Channel access method and device in sidelink communication

Abstract

The invention discloses a channel access method and device in sidelink communication. The method of the first terminal comprises the following steps: initiating COT; multicast SL transmission is executed in the COT; receiving one or more HARQ-ACK feedback for the multicast SL transmission; calculating an ACK ratio based on the one or more HARQ-ACK feedbacks when the ratio threshold is configured to the first terminal; and adjusting the CW based on a comparison result between the ACK ratio and a ratio threshold.

Description

Technical Field

[0001] The present disclosure relates to a channel access technology in a communication system, and more particularly, to a channel access technology for sidelink communication. Background Art

[0002] With the advancement of information and communication technology, various wireless communication technologies are being developed. Representative wireless communication technologies may be Long Term Evolution (LTE), Advanced LTE (LTE-A), New Radio (NR), etc., which are designated as the third generation partnership project (3GPP) standard. LTE and / or LTE-A may be fourth generation (4G) communication technologies. NR may be fifth generation (5G) communication technologies.

[0003] After the commercialization of 4G communication systems (e.g., communication systems supporting LTE and / or LTE-A), 5G communication systems (e.g., communication systems supporting NR) using a higher frequency band (e.g., a frequency band of 6 GHz or more) than the frequency band of the 4G communication system (e.g., a frequency band of 6 GHz or less) are being considered to handle the surge in wireless data. The 5G communication system may support enhanced mobile broadband (eMBB), ultra-reliable low latency communication (URLLC), and / or massive machine type communication (mMTC).

[0004] The 5G communication system may support sidelink communication. In sidelink communication, communication may be performed between terminals. For example, a first terminal may send a signal, information, and / or data to a second terminal, and the second terminal may receive a signal, information, and / or data from the first terminal. The channel used for sidelink communication may be a physical sidelink broadcast channel (PSBCH), a physical sidelink shared channel (PSSCH), a physical sidelink control channel (PSCCH), and / or a physical sidelink feedback channel (PSFCH).

[0005] The 5G communication system may support unlicensed band communications. The unlicensed band may be shared by multiple communication systems. In order to ensure fairness in the use of the unlicensed band, a channel access procedure may be required. The 5G communication system may support sidelink communications in the unlicensed band. In this case, a sidelink channel access procedure may be required for the terminal to use the unlicensed band.

[0006] Meanwhile, the above-mentioned technologies are described for enhancing the understanding of the background of the present disclosure, and they may include non-prior technologies that are not known to those of ordinary skill in the art. Summary of the invention

[0007]

Technical issues

[0008] The present disclosure aims to provide a channel access method and apparatus in sidelink communication.

[0009]

Technical solution

[0010] According to an exemplary embodiment of the present disclosure, a method of a first terminal for achieving the above-mentioned purpose may include: initiating a channel occupancy time (COT); performing a multicast sidelink (SL) transmission within the COT; receiving one or more hybrid automatic repeat request-acknowledgement (HARQ-ACK) feedbacks for the multicast SL transmission; in response to a ratio threshold being configured to the first terminal, calculating an ACK ratio based on one or more HARQ-ACK feedbacks; and adjusting a content window (CW) based on a comparison result between the ACK ratio and the ratio threshold.

[0011] The one or more HARQ-ACK feedbacks considered for adjusting the CW may be one or more HARQ-ACK feedbacks for multicast SL transmission performed within a most recent COT initiated by the first terminal in the COT.

[0012] The one or more HARQ-ACK feedbacks considered for adjusting the CW may be one or more HARQ-ACK feedbacks for multicast SL transmission performed within a reference duration within a most recent COT initiated by the first terminal in the COT.

[0013] HARQ-ACK feedback for multicast SL transmission may be enabled.

[0014] One or more HARQ-ACK feedbacks may be received on a physical sidelink feedback channel (PSFCH) within the same time slot.

[0015] Adjusting the CW may include: when the ACK ratio is greater than or equal to a ratio threshold, changing the CW to a minimum CW.

[0016] Adjusting the CW may include reducing the CW when the ACK ratio is greater than or equal to a ratio threshold.

[0017] Adjusting the CW may include increasing the CW when the ACK ratio is less than a ratio threshold.

[0018] The CW of all priority classes may be increased.

[0019] When the ratio threshold is not configured for the first terminal, calculation of the ACK ratio may not be performed, and when one or more HARQ-ACK feedbacks include at least one ACK, the CW may be changed to the minimum CW.

[0020] The ACK ratio may be a ratio between ACKs in one or more HARQ-ACK feedbacks and the number of terminals expected to send HARQ-ACK feedbacks for the multicast SL transmission.

[0021] The ACK ratio may be a ratio between an ACK among one or more HARQ-ACK feedbacks and the number of HARQ-ACK feedbacks expected for the multicast SL transmission.

[0022] When a negative ACK (NACK)-only transmission scheme is used, HARQ-ACK feedback not received at the transmitting terminal among expected HARQ-ACK feedbacks may be regarded as ACK.

[0023] According to an exemplary embodiment of the present disclosure, a method of a first terminal for achieving the above-mentioned purpose may include: initiating a channel occupancy time (COT); performing a multicast sidelink (SL) transmission within the COT; receiving one or more hybrid automatic repeat request-acknowledgement (HARQ-ACK) feedbacks for the multicast SL transmission; in response to a ratio threshold being configured to the first terminal, calculating a negative ACK (NACK) ratio based on one or more HARQ-ACK feedbacks; and adjusting a content window (CW) based on a comparison result between the NACK ratio and the ratio threshold.

[0024] The one or more HARQ-ACK feedbacks considered for adjusting the CW may be one or more HARQ-ACK feedbacks for multicast SL transmissions performed within a reference duration within a most recent COT initiated by the first terminal in the COT.

[0025] When adjusting the CW, when the NACK ratio is less than the ratio threshold, the first terminal may change the CW to the minimum CW, and when the NACK ratio is equal to or greater than the ratio threshold, the first terminal may increase the CW.

[0026] The NACK ratio can be the ratio between the NACKs in one or more HARQ-ACK feedbacks and the number of terminals expected to send HARQ-ACK feedbacks for groupcast SL transmission, or the ratio between the NACKs in one or more HARQ-ACK feedbacks and the number of HARQ-ACK feedbacks expected for groupcast SL transmission.

[0027] According to an exemplary embodiment of the present disclosure, a first terminal for achieving the above-mentioned purpose may include at least one processor, and the at least one processor may enable the first terminal to execute: initiating a channel occupancy time (COT); performing a multicast sidelink (SL) transmission within the COT; receiving one or more hybrid automatic repeat request-acknowledgement (HARQ-ACK) feedbacks for the multicast SL transmission; in response to a ratio threshold being configured to the first terminal, calculating an ACK ratio based on one or more HARQ-ACK feedbacks; and adjusting a content window (CW) based on a comparison result between the ACK ratio and the ratio threshold.

[0028] When adjusting the CW, the at least one processor may cause the first terminal to execute: when the NACK ratio is less than a ratio threshold, changing the CW to a minimum CW; and when the NACK ratio is equal to or greater than the ratio threshold, increasing the CW.

[0029] The ACK ratio may be a ratio between ACKs in one or more HARQ-ACK feedbacks and the number of terminals expected to send HARQ-ACK feedbacks for the multicast SL transmission, or a ratio between ACKs in one or more HARQ-ACK feedbacks and the number of HARQ-ACK feedbacks expected for the multicast SL transmission.

[0030]

Technical Effect

[0031] According to the present disclosure, the transmitting terminal can receive HARQ-ACK feedback for SL transmission and calculate the ACK ratio or NACK ratio based on the HARQ-ACK feedback. The transmitting terminal can adjust the content window (CW) based on the comparison result between the ACK ratio (or NACK ratio) and the ratio threshold. Therefore, SL communication can be effectively performed in the unlicensed band. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a conceptual diagram illustrating a first exemplary embodiment of a communication network.

[0033] Figure 2 is a block diagram showing a first exemplary embodiment of communication nodes constituting a communication network.

[0034] Figure 3 is a conceptual diagram illustrating a first exemplary embodiment of a system frame in a communication network.

[0035] Figure 4 is a conceptual diagram illustrating a first exemplary embodiment of a subframe in a communication network.

[0036] Figure 5 is a conceptual diagram illustrating a first exemplary embodiment of time slots in a communication network.

[0037] Figure 6 is a conceptual diagram illustrating a first exemplary embodiment of time-frequency resources in a communication network.

[0038] Figure 7 is a conceptual diagram of a first exemplary embodiment showing a configuration of a resource pool, a SL signal, and a SL channel within a SL bandwidth part (BWP).

[0039] Figure 8 is a conceptual diagram illustrating a first exemplary embodiment of an SL resource.

[0040] Fig. 9is a sequence diagram showing a first exemplary embodiment of a CW size adjustment method.

[0041] Fig.10 is a conceptual diagram showing a first exemplary embodiment of a reference duration within channel occupancy.

[0042] Fig.11 is a conceptual diagram illustrating a second exemplary embodiment of a reference duration within channel occupancy. DETAILED DESCRIPTION

[0043] Although the present disclosure is capable of various modifications and alternative forms, specific embodiments thereof are shown by way of example in the accompanying drawings and will be described in detail herein. However, it should be understood that it is not intended to limit the present disclosure to the specific forms disclosed, but on the contrary, the present disclosure is intended to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present disclosure. Throughout the description of the drawings, the same numbers refer to the same elements.

[0044] It should be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element without departing from the scope of the present disclosure. As used herein, the term "and / or" includes any and all combinations of one or more related listed items.

[0045] In an exemplary embodiment of the present disclosure, “at least one of A and B” may mean “at least one of A or B” or “at least one of a combination of one or more of A and B”. Furthermore, in an exemplary embodiment of the present disclosure, “one or more of A and B” may mean “one or more of A or B” or “one or more of a combination of one or more of A and B”.

[0046] In exemplary embodiments of the present disclosure, "(re)transmission" may mean "transmission", "retransmission" or "transmission and retransmission", "(re)configuration" may mean "configuration", "reconfiguration" or "configuration and reconfiguration", "(re)connection" may mean "connection", "reconnection" or "connection and reconnection", and "(re)access" may mean "access", "revisit" or "access and reaccess".

[0047] It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intervening elements. Conversely, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements. Other words used to describe the relationship between elements should be interpreted in a similar manner (i.e., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

[0048] The terms used herein are only used to describe specific embodiments and are not intended to limit the present disclosure. As used herein, the singular forms "one", "an" and "the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include", "comprise", "include" and / or "comprises" specify the presence of the features, integers, steps, operations, elements and / or parts when used herein, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or their groups.

[0049] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those commonly understood by those skilled in the art to which the present disclosure belongs. It should also be understood that terms (such as those defined in commonly used dictionaries) should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0050] Hereinafter, preferred exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. In order to facilitate overall understanding when describing the present disclosure, the same components in the drawings are represented by the same reference numerals, and their repeated description will be omitted.

[0051] A communication network to which an exemplary embodiment according to the present disclosure is applied will be described. The communication network to which an exemplary embodiment according to the present disclosure is applied is not limited to the content described below, and can be applied to various communication networks according to the exemplary embodiment of the present disclosure. Here, a communication network can be used in the same sense as a communication system. A communication network can refer to a wireless communication network, and a communication system can refer to a wireless communication system.

