occur. Therefore, a method for configuring the base station and the user equipment to identify whether the reference subframe of the UL transmission burst received at the base station is the same as the reference subframe sent by the user equipment when determining the CWS for UL LBT performed by the user equipment will be described by solving the problem of mismatch of the reference subframe between the base station and the user equipment for adjusting the CWS and setting to have the same understanding between the base station and the user equipment.

[0305] When assuming that the reference subframe is the start transmission subframe of the UL transmission burst sent from the user equipment by performing cat-4 LBT, the following description is a method for indicating the start transmission subframe of the UL transmission burst in the user equipment and a method for configuring the base station to identify whether the first subframe of the UL transmission burst received by the base station is the first subframe sent by the user equipment.

[0306] Figure 21 is a diagram showing the structure of the UL radio frame, UL subframe, and UL time slot in LTE. In LTE, the cyclic shift index of the sequence of reference signals (e.g., UL DMRS) within the UL subframe is determined by the value set by the cyclic shift index of the UL DMRS in the UL grant and RRC signaling sent from the base station to the user equipment and a function of the time slot index. The cyclic shift value determined by the RRC signaling during a specific time interval is the same, and since the cyclic shift index value determined by the UL grant is constant within the subframe, the cyclic shift value of the UL DMRS in the subframe can be determined to be different values depending on the time slot index.

[0307] As a method P) different from the method of using the cyclic shift index of the UL DM-RS sequence transmitted in the UL subframe transmitted at the first position in the UL transmission burst transmitted after UL LBT using time slots in the conventional art, methods P-1 to P-3 for transmitting the UL DM-RS sequence can be considered. Therefore, when the base station performs UL DMRS detection up to twice when performing PUSCH detection for each subframe of the UL transmission burst scheduled for the base station, the base station determines whether each subframe of the received UL transmission burst is the first successfully transmitted subframe, or whether there is a first successfully transmitted subframe before transmitting the corresponding subframe.

[0308] As a method P-1) of an embodiment, different from the conventional method, the user equipment switches the cyclic shift index of the UL DM-RS sequence transmitted in the UL subframe transmitted at the first position in the UL transmission burst to the index cyclic shift of the UL DM-RS transmitted in each time slot of the UL subframe transmitted at the first transmission, that is, switches the first time slot index and the second time slot index, so that the user equipment transmits the UL subframe including UL DM-RS by setting the cyclic shift of the UL DM-RS sequence transmitted in the first time slot based on the second time slot index and setting the cyclic shift of the DMRS sequence transmitted in the second time slot based on the first time slot index.

[0309] Since when the user equipment transmits the UL subframe to the base station, the user equipment notifies whether the corresponding UL subframe is the first UL subframe of the UL transmission burst scheduled from the base station by switching the cyclic shift index indicating the UL DM-RS between time slots, this can be used as a method for preventing mismatches between the user equipment and the base station for the starting transmission UL subframe.

[0310] For consecutive UL subframes of a UL transmission burst scheduled by a base station, the base station performs two detections (i.e., switching or not switching the UL DM-RS cyclic shift between time slots) based on UL DM-RS generated by two different schemes until a UL subframe with a PUSCH detected is found. Then, when a UL PUSCH is detected with a switched UL DM-RS, the transmission of the corresponding subframe can be determined as a UL subframe when starting the UL transmission burst from the user equipment. In this case, depending on the success of PUSCH decoding in the starting UL subframe, the base station can signal to the user equipment (e.g., UL grant, common control channel, common PDCCH) to reset the CWS or increase the CWS to the next higher allowed value. In contrast, if a UL PUSCH is detected at the base station with a non-switched UL DM-RS, the base station determines that the transmission of the corresponding subframe is not the transmission of the first UL subframe of a UL transmission burst from the user equipment and the first UL subframe of the UL transmission burst in the user equipment is transmitted from the user equipment, but due to the interference conditions of the channel, the first UL subframe may not be detected at the base station, such that the base station can signal to the user equipment (e.g., UL grant, common control channel, common PDCCH) to increase the CWS to the next higher allowed value.

[0311] Method P-2) A method of setting the cyclic shift index of the UL DM-RS sequence in the first time slot and the cyclic shift index of the UL DM-RS sequence in the second time slot according to the same time slot index is considered. There can be a method of setting the cyclic shift index of the UL DM-RS sequence to be the same based on the index of the first time slot of the UL subframe to be transmitted, and there can be a method of setting the same cyclic shift index of the UL DM-RS sequence based on the index of the second time slot.

[0312] Since the user equipment notifies whether the UL subframe is the starting UL subframe of a UL transmission burst scheduled by the base station when sending the UL subframe to the base station by indicating a switch of the UL DM cyclic shift index between time slots, this can be used as a method to prevent a mismatch between the user equipment and the base station for starting the transmission of the UL subframe.

[0313] For consecutive UL subframes of a UL transmission burst scheduled by a base station, the base station performs two detections based on UL DM-RS generated by two different schemes (i.e., based on the same slot index for UL DMRS cyclic shift values between time slots or based on each slot index of UL DM-RS cyclic shift values) until PUSCH detection of the UL subframe. Then, when UL PUSCH is detected by UL DM-RS generated by the value of the same slot index of UL DM-RS cyclic shift values between time slots, the transmission of the corresponding subframe can be determined as a UL subframe when starting the UL transmission burst from the user equipment. In this case, depending on the success of PUSCH decoding in the starting UL subframe, the base station can signal to the user equipment (e.g., UL grant, common control channel, common PDCCH) to reset the CWS or increase the CWS to the next higher allowed value. In contrast, if UL PUSCH is detected at the base station by UL DM-RS generated by values based on slot indices, the base station determines that the transmission of the corresponding subframe is not the transmission of the first UL subframe of the UL transmission from the user equipment and transmits the first UL subframe of the UL transmission burst in the user equipment, but due to the interference conditions of the channel, the first UL subframe may not be detected at the base station, such that the base station can signal to the user equipment (e.g., UL grant, common control channel, common PDCCH) to increase the CWS to the next higher allowed value.

[0314] Method P-3) A method for transmitting a predefined cyclic shift index of a UL DM-RS sequence based on a predefined index of cyclic shift of UL DM-RS pre-set for a base station and a user equipment by applying the UL DM-RS to a UL subframe to be first transmitted by the user equipment can be considered.

[0315] Method Q) As a method different from the method of using a cyclic shift index of a sequence of UL DM-RS transmitted in a UL subframe other than the UL subframe first transmitted in a UL transmission burst excluded based on a slot index used in the conventional art, by using the following methods Q-1 to Q-3 to generate a UL DM-RS sequence for transmission, it is possible to distinguish the start transmission and non-start transmission of a UL transmission burst at a base station.

[0316] As a method for setting a cyclic shift index of a UL DM-RS sequence for a UL subframe that is set to be transmitted to exclude the first UL subframe transmitted in a UL transmission burst Q-1), different from the conventional method, a user equipment switches the cyclic shift index of the UL DMRS transmitted in each time slot between time slots, that is, switches a first time slot index and a second time slot index, so that the user equipment transmits a UL subframe including UL DMRS by setting a cyclic shift of the DMRS sequence of the UL DMRS transmitted in the first time slot based on the second time slot index and setting a cyclic shift of the DMRS sequence of the UL DMRS transmitted in the second time slot based on the first time slot index.

[0317] Method Q-2) In a UL subframe other than the first UL subframe transmitted in a UL transmission burst, a method of setting a cyclic shift index of a UL DMRS sequence in a first time slot and a cyclic shift index of a UL DMRS sequence in a second time slot by a user equipment according to the same time slot index can be considered. There can be a method of setting the cyclic shift index of the UL DMRS sequence to be the same based on the index of the first time slot of the UL subframe to be transmitted, and there can be a method of setting the same cyclic shift index of the UL DMRS sequence based on the index of the second time slot.

[0318] Method Q-3) In a UL subframe other than the first UL subframe transmitted in a UL transmission burst, a method of transmitting a cyclic shift index of a predefined UL DMRS sequence based on a predefined index of a cyclic shift of UL DMRS previously set for a base station and a user equipment by applying the UL DMRS to the UL subframe first transmitted by the user equipment can be considered.

