Patent Publication Number: US-2023164850-A1

Title: Method and apparatus for transmitting and receiving signal for rach procedure by ue in wireless communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/993,480, filed on Aug. 14, 2020, which claims the benefit of Korean Patent Application No. 10-2019-0100626, filed on Aug. 16, 2019. The disclosures of the prior applications are incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a method and apparatus for transmitting and receiving a signal for a random access channel (RACH) procedure by a user equipment (UE) in a wireless communication system, and more particularly, to a method and apparatus for performing a 2-step RACH procedure by a UE in a wireless communication system. 
     BACKGROUND 
     As more and more communication devices require larger communication traffic along with the trend of the era, the next-generation system known as 5th generation (5G) is required to provide improved wireless broadband communication relative to the legacy LTE system. In the 5G system, also called new radio access technology (NewRAT or NR), communication scenarios are classified into enhanced mobile broadband (eMBB), ultra-reliable and low-latency communication (URLLC), and massive machine-Type communications (mMTC). 
     eMBB is a next-generation mobile communication scenario characterized by high spectral efficiency, high user experienced data rate, and high peak data rate. URLLC is a next-generation mobile communication scenario characterized by ultra-high reliability, ultra-low latency, and ultra-high availability (e.g., vehicle-to-everything (V2X), emergency service, and remote control). mMTC is a next-generation mobile communication scenario characterized by low cost, low energy, short packet, and massive connectivity (e.g., Internet of things (IoT)). 
     SUMMARY 
     Provided are a method and apparatus for performing a 2-step random access channel (RACH) procedure by a user equipment (UE). 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the present disclosure. 
     According to an embodiment of the present disclosure, a method of transmitting and receiving a signal for an RACH procedure by a UE in a wireless communication system includes transmitting a message A including a physical random access channel (PRACH) and a physical uplink shared channel (PUSCH) to a base station (BS), and receiving a message B related to contention resolution from the BS in response to the message A. Transmission power for a retransmission of the message A is configured based on that a counter value related to the transmission power is incremented or maintained, the counter value is maintained based on that a transmission spatial filter related to the PRACH is changed for the retransmission of the message A, and the counter value is used for configuring the transmission power based on that the PRACH and the PUSCH are transmitted via the message A. 
     The counter value may be incremented based on that the transmission spatial filter is not changed for the retransmission of the message A. 
     The counter value may be applied commonly to the PRACH and the PUSCH. 
     The method may further include receiving first information indicating a maximum number of retransmission for the message A and second information indicating a threshold number of retransmission for which the configuration of the transmission power is changed. 
     A ramping step size for the retransmission of the message A may be configured to be equal to a ramping step size for transmission of a Message 1 including a preamble, based on that the retransmission of message A is performed as equal or fewer times than the threshold number of retransmission indicated by the second information. 
     A ramping step size for the retransmission of the message A may be configured to be different from a ramping step size for transmission of a Message 1 including a preamble, based on that the retransmission of message A is performed as more times than the threshold number of retransmission indicated by the second information. 
     The threshold number of retransmission indicated by the second information may be lower than the maximum number of retransmission for the message A indicated by the first information and is larger than 1. 
     According to another embodiment of the present disclosure, an apparatus for transmitting and receiving a signal for a RACH procedure in a wireless communication system includes at least one processor, and at least one memory operatively connected to the at least one processor and storing instructions which, when executed, cause the at least one processor to perform a specific operation. The specific operation includes transmitting a message A including a PRACH and a PUSCH, and receiving a message B related to contention resolution in response to the message A. Transmission power for a retransmission of the message A is configured based on that a counter value related to the transmission power is incremented or maintained, the counter value is maintained based on that a transmission spatial filter related to the PRACH is changed for the retransmission of the message A, and the counter value is used for configuring the transmission power based on that the PRACH and the PUSCH are transmitted via the message A. 
     The counter value may be incremented based on that the transmission spatial filter is not changed for the retransmission of the message A. 
     The counter value may be applied commonly to the PRACH and the PUSCH. 
     The specific operation may further include receiving first information indicating a maximum number of retransmission for the message A and second information indicating a threshold number of retransmission for which the configuration of the transmission power is changed. 
     A ramping step size for the retransmission of the message A may be configured to be equal to a ramping step size for transmission of a Message 1 including a preamble, based on that the retransmission of message A is performed as equal or fewer times than the threshold number of retransmission indicated by the second information. 
     A ramping step size for the retransmission of the message A may be configured to be different from a ramping step size for transmission of a Message 1 including a preamble, based on that the retransmission of message A is performed as more times than the threshold number of retransmission indicated by the second information. 
     The threshold number of retransmission indicated by the second information may be lower than the maximum number of retransmission for the message A indicated by the first information and is larger than 1. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the present disclosure and together with the description serve to explain the principle of the present disclosure. In the drawings: 
         FIG.  1    is a diagram illustrating a control-plane protocol stack and a user-plane protocol stack in a radio interface protocol architecture conforming to a 3rd generation partnership project (3GPP) radio access network standard between a user equipment (UE) and an evolved UMTS terrestrial radio access network (E-UTRAN); 
         FIG.  2    is a diagram illustrating physical channels and a general signal transmission method using the physical channels in a 3GPP system; 
         FIGS.  3  to  5    are diagrams illustrating a radio frame structure and a slot structure in a new radio access technology (NewRAT or NR) system; 
         FIGS.  6  to  11    are diagrams illustrating the composition of a synchronization signal/physical broadcast channel (SS/PHCH) block and an SS/PBCH block transmission method; 
         FIGS.  12 A to  14    are diagrams illustrating exemplary random access channel (RACH) procedures; 
         FIGS.  15  to  17    are diagrams illustrating a physical downlink control channel (PDCCH) in the NR system; 
         FIG.  18    is a diagram illustrating an embodiment of a discontinuous reception (DRX) operation; 
         FIGS.  19  and  20    are flowcharts illustrating specific implementation examples of operations of a user equipment (UE) and a base station (BS) according to an embodiment of the present disclosure; 
         FIG.  21    is a diagram illustrating an embodiment of the present disclosure related to a maximum allowed transmission number of message A (Msg A); 
         FIG.  22    is a diagram illustrating an embodiment of the present disclosure related to power boosting of Msg A; 
         FIG.  23    is a diagram illustrating a signal flow for operations of a UE and a BS for performing a 2-step RACH procedure according to embodiments of the present disclosure; 
         FIG.  24    is a diagram illustrating an exemplary communication system to which embodiments of the present disclosure are applied; 
         FIGS.  25  to  28    are diagrams illustrating various exemplary wireless devices to which embodiments of the present disclosure are applied; and 
         FIG.  29    is a diagram illustrating an exemplary signal processing circuit to which embodiments of the present disclosure are applied. 
     
    
    
     DETAILED DESCRIPTION 
     The configuration, operation, and other features of the present disclosure will be easily understood from embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. The following embodiments are examples in which the technical features of the present disclosure are applied to a 3 rd  generation partnership project (3GPP) system. 
     While embodiments of the present disclosure are described in the context of long term evolution (LTE), long term evolution-advanced (LTE-A), and new radio access technology (NewRAT or NR) systems, they are merely examples. The embodiments of the present disclosure are applicable to any communication system corresponding to the above definition. 
     Further, the term used herein “base station (BS)” encompasses “remote radio head (RRH)”, “evolved node B (eNode B or eNB)”, “transmission point (TP)”, “reception point (RP)”, “relay”, and so on. 
     The 3GPP communication standards define downlink (DL) physical channels corresponding to resource elements (REs) carrying information originated from a higher layer and DL physical signals corresponding to REs which are used in the physical (PHY) layer but do not carry information originated from a higher layer. For example, the DL physical channels include physical downlink shared channel (PDSCH), physical broadcast channel (PBCH), physical multicast channel (PMCH), physical control format indicator channel (PCFICH), physical downlink control channel (PDCCH), and physical hybrid automatic repeat request indicator channel (PHICH). The DL physical signals include, for example, reference signal (RS) and synchronization signal (SS). The RS is also called pilot, which is a signal of a predefined special waveform known to both a next-generation node B (gNB) and a user equipment (UE). For example, RSs include cell-specific RS, UE-specific RS (UE-RS), positioning RS (PRS), and channel state information (CSI) RS (CSI-RS). The 3GPP LTE/LTE-A standards define uplink (UL) physical channels corresponding to REs carrying information originated from a higher layer, and UL physical signals corresponding to REs which are used in the PHY layer but do not carry information originated from a higher layer. For example, the UL physical channels include physical uplink shared channel (PUSCH), physical uplink control channel (PUCCH), and physical random access channel (PRACH). The UL physical signals include demodulation reference signal (DMRS) for UL control and data signals, and sounding reference signal (SRS) used for UL channel measurement. 
     In the present disclosure, the PDCCH, PCFICH, PHICH, and PDSCH refer to sets of time-frequency resources or REs that carry downlink control information (DCI), a control format indicator (CFI), a DL acknowledgment/negative acknowledgment (ACK/NACK), and DL data, respectively. Further, the PUCCH, PUSCH, and PRACH refer to sets of time-frequency resources or REs that carry uplink control information (UCI), UL data, and a random access signal, respectively. In the present disclosure, particularly time-frequency resources or REs allocated to or belonging to the PDCCH, PCFICH, PHICH, PDSCH, PUCCH, PUSCH, and PRACH are referred to as PDCCH, PCFICH, PHICH, PDSCH, PUCCH, PUSCH, and PRACH resources or REs, respectively. When it is said that a UE transmits the PUCCH, PUSCH, or PRACH, this implies that the UE transmits UCI, UL data, or a random access signal on or through the PUSCH, PUCCH, or PRACH. Further, when it is said that the gNB transmits the PDCCH, PCFICH, PHICH, or PDSCH, this implies that the gNB transmits DL data or DCI on or through the PDCCH, PCFICH, PHICH, or PDSCH. 
     OFDM symbols, carriers, subcarriers, and REs allocated to or configured with the CRS, DMRS, CSI-RS, SRS, and UE-RS are referred to CRS, DMRS, CSI-RS, SRS, and UE-RS symbols, carriers, subcarriers, and REs, respectively. For example, an OFDM symbol allocated to or configured with a tracking reference signal (TRS) is referred to as a TRS symbol, a subcarrier allocated to or configured with the TRS is referred to as a TRS subcarrier, and an RE allocated to or configured with the TRS is referred to as a TRS RE. Further, a subframe configured for TRS transmission is referred to as a TRS subframe. A subframe carrying a broadcast signal is referred to as a broadcast subframe or a PBCH subframe, and a subframe carrying an SS (e.g., a primary synchronization signal (PSS) and/or a secondary synchronization signal (SSS)) is referred to as an SS subframe or a PSS/SSS subframe. An OFDM symbol, subcarrier, and RE allocated to or configured with the PSS/SSS are referred to as a PSS/SSS symbol, subcarrier, and RE, respectively. 
     In the present disclosure, a CRS port, a UE-RS port, a CSI-RS port, and a TRS port is an antenna port configured for CRS transmission, an antenna port configured for UE-RS transmission, an antenna port configured for CSI-RS transmission, and an antenna port configured for TRS transmission, respectively. Antenna ports configured for transmission of CRSs may be distinguished from each other by the positions of REs occupied by the CRSs according to CRS ports. Antenna ports configured for transmission of UE-RSs may be distinguished from each other by the positions of REs occupied by the UE-RSs according to UE-RS ports. Antenna ports configured for transmission of CSI-RSs may be distinguished from each other by the positions of REs occupied by the CSI-RSs according to CSI-RS ports. Accordingly, the terms CRS port, UE-RS port, CSI-RS port, and TRS port are used in the meaning of patterns of REs occupied by the CRS, UE-RS, the CSI-RS, and the TRS, respectively. 
     Now, a description will be given below of 5th generation (5G) communication in the NR system. 
     Three key requirement areas of 5G include (1) enhanced mobile broadband (eMBB), (2) massive machine type communication (mMTC), and (3) ultra-reliable and low-latency communication (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 use cases in 5G systems including the NR system 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. 
       FIG.  1    illustrates control-plane and user-plane protocol stacks in a radio interface protocol architecture conforming to a 3GPP wireless access network standard between a UE and an evolved UMTS terrestrial radio access network (E-UTRAN). The control plane is a path in which the UE and the network transmit control messages to manage calls, and the user plane is a path in which data generated from an application layer, for example, voice data or Internet packet data is transmitted. 
     A PHY layer at Layer 1 (L1) provides information transfer service to its higher layer, medium access control (MAC). The PHY layer is connected to the MAC layer via transport channels. The transport channels deliver data between the MAC layer and the PHY layer. Data is transmitted on physical channels between the PHY layers of a transmitter and a receiver. The physical channels use time and frequency as radio resources. Specifically, the physical channels are modulated in orthogonal frequency division multiple access (OFDMA) for DL and in single carrier frequency division multiple access (SC-FDMA) for UL. 
     The MAC layer at Layer 2 (L2) provides service to its higher layer, a radio link control (RLC) layer via logical channels. The RLC layer at L2 supports reliable data transmission. RLC functionality may be implemented in a function block of the MAC layer. a packet data convergence protocol (PDCP) layer at L2 performs header compression to reduce the amount of unnecessary control information and thus efficiently transmit Internet protocol (IP) packets such as IP version 4 (IPv4) or IP version 6 (IPv6) packets via an air interface having a narrow bandwidth. 
     A radio resource control (RRC) layer at the lowest part of Layer 3 (or L3) is defined only on the control plane. The RRC layer controls logical channels, transport channels, and physical channels in relation to configuration, reconfiguration, and release of radio bearers. A radio bearer refers to a service provided at L2, for data transmission between the UE and the E-UTRAN. For this purpose, the RRC layers of the UE and the E-UTRAN exchange RRC messages with each other. If an RRC connection is established between the UE and the E-UTRAN, the UE is in RRC Connected mode and otherwise, the UE is in RRC Idle mode. A non-access stratum (NAS) layer above the RRC layer performs functions including session management and mobility management. 
     DL transport channels used to deliver data from the E-UTRAN to UEs include a broadcast channel (BCH) carrying system information, a paging channel (PCH) carrying a paging message, and a shared channel (SCH) carrying user traffic or a control message. DL multicast traffic or control messages or DL broadcast traffic or control messages may be transmitted on a DL SCH or a separately defined DL multicast channel (MCH). UL transport channels used to deliver data from a UE to the E-UTRAN include a random access channel (RACH) carrying an initial control message and a UL SCH carrying user traffic or a control message. Logical channels that are defined above transport channels and mapped to the transport channels include a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), a multicast traffic channel (MTCH), and so on. 
       FIG.  2    illustrates physical channels and a general method for transmitting signals on the physical channels in the 3GPP system. 
     Referring to  FIG.  2   , when a UE is powered on or enters a new cell, the UE performs initial cell search (S 201 ). The initial cell search involves acquisition of synchronization with a BS. Specifically, the UE synchronizes its timing to the BS and acquires a cell identifier (ID) and other information by receiving a PSS and an SSS from the BS. Then the UE may acquire information broadcast in the cell by receiving a PBCH from the BS. During the initial cell search, the UE may monitor a DL channel state by receiving a DL RS. 
     After the initial cell search, the UE may acquire detailed system information by receiving a PDCCH and receiving a PDSCH based on information included in the PDCCH (S 202 ). 
     If the UE initially accesses the BS or has no radio resources for signal transmission to the BS, the UE may perform a ransom access (or RACH) procedure with the BS (S 203  to S 206 ). In the RACH procedure, the UE may transmit a predetermined sequence as a preamble on a PRACH (S 203  and S 205 ) and may receive a random access response (RAR) message to the preamble on a PDCCH and a PDSCH associated with the PDCCH. In the case of a contention-based RACH, the UE may additionally perform a contention resolution procedure (S 206 ). 
     After the above procedure, the UE may receive a PDCCH and/or a PDSCH from the BS (S 207 ) and transmit a PUSCH and/or a PUCCH to the BS (S 208 ), which is a general DL and UL signal transmission procedure. Particularly, the UE may receive DCI on a PDCCH. Herein, the DCI includes control information such as resource allocation information for the UE. Different DCI formats may be defined according to different usages of DCI. 
     Control information that the UE transmits to the BS on the UL or receives from the BS on the DL includes a DL/UL ACK/NACK signal, a channel quality indicator (CQI), a precoding matrix index (PMI), a rank indicator (RI), and so on. The UE may transmit control information such as a CQI, a PMI, an RI, and so on on a PUSCH and/or a PUCCH. 
     Use of an ultra-high frequency band, that is, a millimeter wave frequency band at or above 6 GHz for data transmission in a wide frequency band at higher transmission rates for multiple users is under consideration in the NR system. In 3GPP, this system is called NR. Therefore, this system will be referred to as the NR system in the present disclosure. 
     In NR, various numerologies or subcarrier spacings (SCSs) may be supported to support various 5G services. For example, with an SCS of 15 kHz, a wide area in traditional cellular bands may be supported, while with an SCS of 30 kHz or 60 kHz, a dense urban area, a lower latency, and a wide carrier bandwidth may be supported. With an SCS of 60 kHz or higher, a bandwidth larger than 24.25 kHz may be supported to overcome phase noise. 
     An NR frequency band may be defined by two types of frequency ranges, FR1 and FR2. FR1 may be a sub 6 GHz range, and FR2 may be an above 6 GHz range called millimeter wave (mmW). 
     Table 1 below defines the NR frequency bands. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Frequency Range 
                 Corresponding  
                 Subcarrier  
               
