Patent Publication Number: US-2021168648-A1

Title: Method and device for receiving feedback signal in wireless communication system

Description:
TECHNICAL FIELD 
     The present disclosure relates to a wireless communication system, and more particularly to a method for receiving a feedback signal in a wireless communication system, and a user equipment (UE) for the same. 
     BACKGROUND ART 
     As more and more communication devices demand larger communication capacities, the need for enhanced mobile broadband communication relative to the legacy radio access technologies (RATs) has emerged. Massive machine type communication (mMTC) that provides various services by interconnecting multiple devices and things irrespective of time and place is also one of main issues to be addressed for future-generation communications. A communication system design considering services/user equipments (UEs) sensitive to reliability and latency is under discussion as well. As such, the introduction of a future-generation RAT considering enhanced mobile broadband (eMBB), mMTC, ultra-reliability and low latency communication (URLLC), and so on is being discussed. For convenience, this technology is referred to as new RAT (NR) in the present disclosure. NR is an exemplary 5th generation (5G) RAT. 
     A new RAT system including NR adopts orthogonal frequency division multiplexing (OFDM) or a similar transmission scheme. The new RAT system may use OFDM parameters different from long term evolution (LTE) OFDM parameters. Further, the new RAT system may have a larger system bandwidth (e.g., 100 MHz), while following the legacy LTE/LTE-advanced (LTE-A) numerology. Further, one cell may support a plurality of numerologies in the new RAT system. That is, UEs operating with different numerologies may co-exist within one cell. 
     Vehicle-to-everything (V2X) is a communication technology of exchanging information between a vehicle and another vehicle, a pedestrian, or infrastructure. V2X may cover four types of communications such as vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-network (V2N), and vehicle-to-pedestrian (V2P). V2X communication may be provided via a PC5 interface and/or a Uu interface. 
     DISCLOSURE 
     Technical Problem 
     An object of the present disclosure is to provide an opportunistic feedback method in consideration of channel congestion in multicast/broadcast/groupcast environments. 
     It will be appreciated by persons skilled in the art that the objects that could be achieved with the present disclosure are not limited to what has been particularly described hereinabove and the above and other objects that the present disclosure could achieve will be more clearly understood from the following detailed description. 
     Technical Solutions 
     In accordance with an aspect of the present disclosure, a method for allowing a first user equipment (UE) to receive a feedback signal from a second UE in a wireless communication system may include transmitting, by the first UE, a signal to the second UE, and receiving, by the first UE, a feedback signal to the transmitted signal from the second UE. whether the feedback signal is transmitted is determined based on a result of comparison between a reference signal received power (RSRP) measurement and an RSRP threshold. 
     The RSRP threshold may be determined based on channel congestion between the first UE and the second UE. 
     The channel congestion may be a congestion level or a channel busy ratio (CBR). The RSRP threshold may be determined in proportion to the channel congestion. 
     The RSRP threshold may be determined based on at least one of a received signal strength indicator (RSSI), a signal to noise ratio (SNR), a signal to interference plus noise ratio (SINR), and a reference signal received quality (RSRQ). 
     The RSRP threshold may be determined depending on whether the first user equipment (UE) has received previously a negative acknowledgment (NACK) message. 
     If the first UE has not received previously the NACK message, the RSRP threshold may be reset to a higher threshold. 
     The RSRP threshold may be determined based on at least one of a ProSe (proximity-based service) per packet priority (PPPP) and a ProSe per packet reliability (PPPR). 
     The method may further include determining, by the first UE, transmission (Tx) power needed to transmit the feedback signal based on the RSRP threshold, transmitting, by the first UE, information indicating the determined transmission (Tx) power to the second UE, and receiving, by the first UE, the feedback signal from the second UE based on the determined transmission (Tx) power. 
     The method may further include determining a negative acknowledgment (NACK) detection threshold based on channel congestion, and detecting specific information indicating that the feedback signal indicates negative acknowledgment (NACK) based on the determined NACK detection threshold. 
     In accordance with another aspect of the present disclosure, a first user equipment (UE) configured to receive a feedback signal from a second UE in a wireless communication system may include a transceiver, and a processor. The processor may control the first UE to transmit a signal to the second UE, and to receive a feedback signal to the transmitted signal from the second UE. Whether the feedback signal is transmitted may be determined based on a result of comparison between a reference signal received power (RSRP) measurement and an RSRP threshold. 
     Advantageous Effects 
     As is apparent from the above description, a plurality of reception (Rx) UEs according to the embodiments of the present disclosure may determine whether to transmit a feedback signal based on an RSRP threshold. As a result, the embodiments of the present disclosure can greatly reduce energy consumption of the reception (Rx) UEs as compared to the case in which all of the reception (Rx) UEs transmit a feedback signal. 
     The reception (Rx) UEs can determine whether to transmit a feedback signal based on the RSRP threshold, thereby reducing interference caused by simultaneous transmission of a plurality of feedback signals as compared to the case in which all of the reception (Rx) UEs should transmit the feedback signals, resulting in implementation of higher-accuracy signal transmission/reception. 
     The embodiments of the present disclosure can provide an adaptive system capable of adjusting the RSRP threshold according to the channel environment (e.g., the degree of channel congestion). 
     It will be appreciated by persons skilled in the art that the effects that can be achieved with the present disclosure are not limited to what has been particularly described hereinabove and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure, provide embodiments of the present disclosure together with detail explanation. Yet, a technical characteristic of the present disclosure is not limited to a specific drawing. Characteristics disclosed in each of the drawings are combined with each other to configure a new embodiment. Reference numerals in each drawing correspond to structural elements. 
         FIG. 1  illustrates a frame structure in new radio (NR) 
         FIG. 2  illustrates a resource grid in NR. 
         FIG. 3  illustrates sidelink synchronization. 
         FIG. 4  illustrates a time resource unit for transmitting a sidelink synchronization signal. 
         FIG. 5  illustrates a sidelink resource pool. 
         FIG. 6  illustrates scheduling schemes based on sidelink transmission modes. 
         FIG. 7  illustrates selection of sidelink transmission resources. 
         FIG. 8  illustrates transmission of a physical sidelink control channel (PSCCH). 
         FIG. 9  illustrates PSCCH transmission in sidelink vehicle-to-everything (V2X) communication. 
         FIG. 10  is a flowchart illustrating operations of a method according to the embodiments of the present disclosure. 
         FIG. 11  is a flowchart illustrating operations of a method according to the embodiments of the present disclosure. 
         FIG. 12  is a flowchart illustrating operations of a method according to the embodiments of the present disclosure. 
         FIG. 13  is a diagram illustrating a communication system to which one embodiment of the present disclosure can be applied. 
         FIG. 14  is a block diagram illustrating a wireless device to which one embodiment of the present disclosure can be applied. 
         FIG. 15  is a block diagram illustrating a signal processing circuit for transmission (Tx) signals to which one embodiment of the present disclosure can be applied. 
         FIG. 16  is a block diagram illustrating a wireless device to which another embodiment of the present disclosure can be applied. 
         FIG. 17  is a block diagram illustrating a hand-held device to which another embodiment of the present disclosure can be applied. 
         FIG. 18  is a block diagram illustrating a vehicle or an autonomous driving vehicle to which another embodiment of the present disclosure can be applied. 
         FIG. 19  is a block diagram illustrating a vehicle to which another embodiment of the present disclosure can be applied. 
     
    
    