[0319] Figure 22 The figure illustrates a method for determining a CWS in a subframe in which Cat-4 should be performed for UL transmission. Specifically, it illustrates the case where each UL scheduled subframe of the most recent UL transmission burst has a gap between consecutive subframes and is scheduled by each UL grant (i.e., Figure 20 (a)), the case where scheduling is performed through a gap between consecutive UL subframes scheduled by multi-subframe scheduling from one DL subframe (i.e., Figure 20 (b)), and the case where scheduling is performed through a gap between UL subframes scheduled by multiple UL grants from one DL subframe (i.e., Figure 20 (c)). In these cases, due to the gap between UL subframes, each UL subframe performing each cat-4 LBT can be regarded as a UL transmission burst. As shown in Figure 20 If there is a gap between scheduled UL subframes, when determining the CWS of cat-4 for performing the next UL transmission, the most recent UL transmission burst performing cat-4 as a reference subframe can beFigure 20 (a), the A subframe in 20(b) and 20(c) (e.g., UL SF#(n + 4 + k)), the B subframe (e.g., UL SF#(n + 5 + k)), or the C subframe (e.g., UL SF#(n + 6 + k)). Here, since each subframe of the last transmitted cat-4 can be the subframe of the most recent UL burst, in this case, even if the UL subframe that starts first in the scheduled subframe due to the successful LBT in the previous cat-4 LBT, it is difficult to solve the problem of the reference subframe mismatch of the CWS for adjusting the next UL transmission between the base station and the user equipment by notifying the starting subframe of the UL burst using methods P-1, P-2, P-3 and methods Q-1, Q-2 and Q-3 in the corresponding subframe. In this case, detecting UL DMRS and PUSCH twice in the base station may only increase the detection complexity of the base station. Therefore, in the case where the base station configures the user equipment to perform scheduling with UL gaps, the base station signals to the user equipment the method of not performing the modified transmission of the UL DMRS sequence in the user equipment, that is, methods P-1, P-2, P-3 and methods Q-1, Q-2 and Q-3 can be considered. As a signaling method, for example, it can be indicated through the UL grant on the common control channel or the common PDCCH. As Figure 19 shown, in the case where the base station schedules the UL transmission burst without gaps, the base station can configure the user equipment to use methods P-1, P-2 and P-3 and methods Q-1, Q-2 and Q-3 to solve the mismatch of the reference subframe between the base station and the user equipment. In addition, as Figure 20 shown, in the case where the base station schedules the UL transmission burst using gaps, the base station can signal to the user equipment not to perform methods P-1, P-2 and P-3 and methods Q-1, Q-2 and Q-3 to reduce the number of blind detections at the base station.

[0320] Example 1: Channel access for uplink multi-carrier transmission

[0321] When configuring multiple LAA SCells, the following channel access method is used as the method for the base station to access the channel for downlink multi-carrier transmission.

[0322] - Multi-carrier channel access type A (i.e., type A): For each set (i.e., carrier set) of the combination of carriers through which the base station intends to perform transmission on the LAA SCell, the single-carrier channel access process using cat-4 LBT can be independently performed for each carrier. Thereafter, according to the determination of the base station, the self-delay time that does not reduce the backoff counter is used in a specific carrier so that the transmission time points are matched between multiple carriers.

[0323] -Multi-carrier channel access type B (i.e., type B): Similar to the scheme used in Wi-Fi, randomly select one of the carriers (c_j) to be transmitted by the base station or select a carrier (c_j) without change for at least one second, and perform channel access using cat-4 LBT on the carrier (c_j). When the channel access on the carrier (c_j) is successful, at least T_mc = 25 us of channel sensing is performed on other carriers (c_i) (i ≠ j) before the transmission time of the carrier on which the channel access is successful. In this case, when the channel is idle within T_mc, the base station performs multi-carrier transmission including other carriers.

[0324] In the scheme for transmitting multiple carriers via the downlink, the base station performs channel access on the carrier through which it intends to transmit a signal substantially by assuming cat-4 LBT with backoff. However, in the case of channel access type B, cat-4 LBT can be performed in a specific carrier determined by the base station, and simultaneous transmission with the carrier on which cat-4 LBT is performed can be performed on other carriers through channel sensing at 25 us intervals. If cat-4 LBT fails in the specific carrier determined by the base station, regardless of the sensing results in other carriers, no transmission is performed on all multiple carriers.

[0325] However, in the case of the uplink where the user equipment performs transmission to the base station, the base station notifies the user equipment of the LBT type that should be performed by the user equipment through UL grant. The LBT type can be, for example, (i) cat-4 LBT, i.e., type 1 channel access, or (ii) cat-2 LBT (e.g., LBT based only on 25 us CCA), which performs channel sensing for only a single interval, i.e., type 2 channel access. Therefore, depending on the LBT type indication from the base station, there may be a case where the LBT type in all carriers on which the user equipment performs uplink transmission (e.g., PUSCH) is not cat-4 LBT. That is, cat-4 LBT can be indicated on some carriers, and cat-2 LBT can be indicated on another carrier among the carriers through which the base station intends the user equipment to perform transmission.

[0326] In the following, a channel access method for a user equipment to transmit multiple carriers and its uplink transmission method will be described. In this specification, transmitting a carrier means transmitting a signal (e.g., PUSCH) through or on a carrier. Additionally, unless otherwise specified, a carrier means a carrier operating in an unlicensed band (i.e., an unlicensed carrier) (e.g., LAASCell). Furthermore, multi-carrier transmission in this specification refers to a signal transmission operation when multiple carriers are simultaneously scheduled on an LAA SCell. In actual signal transmission, according to the channel access method, signals may be transmitted only on some of the carriers constituting multiple carriers, and signal transmission on some other carriers may be discarded.

[0327] Figure 23 The figure shows a user equipment performing UL transmission on multiple carriers in a case where a base station independently indicates different UL LBT types to each carrier via a UL grant. It is assumed that self-carrier scheduling is performed.

[0328] First, it is possible to consider reusing the type B scheme in the downlink for multi-carrier channel access in the uplink multi-carrier access scheme. In this case, when the base station has multiple carriers that indicate cat-4 LBT to the user equipment through a UL grant, and there are multiple carriers where the user equipment is instructed to perform cat-4 LBT based on the UL grant received from the base station, the user equipment needs to select one of the carriers that indicate cat-4 LBT. A scheme of performing cat-4 LBT only on one carrier is applied, and in the type B scheme, transmission on the remaining carriers is allowed only by sensing Tmc (e.g., 25 μs). The following method can be used as a method for selecting one of the carriers on which the user equipment should perform cat-4 LBT.

[0329] First, via base station signaling, a user equipment can select one of the carriers to perform cat-4 LBT. In this regard, the base station can define the carriers on which cat-4 LBT should be performed and allocate the carriers to the user equipment (via UL grants for the carriers). However, in this case, if the user equipment misses the corresponding UL grant, the user equipment cannot perform channel access for multi-carrier transmission. Thus, the base station can specify a priority value for the carriers on which cat-4 LBT should be performed and signal this value to the user equipment. Specifically, the base station can indicate the priority value of the corresponding carrier to the user equipment via the UL grant indicating (each) cat-4 LBT (hereinafter referred to as cat-4 LBT UL grant). Thus, the user equipment identifies the value indicated by the base station as the priority value and first performs cat-4 LBT on the carrier with the highest priority. If the cat-4 LBT is successful, the user equipment senses on the other carriers within Tmc (e.g., 25 us) before transmission and can perform UL transmission (e.g., PUSCH) on multiple carriers simultaneously when the channel is busy. Thus, even if the user equipment misses the UL grant for the carrier set by the base station as the highest priority, the user equipment can perform cat-4 LBT for UL transmission according to the next higher priority value.

[0330] A method for selecting one of the signaling carriers on which the user equipment should perform cat-4 LBT between a base station and a user equipment according to a predefined rule is as follows.

[0331] 1) The carrier having the minimum (carrier / cell) index among the carriers indicating cat-4 LBT can be selected. That is, the user equipment performs cat-4 LBT only on the carrier having the minimum index among the carriers that receive the cat-4 LBT UL grant. Additionally, the user equipment can sense on the remaining carriers at least for Tmc before transmission and perform UL transmission when the channel is idle. The present invention is also applicable to the case where the user equipment misses the UL grant by selecting a carrier based on the received UL grant of the user equipment. In this specification, the cat-x LBT UL grant refers to the UL grant indicating cat-x LBT (e.g., x = 2, 4).

[0332] 2) The carrier with the maximum CWS (i.e., the maximum CWS) among the carriers indicating cat-4 LBT can be selected. That is, the user equipment only performs cat-4 LBT on the carrier with the maximum CWS among the received cat-4 LBT UL permission carriers. Additionally, the user equipment can sense at least Tmc on the remaining carriers just before transmission and perform UL transmission when the channel is idle. Thus, coexistence with Wi-Fi can be ensured as much as possible. Moreover, the present invention is also applicable to the situation where the user equipment misses the UL permission by selecting a carrier based on the received UL permission of the user equipment.

