Method and device for performing random access in wireless communication system

Abstract

Disclosed is a method for performing random access by a terminal. The disclosed method comprises the steps of: receiving a reference signal; receiving a broadcasting message; acquiring, from the broadcasting message, information for determining a random access occasion (RO) type; selecting any one of an additional RO and a legacy RO on the basis of the information for determining the RO type; and performing random access by using the selected RO.

Description

Method and device for performing random access in a wireless communication system

[0001] The present disclosure relates to a random access method and apparatus in a wireless communication system, and the present disclosure discloses a method for performing random access in a wireless communication system that supports sub-band full duplex (SBFD).

[0002] The communication system may include a core network, base stations (e.g., macro base stations, small base stations, relays, etc.), terminals, etc. Communication between the base station and the terminal may be performed based on various radio access technologies (RATs) (e.g., 4G communication technology, 5G communication technology, WiBro (wireless broadband) technology, WLAN (wireless local area network) technology, WPAN (wireless personal area network) technology, etc.).

[0003] Handover is one of the mobility management technologies in wireless communication systems. Handover is a technology that allows a terminal to disconnect from its existing source base station and establish a connection with a new target base station when it moves from one cell or base station to another. Through handover, terminals in wireless communication systems can receive stable service.

[0004] Fifth-generation mobile communication considered the allocation of wide bandwidth in the millimeter wave band for high-speed data transmission. However, the utilization of high frequencies in this millimeter wave band resulted in high path loss and led to the degradation of uplink performance for mobile communication terminals that use limited power from batteries. To overcome these limitations of the millimeter wave band, beamforming technology was introduced to increase antenna gain by utilizing multiple antennas; however, due to the characteristics of moving terminals, a new technology called beam management became necessary. In reality, there were limitations in providing sufficient coverage for mobile communication systems because it was difficult to accurately steer a narrow beam with high gain to a moving terminal.

[0005] 3GPP selected the sub-band full duplex system (SBFD) and AI / ML as Study Items for 5G Release 18 and conducted research and discussions.

[0006] Sub-band Full Duplex (SBFD) supports the simultaneous transmission and reception of uplink and downlink. According to SBFD, uplink and downlink can be allocated by sub-band in the frequency domain. SBFD is referred to as Cross Division Duplex (XDD). In XDD, 'X' stands for time or frequency. SBFD differs from existing TDD and FDD in that it separates uplink and downlink by utilizing both the time domain and the frequency domain. In SBFD mode, the frame structure can be much more flexible compared to existing TDD and FDD. Furthermore, by utilizing SBFD, wireless communication systems can improve uplink throughput and uplink transmission latency, and enhance coverage through uplink repeated transmission.

[0007] In a communication system, a terminal may perform random access at the direction of a base station for various reasons, such as receiving services from a base station, or due to synchronization problems of the terminal, downlink data transmission, etc.

[0008] In wireless communication systems where subband full-duplex communication is applied, there may be additional random access occasions configured in SBFD symbols and legacy random access occasions configured in legacy symbols. Accordingly, the terminal must appropriately and efficiently select one of the two types of random access occasions to improve the performance of the wireless communication system.

[0009] According to at least one embodiment, a method and apparatus are disclosed in which at least one communication node in a communication system supporting SBFD can perform a procedure related to random access.

[0010] In one aspect,

[0011] A method for performing random access by a terminal is disclosed. The disclosed method includes the steps of: receiving a reference signal; receiving a broadcasting message; obtaining information for determining the type of random access occasion (RO) from the broadcasting message; selecting either an additional RO or a legacy RO based on the information for determining the type of RO; and performing random access using the selected RO.

[0012] According to at least one embodiment, the selection of additional ROs can be performed appropriately and efficiently. According to at least one embodiment, additional ROs can be appropriately selected to increase the probability of random access success and reduce the delay time required for the random access procedure.

[0013] According to at least one embodiment, the conditions for selecting additional RO are shared between the terminal and the base station and are appropriately reflected, thereby increasing the efficiency of using the UL subband.

[0014] According to at least one embodiment, when the uplink data transmission rate is important, information prohibiting the use of additional RO may be included in the broadcasting message. This allows the uplink data transmission rate to be increased by preventing terminals from using additional RO in advance. On the other hand, when the improvement of random access performance is important, allowing terminals to use additional RO can prevent collisions occurring during the random access process and reduce latency.

[0015] According to at least one embodiment, the effect of interference can be reduced by selecting an additional RO based on the RSRP of the reference signal.

[0016] According to at least one embodiment, flexible communication system operation may be possible by selecting an additional RO based on at least one of a preamble format and a preamble repeat transmission configuration.

[0017] According to at least one embodiment, interference effects or random access latency can be reduced by adjusting additional RO selection probability according to the PRACH resource configuration ratio.

[0018] According to at least one embodiment, the signaling overhead and delay time required for a random access procedure can be efficiently managed by redoing the RO selection when a message transmission fails in a random access procedure.

[0019] According to at least one embodiment, in contention-based random access, a base station uses DCI to indicate the RO type, so that a terminal can use an appropriate type of RO according to network conditions.

[0020] FIG. 1 is a drawing showing a wireless communication system according to an exemplary embodiment.

[0021] FIG. 2 is a block diagram illustrating the configuration of a communication node (200) that constitutes a communication system.

[0022] Figure 3 is a diagram illustrating an exemplary 5G network architecture.

[0023] Figure 4 is a diagram showing the legacy frame structure in TDD mode.

[0024] FIG. 5 is a diagram showing a frame structure in SBFD (subband full-duplex communication) mode according to an exemplary embodiment.

[0025] FIG. 6 is a flowchart illustrating a method for performing random access according to an exemplary embodiment.

[0026] FIG. 7 is a flowchart exemplarily illustrating the process of a base station (110-1) transmitting a broadcasting message in step S130 shown in FIG. 6.

[0027] FIG. 8 is a flowchart illustrating the process of performing step S140 shown in FIG. 6.

[0028] FIG. 9 is a flowchart illustrating the process of performing step S150 of FIG. 6.

[0029] FIG. 10 is a conceptual diagram showing that the terminal (120-1) selects the RO type.

[0030] FIG. 11 is a flowchart illustrating the process of performing step S150 shown in FIG. 6.

[0031] FIG. 12 is a conceptual diagram exemplarily showing that when a long preamble format is configured, the terminal (120-1) selects RO.

[0032] FIG. 13 is a flowchart illustrating the process of performing step S150 shown in FIG. 6.

[0033] FIG. 14 is a conceptual diagram exemplifying the selection of RO by the terminal (120-1) when preamble repetitive transmission is configured.

[0034] FIG. 15 is a flowchart illustrating the process of performing step S150 shown in FIG. 6.

[0035] FIG. 16 is a conceptual diagram exemplifying the terminal (120-1) selecting RO.

[0036] FIG. 17 is a flowchart illustrating the process of performing step S160 of FIG. 6.

[0037] FIG. 18 is a flowchart illustrating a method for performing random access according to an exemplary embodiment.

[0038] FIG. 19 is a flowchart illustrating the process of performing step S270 of FIG. 18.

[0039] FIG. 20 is a flowchart illustrating a random access method according to an exemplary embodiment.

[0040] FIG. 21 is a flowchart illustrating a method for performing random access according to an exemplary embodiment.

[0041] FIG. 22 is a flowchart illustrating the process of performing step S470 of FIG. 21.

[0042] FIG. 23 is a flowchart illustrating the process of performing step S470 of FIG. 21.

[0043] FIG. 24 is a flowchart illustrating the process of performing random access in an exemplary manner.