     BEST MODE 
     In this document, downlink (DL) communication refers to communication from a base station (BS) to a user equipment (UE), and uplink (UL) communication refers to communication from the UE to the BS. In DL, a transmitter may be a part of the BS and a receiver may be a part of the UE. In UL, a transmitter may be a part of the UE and a receiver may be a part of the BS. Herein, the BS may be referred to as a first communication device, and the UE may be referred to as a second communication device. The term ‘BS’ may be replaced with ‘fixed station’, ‘Node B’, ‘evolved Node B (eNB)’, ‘next-generation node B (gNB)’, ‘base transceiver system (BTS)’, ‘access point (AP)’, ‘network node’, ‘fifth-generation (5G) network node’, ‘artificial intelligence (AI) system’, ‘road side unit (RSU)’, ‘robot’, etc. The term ‘UE’ may be replaced with ‘terminal’, ‘mobile station (MS)’, ‘user terminal (UT)’, ‘mobile subscriber station (MSS)’, ‘subscriber station (SS)’, ‘advanced mobile station (AMS)’, ‘wireless terminal (WT)’, ‘machine type communication (MTC) device’, ‘machine-to-machine (M2M) device’, ‘device-to-device (D2D) device’, ‘vehicle’, ‘robot’, ‘Al module’, etc. 
     The technology described herein is applicable to various wireless access systems such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), etc. The CDMA may be implemented as radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. The TDMA may be implemented as radio technology such as global system for mobile communications (GSM), general packet radio service (GPRS), or enhanced data rates for GSM evolution (EDGE). The OFDMA may be implemented as radio technology such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc. The UTRA is a part of a universal mobile telecommunication system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA. LTE-advance (LTE-A) or LTE-A pro is an evolved version of 3GPP LTE. 3GPP new radio or new radio access technology (3GPP NR) is an evolved version of 3GPP LTE, LTE-A, or LTE-A pro. 
     Although the present disclosure is described based on 3GPP communication systems (e.g., LTE-A, NR, etc.) for clarity of description, the spirit of the present disclosure is not limited thereto. LTE refers to technologies beyond 3GPP technical specification (TS) 36.xxx Release 8. In particular, LTE technologies beyond 3GPP TS 36.xxx Release 10 are referred to as LTE-A, and LTE technologies beyond 3GPP TS 36.xxx Release 13 are referred to as LTE-A pro. 3GPP NR refers to technologies beyond 3GPP TS 38.xxx Release 15. LTE/NR may be called ‘3GPP system’. Herein, “xxx” refers to a standard specification number. 
     In the present disclosure, a node refers to a fixed point capable of transmitting/receiving a radio signal for communication with a UE. Various types of BSs may be used as the node regardless of the names thereof. For example, the node may include a BS, a node B (NB), an eNB, a pico-cell eNB (PeNB), a home eNB (HeNB), a relay, a repeater, etc. A device other than the BS may be the node. For example, a radio remote head (RRH) or a radio remote unit (RRU) may be the node. The RRH or RRU generally has a lower power level than that of the BS. At least one antenna is installed for each node. The antenna may refer to a physical antenna or mean an antenna port, a virtual antenna, or an antenna group. The node may also be referred to as a point. 
     In the present disclosure, a cell refers to a prescribed geographical area in which one or more nodes provide communication services or a radio resource. When a cell refers to a geographical area, the cell may be understood as the coverage of a node where the node is capable of providing services using carriers. When a cell refers to a radio resource, the cell may be related to a bandwidth (BW), i.e., a frequency range configured for carriers. Since DL coverage, a range within which the node is capable of transmitting a valid signal, and UL coverage, a range within which the node is capable of receiving a valid signal from the UE, depend on carriers carrying the corresponding signals, the coverage of the node may be related to the coverage of the cell, i.e., radio resource used by the node. Accordingly, the term “cell” may be used to indicate the service coverage of a node, a radio resource, or a range to which a signal transmitted on a radio resource can reach with valid strength. 
     In the present disclosure, communication with a specific cell may mean communication with a BS or node that provides communication services to the specific cell. In addition, a DL/UL signal in the specific cell refers to a DL/UL signal from/to the BS or node that provides communication services to the specific cell. In particular, a cell providing DL/UL communication services to a UE may be called a serving cell. The channel state/quality of the specific cell may refer to the channel state/quality of a communication link formed between the BS or node, which provides communication services to the specific cell, and the UE. 
     When a cell is related to a radio resource, the cell may be defined as a combination of DL and UL resources, i.e., a combination of DL and UL component carriers (CCs). The cell may be configured to include only DL resources or a combination of DL and UL resources. When carrier aggregation is supported, a linkage between the carrier frequency of a DL resource (or DL CC) and the carrier frequency of a UL resource (or UL CC) may be indicated by system information transmitted on a corresponding cell. The carrier frequency may be equal to or different from the center frequency of each cell or CC. A cell operating on a primary frequency may be referred to as a primary cell (PCell) or PCC, and a cell operating on a secondary frequency may be referred to as a secondary cell (SCell) or SCC. The SCell may be configured after the UE and BS establish a radio resource control (RRC) connection therebetween by performing an RRC connection establishment procedure, that is, after the UE enters the RRC_CONNECTED state. The RRC connection may mean a path that enables the RRC of the UE and the RRC of the BS to exchange an RRC message. The SCell may be configured to provide additional radio resources to the UE. The SCell and the PCell may form a set of serving cells for the UE depending on the capabilities of the UE. When the UE is not configured with carrier aggregation or does not support the carrier aggregation although the UE is in the RRC_CONNECTED state, only one serving cell configured with the PCell exists. 
     A cell supports a unique radio access technology (RAT). For example, transmission/reception in an LTE cell is performed based on the LTE RAT, and transmission/reception in a 5G cell is performed based on the 5G RAT. 
     The carrier aggregation is a technology for combining a plurality of carriers each having a system BW smaller than a target BW to support broadband. The carrier aggregation is different from OFDMA in that in the former, DL or UL communication is performed on a plurality of carrier frequencies each forming a system BW (or channel BW) and in the latter, DL or UL communication is performed by dividing a base frequency band into a plurality of orthogonal subcarriers and loading the subcarriers in one carrier frequency. For example, in OFDMA or orthogonal frequency division multiplexing (OFDM), one frequency band with a predetermined system BW is divided into a plurality of subcarriers with a predetermined subcarrier spacing, and information/data is mapped to the plurality of subcarriers. Frequency up-conversion is applied to the frequency band to which the information/data is mapped, and the information/data is transmitted on the carrier frequency in the frequency band. In wireless carrier aggregation, multiple frequency bands, each of which has its own system BW and carrier frequency, may be simultaneously used for communication, and each frequency band used in the carrier aggregation may be divided into a plurality of subcarriers with a predetermined subcarrier spacing. 
     3GPP communication specifications define DL physical channels corresponding to resource elements carrying information originating from higher (upper) layers of physical layers (e.g., a medium access control (MAC) layer, a radio link control (RLC) layer, a protocol data convergence protocol (PDCP) layer, an RRC layer, a service data adaptation protocol (SDAP) layer, a non-access stratum (NAS) layer, etc.) and DL physical signals corresponding to resource elements which are used by physical layers but do not carry information originating from higher layers. For example, a physical downlink shared channel (PDSCH), a physical broadcast channel (PBCH), a physical multicast channel (PMCH), a physical control format indicator channel (PCFICH), and a physical downlink control channel (PDCCH) are defined as the DL physical channels, and a reference signal and a synchronization signal are defined as the DL physical signals. A reference signal (RS), which is called a pilot signal, refers to a predefined signal with a specific waveform known to both the BS and UE. For example, a cell-specific RS (CRS), a UE-specific RS (UE-RS), a positioning RS (PRS), a channel state information RS (CSI-RS), and a demodulation reference signal (DMRS) may be defined as DL RSs. In addition, the 3GPP communication specifications define UL physical channels corresponding to resource elements carrying information originating from higher layers and UL physical signals corresponding to resource elements which are used by physical layers but do not carry information originating from higher layers. For example, a physical uplink shared channel (PUSCH), a physical uplink control channel (PUCCH), and a physical random access channel (PRACH) are defined as the UL physical channels, and a demodulation reference signal (DMRS) for a UL control/data signal and a sounding reference signal (SRS) used for UL channel measurement are defined as the UL physical signals. 
     In the present disclosure, the PDCCH and the PDSCH may refer to a set of time-frequency resources or resource elements carrying downlink control information (DCI) of the physical layer and a set of time-frequency resources or resource elements carrying DL data thereof, respectively. The PUCCH, the PUSCH, and the PRACH may refer to a set of time-frequency resources or resource elements carrying uplink control information (UCI) of the physical layer, a set of time-frequency resources or resource elements carrying UL data thereof, and a set of time-frequency resources or resource elements carrying random access signals thereof, respectively. When it is said that a UE transmits a UL physical channel (e.g., PUCCH, PUSCH, PRACH, etc.), it may mean that the UE transmits DCI, UL data, or a random access signal on or over the corresponding UL physical channel. When it is said that the BS receives a UL physical channel, it may mean that the BS receives DCI, UL data, a random access signal on or over the corresponding UL physical channel. When it is said that the BS transmits a DL physical channel (e.g., PDCCH, PDSCH, etc.), it may mean that the BS transmits DCI or UL data on or over the corresponding DL physical channel. When it is said that the UE receives a DL physical channel, it may mean that the UE receives DCI or UL data on or over the corresponding DL physical channel. 
     In the present disclosure, a transport block may mean the payload for the physical layer. For example, data provided from the higher layer or MAC layer to the physical layer may be referred to as the transport block. 
     In the present disclosure, hybrid automatic repeat request (HARQ) may mean a method used for error control. A HARQ acknowledgment (HARQ-ACK) transmitted in DL is used to control an error for UL data, and a HARQ-ACK transmitted in UL is used to control an error for DL data. A transmitter that performs the HARQ operation waits for an ACK signal after transmitting data (e.g. transport blocks or codewords). A receiver that performs the HARQ operation transmits an ACK signal only when the receiver correctly receives data. If there is an error in the received data, the receiver transmits a negative ACK (NACK) signal. Upon receiving the ACK signal, the transmitter may transmit (new) data but, upon receiving the NACK signal, the transmitter may retransmit the data. Meanwhile, there may be a time delay until the BS receives ACK/NACK from the UE and retransmits data after transmitting scheduling information and data according to the scheduling information. The time delay occurs due to a channel propagation delay or a time required for data decoding/encoding. Accordingly, if new data is transmitted after completion of the current HARQ process, there may be a gap in data transmission due to the time delay. To avoid such a gap in data transmission during the time delay, a plurality of independent HARQ processes are used. For example, when there are 7 transmission occasions between initial transmission and retransmission, a communication device may perform data transmission with no gap by managing 7 independent HARQ processes. When the communication device uses a plurality of parallel HARQ processes, the communication device may successively perform UL/DL transmission while waiting for HARQ feedback for previous UL/DL transmission. 
     In the present disclosure, CSI collectively refers to information indicating the quality of a radio channel (also called a link) created between a UE and an antenna port. The CSI includes at least one of a channel quality indicator (CQI), a precoding matrix indicator (PMI), a CSI-RS resource indicator (CRI), an SSB resource indicator (SSBRI), a layer indicator (LI), a rank indicator (RI), or a reference signal received power (RSRP). 
     In the present disclosure, frequency division multiplexing (FDM) may mean that signals/channels/users are transmitted/received on different frequency resources, and time division multiplexing (TDM) may mean that signals/channels/users are transmitted/received on different time resources. 
     In the present disclosure, frequency division duplex (FDD) refers to a communication scheme in which UL communication is performed on a UL carrier and DL communication is performed on a DL carrier linked to the UL carrier, and time division duplex (TDD) refers to a communication scheme in which UL and DL communication are performed by splitting time. 
     The details of the background, terminology, abbreviations, etc. used herein may be found in documents published before the present disclosure. For example, 3GPP TS 24 series, 3GPP TS 34 series, and 3GPP TS 38 series may be referenced (http://www.3gpp.org/specifications/specification-numbering). 
     Frame Structure 
       FIG. 1  is a diagram illustrating a frame structure in NR. 
     The NR system may support multiple numerologies. The numerology is defined by a subcarrier spacing and cyclic prefix (CP) overhead. A plurality of subcarrier spacings may be derived by scaling a basic subcarrier spacing by an integer N (or μ). The numerology may be selected independently of the frequency band of a cell although it is assumed that a small subcarrier spacing is not used at a high carrier frequency. In addition, the NR system may support various frame structures based on the multiple numerologies. 
     Hereinafter, an OFDM numerology and a frame structure, which may be considered in the NR system, will be described. Table 1 shows multiple OFDM numerologies supported in the NR system. The value of μ for a bandwidth part and a CP may be obtained by RRC parameters provided by the BS. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 μ 
                 Δf = 2 μ *15 [kHz] 
                 Cyclic prefix(CP) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 0 
                 15 
                 Normal 
               
               
                   
                 1 
                 30 
                 Normal 
               
               
                   
                 2 
                 60 
                 Normal, Extended 
               
               
                   
                 3 
                 120 
                 Normal 
               
               
                   
                 4 
                 240 
                 Normal 
               
               
                   
                   
               
            
           
         
       