               
                   
                 designation 
                 frequency range 
                 Spacing (SCS) 
               
               
                   
                   
               
             
            
               
                   
                 FR1 
                 450 MHz-6000 MHz 
                 15, 30, 60 kHz 
               
               
                   
                 FR2 
                 24250 MHz-52600 MHz 
                 60, 120, 240 kHz 
               
               
                   
                   
               
            
           
         
       
     
       FIG.  3    illustrates a radio frame structure in NR. 
     In NR, UL and DL transmissions are configured in frames. Each radio frame has a length of 10 ms and is divided into two 5-ms half-frames. Each half-frame is divided into five 1-ms subframes. A subframe is divided into one or more slots, and the number of slots in a subframe depends on an SCS. Each slot includes 12 or 14 OFDM(A) symbols according to a cyclic prefix (CP). When a normal CP is used, each slot includes 14 OFDM symbols. When an extended CP is used, each slot includes 12 OFDM symbols. A symbol may be an OFDM symbol (or a CP-OFDM symbol) and an SC-FDMA symbol (or a discrete Fourier transform-spread-OFDM (DFT-s-OFDM) symbol). 
     Table 2 exemplarily illustrates that the number of symbols per slot, the number of slots per frame, and the number of slots per subframe vary according to SCSs when the normal CP is used. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 SCS (15*2{circumflex over ( )}u) 
                 N slot   symb   
                 N frame,u   slot   
                 N subframe,u   slot   
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                  15 KHz (u = 0) 
                 14 
                 10 
                 1 
               
               
                   
                  30 KHz (u = 1) 
                 14 
                 20 
                 2 
               
               
                   
                  60 KHz (u = 2) 
                 14 
                 40 
                 4 
               
               
                   
                 120 KHz (u = 3) 
                 14 
                 80 
                 8 
               
               
                   
                 240 KHz (u = 4) 
                 14 
                 160 
                 16 
               
               
                   
                   
               
               
                   
                 * N slot   symb : Number of symbols in a slot 
               
               
                   
                 * N frame,u   slot : Number of slots in a frame 
               
               
                   
                 * N subframe,u   slot : Number of slots in a subframe 
               
            
           
         
       
     
     Table 3 illustrates that the number of symbols per slot, the number of slots per frame, and the number of slots per subframe vary according to SCSs when the extended CP is used. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 SCS (15*2{circumflex over ( )}u) 
                 N slot   symb   
                 N frame,u   slot   
                 N subframe,u   slot   
               
               
                   
                   
               
             
            
               
                   
                 60 KHz (u = 2) 
                 12 
                 40 
                 4 
               
               
                   
                   
               
            
           
         
       
     
     In the NR system, different OFDM(A) numerologies (e.g., SCSs, CP lengths, and so on) may be configured for a plurality of cells aggregated for one UE. Accordingly, the (absolute time) duration of a time resource (e.g., a subframe, a slot, or a transmission time interval (TTI)) (for simplicity, referred to as a time unit (TU)) composed of the same number of symbols may be configured differently between the aggregated cells. 
       FIG.  4    illustrates a slot structure in an NR frame. A slot includes a plurality of symbols in the time domain. For example, one slot includes 14 symbols in a normal CP case and 12 symbols in an extended CP case. A carrier includes a plurality of subcarriers in the frequency domain. A resource block (RB) may be defined by a plurality of (e.g., 12) consecutive subcarriers in the frequency domain. A bandwidth part (BWP) may be defined by a plurality of consecutive (physical) RBs ((P)RBs) in the frequency domain and correspond to one numerology (e.g., SCS, CP length, and so on). A carrier may include up to N (e.g., 4) BWPs. Data communication may be conducted in an active BWP, and only one BWP may be activated for one UE. Each element in a resource grid may be referred to as an RE, to which one complex symbol may be mapped. 
       FIG.  5    illustrates the structure of a self-contained slot. In the NR system, a frame has a self-contained structure in which a DL control channel, DL or UL data, and a UL control channel may all be included in one slot. For example, the first N symbols (hereinafter, referred to as a DL control region) in a slot may be used to transmit a DL control channel, and the last M symbols (hereinafter, referred to as a UL control region) in the slot may be used to transmit a UL control channel. N and M are integers equal to or greater than 0. A resource region (hereinafter, referred to as a data region) between the DL control region and the UL control region may be used for DL data transmission or UL data transmission. For example, the following configurations may be considered. The periods are listed in time order. 
     1. DL only configuration 
     2. UL only configuration 
     3. Mixed UL-DL configuration
         DL region+guard period (GP)+UL control region   DL control region+GP+UL region   DL region: (i) DL data region or (ii) DL control region+DL data region   UL region: (i) UL data region or (ii) UL data region+UL control region       

     A PDCCH may be transmitted in the DL control region, and a PDSCH may be transmitted in the DL data region. A PUCCH may be transmitted in the UL control region, and a PUSCH may be transmitted in the UL data region. The PDCCH may carry DCI, for example, DL data scheduling information and UL data scheduling information. The PUCCH may carry UCI, for example, ACK/NACK information for DL data, CSI, and a scheduling request (SR). The GP provides a time gap in the process of switching from the transmission mode to the reception mode or from the reception mode to the transmission mode at the BS and the UE. Some symbols at the time of switching from DL to UL in a subframe may be configured as the GP. 
       FIG.  6    is a diagram illustrating a synchronization signal block (SSB) structure. A UE may perform cell search, system information acquisition, beam alignment for initial access, DL measurement, and so on based on an SSB. The term SSB is interchangeably used with SS/PBCH block. 
     Referring to  FIG.  6   , an SSB includes a PSS, an SSS, and a PBCH. The SSB includes four consecutive OFDM symbols, which carry the PSS, PBCH, SSS/PBCH, and PBCH, respectively. Each of the PSS and the SSS includes one OFDM symbol by 127 subcarriers, and the PBCH includes three OFDM symbols by 576 subcarriers. Polar coding and quadrature phase shift keying (QPSK) are applied to the PBCH. The PBCH includes data REs and DMRS REs in each OFDM symbol. There are three DMRS REs per RB, with three data REs between every two adjacent DMRS REs. 
     Cell Search 
     Cell search is a process of acquiring time/frequency synchronization with a cell and detecting the cell ID (e.g., physical layer cell ID (PCID)) of the cell at a UE. The PSS is used to detect a cell ID in a cell ID group, and the SSS is used to detect the cell ID group. The PBCH is used to detect an SSB (time) index and a half-frame. 
     The cell search procedure of the UE may be summarized in Table 4 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                 Type of Signals 
                 Operations 
               
               
                   
               
             
            
               
                 1 st  step 
                 PSS 
                 * SS/PBCH block (SSB) symbol timing acquisition 
               
               
                   
                   
                 * Cell ID detection within a cell ID group 
               
               
                   
                   
                 (3 hypothesis) 
               
               
                 2 nd  Step 
                 SSS 
                 * Cell ID group detection (336 hypothesis) 
               
               
                 3 rd  Step 
                 PBCH  
                 * SSB index and Half frame (HF) index 
               
               
                   
                 DMRS 
                 (Slot and frame boundary detection) 
               
               
                 4 th  Step 
                 PBCH 
                 * Time information (80 ms, System Frame  
               
               
                   
                   
                 Number (SFN), SSB index, HF) 
               
               
                   
                   
                 * Remaining Minimum System Information 
               
               
                   
                   
                 (RMSI) Control resource set  
               
               
                   