[0333] 3) The carrier with the minimum CWS (i.e., the minimum CWS) among the carriers indicating cat-4 LBT can be selected. That is, the user equipment only performs cat-4 LBT on the carrier with the minimum CWS among the received cat-4 LBT UL permission carriers. Additionally, the user equipment can sense at least Tmc on the remaining carriers just before transmission and perform UL transmission when the channel is idle. Thus, UL transmission on the LAA SCell can be ensured to the greatest extent, which performs scheduling-based channel access different from Wi-Fi while allowing coexistence with Wi-Fi. Moreover, the present invention is also applicable to the situation where the user equipment misses the UL permission by selecting a carrier based on the received UL permission of the user equipment.

[0334] 4) The carrier with the maximum random backoff counter (i.e., the maximum backoff counter) among the carriers indicating cat-4 LBT can be selected. That is, the user equipment only performs cat-4 LBT on the carrier with the maximum random backoff counter among the received cat-4 LBT UL permission carriers. Additionally, the user equipment can sense at least Tmc on the remaining carriers just before transmission and perform UL transmission when the channel is idle. Thus, coexistence with Wi-Fi can be ensured as much as possible. Moreover, the present invention is also applicable to the situation where the user equipment misses the UL permission by selecting a carrier based on the received UL permission of the user equipment.

[0335] 5) The carrier with the minimum random backoff counter (i.e., the minimum backoff counter) among the carriers indicating cat-4 LBT can be selected. That is, the user equipment only performs cat-4 LBT on the carrier with the minimum random backoff counter among the received cat-4 LBT UL permission carriers. Additionally, the user equipment can sense at least Tmc on the remaining carriers just before transmission and perform UL transmission when the channel is idle. Thus, UL transmission on the LAA SCell can be ensured to the greatest extent, which performs scheduling-based channel access different from Wi-Fi while allowing coexistence with Wi-Fi. Moreover, the present invention is also applicable to the situation where the user equipment misses the UL permission by selecting a carrier based on the received UL permission of the user equipment.

[0336] Figure 24 The figure illustrates the uplink multi-carrier transmission operation when the base station separately indicates different UL LBT types for each carrier via UL grants and there is an LBT failure in a cat-4 LBT carrier. It is assumed that self-carrier scheduling is performed.

[0337] Reference Figure 24 , even when the UL LBT fails in the carrier performing cat-4 LBT, when the UL LBT is successful in the carrier performing cat-2 LBT, multi-carrier transmission can be performed using only the carrier performing cat-2 LBT. In the case of multi-carrier channel access type B in the downlink, if the cat-4 LBT fails in a specific carrier designated by the base station during channel access of multiple carriers, the LBT is not performed in another carrier. Moreover, even if the LBT in other carriers is performed in advance, regardless of the channel detection result, multi-carrier transmission excluding the carrier performing cat-4 LBT is not available. However, in the case of the uplink, the UL LBT type (or UL channel access type) of each carrier is indicated by the UL grant sent from the base station. In this case, depending on the interference condition or the channel condition in the carrier performing cat-4 LBT, an LBT failure may occur, as Figures 23-24 shown. However, in the case of the carrier indicating cat-2 LBT to be performed from the base station, uplink transmission can be performed on the corresponding carrier according to whether the cat-2 LBT is successful. Therefore, regardless of the success or failure of the cat-4 LBT, uplink transmission can be performed by allowing channel access in the carrier indicating cat-2 LBT according to the success of the LBT. That is, the channel access of the carrier indicating cat-4 LBT and the channel access of the carrier indicating cat-2 LBT are managed independently. Therefore, the success or failure of the cat-4 LBT only affects the channel access / multi-carrier transmission of the carrier indicating cat-4 LBT and does not affect the channel access / multi-carrier transmission of the carrier indicating cat-2 LBT. On the other hand, the success or failure of the cat-2 LBT only affects the carrier actually performing the cat-2 LBT and does not affect other carriers.

[0338] Figure 24 The figure illustrates the case where a single subframe is scheduled by one UL grant. However, even when multiple subframes are scheduled by one UL grant, as Figure 25 shown, the UL channel access according to the present invention can also be applied in the same way. Moreover, the UL channel access according to the present invention can be similarly applied to the case where multiple subframes are scheduled by UL grants sent from different downlink subframes, as Figure 26as shown. Moreover, the UL channel access according to the present invention can be similarly applied to the case where each UL scheduling subframe of the UL transmission burst is scheduled by the UL grant of a DL subframe, as Figure 27 shown.

[0339] Figure 25 FIG. shows the user equipment performing UL transmission on multiple carriers in the case where the base station independently indicates different UL LBT types for each carrier via a UL grant for multiple subframes. It is assumed that self-carrier scheduling is performed.

[0340] Figure 26 FIG. shows the user equipment performing UL transmission on multiple carriers in the case where the base station schedules multiple subframes through a UL grant. Specifically, Figure 26 shows the case where it is indicated that the UL LBT types for each carrier and different UL subframes can be the same or different, while UL grants from different downlink subframes are sent for each subframe among multiple subframes. It is assumed that self-carrier scheduling is performed.

[0341] Reference Figure 26 , the number of multiple carriers that can be successfully transmitted according to the UL transmission time and the LBT performed before the transmission time of each subframe can be changed for each subframe. In the case of performing cat-4 LBT in the subframe of the carrier set to perform cat-4 LBT, if the channel access type of the multiple carriers that can be performed by the user equipment is signaled as type B, then the LBT in the other carriers except the carrier performing cat-4 LBT can be sensed within Tmc = 25 us (i.e., sense Tmc just before the LBT completion time in the carrier performing cat-4 LBT) to perform UL transmission on multiple carriers.

[0342] Figure 27 FIG. shows the user equipment performing UL transmission on the LAAS cell on multiple carriers in the case where the base station schedules multiple subframes through a UL grant. Specifically, Figure 27 shows the case where it is indicated that the UL LBT types for each carrier and different UL subframes can be the same or different, while UL grants are sent for each subframe of multiple subframes from the same downlink subframe or different downlink subframes. It is assumed that self-carrier scheduling is performed.

[0343] Reference Figure 27 , the embodiment is the same as Figure 26The embodiments described are the same, except that multiple subframes are scheduled by a UL grant. That is, the number of multi-carriers that can be transmitted according to the success of LBT performed before the transmission time of each subframe and the UL transmission time can be changed for each subframe. In the case where cat-4 LBT is performed in the subframe of the carrier set to perform cat-4 LBT, if the channel access type of the multi-carriers that can be performed by the user equipment is signaled as type B, the LBT in the other carriers except the carrier in which cat-4 LBT is performed can be sensed within Tmc = 25 us (i.e., sense Tmc immediately before the LBT completion time in the carrier in which cat-4 LBT is performed) to perform UL transmission in multiple carriers.

[0344] Since the user equipment performs UL transmission in units of subframes, the user equipment can perform UL transmission in the carriers that can be transmitted at each UL transmission time (e.g., subframe), regardless of whether the scheduling indicated by the UL grant is single-subframe scheduling or multi-subframe scheduling.

[0345] Figures 24 to 27 Self-carrier scheduling is illustrated, but the present invention can be similarly applied to the case where a UL grant indicating cat-4 LBT / cat-2 LBT is cross-carrier scheduled from a PCell using an authorized frequency band or a case where cat-4 LBT is cross-carrier scheduled from an LAA SCell using an unlicensed frequency band. Therefore, cat-4 LBT or cat-2 LBT can be indicated to the user equipment by self-carrier scheduling, or cat-4 LBT or cat-2 LBT can be indicated to the user equipment by cross-carrier scheduling. The UL scheduling method is set to one of self-carrier scheduling or cross-carrier scheduling for each carrier, and the present invention can be applied to the case where different scheduling methods are applied to each carrier.

[0346] Although the LBT gap for performing LBT between consecutive subframes is not specified and described in Figures 25 to 27 the present invention can be applied to both cases where there is or is not an LBT gap between subframes.

[0347] Example 2: CWS adjustment for uplink multi-carrier transmission

[0348] As a channel access method for downlink multi-carrier transmission when configuring multiple LAA SCells, there are type A and type B explained in the first embodiment.