     
     The NR system supports multiple numerologies (e.g., subcarrier spacings) to support various 5G services. For example, the NR system supports a wide area in conventional cellular bands in a subcarrier spacing of 15 kHz and supports a dense urban environment, low latency, and wide carrier BW in a subcarrier spacing of 30/60 kHz. In a subcarrier spacing of 60 kHz or above, the NR system supports a BW higher than 24.25 GHz to overcome phase noise. 
     Resource Grid 
       FIG. 2  illustrates a resource grid in the NR. 
     Referring to  FIG. 2 , a resource grid consisting of Nsize,μgrid*NRBsc subcarriers and 14*2μ OFDM symbols may be defined for each subcarrier spacing configuration and carrier, where Nsize,μgrid is indicated by RRC signaling from the BS. Nsize,μgrid may vary not only depending on the subcarrier spacing configuration μ but also between UL and DL. One resource grid exists for the subcarrier spacing configuration μ, an antenna port p, and a transmission direction (i.e., UL or DL). Each element in the resource gird for the subcarrier spacing configuration μ. and the antenna port p may be referred to as a resource element and identified uniquely by an index pair of (k, l), where k denotes an index in the frequency domain and l denotes the relative location of a symbol in the frequency domain with respect to a reference point. The resource element (k, 1) for the subcarrier spacing configuration μ and the antenna port p may be a physical resource and a complex value, a(p,μ)k,l. A resource block (RB) is defined as NRBsc consecutive subcarriers in the frequency domain (where NRBsc=12). 
     Considering that the UE is incapable of supporting a wide BW supported in the NR system, the UE may be configured to operate in a part of the frequency BW of a cell (hereinafter referred to as a bandwidth part (BWP)). 
     Bandwidth Part (BWP) 
     The NR system may support up to 400 MHz for each carrier. If the UE always keeps a radio frequency (RF) module on for all carriers while operating on such a wideband carrier, the battery consumption of the UE may increase. Considering multiple use cases (e.g., eMBB, URLLC, mMTC, V2X, etc.) operating in one wideband carrier, a different numerology (e.g., subcarrier spacing) may be supported for each frequency band of the carrier. Further, considering that each UE may have a different capability regarding the maximum BW, the BS may instruct the UE to operate only in a partial BW rather than the whole BW of the wideband carrier. The partial bandwidth is referred to as the BWP. The BWP is a subset of contiguous common RBs defined for numerology μi in BWP i of the carrier in the frequency domain, and one numerology (e.g., subcarrier spacing, CP length, and/or slot/mini-slot duration) may be configured for the BWP. 
     The BS may configure one or more BWPs in one carrier configured for the UE. Alternatively, if UEs are concentrated in a specific BWP, the BS may move some UEs to another BWP for load balancing. For frequency-domain inter-cell interference cancellation between neighbor cells, the BS may configure BWPs on both sides of a cell except for some central spectra in the whole BW in the same slot. That is, the BS may configure at least one DL/UL BWP for the UE associated with the wideband carrier, activate at least one of DL/UL BWP(s) configured at a specific time (by L1 signaling which is a physical-layer control signal, a MAC control element (CE) which is a MAC-layer control signal, or RRC signaling), instruct the UE to switch to another configured DL/UL BWP (by L1 signaling, a MAC CE, or RRC signaling), or set a timer value and switch the UE to a predetermined DL/UL BWP upon expiration of the timer value. In particular, an activated DL/UL BWP is referred to as an active DL/UL BWP. While performing initial access or before setting up an RRC connection, the UE may not receive a DL/UL BWP configuration. A DL/UL BWP that the UE assumes in this situation is referred to as an initial active DL/UL BWP. 
     Synchronization Acquisition of Sidelink UE 
     In time division multiple access (TDMA) and frequency division multiple access (FDMA) systems, accurate time and frequency synchronization is essential. If time and frequency synchronization is not accurate, inter-symbol interference (ISI) and inter-carrier interference (ICI) may occur so that system performance may be degraded. This may occur in V2X. For time/frequency synchronization in V2X, a sidelink synchronization signal (SLSS) may be used in the physical layer, and master information block-sidelink-V2X (MIB-SL-V2X) may be used in the RLC layer. 
       FIG. 3  illustrates a synchronization source and a synchronization reference in V2X. 
     Referring to  FIG. 3 , in V2X, a UE may be directly synchronized to global navigation satellite systems (GNSS) or indirectly synchronized to the GNSS through another UE (in or out of the network coverage) that is directly synchronized to the GNSS. When the GNSS is set to the synchronization source, the UE may calculate a direct frame number (DFN) and a subframe number based on coordinated universal time (UTC) and a (pre)configured DFN offset. 
     Alternatively, the UE may be directly synchronized to the BS or synchronized to another UE that is time/frequency synchronized to the BS. For example, if the UE is in the coverage of the network, the UE may receive synchronization information provided by the BS and be directly synchronized to the BS. Thereafter, the UE may provide the synchronization information to another adjacent UE. If the timing of the BS is set to the synchronization reference, the UE may follow a cell associated with a corresponding frequency (if the UE is in the cell coverage at the corresponding frequency) or follow a PCell or serving cell (if the UE is out of the cell coverage at the corresponding frequency) for synchronization and DL measurement. 
     The serving cell (BS) may provide a synchronization configuration for carriers used in V2X sidelink communication. In this case, the UE may follow the synchronization configuration received from the BS. If the UE detects no cell from the carriers used in the V2X sidelink communication and receives no synchronization configuration from the serving cell, the UE may follow a predetermined synchronization configuration. 
     Alternatively, the UE may be synchronized to another UE that fails to directly or indirectly obtain the synchronization information from the BS or GNSS. The synchronization source and preference may be preconfigured for the UE or configured in a control message from the BS. 
     Hereinbelow, the SLSS and synchronization information will be described. 
     The SLSS may be a sidelink-specific sequence and include a primary sidelink synchronization signal (PSSS) and a secondary sidelink synchronization signal (SSSS). 
     Each SLSS may have a physical layer sidelink synchronization identity (ID), and the value may be, for example, any of 0 to 335. The synchronization source may be identified depending on which of the above values is used. For example, 0, 168, and 169 may indicate the GNSS, 1 to 167 may indicate the BS, and 170 to 335 may indicate out-of-coverage. Alternatively, among the values of the physical layer sidelink synchronization ID, 0 to 167 may be used by the network, and 168 to 335 may be used for the out-of-coverage state. 
       FIG. 4  illustrates a time resource unit for SLSS transmission. The time resource unit may be a subframe in LTE/LTE-A and a slot in 5G. The details may be found in 3GPP TS 36 series or 3GPP TS 28 series. A physical sidelink broadcast channel (PSBCH) may refer to a channel for carrying (broadcasting) basic (system) information that the UE needs to know before sidelink signal transmission and reception (e.g., SLSS-related information, a duplex mode (DM), a TDD UL/DL configuration, information about a resource pool, the type of an SLSS-related application, a subframe offset, broadcast information, etc.). The PSBCH and SLSS may be transmitted in the same time resource unit, or the PSBCH may be transmitted in a time resource unit after that in which the SLSS is transmitted. A DMRS may be used to demodulate the PSBCH. 
     Sidelink Transmission Mode 
     For sidelink communication, transmission modes  1 ,  2 ,  3  and  4  are used. 
     In transmission mode  1 / 3 , the BS performs resource scheduling for UE  1  over a PDCCH (more specifically, DCI) and UE  1  performs D2D/V2X communication with UE  2  according to the corresponding resource scheduling. After transmitting sidelink control information (SCI) to UE  2  over a physical sidelink control channel (PSCCH), UE  1  may transmit data based on the SCI over a physical sidelink shared channel (PSSCH). Transmission modes  1  and  3  may be applied to D2D and V2X, respectively. 
     Transmission mode  2 / 4  may be a mode in which the UE performs autonomous scheduling (self-scheduling). Specifically, transmission mode  2  is applied to D2D. The UE may perform D2D operation by autonomously selecting a resource from a configured resource pool. Transmission mode  4  is applied to V2X. The UE may perform V2X operation by autonomously selecting a resource from a selection window through a sensing process. After transmitting the SCI to UE  2  over the PSCCH, UE  1  may transmit data based on the SCI over the PSSCH. Hereinafter, the term ‘transmission mode’ may be simply referred to as ‘mode’. 
     Control information transmitted by a BS to a UE over a PDCCH may be referred to as DCI, whereas control information transmitted by a UE to another UE over a PSCCH may be referred to as SCI. The SCI may carry sidelink scheduling information. The SCI may have several formats, for example, SCI format 0 and SCI format 1. 
     SCI format 0 may be used for scheduling the PSSCH. SCI format 0 may include a frequency hopping flag (1 bit), a resource block allocation and hopping resource allocation field (the number of bits may vary depending on the number of sidelink RBs), a time resource pattern (7 bits), a modulation and coding scheme (MCS) (5 bits), a time advance indication (11 bits), a group destination ID (8 bits), etc. 
     SCI format 1 may be used for scheduling the PSSCH. SCI format 1 may include a priority (3 bits), a resource reservation (4 bits), the location of frequency resources for initial transmission and retransmission (the number of bits may vary depending on the number of sidelink subchannels), a time gap between initial transmission and retransmission (4 bits), an MCS (5 bits), a retransmission index (1 bit), a reserved information bit, etc. Hereinbelow, the term ‘reserved information bit’ may be simply referred to as ‘reserved bit’. The reserved bit may be added until the bit size of SCI format 1 becomes 32 bits. 
     SCI format 0 may be used for transmission modes  1  and  2 , and SCI format 1 may be used for transmission modes  3  and  4 . 
     Sidelink Resource Pool 
       FIG. 5  shows an example of a first UE (UE 1 ), a second UE (UE 2 ) and a resource pool used by UE 1  and UE 2  performing sidelink communication. 
     In  FIG. 5( a ) , a UE corresponds to a terminal or such a network device as a BS transmitting and receiving a signal according to a sidelink communication scheme. A UE selects a resource unit corresponding to a specific resource from a resource pool corresponding to a set of resources and the UE transmits a sidelink signal using the selected resource unit. UE 2  corresponding to a receiving UE receives a configuration of a resource pool in which UE 1  is able to transmit a signal and detects a signal of UE 1  in the resource pool. In this case, if UE 1  is located in the coverage of a BS, the BS may inform UE 1  of the resource pool. If UE 1  is located out of the coverage of the BS, the resource pool may be informed by a different UE or may be determined by a predetermined resource. In general, a resource pool includes a plurality of resource units. A UE selects one or more resource units from among a plurality of the resource units and may be able to use the selected resource unit(s) for sidelink signal transmission.  FIG. 5( b )  shows an example of configuring a resource unit. Referring to  FIG. 8( b ) , the entire frequency resources are divided into the NF number of resource units and the entire time resources are divided into the NT number of resource units. In particular, it is able to define NF*NT number of resource units in total. In particular, a resource pool may be repeated with a period of NT subframes. Specifically, as shown in  FIG. 8 , one resource unit may periodically and repeatedly appear. Alternatively, an index of a physical resource unit to which a logical resource unit is mapped may change with a predetermined pattern according to time to obtain a diversity gain in time domain and/or frequency domain. In this resource unit structure, a resource pool may correspond to a set of resource units capable of being used by a UE intending to transmit a sidelink signal. 
     A resource pool may be classified into various types. First of all, the resource pool may be classified according to contents of a sidelink signal transmitted via each resource pool. For example, the contents of the sidelink signal may be classified into various signals and a separate resource pool may be configured according to each of the contents. The contents of the sidelink signal may include a scheduling assignment (SA or physical sidelink control channel (PSCCH)), a sidelink data channel, and a discovery channel. The SA may correspond to a signal including information on a resource position of a sidelink data channel, information on a modulation and coding scheme (MCS) necessary for modulating and demodulating a data channel, information on a MIMO transmission scheme, information on a timing advance (TA), and the like. The SA signal may be transmitted on an identical resource unit in a manner of being multiplexed with sidelink data. In this case, an SA resource pool may correspond to a pool of resources that an SA and sidelink data are transmitted in a manner of being multiplexed. The SA signal may also be referred to as a sidelink control channel or a physical sidelink control channel (PSCCH). The sidelink data channel (or, physical sidelink shared channel (PSSCH)) corresponds to a resource pool used by a transmitting UE to transmit user data. If an SA and a sidelink data are transmitted in a manner of being multiplexed in an identical resource unit, sidelink data channel except SA information may be transmitted only in a resource pool for the sidelink data channel. In other word, REs, which are used to transmit SA information in a specific resource unit of an SA resource pool, may also be used for transmitting sidelink data in a sidelink data channel resource pool. The discovery channel may correspond to a resource pool for a message that enables a neighboring UE to discover transmitting UE transmitting information such as ID of the UE, and the like. 