[0044] FIG. 25 is a conceptual diagram exemplarily illustrating the DCI transmitted in step S520 of FIG. 24.

[0045] FIG. 26 is a conceptual diagram exemplifying the start time of a random access procedure according to RO coordination in a random access procedure.

[0046] In one aspect,

[0047] A method for performing random access by a terminal is disclosed. The disclosed method includes the steps of: receiving a reference signal; receiving a broadcasting message; obtaining information for determining the type of random access occasion (RO) from the broadcasting message; selecting either an additional RO or a legacy RO based on the information for determining the type of RO; and performing random access using the selected RO.

[0048] The above additional RO may be placed in the SBFD time interval, and the above legacy RO may be placed in the non-SBFD time interval.

[0049] The above broadcasting message includes information regarding the availability of the additional RO, and in the step of selecting either the additional RO or the legacy RO, the terminal can select the type of RO based on the information regarding the availability of the additional RO.

[0050] The broadcasting message above includes information on the RSRP threshold value for the Reference Signal Received Power (RSRP) of the reference signal, and in the step of selecting either an additional RO or a legacy RO, the terminal can select the type of RO based on the result of comparing the RSRP of the reference signal with the RSRP threshold value.

[0051] The terminal can select an additional RO if the RSRP of the reference signal is greater than the RSRP threshold value.

[0052] The above broadcasting message includes information about the preamble format used in the random access procedure, and in the step of selecting either an additional RO or a legacy RO, the terminal can select the type of RO based on the information about the preamble format.

[0053] If the above preamble format is a long preamble format, the terminal can select an additional RO.

[0054] The above broadcasting message includes preamble repeat transmission configuration information, and in the step of selecting either an additional RO or a legacy RO, the terminal can select a type of RO based on the preamble repeat transmission configuration.

[0055] The above broadcasting message includes information related to the resource configuration ratio of a Physical Random Access Channel (PRACH), and the step of selecting either an additional RO or a legacy RO may include the step of determining the resource allocation ratio of the additional RO based on the information related to the PRACH resource configuration ratio, the step of determining the selection probability of the additional RO based on the resource allocation ratio of the additional RO, and the step of selecting the additional RO or the legacy RO based on the selection probability of the additional RO.

[0056] The step of performing random access using a selected RO may include: transmitting a preamble (e.g., Msg1 in 4-Step or MsgA in 2-Step) using the selected RO; counting the number of preamble transmission failures when the preamble transmission fails; and resetting the type of RO when the number of preamble transmission failures reaches a preset maximum number of transmissions.

[0057] In the step of performing random access using a selected RO, if random access is performed based on a 2-step method, the step of performing random access using the selected RO may include: a step of transmitting a preamble using the selected RO; a step of counting the number of preamble transmission failures if the preamble transmission fails; a step of comparing the RSRP of the reference signal with a first threshold value if the number of preamble transmission failures reaches a preset maximum number of transmissions; and a step of switching to a 4-step method to perform random access if the RSRP of the reference signal is smaller than the first threshold value.

[0058] The step of performing random access using the selected RO may include: comparing the RSRP of the reference signal with a second threshold value when the RSRP of the reference signal is greater than a first threshold value; and performing random access in a two-step manner using an additional RO when the RSRP of the reference signal is greater than the second threshold value.

[0059] In the step of performing random access using a selected RO, if random access is performed based on a 2-step method, the step of performing random access using the selected RO may include: a step of transmitting a preamble using the selected RO; a step of comparing the number of preamble transmission failures with at least one of a first threshold number and a second threshold number when the preamble transmission fails; and a step of resetting the type of RO based on the result of comparing the number of preamble transmission failures with at least one of the first threshold number and the second threshold number.

[0060] If the number of preamble transmission failures is greater than the first threshold number, the terminal can switch to a 4-step method to perform random access.

[0061] If the number of preamble transmission failures is less than the first threshold number and greater than the second threshold number, the terminal can perform random access in a 2-step manner using legacy RO.

[0062] A method for performing random access of a base station is disclosed. The disclosed method may include the steps of: obtaining RSRP information of a reference signal measured by the terminal from a terminal; selecting an RO type based on the RSRP information of the reference signal; configuring downlink control information including information about the selected RO type; and transmitting downlink control information including information about the selected RO type.

[0063] Information regarding the selected RO type may include information indicating either an additional RO or a legacy RO.

[0064] In the step of selecting the RO type, the base station may select the RO type based on at least one of the comparison result of the RSRP and RSRP threshold value of the reference signal, the preamble format, the preamble repeat transmission configuration, and the PRACH resource configuration ratio.

[0065] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the invention to specific embodiments, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0066] Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component. The term "and / or" includes a combination of a plurality of related described items or any of a plurality of related described items.

[0067] When it is stated that one component is "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to that other component, there may also be other components in between. On the other hand, when it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0068] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to specify the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0069] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0070] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the attached drawings. In order to facilitate an overall understanding of the present invention, the same reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted.

[0071] Table 1 shows the abbreviations used in the present disclosure.

[0072] 약어전체 이름AI / MLArtificial Intelligence / Machine Learning3GPP3rd Generation Partnership ProjectACKAcknowledgementAFApplication FunctionAIArtificial IntelligenceAMFAccess and Mobility Management FunctionAUSFAuthentication Server FunctionBWPBandwidth PartC-RNTICell RNTICSIChannel State InformationCSI-RSChannel State Information Reference SignalCLICross link InterferenceCEControl ElementDCIDownlink Control InformationIEInformation elementMACMedium Access ControlMLMachine LearningNSSFNetwork Slicing Selection FunctionNEFNetwork Exposure FunctionNRFNF Repository FunctionPCFPolicy Control FunctionPDCCHPhysical Downlink Control ChannelPDSCHPhysical Downlink Shared ChannelPDUProtocol Data UnitPRACHPhysical Random Access ChannelPT-RSPhase Tracking Reference SignalPUCCHPhysical Uplink Control ChannelPUSCHPhysical Uplink Shared ChannelRARandom AccessRACHRandom Access ChannelRANRadio Access NetworkRBResource BlockRORandom access occasionRRCRadio Resource ControlRSRPReference Signal ReceivedPowerRSRQReference Signal Received QualityRSSIReceived Signal Strength IndicatorSBFDSub-Band Full DuplexSISelf InterferenceSIBSystem information blockUEUser EquipmentDLDownlinkULUplinkRARRandom Access ResponseRRMRadio Resource ManagementRRCRadio Resource ControlRSRPReference Signal Received PowerQoSQuality of ServiceDRBData Radio BearerDAPSDual Active Protocol StackTDDTime Division DuplexingFDDFrequency Division DuplexingSSBSS BlockCQIChannel Quality IndicatorPMIPrecoding Matrix IndicatorLILayer IndicatorRIRank IndicatorQCLQuasi coLocationMIBMaster Information BlockPBCHPhysical Broadcast ChannelPSSPrimary Synchronization SignalSSSSecondary Synchronization Signal

[0073] FIG. 1 is a drawing showing a wireless communication system (100) according to an exemplary embodiment. Referring to FIG. 1, the wireless communication system (100) may be composed of a plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 120-3, 120-4). Here, a communication node refers to a node capable of transmitting and receiving signals in the wireless communication system (100), and each of the plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 120-3, 120-4) may support at least one communication protocol. For example, each of the multiple communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 120-3, 120-4) can support cellular communication (e.g., LTE (long term evolution), LTE-A (advanced), 5G NR, 5G-Advanced, etc. as defined in the 3GPP (3rd generation partnership project) standard).