[0052] In the present disclosure, “an operation (e.g., a transmission operation) is configured” may mean “configuration information (e.g., an information element or parameter) for the operation and / or information indicating the execution of the operation is transmitted by signal”. “Information elements (e.g., parameters) are configured” may mean “corresponding information elements are transmitted by signal”. In the present disclosure, signaling may be at least one of system information (SI) signaling (e.g., transmission of system information blocks (SIBs) and / or master information blocks (MIBs)), RRC signaling (e.g., transmission of RRC parameters and / or higher layer parameters), MAC control element (CE) signaling, or PHY signaling (e.g., transmission of downlink control information (DCI), uplink control information (UCI), and / or sidelink control information (SCI)).

[0053] Figure 1 is a conceptual diagram illustrating a first exemplary embodiment of a communication network.

[0054] Reference Figure 1 The base station 110 may support cellular communications (e.g., Long Term Evolution (LTE), Advanced LTE (LTE-A), LTE-A Pro, Unlicensed LTE (LTE-U), New Radio (NR), and Unlicensed NR (NR-U) specified as 3rd Generation Partnership Project (3GPP) standards), etc. The base station 110 may support Multiple Input Multiple Output (MIMO) (e.g., Single User MIMO (SU-MIMO), Multi-User MIMO (MU-MIMO), Massive MIMO, etc.), Coordinated Multi-Point (CoMP), Carrier Aggregation (CA), etc.).

[0055] The first terminal 120 and the second terminal 130 may perform sidelink communication. The sidelink communication may be performed based on mode 1 or mode 2. When mode 1 is used, the sidelink communication between the first terminal 120 and the second terminal 130 may be performed using resources allocated by the base station 110. When mode 2 is used, the sidelink communication between the first terminal 120 and the second terminal 130 may be performed using resources selected by the first terminal 120 or the second terminal 130.

[0056] The communication nodes (i.e., base stations, terminals, etc.) that constitute the above-mentioned communication network can support communication protocols based on code division multiple access (CDMA), communication protocols based on wideband CDMA (WCDMA), communication protocols based on time division multiple access (TDMA), communication protocols based on frequency division multiple access (FDMA), communication protocols based on single carrier FDMA (SC-FDMA), communication protocols based on orthogonal frequency division multiplexing (OFDM), communication protocols based on orthogonal frequency division multiple access (OFDMA), etc.

[0057] In the communication node, the base station may be referred to as Node B, evolved Node B, 5G Node B (gNodeB), base transceiver station (BTS), radio base station, radio transceiver, access point, access node, transmission / reception point (Tx / Rx Point), etc. In the communication node, the terminal may be referred to as user equipment (UE), access terminal, mobile terminal, station, user station, portable user station, mobile station, node, device, etc. The communication node may have the following structure.

[0058] Figure 2 is a block diagram showing a first exemplary embodiment of communication nodes constituting a communication network.

[0059] See also Figure 2 , the communication node 200 may include at least one processor 210, a memory 220, and a transceiver 230 connected to a network to perform communication. In addition, the communication node 200 may also include an input interface device 240, an output interface device 250, a storage device 260, etc. Each component included in the communication node 200 can be connected through a bus 270 to communicate with each other.

[0060] However, each component included in the communication node 200 may not be connected to the common bus 270, but may be connected to the processor 210 via a separate interface or a separate bus. For example, the processor 210 may be connected to at least one of the memory 220, the transceiver 230, the input interface device 240, the output interface device 250, and the storage device 260 via a dedicated interface.

[0061] The processor 210 may execute a program stored in at least one of the memory 220 and the storage device 260. The processor 210 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor, on which the method according to the embodiment of the present disclosure is executed. Each of the memory 220 and the storage device 260 may be composed of at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 220 may include at least one of a read-only memory (ROM) and a random access memory (RAM).

[0062] The following will describe the operation method of the communication node in the communication network. Even when describing the method to be performed at the first communication node in the communication node (e.g., the transmission or reception of a signal), the corresponding second communication node may also perform a method corresponding to the method performed at the first communication node (e.g., the reception or transmission of a signal). That is, when describing the operation of the first terminal (e.g., the transmitting terminal), the corresponding second terminal (e.g., the receiving terminal) may perform an operation corresponding to the operation of the first terminal. Conversely, when describing the operation of the second terminal, the corresponding first terminal may perform an operation corresponding to the operation of the second terminal.

[0063] Figure 3 is a conceptual diagram illustrating a first exemplary embodiment of a system frame in a communication network.

[0064] Reference Figure 3 , time resources in a communication network can be divided into frames. For example, each system frame of 10 milliseconds (ms) in length can be continuously configured in the time domain of the communication network. The system frame number (SFN) can be set to #0 to #1023. In this case, 1024 system frames can be repeated in the time domain of the communication network. For example, the SFN of the system frame after system frame #1023 can be set to #0.

[0065] One system frame may include two half frames, and the length of one half frame may be 5 ms. A half frame located in the starting area of ​​the system frame may be referred to as "half frame #0", and a half frame located in the ending area of ​​the system frame may be referred to as "half frame #1". The system frame may include 10 subframes, and the length of one subframe may be 1 ms. The 10 subframes in one system frame may be referred to as "subframes #0 to #9".

[0066] Figure 4 is a conceptual diagram illustrating a first exemplary embodiment of a subframe in a communication network.

[0067] Reference Figure 4 , a subframe may include n time slots, and n may be a natural number. Therefore, a subframe may consist of one or more time slots.

[0068] Figure 5 is a conceptual diagram illustrating a first exemplary embodiment of time slots in a communication network.

[0069] Reference Figure 5 , a time slot may include one or more symbols. Figure 5One time slot shown may consist of 14 symbols. Here, the length of the time slot may vary according to the number of symbols included in the time slot and the length of the symbol. Alternatively, the length of the time slot may vary according to the parameter set. When the subcarrier spacing is 15kHz (e.g., μ=0), the length of the time slot may be 1ms. In this case, one system frame may include 10 time slots. When the subcarrier spacing is 30kHz (e.g., μ=1), the length of the time slot may be 0.5ms. In this case, one system frame may include 20 time slots.

[0070] When the subcarrier spacing is 60kHz (e.g., μ=2), the length of the time slot may be 0.25ms. In this case, one system frame may include 40 time slots. When the subcarrier spacing is 120kHz (e.g., μ=3), the length of the time slot may be 0.125ms. In this case, one system frame may include 80 time slots. When the subcarrier spacing is 240kHz (e.g., μ=4), the length of the time slot may be 0.0625ms. In this case, one system frame may include 160 time slots.

[0071] Figure 6 is a conceptual diagram illustrating a first exemplary embodiment of time-frequency resources in a communication network.

[0072] Reference Figure 6 , a resource configured with one OFDM symbol in the time domain and one subcarrier in the frequency domain may be defined as a 'resource element (RE)'. A resource configured with one OFDM symbol in the time domain and K subcarriers in the frequency domain may be defined as a 'resource element group (REG)'. One REG may include K REs. REG may be used as a basic unit for resource allocation in the frequency domain. K may be a natural number. For example, K may be 12. N may be a natural number. Figure 5 The N in the time slot shown in can be 14, while Figure 6 The N in the time slot shown in can be 7. N OFDM symbols can be used as a basic unit of resource allocation in the time domain.

[0073] A method for sending and receiving data in a communication network will be described. In downlink communication, downlink data may be sent via a physical downlink shared channel (PDSCH). In uplink communication, uplink data may be sent via a physical uplink shared channel (PUSCH). In the present disclosure, PDSCH may refer to downlink data or resources for sending and receiving downlink data, and PUSCH may refer to uplink data or resources for sending and receiving uplink data. A base station may send downlink control information (DCI) including configuration information (e.g., resource allocation information, scheduling information) of the PDSCH on a physical downlink control channel (PDCCH). In the present disclosure, PDCCH may refer to DCI (e.g., control information) or resources for sending DCI.

[0074] The terminal may receive DCI on the PDCCH and identify the configuration information of the PDSCH included in the DCI. For example, the configuration information of the PDSCH may include time domain resource allocation (TDRA), frequency domain resource allocation (FDRA) and / or modulation and coding scheme (MCS) information. TDRA may indicate the resource region of the PDSCH in the time domain. FDRA may indicate the resource region of the PDSCH in the frequency domain. MCS information may indicate the MCS level or MCS index.

[0075] A sidelink (SL) communication method in a communication network will be described. SL communication can be performed in a licensed band and / or an unlicensed band. SL communication in an unlicensed band may be referred to as sidelink-unlicensed (SL-U) communication or unlicensed-sidelink (U-SL) communication. SL resources may be used to transmit SL signals and / or channels. SL resources may be configured based on a resource pool. A resource pool may be referred to as an SL resource pool. A resource pool may include a Tx resource pool and / or an Rx resource pool. A Tx resource pool may be used for SL transmission, and an Rx resource pool may be used for SL reception. A Tx resource pool and an Rx resource pool may be distinguished from each other. A Tx resource pool and an Rx resource pool may be configured independently.

[0076] In the time domain, a resource pool may include one or more time slots, and in the frequency domain, a resource pool may include one or more subchannels. A subchannel may include N PRB Physical Resource Blocks (PRBs). PRBIt can be one of 10, 12, 15, 20, 25, 50, 75 or 100. The resource pool can be configured periodically. For example, the resource pool can be configured with a periodicity of 10240 milliseconds (ms) in the time domain. Some of all time slots belonging to a period corresponding to a periodicity of 10240ms can be configured as a resource pool. According to the time division duplex (TDD) configuration, a time slot including a downlink (DL) symbol may not be configured as a resource pool. A time slot including a resource that can send a sidelink synchronization signal block (S-SSB) may not be configured as a resource pool. A time slot that can be configured as a resource pool can be defined by a bitmap. In other words, a bitmap can indicate a time slot that can be configured as a resource pool.

[0077] The SL channel can be used to send and receive traffic (e.g., data), management information and / or control information (e.g., control information related to scheduling) related to SL services. The SL channel may include a physical sidelink broadcast channel (PSBCH), a physical sidelink shared channel (PSSCH), a physical sidelink control channel (PSCCH) and / or a physical sidelink feedback channel (PSFCH). The SL signal may include a synchronization signal (e.g., a sidelink primary synchronization signal (S-PSS), a sidelink secondary synchronization signal (S-SSS)) and / or a reference signal (e.g., a demodulation reference signal (DMRS), a channel state information reference signal (CSI-RS), a phase tracking (PT)-RS, and a positioning reference signal (PRS)).

[0078] The PSSCH may be a channel for sending and receiving transport blocks (TBs), data, and / or traffic. The PSCCH may be a channel for sending and receiving control information. The PSFCH may be a channel for sending and receiving hybrid automatic repeat request (HARQ) feedback indicating the reception status of the PSSCH. The S-SSB may include at least one of the PSBCH, S-PSS, or S-SSS. The S-SSB may also include a DMRS. Synchronization between terminals may be performed using a synchronization signal (e.g., S-PSS and / or S-SSS).