     Despite the same contents, sidelink signals may use different resource pools according to the transmission and reception properties of the sidelink signals. For example, despite the same sidelink data channels or the same discovery messages, they may be distinguished by different resource pools according to transmission timing determination schemes for the sidelink signals (e.g., whether a sidelink signal is transmitted at the reception time of a synchronization reference signal or at a time resulting from applying a predetermined TA to the reception time of the synchronization reference signal), resource allocation schemes for the sidelink signals (e.g., whether a BS configures the transmission resources of an individual signal for an individual transmitting UE or the individual transmitting UE autonomously selects the transmission resources of an individual signal in a pool), the signal formats of the sidelink signals (e.g., the number of symbols occupied by each sidelink signal in one subframe or the number of subframes used for transmission of a sidelink signal), signal strengths from the BS, the transmission power of a sidelink UE, and so on. In sidelink communication, a mode in which a BS directly indicates transmission resources to a sidelink transmitting UE is referred to as sidelink transmission mode  1 , and a mode in which a transmission resource area is preconfigured or the BS configures a transmission resource area and the UE directly selects transmission resources is referred to as sidelink transmission mode  2 . In sidelink discovery, a mode in which a BS directly indicates resources is referred to as Type 2, and a mode in which a UE selects transmission resources directly from a preconfigured resource area or a resource area indicated by the BS is referred to as Type 1. 
     In V2X, sidelink transmission mode  3  based on centralized scheduling and sidelink transmission mode  4  based on distributed scheduling are available. 
       FIG. 6  illustrates scheduling schemes based on these two transmission modes. Referring to  FIG. 6 , in transmission mode  3  based on centralized scheduling of  FIG. 6( a ) , a vehicle requests sidelink resources to a BS (S 901   a ), and the BS allocates the resources (S 902   a ). Then, the vehicle transmits a signal on the resources to another vehicle (S 903   a ). In the centralized transmission, resources on another carrier may also be scheduled. In transmission mode  4  based on distributed scheduling of  FIG. 6( b ) , a vehicle selects transmission resources (S 902   b ) by sensing a resource pool, which is preconfigured by a BS (S 901   b ). Then, the vehicle may transmit a signal on the selected resources to another vehicle (S 903   b ). 
     When the transmission resources are selected, transmission resources for a next packet are also reserved as illustrated in  FIG. 7 . In V2X, transmission is performed twice for each MAC PDU. When resources for initial transmission are selected, resources for retransmission are also reserved with a predetermined time gap from the resources for the initial transmission. The UE may identify transmission resources reserved or used by other UEs through sensing in a sensing window, exclude the transmission resources from a selection window, and randomly select resources with less interference from among the remaining resources. 
     For example, the UE may decode a PSCCH including information about the cycle of reserved resources within the sensing window and measure PSSCH RSRP on periodic resources determined based on the PSCCH. The UE may exclude resources with PSCCH RSRP more than a threshold from the selection window. Thereafter, the UE may randomly select sidelink resources from the remaining resources in the selection window. 
     Alternatively, the UE may measure received signal strength indication (RSSI) for the periodic resources in the sensing window and identify resources with less interference, for example, the bottom 20 percent. After selecting resources included in the selection window from among the periodic resources, the UE may randomly select sidelink resources from among the resources included in the selection window. For example, when PSCCH decoding fails, the above method may be applied. 
     The details thereof may be found in clause 14 of 3GPP TS 3GPP TS 36.213 V14.6.0, which are incorporated herein by reference. 
     Transmission and Reception of PSCCH 
     In sidelink transmission mode  1 , a UE may transmit a PSCCH (sidelink control signal, SCI, etc.) on a resource configured by a BS. In sidelink transmission mode  2 , the BS may configure resources used for sidelink transmission for the UE, and the UE may transmit the PSCCH by selecting a time-frequency resource from among the configured resources. 
       FIG. 8  shows a PSCCH period defined for sidelink transmission mode  1  or  2 . 
     Referring to  FIG. 8 , a first PSCCH (or SA) period may start in a time resource unit apart by a predetermined offset from a specific system frame, where the predetermined offset is indicated by higher layer signaling. Each PSCCH period may include a PSCCH resource pool and a time resource unit pool for sidelink data transmission. The PSCCH resource pool may include the first time resource unit in the PSCCH period to the last time resource unit among time resource units indicated as carrying a PSCCH by a time resource unit bitmap. In mode  1 , since a time-resource pattern for transmission (T-RPT) or a time-resource pattern (TRP) is applied, the resource pool for sidelink data transmission may include time resource units used for actual transmission. As shown in the drawing, when the number of time resource units included in the PSCCH period except for the PSCCH resource pool is more than the number of T-RPT bits, the T-RPT may be applied repeatedly, and the last applied T-RPT may be truncated as many as the number of remaining time resource units. A transmitting UE performs transmission at a T-RPT position of 1 in a T-RPT bitmap, and transmission is performed four times in one MAC PDU. 
     In V2X, that is, sidelink transmission mode  3  or  4 , a PSCCH and data (PSSCH) are frequency division multiplexed (FDM) and transmitted, unlike sidelink communication. Since latency reduction is important in V2X in consideration of the nature of vehicle communication, the PSCCH and data are FDM and transmitted on the same time resources but different frequency resources.  FIG. 9  illustrates examples of this transmission scheme. The PSCCH and data may not be contiguous to each other as illustrated in  FIG. 9( a )  or may be contiguous to each other as illustrated in  FIG. 9( b ) . A subchannel is used as the basic unit for the transmission. The subchannel is a resource unit including one or more RBs in the frequency domain within a predetermined time resource (e.g., time resource unit). The number of RBs included in the subchannel, i.e., the size of the subchannel and the starting position of the subchannel in the frequency domain are indicated by higher layer signaling. 
     For V2V communication, a periodic type of cooperative awareness message (CAM) and an event-triggered type of decentralized environmental notification message (DENM) may be used. The CAM may include dynamic state information of a vehicle such as direction and speed, vehicle static data such as dimensions, and basic vehicle information such as ambient illumination states, path details, etc. The CAM may be 50 to 300 bytes long. In addition, the CAM is broadcast, and its latency should be less than 100 ms. The DENM may be generated upon occurrence of an unexpected incident such as a breakdown, an accident, etc. The DENM may be shorter than 3000 bytes, and it may be received by all vehicles within the transmission range. The DENM may have priority over the CAM. When it is said that messages are prioritized, it may mean that from the perspective of a UE, if there are a plurality of messages to be transmitted at the same time, a message with the highest priority is preferentially transmitted, or among the plurality of messages, the message with highest priority is transmitted earlier in time than other messages. From the perspective of multiple UEs, a high-priority message may be regarded to be less vulnerable to interference than a low-priority message, thereby reducing the probability of reception error. If security overhead is included in the CAM, the CAM may have a large message size compared to when there is no security overhead. 
     Sidelink Congestion Control 
     A sidelink radio communication environment may easily become congested according to increases in the density of vehicles, the amount of information transfer, etc. Various methods are applicable for congestion reduction. For example, distributed congestion control may be applied. 
     In the distributed congestion control, a UE understands the congestion level of a network and performs transmission control. In this case, the congestion control needs to be performed in consideration of the priorities of traffic (e.g., packets). 
     Specifically, each UE may measure a channel busy ratio (CBR) and then determine the maximum value (CRlimitk) of a channel occupancy ratio (CRk) that can be occupied by each traffic priority (e.g., k) according to the CBR. For example, the UE may calculate the maximum value (CRlimitk) of the channel occupancy ratio for each traffic priority based on CBR measurement values and a predetermined table. If traffic has a higher priority, the maximum value of the channel occupancy ratio may increase. 
     The UE may perform the congestion control as follows. The UE may limit the sum of the channel occupancy ratios of traffic with a priority k such that the sum does not exceed a predetermined value, where k is less than i. According to this method, the channel occupancy ratios of traffic with low priorities are further restricted. 
     Besides, the UE may use methods such as control of the magnitude of transmission power, packet drop, determination of retransmission or non-retransmission, and control of the size of a transmission RB (MCS adjustment). 
     5G Use Cases 
     Three key requirement areas of 5G (e.g., NR) include (1) enhanced mobile broadband (eMBB), (2) massive machine type communication (mMTC), and (3) ultra-reliable and low latency communications (URLLC). 
     Some use cases may require multiple dimensions for optimization, while others may focus only on one key performance indicator (KPI). 5G supports such diverse use cases in a flexible and reliable way. 
     eMBB goes far beyond basic mobile Internet access and covers rich interactive work, media and entertainment applications in the cloud or augmented reality (AR). Data is one of the key drivers for 5G and in the 5G era, we may for the first time see no dedicated voice service. In 5G, voice is expected to be handled as an application program, simply using data connectivity provided by a communication system. The main drivers for an increased traffic volume are the increase in the size of content and the number of applications requiring high data rates. Streaming services (audio and video), interactive video, and mobile Internet connectivity will continue to be used more broadly as more devices connect to the Internet. Many of these applications require always-on connectivity to push real time information and notifications to users. Cloud storage and applications are rapidly increasing for mobile communication platforms. This is applicable for both work and entertainment. Cloud storage is one particular use case driving the growth of uplink data rates. 5G will also be used for remote work in the cloud which, when done with tactile interfaces, requires much lower end-to-end latencies in order to maintain a good user experience. Entertainment, for example, cloud gaming and video streaming, is another key driver for the increasing need for mobile broadband capacity. Entertainment will be very essential on smart phones and tablets everywhere, including high mobility environments such as trains, cars and airplanes. Another use case is augmented reality (AR) for entertainment and information search, which requires very low latencies and significant instant data volumes. 
     One of the most expected 5G use cases is the functionality of actively connecting embedded sensors in every field, that is, mMTC. It is expected that there will be 20.4 billion potential Internet of things (IoT) devices by 2020. In industrial IoT, 5G is one of areas that play key roles in enabling smart city, asset tracking, smart utility, agriculture, and security infrastructure. 
     URLLC includes services which will transform industries with ultra-reliable/available , low latency links such as remote control of critical infrastructure and self-driving vehicles. The level of reliability and latency are vital to smart-grid control, industrial automation, robotics, drone control and coordination, and so on. 
     Now, multiple 5G use cases will be described in detail. 
     5G may complement fiber-to-the home (FTTH) and cable-based broadband (or data-over-cable service interface specifications (DOCSIS)) as a means of providing streams at data rates of hundreds of megabits per second to giga bits per second. Such a high speed is required for TV broadcasts at or above a resolution of 4K (6K, 8K, and higher) as well as virtual reality (VR) and AR. VR and AR applications mostly include immersive sport games. A special network configuration may be required for a specific application program. For VR games, for example, game companies may have to integrate a core server with an edge network server of a network operator in order to minimize latency. 
     The automotive sector is expected to be a very important new driver for 5G, with many use cases for mobile communications for vehicles. For example, entertainment for passengers requires simultaneous high capacity and high mobility mobile broadband, because future users will expect to continue their good quality connection independent of their location and speed. Other use cases for the automotive sector are AR dashboards. These display overlay information on top of what a driver is seeing through the front window, identifying objects in the dark and telling the driver about the distances and movements of the objects. In the future, wireless modules will enable communication between vehicles themselves, information exchange between vehicles and supporting infrastructure and between vehicles and other connected devices (e.g., those carried by pedestrians). Safety systems may guide drivers on alternative courses of action to allow them to drive more safely and lower the risks of accidents. The next stage will be remote-controlled or self-driving vehicles. These require very reliable, very fast communication between different self-driving vehicles and between vehicles and infrastructure. In the future, self-driving vehicles will execute all driving activities, while drivers are focusing on traffic abnormality elusive to the vehicles themselves. The technical requirements for self-driving vehicles call for ultra-low latencies and ultra-high reliability, increasing traffic safety to levels humans cannot achieve. 
     Smart cities and smart homes, often referred to as smart society, will be embedded with dense wireless sensor networks. Distributed networks of intelligent sensors will identify conditions for cost- and energy-efficient maintenance of the city or home. A similar setup can be done for each home, where temperature sensors, window and heating controllers, burglar alarms, and home appliances are all connected wirelessly. Many of these sensors are typically characterized by low data rate, low power, and low cost, but for example, real time high definition (HD) video may be required in some types of devices for surveillance. 