[0074] For example, each of the multiple communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 120-3, 120-4) can support a CDMA (code division multiple access) based communication protocol, a WCDMA (wideband CDMA) based communication protocol, a TDMA (time division multiple access) based communication protocol, a FDMA (frequency division multiple access) based communication protocol, an OFDM (orthogonal frequency division multiplexing) based communication protocol, an OFDMA (orthogonal frequency division multiple access) based communication protocol, a SC (single carrier)-FDMA based communication protocol, a NOMA (non-orthogonal multiple access) based communication protocol, a SDMA (space division multiple access) based communication protocol, a SBFD (sub-band full duplex), AI / ML, etc.

[0075] A plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 120-3, 120-4) may include a plurality of base stations (110-1, 110-2, 110-3) and a plurality of terminals (120-1, 120-2, 120-3, 120-4). Each of the base stations (110-1, 110-2, 110-3) may form a cell. The cell may include a small cell, a macro cell, a pico cell, a femto cell, etc., but the embodiments are not limited thereto. For example, the first terminal (120-1) and the second terminal (120-2) may be in the coverage of the first base station (110-1), the third terminal (120-3) may be in the coverage of the second base station (110-2), and the fourth terminal (120-4) may be in the coverage of the third base station (110-3).

[0076] Multiple base stations (110-1, 110-2, 110-3) may be referred to as gNodeB (gNB), NodeB, evolved NodeB, BTS (base transceiver station), radio base station, radio transceiver, access point, access node, roadside unit (RSU), RRH (radio remote head), TP (transmission point), TRP (transmission and reception point), relay node, etc. Multiple base stations (110-1, 110-2, 110-3) may form a Radio Access Network (RAN). The Radio Access Network may be connected to a core network.

[0077] Each of the multiple terminals (120-1, 120-2, 120-3, 120-4) may be referred to as a terminal, access terminal, mobile terminal, station, subscriber station, mobile station, portable subscriber station, node, device, etc.

[0078] The communication protocol support ranges of each of the multiple base stations (110-1, 110-2, 110-3) may differ from one another. For example, some of the multiple base stations (110-1, 110-2, 110-3) may support AI / ML functions while others do not. Similarly, the communication protocol support ranges of each of the terminals (120-1, 120-2, 120-3, 120-4) may also differ from one another. For example, some of the multiple terminals (120-1, 120-2, 120-3, 120-4) may support AI / ML functions while others do not.

[0079] FIG. 2 is a block diagram illustrating the configuration of a communication node (200) that constitutes a communication system. At least some of the communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 120-3) shown in FIG. 1 may correspond to the communication node (200) shown in FIG. 2.

[0080] Referring to FIG. 2, the communication node (200) may include at least one processor (210), a memory (220), and a transceiver (230) that is connected to a network to perform communication. Additionally, the communication node (200) may further include an input interface device (240), an output interface device (250), a storage device (260), etc. Each component included in the communication node (200) may be connected by a bus (270) to communicate with one another.

[0081] The processor (210) can execute a program command stored in at least one of the memory (220) and the storage device (260). The processor (210) may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present invention are performed. Each of the memory (220) and the storage device (260) may be composed of at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory (220) may be composed of at least one of read-only memory (ROM) and random access memory (RAM).

[0082] Figure 3 is a diagram illustrating an exemplary 5G network architecture.

[0083] Referring to FIG. 3, the 5G network architecture may include an NSSF providing a network slicing control solution, an NEF providing a network function opening solution, an NRF providing an NF interoperability control solution within the 5G network, a PCF providing a data packet flow policy control solution, a UDM providing a user information and policy management solution, an AMF providing a network access and mobility management solution, an SMF providing a terminal / network session management solution, a UPF providing a solution for user packet routing and terminal connectivity between base stations, a radio access network (RAN), and a user terminal (UE).

[0084] N1 reference point is defined to transmit signaling between the UE and the AMF, N2 is defined as the reference point to connect the RAN access node and the AMF, and N3 is defined as the reference point to connect the RAN access node and the UPF.

[0085] Figure 4 is a diagram showing the legacy frame structure in TDD mode.

[0086] Referring to FIG. 4, a time interval (40) can be defined in the time domain. The time interval may also be referred to as a time unit. The time interval (40) may correspond to any one of a slot, a symbol, and a subframe. As another example, the time interval (40) may be defined to include a plurality of slots. As yet another example, the time interval (40) may be defined to include a plurality of symbols. As yet another example, the time interval (40) may be defined to include a plurality of subframes.

[0087] In TDD mode, downlink resources may be allocated to the first to fourth time intervals (40, 41, 42, 43). Downlink signals may be transmitted during the first to fourth time intervals (40, 41, 42, 43). Uplink resources may be allocated during the fifth time interval (44). Downlink signals may be transmitted during the fifth time interval (44). According to the legacy frame structure shown in FIG. 4, even if the terminal (120-1) needs to transmit an uplink signal between the first to fourth time intervals (40, 41, 42, 43), it may transmit the uplink signal after waiting until the fifth time interval (44), where uplink resources are allocated, arrives. This may result in latency until the terminal (200-1) transmits the uplink signal.

[0088] FIG. 5 is a diagram showing a frame structure in SBFD (subband full-duplex communication) mode according to an exemplary embodiment.

[0089] Referring to FIG. 5, in SBFD mode, uplink resources and downlink resources can be allocated simultaneously in the first to fourth time intervals (40, 41, 42, 43). In the first to fourth time intervals (40, 41, 42, 43), UL subbands for uplink transmission and DL subbands for downlink transmission can be allocated simultaneously. The time interval in which UL subbands and DL subbands are allocated simultaneously to enable subband full-duplex communication can be referred to as the SBFD time domain.

[0090] Although not shown in FIG. 5, there may be a time region in which a downlink is allocated prior to the first to fourth time intervals (40, 41, 42, 43) corresponding to the SBFD time region. Through the downlink allocated prior to the SBFD time region, the base station can transmit scheduling information for the SBFD time region and the SBFD subband to the terminal.

[0091] In FIG. 5, the first to fourth time intervals (40, 41, 42, 43) may correspond to an SBFD time domain. An SBFD time domain may be defined to include at least one slot. As another example, an SBFD time domain may be defined to include at least one symbol. As another example, an SBFD time domain may be defined to include at least one subframe.

[0092] Each of the UL subband and the DL subband may include at least one RB. For example, each of the UL subband and the DL subband may include RBs arranged continuously. As another example, each of the UL subband and the DL subband may include RBs arranged discontinuously in at least a portion.

[0093] Each of the UL subband and DL subband may include at least one BWP. For example, each of the UL subband and DL subband may include at least one legacy BWP. As another example, each of the UL subband and DL subband may include at least one BWP separately defined to support SBFD.

[0094] As described above, an SBFD subband may be configured within a carrier in TDD mode for SBFD mode operation. The SBFD subband may include a UL subband and a DL subband. FIG. 5 illustrates an exemplary case where the UL subband is located in the middle part of the carrier. However, the embodiment is not limited thereto. For example, the UL subband may be located at the edge of the carrier. As another example, the UL subband may be located elsewhere than the exact center of the carrier.

[0095] Additionally, a guard period may be placed between the SBFD time domain and the non-SBFD time domain to which SBFD is not applied. Each of the SBFD time domain and the non-SBFD time domain may include at least one symbol.

[0096] The time and frequency positions of the SBFD subband can be configured and indicated semi-statically. As another example, the time and frequency positions of the SBFD subband can be configured and indicated dynamically.