[0079] Figure 7 is a conceptual diagram of a first exemplary embodiment showing a configuration of a resource pool, a SL signal, and a SL channel within a SL bandwidth part (BWP).

[0080] Reference Figure 7 , the resource pool may include one or more time slots, but does not include time slots that do not meet the configuration conditions of the resource pool and / or time slots that are not indicated by the bitmap. Time slots that are not continuous in the time domain can be interpreted as continuous within the resource pool. In other words, even when the time slots configured as the resource pool are not continuous, the indexes of the time slots within the resource pool can be continuous.

[0081] In the present disclosure, SL resources (e.g., SL transmission resources) may refer to resources within a resource pool. SL resources may refer to resources used to transmit SL signals and / or SL channels. In the present disclosure, signal sending may refer to sending SL signals and / or SL channels, and signal reception may refer to receiving SL signals and / or SL channels. "Signal" may be interpreted as "signal" or "signal+channel", and "channel" may be interpreted as "channel" or "channel+signal". "SL signal / channel" may be interpreted as "SL signal", "SL channel" or "SL signal+SL channel".

[0082] Figure 8 is a conceptual diagram illustrating a first exemplary embodiment of an SL resource.

[0083] See also Figure 8 , the basic transmission unit of the SL signal / channel in the time domain may be a time slot, and the basic transmission unit of the SL signal / channel in the frequency domain may be a subchannel. The transmission resources of the SL signal / channel may include one or more time slots and / or one or more subchannels. The transmission resources may include PSCCH and / or PSSCH. In addition, the transmission resources may include PSFCH. The time slots including PSFCH may be predefined (e.g., the positions of the time slots). The time slots including PSFCH may be referred to as PSFCH time slots. The configuration conditions of the PSFCH time slots in the licensed band may be different from the configuration conditions of the PSFCH time slots in the unlicensed band. The transmission operation of the HARQ feedback in the PSFCH time slots of the licensed band may be different from the transmission operation of the HARQ feedback in the PSFCH time slots of the unlicensed band. The configuration information of the SL channel actually sent in the transmission resource may be sent through signaling (e.g., RRC message, SCI). The configuration information of the SL channel may include frequency resource information (e.g., the position of the frequency resource area), time resource information (e.g., the position of the time resource area), etc.

[0084] The base station may send configuration information (e.g., transmission resource information) of the SL channel to the terminal. The terminal may receive the configuration information of the SL channel from the base station, and send the SL channel based on the configuration information (e.g., the transmission resource indicated by the configuration information). Alternatively, the terminal may select a resource by performing a resource sensing operation and / or a resource selection operation, and may send the SL channel in the selected resource. The selected resource may represent a transmission resource. The transmission resource may include one or more subchannels and one or more time slots.

[0085] The transmitting terminal may send an SCI including transmission resource information (e.g., scheduling information) of the PSSCH to the receiving terminal. The transmission resource information may be allocation information of subchannels and / or time slots of the PSSCH. The transmitting terminal may refer to a terminal that transmits the PSSCH (e.g., data). The receiving terminal may refer to a terminal that receives the PSSCH (e.g., data). The transmission resource information included in the SCI may indicate the transmission resources of the PSSCH in the time slot in which the SCI is transmitted. Alternatively, the transmission resource information included in the SCI may indicate the transmission resources of the PSSCH in a time slot other than the time slot in which the SCI is transmitted.

[0086] In SL-U communication, a listen-before-talk (LBT) operation can be performed to coexist with other communication nodes (e.g., communication devices). The actual transmission resources can be determined based on the result of the LBT operation. The terminal can perform an LBT operation, and when the LBT operation is successful, the terminal can use the channel for a specific period of time (e.g., channel occupancy time (COT)). For example, when the LBT operation of the terminal is successful, the COT can be initiated by the terminal, and the terminal can perform communication (e.g., SL-U communication) during the COT. Depending on specific conditions, other terminals (e.g., terminals that did not initiate COT) can perform communication (e.g., SL-U communication) during the COT. In other words, the COT can be shared with other terminals, and in this case, other terminals can perform communication within the shared COT.

[0087] The transmission unit (e.g., symbol configuration) within the COT may vary. Configuration information of the transmission unit within the COT may be sent via signaling (e.g., SCI). A symbol may refer to an OFDM symbol. Figure 8 In an exemplary embodiment of the present invention, the PSCCH and the PSSCH may be configured together in the transmission resource. The PSCCH may be configured starting from the PRB with the lowest index in the subchannel with the lowest index among the subchannels configured for the PSSCH transmission.

[0088] The operations, processes, control information and / or configuration information for working channel occupation in SL-U communication will be described. A working channel may refer to a frequency resource having a bandwidth of a predefined size. Resources (e.g., time resources, frequency resources, carriers, subcarriers, subchannels) of an unlicensed band may be occupied by communication nodes belonging to a network other than a cellular network (e.g., a 4G network, a 5G network) (e.g., a wireless local area network (WLAN)). Resources in an unlicensed band may be occupied by signals / channels sent and received between a base station and a terminal belonging to a cellular network. Resources in an unlicensed band may be occupied by signals / channels sent and received between terminals belonging to a cellular network.

[0089] In the present disclosure, a communication node (e.g., a base station, a terminal) that sends a signal / channel may be represented as a sending node, and a communication node (e.g., a base station, a terminal) that receives a signal / channel may be represented as a receiving node. In an unlicensed band, a communication node may share a working channel. An LBT operation may be performed to minimize interference between communication nodes. An LBT operation may include an operation of identifying whether a working channel is occupied by another signal before sending a signal / channel. When supporting an LBT operation, a communication node (e.g., a sending node) may perform a random backoff procedure.

[0090] When the LBT operation is successful, the communication node may occupy the working channel. The occupation of the working channel may be referred to as channel occupation (CO). The terminal may ensure the CO by performing the LBT operation. The configuration of the CO may vary according to the type of LBT operation performed by the terminal. For example, the maximum length of the CO may vary according to the type of LBT operation performed by the terminal. The type of LBT operation performed by the terminal may vary according to the priority class of the data to be sent by the terminal in the CO.

[0091] The terminal may perform an LBT operation using different parameters (e.g., different LBT parameters) to obtain a CO corresponding to each priority class. When performing an LBT operation according to a priority class, the parameter determining the execution time of the LBT operation may vary. In an LBT operation involving a random backoff procedure, the minimum and / or maximum size of a contention window (CW) may be set differently for each priority class. The terminal may select a random backoff counter within a CW and perform a random backoff procedure based on the selected random backoff counter.

[0092] The fixed time period for performing the LBT operation may be determined based on the type of the LBT operation and / or the LBT parameters. The length of the fixed time period may be 16 μs or 25 μs. A communication node (e.g., a sending node) performing the LBT operation may send information about the CO obtained through the LBT operation (e.g., CO configuration information) to another communication node (e.g., a receiving node). The CO configuration information may include LBT parameters for the LBT operation of the terminal. The LBT parameters may include information on priority categories. The CO configuration information may include at least one of information on the start time of the CO, information on the length of the CO, and information on the end time of the CO. In the present disclosure, "time point" may be interpreted as "time".

[0093] The receiving node may receive CO configuration information from the transmitting node, and identify LBT parameters for obtaining the CO based on the CO configuration information. The receiving node may identify the priority category of the CO initiated by the transmitting node based on the LBT parameters. The receiving node may identify the CO initiated by the transmitting node based on the CO configuration information, and perform communication within the CO. For example, the receiving node may send and receive signals / channels within the CO.

[0094] The sending node can configure the channel occupation time (COT). The configuration of COT means the initiation of COT. COT can be configured within time resources and / or frequency resources. The configuration information of COT (i.e., COT configuration information) can indicate the time resources and / or frequency resources in which COT is configured. COT can be referred to as CO or channel occupation resource (COR). In an unlicensed band, resources can be shared by multiple communication nodes. Communication nodes can use non-continuous resources (e.g., non-continuous time resources and / or non-continuous frequency resources). In this case, signal / channel transmission in the unlicensed band can be performed in a non-continuous burst scheme. The burst scheme can refer to a transmission performed in a transmission resource including one or more time slots.

[0095] The signal / channel may be transmitted in a time shorter than a time slot. The time shorter than a time slot may include continuous symbols. The time shorter than a time slot may be a micro-slot. Continuous transmission resources may be configured within the COT. The transmitting node may transmit an initial signal and / or a burst signal (e.g., PSSCH, PSFCH, PSCCH, reference signal) within the COT. The initial signal may be a signal obtained by copying the signal of the first symbol of the SL transmission. Alternatively, the initial signal may be a signal including a cyclic prefix (CP).

[0096] SL resources may be allocated based on mode 1 or mode 2. Mode 1 may be referred to as resource allocation (RA)-mode 1, and mode 2 may be referred to as RA-mode 2. When RA-mode 1 is used, the base station may send a DCI (e.g., SL grant) including SL resource allocation information to the terminal, and the terminal may perform SL communication using the SL resources allocated by the base station. When RA-mode 2 is used, the terminal may perform a resource sensing operation within a resource pool, perform a resource selection operation on the resources sensed by the resource sensing operation, and perform SL communication using the resources selected by the resource selection operation.

[0097] In RA-mode 1, when transmission data occurs, the terminal can send a scheduling request (SR) for the transmission data to the base station, and the base station can allocate resources (e.g., SL resources) to the terminal based on the SR by using a dynamic grant (DG). In RA-mode 1, the base station can allocate periodic resources to the terminal in a semi-static scheme, and the terminal can perform SL communication using the periodic resources allocated by the base station.

[0098] The periodic resources allocated in a semi-static scheme may be configured grant (CG) resources. The base station may send allocation information of CG resources to the terminal. The allocation information of CG resources may include at least one of the location information of CG resources, the time resource information of CG resources, the frequency resource information of CG resources, or the periodic information of CG resources. According to the release process or deactivation process of CG resources, the CG scheme may be divided into CG-type 1 and CG-type 2. In CG-type 1, CG resources may be released through RRC signaling. In CG-type 2, CG resources may be deactivated through DCI signaling.

[0099] In RA-mode 2, the terminal may perform a resource sensing operation during a sensing window, select a resource that satisfies a predefined condition from among the resources sensed by the resource sensing operation, and send an SL signal / channel using the selected resource. The resource sensing / selection method according to RA-mode 2 may be divided into a dynamic scheme and a semi-static scheme. According to the semi-static scheme, specific time resources may be occupied. The dynamic scheme and the semi-static scheme may be distinguished according to the time when new resources are selected. When using the dynamic scheme, the terminal may select resources for TB transmission each time it wants to send a new TB. TB transmission may include 'new TB transmission (e.g., initial TB transmission)' and / or 'TB retransmission'. One or more resources (e.g., one or more transmission resources) may be used, occupied and / or reserved for TB transmission.

[0100] When a semi-static scheme is used, the counter value of the TB transmission can be 0 during a specific time (e.g., a resource reservation interval (RRI)). Alternatively, when a semi-static scheme is used, a new transmission resource can be selected under specific conditions. The counter value of the TB transmission can be randomly selected. When a TB transmission is completed (e.g., a new TB transmission and / or a TB retransmission), the selected counter value can be reduced by 1. When a semi-static scheme is used, the terminal can continue to occupy the selected resource within a specific time. In other words, the terminal can continue to use the selected resource within a specific time. The specific time can represent the time that the terminal can exclusively occupy. The specific time can be defined as the RRI.