     The consumption and distribution of energy, including heat or gas, is becoming highly decentralized, creating the need for automated control of a very distributed sensor network. A smart grid interconnects such sensors, using digital information and communications technology to gather and act on information. This information may include information about the behaviors of suppliers and consumers, allowing the smart grid to improve the efficiency, reliability, economics and sustainability of the production and distribution of fuels such as electricity in an automated fashion. A smart grid may be seen as another sensor network with low delays. 
     The health sector has many applications that may benefit from mobile communications. Communications systems enable telemedicine, which provides clinical health care at a distance. It helps eliminate distance barriers and may improve access to medical services that would often not be consistently available in distant rural communities. It is also used to save lives in critical care and emergency situations. Wireless sensor networks based on mobile communication may provide remote monitoring and sensors for parameters such as heart rate and blood pressure. 
     Wireless and mobile communications are becoming increasingly important for industrial applications. Wires are expensive to install and maintain, and the possibility of replacing cables with reconfigurable wireless links is a tempting opportunity for many industries. However, achieving this requires that the wireless connection works with a similar delay, reliability and capacity as cables and that its management is simplified. Low delays and very low error probabilities are new requirements that need to be addressed with 5G. 
     Finally, logistics and freight tracking are important use cases for mobile communications that enable the tracking of inventory and packages wherever they are by using location-based information systems. The logistics and freight tracking use cases typically require lower data rates but need wide coverage and reliable location information. 
     The present disclosure proposes an opportunistic feedback method in consideration of channel congestion in multicast/broadcast/groupcast environments. 
     The present disclosure assumes multicast/broadcast/groupcast scenarios. It is assumed that one UE transmits the same packet to the plurality of reception (Rx) UEs and the reception (Rx) UEs receive the packet from the one UE. In this case, the transmitter may refer to a base station (BS) or a mobile user equipment (UE). The receiver may refer to a mobile UE, a relay UE, a fixed access point (AP), or a relay AP. However, the above-mentioned description is merely an example of the transmitter and the receiver, and the method described herein can be applied to various transmitters and/or receivers. On the other hand, it is assumed that the reception (Rx) UEs receive a coded packet of a specific message from a specific transmitter (Tx UE) and transmit information (e.g., ACK/NACK) about whether a message for the received packet has been successfully decoded to the transmit (Tx) UE. 
     In multicast/broadcast/groupcast HARQ feedback, whether a packet has been successfully decoded (e.g., ACK or NACK) may be changed differently for each reception (Rx) UE according to a channel situation of each UE. In this case, whether the transmission (Tx) terminal retransmits a message (to the Rx UE) may be determined either according to the presence or absence of a NACK UE (i.e., UE staying in NACK) from among all UEs contained in a target coverage of the message or according to the number of NACK UEs from among all UEs contained in the target coverage. In multicast/broadcast/groupcast feedback methods, the NACK UEs in specific common resources may transmit a specific signal (e.g., a signal based on a predetermined sequence) using specific resources, and the transmission (Tx) UEs having transmitted the packet may measure reception (Rx) power (or energy in the corresponding resources) of a sequence received through the corresponding resources, and may determine whether NACK occurs. For example, in the present disclosure, the term “RSRP” (or “power”) may be interpreted as “energy” (or “PL”). 
     In order to reduce the amount of feedback, a method for performing feedback of only a UE in which an RSRP measurement value or a pathloss (PL) is equal to or less than a threshold may be considered. In this case, PL (pathloss) is measured in dB. The longer the distance between the UEs, the greater the minus value. For example, a first PL value between one UE and another UE spaced apart from the one UE by a predetermined distance of 20 m may be less than a second PL value between one UE and another UE spaced apart from one UE by a predetermined distance of 10 m. 
     Prior to describing detailed contents of the above-mentioned operations, the embodiments of the present disclosure can use various RSRP measurement methods as follows. For example, the Rx UE may measure the RSRP based on the measured power in a process for enabling the reception (Rx) UE to receive a reference signal from the transmission (Tx) UE. In another example, in the sensing window, the UE can decode a PSCCH (and/or PSSCH) including information about cycles (or periods) of reserved resources, and can measure the RSRP in periodically determined resources on the basis of the PSCCH (and/or PSSCH). For example, the UE can measure the RSRP either based on a PSSCH (and/or PSCCH) DMRS or based on RS (e.g., CSI-RS) for RSRP measurement on PSSCH. In another example, RSRP may be defined as a linear average for power distribution of resource elements through which a reference signal (RS) (e.g., a cell-specific RS (CRS)) is transmitted in a measurement frequency band. 
       FIG. 10  is a flowchart illustrating operations of a method according to the embodiments of the present disclosure. 
     Referring to  FIG. 10 , a method for allowing a first UE to receive a feedback signal from a second UE in a wireless communication system may include transmitting (S 1001 ), by the first UE, a signal to the second UE, and receiving (S 1002 ), by the first UE, a feedback signal to the transmitted signal from the second UE. In addition, whether the feedback signal is transmitted may be decided based on the result of comparison between an RSRP (reference signal received power) measurement and an RSRP threshold. For example, one transmission (Tx) UE (e.g., a first UE) may transmit a predetermined signal (for example, RS) to the plurality of Rx UEs (e.g., second UEs). The Rx UEs having received the predetermined signal may compare the RSRP measurement with the RSRP threshold, and may determine whether to transmit a feedback signal to the Tx UE based on the result of comparison. In this case, information about whether the feedback signal is transmitted may be determined differently according to the respective Rx UEs. If transmission or non-transmission of such feedback signal is decided, the plurality of reception (Rx) UEs may transmit the feedback signal to the reception (Rx) UE or may drop the feedback signal. 
     In accordance with one embodiment of the present disclosure, a method for performing feedback of only the UE having an RSRP measurement value (or a PL measurement value) that is equal to or less than a threshold will hereinafter be described. If the UE has a high RSRP or PL value, the probability of ACK may be high. Therefore, the UE having a high RSRP or PL value does not perform feedback, such that interference caused by transmission of a feedback signal or energy consumption of a packet reception (Rx) UE can be reduced. For example, specific resources are established as feedback resources, and it is possible to transmit a NACK message for the case in which a decoding error has occurred in only some UEs, each of which has the RSRP (RSRP measurement value) or PL (PL measurement value) that is equal to or less than a predetermined threshold, from among the UEs having received the signal (e.g., packet). Here, the NACK message can be transmitted based on a sequence. For example, the Tx UE having transmitted detects/measures an average reception (Rx) power (or (average) energy on resources through which a sequence of Rx UEs is transmitted) of the sequence (e.g., a feedback signal) transferred from the Rx UEs. In this case, if the measured average Rx power is equal to or higher than a predetermined threshold (e.g., RSRP detection threshold or energy measurement threshold), the Tx UE may determine the NACK so that the Rx UEs can perform retransmission. 
     In this case, the RSRP threshold may be determined based on the degree of channel congestion. In more detail, the RSRP threshold may be determined by one or more combinations of the following methods. 
     For example, the Tx UE may determine whether to transmit (HARQ) feedback to the Rx UEs under the condition that RSRP (or RSRP measurement) satisfies a certain condition. For example, the Tx UE may signal the RSRP threshold for the HARQ feedback to the Rx UE through physical layer signaling or higher layer signaling (e.g., RRC signaling). In this case, among the plurality of Rx UEs, only the Rx UE having an RSRP measurement that is equal to or less than the RSRP threshold can perform HARQ feedback. 
     In another example, the RSRP threshold may also be determined by the Rx UE or network (e.g., eNB or gNB). The determined RSRP threshold can be transferred to another network entity (e.g., Tx UE, Rx UE, and/or network) through signaling. 
     In accordance with one embodiment of the present disclosure, the RSRP threshold may be determined based on at least one of PPPP (ProSe per packet priority), PPPR (ProSe per packet reliability), service/traffic types (or priority or requirements), and CAST (e.g., UNICAST, GROUPCAST, etc.) types. In other words, the RSRP threshold may be established differently according to PPPP (ProSe per packet priority), PPPR (ProSe per packet reliability), service traffic types (or priority or requirements), and/or CAST types. To this end, an offset of the RSRP threshold for each PPPP (or service/traffic types (or priority or requirements), or CAST types), an offset of the RSRP threshold for each PPPR, an available RSRP threshold for each PPPP (or service/traffic types (or priority or requirements) or CAST types), or an available RSRP threshold for each PPPR may be predetermined, or may be signaled to the UE through physical layer signaling or higher layer signaling. In this case, PPPP may be a priority parameter used to indicate priority of the MAC PDU. 
     In accordance with one embodiment of the present disclosure, the RSRP threshold may be determined based on the degree of channel congestion including at least one of congestion level and CBR measurement (or CBR level). The RSRP threshold may be established differently depending on channel congestion such as a congestion level or a CBR (channel busy ratio) measurement. In other words, the RSRP threshold may be changed depending on a peripheral congestion situation. In addition, the RSRP threshold may be determined in inverse proportion to (or in proportion to) the channel congestion. For example, when the congestion situation occurs in the peripheral region, the number of UEs designed to transmit NACK will increase. In this case, the number of UEs designed to perform feedback can be reduced by reducing the RSRP threshold. If the degree of channel congestion (e.g., a congestion level or CBR) is high, many UEs will transmit the NACK even when the same RSRP is used. In contrast, fewer UEs will transmit the NACK when the congestion level (or CBR) is low. Even when the same RSRP is used, SINR may be changed depending on the degree of congestion (e.g., congestion level), such that success or failure of such decoding can be changed based on the changed SINR. As described above, the RSRP threshold is determined in consideration of the channel congestion and the number of Rx UEs scheduled to transmit the NACK is adjusted. As a result, although the Rx UE is determined to be a nearby Rx UE, the nearby Rx UE can determine whether to transmit the NACK according to whether the channel situation is good or bad (or the channel congestion level), thereby providing an adaptive communication system for such channel environment/congestion. In addition, if the congestion level (or CBR) is low, a NACK detection threshold may be set to be low (or high). That is, the NACK detection threshold can be determined in proportion to (or in inverse proportion to) the degree of channel congestion. 
     In accordance with one embodiment of the present disclosure, the RSRP threshold may be determined based on at least one of RSSI, SNR, SINR, and RSRQ. For example, the RSRP threshold may be changed depending on (average/measured) RSSI, SNR (Signal to Noise Ratio), RSRQ (or SNR or metric data for SINR (Signal to Interference plus Noise Ratio) measurement), etc. Thus, although a channel quality (e.g., SNR, SINR, RSRQ, etc.) is low under the condition that the distance between the UEs is set to the same distance, the feedback operation can be performed. In another example, when SINR becomes lower in a channel congestion state, the probability of decoding error becomes higher. In this case, a threshold can be changed such that a suitable number of UEs can perform feedback. For example, as the channel quality (e.g., SNR, SINR, RSRQ, etc.) is reduced, the RSRP threshold can be set to a higher value so that many more UEs can perform feedback. 
     In accordance with one embodiment of the present disclosure, the RSRP threshold can be determined depending on whether the Tx UE has received a NACK message to the previously transmitted signal (e.g., the previous packet), and/or can be determined depending on whether the Rx UE has transmitted a NACK message. In other words, if no UE transmits the NACK after transmission of the previous packet, the RSRP threshold may be set to a higher value (or a lower value) in a manner that NACK transmission of many more UEs can be allowed. For example, if the Tx UE has not received the NACK (in the previous stage), the Tx UE may reset a current RSRP threshold to a new RSRP threshold higher (or lower) than the previous RSRP threshold. During transmission of an initial signal (e.g., packet), the RSRP threshold increases to a maximum value (or drops to a minimum value) so that all UEs can perform HARQ feedback. Subsequently, the RSRP threshold gradually decreases (or increases), so that the number of UEs designed to perform feedback can be adjusted. For example, the RSRP threshold decreases (or increases), so that the number of UEs designed to perform such feedback can be reduced. 
     In accordance with one embodiment of the present disclosure, it may be possible to use or consider a method for configuring resources of a plurality of HARQ NACKs according to the RSRP threshold so that the UEs can transmit a sequence in the NACK condition using HARQ NACK resources corresponding to RSRP observed by the UEs. The above-mentioned method can recognize which one of UEs having a certain (average) channel state or a certain (approximate) distance has generated the NACK as compared to the case in which a single HARQ feedback resource is configured, such that Tx parameters (e.g., MCS (modulation coding scheme), transmission (Tx) power, etc.) can be easily adjusted in a retransmission process. The Tx UE may measure the RSRP (or energy) for each feedback resource, and may thus determine whether to perform retransmission based on the measured RSRP. 