                   
                 (CORESET)/Search space configuration 
               
               
                 5 th  Step 
                 PDCCH and 
                 * Cell access information 
               
               
                   
                 PDSCH 
                 * RACH configuration 
               
               
                   
               
            
           
         
       
     
       FIG.  7    illustrates exemplary SSB transmission. 
     Referring to  FIG.  7   , an SSB is transmitted periodically according to an SSB periodicity. A default SSB periodicity that the UE assumes during initial cell search is defined as 20 ms. After cell access, the SSB periodicity may be set to one of {5 ms, 10 ms, 20 ms, 40 ms, 80 ms, 160 ms} by a network (e.g., a BS). An SSB burst set is configured at the start of an SSB period. The SSB burst set includes a 5-ms time window (i.e., a half-frame), and an SSB may be transmitted up to L times in the SSB burst set. The maximum allowed transmission number L of an SSB may be given as follows according to the frequency band of a carrier. One slot includes up to two SSBs.
         For frequency range of up to 3 GHz, L=4   For frequency range from 3 GHz to 6 GHz, L=8   For frequency range from 6 GHz to 52.6 GHz, L=64       

     The time positions of SSB candidates in an SS burst set may be defined as follows according to SCSs. The time positions of SSB candidates are indexed with (SSB indexes) 0 to L−1 in time order in the SSB burst set (i.e., half-frame).
         Case A—15-kHz SCS: The indexes of the first symbols of candidate SSBs are given as {2, 8}+14*n where n=0, 1 for a carrier frequency equal to or lower than 3 GHz, and n=0, 1, 2, 3 for a carrier frequency of 3 GHz to 6 GHz.   Case B—30-kHz SCS: The indexes of the first symbols of candidate SSBs are given as {4, 8, 16, 20}+28*n where n=0 for the carrier frequency equal to or lower than 3 GHz, and n=0, 1 for the carrier frequency of 3 GHz to 6 GHz.   Case C—30-kHz SCS: The indexes of the first symbols of candidate SSBs are given as {2, 8}+14*n where n=0, 1 for the carrier frequency equal to or lower than 3 GHz, and n=0, 1, 2, 3 for the carrier frequency of 3 GHz to 6 GHz.   Case D—120-kHz SCS: The indexes of the first symbols of candidate SSBs are given as {4, 8, 16, 20}+28*n where n=0, 1, 2, 3, 5, 6, 7, 8, 10, 11, 12, 13, 15, 16, 17, 18 for a carrier frequency above 6 GHz.   Case E—240-kHz SCS: The indexes of the first symbols of candidate SSBs are given as {8, 12, 16, 20, 32, 36, 40, 44}+56*n where n=0, 1, 2, 3, 5, 6, 7, 8 for the carrier frequency above 6 GHz.       

       FIG.  8    illustrates acquisition of DL time synchronization information at a UE. 
     The UE may acquire DL synchronization by detecting an SSB. The UE may identify the structure of an SSB burst set based on the index of the detected SSB and thus detect a symbol, slot, or half-frame boundary. The number of a frame or half-frame to which the detected SSB belongs to may be identified by SFN information and half-frame indication information. 
     Specifically, the UE may acquire 10-bit SFN system information s0 to s9 from the PBCH. 6 bits out of the 10-bit SFN information is obtained from a master information block (MIB), and the remaining 4 bits are obtained from a PBCH transport block (TB). 
     The UE may then acquire 1-bit half-frame indication information c0. When a carrier frequency is 3 GHz or below, the half-frame indication information may be signaled implicitly by a PBCH DMRS. The PBCH DMRS uses one of 8 PBCH DMRS sequences to indicate 3-bit information. Therefore, when L=4, the remaining one bit except for bits indicating an SSB index among 3 bits that may be indicated by the 8 PBCH DMRS sequences may be used as a half-frame indication. 
     Finally, the UE may acquire an SSB index based on the DMRS sequence and PBCH payload. SSB candidates are indexed with 0 to L−1 in time order in an SSB burst set (i.e., half-frame). When L=8 or L=64, three least significant bits (LSBs) b0, b1 and b2 of an SSB index may be indicated by 8 different PBCH DMRS sequences. When L=64, three most significant bits (MSBs) b3, b4 and b5 of the SSB index are indicated by the PBCH. When L=2, two LSBs b0 and b1 of the SSB index may be indicated by 4 different PBCH DMRS sequences. When L=4, the remaining one bit b2 except for the bits indicating the SSB index among the three bits may be used as a half-frame indication. 
     System Information Acquisition 
       FIG.  9    illustrates a system information (SI) acquisition procedure. The UE may acquire access stratum (AS)-/non-access stratum (NAS)-information in the SI acquisition procedure. The SI acquisition procedure may be applied to UEs in RRC_IDLE, RRC_INACTIVE, and RRC_CONNECTED states. 
     SI is divided into a master information block (MIB) and a plurality of system information blocks (SIBs). The MIB and the plurality of SIBs are further divided into minimum SI and other SI. The minimum SI may include the MIB and systemInformationBlock1 (SIB1), carrying basic information required for initial access and information required to acquire the other SI. SIB1 may also be referred to as remaining minimum system information (RMSI). For details, the following may be referred to.
         The MIB includes information/parameters related to reception of SIB1 and is transmitted on the PBCH of an SSB. The UE assumes that a half-frame including an SSB is repeated every 20 ms during initial cell selection. The UE may determine from the MIB whether there is any control resource set (CORESET) for a Type0-PDCCH common search space. The Type0-PDCCH common search space is a kind of PDCCH search space and used to transmit a PDCCH that schedules an SI message. In the presence of a Type0-PDCCH common search space, the UE may determine (1) a plurality of contiguous RBs and one or more consecutive symbols included in a CORESET, and (ii) a PDCCH occasion (e.g., a time-domain position at which a PDCCH is to be received), based on information (e.g., pdcch-ConfigSIB1) included in the MIB. In the absence of a Type0-PDCCH common search space, pdcch-ConfigSIB1 provides information about a frequency position at which the SSB/SIB1 exists and information about a frequency range without any SSB/SIB1.   SIB1 includes information related to availability and scheduling (e.g., a transmission periodicity and an SI-window size) of the remaining SIB s (hereinafter, referred to as SIBx where x is an integer equal to or larger than 2). For example, SIB1 may indicate whether SIBx is broadcast periodically or in an on-demand manner upon UE request. If SIBx is provided in the on-demand manner, SIB1 may include information required for the UE to transmit an SI request. A PDCCH that schedules SIB1 is transmitted in the Type0-PDCCH common search space, and SIB1 is transmitted on a PDSCH indicated by the PDCCH.   SIBx is included in an SI message and transmitted on a PDSCH. Each SI message is transmitted within a periodic time window (i.e., SI-window).       

     Beam Alignment 
       FIG.  10    illustrates exemplary multi-beam transmission of SSBs. 
     Beam sweeping refers to changing the beam (direction) of a wireless signal over time at a transmission reception point (TRP) (e.g., a BS/cell) (hereinafter, the terms beam and beam direction are interchangeably used). An SSB may be transmitted periodically by beam sweeping. In this case, SSB indexes are implicitly linked to SSB beams. An SSB beam may be changed on an SSB (index) basis or on an SS (index) group basis. In the latter, the same SSB beam is maintained in an SSB (index) group. That is, the transmission beam direction of an SSB is repeated for a plurality of successive SSBs. The maximum allowed transmission number L of an SSB in an SSB burst set is 4, 8 or 64 according to the frequency band of a carrier. Accordingly, the maximum number of SSB beams in the SSB burst set may be given according to the frequency band of a carrier as follows.
         For frequency range of up to 3 GHz, maximum number of beams=4   For frequency range from 3 GHz to 6 GHz, maximum number of beams=8   For frequency range from 6 GHz to 52.6 GHz, maximum number of beams=64   Without multi-beam transmission, the number of SSB beams is 1.       

     When the UE attempts initial access to the BS, the UE may align beams with the BS based on an SSB. For example, the UE performs SSB detection and then identifies a best SSB. Subsequently, the UE may transmit an RACH preamble in PRACH resources linked/corresponding to the index (i.e., beam) of the best SSB. The SSB may also be used for beam alignment between the BS and the UE even after the initial access. 
     Channel Measurement and Rate Matching 
       FIG.  11    illustrates an exemplary method of indicating actually transmitted SSB s, SSB_tx. 
     Up to L SSBs may be transmitted in an SSB burst set, and the number and positions of actually transmitted SSBs may be different for each BS or cell. The number and positions of actually transmitted SSBs are used for rate-matching and measurement, and information about actually transmitted SSBs is indicated as follows.
         If the information is related to rate matching, the information may be indicated by UE-specific RRC signaling or RMSI. The UE-specific RRC signaling includes a full bitmap (e.g., of length L) for frequency ranges below and above 6 GHz. The RMSI includes a full bitmap for a frequency range below 6 GHz and a compressed bitmap for a frequency range above 6 GHz, as illustrated in  FIG.  11   . Specifically, the information about actually transmitted SSBs may be indicated by a group-bitmap (8 bits)+an in-group bitmap (8 bits). Resources (e.g., REs) indicated by the UE-specific RRC signaling or the RMSI may be reserved for SSB transmission, and a PDSCH and/or a PUSCH may be rate-matched in consideration of the SSB resources.   If the information is related to measurement, the network (e.g., BS) may indicate an SSB set to be measured within a measurement period, when the UE is in RRC connected mode. The SSB set may be indicated for each frequency layer. Without an indication of an SSB set, a default SSB set is used. The default SSB set includes all SSBs within the measurement period. An SSB set may be indicated by a full bitmap (e.g., of length L) in RRC signaling. When the UE is in RRC idle mode, the default SSB set is used.       

     Random Access (or RACH) Procedure 
     4-Step RACH Procedure: Type-1 Random Access Procedure 
       FIGS.  12 A and  12 B  are diagrams illustrating an exemplary 4-step RACH procedure to which various embodiments of the present disclosure are applicable. 
     When a (contention-based) RACH procedure is performed in four steps (4-step RACH procedure), the UE may transmit a message (Message 1 (Msg 1)) including a preamble related to a specific sequence on a PRACH ( 1201 ) and receive a PDCCH and an RAR message (Message 2 (Msg 2)) on a PDSCH corresponding to the PDCCH in response to the preamble ( 1203 ). The UE may transmit a message (Message 3 (Msg 3)) including a PUSCH by using scheduling information included in the RAR ( 1205 ) and perform a contention resolution procedure such as reception of a PDCCH signal and a PDSCH signal corresponding to the PDCCH signal. The UE may receive a message (Message 4 (Msg 4)) including contention resolution information for the contention resolution procedure from the BS ( 1207 ). 
     The 4-step RACH procedure of the UE may be summarized in Table 5 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Type of Signals 
                 Operations/Information obtained 
               
               
                   
               
             
            
               
                 1 st  step 
                 PRACH 
                 * Initial beam acquisition 
               
               
                   
                 preamble in UL 
                 * Random election of RA-preamble ID 
               
               
                 2 nd  Step 
                 Random Access  
                 * Timing alignment information 
               
               
                   
                 Response on  
                 * RA-preamble ID 
               
               
                   
                 DL-SCH 
                 * initial UL grant, Temporary C-RNTI 
               
               
                 3 rd  Step 
                 UL transmission on  
                 * RRC connection request 
               
               
                   
                 UL-SCH 
                 * UE identifier 
               
               
                 4 th  Step 
                 Contention  
                 * Temporary C-RNI on PDCCH for initial 
               
               
                   
                 Resolution 
                 access 
               
               
                   
                 on DL 
                 * C-RNTI on PDCCH for UE in 
               
               
                   
                   
                 RRC_CONNECTED 
               
               
                   
               
            
           
         
       
     