[0101] The base station may signal an RRI list to the terminal. The RRI list may include up to 16 RRIs (e.g., up to 16 RRI values). The signaling may be at least one of system information (SI) signaling, RRC signaling, MAC CE signaling, or PHY signaling. The terminal may receive an RRI list from the base station, select an RRI from the RRIs belonging to the RRI list, and use the selected resources (e.g., the selected transmission resources) during the selected RRI. The terminal may occupy continuous resources during the RRI. The continuous resources may be configured in a logical resource area of ​​the SL.

[0102] The first terminal may send an SCI including information of the selected RRI to the second terminal. The second terminal may receive the SCI from the first terminal and identify the RRI selected by the first terminal based on the information element included in the SCI. The second terminal may not select a resource (e.g., a resource selected by the first terminal) during the RRI indicated by the SCI. Information about the resource selected by the first terminal may be included in the SCI.

[0103] When RA-mode 2 is used, a resource sensing window and / or a resource selection window may be configured. The resource sensing window may be referred to as a sensing window (SSW), and a resource sensing operation may be performed within the SSW. The resource selection window may be referred to as a selection window (SLW), and a resource selection operation may be performed within the SLW. The resources used during the RRI (e.g., RRI value) indicated by the SCI may be identified by the resource sensing operation performed in the SSW.

[0104] Sidelink control information (SCI) may include scheduling information (e.g., scheduling information of a TB) and / or parameters applicable to TB transmission. The parameters applied to TB transmission may be used for demodulation / decoding of the TB at a receiving terminal. SCI may be divided into first-level SCI (1 st SCI) and second level SCI (2 nd The first-level SCI may be sent on the PSCCH, and the second-level SCI may be sent on the PSSCH. The second-level SCI may be associated with the first-level SCI. The first-level SCI may include scheduling information for initial TB transmission and / or scheduling information for TB retransmission. The second-level SCI may include at least one of information about a PSSCH transmitting terminal, information about a PSSCH receiving terminal, HARQ feedback information, or retransmission information.

[0105] Y transmission resources including a time slot for sending a first-level SCI may be configured. Y may be a natural number. For example, Y may be 2 or 3. The first transmission resource of the Y transmission resources may be configured in a time slot for sending a first-level SCI. In other words, the first transmission resource of the Y transmission resources may be a time slot for sending a first-level SCI. The time slot for configuring (Y-1) transmission resources may be defined by a time slot offset. The time slot offset may be a positive integer. The maximum value of the time slot offset may be 32.

[0106] The scheduled first transmission resource may include N subchannel sub-channels. subchannel The first subchannel (eg, the starting subchannel) of the N subchannels may be the subchannel through which the first-level SCI is sent. subchannel Can be a natural number. N subchannel The first-level SCI may include frequency resource information of the second transmission resource (e.g., information of the N subchannels, information about the starting subchannel in the N subchannels) and / or frequency resource information of the third transmission resource (e.g., information of the N subchannels, information about the starting subchannel in the N subchannels). The number N of subchannels of the second transmission resource may be equal to or less than the number N of subchannels of the first transmission resource. subchannel The number N of subchannels of the third transmission resource may be the same as the number N of subchannels of the first transmission resource. subchannel The first transmission resource among the Y transmission resources may be a transmission resource for a first TB transmission (eg, an initial TB transmission). The remaining (Y-1) transmission resources may be transmission resources for TB retransmission.

[0107] The first level SCI may include one or more information elements defined in Table 1 below.

[0108] [Table 1]

[0109]

[0110]

[0111] The second level 2 SCI may include one or more information elements. The information elements included in the second level SCI may vary according to the format of the second level SCI. The second level SCI may include one or more information elements defined in Table 2 below.

[0112] [Table 2]

[0113] Information Elements HARQ process number New Data Indicator (NDI) Redundancy Version (RV) Source ID Target ID HARQ feedback enable / disable indicator Broadcast Type Indicator Other information elements

[0114] PSFCH can be periodically configured within the SL resource area. The time slot in which PSFCH is configured can be called PSFCH time slot. PSFCH time slot can be configured according to periodicity. The periodicity of PSFCH time slot can be called PSFCH transmission timing resource (TPR). PSFCH TPR can be defined on a time slot basis within the resource pool. PSFCH TPR can be 1 time slot, 2 time slots or 4 time slots. The PRBs in which PSFCH can be sent in the frequency domain can be indicated by a bitmap. The PRBs that can be used for PSFCH transmission can be all PRBs or some PRBs. One PSFCH can be sent in one PRB. Alternatively, in an unlicensed band, one PSFCH can be sent in one or more PRBs.

[0115] The PRB for transmitting the PSFCH may be determined based on the position of the time slot in which the PSSCH associated with the PSFCH is received. The difference (e.g., time slot offset, interval) between the time slot in which the PSSCH is received and the time slot in which the PSFCH is to be transmitted may be considered. For example, the PSFCH may be transmitted in the PSFCH time slot that first occurs after K time slots from the time slot n in which the PSSCH is received. The PRB for transmitting the PSFCH may be determined based on the function f(P PSFCH ,n,K,k subch ) is used to define the PRB index (e.g., the index of the PRB in which the PSFCH is transmitted). PSFCH may be the periodicity of the PSFCH. n may be the index of the time slot in which the PSSCH is received. K may be the time slot offset used to determine the PSFCH time slot in which the PSFCH is transmitted. k subch It can be the index of the subchannel where PSCCH is configured.

[0116] In the function f(.) for determining the PRB index, at least one of different codes q, an identifier (ID) of a transmitting terminal, or an ID of a receiving terminal transmitting the PSFCH may be considered. The code q may be defined by a cyclic shift or a cyclic shift pair. The cyclic shift may be associated with different Zadoff-Chu sequences. A cyclic shift pair may refer to a pair of different sequences according to an acknowledgement (ACK) or a negative ACK (NACK).

[0117] A set of PRBs for transmitting the PSFCH may be determined based on the time slot #n in which the PSSCH is transmitted and / or the index of the subchannel in which the PSSCH is transmitted. The code conveyed by the PSFCH and the PRBs in the PRB set may be determined based on a function that considers at least one of the ID of the transmitting terminal or the ID of the receiving terminal that transmits the PSFCH.

[0118] The first terminal may use the SL transmission method to send a signal / channel to the second terminal. The second terminal may use the SL reception method to receive a signal / channel from the first terminal. The first terminal may send a TB on the PSSCH. The first terminal may send control information on the PSCCH. The control information may include information elements required for demodulation and / or decoding of the TB sent on the PSSCH. The first terminal may send control information on the PSCCH. The second terminal may receive control information from the first terminal and identify resource usage information based on the control information. The second terminal may receive the PSSCH (e.g., TB) and send HARQ-ACK feedback (e.g., HARQ feedback, HARQ response) for the PSSCH to the first terminal. HARQ-ACK feedback for the PSSCH may be sent on the PSFCH.

[0119] In the present disclosure, a terminal that performs PSCCH transmission, PSSCH transmission and / or PSFCH reception may be referred to as a transmitting terminal or a first terminal, and a terminal that performs PSCCH reception, PSSCH reception and / or PSFCH transmission may be referred to as a receiving terminal or a second terminal.

[0120] In SL-U communication, the terminal may perform an LBT operation before sending a signal / channel. If the result of the LBT operation indicates an idle state, the terminal may send a signal / channel. If the result of the LBT operation indicates a busy state, the terminal may not send a signal / channel. "The result of the LBT operation indicates an idle state" may mean "the LBT operation is successful". "The result of the LBT operation indicates a busy state" may mean "the LBT operation fails". Based on the comparison result between the energy detection level and the predefined threshold, the result of the LBT operation may be determined to indicate an idle state or a busy state.

[0121] LBT operation can be divided into type 1 LBT operation and type 2 LBT operation. In type 1 LBT operation, the channel sensing time may be variable. The channel sensing time may be changed by a random variable. Type 1 LBT operation may refer to an LBT operation involving a random backoff procedure. In type 2 LBT operation, the channel sensing time may be fixed. The channel sensing time may be mμs. m may be a natural number.

[0122] When performing type 1 LBT operation, the terminal may randomly select a value N according to a uniform probability within the CW. The value N may be an integer. The value N may be a random backoff counter. The terminal may perform a channel sensing operation within a predefined sensing period (e.g., a sensing slot period). The channel sensing operation may represent an energy detection operation of time and / or frequency resources. If the result of the channel sensing operation within one sensing period indicates an idle state, the terminal may reduce the value N selected within the CW by 1. If the result of the channel sensing operation within one sensing period indicates a busy state, the terminal may perform a channel sensing operation in addition. If the result of the channel sensing operation within N sensing periods indicates an idle state, the terminal may send a signal / channel.

[0123] In type 1 LBT operation, the CW (e.g., CW size) can be changed. The CW of the transmitting terminal can be changed based on the reception status (e.g., ACK and / or NACK) of the signal / channel sent by the transmitting terminal. The receiving terminal can send HARQ-ACK feedback for the signal / channel of the transmitting terminal to the transmitting terminal. The transmitting terminal can identify the reception status at the receiving terminal based on the HARQ-ACK feedback received from the receiving terminal. When the HARQ-ACK feedback received from the receiving terminal indicates ACK, the transmitting terminal can reduce the CW (e.g., CW size). When the HARQ-ACK feedback received from the receiving terminal indicates NACK, the transmitting terminal can increase the CW.

[0124] CWs (eg, CW sizes) may be managed individually according to channel access priority classes (CAPCs). CAPCs may be associated with the quality of service (QoS) of data that a terminal wishes to transmit. Different CWs may be applied to each CAPC.

[0125] The transmitting terminal may transmit data for CAPC#N and may adjust the CW (e.g., CW size) based on the HARQ-ACK feedback for the data. In this case, only the CW of CAPC#N may be changed without changing the CW of other CAPCs. In other words, the CW of other CAPCs may remain unchanged. The change of CW may mean a change of CW size.

[0126] Alternatively, the transmitting terminal may transmit data of CAPC#N and may adjust the CW (e.g., CW size) based on the HARQ-ACK feedback for the data. In this case, the CW of all CAPCs may be changed. When it is determined to increase the CW of CAPC#N based on the HARQ-ACK feedback for the data, the transmitting terminal may increase the CW of all CAPCs. When it is determined to reduce or initialize the CW of CAPC#N based on the HARQ-ACK feedback for the data, the transmitting terminal may reduce or initialize the CW of all CAPCs.

[0127] An initial value of CW (e.g., initial CW) may be predefined. A minimum value of CW (e.g., minimum CW) and / or a maximum value of CW (e.g., maximum CW) may be predefined. The initial CW may be equal to the minimum CW. The initial CW may be referred to as CW. initial The minimum CW can be called CW min The maximum CW can be called CW max .CW initial , CW min and CW max You can set it differently for each CAPC. max And based on the HARQ-ACK feedback for data, the CW needs to be increased max When the terminal can maintain CW max In other words, the terminal may not increase CW max .