[0097] In SBFD mode, the efficiency of wireless resource usage can be increased by flexibly distributing uplink and downlink resources. Additionally, the delay can be reduced as the time the terminal (120-1) waits for uplink signal transmission and downlink signal reception is reduced. Furthermore, in SBFD mode, the transmission gain of the UL signal and DL signal is increased by the terminal (120-1) repeatedly transmitting UL signals and repeatedly receiving DL signals in multiple time intervals (40, 41, 42, 43), and the coverage of the first base station (110-1) and the first terminal (120-1) can be expanded.

[0098] For convenience, the first terminal (120-1) is referred to as the terminal below, and the first base station (110-1) is referred to as the base station.

[0099] FIG. 6 is a flowchart illustrating a method for performing random access according to an exemplary embodiment.

[0100] Referring to FIG. 6, in step S110, the base station (110-1) can transmit a synchronization signal block (SSB). The base station (110-1) can transmit the SSB. The terminal (120-1) can receive the SSB. The terminal (120-1) can receive system information from the base station (110-1) using the SSB. The terminal (120-1) can perform downlink synchronization based on the SSB. The SSB may include PSS, SSS, and PBCH.

[0101] The base station (110-1) can transmit SSBs by mapping them in beam units. The base station (120-1) can periodically transmit multiple SSBs. For example, the base station (120-1) can transmit SSBs in multiple directions using a beam sweeping method.

[0102] In step S120, the terminal (120-1) can perform downlink synchronization. The terminal (120-1) can synchronize time and frequency based on PSS and obtain information regarding at least some of the cell IDs. The terminal (120-1) can synchronize frames based on SSS. The terminal (120-1) can determine the cell ID based on PSS and SSS. The terminal (120-1) can obtain an MIB from the PBCH. The MIB may contain information regarding the location of SIB1 in the wireless resource. For example, the MIB may contain an index related to the location of SIB1. The terminal (120-1) can obtain location-related information of SIB1 by receiving the SSB and decoding the MIB.

[0103] In step S130, the terminal (120-1) can receive a broadcasting message from the base station (120-1). The broadcasting message may include system information of the base station (110-1). For example, the system information may include SIB1. The terminal (120-1) can determine the location of CORESET 0 based on the system information. CORESET 0 (Control Resource Set 0) may be a common control resource area reserved by the base station in 5G NR to initially transmit downlink control information to the terminal. The terminal (120-1) can obtain control information through CORESET 0 before establishing an RRC connection with the base station (110-1).

[0104] The terminal (120-1) can obtain information for connecting to the base station (120-1) from system information (e.g., SIB1). For example, the terminal (120-1) can obtain resource allocation information and timing adjustment information provided by the base station (120-1) from the system information. The terminal (120-) can obtain RACH configuration information from the system information. The RACH configuration information may include information about RACH resources, information about ROs, and information about preamble formats. Additionally, SIB1 may include information about the mapping relationship between SSBs and ROs. For example, SIB1 may include information about at least one of the RACH resources and ROs mapped by SSB index.

[0105] In a wireless communication system using SBFD, not only legacy ROs configured in uplink (UL) symbols but also additional random access opportunities (Additional ROs, hereinafter referred to as Additional ROs) placed in SBFD symbols may be configured. Accordingly, the base station (110-1) may include information related to the Additional ROs in a broadcasting message. For example, the base station (110-1) may include information related to the Additional ROs in system information transmitted through a broadcasting message.

[0106] FIG. 7 is a flowchart exemplarily illustrating the process of a base station (110-1) transmitting a broadcasting message in step S130 shown in FIG. 6.

[0107] Referring to FIG. 7, in step S132, the base station (110-1) can determine whether to use additional ROs. For example, the base station (110-1) can determine whether to use additional ROs collectively regardless of the SSB index. As another example, the base station (110-1) may determine whether to use additional ROs by SSB index. The use of additional ROs can be determined statically or dynamically.

[0108] For example, when a base station (110-1) services terminals with high uplink data transmission, such as smartphones, tablets, and drones, the base station (110-1) may prioritize the uplink data transmission rate over random access performance. The base station (110-1) may not allow the use of additional RO to utilize the UL subband for uplink data transmission. As another example, when the base station (110-1) communicates with IoT terminals deployed in a smart factory, it may prioritize the improvement of random access performance. While the uplink data of each IoT terminal is not large, the number of terminals is large, so there is a high possibility of collisions occurring during the random access process. In this case, the base station (110-1) may allow the use of additional RO.

[0109] In step S134, the base station (110-1) may include information regarding whether additional ROs are available in the system information. For example, whether additional ROs are available may be indicated by a 1-bit parameter. However, the embodiments are not limited thereto. For example, whether additional ROs are available may be indicated in an explicit manner or in an implicit manner.

[0110] The base station (110-1) can utilize the UL subband more efficiently by including information regarding whether additional RO can be used in the broadcasting message. As described above, when the uplink data transmission rate is important, information prohibiting the use of additional RO can be included in the broadcasting message. By doing so, the uplink data transmission rate can be increased by preventing terminals from using additional RO in advance. On the other hand, when improving random access performance is important, the terminal (120-1) can be allowed to use additional RO to prevent collisions occurring during the random access process and reduce the delay time.

[0111] The base station (110-1) may construct a broadcasting message based on information regarding whether the additional RO can be used. The broadcasting message may further include information regarding whether the additional RO can be used and information regarding the conditions for using the additional RO. The conditions for using the additional RO will be discussed in more detail in the description below. If the base station (110-1) decides to prohibit the use of the additional RO, information regarding the conditions for using the additional RO may not be included in the broadcasting message.

[0112] In step S136, the base station (110-1) may transmit a broadcasting message containing at least one of information regarding whether additional RO can be used and information regarding the conditions for using additional RO.

[0113] Referring again to FIG. 6, at step S140, the terminal (120-1) can check the broadcasting message. For example, the terminal (120-1) can check the system information included in the broadcasting message.

[0114] FIG. 8 is a flowchart illustrating the process of performing step S140 shown in FIG. 6.

[0115] Referring to FIG. 8, at step S142, the terminal (120-1) can receive a broadcasting message.

[0116] In step S144, the terminal (120-1) can check information regarding whether additional RO can be used, which is included in the broadcasting message. For example, the terminal (120-1) can check whether additional RO can be used by checking the indicator included in the broadcasting message. If additional RO usage is prohibited, the terminal (120-1) can perform random access using legacy RO. In this case, step S146 may be omitted.

[0117] If additional RO usage is permitted, the terminal (120-1) can check the usage conditions of the additional RO. The broadcasting message may not include information regarding whether the additional RO can be used, but may only include information regarding the usage conditions of the additional RO. In this case, the terminal (120-1) can skip step S144 and check the information regarding the usage conditions of the additional RO at step S146. The terminal (120-1) can determine the type of RO by determining whether the usage conditions of the additional RO are satisfied.

[0118] The broadcasting message may further include configuration information for using additional ROs. The terminal (120-1) can check the configuration information for using additional ROs at step S146. Based on the configuration information, the terminal (120-1) can perform random access using additional ROs.

[0119] Referring again to FIG. 6, at step S150, the terminal (120-1) can select a type of RO based on additional RO usage conditions. The terminal (120-1) can select either a legacy RO or an additional RO.