     It is assumed that the feedback resource is a shared resource between UEs. For example, a method for indicating the ACK or NACK state by transmitting a predetermined sequence to the same resource shared between the UEs can be used. At this time, the predetermined sequence may be generated by parameters (required for sequence generation input), for example, an ID (Tx UE ID) of the Tx UE, a packet ID, or an indicator signaled by a control signal. 
     As described above, the plurality of Rx UEs according to the present disclosure may determine whether to transmit the feedback signal based on the RSRP threshold, i) energy consumption of the Rx UEs can be greatly reduced to implement the effect of resource saving (or energy saving) as compared to the case in which all of the Rx UEs transmit the feedback signal, and ii) interference caused by simultaneous transmission of the plurality of feedback signals can be greatly reduced as compared to the case in which all of the Rx UEs transmit the feedback signal, so that signal transmission/reception can be carried out with higher accuracy. Alternatively, iii) when the Rx UE located outside a (minimum) communication request distance associated with a packet (or service) (excessively) transmits a feedback signal, the embodiments of the present disclosure can mitigate meaningless (or excessive) retransmission execution of the Tx UE. In addition, the embodiments of the present disclosure can provide an adaptive system capable of adjusting the RSRP threshold according to channel environments (e.g., the degree of channel congestion). 
     Meanwhile, at least one of various embodiments of the present disclosure associated with the above-mentioned method for determining the RSRP threshold can also be applied to a method for determining transmission (Tx) power required for (HARQ) feedback transmission. For example, the method for determining Tx power may also be interpreted as a method for establishing a HARQ feedback Tx power (range) for each RSRP measurement/threshold. Here, it can be assumed that the RSRP value is measured based on a PSCCH DMRS, PSSCH DMRS, or CSI-RS (or RS pre-defined for the corresponding usage). In other words, the embodiments of the present disclosure can determine Tx power required for (HARQ) feedback transmission using the following method. 
       FIG. 11  is a flowchart illustrating operations of the method according to the embodiments of the present disclosure. Referring to  FIG. 11 , the method according to the embodiment may include determining (S 1101 ), by the Tx UE (e.g., a first UE), transmission (Tx) power needed to transmit a feedback signal based on an RSRP threshold, transmitting (S 1101 ), by the Tx UE, information indicating the determined Tx power to (at least one) Rx UE (e.g., the second UE), and receiving (S 1103 ), by the Tx UE, a feedback signal from the (at least one) Rx UE based on the determined Tx power. 
     For example, in association with the step S 1102 , the Tx UE may signal all or some of the Tx power parameters (e.g., P0, alpha, and offset) to the at least one Rx UE through physical layer signaling or higher layer signaling (e.g., RRC signaling), or may signal all or some of the (HARQ) feedback Tx power value (or range) for each RSRP measurement/threshold to the at least one Rx UE through physical layer signaling or higher layer signaling (e.g., RRC signaling). In this case, the feedback Tx power value/range (for each RSRP measurement/threshold) or Tx parameter information (along with resource pool configuration information) may be pre-configured in or pre-signaled to the Rx UE (and/or Tx UE) by a network (or base station). 
     For example, in association with the step S 1101 , the HARQ feedback Tx power (for each RSRP measurement/threshold) may be established differently according to PPPP (ProSe per packet priority) and/or PPPR (ProSe per packet reliability). To this end, the HARQ feedback Tx power offset for each PPPP and/or for each PPPR (according to RSRP measurement/threshold) or the HARQ feedback Tx power value available for each PPPP/PPPR (for each RSRP measurement/threshold) may be predetermined, or may be signaled from the network to the UE through physical layer signaling or higher layer signaling. 
     In addition, in association with the step S 1101 , the Tx power may be determined using the following methods. 
     Congestion level or Channel Busy Ratio (CBR) measurement: In this method, the HARQ feedback Tx power value (for each RSRP measurement/threshold) may be changed differently according to the peripheral congestion situation. If the congestion situation occurs in the peripheral region, the number of UEs transmitting the NACK will increase. In this case, the HARQ feedback Tx power value (for each RSRP measurement/threshold) may be further reduced so that total power of a feedback channel can be maintained at a constant power level. 
     Metric data capable of measuring RSSI, SNR, RSRQ or SNR, SINR: In this method, the HARQ feedback Tx power (for each RSRP measurement/threshold) can be changed according to (average/measured) RSSI, SNR, RSRQ or according to SNR or metric data capable of measuring SINR. 
     Information about whether NACK to the previous packet has been received: In this method, in the case where the previous packet is first transmitted and no UE transmits the NACK associated with the previous packet, or in the case where NACK is not detected, the HARQ feedback Tx power (for each RSRP measurement/threshold) increases (or decreases), so that the NACK can be received with a higher level (or a lower level). To this end, when NACK is not received, the Tx UE may signal, to the Rx UE, an indicator or transmission (Tx) power offset value needed to increase (or reducing) the HARQ feedback Tx power (for each RSRP measurement/threshold) in subsequent control signal transmission. 
     On the other hand, at least one of various embodiments of the present disclosure associated with the above-mentioned method for adjusting the RSRP threshold can also be applied to a method for determining the NACK detection threshold. For example, the method for determining the NACK detection threshold may also be interpreted as a method for establishing a NACK detection threshold (range) for each RSRP measurement/threshold. Here, it can be assumed that the RSRP value is measured based on a PSCCH DMRS, PSSCH DMRS, or CSI-RS (or RS pre-defined for the corresponding usage). 
       FIG. 11  is a flowchart illustrating operations of the method according to the embodiments of the present disclosure. Referring to  FIG. 12 , the method may include determining (S 1201 ) a NACK (negative acknowledgment) detection threshold based on the degree of channel congestion (by a Tx UE), and detecting (S 1202 ), by the Tx UE, information indicating that a feedback signal (which is transmitted or received by the Rx UE) indicates NACK based on the determined NACK detection threshold. 
     For example, in association with the step S 1201 , the embodiments of the present disclosure can determine the NACK detection threshold (for each RSRP measurement/threshold) using the following method. 
     The NACK detection threshold (for each RSRP measurement/threshold) may be established differently according to PPPP (ProSe per packet priority) and/or PPPR (ProSe per packet reliability). The network may signal, to the UE, the NACK detection threshold (for each RSRP measurement/threshold) available according to PPPP/PPPR. 
     Congestion level or CBR measurement: In this method, the NACK detection threshold (for each RSRP measurement/threshold) may be established differently according to the peripheral congestion situation. 
     Metric data capable of measuring RSSI, SNR, RSRQ or SNR, SINR: In this method, the NACK detection threshold (for each RSRP measurement/threshold) can be changed according to (average/measured) RSSI, SNR, RSRQ or according to SNR or metric data capable of measuring SINR. 
     Information about whether NACK of the previous packet has been detected: In this method, in the case where the previous packet is first transmitted and NACK is not detected, a NACK detection threshold (for each RSRP measurement/threshold) can gradually decrease (or increase). In this case, if the NACK detection threshold is set to a very low value, there is a high possibility that unnecessary transmission is performed. In order to prevent unnecessary retransmission, the lower limit value of the NACK detection threshold may be set to a predetermined value or greater. (Alternatively, if the lower limit value of the NACK detection threshold is set to a very high value, NACK detection failure may occur. In order to prevent such NACK detection failure, the upper limit value of the NACK detection threshold may be set to a predetermined value or less). Alternatively, the above-mentioned value may be indicated by the network. 
     Example of Communication System to Which the Present Disclosure is Applied 
     The various descriptions, functions, procedures, proposals, methods, and/or operation flowcharts of the present disclosure described herein may be applied to, but not limited to, various fields requiring wireless communication/connectivity (e.g., 5G) between devices. 
     More specific examples will be described below with reference to the drawings. In the following drawings/description, like reference numerals denote the same or corresponding hardware blocks, software blocks, or function blocks, unless otherwise specified. 
       FIG. 13  illustrates a communication system  1  applied to the present disclosure. Referring to  FIG. 13 , the communication system  1  applied to the present disclosure includes wireless devices, BSs, and a network. A wireless device is a device performing communication using radio access technology (RAT) (e.g., 5G NR (or New RAT) or LTE), also referred to as a communication/radio/5G device. The wireless devices may include, not limited to, a robot  100   a,  vehicles  100   b - 1  and  100   b - 2 , an extended reality (XR) device  100   c,  a hand-held device  100   d,  a home appliance  100   e,  an IoT device  100   f,  and an artificial intelligence (AI) device/server  400 . For example, the vehicles may include a vehicle having a wireless communication function, an autonomous driving vehicle, and a vehicle capable of vehicle-to-vehicle (V2V) communication. Herein, the vehicles may include an unmanned aerial vehicle (UAV) (e.g., a drone). The XR device may include an augmented reality (AR)/virtual reality (VR)/mixed reality (MR) device and may be implemented in the form of a head-mounted device (HMD), a head-up display (HUD) mounted in a vehicle, a television (TV), a smartphone, a computer, a wearable device, a home appliance, a digital signage, a vehicle, a robot, and so on. The hand-held device may include a smartphone, a smart pad, a wearable device (e.g., a smart watch or smart glasses), and a computer (e.g., a laptop). The home appliance may include a TV, a refrigerator, a washing machine, and so on. The IoT device may include a sensor, a smart meter, and so on. For example, the BSs and the network may be implemented as wireless devices, and a specific wireless device  200   a  may operate as a BS/network node for other wireless devices. 
     The wireless devices  100   a  to  100   f  may be connected to the network  300  via the BSs  200 . An AI technology may be applied to the wireless devices  100   a  to  100   f,  and the wireless devices  100   a  to  100   f  may be connected to the AI server  400  via the network  300 . The network  300  may be configured using a 3G network, a 4G (e.g., LTE) network, or a 5G (e.g., NR) network. Although the wireless devices  100   a  to  100   f  may communicate with each other through the BSs  200 /network  300 , the wireless devices  100   a  to  100   f  may perform direct communication (e.g., sidelink communication) with each other without intervention of the BSs/network. For example, the vehicles  100   b - 1  and  100   b - 2  may perform direct communication (e.g. V2V/vehicle-to-everything (V2X) communication). The IoT device (e.g., a sensor) may perform direct communication with other IoT devices (e.g., sensors) or other wireless devices  100   a  to  100   f.    
     Wireless communication/connections  150   a,    150   b,  and  150   c  may be established between the wireless devices  100   a  to  100   f/ BS  200  and between the BSs  200 . Herein, the wireless communication/connections may be established through various RATs (e.g., 5G NR) such as UL/DL communication  150   a,  sidelink communication  150   b  (or, D2D communication), or inter-BS communication (e.g. relay or integrated access backhaul (IAB)). Wireless signals may be transmitted and received between the wireless devices, between the wireless devices and the BSs, and between the BSs through the wireless communication/connections  150   a,    150   b,  and  150   c.  For example, signals may be transmitted and receive don various physical channels through the wireless communication/connections  150   a,    150   b  and  150   c.  To this end, at least a part of various configuration information configuring processes, various signal processing processes (e.g., channel encoding/decoding, modulation/demodulation, and resource mapping/demapping), and resource allocation processes, for transmitting/receiving wireless signals, may be performed based on the various proposals of the present disclosure. 
     Example of Wireless Device to Which the Present Disclosure is Applied 
       FIG. 14  illustrates wireless devices applicable to the present disclosure. 
     Referring to  FIG. 14 , a first wireless device  100  and a second wireless device  200  may transmit wireless signals through a variety of RATs (e.g., LTE and NR). {The first wireless device  100  and the second wireless device  200 } may correspond to {the wireless device  100   x  and the BS  200 } and/or {the wireless device  100   x  and the wireless device  100   x } of  FIG. 20 . 
     The first wireless device  100  may include one or more processors  102  and one or more memories  104 , and further include one or more transceivers  106  and/or one or more antennas  108 . The processor(s)  102  may control the memory(s)  104  and/or the transceiver(s)  106  and may be configured to implement the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document. For example, the processor(s)  102  may process information in the memory(s)  104  to generate first information/signals and then transmit wireless signals including the first information/signals through the transceiver(s)  106 . The processor(s)  102  may receive wireless signals including second information/signals through the transceiver(s)  106  and then store information obtained by processing the second information/signals in the memory(s)  104 . The memory(s)  104  may be connected to the processor(s)  102  and may store various pieces of information related to operations of the processor(s)  102 . For example, the memory(s)  104  may store software code including instructions for performing all or a part of processes controlled by the processor(s)  102  or for performing the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document. The processor(s)  102  and the memory(s)  104  may be a part of a communication modem/circuit/chip designed to implement RAT (e.g., LTE or NR). The transceiver(s)  106  may be connected to the processor(s)  102  and transmit and/or receive wireless signals through the one or more antennas  108 . Each of the transceiver(s)  106  may include a transmitter and/or a receiver. The transceiver(s)  106  may be interchangeably used with radio frequency (RF) unit(s). In the present disclosure, the wireless device may be a communication modem/circuit/chip. 