[0349] Type A has two schemes as the CWS adjustment method. In the first scheme (i.e., Type A1), it manages the CWS in each carrier and independently extracts the BO counter for each carrier according to the scheme used in single-carrier channel access. In the second scheme (i.e., Type A2), it manages the CWS in each carrier in the same way as that used for single-carrier channel access, but sets a common BO counter for multi-carrier transmission. The BO counter selected from the maximum CWS among the CWSs of each carrier (i.e., the maximum CWp) is set as the common BO counter.

[0350] Type B also has two schemes as the CWS adjustment method. In the first scheme (i.e., Type B1), the set of carriers for multi-carrier transmission (hereinafter referred to as Set C) has a single CWS (hereinafter referred to as CWS Set C). Based on the HARQ-ACK feedback corresponding to the PDSCH transmission in the reference subframe transmitted in all carriers of Set C, if the HARQ-ACK value determined to be NACK is at least 80% or more, CWS Set C is increased, otherwise it is reset to the minimum value. In the second scheme (i.e., Type B2), it manages the CWS in each carrier according to the scheme used in single-carrier channel access, but the BO counter of the carrier (c_j) that performs cat-4 LBT for multi-carrier transmission using multiple carrier Type B schemes is set as the BO counter selected from the maximum CWS among the CWSs of each carrier (i.e., the maximum CWp). In the Type B method, Cat-2 LBT (i.e., Tmc = 25us) occurs in the carriers (c_i) (i≠j) other than the carrier (c_j), but the DL transmission always regards cat-4 as the basic LBT. Therefore, even if cat-2 LBT is performed on the carrier (c_i) when managing the CWS in each carrier according to Type B2, the result of the DL transmission in the carrier is reflected in the corresponding CWS.

[0351] Meanwhile, different from the traditional method, the following method can be considered as a CWS adjustment method in the downlink multi-carrier type B transmission method. The base station performs cat-2 LBT (i.e., Tmc = 25 us) in carriers (c_i) (i≠j) other than the carrier (c_j) set to perform cat-4 LBT. In this case, even if the base station always regards cat-4 as the basic LBT in DL transmission, different from the traditional type B2 scheme, the CWS update that increases or resets the CWS may not be performed according to the transmission from the base station for the carriers that do not perform cat-4 LBT. Therefore, when managing the CWS in each carrier in type B2 of the type B method and performing cat-2 LBT in the carrier (c_i), it is possible to prevent the result of DL transmission in the carrier from being reflected in the corresponding CWS. That is, in the case of managing the CWS of each carrier by the type B method, the result of DL transmission in the carrier where cat-2 LBT is performed is not reflected in the CWS of the corresponding carrier. In this case, only the result of DL transmission in the carrier where cat-4 LBT is performed can be reflected in the CWS of the corresponding carrier. On the other hand, in the case of uplink transmission, when scheduling PUSCH transmission, the base station notifies the user equipment of the LBT type to be performed by the user equipment through a UL grant. The LBT type can be, for example, (i) Cat-4 LBT (or type 1 channel access), or (ii) Cat-2 LBT that only performs sensing for a single interval (e.g., LBT based on 25 us CCA, or type 2 channel access). The user equipment performs LBT according to the indicated LBT type and transmits PUSCH. Therefore, according to the LBT type indication of the base station, there may be a case where the LBT type in all carriers where the user equipment performs uplink transmission (e.g., PUSCH) is not cat-4 LBT. That is, cat-4 LBT can be indicated for some carriers, while cat-2 LBT can be indicated for other carriers among the carriers where the base station intends the user equipment to perform transmission. Therefore, in the channel access method for uplink multi-carrier transmission, a CWS adjustment method different from that of the downlink that only assumes cat-4 LBT is required. Hereinafter, the uplink CWS adjustment method in the base station and the user equipment for UL transmission in the case of UL transmission (e.g., PUSCH) on multiple carriers will be described.

[0352] Unlike the downlink multi-carrier transmission method, in the uplink transmission where the user equipment performs transmission, cat-4 LBT or cat-2 LBT can be dynamically indicated to each carrier at a single subframe level or multiple subframe levels through UL grants. Therefore, the user equipment can be configured to manage the CWS for each carrier used for uplink multi-carrier transmission. The user equipment can manage the CWS for each carrier according to the LBT type indicated by the UL grant for each carrier, regardless of whether cat-4 LBT or cat-2 LBT is performed for PUSCH transmission on each carrier. Therefore, if necessary, when multiple carriers are required to perform simultaneous transmission at the terminal, when the base station requests the user equipment to perform simultaneous transmission on multiple carriers, or until the time point when simultaneous transmission can start within the interval allowing LBT, the terminal is allowed to have a self-delay time for each carrier used for PUSCH transmission on multiple carriers.

[0353] As a method for setting the carriers allowed to have a self-delay time, multi-carrier transmission can be performed with a self-delay time on all carriers where multi-carrier transmission is intended, regardless of the LBT type (e.g., cat-2 LBT, cat-4). Therefore, when the channel sensing in the carrier performing cat-4 LBT ends after the channel sensing period in the carrier performing cat-2 LBT, a self-delay time can be set for the carrier performing cat-2 LBT so that multi-carrier transmission can be achieved.

[0354] As another method, a self-delay time can be set only in the carriers indicating cat-4 LBT, but if transmission can be performed on all carriers at the time of transmission, multi-carrier transmission can be performed regardless of the cat-2 LBT / cat-4 LBT setting. Since the LBT interval in the carrier indicating the execution of cat-2 LBT is presumably shorter than the LBT interval in the carrier indicating the execution of cat-4 LBT, multi-carrier transmission can be performed by setting a self-delay time only in the carriers indicated to perform cat-4 LBT.

[0355] As yet another method, a self-delay time can be set only in the carriers indicating cat-4 LBT to perform multi-carrier transmission consisting only of carriers carrying cat-4. Since the LBT interval in the carrier indicating the execution of cat-2 LBT is presumably shorter than the LBT interval in the carrier indicating the execution of cat-4 LBT, multi-carrier transmission can be performed by setting a self-delay time only in the carriers indicating the execution of cat-4 LBT. Additionally, when the channels of one or more carriers performing cat-4 LBT are not idle, multi-carrier transmission can be enabled at the possible transmission time of the carriers indicating cat-2 LBT.

[0356] Meanwhile, as a method for adjusting the CWS to perform cat-4 LBT in downlink multi-carrier transmission, a common random backoff (BO) counter can be selected from the CWS of the carrier with the maximum CWS in the set of CWSs managed by each carrier to apply the corresponding BO counter to all carriers where multi-carrier transmission is expected. However, unlike the downlink where cat-4 LBT is always performed, since cat-2 LBT or cat-4 LBT can be performed for each carrier in the uplink, the CWS adjustment method for the carrier indicating cat-2 LBT can be further considered.

[0357] First, when a method such as type-A2 for downlink multi-carrier transmission is applied to the uplink, ambiguity may occur as to whether the set of carriers for selecting the maximum CWS includes the CWSs separately managed in the carriers scheduled to perform cat-2 LBT. To solve this problem, the following two methods can be considered. The first method is to select the maximum CWS among the CWSs of all carriers scheduled for UL transmission on multiple carriers and extract the common BO counter N therefrom. Since cat-4 LBT / cat-2 LBT is dynamically set by the UL grant for each carrier and it is configured to manage the CWS of each carrier, even if the LBT type of a specific carrier is indicated as cat-2 LBT, the common backoff counter can be extracted considering the CWSs of the multi-carriers where multi-carrier transmission is expected. The second method is to select the maximum CWS among the CWSs of the carriers scheduled for UL transmission on multiple carriers that are indicated to perform cat-4 LBT and extract the common BO counter N therefrom. Even if the CWSs are managed in each carrier, only the CWSs of the carriers performing cat-4 LBT at the current time can be considered. Therefore, by excluding the possibility of performing more unnecessary backoffs when the CWS of the carrier performing cat-2 LBT is greater than that of the carrier performing cat-4 LBT, the possibility of acquiring the channel when uplink multi-carrier transmission is required can be increased.