[0120] Information regarding additional RO usage conditions may include information regarding the threshold value of the signal reception strength of the terminal (120-1). That is, the broadcasting information may include the threshold value of the signal reception strength that serves as the criterion for additional RO usage. The base station (110-1) may include RSRP threshold value information in the broadcasting message. The base station (110-1) may indicate the RSRP threshold value for additional RO selection using at least one of the IEs rsrp-ThresholdSSB and rsrp-ThresholdCSI specified in the 5G standard. As another example, the base station (110-1) may indicate the RSRP threshold value for additional RO selection by adding a new parameter to the IE rach-ConfigCommon, which includes configuration information for random access.

[0121] FIG. 9 is a flowchart illustrating the process of performing step S150 of FIG. 6.

[0122] Referring to FIG. 9, in step S152-1, the terminal (120-1) can check the RSRP threshold value included in the broadcasting message. For example, the terminal (120-1) can check the threshold value for the RSRP of the SSB from the broadcasting message.

[0123] In step S154-1, the terminal (120-1) can compare the RSRP of the reference signal it measured with the RSRP threshold value.

[0124] In step S156-1, the terminal (120-1) can select the RO type based on the result of comparing the RSRP of the reference signal it measured with the RSRP threshold value.

[0125] For example, the terminal (120-1) can compare the RSRP of the SSB with the RSRP threshold value for selecting an additional RO. Here, the RSRP of the SSB may be the average received power of the reference signals (PSS, SSS, PBCH-DMRS) included in the SSB. The terminal (120-1) can measure the RSRP of the SSBs. If there is an SSB whose measured RSRP is higher than the RSRP threshold value, the terminal (120-1) can select an additional RO using that SSB. If the RSRP of all the SSBs measured by the terminal (120-1) is lower than the RSRP threshold value, the terminal (120-1) can select a legacy RO. However, even if the RSRP of all the SSBs measured by the terminal (120-1) is lower than the RSRP threshold value, the terminal (120-1) may also consider additional conditions as described below and select an additional RO other than a legacy RO if the additional conditions are satisfied.

[0126] Although the above description uses the RSRP of the SSB, it is not limited thereto. For example, the terminal (120-1) may select the RO type based on the RSRP of the CSI-RS. The terminal (120-1) may select the RO type by comparing the RSRP of the CSI-RS with the RSRP threshold value.

[0127] FIG. 10 is a conceptual diagram showing that the terminal (120-1) selects the RO type.

[0128] Referring to FIG. 10(a), the terminal (120-1) measures the strength of a reference signal (e.g., RSRP of an SSB or RSRP of CSI-RS), and as a result, the RSRP of at least one SSB may be greater than a preset RSRP threshold. In this case, the terminal (120-1) may decide to perform random access using any one of the SSBs that have an RSRP greater than the RSRP threshold. The terminal (120-1) may perform random access by selecting an additional RO through the corresponding SSB.

[0129] Referring to FIG. 10(b), the terminal (120-1) measures the strength of the reference signal and finds that the RSRP of all SSBs is lower than a preset RSRP threshold. In this case, the terminal (120-1) can perform random access by selecting a legacy RO through any one of the SSBs. As described below, if the broadcasting message includes additional conditions for selecting an additional RO, the terminal (120-1) can check the additional conditions further without immediately selecting a legacy RO. The terminal (120-1) may also select an additional RO through an SSB that meets the additional conditions.

[0130] The terminal (120-1) can select the RO type based on the result of measuring the RSRP of the reference signal and comparing it with the RSRP threshold value. Typically, SBFD symbols may have more interference than UL symbols. By allowing the terminal (120-1) to use an additional RO when the reception strength of the reference signal is sufficiently high, the effect of interference when selecting an additional RO can be reduced.

[0131] Referring again to FIG. 6, a 4-step random access procedure can be performed through steps S160 to S190.

[0132] In step S160, the terminal (120-1) can send msg1 (random access request message) to request random access. The terminal (120-1) can send a PRACH preamble.

[0133] In step S170, the base station (110-1) may transmit msg2 (random access response message) in response to msg1. msg2 may include resource allocation information and timing information for the terminal (120-1).

[0134] In step S180, the terminal (120-1) can transmit msg3 (data) at a specified timing according to the resource allocation information received from the base station (110-1).

[0135] The base station (110-1) receives msg3 (data) transmitted from the terminal (120-1), checks whether msg3 has been received, and can transmit a msg4 (contention resolution) message to the terminal (120-1) at step S190.

[0136] The terminal (120-1) may select an additional RO or legacy RO by considering other conditions even if the RSRP of the reference signal is smaller than the RSRP threshold. As another example, the terminal (120-1) may select an additional RO or legacy RO by considering only conditions other than the RSRP of the reference signal.

[0137] FIG. 11 is a flowchart illustrating the process of performing step S150 shown in FIG. 6.

[0138] Referring to FIG. 11, in step S152-2, the terminal (120-1) can check the RSRP threshold value from the broadcasting message.

[0139] In step S154-2, the terminal (120-1) can compare the RSRP of a reference signal with the RSRP threshold value. If there is a reference signal with an RSRP higher than the RSRP threshold value, the terminal (120-1) can perform a random access procedure using an additional RO of a wireless resource mapped to the reference signal.

[0140] If there is no reference signal having an RSRP higher than the RSRP threshold, in step S156-2, the terminal (120-1) may consider additional conditions.

[0141] The broadcasting message transmitted in step S130 may further include information regarding additional conditions for additional RO selection. For example, the broadcasting message may include information regarding the format of the PRACH preamble (hereinafter, preamble). The base station (110-1) may construct the broadcasting message based on the information regarding the preamble format in step S130 and transmit the broadcasting message.

[0142] The terminal (120-1) can check the preamble configuration based on the broadcasting message in step S156-2. The preamble configuration may include preamble format information. If a long preamble format is configured, the terminal (120-1) can select an RO that can use the long preamble format. Typically, since the UL time interval is allocated short, it may be difficult to allocate a long preamble format to the UL time interval. Therefore, if a long preamble format is configured, the terminal (120-1) can select an additional RO allocated to the SBFD symbol.

[0143] FIG. 12 is a conceptual diagram exemplarily showing that when a long preamble format is configured, the terminal (120-1) selects RO.

[0144] In Fig. 12, the vertical axis represents the frequency domain and the horizontal axis represents the time domain.

[0145] Referring to FIG. 12, additional RO (80) may be assigned to SBFD symbols, and legacy RO may be assigned to UL symbols.

[0146] Typically, long preambles may be difficult to use in the UL time interval because the UL time interval is short. However, exceptionally, if the UL time interval is allocated to be long, long preambles may be transmitted through UL symbols, but this situation does not occur frequently in wireless communication systems.

[0147] As shown in FIG. 12, using SBFD symbols allows for more symbols to be obtained for sending uplink signals. If the terminal (120-1) can transmit a long preamble using an additional RO, it may select an additional RO even though the RSRP of the reference signal is small.

[0148] FIG. 11 describes an embodiment in which steps S156-2 and S156-4 are performed after steps S152-2 and S154-2 are performed. However, in other embodiments, steps S152-2 and S154-2 may be omitted. That is, in other embodiments, the step of comparing RSRP by the terminal (120-1) may be omitted, and the selection of RO may be made according to the preamble format and configuration. For example, the terminal (120-1) may select an additional RO or a legacy RO by considering the preamble format without considering the RSRP of the reference signal.

[0149] The terminal (120-1) can select the RO type based on the preamble format. This allows the probability of a successful random access to be increased because, even when the RSRP of the reference signal is low, if the terminal (120-1) transmits a long preamble through an additional RO, the preamble transmission time increases and a repeat transmission gain occurs. In addition, long preambles, which were previously less available in the UL time interval of conventional wireless communication systems, can be utilized more flexibly and efficiently.