     First, the UE may transmit an RACH preamble as Msg 1 on a PRACH in an RACH procedure. 
     Random access preamble sequences of two different lengths are supported. The length 839 of the longer sequence is applied to the SCSs of 1.25 kHz and 5 kHz, whereas the length 139 of the shorter sequence is applied to the SCSs of 15 kHz, 30 kHz, 60 kHz, and 120 kHz. 
     Multiple preamble formats are defined by one or more RACH OFDM symbols and different CPs (and/or guard times). An RACH configuration for a cell is provided in system information of the cell to the UE. The RACH configuration includes information about a PRACH SCS, available preambles, and a preamble format. The RACH configuration includes information about associations between SSBs and RACH (time-frequency) resources. The UE transmits an RACH preamble in RACH time-frequency resources associated with a detected or selected SSB. 
     An SSB threshold for RACH resource association may be configured by the network, and an RACH preamble is transmitted or retransmitted based on an SSB having a reference signal received power (RSRP) measurement satisfying the threshold. For example, the UE may select one of SSBs satisfying the threshold, and transmit or retransmit an RACH preamble in RACH resources associated with the selected SSB. 
     Upon receipt of the RACH preamble from the UE, the BS transmits an RAR message (Msg 2) to the UE. A PDCCH that schedules a PDSCH carrying the RAR is cyclic redundancy check (CRC)-masked by a random access radio network temporary identifier (RA-RNTI) and transmitted. Upon detection of the PDCCH masked by the RA-RNTI, the UE may receive an RAR on a PDSCH scheduled by DCI carried on the PDCCH. The UE determines whether the RAR includes RAR information for its transmitted preamble, that is, Msg 1. The UE may make the determination by checking the presence or absence of the RACH preamble ID of its transmitted preamble in the RAR. In the absence of the response to Msg 1, the UE may retransmit the RACH preamble a predetermined number of or fewer times, while performing power ramping. The UE calculates PRACH transmission power for a preamble retransmission based on the latest path loss and a power ramping counter. 
     The RAR information may include the preamble sequence transmitted by the UE, a cell RNTI (C-RNTI) that the BS has allocated to the UE attempting random access, UL transmit time alignment information, UL transmission power adjustment information, and UL radio resource allocation information. Upon receipt of its RAR information on the PDSCH, the UE may acquire time advance information for UL synchronization, an initial UL grant, and a temporary C-RNTI. The timing advance information is used to control a UL signal transmission timing. To align a PUSCH and/or PUCCH transmission of the UE with a subframe timing of a network end, the network (e.g., the BS) may measure the time difference between PUSCH, PUCCH, or SRS reception and a subframe and transmit the timing advance information based on the time difference. The UE may transmit a UL signal as Msg 3 of the RACH procedure on a UL-SCH based on the RAR information. Msg 3 may include an RRC connection request and a UE ID. The network may transmit Msg 4 in response to Msg 3. Msg 4 may be handled as a contention resolution message on DL. As the UE receives Msg 4, the UE may enter the RRC_CONNECTED state. 
     As described before, the UL grant included in the RAR schedules a PUSCH transmission for the UE. A PUSCH carrying an initial UL transmission based on the UL grant of the RAR is referred to as an Msg 3 PUSCH. The contents of the RAR UL grant start from the MSB and ends in the LSB, given as Table 6. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                   
                 Number of 
               
               
                   
                 RAR UL grant field 
                 bits 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Frequency hopping flag 
                 1 
               
               
                   
                 Msg3 PUSCH frequency resource 
                 12 
               
               
                   
                 allocation 
                   
               
               
                   
                 Msg3 PUSCH time resource allocation 
                 4 
               
               
                   
                 Modulation and coding scheme (MCS) 
                 4 
               
               
                   
                 Transmit power control (TPC) for 
                 3 
               
               
                   
                 Msg3 PCSCH 
                   
               
               
                   
                 CSI request 
                 1 
               
               
                   
                   
               
            
           
         
       
     
     The transmit power control (TPC) command is used to determine the transmission power of the Msg 3 PUSCH. For example, the TPC command is interpreted according to Table 7. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 TPC command 
                 value [dB] 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0 
                 −6 
               
               
                   
                 1 
                 −4 
               
               
                   
                 2 
                 −2 
               
               
                   
                 3 
                 0 
               
               
                   
                 4 
                 2 
               
               
                   
                 5 
                 4 
               
               
                   
                 6 
                 6 
               
               
                   
                 7 
                 8 
               
               
                   
                   
               
            
           
         
       
     
     2-Step RACH Procedure: Type-2 Random Access Procedure 
       FIG.  13    is a diagram illustrating an exemplary 2-step RACH procedure to which various embodiments of the present disclosure are applicable. 
     A (contention-based) RACH procedure performed in two steps, that is, a 2-step RACH procedure has been proposed to simplify the RACH procedure and thus achieve low signaling overhead and low latency. 
     In the 2-step RACH procedure, the operation of transmitting Msg 1 and the operation of transmitting Msg 3 in the 4-step RACH procedure may be incorporated into an operation of transmitting one message, Message A (Msg A) including a PRACH and a PUSCH by the UE. The operation of transmitting Msg 2 by the BS and the operation of transmitting Msg 4 by the BS in the 4-step RACH procedure may be incorporated into an operation of transmitting one message, Message B (Msg B) including an RAR and contention resolution information. 
     That is, in the 2-step RACH procedure, the UE may combine Msg 1 and Msg 3 of the 4-step RACH procedure into one message (e.g., Msg A) and transmit the message to the BS ( 1301 ). 
     Further, in the 2-step RACH procedure, the BS may combine Msg 2 and Msg 4 of the 4-step RACH procedure into one message (e.g., Msg B) and transmit the message to the UE ( 1303 ). 
     The 2-step RACH procedure may become a low-latency RACH procedure based on the combinations of these messages. 
     More specifically, Msg A may include a PRACH preamble included in Msg 1 and data included in Msg 3 in the 2-step RACH procedure. In the 2-step RACH procedure, Msg B may include an RAR included in Msg 2 and contention resolution information included in Msg 4. 
     Contention-Free RACH Procedure 
       FIG.  14    is a diagram illustrating an exemplary contention-free RACH procedure to which various embodiments of the present disclosure are applicable. 
     The contention-free RACH procedure may be used for handover of the UE to another cell or BS or may be performed when requested by a BS command. The contention-free RACH procedure is basically similar to the contention-based RACH procedure. However, compared to the contention-based RACH procedure in which a preamble to be used is randomly selected from among a plurality of RACH preambles, a preamble to be used by the UE (referred to as a dedicated RACH preamble) is assigned to the UE by the BS in the contention-free RACH procedure ( 1401 ). Information about the dedicated RACH preamble may be included in an RRC message (e.g., a handover command) or provided to the UE by a PDCCH order. When the RACH procedure starts, the UE transmits the dedicated RACH preamble to the BS ( 1403 ). When the UE receives an RAR from the BS, the RACH procedure is completed ( 1405 ). 
     In the contention-free RACH procedure, a CSI request field in an RAR UL grant indicates whether the UE is to include an aperiodic CSI report in a corresponding PUSCH transmission. An SCS for Msg 3 PUSCH transmission is provided by an RRC parameter. The UE may transmit the PRACH and the Msg 3 PUSCH on the same UL carrier of the same serving cell. A UL BWP for the Msg 3 PUSCH transmission is indicated by SIB  1 . 
     Bandwidth Part (BWP) 
     In the NR system, up to 400 MHz per carrier may be supported. When a UE operating in such a wideband carrier always operates with a radio frequency (RF) module for the entire carrier turned on, battery consumption of the UE may increase. Alternatively, considering various use cases (e.g., eMBB, URLLC, mMTC, and so on) operating within a single wideband carrier, a different numerology (e.g., SCS) may be supported for each frequency band within the carrier. Alternatively, each UE may have a different maximum bandwidth capability. In this regard, the BS may indicate to the UE to operate only in a partial bandwidth instead of the total bandwidth of the wideband carrier. The partial bandwidth may be defined as a BWP. A BWP is a subset of contiguous common RBs defined for numerology ui in BWP i on the carrier, and one numerology (e.g., SCS, CP length, or slot or 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, when UEs are concentrated on a specific BWP, the BS may configure another BWP for some of the UEs, for load balancing. Alternatively, the BS may exclude some spectrum of the total bandwidth and configure both-side BWPs of the cell in the same slot in consideration of frequency-domain inter-cell interference cancellation between neighboring cells. That is, the BS may configure at least one DL/UL BWP for a UE associated with the wideband carrier, activate at least one of DL/UL BWP(s) configured at a specific time point (by L1 signaling being a physical-layer control signal, a MAC control element (CE) being a MAC-layer control signal, or RRC signaling), or set a timer value and switch the UE to a predetermined DL/UL BWP, upon expiration of the timer. To indicate switching to another configured DL/UL BWP, DCI format 1_1 or DCI format 0_1 may be used. The activated DL/UL BWP may be referred to as an active DL/UL BWP. During initial access or before an RRC connection setup, the UE may not receive a configuration for a DL/UL BWP from the BS. A DL/UL BWP that the UE assumes in this situation is defined as an initial active DL/UL BWP. 
     A DL BWP is a BWP in which a DL signal such as a PDCCH and/or a PDSCH is transmitted and received, whereas a UL BWP is a BWP in which a UL signal such as a PUCCH and/or a PUSCH is transmitted and received. 
     In the NR system, a DL channel and/or a DL signal may be transmitted and received in an active DL BWP. Further, a UL channel and/or a UL signal may be transmitted and received in an active UL BWP. 
     DL Channel Structures 
     A BS transmits related signals on later-described DL channels to a UE, and the UE receives the related signals on the DL channels from the BS. 
     (1) Physical Downlink Shared Channel (PDSCH) 
     The PDSCH delivers DL data (e.g., a DL-SCH TB) and adopts a modulation scheme such as quadrature phase shift keying (QPSK), 16-ary quadrature amplitude modulation (16 QAM), 64-ary QAM (64 QAM), or 256-ary QAM (256 QAM). A TB is encoded to a codeword. The PDSCH may deliver up to two codewords. The codewords are individually subjected to scrambling and modulation mapping, and modulation symbols from each codeword are mapped to one or more layers. An OFDM signal is generated by mapping each layer together with a DMRS to resources, and transmitted through a corresponding antenna port. 
     (2) Physical Downlink Control Channel (PDCCH) 
     The PDCCH delivers DCI and adopts QPSK as a modulation scheme. One PDCCH includes 1, 2, 4, 8, or 16 control channel elements (CCEs) according to its aggregation level (AL). One CCE includes 6 resource element groups (REGs), each REG being defined by one OFDM symbol by one (P)RB). 
       FIG.  15    illustrates an exemplary structure of one REG. In  FIG.  15   , D represents an RE to which DCI is mapped, and R represents an RE to which a DMRS is mapped. The DMRS is mapped to RE #1, RE #5, and RE #9 along the frequency direction in one symbol. 
     The PDCCH is transmitted in a CORESET. A CORESET is defined as a set of REGs with a given numerology (e.g., an SCS, a CP length, or the like). A plurality of CORESETs for one UE may overlap with each other in the time/frequency domain. A CORESET may be configured by system information (e.g., an MIB) or UE-specific higher-layer signaling (e.g., RRC signaling). Specifically, the number of RBs and the number of symbols (3 at maximum) in the CORESET may be configured by higher-layer signaling. 
     For each CORESET, a precoder granularity in the frequency domain is set to one of the followings by higher-layer signaling:
         sameAsREG-bundle: It equals to an REG bundle size in the frequency domain.   allContiguousRBs: It equals to the number of contiguous RBs in the frequency domain within the CORESET.       

     The REGs of the CORESET are numbered in a time-first mapping manner. That is, the REGs are sequentially numbered in an ascending order, starting from 0 for the first OFDM symbol of the lowest-numbered RB in the CORESET. 
     CCE-to-REG mapping for the CORESET may be an interleaved type or a non-interleaved type.  FIG.  16 A  is a diagram illustrating non-interleaved CCE-REG mapping, and  FIG.  16 B  is a diagram illustrating interleaved CCE-REG mapping.
         Non-interleaved CCE-to-REG mapping (or localized CCE-to-REG mapping): 6 REGs for a given CCE are grouped into one REG bundle, and all of the REGs for the given CCE are contiguous. One REG bundle corresponds to one CCE.   Interleaved CCE-to-REG mapping (or distributed CCE-to-REG mapping): 2, 3 or 6 REGs for a given CCE are grouped into one REG bundle, and the REG bundle is interleaved in the CORESET. In a CORESET including one or two OFDM symbols, an REG bundle includes 2 or 6 REGs, and in a CORESET including three OFDM symbols, an REG bundle includes 3 or 6 REGs. An REG bundle size is configured on a CORESET basis.       