[0128] CW can be defined differently for each CAPC initial Based on the HARQ-ACK feedback for the signal / channel (e.g., data), the CW can be set to CW initial Based on the HARQ-ACK feedback for the signal / channel (e.g., data), the CW may be increased by a factor of 2. In other words, the CW may be doubled. Based on the HARQ-ACK feedback for the signal / channel (e.g., data), the CW may remain unchanged. The terminal may use the changed CW or the maintained CW for the next transmission in the LBT operation.

[0129] The transmitting terminal can send PSSCH to the receiving terminal based on the unicast scheme. When using the unicast scheme, one transmitting terminal can send a signal / channel to one receiving terminal. The receiving terminal can receive PSSCH from the transmitting terminal. In other words, the receiving terminal can receive the TB of the transmitting terminal on the PSSCH.

[0130] The transmitting terminal may transmit the first level SCI including the information elements required for demodulating / decoding the TB and / or the second level SCI. The receiving terminal may receive the first level SCI from the transmitting terminal and identify the information elements included in the first level SCI. In other words, the receiving terminal may identify the information elements required for demodulating / decoding the TB and / or the second level SCI by receiving the first level SCI of the transmitting terminal.

[0131] The receiving terminal may receive the PSSCH from the transmitting terminal and send the reception result of the PSSCH (e.g., HARQ-ACK feedback) to the transmitting terminal on the PSFCH. When it is indicated that HARQ-ACK feedback is not to be sent (e.g., when a HARQ feedback disable indicator is received), the receiving terminal may not send HARQ-ACK feedback for the PSSCH to the transmitting terminal.

[0132] The receiving terminal may use the PSFCH to send HARQ-ACK feedback to the transmitting terminal. When the PSSCH is successfully received (e.g., when the demodulation / decoding operation for the PSSCH is completed normally), the receiving terminal may send HARQ-ACK feedback indicating ACK. When the reception of the PSSCH fails (e.g., when the demodulation / decoding operation for the PSSCH fails), the receiving terminal may send HARQ-ACK feedback indicating NACK. Whether the reception of the PSSCH is successful can be determined based on whether the cyclic redundancy check (CRC) code is decoded normally.

[0133] When the first level SCI is received from the transmitting terminal and the second level SCI is not received from the transmitting terminal, the receiving terminal may send HARQ-ACK feedback indicating NACK to the transmitting terminal. When the transmitting terminal sends PSSCH to the receiving terminal but does not receive HARQ-ACK feedback for PSSCH from the receiving terminal, the transmitting terminal may consider that the receiving terminal has sent NACK.

[0134] When receiving ACK from the receiving terminal, the transmitting terminal can change CW to CW initial or CW min . When a NACK is received from the receiving terminal, the transmitting terminal may increase the CW. When an ACK is not received from the receiving terminal, the transmitting terminal may increase the CW. In cases other than the case where an ACK is received from the receiving terminal, the transmitting terminal may increase the CW. When it is considered that a NACK has been received from the receiving terminal, the transmitting terminal may increase the CW. When the transmitting terminal instructs the receiving terminal not to send HARQ-ACK feedback (for example, when the transmitting terminal sends an SCI including a HARQ feedback disable indicator to the receiving terminal), the transmitting terminal may maintain the CW regardless of the PSSCH reception state at the receiving terminal. In other words, when HARQ feedback is disabled, the transmitting terminal does not change the CW regardless of the reception state of the PSSCH at the receiving terminal.

[0135] Fig. 9 is a sequence diagram showing a first exemplary embodiment of a CW size adjustment method.

[0136] Reference Fig. 9, the transmitting terminal may perform a channel access procedure (S910) for PSSCH transmission (e.g., data transmission, unicast SL transmission, multicast SL transmission). The channel access procedure may include an LBT operation. When the channel access procedure is successful, the transmitting terminal may send PSSCH to the receiving terminal (S920). The receiving terminal may receive PSSCH from the transmitting terminal and perform a demodulation / decoding operation on PSSCH. The receiving terminal may generate HARQ-ACK feedback based on the result of the demodulation / decoding operation on PSSCH (S930). HARQ-ACK feedback may indicate ACK or NACK. The receiving terminal may send HARQ-ACK feedback to the transmitting terminal (S940). HARQ-ACK feedback may be sent on PSFCH. The transmitting terminal may receive HARQ-ACK feedback from the receiving terminal. The transmitting terminal may adjust CW (e.g., CW size) based on HARQ-ACK feedback (S950). For example, the transmitting terminal may increase or decrease CW. Alternatively, the transmitting terminal may maintain CW.

[0137] The transmitting terminal may send PSSCH to one or more receiving terminals (e.g., receiving terminals belonging to a group) based on a multicast scheme. The transmitting terminal may send PSSCH in a multicast scheme within a COT initiated or configured by the transmitting terminal. PSSCH transmission based on a multicast scheme may be a multicast SL transmission. Multicast SL transmission may be sent within a reference duration within a COT (e.g., the latest COT) initiated by the transmitting terminal. The transmitting terminal may receive HARQ-ACK feedback from one or more receiving terminals on PSFCH. The transmitting terminal may receive HARQ-ACK feedback for PSSCH sent in the same time slot from one or more receiving terminals.

[0138] The transmitting terminal may adjust the CW based on the HARQ-ACK feedback of the multicast SL transmission. When one or more of the HARQ-ACK feedbacks indicate ACK, the transmitting terminal may change the CW (e.g., the current CW) to the initial CW (e.g., CW initial ) or minimum CW (e.g., CW min ). When at least one of the HARQ-ACK feedbacks does not indicate ACK, the transmitting terminal may increase the CW.

[0139] Alternatively, the transmitting terminal may adjust the CW based on the ACK ratio and / or the NACK ratio.

[0140] [Formula 1]

[0141]

[0142] A may represent the number of ACKs received by the transmitting terminal or (the number of ACKs received by the transmitting terminal + the number of HARQ-ACK feedbacks regarded as ACKs in the HARQ-ACK feedbacks not received by the transmitting terminal). When a NACK-only feedback scheme is used, A may represent the number of HARQ-ACK feedbacks not received by the transmitting terminal. In this case, the transmitting terminal may regard the HARQ-ACK feedbacks not received as ACKs. F may represent the total number of HARQ-ACK feedbacks received by the transmitting terminal, the estimated number of HARQ-ACK feedbacks for multicast SL transmissions, the number of receiving terminals participating in multicast SL communication, (the number of terminals participating in multicast SL communication - 1), the number of receiving terminals expected to send HARQ-ACK feedbacks, or the number of HARQ-ACKs expected to be received from receiving terminals participating in multicast SL communication.

[0143] [Formula 2]

[0144]

[0145] N may represent the number of NACKs received by the transmitting terminal or (the number of NACKs received by the transmitting terminal + the number of HARQ-ACK feedbacks that are regarded as NACKs in the HARQ-ACK feedbacks not received by the transmitting terminal). F may represent the total number of HARQ-ACK feedbacks received by the transmitting terminal, the estimated number of HARQ-ACK feedbacks for multicast SL transmission, the number of receiving terminals participating in multicast SL communication, (the number of terminals participating in multicast SL communication - 1), the number of receiving terminals expected to send HARQ-ACK feedback, or the number of HARQ-ACKs expected to be received from receiving terminals participating in multicast SL communication.

[0146] The transmitting terminal may calculate the ACK ratio based on Formula 1. If the ACK ratio is greater than or equal to the ratio threshold, the transmitting terminal may change the CW (eg, current CW) to the initial CW (eg, CW initial ) or minimum CW (e.g., CW min ). Alternatively, if the ACK ratio is equal to or greater than the ratio threshold, the transmitting terminal may reduce the CW. If the ACK ratio is less than the ratio threshold, the transmitting terminal may increase the CW. The ratio threshold may be referred to by other terms (e.g., a specific threshold, a first threshold).

[0147] The transmitting terminal may calculate the NACK ratio based on Equation 2. If the NACK ratio is less than the ratio threshold, the transmitting terminal may change the CW to the initial CW (eg, CW initial ) or minimum CW (e.g., CW min). Alternatively, if the NACK ratio is less than the ratio threshold, the transmitting terminal may reduce the CW. If the NACK ratio is equal to or greater than the ratio threshold, the transmitting terminal may increase the CW.

[0148] The ratio threshold may be configured to the terminal by signaling. For example, the base station may send an RRC message including the ratio threshold to the terminal. When the ratio threshold is configured to the terminal, the transmitting terminal may adjust the CW based on the comparison result between the ACK ratio and the ratio threshold or the comparison result between the NACK ratio and the ratio threshold. When the ratio threshold is not configured to the terminal, the transmitting terminal may adjust the CW regardless of the ACK ratio and / or the NACK ratio. In this case, when at least one ACK is received, the transmitting terminal may change the CW to the initial CW or the minimum CW. Alternatively, when at least one ACK is received, the transmitting terminal may reduce the CW. When at least one ACK is not received, the transmitting terminal may increase the CW.

[0149] The transmitting terminal may receive HARQ-ACK feedback for PSSCH (e.g., multicast SL transmission) from one or more receiving terminals on PSFCH in the same time slot. The transmitting terminal may adjust the CW based on the HARQ-ACK feedback for the multicast SL transmission within the reference duration within the COT most recently initiated by the transmitting terminal. Alternatively, the transmitting terminal may adjust the CW based on the HARQ-ACK feedback for the most recently transmitted PSSCH (e.g., most recently multicast SL transmission).

[0150] When HARQ-ACK feedback #N for the PSSCH sent in time slot #N and HARQ-ACK feedback #N+M for the PSSCH sent in time slot #N+M are received on the PSFCH in the same time slot, the transmitting terminal uses the HARQ-ACK feedback #N+M in the HARQ-ACK feedback to adjust the CW. Each of N and M can be a natural number. For the selection of HARQ-ACK feedback for CW adjustment, the CAPC of the PSSCH sent in time slot #N and the CAPC of the PSSCH sent in time slot #N+M can be ignored. In other words, CW adjustment can be performed regardless of the CAPC of the PSSCH sent in time slot #N and the CAPC of the PSSCH sent in time slot #N+M.

[0151] When the CAPC of the PSSCH sent in time slot #N is the same as the CAPC of the PSSCH sent in time slot #N+M, a CW adjustment operation can be performed. If the CAPC of the PSSCH sent in time slot #N is different from the CAPC of the PSSCH sent in time slot #N+M, CW adjustment can be performed on each CAPC based on the HARQ-ACK feedback for the PSSCH corresponding to each CAPC.

[0152] The transmitting terminal may receive one or more HARQ-ACK feedbacks for one or more PSSCHs from one or more receiving terminals on the PSFCH in the same time slot. One or more PSSCHs associated with one or more HARQ-ACK feedbacks received on the PSFCH in the same time slot may be continuous or discontinuous in the time domain. The transmitting terminal may change CW individually based on one or more HARQ-ACK feedbacks for one or more PSSCHs that are discontinuous in the time domain. The transmitting terminal may receive HARQ-ACK feedback #N for PSSCH #N sent in time slot #N and HARQ-ACK feedback #N+M for PSSCH #N+M sent in time slot #N+M on the PSFCH in the same time slot. In this case, the transmitting terminal may change CW using HARQ-ACK feedback #N. In addition, the transmitting terminal may change the CW based on the change of HARQ-ACK feedback #N by using HARQ-ACK feedback #N+M. Each of N and M may be a natural number.