[0150] FIG. 13 is a flowchart illustrating the process of performing step S150 shown in FIG. 6.

[0151] Referring to FIG. 13, in step S152-3, the terminal (120-1) can check the RSRP threshold value from the broadcasting message.

[0152] In step S154-3, the terminal (120-1) can compare the RSRP of a reference signal with the RSRP threshold value. If there is a reference signal with an RSRP higher than the RSRP threshold value, the terminal (120-1) can perform a random access procedure using an additional RO of a wireless resource mapped to the reference signal.

[0153] If there is no reference signal having an RSRP higher than the RSRP threshold, in step S156-3, the terminal (120-1) may consider additional conditions.

[0154] The broadcasting message transmitted in step S130 may further include information regarding additional conditions for additional RO selection. For example, the broadcasting message may include configuration information for the repeated transmission of the preamble.

[0155] In step S156-3, the terminal (120-1) can check the configuration for preamble repeat transmission (or PRACH repeat transmission) based on the broadcasting message. If the base station (110-1) has configured preamble repeat transmission, the terminal (120-1) can select an RO utilizing the preamble repeat transmission to perform a random access subsequent process.

[0156] Typically, preamble repeated transmission may require a long time interval. Therefore, the terminal (120-1) may select an additional RO assigned to the SBFD symbol when the number of preamble repeated transmissions is large.

[0157] FIG. 14 is a conceptual diagram exemplifying the selection of RO by the terminal (120-1) when preamble repetitive transmission is configured.

[0158] In Fig. 14, the vertical axis represents the frequency domain and the horizontal axis represents the time domain.

[0159] Referring to FIG. 14, additional ROs (83, 84, 85) may be assigned to SBFD symbols, and a legacy RO (86) may be assigned to UL symbols. The additional ROs (83, 84, 85) may form an RO group. An RO group may be a set of resources defined by grouping ROs associated with a specific SSB. In FIG. 14, for convenience, ROs included in the same RO group are shown adjacently, but the spacing between the ROs (83, 84, 85) included in the RO group may be set larger than shown in FIG. 14.

[0160] The terminal (120-1) can perform preamble repeat transmission using RO groups (including additional ROs 83, 84, and 85) placed in the SBFD symbol. Accordingly, according to the embodiment shown in FIG. 14, the terminal (120-1) can select additional ROs based on the preamble repeat transmission configuration.

[0161] Typically, it may be difficult to apply a large number of preamble repeat transmissions because the UL time interval is short. However, exceptionally, if the UL time interval is allocated to be long, multiple preamble repeat transmissions may be used, but such a situation does not occur frequently in wireless communication systems.

[0162] As shown in FIG. 14, using SBFD symbols allows for more symbols to be obtained for sending uplink signals. If the terminal (120-1) can perform repetitive transmission of the preamble configured by the base station (110-1) using additional RO, it can select additional RO even though the RSRP of the reference signal is small.

[0163] FIG. 14 describes an embodiment in which steps S156-2 and S156-4 are performed after steps S152-2 and S154-2 are performed. However, in other embodiments, steps S152-2 and S154-2 may be omitted. For example, the terminal (120-1) may select an additional RO or legacy RO by considering the preamble format without considering the RSRP of the reference signal.

[0164] The terminal (120-1) can select a type of RO based on the preamble repeat transmission configuration. This allows the probability of a successful random access to be increased because, even when the RSRP of the reference signal is low, if the terminal (120-1) performs preamble repeat transmission through an additional RO, a repeat transmission gain is generated. In addition, a high number of preamble repeat transmissions, which were previously less available in the UL time interval of conventional wireless communication systems, can be utilized more flexibly and efficiently.

[0165] FIG. 15 is a flowchart illustrating the process of performing step S150 shown in FIG. 6.

[0166] Referring to FIG. 15, in step S152-4, the terminal (120-1) can check the RSRP threshold value from the broadcasting message.

[0167] In step S154-4, the terminal (120-1) can compare the RSRP of a reference signal with the RSRP threshold value. If there is a reference signal with an RSRP higher than the RSRP threshold value, the terminal (120-1) can perform a random access procedure using an additional RO of a wireless resource mapped to the reference signal.

[0168] If there is no reference signal having an RSRP higher than the RSRP threshold, in step S156-4, the terminal (120-1) may consider additional conditions.

[0169] The broadcasting message transmitted in step S130 may include information related to the PRACH resource configuration ratio. For example, the broadcasting message may include PRACH configuration information. The PRACH configuration information may be indicated in the 5G prach-Configcommon and / or prach-ConfigurationIndex IE. As another example, the broadcasting message may separately include additional information indicating the resource allocation ratios of additional ROs and / or legacy ROs.

[0170] The terminal (120-1) can select an RO based on the ratio of the allocated resources of the legacy RO and the additional RO allocated resources.

[0171] In step S156-4, the terminal (120-1) can check the PRACH resource configuration ratio based on information related to the PRACH resource configuration ratio. The terminal (120-1) can check the resource allocation ratio of additional ROs and / or the resource allocation ratio of legacy ROs.

[0172] In step S158-4, the terminal (120-1) can determine the probability of selecting an additional RO based on the wireless resource allocation ratio of the additional RO. For example, the wireless resource allocation ratio of the additional RO can be determined based on the size or amount of wireless resources allocated to the additional RO in the time and frequency domains and the size or amount of wireless resources allocated to the legacy RO.

[0173] FIG. 16 is a conceptual diagram exemplifying the terminal (120-1) selecting RO.

[0174] Referring to FIG. 16, the terminal (120-1) can determine the probability of selecting an additional RO based on the ratio of wireless resources allocated to the additional RO. For example, the terminal (120-1) can increase the probability of selecting an additional RO as the ratio of wireless resources allocated to the additional RO increases.

[0175] For example, in FIG. 16, since the resource allocation ratio between the additional RO and the legacy RO is 3:1, the terminal (120-1) can select the additional RO with a probability of 75% and select the legacy RO with a probability of 25%. However, the resource allocation ratio and the RO selection probability may not be exactly the same.

[0176] According to the above-described embodiment, the base station (110-1) can control the probability of the additional RO being used by adjusting the resource allocation ratio of the additional RO and the legacy RO. If the base station (110-1) intends to use SBFD symbols to improve UL throughput according to the service environment (for example, when there are many terminals that transmit a large amount of uplink data, such as drones), the resource allocation ratio of the additional RO can be lowered. In this case, by lowering the probability that the terminal (120-1) selects the additional RO, the SBFD symbols can naturally be used to improve UL throughput. In addition, by reducing the probability that the additional RO is selected, interference effects that may occur in the UL subband can be reduced.

[0177] If the base station (110-1) intends to use SBFD symbols for priority in random access (for example, when there are many IoT terminals), it can increase the resource allocation ratio of additional ROs. In this case, by increasing the probability that the terminal (120-1) selects additional ROs, SBFD symbols can naturally be used for random access. Through this, the probability of random access success can be increased and the delay time required for random access can be reduced.

[0178] FIG. 17 is a flowchart illustrating the process of performing step S160 of FIG. 6.

[0179] Referring to FIG. 17, in step S162-1, the terminal (120-1) may wait until the selected RO is available. For example, if the terminal (120-1) decides to select an additional RO in step S150, the terminal (120-1) may wait without using the legacy RO even if the legacy RO appears first.

[0180] In step S164-1, the terminal (120-1) can transmit msg1 using a selected type of RO.

[0181] If the terminal (120-1) fails to perform a random access procedure while performing a random access procedure, it can perform a subsequent procedure using another RO.