       FIG.  17    illustrates an exemplary block interleaver. For the above interleaving operation, the number A of rows in a (block) interleaver is set to one or 2, 3, and 6. When the number of interleaving units for a given CORESET is P, the number of columns in the block interleaver is P/A. In the block interleaver, a write operation is performed in a row-first direction, and a read operation is performed in a column-first direction, as illustrated in  FIG.  17   . Cyclic shift (CS) of an interleaving unit is applied based on an ID which is configurable independently of a configurable ID for the DMRS. 
     The UE acquires DCI delivered on a PDCCH by decoding (so-called blind decoding) a set of PDCCH candidates. A set of PDCCH candidates decoded by a UE are defined as a PDCCH search space set. A search space set may be a common search space or a UE-specific search space. The UE may acquire DCI by monitoring PDCCH candidates in one or more search space sets configured by an MIB or higher-layer signaling. Each CORESET configuration is associated with one or more search space sets, and each search space set is associated with one CORESET configuration. One search space set is determined based on the following parameters.
         controlResourceSetId: A set of control resources related to the search space set.   monitoringSlotPeriodicityAndOffset: A PDCCH monitoring periodicity (in slots) and a PDCCH monitoring offset (in slots).   monitoringSymbolsWithinSlot: A PDCCH monitoring pattern (e.g., the first symbol(s) in the CORESET) in a PDCCH monitoring slot.   nrofCandidates: The number of PDCCH candidates (one of 0, 1, 2, 3, 4, 5, 6, and 8) for each AL={1, 2, 4, 8, 16}.       

     Table 8 lists features of the respective search space types. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 8 
               
               
                   
               
               
                   
                 Search 
                   
                   
               
               
                 Type 
                 Space 
                 RNTI 
                 Use Case 
               
               
                   
               
             
            
               
                 Type0- 
                 Common 
                 SI-RNTI on a primary cell 
                 SIB Decoding 
               
               
                 PDCCH 
                   
                   
                   
               
               
                 Type0A- 
                 Common 
                 SI-RNTI on a primary cell 
                 SIB Decoding 
               
               
                 PDCCH 
                   
                   
                   
               
               
                 Type1- 
                 Common 
                 RA-RNTI or TC-RNTI  
                 Msg 2, Msg 4 
               
               
                 PDCCH 
                   
                 on a primary cell 
                 decoding in 
               
               
                   
                   
                   
                 RACH 
               
               
                 Type2- 
                 Common 
                 P-RNTI on a primary cell 
                 Paging  
               
               
                 PDCCH 
                   
                   
                 Decoding 
               
               
                 Type3- 
                 Common 
                 INT-RNTI, SFI-RNTI, TPC- 
                   
               
               
                 PDCCH 
                   
                 PUSCH-RNTI, TPC-PUCCH-RNTI, 
                   
               
               
                   
                   
                 TPC-SRS-RNTI, C-RNTI, MCS-C- 
                   
               
               
                   
                   
                 RNTI, or CS-RNTI(s) 
                   
               
               
                   
                 UE 
                 C-RNTI, or MCS-C-RNTI, or CS- 
                 User specific 
               
               
                   
                 Specific 
                 RNTI(s) 
                 PDSCH 
               
               
                   
                   
                   
                 decoding 
               
               
                   
               
            
           
         
       
     
     Table 9 lists exemplary DCI formats transmitted on the PDCCH. 
     
       
         
           
               
               
             
               
                 TABLE 9 
               
               
                   
               
               
                 DCI format 
                 Usage 
               
               
                   
               
             
            
               
                 0_0 
                 Scheduling of PUSCH in one cell 
               
               
                 0_1 
                 Scheduling of PUSCH in one cell 
               
               
                 1_0 
                 Scheduling of PDSCH in one cell 
               
               
                 1_1 
                 Scheduling of PDSCH in one cell 
               
               
                 2_0 
                 Notifying a group of UEs of the slot format 
               
               
                 2_1 
                 Notifying a group of UEs of the PRB(s) and OFDM symbol(s) 
               
               
                   
                 where UE may assume no transmission is intended for the UE 
               
               
                 2_2 
                 Transmission of TPC commands for PUCCH and PUSCH 
               
               
                 2_3 
                 Transmission of a group of TPC commands for SRS transmissions 
               
               
                   
                 by one or more UEs 
               
               
                   
               
            
           
         
       
     
     DCI format 0_0 may be used to schedule a TB-based (or TB-level) PUSCH, and DCI format 0_1 may be used to schedule a TB-based (or TB-level) PUSCH or a code block group (CBG)-based (or CBG-level) PUSCH. DCI format 1_0 may be used to schedule a TB-based (or TB-level) PDSCH, and DCI format 1_1 may be used to schedule a TB-based (or TB-level) PDSCH or a CBG-based (or CBG-level) PDSCH. DCI format 2_0 is used to deliver dynamic slot format information (e.g., a dynamic slot format indicator (SFI)) to a UE, and DCI format 2_1 is used to deliver DL pre-emption information to a UE. DCI format 2_0 and/or DCI format 2_1 may be delivered to a corresponding group of UEs on a group common PDCCH which is a PDCCH directed to a group of UEs. 
     Discontinuous Reception (DRX) Operation 
     While the UE performs the above-described/proposed procedures and/or methods, the UE may perform the DRX operation. The UE for which DRX is configured may reduce power consumption by discontinuously receiving a DL signal. DRX may be performed in a radio resource control (RRC)_IDLE state, an RRC_INACTIVE state, or an RRC_CONNECTED state. DRX in the RRC_IDLE state and the RRC_INACTIVE state is used to discontinuously receive a paging signal. Hereinafter, DRX performed in the RRC_CONNECTED state will be described (RRC_CONNECTED DRX). 
       FIG.  18    illustrates a DRX cycle (RRC_CONNECTED state). 
     Referring to  FIG.  18   , the DRX cycle includes an On-duration and an opportunity for DRX. The DRX cycle defines a time interval at which the On-duration is cyclically repeated. The On-Duration indicates a time duration that the UE monitors to receive a PDCCH. If DRX is configured, the UE performs PDCCH monitoring during the On-duration. If the PDCCH is successfully detected during PDCCH monitoring, the UE operates an inactivity timer and maintains an awoken state. On the other hand, if there is no PDCCH which has been successfully detected during PDCCH monitoring, the UE enters a sleep state after the On-duration is ended. Therefore, when DRX is configured, the UE may discontinuously perform PDCCH monitoring/reception in the time domain upon performing the above-described/proposed procedures and/or methods. For example, when DRX is configured, a PDCCH reception occasion (e.g., a slot having a PDCCH search space) in the present disclosure may be discontinuously configured according to DRX configuration. When DRX is not configured, PDCCH monitoring/reception may be continuously performed in the time domain. For example, when DRX is not configured, the PDCCH reception occasion (e.g., the slot having the PDCCH search space) in the present disclosure may be continuously configured. Meanwhile, PDCCH monitoring may be restricted in a time duration configured as a measurement gap regardless of whether DRX is configured or not. 
     Table 10 illustrates a UE procedure related to DRX (RRC_CONNECTED state). Referring to Table 10, DRX configuration information is received through higher-layer (e.g., RRC) signaling. Whether DRX is ON or OFF is controlled by a DRX command of a MAC layer. If DRX is configured, the UE may discontinuously perform PDCCH monitoring in the above-described/proposed procedures and/or methods in the present disclosure, as illustrated in  FIG.  18   . 
     
       
         
           
               
               
               
             
               
                 TABLE 10 
               
               
                   
               
               
                   
                 Type of signals 
                 UE procedure 
               
               
                   
               
             
            
               
                 1 st  step 
                 RRC signalling 
                 Receive DRX configuration 
               
               
                   
                 (MAC- 
                 information 
               
               
                   
                 CellGroupConfig) 
                   
               
               
                 2 nd  Step 
                 MAC CE 
                 Receive DRX command 
               
               
                   
                 ((Long) DRX 
                   
               
               
                   
                 command MAC 
                   
               
               
                   
                 CE) 
                   
               
               
                 3 rd  Step 
                 — 
                 Monitor a PDCCH during an  
               
               
                   
                   
                 on-duration of a DRX cycle 
               
               
                   
               
            
           
         
       
     
     Herein, MAC-CellGroupConfig includes configuration information needed to configure a MAC parameter for a cell group. MAC-CellGroupConfig may also include configuration information regarding DRX. For example, MAC-CellGroupConfig may include information for defining DRX as follows.
         Value of drx-OnDurationTimer: defines the length of the starting duration of a DRX cycle.   Value of drx-InactivityTimer: defines the length of the starting duration in which the UE is in an awoken state, after a PDCCH occasion in which a PDCCH indicating initial UL or DL data is detected.   Value of drx-HARQ-RTT-TimerDL: defines the length of a maximum time duration until a DL retransmission is received, after an DL initial transmission is received.   Value of drx-HARQ-RTT-TimerDL: defines the length of a maximum time duration until a grant for UL retransmission is received, after a grant for UL initial transmission is received.   drx-LongCycleStartOffset: defines the time length and starting time of a DRX cycle   drx-ShortCycle (optional): defines the time length of a short DRX cycle.       