     The second wireless device  200  may include one or more processors  202  and one or more memories  204 , and further include one or more transceivers  206  and/or one or more antennas  208 . The processor(s)  202  may control the memory(s)  204  and/or the transceiver(s)  206  and may be configured to implement the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document. For example, the processor(s)  202  may process information in the memory(s)  204  to generate third information/signals and then transmit wireless signals including the third information/signals through the transceiver(s)  206 . The processor(s)  202  may receive wireless signals including fourth information/signals through the transceiver(s)  106  and then store information obtained by processing the fourth information/signals in the memory(s)  204 . The memory(s)  204  may be connected to the processor(s)  202  and store various pieces of information related to operations of the processor(s)  202 . For example, the memory(s)  204  may store software code including instructions for performing all or a part of processes controlled by the processor(s)  202  or for performing the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document. The processor(s)  202  and the memory(s)  204  may be a part of a communication modem/circuit/chip designed to implement RAT (e.g., LTE or NR). The transceiver(s)  206  may be connected to the processor(s)  202  and transmit and/or receive wireless signals through the one or more antennas  208 . Each of the transceiver(s)  206  may include a transmitter and/or a receiver. The transceiver(s)  206  may be interchangeably used with RF unit(s). In the present disclosure, the wireless device may be a communication modem/circuit/chip. 
     Now, hardware elements of the wireless devices  100  and  200  will be described in greater detail. One or more protocol layers may be implemented by, not limited to, one or more processors  102  and  202 . For example, the one or more processors  102  and  202  may implement one or more layers (e.g., functional layers such as physical (PHY), medium access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), RRC, and service data adaptation protocol (SDAP)). The one or more processors  102  and  202  may generate one or more protocol data units (PDUs) and/or one or more service data Units (SDUs) according to the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document. The one or more processors  102  and  202  may generate messages, control information, data, or information according to the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document and provide the messages, control information, data, or information to one or more transceivers  106  and  206 . The one or more processors  102  and  202  may generate signals (e.g., baseband signals) including PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document and provide the generated signals to the one or more transceivers  106  and  206 . The one or more processors  102  and  202  may receive the signals (e.g., baseband signals) from the one or more transceivers  106  and  206  and acquire the PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document. 
     The one or more processors  102  and  202  may be referred to as controllers, microcontrollers, microprocessors, or microcomputers. The one or more processors  102  and  202  may be implemented by hardware, firmware, software, or a combination thereof. For example, one or more application specific integrated circuits (ASICs), one or more digital signal processors (DSPs), one or more digital signal processing devices (DSPDs), one or more programmable logic devices (PLDs), or one or more field programmable gate arrays (FPGAs) may be included in the one or more processors  102  and  202 . The descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document may be implemented using firmware or software, and the firmware or software may be configured to include the modules, procedures, or functions. Firmware or software configured to perform the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document may be included in the one or more processors  102  and  202  or may be stored in the one or more memories  104  and  204  and executed by the one or more processors  102  and  202 . The descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document may be implemented using firmware or software in the form of code, an instruction, and/or a set of instructions. 
     The one or more memories  104  and  204  may be connected to the one or more processors  102  and  202  and store various types of data, signals, messages, information, programs, code, instructions, and/or commands. The one or more memories  104  and  204  may be configured to include read-only memories (ROMs), random access memories (RAMs), electrically erasable programmable read-only memories (EPROMs), flash memories, hard drives, registers, cash memories, computer-readable storage media, and/or combinations thereof. The one or more memories  104  and  204  may be located at the interior and/or exterior of the one or more processors  102  and  202 . The one or more memories  104  and  204  may be connected to the one or more processors  102  and  202  through various technologies such as wired or wireless connection. 
     The one or more transceivers  106  and  206  may transmit user data, control information, and/or wireless signals/channels, mentioned in the methods and/or operation flowcharts of this document, to one or more other devices. The one or more transceivers  106  and  206  may receive user data, control information, and/or wireless signals/channels, mentioned in the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document, from one or more other devices. For example, the one or more transceivers  106  and  206  may be connected to the one or more processors  102  and  202  and transmit and receive wireless signals. For example, the one or more processors  102  and  202  may perform control so that the one or more transceivers  106  and  206  may transmit user data, control information, or wireless signals to one or more other devices. The one or more processors  102  and  202  may perform control so that the one or more transceivers  106  and  206  may receive user data, control information, or wireless signals from one or more other devices. The one or more transceivers  106  and  206  may be connected to the one or more antennas  108  and  208  and the one or more transceivers  106  and  206  may be configured to transmit and receive user data, control information, and/or wireless signals/channels, mentioned in the descriptions, functions, procedures, proposals, methods, and/or operation flowcharts disclosed in this document, through the one or more antennas  108  and  208 . In this document, the one or more antennas may be a plurality of physical antennas or a plurality of logical antennas (e.g., antenna ports). The one or more transceivers  106  and  206  may convert received wireless signals/channels from RF band signals into baseband signals in order to process received user data, control information, and wireless signals/channels using the one or more processors  102  and  202 . The one or more transceivers  106  and  206  may convert the user data, control information, and wireless signals/channels processed using the one or more processors  102  and  202  from the baseband signals into the RF band signals. To this end, the one or more transceivers  106  and  206  may include (analog) oscillators and/or filters. 
     Example of Signal Processing Circuit to Which the Present Disclosure is Applied 
       FIG. 15  is a block diagram illustrating a signal processing circuit  1000  for transmission (Tx) signals to which one embodiment of the present disclosure can be applied. 
     Referring to  FIG. 15 , the signal processing circuit  1000  may include a scrambler  1010 , a modulator  1020 , a layer mapper  1030 , a precoder  1040 , a resource mapper  1050 , and a signal generator  1060 . The operations/functions shown in  FIG. 15  may be performed by the processors  102  and  202  and/or the transceivers  106  and  206  shown in  FIG. 14 , without being limited thereto. Hardware elements shown in  FIG. 15  may be implemented by the processors  102  and  202  and/or the transceivers  106  and  206  shown in  FIG. 14 . For example, the blocks  1010  to  1060  may be implemented by the processors  102  and  202 . In addition, the blocks  1010  to  1050  may be implemented by the processors  102  and  202  shown in  FIG. 14 , and the block  1060  may be implemented by the transceivers  106  and  206  shown in  FIG. 14 . 
     The codeword may be converted into a radio signal (or a radio frequency (RF) signal) through the signal processing circuit  1000  shown in  FIG. 15 . Here, the codeword may be a coded bit sequence of an information block. The information block may include a transmission (Tx) block (e.g., UL-SCH transmission block, and/or DL-SCH transmission block). The radio signal may be transmitted through various physical channels (e.g., PUSCH, and PDSCH). 
     In more detail, the codeword may be converted into a bit sequence scrambled by the scrambler  1010 . The scramble sequence used for such scrambling may be generated based on an initialization value, and the initialization value may include ID information of a wireless device, etc. The scrambled bit-sequence may be modulated into a modulated symbol sequence by the demodulator  1020 . The modulation scheme may include pi/2-BPSK(pi/2-Binary Phase Shift Keying), m-PSK(m-Phase Shift Keying), m-QAM(m-Quadrature Amplitude Modulation), etc. The complex modulated symbol sequence may be mapped to one or more transmission (Tx) layers by the layer mapper  1030 . Modulated symbols of the respective Tx layers may be mapped (precoded) to the corresponding antenna port(s) by the precoder  1040 . The output value (z) of the precoder  1040  may be obtained by multiplying the output value (y) of the layer mapper  1030  by the (N×M) precoding matrix (W). In this case, N is the number of antenna ports, and M is the number of Tx layers. In this case, the precoder  1040  may perform precoding after transform precoding (e.g., DFT transform) is performed on the complex modulated symbols. In this case, the precoder  1040  may perform precoding without performing transform precoding. 
     The resource mapper  1050  may map the modulated symbols of the respective antenna ports to time-frequency resources. The time-frequency resources may include a plurality of symbols (e.g., CP-OFDMA symbol and DFT-s-OFDMA symbol) in the time domain, and may include a plurality of subcarriers in the frequency domain. The signal generator  1060  may generate radio signals from the mapped modulated symbols, and the generated radio signals may be transferred to other devices through the respective antennas. To this end, the signal generator  1060  may include an Inverse Fast Fourier Transform (IFFT) module, a Cyclic Prefix (CP) inserter, a Digital-to-Analog Converter (DAC), a frequency uplink converter, etc. 
     The signal processing steps for reception (Rx) signals in the wireless device may be arranged in the reverse order of the signal processing steps  1010  to  1060  shown in  FIG. 15 . For example, the wireless devices  100  and  200  (shown in  FIG. 4 ) may receive radio signals from the outside through the antenna ports/transceivers. The received radio signals may be converted into a baseband signal through a signal restorer. To this end, the signal restorer may include a frequency downlink converter, an analog-to-digital converter (ADC), a CP remover, and a Fast Fourier Transform (FFT) module. Thereafter, the baseband signal may be restored to the codeword after passing through the resource demapper process, the postcoding process, the demodulation process, and the descrambling process. The codeword may be restored to an original information block through decoding. Therefore, the signal processing circuit (not shown) for Rx signals may include a signal restorer, a resource demapper, a postcoder, a demodulator, a descrambler, and a decoder. 
     Example of Wireless Device to Which the Present Disclosure is Applied 
       FIG. 16  illustrates another example of a wireless device applied to the present disclosure. The wireless device may be implemented in various forms according to a use case/service (refer to  FIGS. 13, 17, 18 and 19 ). 
     Referring to  FIG. 16 , wireless devices  100  and  200  may correspond to the wireless devices  100  and  200  of  FIG. 19  and may be configured to include various elements, components, units/portions, and/or modules. For example, each of the wireless devices  100  and  200  may include a communication unit  110 , a control unit  120 , a memory unit  130 , and additional components  140 . The communication unit  110  may include a communication circuit  112  and transceiver(s)  114 . For example, the communication circuit  112  may include the one or more processors  102  and  202  and/or the one or more memories  104  and  204  of  FIG. 14 . For example, the transceiver(s)  114  may include the one or more transceivers  106  and  206  and/or the one or more antennas  108  and  208  of  FIG. 14 . The control unit  120  is electrically connected to the communication unit  110 , the memory  130 , and the additional components  140  and provides overall control to the wireless device. For example, the control unit  120  may control an electric/mechanical operation of the wireless device based on programs/code/instructions/information stored in the memory unit  130 . The control unit  120  may transmit the information stored in the memory unit  130  to the outside (e.g., other communication devices) via the communication unit  110  through a wireless/wired interface or store, in the memory unit  130 , information received through the wireless/wired interface from the outside (e.g., other communication devices) via the communication unit  110 . For example, the controller  120  may be configured to implement at least one operation associated with the above-mentioned methods shown in  FIGS. 10 to 12 . For example, the controller  120  may transmit signals to the other wireless device  200  by controlling a communication unit  110 , and may receive a feedback signal to the transmitted signal from the other wireless device  200  by controlling the communication unit  110 . Whether to transmit the feedback signal may be determined based on the result of comparison between the RSRP (reference signal received power) measurement and the RSRP threshold. 
     The additional components  140  may be configured in various manners according to type of the wireless device. For example, the additional components  140  may include at least one of a power unit/battery, input/output (I/O) unit, a driving unit, and a computing unit. The wireless device may be implemented in the form of, not limited to, the robot ( 100   a  of  FIG. 13 ), the vehicles ( 100   b - 1  and  100   b - 2  of  FIG. 13 ), the XR device ( 100   c  of  FIG. 13 ), the hand-held device ( 100   d  of  FIG. 13 ), the home appliance ( 100   e  of  FIG. 13 ), the IoT device ( 100   f  of  FIG. 13 ), a digital broadcasting terminal, a hologram device, a public safety device, an MTC device, a medical device, a FinTech device (or a finance device), a security device, a climate/environment device, the AI server/device ( 400  of  FIG. 13 ), the BSs ( 200  of  FIG. 13 ), a network node, or the like. The wireless device may be mobile or fixed according to a use case/service. 