[0153] The transmitting terminal may perform PSSCH transmission in consecutive time slots in the time domain. The transmitting terminal may receive HARQ-ACK feedback for PSSCH transmitted in consecutive time slots in the time domain on PSFCH within the same time slot. The transmitting terminal may change CW using HARQ-ACK feedback for the PSSCH transmitted first among the PSSCH transmitted in consecutive time slots in the time domain. For example, when PSSCH transmission is performed in time slot #N, time slot #N+1, ..., and time slot #N+M, and HARQ-ACK feedback for PSSCH transmission is received on PSFCH (e.g., PSFCH within the same time slot), the transmitting terminal may change CW using HARQ-ACK feedback for PSSCH transmitted in time slot #N.

[0154] The transmitting terminal may calculate an ACK ratio and / or a NACK ratio based on one or more HARQ-ACK feedbacks, and may adjust the CW based on the ACK ratio and / or the NACK ratio. The transmitting terminal may receive HARQ-ACK feedback for one or more PSSCH transmissions on the PSFCH within time slot #N. One or more PSSCH transmissions may be sent in the most recent COT (e.g., a reference duration within the most recent COT) initiated by the transmitting terminal. The transmitting terminal may calculate the ACK ratio based on the above formula 1. The transmitting terminal may calculate the NACK ratio based on the above formula 2.

[0155] When the ACK ratio is equal to or greater than the ratio threshold, the transmitting terminal may change the CW to the initial CW or the initial CW. Alternatively, when the ACK ratio is equal to or greater than the ratio threshold, the transmitting terminal may reduce the CW. When the ACK ratio is less than the ratio threshold, the transmitting terminal may increase the CW. When the NACK ratio is equal to or greater than the ratio threshold, the transmitting terminal may increase the CW. When the NACK ratio is less than the ratio threshold, the transmitting terminal may change the CW to the initial CW or the initial CW. Alternatively, when the NACK ratio is less than the ratio threshold, the transmitting terminal may reduce the CW.

[0156] When the CW is adjusted based on the HARQ-ACK feedback received on the PSFCH, the transmitting terminal may perform the next LBT operation (eg, a Type 1 LBT operation) using the adjusted CW.

[0157] When HARQ-ACK feedback of the receiving terminal is received on PSFCH, the transmitting terminal can adjust the CW based on the HARQ-ACK feedback after a predefined time from the reception time of the HARQ-ACK feedback, the transmission time of the PSSCH associated with the HARQ-ACK feedback, or the transmission time of the PSCCH associated with the PSSCH, and can use the adjusted CW to perform the next LBT operation. Alternatively, when the CW is adjusted based on the HARQ-ACK feedback received on PSFCH, the transmitting terminal can use the adjusted CW to perform the next LBT operation after a predefined time from the reception time of the HARQ-ACK feedback, the transmission time of the PSSCH associated with the HARQ-ACK feedback, the transmission time of the PSCCH associated with the PSSCH, or the generation time of the adjusted CW. The predefined time can be configured to the terminal through signaling. The predefined time can be set based on the time slot. When HARQ-ACK feedback is received on the PSFCH in time slot #N, the transmitting terminal can adjust the CW based on the HARQ-ACK feedback and perform LBT operation starting from time slot #N+M using the adjusted CW. Each of N and M can be a natural number.

[0158] The transmitting terminal can perform SL transmission to one or more receiving terminals. The transmitting terminal can send PSSCH to one or more receiving terminals based on a multicast scheme. In other words, the transmitting terminal can perform multicast SL transmission. In multicast SL transmission, one transmitting terminal can send a signal / channel to one or more receiving terminals. For multicast SL transmission, a communication system (e.g., a network node, a base station, a transmitting terminal) can assign an identifier (ID) for multicast SL transmission to one or more terminals (e.g., a transmitting terminal and / or a receiving terminal). The ID used for multicast SL transmission may be referred to as a multicast SL ID. The multicast SL ID may be delivered to the terminal via signaling (e.g., RRC signaling). The terminal may receive the multicast SL ID via signaling, and may receive a signal / channel associated with the multicast SL ID (e.g., a multicast signal / channel).

[0159] The transmitting terminal may generate a first-level SCI including information required to receive the second-level SCI and / or information required to demodulate / decode the TB, and transmit the first-level SCI on the PSCCH. The receiving terminal may receive the first-level SCI from the transmitting terminal and identify the information (e.g., information element) included in the first-level SCI. The transmitting terminal may transmit the second-level SCI and / or TB on the PSSCH. The receiving terminal may receive the second-level SCI and / or TB from the transmitting terminal on the PSSCH.

[0160] The second-level SCI may include information indicating whether to perform multicast SL transmission. The second-level SCI may indicate a transmission scheme for HARQ-ACK feedback for PSSCH transmission (e.g., data transmission). The transmission scheme for HARQ-ACK feedback may represent at least one of transmitting HARQ-ACK feedback (e.g., enabling HARQ-ACK feedback), not transmitting HARQ-ACK feedback (e.g., disabling HARQ-ACK feedback), ACK / NACK transmission, or only NACK transmission. In the ACK / NACK transmission scheme, ACK or NACK may be sent. In the NACK-only transmission scheme, only NACK may be sent. In other words, in the NACK-only transmission scheme, ACK may not be sent even if ACK occurs. The receiving terminal may receive the second-level SCI and identify whether to perform multicast SL transmission based on the information included in the second-level SCI. In addition, the receiving terminal may identify the transmission scheme for HARQ-ACK feedback based on the information included in the second-level SCI.

[0161] The receiving terminal may receive a multicast PSSCH (e.g., a multicast SL transmission) from the transmitting terminal. If the destination ID included in the second-level SCI is set to an ID for multicast SL transmission, the receiving terminal may determine the PSSCH associated with the second-level SCI as a multicast PSSCH. Alternatively, if the broadcast type indicator included in the second-level SCI indicates multicast transmission, the receiving terminal may determine the PSSCH associated with the second-level SCI as a multicast PSSCH.

[0162] The receiving terminal may receive the PSSCH from the transmitting terminal and send the reception result of the PSSCH (e.g., HARQ-ACK feedback) to the transmitting terminal on the PSFCH. If the transmitting terminal instructs the receiving terminal not to send HARQ-ACK feedback (e.g., disabling HARQ-ACK feedback), the receiving terminal may not send HARQ-ACK feedback for the PSSCH to the transmitting terminal.

[0163] The HARQ-ACK feedback scheme can be divided into HARQ-ACK feedback scheme 1 and HARQ-ACK feedback scheme 2. In HARQ-ACK feedback scheme 1, when the PSSCH is successfully received, the receiving terminal can send ACK, and when the PSSCH reception fails, the receiving terminal can send NACK. HARQ-ACK feedback scheme 1 can be an ACK / NACK transmission scheme. Whether the PSSCH is successfully received can be determined based on the demodulation / decoding result of the TB. Whether the PSSCH is successfully received can be determined based on the CRC check result. In HARQ-ACK feedback scheme 1, the transmitting terminal can adjust the CW based on at least one of the number of ACKs, the ACK ratio, the number of NACKs, or the NACK ratio.

[0164] In HARQ-ACK feedback scheme 2, when PSSCH is successfully received, the receiving terminal may not send ACK, and when PSSCH reception fails, the receiving terminal may send NACK (e.g., HARQ-ACK feedback). HARQ-ACK feedback scheme 2 may be a NACK-only transmission scheme. In HARQ-ACK feedback scheme 2, the transmitting terminal may adjust the CW based on at least one of the number of NACKs or the NACK ratio. HARQ-ACK feedback scheme 1 or HARQ-ACK feedback scheme 2 may be applied to multicast SL transmission.

[0165] The HARQ-ACK feedback scheme may be configured by signaling (e.g., RRC signaling). The base station may send a signaling message including information indicating the HARQ-ACK feedback scheme to the terminal. The terminal may receive a signaling message from the base station and identify the HARQ-ACK feedback scheme based on the information included in the signaling message. If a signaling message indicating the HARQ-ACK feedback scheme is not received, the terminal may use a default HARQ-ACK feedback scheme. The default HARQ-ACK feedback scheme may be HARQ-ACK feedback scheme 1 or HARQ-ACK feedback scheme 2.

[0166] The HARQ-ACK feedback scheme may be indicated by control information (e.g., SCI, PHY signaling). The transmitting terminal may send control information including information indicating the HARQ-ACK feedback scheme to the receiving terminal. The control information may be sent on the PSCCH or the PSSCH. The control information may be sent via the first-level SCI and / or the second-level SCI. The receiving terminal may receive control information from the transmitting terminal and identify the HARQ-ACK feedback scheme based on the information included in the control information. If control information indicating the HARQ-ACK feedback scheme is not received, the receiving terminal may use the default HARQ-ACK feedback scheme. The default HARQ-ACK feedback scheme may be HARQ-ACK feedback scheme 1 or HARQ-ACK feedback scheme 2.

[0167] The transmitting terminal may adjust the CW based on the HARQ-ACK feedback for the multicast SL transmission. The HARQ-ACK feedback scheme for the multicast SL transmission may be HARQ-ACK feedback scheme 1 or HARQ-ACK feedback scheme 2.

[0168] The transmitting terminal may perform multicast SL transmission using PSSCH. The receiving terminal may receive multicast SL transmission from the transmitting terminal. The receiving terminal receiving the multicast SL transmission may be a terminal participating in the multicast SL communication. The receiving terminal may send ACK or NACK to the transmitting terminal based on the demodulation / decoding result for PSSCH (e.g., multicast SL transmission). The receiving terminal may send HARQ-ACK feedback (e.g., ACK or NACK) to the transmitting terminal using PSFCH.

[0169] The transmitting terminal may receive HARQ-ACK feedback from the receiving terminal and may adjust the CW based on the HARQ-ACK feedback. For example, the transmitting terminal may adjust the CW based on the ACK ratio or NACK ratio for multicast SL transmission. The transmitting terminal may determine the ACK ratio based on the above formula 1. The transmitting terminal may determine the NACK ratio based on the above formula 2. The transmitting terminal may adjust the CW based on the ACK ratio. If the ACK ratio is equal to or greater than the ratio threshold, the transmitting terminal may change the CW (e.g., the current CW) to the initial CW or the minimum CW. Alternatively, if the ACK ratio is equal to or greater than the ratio threshold, the transmitting terminal may reduce the CW. If the ACK ratio is less than the ratio threshold, the transmitting terminal may increase the CW.

[0170] Information about the ACK ratio (or NACK ratio) and / or the ratio threshold may be transmitted to the terminal via signaling. The signaling may be at least one of SI signaling, RRC signaling, MAC CE signaling, or PHY signaling. The terminal may determine the ratio threshold for CW adjustment based on the information about the ACK ratio indicated by the signaling. In other words, when the ratio threshold is not explicitly indicated, the terminal may determine the ratio threshold for CW adjustment based on the information about the ACK ratio indicated by the signaling.