     Herein, if any one of drx-OnDurationTimer, drx-InactivityTimer, drx-HARQ-RTT-TimerDL, and drx-HARQ-RTT-TimerDL is running, the UE performs PDCCH monitoring in every PDCCH occasion while maintaining the awoken state. 
     Before a detailed description, implementation examples of operations of a UE and a BS according to an embodiment of the present disclosure will be described below with reference to  FIGS.  19  and  20   . 
       FIG.  19    is a diagram illustrating an implementation example of an operation of a UE according to the present disclosure. Referring to  FIG.  19   , the UE may transmit Msg A including a PRACH and PUSCH to a BS (S 1901 ). The UE may then receive Msg B related to contention resolution from the BS in response to Msg A (S 1903 ). A specific method of performing an RACH procedure by the UE in steps S 1901  and S 1903  may be based on the later-described embodiments and features. 
     The UE illustrated in  FIG.  19    may be one of various wireless devices illustrated in  FIGS.  25  to  28   . For example, the UE of  FIG.  19    may be a first wireless device  100  illustrated in  FIG.  25    or a wireless device  100  or  200  illustrated in  FIG.  26   . In other words, the operation of  FIG.  19    may be performed by one of the various wireless devices illustrated in  FIGS.  25  to  28   . 
       FIG.  20    is a diagram illustrating an implementation example of an operation of a BS according to the present disclosure. Referring to  FIG.  20   , the BS may receive Msg A including a PRACH and PUSCH from a UE (S 2001 ). The BS may then transmit Msg B related to contention resolution to the UE in response to Msg A (S 2003 ). A specific method of performing an RACH procedure by the BS in steps S 2001  and S 2003  may be based on the later-described embodiments and features. 
     The BS illustrated in  FIG.  20    may be one of various wireless devices illustrated in  FIGS.  25  to  28   . For example, the BS of  FIG.  20    may be a second wireless device  200  illustrated in  FIG.  25    or the wireless device  100  or  200  illustrated in  FIG.  26   . In other words, the operation of  FIG.  20    may be performed by one of the various wireless devices illustrated in  FIGS.  25  to  28   . 
     In the LTE and/or NR system, a UE may perform a UL transmission by an RACH procedure without being scheduled for the UL transmission directly by a given BS or cell. From the perspective of the UE, the RACH procedure in the LTE and/or NR system is a 4-step procedure including 1) random access preamble transmission, 2) reception of Msg 2 corresponding to an RAR, 3) transmission of Msg 3 including a PUSCH, and 4) reception of Msg 4 including contention resolution information. 
     Msg 2 is a message by which the BS allocates UL resources to be used for transmission of Msg 3 from the UE which has transmitted a preamble, upon receipt of the preamble. The UE may transmit its identification information such as an IMSI or a TMSI and information about a connection request by Msg 3. Upon receipt of Msg 3, the BS transmits the identification information of the UE and information required for random access in Msg 4, thereby preventing collision between different UEs during the RACH procedure and completing the RACH procedure for the UE. 
     Compared to legacy LTE and NR Rel-15 in which the RACH procedure is performed in four steps as described above, the 2-step RACH procedure is under study to reduce the processing delay of the 4-step RACH procedure and use the RACH procedure even in a small cell or an unlicensed bandwidth in the newly introduced NR Rel-6. The 2-step RACH procedure does not include the step of transmitting Msg 3 and the step of transmitting Msg 4 including a contention resolution message. Instead, the UE transmits both a message corresponding to Msg 3 and a preamble as Msg A to the BS in the first step of the RACH procedure, and the BS transmits both a message corresponding to Msg 4 and an RAR as Msg B in response to Msg A to the UE. Upon receipt of Msg B, the UE completes the RACH procedure by decoding Msg B and then performs data transmission and reception. 
     Before embodiments of the present disclosure are described, resources used for transmission of Msg A including a preamble and a PUSCH, that is, an RACH occasion (RO) and a PUSCH occasion (PO) will be described in brief. 
     The UE transmits a preamble in an RO associated with a beam satisfying an RSRP threshold among candidate beams transmitted to the BS. For example, when a plurality of beams have RSRPs exceeding a pre-indicated RSRP threshold among indicated candidate beams, the UE selects a beam having the largest RSRP or randomly selects a beam from among the plurality of beams and transmits the preamble in an RO associated with the selected beam. 
     An Msg A PUSCH and an Msg A PRACH may be transmitted successively with or without a predetermined gap between them in the time domain. Alternatively, the Msg A PUSCH and the Msg A PRACH may be transmitted simultaneously in frequency time multiplexing (FDM). A PO carrying the Msg A PUSCH may be associated with the RO carrying the preamble. For example, POs may be mapped to a plurality of ROs configured for the UE in a one-to-one or one-to-multi correspondence. In another example, total preambles allocated to the ROs may be divided into a plurality of sub-groups and POs may be mapped to the sub-groups by applying a predetermined time or frequency offset to each sub-group. The number of sub-groups may vary according to a situation or may be fixed. The number of sub-groups may be used in one-to-one mapping between sub-grouped preambles and POs in a table. A time offset may be understood as an offset in symbols, slots, or subframes from the last symbol of an RO, indicating the starting time of a PO. The position of the PO indicated by the offset may be set in available UL resources after the offset among resources indicated by DL/UL configurations. Further, a frequency offset may indicate the starting point of the PO on the frequency axis from a subcarrier with the lowest or highest index among subcarriers or RBs of the RO. 
     In the present disclosure, when a UE transmits a preamble and a PUSCH in Msg A based on an RO and a PO configured in the above manner, configuration of a maximum allowed transmission number and a counter for Msg A will be described below. 
     Maximum Allowed Transmission Number of Msg A 
     An RACH configuration transmitted in system information includes information about the maximum allowed transmission number of Msg A. The UE attempts an RACH procedure until before the maximum allowed transmission number of Msg A indicated by the RACH configuration is reached. The maximum allowed transmission number of Msg A in the 2-step RACH procedure may be set in consideration of the maximum allowed transmission number of Msg 1 in the 4-step RACH procedure, and indicated in the following methods. 
     (1) The maximum allowed transmission number of Msg 1 is used as the maximum allowed transmission number of Msg A. 
     The maximum allowed transmission number of Msg 1 may be limited by a preambleTransMax parameter in the 4-step RACH procedure. In this method, the maximum allowed transmission number of the PRACH and/or the PUSCH of Msg A is also limited by the parameter. Accordingly, the BS may be burdened less with configuration of the transmission number of the message. However, because the PRACH and the PUSCH are transmitted together in Msg A in the 2-step RACH procedure, compared to Msg 1 in the 4-step RACH procedure, a larger maximum allowed transmission number set for Msg A may increase time/frequency resources and power consumption due to transmission failures and retransmissions. 
     (2) The maximum allowed transmission number of Msg A is configured separately. 
     In contrast to the method of still using the parameter indicating the maximum allowed transmission number of Msg 1 for Msg A, the maximum allowed transmission number of Msg A may be indicated by a separate parameter. In consideration of transmission of both the PRACH and the PUSCH in Msg A, a common maximum allowed transmission number may be configured for the PRACH and the PUSCH. Alternatively, a maximum allowed transmission number may be configured separately for each of the PRACH and the PUSCH depending on whether transmission (Tx) spatial filters or beams available for the PRACH and the PUSCH of Msg A are differently configured or whether transmission resources are efficiently used. 
     When a common maximum allowed transmission number is indicated for the PRACH and the PUSCH of Msg A, the maximum allowed transmission number of each of the PRACH and the PUSCH may be indicated by one parameter. The parameter is a separate parameter for Msg A of the 2-step RACH procedure, independent of the maximum allowed transmission number of Msg 1 of the 4-step RACH procedure. If the parameter indicating the maximum allowed transmission number of Msg A is not configured separately for the UE, the UE may be configured to use a maximum allowed transmission number indicated for Msg 1 of the 4-step RACH procedure. 
     If different maximum allowed transmission numbers are indicated for the PRACH and the PUSCH of Msg A, the maximum allowed transmission numbers may be indicated by separate parameters for the PRACH and the PUSCH. This method gives a consideration to use of different transmission spatial filters or beams for the PRACH and the PUSCH at the UE under circumstances, even though the PRACH and the PUSCH are successively transmitted in Msg A. 
     A method of using a retransmission power counter for Msg A according to each spatial filter or beam based on the method of indicating different maximum allowed transmission numbers for the PRACH and the PUSCH of Msg A will be described below. 
     Retransmission Power Counter for Msg A 
     As described above, when the UE is notified of the maximum allowed transmission number of Msg A and fails to receive a response signal such as Msg B or a response signal related to the UE from the BS after transmitting Msg A, the UE retransmits Msg A within the indicated maximum allowed transmission number. Although the transmission of Msg A involves transmissions of the PRACH and the PUSCH, the UE may configure different transmission spatial filters or beams for the PRACH and the PUSCH according to transmission channel environment estimation for each message. Accordingly, retransmission counters may be used independently for the PRACH and the PUSCH to retransmit Msg A. Particularly, a counter for setting the retransmission power of Msg A may be configured as follows. 
     (1) The same power counter value is applied to the Msg A PRACH and the Msg A PUSCH. 
     According to this method, a common counter is applied to the Msg A PRACH and the Msg A PUSCH. That is, the same counter value is set for the Msg A PRACH and the Msg A PUSCH during power ramping for a retransmission. A single maximum allowed number may be indicated for retransmission of Msg A, or a plurality of maximum allowed numbers may be indicated respectively for the Msg A PRACH and the Msg A PUSCH. The power ramping counter may be used in different manners in both cases. 
     1) When system information received by the UE indicates a single maximum allowed transmission number for retransmission of Msg A, the UE may retransmit Msg A until the single maximum allowed transmission number is reached. The power counter value is set to 1 at the initial transmission of Msg A. Basically, the power counter value is incremented by 1 or maintained at each subsequent retransmission according to whether a spatial filter or beam is changed for the retransmission. That is, when the transmission spatial filter or beam used for a current transmission of the Msg A PRACH is different from that used for a previous transmission of the Msg A PRACH due to a change in the channel environment, the power counter value is maintained equal. When the same transmission spatial filter or beam is used in the previous and current transmissions of the Msg A PRACH, the power counter value is incremented. That is, it may be indicated that when the UE changes the transmission spatial filter or beam before the transmission of the Msg A PRACH, the power counter value is to be maintained, and without this indication, the power counter value for the transmission of the Msg A PRACH may be incremented. 
     Herein, a single counter value is used for power ramping and set based on the transmission spatial filter or beam used for a transmission of the Msg A PRACH, with no regard to the transmission spatial filter of beam used for a transmission of the Msg A PUSCH. That is, the counter value may be incremented or maintained based on whether the transmission spatial filter or beam is unchanged for the Msg A PRACH transmission regardless of whether the transmission spatial filter or beam used for the current Msg A PUSCH transmission is identical to that used for the previous Msg A PRACH transmission or whether the transmission spatial filter or beam used for the Msg A PUSCH transmission is identical to that used for the previous attempted Msg A PUSCH transmission. The used counter value may be incremented until the maximum allowed transmission number received by the UE is reached. 
     2) When system information broadcast to the UE indicates a plurality of maximum allowed transmission numbers for retransmission of Msg A, the plurality of maximum allowed transmission numbers may be applied individually to the Msg A PRACH and the Msg A PUSCH. Because a single power counter value is used and thus incremented or maintained equally for transmissions of the Msg A PRACH and the Msg A PUSCH, the power counter value is maintained or incremented according to whether the same transmission spatial filter or beam as used for the previous Msg A PRACH transmission is used for the current Msg A PRACH transmission, as in the case of using a single maximum allowed transmission number. That is, when the transmission spatial filter or beam used for the previous Msg A PRACH transmission is identical to that to be used for the current Msg A PRACH transmission, the power counter value is incremented, whereas when the transmission spatial filter or beam used for the previous Msg A PRACH transmission is different from that to be used for the current Msg A PRACH transmission, the power counter value is maintained. Because the maximum allowed transmission numbers are set individually for the Msg A PRACH and the Msg A PUSCH, the used power counter value may be configured to increase until the larger or smaller of the two maximum allowed transmission numbers is reached. 
     (2) Power counter values are applied separately to the Msg A PRACH and the Msg A PUSCH. 
     When separate counter values are applied to the Msg A PRACH and the Msg A PUSCH, power counters may also be used differently depending on whether one or more maximum allowed transmission numbers are indicated for retransmission of Msg A from the UE. 
     1) First, a method of configuring a single maximum allowed transmission number for Msg A for the UE and applying power counter values individually to the Msg A PRACH and the Msg A PUSCH may be considered. When the transmission spatial filter or beam used for the current Msg A PRACH transmission is identical to that used for the Msg A PRACH transmission at the previous attempt, the power counter value used for the Msg A PRACH transmission is incremented, whereas when the transmission spatial filter or beam is changed, the power counter value is maintained. Likewise, when the transmission spatial filter or beam used for the current Msg A PUSCH transmission is identical to that used for the Msg A PUSCH transmission at the previous attempt, the power counter value used for the Msg A PUSCH transmission is incremented, whereas when the transmission spatial filter or beam is changed, the power counter value is maintained. 
     Due to the single maximum allowed transmission number for Msg A at the UE, the UE may be configured to attempt to retransmit Msg A in the 2-step RACH procedure until one or both of the power counter values for the Msg A PRACH and the Msg A PUSCH reach the single maximum allowed transmission number. In the case where either the power counter value for the Msg A PRACH or the power counter value for the Msg A PUSCH reaches the single maximum allowed transmission number, the UE performs no more retransmission regardless of the other power counter value. 
     2) In the case where a plurality of maximum allowed transmission numbers are configured for Msg A for the UE, both of a maximum allowed transmission number and a power counter value are configured for each of the Msg A PRACH and the Msg A PUSCH. Therefore, it is determined for each individual message whether the power counter value of the message reaches a maximum allowed transmission number. That is, the power counter value for each of the Msg A PRACH and the Msg A PUSCH is incremented or maintained depending on whether the same transmission spatial filter or beam is used in both of the previous and current transmissions of the message. 
     However, considering that the Msg A PRACH and the Msg A PUSCH are transmitted together in view of the transmission feature of Msg A in the 2-step RACH procedure, the UE uses one power counter value in setting power for an Msg A retransmission, although a maximum allowed transmission number is configured separately for each message. In other words, when the power counter value for one of the Msg A PRACH and the Msg A PUSCH reaches a reference maximum allowed transmission number which is the larger or smaller of the maximum allowed transmission numbers configured for the Msg A PRACH and the Msg A PUSCH, the UE does not retransmit Msg A. 