     In  FIG. 16 , all of the various elements, components, units/portions, and/or modules in the wireless devices  100  and  200  may be connected to each other through a wired interface or at least a part thereof may be wirelessly connected through the communication unit  110 . For example, in each of the wireless devices  100  and  200 , the control unit  120  and the communication unit  110  may be connected by wire and the control unit  120  and first units (e.g.,  130  and  140 ) may be wirelessly connected through the communication unit  110 . Each element, component, unit/portion, and/or module in the wireless devices  100  and  200  may further include one or more elements. For example, the control unit  120  may be configured with a set of one or more processors. For example, the control unit  120  may be configured with a set of a communication control processor, an application processor, an electronic control unit (ECU), a graphical processing unit, and a memory control processor. In another example, the memory  130  may be configured with a RAM, a dynamic RAM (DRAM), a ROM, a flash memory, a volatile memory, a non-volatile memory, and/or a combination thereof. 
     The implementation example of  FIG. 16  will hereinafter be described with reference to the attached drawings. 
     Example of Hand-Held Device to Which the Present Disclosure is Applied 
       FIG. 17  is a block diagram illustrating a hand-held device  100  to which another embodiment of the present disclosure can be applied. The hand-held device may include a smartphone, a tablet (also called a smartpad), a wearable device (e.g., a smartwatch or smart glasses), and a portable computer (e.g., a laptop). The hand-held device  100  may be referred to as a mobile station (MS), a user terminal (UT), a mobile subscriber station (MSS), a subscriber station (SS), an advanced mobile station (AMS), or a wireless terminal (WT). 
     Referring to  FIG. 17 , the hand-held device  100  may include an antenna unit  108 , a communication unit  110 , a control unit  120 , a memory unit  130 , a power supply unit  140   a,  an interface unit  140   b,  and an input/output (I/O) unit  140   c.  The antenna unit  108  may be configured as a part of the communication unit  110 . The blocks  110  to  130 / 140   a  to  140   c  correspond to the blocks  110  to  130 / 140  of  FIG. 16 , respectively. 
     The communication unit  110  may transmit and receive signals (e.g., data and control signals) to and from another wireless device and a BS. The control unit  120  may perform various operations by controlling elements of the hand-held device  100 . The control unit  120  may include an application processor (AP). The memory unit  130  may store data/parameters/programs/code/commands required for operation of the hand-held device  100 . Further, the memory unit  130  may store input/output data/information. The power supply unit  140   a  may supply power to the hand-held device  100 , and include a wired/wireless charging circuit and a battery. The interface unit  140   b  may support connection between the hand-held device and other external devices. The interface unit  140   b  may include various ports (e.g., an audio I/O port and a video I/O port) for connection to external devices. The I/O unit  140   c  may receive or output video information/signal, audio information/signal, data, and/or user-input information. The I/O unit  140   c  may include a camera, a microphone, a user input unit, a display  140   d,  a speaker, and/or a haptic module. 
     For example, for data communication, the I/O unit  140   c  may acquire information/signals (e.g., touch, text, voice, images, and video) received from the user and store the acquired information/signals in the memory unit  130 . The communication unit  110  may convert the information/signals into radio signals and transmit the radio signals directly to another device or to a BS. Further, the communication unit  110  may receive a radio signal from another device or a BS and then restore the received radio signal to original information/signal. The restored information/signal may be stored in the memory unit  130  and output in various forms (e.g., text, voice, an image, video, and a haptic effect) through the I/O unit  140   c.    
     Example of Vehicle or Autonomous Driving Vehicle to Which the Present Disclosure is Applied 
       FIG. 18  illustrates a vehicle or an autonomous driving vehicle applied to the present disclosure. The vehicle or autonomous driving vehicle may be implemented as a mobile robot, a car, a train, a manned/unmanned aerial vehicle (AV), a ship, or the like. 
     Referring to  FIG. 18 , a vehicle or autonomous driving vehicle  100  may include an antenna unit  108 , a communication unit  110 , a control unit  120 , a driving unit  140   a,  a power supply unit  140   b,  a sensor unit  140   c,  and an autonomous driving unit  140   d.  The antenna unit  108  may be configured as a part of the communication unit  110 . The blocks  110 / 130 / 140   a  to  140   d  correspond to the blocks  110 / 130 / 140  of  FIG. 16 , respectively. 
     The communication unit  110  may transmit and receive signals (e.g., data and control signals) to and from external devices such as other vehicles, BSs (e.g., gNBs and road side units), and servers. The control unit  120  may perform various operations by controlling elements of the vehicle or the autonomous driving vehicle  100 . The control unit  120  may include an ECU. For example, the controller  120  may be configured to implement at least one operation associated with the above-mentioned methods shown in  FIGS. 10 to 12 . For example, the controller  120  may transmit signals to the other wireless device  200  by controlling a communication unit  110 , and may receive a feedback signal to the transmitted signal from the other wireless device  200  by controlling the communication unit  110 . Whether to transmit the feedback signal may be determined based on the result of comparison between the RSRP (reference signal received power) measurement and the RSRP threshold. 
     The driving unit  140   a  may enable the vehicle or the autonomous driving vehicle  100  to drive on a road. The driving unit  140   a  may include an engine, a motor, a powertrain, a wheel, a brake, a steering device, and so on. The power supply unit  140   b  may supply power to the vehicle or the autonomous driving vehicle  100  and include a wired/wireless charging circuit, a battery, and so on. The sensor unit  140   c  may acquire information about a vehicle state, ambient environment information, user information, and so on. The sensor unit  140   c  may include an inertial measurement unit (IMU) sensor, a collision sensor, a wheel sensor, a speed sensor, a slope sensor, a weight sensor, a heading sensor, a position module, a vehicle forward/backward sensor, a battery sensor, a fuel sensor, a tire sensor, a steering sensor, a temperature sensor, a humidity sensor, an ultrasonic sensor, an illumination sensor, a pedal position sensor, and so on. The autonomous driving unit  140   d  may implement technology for maintaining a lane on which the vehicle is driving, technology for automatically adjusting speed, such as adaptive cruise control, technology for autonomously driving along a determined path, technology for driving by automatically setting a route if a destination is set, and the like. 
     For example, the communication unit  110  may receive map data, traffic information data, and so on from an external server. The autonomous driving unit  140   d  may generate an autonomous driving route and a driving plan from the obtained data. The control unit  120  may control the driving unit  140   a  such that the vehicle or autonomous driving vehicle  100  may move along the autonomous driving route according to the driving plan (e.g., speed/direction control). During autonomous driving, the communication unit  110  may aperiodically/periodically acquire recent traffic information data from the external server and acquire surrounding traffic information data from neighboring vehicles. During autonomous driving, the sensor unit  140   c  may obtain information about a vehicle state and/or surrounding environment information. The autonomous driving unit  140   d  may update the autonomous driving route and the driving plan based on the newly obtained data/information. The communication unit  110  may transfer information about a vehicle position, the autonomous driving route, and/or the driving plan to the external server. The external server may predict traffic information data using AI technology based on the information collected from vehicles or autonomous driving vehicles and provide the predicted traffic information data to the vehicles or the autonomous driving vehicles. 
     Example of Augmented Reality (AR)/Virtual Reality (VR) and Vehicle 
       FIG. 19  illustrates a vehicle or an autonomous driving vehicle  100  to which another embodiment of the present disclosure can be applied. The vehicle or autonomous driving vehicle may be configured as a transportation means, a train, an aircraft, a ship, or the like. 
     Referring to  FIG. 19 , the vehicle  100  may include a communication unit  110 , a control unit  120 , a memory unit  130 , an I/O unit  140   a,  and a position measurement unit  140   b.  The blocks  110  to  130 / 140   a  to 140 c  correspond to the blocks  110  to  130 / 140  of  FIG. 16 , respectively. 
     Referring to  FIG. 19 , the vehicle  100  may include a communication unit  110 , a control unit  120 , a memory unit  130 , an input/output unit  140   a,  and a position measuring unit  140   b.  Here, blocks  110  to  130 / 140   a  to 140 b  correspond to blocks  110  to  130 / 140  of  FIG. 16 , respectively. The communication unit  110  may transmit and receive signals (e.g., data and control signals) to and from external devices such as other vehicles or BSs. The control unit  120  may perform various operations by controlling elements of the vehicle  100 . The memory unit  130  may store data/parameters/programs/code/commands required for operation of the hand-held device  100 . The I/O unit  140   a  may output AR/VR objects based on information stored in the memory unit  130 . The I/O unit  140   a  may include a head-up display (HUD). The position measurement unit  140   b  may acquire position information of the vehicle  100 . The position information of the vehicle  100  may include absolute position information of the vehicle  100 , position information within a vehicle traveling lane, acceleration information, position information about peripheral vehicles, etc. The position measurement unit  140   b  may include various sensors. 
     For example, the communication unit  110  of the vehicle  100  may receive map data, traffic information data, and so on from an external server, and may store the received information in the memory unit  130 . The position measurement unit  140   b  may acquire position information of the vehicle  100  through GPS and various sensors, and may store the acquired information in the memory unit  130 . The controller  130  may generate a virtual object based on map information, traffic information, vehicle position information, etc. The I/O unit  140   b  may display the virtual object on a windshield of the vehicle, as represented by  1410  and  1420 . In addition, the controller  120  may determine whether the vehicle  100  is normally driving in the traveling lane based on vehicle position information. If the vehicle  100  abnormally deviates from the traveling lane, the control unit  140  may display a warning message on the windshield of the vehicle  100 . In addition, the control unit  120  may broadcast a warning message indicating an abnormal driving state to the peripheral vehicles through the communication unit  110 . In accordance with various situations, the controller  120  may control the communication unit  110  to transmit vehicle position information, information about abnormal driving, and information about an abnormal vehicle state to the organizations concerned. 
     The embodiments of the present disclosure described above are combinations of elements and features of the present disclosure. The elements or features may be considered selective unless otherwise mentioned. Each element or feature may be practiced without being combined with other elements or features. Further, an embodiment of the present disclosure may be constructed by combining parts of the elements and/or features. Operation orders described in embodiments of the present disclosure may be rearranged. Some constructions of any one embodiment may be included in another embodiment and may be replaced with corresponding constructions of another embodiment. It is obvious to those skilled in the art that claims that are not explicitly cited in each other in the appended claims may be presented in combination as an embodiment of the present disclosure or included as a new claim by a subsequent amendment after the application is filed. 
     The embodiments of the present disclosure have been described above, focusing on the signal transmission and reception relationship between a UE and a BS. The signal transmission and reception relationship is extended to signal transmission and reception between a UE and a relay or between a BS and a relay in the same manner or a similar manner. A specific operation described as performed by a BS may be performed by an upper node of the BS. Namely, it is apparent that, in a network comprised of a plurality of network nodes including a BS, various operations performed for communication with a UE may be performed by the BS, or network nodes other than the BS. The term BS may be replaced with the term fixed station, Node B, enhanced Node B (eNode B or eNB), access point, and so on. Further, the term UE may be replaced with the term terminal, mobile station (MS), mobile subscriber station (MSS), and so on. 
     The embodiments of the present disclosure may be achieved by various means, for example, hardware, firmware, software, or a combination thereof. In a hardware configuration, the methods according to the embodiments of the present disclosure may be achieved by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, etc. 
     In a firmware or software configuration, the embodiments of the present disclosure may be implemented in the form of a module, a procedure, a function, etc. For example, software code may be stored in a memory unit and executed by a processor. The memory unit is located at the interior or exterior of the processor and may transmit and receive data to and from the processor via various known means. 
     Those skilled in the art will appreciate that the present disclosure may be carried out in other specific ways than those set forth herein without departing from the spirit and essential characteristics of the present disclosure. The above embodiments are therefore to be construed in all aspects as illustrative and not restrictive. The scope of the disclosure should be determined by the appended claims and their legal equivalents, not by the above description, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein. 
     INDUSTRIAL APPLICABILITY 
     The above-mentioned embodiments of the present disclosure are applicable to various mobile communication systems.