[0171] When the information about the ACK ratio is not indicated by the signaling, the terminal may use a default threshold to adjust the CW. The default threshold may be 0. If the default threshold is used, the terminal may change the CW to the initial CW or the minimum CW if at least one ACK is received. Alternatively, the terminal may reduce the CW if at least one ACK is received. If the default threshold is used, the terminal may increase the CW if at least one ACK is not received.

[0172] The transmitting terminal may adjust the CW based on the ratio of the ACK or NACK for PSSCH (e.g., multicast SL transmission) to the total number of HARQ-ACK feedbacks. If the ACK ratio is equal to or greater than a specific predefined threshold, the transmitting terminal may change the CW to the initial CW or the minimum CW. Alternatively, if the ACK ratio is equal to or greater than a specific predefined threshold, the transmitting terminal may reduce the CW. If the ACK ratio is less than a specific predefined threshold, the transmitting terminal may increase the CW. If the NACK ratio is equal to or greater than a specific predefined threshold, the transmitting terminal may increase the CW. If the NACK ratio is less than a specific predefined threshold, the transmitting terminal may change the CW to the initial CW or the minimum CW. Alternatively, if the NACK ratio is less than a specific predefined threshold, the transmitting terminal may reduce the CW.

[0173] When one or more ACKs for PSSCH (e.g., multicast SL transmission) are received, the transmitting terminal may change the CW to the initial CW or the minimum CW. Alternatively, when one or more ACKs for PSSCH (e.g., multicast SL transmission) are received, the transmitting terminal may reduce the CW. When one or more ACKs for PSSCH (e.g., multicast SL transmission) are not received, the transmitting terminal may increase the CW. When one or more NACKs for PSSCH (e.g., multicast SL transmission) are received, the transmitting terminal may increase the CW.

[0174] When the transmitting terminal instructs the receiving terminal not to send HARQ-ACK feedback (eg, disables HARQ-ACK feedback), the transmitting terminal may maintain the CW (eg, the current CW) regardless of the HARQ-ACK feedback for the PSSCH.

[0175] The transmitting terminal may perform multicast SL transmission using PSSCH. The receiving terminal may receive multicast SL transmission from the transmitting terminal. When HARQ-ACK feedback scheme 2 (e.g., NACK-only transmission scheme) is used, the receiving terminal may send NACK to the transmitting terminal based on the demodulation / decoding result of PSSCH. The receiving terminal may send NACK to the transmitting terminal using PSFCH. Alternatively, the receiving terminal may not send HARQ-ACK feedback (e.g., ACK) to the transmitting terminal based on the demodulation / decoding result of PSSCH.

[0176] The transmitting terminal may adjust the CW based on HARQ-ACK feedback for PSSCH (e.g., multicast SL transmission). For example, the transmitting terminal may adjust the CW based on the ratio between the number of receiving terminals receiving PSSCH and the received NACK. The transmitting terminal may calculate the NACK ratio based on equation 2 described above.

[0177] If the NACK ratio is greater than or equal to a specific predefined threshold, the transmitting terminal may increase the CW. If the NACK ratio is less than a specific predefined threshold, the transmitting terminal may change the CW to the initial CW or the minimum CW. Alternatively, if the NACK ratio is less than a specific predefined threshold, the transmitting terminal may reduce the CW.

[0178] If even one NACK for PSSCH is not received, the transmitting terminal may change the CW to the initial CW or the minimum CW. Alternatively, if even one NACK for PSSCH is not received, the transmitting terminal may reduce the CW. When NACK for PSSCH is received from all receiving terminals, the transmitting terminal may increase the CW. If the number of received NACKs is less than or equal to a predefined threshold, the transmitting terminal may change the CW to the initial CW or the minimum CW. Alternatively, if the number of received NACKs is less than or equal to a predefined threshold, the transmitting terminal may reduce the CW. If the number of received NACKs exceeds the predefined threshold, the transmitting terminal may increase the CW. If even one NACK for PSSCH is not received, the transmitting terminal may maintain the CW (e.g., the current CW). If even one NACK for PSSCH is received, the transmitting terminal may increase the CW.

[0179] When using HARQ-ACK feedback scheme 2, the transmitting terminal may maintain a CW (e.g., the current CW) regardless of HARQ-ACK feedback for PSSCH. The current CW may be the CW used for the most recent LBT operation (e.g., the most recent type 1 LBT operation). The transmitting terminal may maintain CWs (e.g., the current CW) for all priority categories.

[0180] When the transmitting terminal instructs the receiving terminal not to send HARQ-ACK feedback (eg, disables HARQ-ACK feedback), the transmitting terminal may maintain the CW (eg, the current CW) regardless of the HARQ-ACK feedback for the PSSCH.

[0181] The transmission of the terminal (eg, the transmitting terminal) may not require HARQ-ACK feedback. In other words, it may not be necessary to transmit ACK or NACK according to HARQ-ACK feedback scheme 1. The transmission of the terminal may not meet the requirements of the reference duration for CW adjustment.

[0182] The terminal may perform a Type 1 LBT operation for transmission. The terminal may perform a transmission with a specific priority class e. The terminal may perform a Type 1 LBT operation on the current transmission based on the CW used in the most recent transmission for priority class e. If a transmission with priority class e has not been performed, the terminal may perform a Type 1 LBT operation using an initial CW or a minimum CW defined for priority class e.

[0183] After performing a transmission with priority class e, the terminal may keep the CW of priority class e the same as the CW of the previous transmission. If the same CW is used more than a predefined number of times, the terminal may increase the CW. If the same CW is used r times, the terminal may increase the CW. r may be a predefined value. r may vary according to the configuration of the communication system. r may be notified to the terminal by signaling (e.g., higher layer signaling). r may be a natural number. When the CW increases, the terminal may increase the CW of all priority classes. In other words, if it is determined to increase the CW of one priority class, the terminal may increase the CW of all priority classes.

[0184] If the number of times the CW (e.g., maximum CW) for type 1 LBT operation of priority category t is used exceeds a predefined number (y), the terminal may change the CW of priority category t to an initial CW or a minimum CW. The predefined number y may be set differently for each priority category. y may be a predefined value. y may vary according to the configuration of the communication system. y may be notified to the terminal by signaling (e.g., higher layer signaling). y may vary according to the implementation of the terminal. y may be a natural number. For example, y may be a natural number from 1 to 8.

[0185] The terminal (e.g., receiving terminal) that will send HARQ-ACK feedback for multicast SL transmission may be indicated or configured. The transmitting terminal may notify the receiving terminal of the location information of the transmitting terminal. The transmitting terminal may notify the receiving terminal of an identifier (ID) of the area (e.g., zone) to which the transmitting terminal belongs. The transmitting terminal may send an SCI including the location information of the transmitting terminal. The receiving terminal may receive the location information of the transmitting terminal and identify the location of the transmitting terminal based on the location information. The receiving terminal may identify the location of the transmitting terminal based on the ID of the area to which the transmitting terminal belongs.

[0186] The transmitting terminal may inform the receiving terminal of the communication distance requirement of the transmission of the transmitting terminal. The transmitting terminal may transmit the SCI including information about the communication distance requirement. The receiving terminal may identify the communication distance requirement of the transmitting terminal and identify the transmission range of the transmitting terminal based on the communication distance requirement.

[0187] The receiving terminal can determine the transmission coverage of the transmitting terminal based on the location information of the transmitting terminal and the communication distance requirement. The receiving terminal can determine whether the receiving terminal is within the transmission coverage of the transmitting terminal by using the location information of the receiving terminal.

[0188] The transmitting terminal may use different SCIs to determine the range of receiving terminals to which HARQ-ACK feedback will be sent. The transmitting terminal may use SCI format A (e.g., SCI format 1-A and / or SCI format 2-A) so that all receiving terminals receiving PSSCH can send HARQ-ACK feedback for PSSCH. A receiving terminal receiving PSSCH using SCI format A may send HARQ-ACK feedback for PSSCH to the transmitting terminal.

[0189] The transmitting terminal may use SCI format B (e.g., SCI format 2-B) to allow a receiving terminal within a specific range (e.g., a transmission coverage range) of the receiving terminals receiving the PSSCH to send HARQ-ACK feedback for the PSSCH. A receiving terminal receiving the PSSCH using SCI format B may determine whether it is within the transmission coverage range of the transmitting terminal. If the receiving terminal is within the transmission coverage range of the transmitting terminal, the receiving terminal may send HARQ-ACK feedback for the PSSCH to the transmitting terminal. If the receiving terminal is not within the transmission coverage range of the transmitting terminal, the receiving terminal may not send HARQ-ACK feedback for the PSSCH to the transmitting terminal. In order to determine whether the receiving terminal is within the transmission coverage range of the transmitting terminal, the receiving terminal may use at least one of the location information of the transmitting terminal, the communication distance requirement of the transmitting terminal, or the location information of the receiving terminal.

[0190] The receiving terminal may perform a demodulation / decoding operation on the PSSCH using SCI format B. If the receiving terminal is within the transmission coverage of the transmitting terminal, the receiving terminal may send HARQ-ACK feedback for the PSSCH to the transmitting terminal. If the receiving terminal is not within the transmission coverage of the transmitting terminal, the receiving terminal may not send HARQ-ACK feedback for the PSSCH to the transmitting terminal.

[0191] The transmitting terminal may receive one or more HARQ-ACK feedbacks for one or more multicast SL transmissions from one or more receiving terminals on the PSFCH in the same time slot. The transmitting terminal may use the HARQ-ACK feedback for the most recent multicast SL transmission in the one or more HARQ-ACK feedbacks to adjust the CW. The transmitting terminal may receive HARQ-ACK feedback #N for the PSSCH (e.g., multicast SL transmission) sent in time slot #N and HARQ-ACK feedback #N+M for the PSSCH (e.g., multicast SL transmission) sent in time slot #N+M on the PSFCH in the same time slot. In this case, the transmitting terminal may use HARQ-ACK feedback #N and HARQ-ACK feedback #N+M in the HARQ-ACK feedback #N+M to adjust the CW. When the CAPC of the PSSCH sent in time slot #N is the same as the CAPC of the PSSCH sent in time slot #N+M, a CW adjustment operation may be performed. When the CAPC of the PSSCH transmitted in slot #N is different from the CAPC of the PSSCH transmitted in slot #N+M, the transmitting terminal may adjust the CW of each CAPC based on the HARQ-ACK feedback for the PSSCH corresponding to each CAPC. Each of N and M may be a natural number.

[0192] The transmitting terminal may receive one or more HARQ-ACK feedbacks for one or more multicast SL transmissions from one or more receiving terminals on the PSFCH in the same time slot. The transmitting terminal may receive HARQ-ACK feedback for multicast SL transmissions that are discontinuous in the time domain on the PSFCH in the same time slot. In this case, the transmitting terminal may adjust the CW individually based on each HARQ-ACK feedback for multicast SL transmissions that are discontinuous in the time domain. When HARQ-ACK feedback #N for PSSCH (e.g., multicast SL transmission) sent in time slot #N and HARQ-ACK feedback #N+M for PSSCH (e.g., multicast SL transmission) sent in time slot #N+M are received on the PSFCH in the same time slot, the transmitting terminal may adjust the CW using HARQ-ACK feedback #N, and adjust the adjusted CW again based on HARQ-ACK feedback #N+M (e.g., CN adjusted based on HARQ-ACK feedback #N). Each of N and M may be a natural number.