     Embodiment Related to Power Setting of Msg A 
     (1) Setting of maximum allowed transmission number for Msg A in 2-step RACH procedure 
     As described before, because the PRACH and the PUSCH are transmitted together in Msg A in the 2-step RACH procedure, compared to Msg 1 in the 4-step RACH procedure, a larger maximum allowed transmission number set for Msg A may increase time/frequency resources and power consumption due to transmission failures and retransmissions. To avert the problem, a method of indicating a maximum allowed transmission number for Msg A and a method of boosting the transmission power of Msg A by using an additional parameter will be described below. 
       FIG.  21    is a diagram illustrating an embodiment of the present disclosure related to a maximum allowed transmission number of Msg A. Basically, as the maximum allowed transmission number of Msg 1 may be limited by the preambleTransMax parameter in the 4-step RACH procedure, it should be considered that the maximum allowed transmission number of Msg A may also be limited. In the case where the maximum allowed transmission number of Msg A is set equal to the maximum allowed transmission number of Msg 1, if the maximum allowed transmission number is large, repeated retransmissions of Msg A may increase power consumption significantly until the maximum allowed transmission number is reached and hence result in inefficient resource utilization, considering that both the Msg A PRACH and the Msg A PUSCH are transmitted in Msg A. Accordingly, it may be appropriate to configure the maximum allowed transmission number of Msg A separately from the maximum allowed transmission number of Msg 1, for the 2-step RACH procedure. For example, as illustrated in  FIG.  21   , an Msg ATransMax parameter may be configured for the maximum allowed transmission number of Msg A, independently of the preambleTransMax parameter for the maximum allowed transmission number of Msg 1, and the value of Msg ATransMax may be set to be smaller than the value of preambleTransMax. 
     (2) An RACH occasion (RO) is shared. 
     If an RO is shared between Msg 1 of the 4-step RACH procedure and the Msg A PRACH of the 2-step RACH Procedure, the total number of attempts of initial access may have to be equal regardless of RACH procedure types in order to ensure fairness between the 4-step RACH procedure and the 2-step RACH procedure. That is, even though different maximum allowed transmission numbers are configured for Msg A and Msg 1, the total number of attempts may be equal for UEs attempting initial access in the same time/frequency resources regardless of RACH procedure types. If the maximum allowed transmission number of Msg A is different from the maximum allowed transmission number of Msg 1, the UE should attempt initial access according to one of the two values. 
     If the maximum allowed transmission number of Msg A is set to be smaller than the maximum allowed transmission number of Msg 1, the UE performs retransmissions of Msg A only until the maximum allowed transmission number of Msg A is reached and then transmits only the Msg A PRACH like Msg 1 of the 4-step RACH procedure, to match the sum of the total number of attempts of initial access. To increase the detection possibility of the message, the power counter value used for preamble transmission may be the power counter value increased according to the existing maximum allowed transmission number of Msg A. 
     For example, referring to  FIG.  21   , the UE retransmits Msg A as many times as the number indicated by the Msg ATransMax parameter indicating the maximum allowed transmission number of Msg A, and then transmits only the preamble as many times as the number indicated by the preambleTransMax parameter indicating the maximum allowed transmission number of Msg 1, without transmitting the Msg A PUSCH. In the step of transmitting only the preamble after as many repeated retransmissions of Msg A as a predetermined number, a power counter valued incremented according to the existing maximum allowed transmission number of Msg A may be maintained as the power counter value for the preamble in order to increase the detection possibility of the preamble. 
     (3) Setting of parameter for power boosting 
     To boost the transmission power of Msg A at the UE, a parameter serving as an indicator for boosting the transmission power of Msg A may be considered. If the same preamble target received power (PTRP) and/or the same ramping step size are configured for balancing detection possibilities between the 2-step RACH procedure and the 4-step RACH procedure, inefficiency may occur in view of use of more resources for transmission of Msg A including the PUSCH in the 2-step RACH procedure. 
     To solve the problem, besides setting of a different PTRP or ramping step size for the 2-step RACH procedure, a parameter such as Msg ATransMin indicating information about a transmission number threshold that leads to application of the same PTRP or ramping step size as for Msg 1 to Msg A transmission may be introduced. The parameter may be set to a value larger than 1 and less than the maximum allowed transmission number of Msg A. When (re)transmitting Msg A, the UE may apply a PTRP and/or ramping step size equal to that of Msg 1 for a transmission number equal to or less than the value of the parameter, and a PRTP and/or ramping step size different from that of Msg 1 for a transmission number larger than the value of the parameter. 
       FIG.  22    is a diagram illustrating an embodiment of the present disclosure related to power boosting of Msg A. In  FIG.  22   , when (re)transmitting Msg A, the UE may receive the Msg ATransMin parameter indicating an allowed transmission number for Msg A with the same PTRP and/or ramping step size as Msg 1. That is, when (re)transmitting Msg A, the UE allocates transmission power to Msg A by applying the existing PTRP and/or ramping step size set for Msg 1, for a transmission number equal to or less than the value indicated by Msg ATransMin. In contrast, the UE allocates transmission power to Msg A by applying a different PTRP and/or ramping step size from the existing PTRP and/or ramping step size set for Msg 1, for a transmission number larger than the value indicated by Msg ATransMin. 
       FIG.  23    is a diagram illustrating a signal flow for operations of a UE and a BS for performing the 2-step RACH procedure according to embodiments of the present disclosure. The UE and the BS transmit and receive RACH configuration information to perform the 2-step RACH procedure. The RACH configuration information may include information related to the embodiments of the present disclosure such as a power ramping step size and/or a ramping counter for setting transmission power, and a transmission beam or a spatial filter (S 2301 ). Specifically, the BS may transmit the RACH configuration information by an SSB and/or RRC signaling, such as an MIB and an SIB. 
     Step S 2301  may not be performed for a UE which has established a connection with the BS, such as a UE which has already received the RACH configuration information or a UE re-accessing the BS which has transmitted the RACH configuration information to the UE. Because Such a UE has already acquired the RACH configuration information, step S 2301  may be omitted to reduce a processing delay caused by redundant transmission and reception of the RACH configuration information. 
     In step S 2301 , the UE may be the wireless device  100  of  FIG.  25    or the wireless device  100  or  200  of  FIG.  26   , and the BS may be the second wireless device  200  of  FIG.  25    or the wireless device  100  or  200  of  FIG.  26   . That is, step S 2501  in which the UE receives the RACH configuration information may be performed by various wireless devices illustrated in  FIGS.  25  to  28    as described later. For example, when the UE is the wireless device  100  of  FIG.  25   , a processor  102  of  FIG.  25    may control one or more transceivers  106  and/or one or more memories  104  to receive the RACH configuration information, and the one or more transceivers  106  may receive the RACH configuration information from the BS. 
     Subsequently, the UE may acquire contents of Msg A based on the received RACH configuration, select an RO/preamble and a PO/PUSCH resource unit (PRU) based on the acquired information, and transmit Msg A to the BS to perform the 2-step RACH procedure (S 2303 ). The UE may transmit Msg A based on a configuration related to embodiments of the present disclosure, such as a ramping step size and/or a counter for setting transmission power, and a transmission beam or a spatial filter. 
     In step S 2303 , the UE may be the wireless device  100  of  FIG.  25    or the wireless device  100  or  200  of  FIG.  26   , and the BS may be the second wireless device  200  of  FIG.  25    or the wireless device  100  or  200  of  FIG.  26   . That is, step S 2303  in which the UE transmits Msg A to the BS may be performed by various wireless devices illustrated in  FIGS.  25  to  28    as described later. For example, when the UE is the wireless device  100  of  FIG.  25   , the processor  102  of FIG.  25  may control the one or more transceivers  106  and/or the one or more memories  104  to transmit Msg A, and the one or more transceivers  106  may transmit Msg A to the BS. 
     In an example of the transmission of Msg A in step S 2303 , an RO for the 2-step RACH procedure may be allocated in consideration of an RO allocated for the 4-step RACH procedure as follows. i) ROs and preambles may be configured independently for the 2-step RACH procedure and the 4-step RACH procedure, ii) the same RO may be shared between the 2-step RACH procedure and the 4-step RACH procedure, with preambles separately configured for the RACH procedures, or iii) the same RO and the same preamble may be shared between the 2-step RACH procedure and the 4-step RACH procedure. 
     In another example of the transmission of Msg A in step S 2303 , a PRU for transmission of the Msg A PUSCH may be defined in consideration of a PO, a DMRS port, and a DMRS sequence. A PO may be defined as time-frequency resources for payload transmission. A PO for the Msg A PUSCH may be configured independently of the RO, or configured as a relative time and/or frequency position in consideration of the associated RO. One or more POs may be configured within a configured period of the Msg A PUSCH. 
     In another example of the transmission of Msg A in step S 2303 , the PRACH and the PUSCH included in Msg A may be transmitted in different slots in time division multiplexing (TDM) or in the same slot. In other words, the Msg A PUSCH and the Msg A PRACH may be transmitted successively in the time domain with or without a predetermined gap. 
     In another example of the transmission of Msg A in step S 2303 , the PRACH and the PUSCH included in Msg A may be transmitted by using i) the same beam or the same Tx spatial filter, ii) the same or different beams or spatial filters according to determination of the UE, or iii) a beam or spatial filter configured by the BS. 
     In another example of the transmission of Msg A in step S 2303 , the UE may configure an RAR window to monitor Msg B after transmitting Msg A. To record the number of reattempts of the 2-step RACH procedure, the UE may set a retransmission counter for Msg A. A maximum counter value may be configured by the BS or the network. 
     In another example of the transmission of Msg A in step S 2303 , the BS may detect the preamble of the Msg A PRACH and decode the payload/data of the Msg A PUSCH. When the BS fails to detect the preamble of the Msg A PRACH, the BS may transmit no information to the UE. 
     As described above, embodiments of the present disclosure may be applied appropriately in step S 2303  for transmitting Msg A to the BS by the UE. Specifically, in the foregoing methods according to the embodiments of the present disclosure, a value of or information about a ramping step size and/or a ramping counter for the preamble and the PUSCH included in Msg A may be determined by the UE or the BS or configured for or indicated to the UE by the BS. Alternatively, the transmission power based on a beam configuration for the preamble and the PUSCH included in Msg A may be determined by the UE or the BS or configured for or indicated to the UE by the BS. 
     After transmitting Msg A, the UE may receive Msg B (S 2305 ). Msg B may be scheduled by a PDCCH corresponding to a DMRS and transmitted on a PDSCH corresponding to the DMRS. The contents of Msg B may vary according to the result of decoding and processing the Msg A PUSCH. 
     Specifically, when the BS succeeds in decoding the Msg A PUSCH, Msg B may include a contention resolution ID such as a UE ID transmitted in a common control channel (CCCH) service data unit (SDU) that the UE transmits as a success RAR. When the BS fails in decoding the Msg A PUSCH, Msg B may include, as a fallback RAR, a radon access preamble ID (RAPID) and a UL grant for retransmission of the Msg A PUSCH. When the BS transmits the fallback RAR in Msg B and the UE succeeds in decoding the RAPID and the UL grant included in Msg B, the UE may fall back to the 4-step RACH procedure. 
     In step S 2305 , the UE may be the wireless device  100  of  FIG.  25    or the wireless device  100  or  200  of  FIG.  26   , and the BS may be the second wireless device  200  of  FIG.  25    or the wireless device  100  or  200  of  FIG.  26   . That is, step S 2305  in which the UE receives Msg B from the BS may be performed by various wireless devices illustrated in  FIGS.  25  to  28    as described later. For example, when the UE is the wireless device  100  of  FIG.  25   , the processor  102  of  FIG.  25    may control the one or more transceivers  106  and/or the one or more memories  104  to receive Msg B, and the one or more transceivers  106  may receive Msg B from the BS. 
     Depending on whether the UE decodes and receives Msg B, the UE may operate in the same manner as or a similar manner to the operations subsequent to reception of Msg 4 in the 4-step RACH procedure. When the UE successfully receives Msg B within an RAR window, the UE may determine that the 2-step RACH procedure is successful. Alternatively, when the UE receives the fallback RAR, the UE may perform the Msg 3 transmission procedure of the 4-step RACH procedure based on the information included in Msg B, like a UL grant. 
     On the contrary, when the UE fails to receive Msg B within the RAR window and the retransmission counter value is less than a maximum allowed value, the UE may retransmit Msg A to reattempt the 2-step RACH procedure. When the retransmission counter value reaches the maximum allowed value, the UE may perform a back-off operation, determining that the 2-step RACH procedure is failed. A retransmission of Msg A may mean a retransmission of the Msg A PRACH including preamble reselection and a retransmission of the Msg A PUSCH. When a different transmission beam or spatial filter from that of the latest transmitted Msg A PRACH is used for the retransmission of the Msg A PRACH, the power ramping counter value for the Msg A PRACH may not be incremented. 
     The embodiments related to the above-described 2-step RACH procedure of the present disclosure may be applied even in the RRC_INACTIVE, RRC_CONNECTED, and RRC_IDLE states, and may be implemented as a general MAC procedure. Exceptionally, the embodiments related to the above-described 2-step RACH procedure of the present disclosure may not be applied to an SI request/beam failure recovery (BFR) procedure. Further, it may be configured that the legacy 4-step RACH procedure is re-performed in consideration of fall-back in the 2-step RACH procedure. 
     The various descriptions, functions, procedures, proposals, methods, and/or operational flowcharts of the present disclosure described in this document may be applied to, without being limited to, a variety of fields requiring wireless communication/connection (e.g., 5G) between devices. 
     A detailed description will be given of examples below with reference to the drawings. In the following drawings/description, the same reference symbols may denote the same or corresponding hardware blocks, software blocks, or functional blocks, unless specified otherwise. 
       FIG.  24    illustrates a communication system  1  applied to the present disclosure. 
     Referring to  FIG.  24   , the communication system  1  applied to the present disclosure includes wireless devices, BSs, and a network. The wireless devices are devices performing communication using RAT (e.g., 5G NR or LTE) and may be referred to as communication/radio/5G devices. The wireless devices may include, but 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 performing communication between vehicles. 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, a smartphone, a computer, a wearable, 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 a smart glasses), and a computer (e.g., a laptop). The home appliance may include a television, a refrigerator, and a washing machine. The IoT device may include a sensor and a smart meter. 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 . 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  or the 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 or the network. For example, the vehicles  100   b - 1  and  100   b - 2  may perform direct communication (e.g. V2V/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 , or  150   c  may be established between the wireless devices  100   a  to  100   f  and the BSs  200 , or between BSs  200 . 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  150   c  (e.g. relay and integrated access backhaul (IAB)). Radio 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 received on various physical signals 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 allocating processes, for transmitting/receiving radio signals may be performed based on the various proposals of the present disclosure. 