[0182] FIG. 18 is a flowchart illustrating a method for performing random access according to an exemplary embodiment.

[0183] In describing the embodiment of FIG. 18, each of steps S210, S220, S230, S240, and S250 may be similar to steps S110, S120, S130, S140, and S150 of FIG. 6. Therefore, in describing the embodiment of FIG. 18, content that overlaps with FIG. 6 is omitted.

[0184] Referring to FIG. 18, in step S260, the terminal (120-1) can transmit msg1 using the selected RO. However, the base station (110-1) may not receive msg1. Even though the base station (110-1) transmits msg2 after receiving msg1, the terminal (120-1) may not receive msg2.

[0185] If such an error or failure occurs, the terminal (120-1) can repeat the procedure of transmitting msg1 using the previously selected type of RO. For example, if the terminal (120-1) chooses to use an additional RO, when a failure to transmit msg1 occurs, the terminal (120-1) can retransmit msg1 using another additional RO.

[0186] The broadcasting message transmitted in step S230 may include setting information for the maximum number of transmissions (N). The maximum number of transmissions may be specified by the preambleTransMaxIE of the 5G standard specification. However, the embodiments are not limited thereto. The maximum number of transmissions may also be specified by other IEs or parameters.

[0187] In step S270, when the number of msg1 transmission failures (the number of preamble transmission failures caused by the transmission failure of msg1 and / or msg2) reaches the maximum number of transmissions, the terminal (120-1) may reset the type of RO. During the reset process, the terminal (120-1) may evaluate certain conditions and decide to use a different type of RO than the one previously used. As another example, the terminal (120-1) may use the same type of RO as before even after the reset.

[0188] In steps S282 to S288, the terminal (120-1) can select an RO based on the type of RO set in step S270 and proceed with a subsequent procedure for random access using the selected RO.

[0189] Steps S282 to S288 of FIG. 18 may be similar to steps S160 to S190 of FIG. 6. Therefore, redundant descriptions are omitted.

[0190] FIG. 19 is a flowchart illustrating the process of performing step S270 of FIG. 18.

[0191] In step S272, the terminal (120-1) can transmit msg1 using a selected type of RO. If the transmission of msg1 fails, the terminal (120-1) can repeat the transmission of msg1 using the same type of RO. The terminal (120-1) can count the number of times msg1 is transmitted and compare the number of times msg1 is transmitted with the maximum number of times. The terminal (120-1) can transmit msg1 as many times as the maximum number of times.

[0192] In step S276, if the number of msg1 transmission failures (the number of preamble transmission failures caused by the transmission failure of msg1 and / or the transmission failure of msg2) reaches the maximum number of transmissions, the terminal (120-1) can check the conditions for changing the RO type.

[0193] In step S278, the terminal (120-1) can select an RO based on the RO change condition confirmed in step S166-2.

[0194] For example, if the RO that was previously used is an additional RO, the terminal (120-1) can select the legacy RO without considering other conditions.

[0195] If the RO currently in use is a legacy RO, the terminal (120-1) can check the factors for selecting an additional RO described with reference to FIGS. 6 to 17. The terminal (120-1) can determine whether to select an additional RO based on at least one of the information regarding the availability of the additional RO included in the broadcasting message, the RSRP of the reference signal, the preamble format, the preamble repeat transmission configuration, and the PRACH resource configuration ratio.

[0196] As described above, if the number of message transmissions or receptions in the random access procedure exceeds the maximum number of transmissions, the terminal (120-1) can reset the RO type to increase the probability of a successful random access.

[0197] FIG. 20 is a flowchart illustrating a random access method according to an exemplary embodiment.

[0198] Referring to FIG. 20, a 2-step random access can be performed. Since steps S310, S320, S330, S340, and S350 of FIG. 20 are similar to steps S110, S120, S130, 140, and S150 of FIG. 6, a redundant description is omitted.

[0199] In step S360, the terminal (120-1) can transmit msgA. msgA can perform the functions of msg1 and msg3 of the 4-step random access. msgA may include PRACH and some UL data.

[0200] The base station (110-1) that receives msgA in step S370 can transmit msgB. msgB can perform the functions of msg2 and msg4 of the 4th stage random access. msgB may include a random access response and allocation information for the terminal (120-1).

[0201] FIG. 21 is a flowchart illustrating a method for performing random access according to an exemplary embodiment.

[0202] In describing the embodiment of FIG. 21, content that overlaps with FIG. 20 is omitted.

[0203] Referring to FIG. 21, in step S460, the terminal (120-1) can transmit msgA using the selected RO. However, the base station (110-1) may not receive msgA. Even though the base station (110-1) transmits msgB after receiving msgA, the terminal (120-1) may not receive msgB.

[0204] If such an error or failure occurs, the terminal (120-1) can repeat the procedure of transmitting msgA using the previously selected type of RO.

[0205] The broadcasting message transmitted in step S230 may include setting information for the maximum number of transmissions. As described below, the setting information for the maximum number of transmissions may include a first reference number and a second reference number. The terminal (120-1) may compare the number of transmissions of msgA with at least one of the first reference number and the second reference number to reset at least one of the RO type and random access method (2-step or 4-step).

[0206] In step S470, when the number of msgA transmission failures (the number of preamble transmission failures caused by the transmission failure of msgA and / or the transmission failure of msgB) reaches the maximum number of transmissions, the terminal (120-1) may reset the type of RO. During the reset process, the terminal (120-1) may reset at least one of the type of RO and the random access method (2-step or 4-step). The terminal (120-1) may perform a random access subsequent procedure in steps S482 and S484 using the type of RO determined by the reset.

[0207] FIG. 22 is a flowchart illustrating the process of performing step S470 of FIG. 21.

[0208] Referring to FIG. 22, in step S472, the terminal (120-1) can count the number of transmission failures of msgA. When the number of transmission failures of msgA (number of preamble transmission failures caused by transmission failure of msgA and / or transmission failure of msgB) reaches the maximum number of transmissions, the terminal (120-1) can perform step S474.

[0209] In step S474, the terminal (120-1) can compare the RSRP of the reference signal with a first threshold value. The first threshold value may serve as a criterion for performing 2-step random access. The first threshold value may be indicated by the msgA-RSRP-Threshold-r16IE of the 5G standard specification. However, the embodiment is not limited thereto, and the first threshold value may be indicated by other IEs or parameters.

[0210] If the RSRP of the reference signal is less than the first threshold value, the terminal (120-1) may change the procedure to a 4-step random access and perform a subsequent random access procedure. In this case, step S476-1 may be omitted. And in step S478-1, the terminal (120-1) may select an RO for performing the 4-step random access procedure.

[0211] When the RSRP of the reference signal is low, the terminal (120-1) can increase the probability of a successful random access by converting from a 2-step random access procedure to a 4-step random access procedure based on a first threshold value. When both 2-step random access and 4-step random access are allowed, the terminal (120-1) can select a random access method and an RO through RSRP comparison.

[0212] When the RSRP of the reference signal is greater than the first threshold value, the operation of the terminal (120-1) may vary depending on the type of RO previously used. For example, if the RO used by the terminal (120-1) is an additional RO, the terminal (120-1) may select a legacy RO in step S478-1 and terminate step S470 of FIG. 21. In this case, step S476-1 may be omitted. When the RSRP of the reference signal is greater than the first threshold value and the type of RO used by the terminal (120-1) is an additional RO, the terminal (120-1) may use a legacy RO while maintaining the 2-step random access procedure. Through this, the terminal (120-1) can reduce the number of signalings while maintaining the 2-step random access procedure, reduce interference effects by using a legacy RO, and increase the probability of a successful random access.