[0358] As another method, when a method such as type-B2 for downlink multi-carrier transmission is applied to the uplink, ambiguity may occur as to whether the carrier set for selecting the maximum CWS includes the individually managed CWSs in the carriers scheduled to perform cat-2 LBT. Two methods can be considered. The first method is to select the maximum CWS among the CWSs of all carriers scheduled for UL transmission on multiple carriers and extract the common BO counter N of the representative carrier for performing cat-4 LBT therefrom. Since cat-4 LBT / cat-2 LBT is dynamically set by the UL grant for each carrier and it is configured to manage the CWS of each carrier, even if the LBT type of a specific carrier is indicated as cat-2 LBT, considering the CWSs of all carriers expected for multi-carrier transmission, the BO counter of the representative carrier performing cat-4 LBT can be extracted. The second method is to select the maximum CWS among the CWSs of the carriers indicated to perform cat-4 LBT among the carriers scheduled for UL transmission on multiple carriers and extract the common BO counter N of the representative carrier for performing cat-4 LBT therefrom. Even if the CWS is managed in each carrier, only the CWSs of the carriers performing cat-4 LBT at the current time can be considered. Therefore, by excluding the possibility of unnecessarily performing more backoffs when the CWS of the carrier performing cat-2 LBT is greater than the CWS of the carrier performing cat-4 LBT, the possibility of acquiring the channel when uplink multi-carrier transmission is required can be increased.

[0359] In the case where the type B scheme for downlink is applied to uplink multi-carrier transmission (i.e., cat-4 LBT is only applied to the representative carrier, and even if cat-4 LBT or cat-2 LLT is signaled to other carriers other than the representative carrier among the carriers expected for multi-carrier transmission via the UL grant, the user equipment performs channel sensing via CCA with T_mc (e.g., 25 us) before the transmission time of the carrier on which the representative carrier has successfully performed channel access. A solution as to whether the CWS for the next UL transmission should be adjusted by considering / refecting the previous UL transmission (e.g., the UL transmission in which cat-4 LBT or cat-2 LBT is signaled on the corresponding carrier) on the corresponding carrier. The process of adjusting the CWS can refer to Figure 18 and its description.

[0360] As a method, when a user equipment performs uplink multi-carrier transmission, regardless of which LBT type is signaled by the base station or which LBT type is performed for each carrier, the user equipment can perform CWS adjustment for the next UL transmission for each carrier by determining ACK, NACK, or DTX based on the detection of the base station for the UL transmission of the corresponding carrier. When managing a single CWS for multiple carriers, the CWS adjustment can be performed by determining ACK, NACK, or DTX of the UL transmission in the reference subframe of all carriers where UL transmission is performed. The method for the user equipment to determine ACK, NACK, or DTX for the corresponding UL transmission and adjust the CWS can be determined based on the value of NDI signaled by the UL grant, as Figure 18 described in

[0361] As another method, by performing UL transmission only for the carriers for which cat-4 LBT is signaled as the type of the user equipment, and determining ACK, NACK, or DTX based on the detection of the base station for the UL transmission of the corresponding carrier, the user equipment can perform CWS adjustment for the next UL transmission. The method for the user equipment to determine ACK, NACK, or DTX for the corresponding UL transmission and adjust the CWS can be determined based on the value of NDI signaled by the UL grant as Figure 18 described in. Since the CWS adjustment of the user equipment is expected to be configured by the base station for the carriers that perform cat-4 LBT, the user equipment can perform CWS adjustment even if it has performed channel sensing with Tmc = 25 us by type-B and participated in multi-carrier transmission. Therefore, for the UL transmission of each carrier, the user equipment can perform CWS adjustment based on the signaled LBT type, regardless of the actual LBT type performed. That is, the user equipment can perform CWS adjustment by determining ACK, NACK, or DTX for the UL transmission in the reference subframe of the carriers for which cat-4 LBT is signaled. The method for the user equipment to determine ACK, NACK, or DTX for the corresponding UL transmission and adjust the CWS can be determined based on the value of NDI signaled by the UL grant as Figure 18 described in.

[0362] As yet another method, by performing UL transmission only for the carriers for which cat-4 LBT is signaled as the LBT type of the user equipment and where cat-4 LBT is performed, and determining ACK, NACK, or DTX based on the detection of the base station for the UL transmission of the corresponding carrier, the user equipment can perform CWS adjustment for the next UL transmission. The method for the user equipment to determine ACK, NACK, or DTX for the corresponding UL transmission and adjust the CWS can be determined based on the value of NDI signaled by the UL grant as Figure 18Determined by the value of NDI sent with UL permission as described in. Considering that the CWS adjustment does not refer to the carrier on which cat-2 LBT is performed in single-carrier transmission, it may be difficult to obtain a channel for transmitting multiple carriers according to the CWS adjustment method compared to the user equipment transmitting LAA UL without multi-carrier transmission. Therefore, the CWS adjustment can be configured not to be performed for UL transmission of carriers on which cat-4 LBT has not actually been performed, even if they have participated in multi-carrier transmission.

[0363] Next, the operation of the user equipment after the LBT failure in the previous subframe when multi-subframe scheduling is performed in a single carrier will be described.

[0364] - If there is an LBT gap or a CCA gap for performing LBT between consecutive subframes scheduled for multi-subframe scheduling

[0365] ● When the LBT type is specified as cat-4 LBT in the UL permission for multi-subframe scheduling, or when the LBT type is specified as cat-4 LBT in the UL permission for scheduling each subframe in the multi-subframe, if the LBT of the previous subframe has failed, it is configured to obtain a new BO counter for transmission to the subsequent UL subframe and follow the uplink channel access procedure.

[0366] ● When the LBT type is specified as cat-4 LBT in the UL permission for multi-subframe scheduling, or when the LBT type is specified as cat-4 LBT in the UL permission for scheduling each subframe in the multi-subframe, if the LBT of the previous subframe fails, it is configured to recover the previous BO counter and follow the uplink channel access procedure.

[0367] - If there is no LBT gap or CCA gap for performing LBT between consecutive subframes scheduled for multi-subframe scheduling,

[0368] ● When the LBT type is specified as cat-4 LBT in the UL permission for multi-subframe scheduling, or when the LBT type is specified as cat-4 LBT in the UL permission for scheduling each subframe in the multi-subframe, it is configured to recover the BO counter after the failure of the LBT in the previous subframe and follow the uplink channel access procedure.

[0369] Next, the operation of the user equipment after the LBT in the previous subframe has failed when multi-subframe scheduling is performed on multiple carriers will be described. If the multi-subframe scheduling is scheduled without gaps between subframes in at least one carrier, due to the continuous transmission in that carrier, uplink transmission may not always be possible in other carriers where the LBT has failed. To solve this problem, when the user equipment is scheduled for multiple carriers and undergoes multi-subframe scheduling such that there are no gaps between subframes for a specific carrier, the user equipment can be configured to give an arbitrary gap within the multi-subframes of the corresponding carrier. Thus, another carrier where the previous LBT failed and the carrier where the current LBT is successful can perform multi-carrier transmission simultaneously.

[0370] Example 3: Channel access for uplink multi-subframe transmission

[0371] When scheduling the transmission of consecutive subframes on the LAA SCell, the user equipment may discard some subframes of the consecutive subframes for some reasons. Here, discarding a subframe means stopping / discarding the UL transmission (e.g., PUSCH) in the subframe. That is, the UL transmission in the consecutive subframes can be paused / stopped before completion. For example, if the user equipment is in a power-limited situation, the UL transmission can be discarded in some subframes according to the power scaling rule. Thus, different from the intention of the base station, the UL transmission can be performed in non-consecutive subframes.

[0372] Hereinafter, the channel access procedure when performing UL transmission in non-consecutive subframes due to the discarding of some subframes when scheduling the transmission of consecutive subframes will be described. For ease of understanding, the power-limited situation of the user equipment is illustrated as the situation of discarding subframes in the present invention. However, the present invention can be applied to the channel access procedure in the case of scheduling consecutive subframes but performing UL transmission in non-consecutive subframes without limitation.

[0373] As a reference, according to Section 5.1.1.1 of 3GPP TS 36.213 v13.2.0, the following rules are used in the power scaling operation of the user equipment in the power-limited scenario of the user equipment: If the secondary cell group (SCG) is not configured and the total transmission power exceeds the power allowance limit value of the user equipment, the user equipment allocates the transmission power by prioritizing the transmission of PUCCH or by prioritizing the PUSCH transmission including UCI, and equally allocates the remaining transmission power to the PUSCHs transmitted on the remaining scheduled carriers. The transmission power of the user equipment is determined subframe by subframe.

[0374] In the case of an LAA SCell, the base station may allocate consecutive subframes (hereinafter, referred to as UL bursts) to a user equipment, and the user equipment performs one of cat-4 LBT and cat-2 LBT according to the LBT type signaled immediately before the transmission of the UL burst, and transmits the corresponding UL burst when the LBT is successful. Here, if UL bursts are scheduled without a gap between subframes and the LBT is successful at the start of the UL transmission burst, the transmission of the UL transmission burst may be performed without an additional LBT. However, when the user equipment is in a power-limited state, specific subframes of the LAA SCell may be discarded due to UL transmissions of the authorized cell according to the power scaling operation. For this reason, gaps may occur in the UL bursts.