       FIG.  25    illustrates wireless devices applicable to the present disclosure. 
     Referring to  FIG.  25   , a first wireless device  100  and a second wireless device  200  may transmit radio signals through a variety of RATs (e.g., LTE and NR). Herein, {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.  24   . 
     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 operational flowcharts disclosed in this document. For example, the processor(s)  102  may process information within the memory(s)  104  to generate first information/signals and then transmit radio signals including the first information/signals through the transceiver(s)  106 . The processor(s)  102  may receive radio 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 commands 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 operational flowcharts disclosed in this document. Herein, the processor(s)  102  and the memory(s)  104  may be 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 radio 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 RF unit(s). In the present disclosure, a wireless device may refer to a communication modem/circuit/chip. 
     A processor  102  may control a transceiver  106  to transmit Msg A including a PRACH and a PUSCH. The processor  102  may control the transceiver  106  to receive Msg B related to contention resolution. A specific method of controlling the transceiver  106  to transmit Msg A and receive a threshold and Msg B by the processor  102  may be based on the foregoing embodiments. 
     Specifically, commands stored in a memory  204  and/or operations, which are controlled by a processor  202  of the second wireless device  200  according to an embodiment of the present disclosure will be described below. 
     While the following operations are described in the context of control operations of the processor  202  from the perspective of the processor  202 , software code for performing these operations may be stored in the memory  204 . 
     The processor  202  may control a transceiver  206  to receive Msg A including a PRACH and a PUSCH. The processor  202  may control the transceiver  206  to transmit Msg B related to contention resolution. A specific method of controlling the transceiver  106  to receive Msg A and transmit a threshold and Msg B by the processor  202  may be based on the foregoing embodiments. 
     Hardware elements of the wireless devices  100  and  200  will be described in more detail. One or more protocol layers may be implemented by, but 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 PHY, MAC, RLC, PDCP, RRC, and 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 unit (SDUs) according to the descriptions, functions, procedures, proposals, methods, and/or operational 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 operational flowcharts disclosed in this document. 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 operational 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 signals (e.g., baseband signals) from the one or more transceivers  106  and  206  and acquire PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, proposals, methods, and/or operational 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. As an 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 operational 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 operational flowcharts disclosed in this document may be included in the one or more processors  102  and  202  or stored in the one or more memories  104  and  204  so as to be driven by the one or more processors  102  and  202 . The descriptions, functions, procedures, proposals, methods, and/or operational flowcharts disclosed in this document may be implemented using firmware or software in the form of code, instructions, 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 by 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, to one or more other devices, user data, control information, and/or radio signals/channels mentioned in the methods and/or operational flowcharts of this document. The one or more transceivers  106  and  206  may receive, from one or more other devices, user data, control information, and/or radio signals/channels mentioned in the descriptions, functions, procedures, proposals, methods, and/or operational flowcharts disclosed in this document. 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 radio 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 radio signals to one or more other devices. The one or more processors  102  and  202  may control the one or more transceivers  106  and  206  to receive user data, control information, or radio 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 configured to transmit and receive user data, control information, and/or radio signals/channels, mentioned in the descriptions, functions, procedures, proposals, methods, and/or operational 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 radio signals/channels from RF band signals into baseband signals in order to process received user data, control information, and radio 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 radio signals/channels processed using the one or more processors  102  and  202  from the base band signals into the RF band signals. To this end, the one or more transceivers  106  and  206  may include (analog) oscillators and/or filters. 
       FIG.  26    illustrates another exemplary 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  FIG.  24   ). 
     Referring to  FIG.  26   , wireless devices  100  and  200  may correspond to the wireless devices  100  and  200  of  FIG.  25    and may be configured with 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 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.  25   . 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.  25   . The control unit  120  is electrically connected to the communication unit  110 , the memory  130 , and the additional components  140  and controls overall operations of the wireless devices. For example, the control unit  120  may control an electric/mechanical operation of the wireless device based on programs/code/commands/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) through the communication unit  110  via a wireless/wired interface or store, in the memory unit  130 , information received from the outside (e.g., other communication devices) through the communication unit  110  via the wireless/wired interface. Therefore, a specific operation of the control unit  120  and programs/code/commands/information stored in the memory unit  130  according to the present disclosure may corresponding to at least one operation of the processors  102  and  202  and at least one operation of the memories  104  and  204  illustrated in  FIG.  25   . 
     The additional components  140  may be configured in various ways according to the type of 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, or a computing unit. The wireless device may be implemented in the form of, but not limited to, the robot ( 100   a  of  FIG.  24   ), the vehicles ( 100   b - 1  and  100   b - 2  of  FIG.  24   ), the XR device ( 100   c  of  FIG.  24   ), the hand-held device ( 100   d  of  FIG.  24   ), the home appliance ( 100   e  of  FIG.  24   ), the IoT device ( 100   f  of  FIG.  24   ), a digital broadcasting terminal, a hologram device, a public safety device, an MTC device, a medical device, a FinTech device (or a financial machine), a security device, a climate/environment device, the AI server/device ( 400  of  FIG.  24   ), a BS ( 200  of  FIG.  24   ), a network node, or the like. The wireless device may be used in a mobile or fixed place according to a use case/service. 
     In  FIG.  26   , all of the various elements, components, units/portions, and/or modules in the wireless devices  100  and  200  may be inter-connected through a wired interface or at least a part thereof may be wirelessly inter-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 wiredly, and the control unit  120  and first units (e.g.,  130  and  140 ) may be connected wirelessly 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 as a set of one or more processors. For example, the control unit  120  may be configured as 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 unit  130  may be configured as a RAM, a DRAM, a ROM, a flash memory, a volatile memory, a non-volatile memory, and/or a combination thereof. 
     Now, a detailed description will be given of an implementation example of the devices illustrated in  FIG.  26    with reference to the drawings. 
       FIG.  27    illustrates a hand-held device applied to the present disclosure. The hand-held device may include a smartphone, a smart pad, a wearable device (e.g., a smart watch or smart glasses), or a portable computer (e.g., a laptop). The hand-held device 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 (TW). 
     Referring to  FIG.  27   , a 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 I/O unit  140   c . The antenna unit  108  may be configured as a part of the communication unit  110 . Blocks  110  to  130 / 140   a  to  140   c  correspond to the blocks  110  to  130 / 140  of  FIG.  26   , respectively. 
     The communication unit  110  may transmit and receive signals (e.g., data and control signals) to and from other wireless devices or BSs. The control unit  120  may perform various operations by controlling components 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 needed to drive the hand-held device  100 . 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, a battery, and so on. The interface unit  140   b  may support connection between the hand-held device  100  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 input or output video information/signals, audio information/signals, data, and/or information input by a user. The I/O unit  140   c  may include a camera, a microphone, a user input unit, a display unit  140   d , a speaker, and/or a haptic module. 
     For example, in the case of data communication, the I/O unit  140   c  may acquire information/signals (e.g., touch, text, voice, images, or video) input by the user and the acquired information/signals may be stored in the memory unit  130 . The communication unit  110  may convert the information/signals stored in the memory into radio signals and transmit the radio signals to other wireless devices directly or to a BS. The communication unit  110  may receive radio signals from other wireless devices or the BS and then restore the received radio signals to original information/signals. The restored information/signals may be stored in the memory unit  130  and output as various types (e.g., text, voice, images, video, or haptic) through the I/O unit  140   c.    
       FIG.  28    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.  28   , 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.  26   , 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 components of the vehicle or the autonomous driving vehicle  100 . The control unit  120  may include an ECU. The driving unit  140   a  may cause 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 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, an inclination 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 path 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 path and a driving plan based on the obtained data. The control unit  120  may control the driving unit  140   a  to drive the vehicle or the autonomous driving vehicle  100  along the autonomous driving path according to the driving plan (e.g., speed/direction control). In the middle of autonomous driving, the communication unit  110  may aperiodically or periodically acquire the latest traffic information data from the external server and acquire surrounding traffic information data from neighboring vehicles. In the middle of 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 path 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 path, and 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. 
       FIG.  29    illustrates a signal processing circuit for a transmission signal. 
     Referring to  FIG.  29   , a signal processing circuit  1000  may include scramblers  1010 , modulators  1020 , a layer mapper  1030 , a precoder  1040 , resource mappers  1050 , and signal generators  1060 . An operation/function of  FIG.  29    may be performed by, but not limited to, the processors  102  and  202  and/or the transceivers  106  and  206  of  FIG.  25   . Hardware elements of  FIG.  29    may be implemented by the processors  102  and  202  and/or the transceivers  106  and  206  of  FIG.  25   . For example, the blocks  1010  to  1060  may be implemented by the processors  102  and  202  of  FIG.  25   . Alternatively, the blocks  1010  to  1050  may be implemented by the processors  102  and  202  of  FIG.  25    and the block  1060  may be implemented by the transceivers  106  and  206  of  FIG.  25   . 
     Codewords may be converted into radio signals through the signal processing circuit  1000  of  FIG.  29   . The codewords are coded bit sequences of information blocks. The information blocks may include TBs (e.g., UL-SCH TBs or DL-SCH TBs). The radio signals may be transmitted on various physical channels (e.g., a PUSCH or a PDSCH). 
     Specifically, the codewords may be converted into scrambled bit sequences by the scramblers  1010 . Scramble sequences used for scrambling may be generated based on an initialization value, and the initialization value may include ID information about a wireless device. The scrambled bit sequences may be modulated to modulation symbol sequences by the modulators  1020 . A modulation scheme may include pi/2-binary phase shift keying (pi/2-BPSK), m-phase shift keying (m-PSK), and m-quadrature amplitude modulation (m-QAM). Complex modulation symbol sequences may be mapped to one or more transport layers by the layer mapper  1030 . Modulation symbols of each transport layer may be mapped (precoded) to corresponding antenna port(s) by the precoder  1040 . Outputs z of the precoder  1040  may be obtained by multiplying outputs y of the layer mapper  1030  by an N*M precoding matrix W. N is the number of antenna ports, and M is the number of transport layers. The precoder  1040  may perform precoding after transform precoding (e.g., DFT) for complex modulation symbols. Alternatively, the precoder  1040  may perform precoding without transform precoding. 
     The resource mappers  1050  may map modulation symbols of each antenna port to time-frequency resources. The time-frequency resources may include a plurality of symbols (e.g., CP-OFDMA symbols or DFT-s-OFDMA symbols) in the time domain and a plurality of subcarriers in the frequency domain. The signal generators  1060  may generate radio signals from the mapped modulation symbols, and the generated radio signals may be transmitted to other devices through each antenna. For this purpose, the signal generators  1060  may include inverse fast Fourier transform (IFFT) modules, CP inserters, digital-to-analog converters (DACs), and frequency upconverters. 
     Signal processing procedures for a signal received in the wireless device may be configured reversely to the signal processing procedures  1010  to  1060  of  FIG.  29   . For example, the wireless devices (e.g.,  100  and  200  of  FIG.  25   ) may receive radio signals from the outside through the antenna ports/transceivers. The received radio signals may be converted into baseband signals through signal restorers. To this end, the signal restorers may include frequency downconverters, analog-to-digital converters (ADCs), CP remover, and FFT modules. Subsequently, the baseband signals may be restored to codewords by resource demapping, postcoding, demodulation, and descrambling. The codewords may be decoded to original information blocks. Therefore, the signal processing circuit (not shown) for a received signal may include signal restorers, resource demappers, a postcoder, demodulators, descramblers, and decoders. 
     As is apparent from the foregoing description, according to the present disclosure, a more suitable 2-step RACH procedure may be performed by appropriately setting the power of a signal for the 2-step RACH procedure in a wireless communication system. 
     While the method and apparatus for transmitting and receiving a signal for an RACH procedure in a wireless communication system have been described above in the context of a 5G NewRAT system, the method and apparatus are also applicable to various wireless communication systems other than the 5G NewRAT system. 
     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. 
     A specific operation described as performed by the 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, gNode B (gNB), Node B, enhanced Node B (eNode B or eNB), access point, and so on. 
     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.