[0193] The transmitting terminal may receive HARQ-ACK feedback for continuous multicast SL transmissions in the time domain on the PSFCH within the same time slot. The multicast SL transmission may be performed in continuous time slots. In this case, the transmitting terminal may adjust the CW using the HARQ-ACK feedback for the first executed multicast SL transmission in the HARQ-ACK feedback. For example, when HARQ-ACK feedback for continuous multicast SL transmissions in time slot #N, time slot #N+1, ... and time slot #N+M is received on the PSFCH within the same time slot, the transmitting terminal may adjust the CW using the HARQ-ACK feedback for the multicast SL transmission in time slot #N.

[0194] The transmitting terminal may adjust the CW based on HARQ-ACK feedback for PSSCH transmission (eg, multicast SL transmission) within a reference period. The reference period may belong to a COT initiated by the transmitting terminal. The reference period may represent a reference duration.

[0195] The start time of the reference duration may be a transmission start time of the transmitting terminal, which starts from the start time of the channel occupancy (e.g., COT). The end time of the reference duration may be the end time of the time slot after the start time of the reference duration. Alternatively, the end time of the reference duration may be the end time of the transmission of the transmitting terminal, which starts from the start time of the channel occupancy.

[0196] Fig.10 is a conceptual diagram showing a first exemplary embodiment of a reference duration within channel occupancy.

[0197] Reference Fig.10 , the transmission of the transmitting terminal (e.g., multicast SL transmission) may start at the start time T1 of the channel occupancy (e.g., COT). The start time of the reference duration may be T1. The end time of the reference duration may be the end time of the time slot (e.g., the first time slot) after the start time T1 of the reference duration. In this case, the end time of the reference duration may be the end time of time slot #N. When the start time of the reference duration is T1 and the end time of the reference duration is the end time of time slot #N, the reference duration may be time slot #N. Alternatively, the end time of the reference duration may be the end time of the transmission of the transmitting terminal, which starts at the start time T1 of the channel occupancy. At this time, the end time of the reference duration may be T2. Therefore, the reference duration may be a period corresponding to time slot #N and time slot #N+1.

[0198] Fig.11 is a conceptual diagram illustrating a second exemplary embodiment of a reference duration within channel occupancy.

[0199] Reference Fig.11, the transmission of the transmitting terminal (e.g., multicast SL transmission) may start from the start time T1 of the channel occupancy (e.g., COT). The start time of the reference duration may be T1. The end time of the reference duration may be the end time of the time slot (e.g., the first time slot) after the start time T1 of the reference duration. In this case, the end time of the reference duration may be the end time of time slot #N. When the start time of the reference duration is T1 and the end time of the reference duration is the end time of time slot #N, the reference duration may be the period from T1 to the end time of time slot #N. Alternatively, the end time of the reference duration may be the end time of the transmission of the transmitting terminal, which starts at the start time T1 of the channel occupancy. In this case, the end time of the reference duration may be T2. Therefore, the reference duration may be the period from T1 to T2 (e.g., the end time of time slot #N+1).

[0200] When one or more unicast SL transmissions are performed within a time period and HARQ feedback for the one or more unicast SL transmissions is enabled, and / or when one or more multicast SL transmissions are performed within a time period and HARQ feedback for the one or more multicast SL transmissions is enabled, the time period may be interpreted as a reference duration. The transmitting terminal may adjust the CW based on HARQ-ACK feedback for transmission within the time period (e.g., the reference duration). Enabling HARQ feedback may mean activating HARQ feedback and / or using HARQ-ACK feedback scheme 1 (e.g., ACK / NACK transmission scheme).

[0201] When no unicast SL transmission with HARQ feedback enabled is performed in a time period and / or when no groupcast SL transmission with HARQ feedback enabled is performed in a time period, the time period may not be a reference duration. The transmitting terminal may not use HARQ-ACK feedback for transmission in the time period (e.g., a time period other than the reference duration) for CW adjustment.

[0202] The start time of the reference duration may be the same as the start time of the channel occupancy. The channel occupancy time (COT) may include PSSCH transmission. The end time of the reference duration may be the end time of the first time slot in which PSSCH transmission to which the HARQ-ACK feedback scheme 1 (eg, ACK / NACK transmission scheme) is applied is performed. Fig.10In an exemplary embodiment of the present invention, the start time of the reference duration may be the start time T1 of the channel occupancy time. The end time of the reference duration may be determined according to the position of the first PSSCH transmission to which the HARQ-ACK feedback scheme 1 is applied. When the PSSCH transmission to which the HARQ-ACK feedback scheme 1 is applied is performed in time slot #N, the end time of the reference duration may be the end time of time slot #N.

[0203] When PSSCH transmission to which HARQ-ACK feedback scheme 1 is applied is not performed in time slot #N, and PSSCH transmission to which HARQ-ACK feedback scheme 1 is applied is performed in time slot #N+1, the end time of the reference duration may be the end time of time slot #N+1. When PSSCH transmission to which HARQ-ACK feedback scheme 1 is applied does not occur during the channel occupancy time, the reference duration may not exist during the channel occupancy time. If the reference duration does not exist, the CW may be maintained. In other words, if the reference duration does not exist, the CW may not be adjusted.

[0204] The method according to the present disclosure can be implemented as a program instruction executable by various computers and recorded on a computer-readable medium. The computer-readable medium may include a program instruction, a data file, a data structure or a combination thereof. The program instruction recorded on the computer-readable medium may be specially designed and configured for the present disclosure, or may be known and available to a technician in the field of computer software.

[0205] Examples of computer-readable media may include hardware devices, such as ROM, RAM, and flash memory, which are specifically configured to store and execute program instructions. Examples of program instructions include machine code generated by, for example, a compiler, and high-level language codes executed by a computer using an interpreter. The above exemplary hardware devices may be configured to run as at least one software module to perform embodiments of the present disclosure, and vice versa.

[0206] Although the embodiments of the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the scope of the disclosure.

Claims

1. A method of a first terminal, comprising: Initiate channel occupation time (COT); performing a multicast sidelink (SL) transmission within the COT; receiving one or more hybrid automatic repeat request-acknowledgement (HARQ-ACK) feedbacks for the multicast SL transmission; In response to a ratio threshold being configured for the first terminal, calculating an ACK ratio based on the one or more HARQ-ACK feedbacks; and A content window (CW) is adjusted based on a comparison result between the ACK ratio and the ratio threshold.

2. The method according to claim 1, wherein: The one or more HARQ-ACK feedbacks considered for adjusting the CW are one or more HARQ-ACK feedbacks for the multicast SL transmission performed within a most recent COT initiated by the first terminal in the COT.

3. The method according to claim 1, wherein: The one or more HARQ-ACK feedbacks considered for adjusting the CW are one or more HARQ-ACK feedbacks for the multicast SL transmission performed within a reference duration within a most recent COT initiated by the first terminal in the COT.

4. The method according to claim 1, wherein: HARQ-ACK feedback for the multicast SL transmission is enabled.

5. The method according to claim 1, wherein: The one or more HARQ-ACK feedbacks are received on a physical sidelink feedback channel (PSFCH) within the same time slot.

6. The method according to claim 1, wherein: Adjusting the CW includes: when the ACK ratio is greater than or equal to the ratio threshold, changing the CW to a minimum CW.

7. The method according to claim 1, wherein: Adjusting the CW includes: when the ACK ratio is greater than or equal to the ratio threshold, reducing the CW.

8. The method according to claim 1, wherein: Adjusting the CW includes: when the ACK ratio is less than the ratio threshold, increasing the CW.

9. The method according to claim 8, wherein: Increase the CW for all priority classes.

10. The method according to claim 1, wherein: When the ratio threshold is not configured for the first terminal, the calculation of the ACK ratio is not performed, and when the one or more HARQ-ACK feedbacks include at least one ACK, the CW is changed to a minimum CW.

11. The method according to claim 1, wherein: The ACK ratio is a ratio between ACKs in the one or more HARQ-ACK feedbacks and the number of terminals expected to send HARQ-ACK feedbacks for the multicast SL transmission.

12. The method according to claim 1, wherein: The ACK ratio is a ratio between ACKs among the one or more HARQ-ACK feedbacks and a number of HARQ-ACK feedbacks expected for the multicast SL transmission.

13. The method according to claim 12, wherein: When a negative ACK (NACK)-only transmission scheme is used, HARQ-ACK feedback not received at the transmitting terminal among expected HARQ-ACK feedbacks is regarded as ACK.

14. A method of a first terminal, comprising: Initiate channel occupation time (COT); Performing multicast sidelink (SL) transmission within the COT; receiving one or more hybrid automatic repeat request-acknowledgement (HARQ-ACK) feedbacks for the multicast SL transmission; In response to a ratio threshold being configured for the first terminal, calculating a negative ACK (NACK) ratio based on the one or more HARQ-ACK feedbacks; as well as A content window (CW) is adjusted based on a comparison result between the NACK ratio and the ratio threshold.

15. The method according to claim 14, wherein: The one or more HARQ-ACK feedbacks considered for adjusting the CW are one or more HARQ-ACK feedbacks for the multicast SL transmission performed within a reference duration within a most recent COT initiated by the first terminal in the COT.

16. The method according to claim 14, wherein: In adjusting the CW, when the NACK ratio is less than the ratio threshold, the first terminal changes the CW to a minimum CW, and when the NACK ratio is equal to or greater than the ratio threshold, the first terminal increases the CW.

17. The method according to claim 14, wherein: The NACK ratio is a ratio between the NACKs in the one or more HARQ-ACK feedbacks and the number of terminals expected to send HARQ-ACK feedbacks for the multicast SL transmission, or a ratio between the NACKs in the one or more HARQ-ACK feedbacks and the number of HARQ-ACK feedbacks expected for the multicast SL transmission.

18. A first terminal comprising at least one processor, in, The at least one processor causes the first terminal to execute: Initiate channel occupation time (COT); performing a multicast sidelink (SL) transmission within the COT; receiving one or more hybrid automatic repeat request acknowledgement (HARQ-ACK) feedbacks for the multicast SL transmission; In response to a ratio threshold being configured for the first terminal, calculating an ACK ratio based on the one or more HARQ-ACK feedbacks; and A content window (CW) is adjusted based on a comparison result between the ACK ratio and the ratio threshold.

19. The first terminal according to claim 18, wherein: When adjusting the CW, the at least one processor causes the first terminal to execute: When the NACK ratio is less than the ratio threshold, changing the CW to a minimum CW; as well as When the NACK ratio is equal to or greater than the ratio threshold, the CW is increased.

20. The first terminal according to claim 18, wherein: The ACK ratio is a ratio between the ACKs in the one or more HARQ-ACK feedbacks and the number of terminals expected to send HARQ-ACK feedbacks for the multicast SL transmission, or a ratio between the ACKs in the one or more HARQ-ACK feedbacks and the number of HARQ-ACK feedbacks expected for the multicast SL transmission.

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