[0375] Figure 28 The figure shows a case where a subframe is discarded on the LAA SCell.

[0376] Reference Figure 28 , four consecutive UL subframes are scheduled on the LAA SCell. However, in the power-limited state of the user equipment, priority is given to the power of the UL SF#(n + 1) of the authorized cell, and the UL subframe in the UL SF#(n + 1) of the LAA SCell may be discarded. In this case, the user equipment may intend to perform data transmission on consecutive UL subframes after the UL LBT on the LAA SCell is successful. However, there are ambiguities regarding whether to perform transmission on UL#(n + 2) and UL SF#(n + 3) without an LBT, which LBT type should be performed thereon, and which LBT parameter should be used if cat-4 LBT is to be performed. Therefore, the present invention provides a solution for the following situation.

[0377] First, the case where cat-2 LBT is configured to be performed at the start of a UL transmission burst for UL transmission on the LAA Scell will be described.

[0378] - If only 25 us LBT is performed and the LBT is successful immediately before the SF#(n + 2) transmission on the LAA SCell (i.e., if the channel is continuously idle or if the channel is continuously idle and the 25 us LBT is successful), UL data transmission can be performed in UL SF#(n + 2) and UL SF#(n + 3). If the 25 us LBT fails, the following two methods can be considered.

[0379] ● As the first method, if 25 us LBT is continuously performed and LBT is successful, transmission can be performed in UL SF#(n+3). In this case, if 25 us LBT is successful in UL SF#(n+2), UL transmission starts after the LBT success time, but the CP of the next symbol, i.e., SF#(n+3), can be extended to occupy a part of UL SF#(n+2) after LBT success.

[0380] ● As the second method, in order to transmit UL data in UL SF#(n+3), cat-4 LBT can be performed from UL SF#(n+2). In this case, cat-4 LBT can be performed by setting the LBT parameters based on LBT priority class 1 which has the highest priority among the priority classes.

[0381] ● As another method, the base station can specify the LBT priority class and the LBT type indication via UL grant, and the user equipment can perform cat-4 LBT by setting the LBT parameters based on the specified LBT priority class. However, since the UL transmission burst is configured to perform cat-2 LBT when receiving the initial signaling from the base station, even if cat-4 LBT is performed to transmit the remaining subframes, the corresponding cat-4 LBT may not be reflected in the CWS adjustment. Alternatively, the cat-4 LBT in SF#(n+2) performed by the user equipment can be applied / reflected in the CWS adjustment when the cat-4 LBT UL scheduling is received after the next 4 ms (e.g., SF#(n+2) is set as the reference subframe).

[0382] Next, the case where cat-4 LBT is configured to be performed at the start of the UL transmission burst for UL transmission on the LAA Scell will be described.

[0383] - As an embodiment, if cat-4 LBT to be performed from SF#(n+1) is set on the LAA SCell and cat-4 LBT is completed before the SF#(n+2) transmission on the LAA SCell, UL data transmission scheduled in UL SF#(n+2) and UL SF#(n+3) can be performed. If cat-4 LBT is not completed before the SF#(n+2) transmission on the LAA SCell, cat-4 LBT can continue until the SF#(n+3) transmission on the LAA SCell. The random backoff counter for cat-4 LBT can be used continuously.

[0384] - As another embodiment, if 25 us LBT is performed only before the SF#(n+2) transmission on the LAA SCell and the cat-2 LBT is successful (i.e., if the channel is continuously idle or if the channel is continuously idle and the 25 us LBT is successful), UL data transmission can be performed in UL SF#(n+2) and UL SF#(n+3). Here, if the 25 us LBT fails, the following two methods can be considered.

[0385] ● As the first method, if 25 us LBT is continuously performed and the LBT is successful, transmission can be performed in UL SF#(n+3). In this case, if the 25 us LBT is successful in UL SF#(n+2), UL transmission starts after the LBT success time, but the CP of the next symbol, i.e., SF#(n+3), can be extended so as to occupy a part of UL SF#(n+2) after the LBT success.

[0386] ● As the second method, in order to transmit UL data in UL SF#(n+3), cat-4 LBT can be performed starting from UL SF#(n+2). In this case, cat-4 LBT can be performed by setting the LBT parameters based on LBT priority 1 which has the highest priority among the priority categories.

[0387] ● As another method, the base station can specify the LBT priority category and the LBT type indication via UL grant, and the user equipment can perform cat-4 LBT by setting the LBT parameters based on the specified LBT priority category. In this regard, since the UL transmission burst is configured to perform cat-4 LBT when receiving the initial signaling from the base station, even if cat-4 LBT is performed to transmit the remaining subframes, the corresponding cat-4 LBT may not be reflected in the CWS adjustment. In this regard, since the UL transmission burst is configured to perform cat-4 LBT when receiving the initial signaling from the base station, CWS adjustment can be performed by regarding the transmission start time of the UL transmission (e.g., Figure 28 UL SF#n therein) as the reference subframe. In addition, from the viewpoint of splitting a single UL transmission burst and performing different cat-4 LBTs, each UL transmission burst can be regarded as a different UL burst. Therefore, when the cat-4 LBT UL scheduling is received after the next 4 ms (e.g., SF#(n+2) or SF#(n+3)) is set as the reference subframe, the cat-4 LBT performed by the user equipment in SF#(n+2) or SF#(n+3) can be applied / reflected in the CWS adjustment.

[0388] Alternatively, the following operations can be considered, regardless of whether it is configured to perform cat-4 LBT or cat-2 LBT at the start of a UL transmission burst for UL transmission on an LAA SCell. Specifically, if a particular subframe is not transmitted in the consecutive UL subframe scheduling of a particular LAA SCell (i.e., UL transmission is stopped) (e.g., due to a power limitation situation between the authorized carrier and the LAA SCell), then (starting from the time point when UL transmission stops) consecutive 25 us LBT can be performed for the transmission of a later UL subframe, and if the channel is idle, the later UL subframe is transmitted (e.g., Figure 28 the UL SF#(n + 2) in Figure 28 ). Additionally, when the channel is not idle during the execution of consecutive 25 us LBT (starting from the time point when UL transmission stops), the user equipment can perform cat-4 LBT, and if the LBT is successful, the later subframe is transmitted (e.g.,

[0389] the UL SF#(n + 2) in

[0390] Here, the LBT parameters used in cat-4 LBT can be configured considering the LBT priority indicated by the UL grant. Furthermore, the UL grant refers to the UL grant scheduling the UL subframe being transmitted. Depending on the scheduling scheme, the UL grant can be a UL grant scheduling multiple subframes, or can be a UL grant scheduling each subframe in multiple subframes individually.

[0391] Here, performing consecutive 25 us LBT is to check whether the channel is continuously idle. Considering that LBT should be performed during UL transmission, the above method can be summarized as follows.

[0392] If a particular subframe is not transmitted in the consecutive UL subframe scheduling of an LAA SCell (i.e., UL transmission is stopped / paused during consecutive UL subframe transmission),

[0393] If LBT is successful according to the above process, the user equipment can resume the transmission of subsequent UL subframes (i.e., the remaining UL subframes). On the other hand, if LBT fails, since the channel is not idle, the user equipment can alternatively perform cat-4 LBT for the transmission of subsequent UL subframes (e.g., Figure 28 the UL SF#(n + 3) in

[0394] On the other hand, in the case of multi-carrier transmission with multiple LAA SCells, for UL transmission,

[0395] (UL multi-carrier (MC) LBT type 1) perform independent LBT to send UL subframes for each LAA SCell corresponding to the LAA SCell, and perform UL transmission through the LAA SCell carrier that has succeeded in LBT, or

[0396] Regarding the subframes that perform cat-4 LBT among one or more LAA SCell carriers, (UL MC LBT type 2) cat-4 LBT is performed on a specific carrier (hereinafter referred to as the designated carrier), and when the channel is detected to be idle by performing 25 us LBT just before the transmission on other carriers for subframe transmission, UL multi-carrier transmission through multiple carriers is performed. One carrier randomly selected uniformly from the carriers scheduled to perform cat-4 LBT is used as the designated carrier.

[0397] UL MC LBT type 2 can be performed within a specific carrier set. For example, if a UL grant is received in a carrier set that has the same start time in a subframe and is scheduled using cat-4 LBT, if the cat-4 LBT in a specific carrier in the carrier set has been successfully completed, the user equipment can perform 25 us LBT just before the transmission on other carriers in the carrier set. The corresponding carrier set can be set considering the regulations of each country. For example, in Europe, considering the channelization of 5 GHz, part / whole of the carriers bound by the corresponding channels can be set as one carrier set. In addition, the UL subframes configured with cat-2 LBT UL grants can be sent by independently performing 25 us LBT without participating in the MC LBT in the corresponding carrier set. Additionally, even if the cat-4 LBT of the designated carrier among the subframes configured with cat-4 LBT fails, the UL transmission of the carrier that has received the UL grant with cat-2 LBT can be independently performed.

[0398] In addition, when transmitting through multiple LAA SCell carriers, the MCOT set in a specific carrier can be shared by multiple carriers as follows. In addition, the corresponding MCOT can be configured to start from the channel occupancy in the carrier that performs cat-4 LBT.

[0399] - A base station that initiates DL transmission based on type B multi-carrier LBT for obtaining MCOT can share channel occupancy with a user equipment on all carriers on which type B LBT has been completed.

[0400] - After an operator that performs cat-4 LBT has completed cat-4 LBT, DL transmission can be used to start channel occupancy.

[0401] On the other hand, when it is configured to perform cat-4 LBT as the LBT type at the start time of a UL transmission burst for UL transmission on an LAA SCell, the following two methods can be considered.

[0402] - As one method, if cat-4 LBT to be performed from SF#(n + 1) on an LAA SCell is completed before the transmission of SF#(n + 2) on the LAA SCell by setting, UL data transmission scheduled in UL SF#(n + 2) and UL SF#(n + 3) can be performed. If cat-4 LBT is not completed before the transmission of SF#(n + 2) on the LAA SCell, cat-4 LBT can be performed until the transmission of SF#(n + 3) on the LAA SCell.

[0403] - As another method, if only 25 us LBT is performed before the transmission of SF#(n + 2) on an LAA SCell and cat-2 LBT is successful, UL data transmission can be performed in UL SF#(n + 2) and UL SF#(n + 3). Here, if the 25 us LBT fails, the following two methods can be considered.

[0404] ● As the first method, if 25 us LBT is continuously performed and the LBT is successful, transmission can be performed in UL SF#(n + 3). In this case, if the 25 us LBT is successful in UL SF#(n + 2), the UL transmission is configured to start after the LBT success time but the CP of the next symbol, i.e., SF#(n + 3) can be extended so as to occupy a part of UL SF#(n + 2) after the LBT success.

[0405] During the process of (consecutive) UL subframe transmission in LAA SCell carriers to be sent by multiple carriers, it may not be possible to send a specific subframe together with implementing a power scaling operation in a power-limited state for the transmission of an authorized carrier. When the transmission of subframes (e.g., UL SF#(n + 1)) of multiple LAA SCell carriers becomes impossible due to the transmission of an authorized carrier, as Figure 29As shown, it is necessary to perform the additional LBT as described above for the transmission of the subsequent subframe of the LAA SCell carrier (e.g., UL SF#(n + 2)). However, there are various LBT procedures for multi - carrier transmission (e.g., UL MC LBT type 1 or UL MC LBT type 2), and the LBT procedure for UL subframe transmission should be determined after discarding the transmitted subframe according to each MC LBT procedure.

[0406] - In the case of performing independent UL LBT (e.g., UL MC LBT type 1) for each LAA SCell carrier, the later UL subframe transmission can be performed by the additional LBT in the UL subframe where the transmission is discarded as follows.

[0407] ● As in UL MC LBT type 1, the LAA SCell LBT (e.g., cat - 4 or 25us LBT) can be implemented independently for each carrier. In this case, if UL transmission is not performed in UL SF#(n + 1) for each LAA SCell carrier, 25us LBT can be performed for UL SF#(n + 2) transmission, and UL transmission can be performed in the carrier where the channel is not idle. In the carrier where the channel is not idle, additional cat - 4 LBT can be performed (in this case, considering the LBT priority category defined in the UL grant or selecting the above - mentioned priority category), and if the channel is idle, UL transmission is possible in the later UL subframe.

[0408] ● Even if the LAA SCell LBT is implemented independently for each carrier as in UL MC LBT type 1, if a subframe to be discarded occurs as in UL SF#(n + 1), 25us LBT can be performed independently of each carrier. In this regard, if a carrier where the channel is not idle occurs, a specific carrier can be selected and cat - 4 LBT can be performed on the selected carrier. In addition, only 25us LBT can be performed on other carriers (including the remaining carriers where the channel is not idle), and it can be determined for each carrier whether to perform the later UL subframe transmission.

[0409] ● In the subframe configured to perform 25us LBT through UL grant according to the above process, by performing only 25us LBT without the cat - 4 LBT process, UL transmission can be performed in a later subframe (e.g., UL SF#(n + 2)) after discarding the transmitted subframe. In addition, when cat - 4 LBT is performed only on a specific carrier and 25us LBT is performed on other carriers, it is possible to participate in simultaneous transmission on the subframe configured with 25us LBT through UL grant.

[0410] - In the case of the UL multi-carrier transmission scheme, such as UL MC LBT type 2, cat-4 LBT is performed based on a specific designated carrier in the LAA SCell, and 25 us LBT is performed on other carriers that receive a cat-4 LBT UL grant for subframe transmission. The following method can be regarded as an additional LBT scheme for UL subframe transmission before the UL subframe (e.g., UL SF#(n + 1)) in which transmission is abandoned.

[0411] ● In the case of receiving a cat-4 LBT UL grant UL subframe as in UL MC LBT type 2, if a UL subframe with discarded transmission occurs before completion, 25 us LBT is performed for each carrier for subsequent UL subframe transmission, and subsequent UL subframe transmission is possible on carriers where the channel is idle. For carriers where the channel is not idle, additional cat-4 LBT is performed, and UL subframe transmission is possible if the channel is idle.

[0412] ● In the case of receiving a cat-4 LBT UL grant UL subframe as in UL MC LBT type 2, if a UL subframe with discarded transmission occurs before completion, the designated carrier can be set otherwise (or the previously defined designated carrier can be reused) for subsequent UL subframe transmission. Then, LBT similar to UL MC LBT type 2 is performed by performing 25 us LBT on other carriers and cat-4 LBT on the designated carrier, and then it can be determined for each carrier whether to perform transmission in subsequent UL subframes after the UL subframe with discarded transmission. In this regard, 25 us LBT can be performed before setting the designated carrier for cat-4 LBT, and the designated carrier can be added on carriers where the channel is not idle at this time.

[0413] ● In the case of receiving a cat-4 LBT UL grant UL subframe as in UL MC LBT type 2, if a UL subframe with discarded transmission occurs before completion, only 25 us LBT can be performed for subsequent UL subframe transmission. That is, it is also possible to send subsequent UL subframes only on carriers where the channel is idle for 25 us, and transmission is performed by checking only for 25 us immediately before the transmission of the immediately following UL subframe (e.g., UL SF#(n + 2)).

[0414] ● When performing additional cat-4 LBT or 25 us LBT as described above, it can be performed on the carrier assigned with cat-4 LBT by UL grant. Meanwhile, in the case of a UL subframe configured with 25 us LBT by UL grant, if additional LBT is performed due to transmission discard, subsequent UL subframe transmission can be performed considering the success of the independent 25 us LBT. However, in order to perform simultaneous MC transmission by a user equipment, operations similar to those of the subframe with cat-4 LBT UL grant are configured by participating in additional cat-4 LBT or 25 us LBT.

[0415] For UL subframe transmission after the subframe in which transmission is discarded, in the case of carrier transmission in which 25 us LBT (including cat-4 LBT) for the above-mentioned additional LBT scheme is successful, it is possible to extend the CP by copying the signal sent from the OFDM symbol with CP extension to send a signal for channel reservation.

[0416] Figure 30 The configurations of a user equipment and a base station according to an exemplary embodiment of the present invention are illustrated. In the present invention, the user equipment can be implemented by various types of wireless communication devices or computing devices that ensure portability and mobility. The user equipment (UE) can be referred to as a terminal, a station (STA), a mobile user (MS), etc. In the present invention, the base station can control and manage a cell corresponding to a service area (e.g., a macro cell, a femto cell, a pico cell, etc.), and perform functions including signal transmission, channel designation, channel monitoring, self-diagnosis, relaying, etc. The base station can be referred to as an evolved Node B (eNB), an access point (AP), etc.

[0417] Referring to Figure 30 , the user equipment 100 may include a processor 110, a communication module 120, a memory 130, a user interface unit 140, and a display unit 150.

[0418] The processor 110 may execute various commands or programs according to the present invention and process data in the user equipment 100. Further, the processor 110 may control all operations of the corresponding units of the user equipment 100 and control data transmission / reception between these units. For example, the processor 110 may perform DL / UL transmission / reception in an LTE-U cell in an LAA environment. Specifically, the processor 110 may perform the foregoing various operations, such as DL / UL transmission / reception, verification of a HARQ-ACK feedback set, CWS adjustment, etc.

[0419] The communication module 120 may be an integrated module that performs mobile communication by using a mobile communication network and performs wireless LAN access by using a wireless LAN. To this end, the communication module 120 may include a plurality of network interface cards, such as cellular communication interface cards 121 and 122 and an internal or external type of wireless LAN interface card 123. In Figure 30 , the communication module 120 is illustrated as an integrated module, but the corresponding network interface cards may be independently provided according to a circuit configuration or a use different from Figure 30 .

[0420] The cellular communication interface card 121 transmits / receives radio signals to / from at least one of the base station 200, an external device, and a server by using a mobile communication network, and provides cellular communication services at a first frequency band based on a command of the processor 110. The cellular communication interface card 121 may include at least one NIC module that uses an LTE licensed band. The cellular communication interface card 122 transmits / receives radio signals to / from at least one of the base station 200, an external device, and a server by using a mobile communication network, and provides cellular communication services at a second frequency band based on a command of the processor 110. The cellular communication interface card 122 may include at least one NIC module that uses an LTE unlicensed band. For example, the LTE unlicensed band may be a band of 2.4 GHz or 5 GHz.

[0421] The wireless LAN interface card 123 transmits / receives radio signals to / from at least one of the base station 200, an external device, and a server through wireless LAN access, and provides wireless LAN services at a second frequency band based on a command of the processor 110. The wireless LAN interface card 123 may include at least one NIC module that uses a wireless LAN band. For example, the wireless LAN band may be an unlicensed radio band, such as a band of 2.4 GHz or 5 GHz.

[0422] The memory 130 stores control programs and various result data used in the user equipment 100. The control programs may include programs required for the user equipment 100 to perform wireless communication with at least one of the base station 200, an external device, and a server. The user interface 140 includes various types of input / output devices provided in the user equipment 100. The display unit 150 outputs various images on a display screen.

[0423] Furthermore, the base station 200 according to an exemplary embodiment of the present invention may include a processor 210, a communication module 220, and a memory 230.

[0424] The processor 210 may execute various commands or programs according to the present invention and process data in the base station 200. Further, the processor 210 may control all operations of the corresponding units of the base station 200 and control data transmission / reception between these units. For example, the processor 210 may perform DL / UL transmission / reception based on LBT in the LAA environment. Specifically, the processor 210 may perform the foregoing various operations, such as DL / UL transmission / reception, verification of HARQ-ACK feedback sets, CWS adjustment, etc.

[0425] The communication module 220 may be an integrated module that performs mobile communication by using a mobile communication network and performs wireless LAN access by using a wireless LAN, such as the communication module 120 of the user equipment 100. To this end, the communication module 120 may include a plurality of network interface cards, such as cellular communication interface cards 221 and 222 and internal or external types of wireless LAN interface cards 223. In Figure 25 this, the communication module 220 is illustrated as an integrated module, but the corresponding network interface cards may be independently provided according to the circuit configuration or uses different from Figure 25 this.

[0426] The cellular communication interface card 221 transmits / receives radio signals to / from at least one of the user equipment 100, an external device, and a server by using a mobile communication network and provides cellular communication services at a first frequency band based on a command of the processor 210. The cellular communication interface card 221 may include at least one NIC module that uses an LTE licensed frequency band. The cellular communication interface card 222 transmits / receives radio signals to / from at least one of the user equipment 100, an external device, and a server by using a mobile communication network and provides cellular communication services at a second frequency band based on a command of the processor 210. The cellular communication interface card 222 may include at least one NIC module that uses an LTE unlicensed frequency band. The LTE unlicensed frequency band may be a band of 2.4 GHz or 5 GHz.

[0427] The wireless LAN interface card 223 transmits / receives radio signals to / from at least one of the user equipment 100, an external device, and a server through wireless LAN access and provides wireless LAN services at a second frequency band based on a command of the processor 210. The wireless LAN interface card 223 may include at least one NIC module that uses a wireless LAN frequency band. For example, the wireless LAN frequency band may be an unlicensed radio band, such as a band of 2.4 GHz or 5 GHz.

[0428] In Figure 25Among them, the blocks of the user equipment and the base station are logically divided and the components of the illustrated device. According to the design of the device, the components of the device can be installed as one chip or multiple chips. Further, some components of the user equipment 100 (that is, the user interface 140 and the display unit 150) can be selectively arranged in the user equipment 100. Further, some components of the base station 200 (that is, the wireless LAN interface 223, etc.) can be selectively arranged in the base station 200. If necessary, the user interface 140 and the display unit 150 can also be arranged in the base station 200.

[0429] The methods and systems of the present invention are described in connection with specific embodiments, but some or all of the components and operations of the present invention can be implemented by using a computer system with a general hardware architecture.

[0430] The specification of the present invention is for illustrative purposes, and those skilled in the art should understand that the present invention can be easily modified into other detailed forms without changing the technical spirit or essential features of the present invention. Therefore, the foregoing exemplary embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single type can be implemented as a distributed component, and similarly, components described as distributed components can also be implemented in a combined form.

[0431] The scope of the present invention is represented by the claims to be described below (rather than the detailed description), but the scope of the present invention should be construed as meaning and scope of the claims and all variations or modifications from their equivalents are within the scope of the present invention.

[0432] Industrial Applicability

[0433] The present invention can be used in various communication devices (for example, stations or access points using unlicensed band communication, stations or base stations using cellular communication, etc.) that can be used in a wireless communication system.

Claims

1. A method for a user equipment to perform uplink transmission in an unlicensed cell in a wireless communication system, the method comprising: Receive uplink scheduling information; and When the user equipment has stopped transmission during uplink transmission being performed in an unlicensed cell according to the uplink scheduling information, perform channel access to resume the uplink transmission, wherein, when the channel sensed by the user equipment after the transmission has stopped is not continuously idle, perform a first type of channel access, and when the channel sensed by the user equipment after the transmission has stopped is continuously idle, perform a second type of channel access. Wherein, the first type of channel access includes performing random backoff using a variable-size contention window CW after a first channel sensing, and the second type of channel access only includes performing a second channel sensing without the random backoff.

2. The method according to claim 1, wherein, The uplink transmission includes transmission on a plurality of subframes, and wherein, the user equipment stopping the transmission during the uplink transmission being performed includes stopping the transmission in subframes other than the last subframe of the plurality of subframes.

3. The method according to claim 1, wherein, The wireless communication system includes a wireless communication system based on the 3rd Generation Partnership Project 3GPP, and wherein, the first type of channel access includes Category-4 Listen Before Talk LBT and the second type of channel access includes Category-2 LBT.

4. The method according to claim 1, wherein, The second type of channel access includes performing the second channel sensing for a duration of 25 μs without the random backoff.

5. A user equipment used in a wireless communication system, the user equipment comprising: A wireless communication module; and A processor, wherein, the processor is configured to: Receive uplink scheduling information, and When the user equipment has stopped transmission during uplink transmission being performed in an unlicensed cell according to the uplink scheduling information, perform channel access to resume the uplink transmission, wherein, when the channel sensed by the user equipment after the transmission has stopped is not continuously idle, perform a first type of channel access, and when the channel sensed by the user equipment after the transmission has stopped is continuously idle, perform a second type of channel access. Wherein, the first type of channel access includes performing random backoff using a variable-size contention window CW after a first channel sensing, and the second type of channel access only includes performing a second channel sensing without the random backoff.

6. The user equipment according to claim 5, wherein, The uplink transmission includes transmission on a plurality of subframes, and wherein, the user equipment stopping the transmission during the uplink transmission being performed includes stopping the transmission in subframes other than the last subframe of the plurality of subframes.

7. The user equipment according to claim 5, wherein, The wireless communication system includes a wireless communication system based on the 3rd Generation Partnership Project 3GPP, and wherein, the first type of channel access includes Category-4 Listen Before Talk LBT and the second type of channel access includes Category-2 LBT.

8. The user equipment according to claim 5, wherein, The second type of channel access includes performing the second channel sensing for a duration of 25 μs without the random backoff.

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