[0213] Although the previous description exemplarily explained that step S476-1 is omitted, the embodiments are not limited thereto. Under the same conditions, e.g., when the RSRP of the reference signal is greater than the first threshold value and the RO used by the terminal (120-1) is an additional RO, the terminal (120-1) may perform step S476-1. The terminal (120-1) may compare the RSRP of the reference signal with the second threshold value. The second threshold value may serve as a selection criterion for the additional RO. If the RSRP of the reference signal is greater than the second threshold value, the terminal (120-1) may continue to select the additional RO. If the RSRP of the reference signal is less than the second threshold value, the terminal (120-1) may select the legacy RO.

[0214] If the RSRP of the reference signal is greater than the first threshold and the RO used by the terminal (120-1) is a legacy RO, the terminal (120-1) can compare the RSRP of the reference signal with the second threshold in step S476-1. Information regarding the first threshold and the second threshold may be included in the broadcasting message transmitted in step S430.

[0215] The terminal (120-1) can compare the RSRP of the reference signal with a second threshold value. The second threshold value can be a selection criterion for an additional RO. If the RSRP of the reference signal is greater than the second threshold value, the terminal (120-1) can select an additional RO. If the RSRP of the reference signal is less than the second threshold value, the terminal (120-1) can select a legacy RO.

[0216] When the RSRP of the reference signal is greater than the first threshold value, the terminal (120-1) can reduce the number of signaling operations while maintaining 2-step random access. Additionally, the terminal (120-1) can increase the probability of a successful random access by selecting an RO type by comparing the RSRP of the reference signal with the second threshold value.

[0217] The terminal (120-1) can reset at least one of a random access method (2-step or 4-step) and a type of RO (additional RO or legacy RO) by comparing the number of msgA transmission failures with a plurality of threshold count values.

[0218] FIG. 23 is a flowchart illustrating the process of performing step S470 of FIG. 21.

[0219] Referring to FIG. 23, in step S472-2, the terminal (120-1) can compare the number of msgA transmission failures with at least one of a first threshold number and a second threshold number. For convenience, the first threshold number is referred to as N below. 2step Indicate as , and the second critical number is N add It is indicated as.

[0220] N 2step ... may be indicated by the preambleTransMaxIE of the RACH-ConfigGenericTwoStepRA-r16 of the 5G standard, but embodiments are not limited thereto. N addcan be indicated by the IE or parameters included in the broadcasting message. For example, N add The IE or parameter indicating [this] may be referred to as preambleTransMax-SBFD. However, this is merely an exemplary designation and does not limit the examples.

[0221] Terminal (120-1) is N 2step It can be considered first.

[0222] N 2step < N add In this case, the terminal (120-1) has N number of preamble transmission failures. 2step It can be compared with. The number of preamble transmission failures is N 2step When it becomes larger, the terminal (120-1) can convert the random access method to a 4-step method in step S474-2.

[0223] N 2step > N add In this case, the terminal (120-1) has N number of preamble transmission failures. add It can be compared with. The number of preamble transmission failures is N add When it becomes larger, the terminal (120-1) may select a legacy RO without selecting an additional RO. Even after selecting a legacy RO, transmission failures persist, and the number of preamble transmission failures is N. 2step When it becomes larger, the terminal (120-1) can convert the random access method to a 4-step method.

[0224] As described above, the terminal (120-1) is N 2step By prioritizing , the random access method can be appropriately selected. In addition, the number of preamble transmission failures is N 2step Smaller than N add In the case of a large amount, the random access success probability can be increased without excessive procedure changes by performing the random access procedure using the legacy RO before the terminal (120-1) changes the random access method.

[0225] The following describes the method for selecting RO in a non-competitive, random access procedure.

[0226] Contention-Free Random Access (CFRA) is a method that guarantees fast access without collisions to a specific terminal. Contention-Free Random Access can be triggered by a PDCCH. The base station (110-1) can transmit a DCI to the terminal (120-1) via the PDCCH and instruct the start of the contention-free random access procedure.

[0227] Non-contention random access can be used in special service environments such as handover, RRC connection reconfiguration, and URLLC. Non-contention random access can be used when the base station (110-1) recognizes the terminal (120-1) in advance. Therefore, non-contention random access can be used when the terminal (120-1) is in an RRC connection state or an asynchronous state.

[0228] FIG. 24 is a flowchart illustrating the process of performing random access in an exemplary manner.

[0229] In the embodiments of FIGS. 1 to 23, the terminal (120-1) could select an RO. That is, the type of RO of the terminal (120-1) can be selected in a contention-based random access procedure. In a non-contention random access method, the base station (110-1) can select an RO.

[0230] In step S510, the base station (110-1) can select an RO. The base station (110-1) can select a type of RO (legacy RO or additional RO). The method by which the base station (110-1) selects an RO may be similar to the method of selecting an RO of the terminal (120-1) described with reference to the embodiments of FIGS. 1 to 23.

[0231] The base station (110-1) can determine whether to select an additional RO based on at least one of the RSRP of the reference signal, the preamble format, the preamble repeat transmission configuration and the PRACH resource configuration ratio.

[0232] The base station (110-1) can obtain information from the terminal (120-1) regarding the RSRP of the reference signal measured by the terminal (120-1). If the RSRP of the reference signal exceeds the RSRP threshold value, the base station (110-1) can select an additional RO.

[0233] The base station (110-1) can select an RO based on the preamble format. For example, if it is decided to use a long preamble format, the base station (110-1) can select an RO capable of transmitting the long preamble format. The base station (110-1) can select an additional RO to transmit the long preamble format.

[0234] The base station (110-1) can select an RO based on the preamble repeat transmission configuration. The base station (110-1) can select an RO capable of preamble repeat transmission. If the number of preamble repeat transmissions is set to be large, the base station (110-1) can select an additional RO.

[0235] The base station (110-1) can adjust the probability of selecting additional ROs based on the PRACH resource composition ratio.

[0236] In step S520, the base station (110-1) can transmit downlink control information. The base station (110-1) can transmit DCI via PDCCH. The base station (110-1) can include RO selection information in the downlink control information. The downlink control information may include information indicating the type of RO selected by the base station (110-1). For example, DCI 1_0 may include information indicating the type of RO selected by the base station (110-1). DCI 1_0 may include information regarding the PRACH resources used by the terminal (120-) and the conditions for using the PRACH resources.

[0237] In step S530, the terminal (120-1) can transmit msg1. The terminal (120-1) can transmit msg1 based on DCI 1_0 transmitted by the base station (110-1).

[0238] In step S540, the base station (110-1) may transmit Msg2 to the terminal (120-1). Msg2 may include a timing adjustment command, an uplink transmission permission (UL grant), and the terminal's ID (temporary C-RNTI).

[0239] In step S550, the base station (110-1) can transmit RRCConnectionReconfiguration. The base station (110-1) can instruct the terminal to set up or update the connection through the RRCConnectionReconfiguration message. The RRCConnectionReconfiguration message can provide network configuration information, including resource allocation and security key updates.

[0240] In step S560, the terminal (120-1) can transmit RRCReconfigurationComplete. The connection and synchronization between the terminal (120-1) and the base station (110-1) can be completed.

[0241] FIG. 25 is a conceptual diagram exemplarily illustrating the DCI transmitted in step S520 of FIG. 24.

[0242] Referring to FIG. 25, the DCI may include a plurality of fields.

[0243] The DCI Format Identifier can be used to identify the format of a DCI message. The terminal (120-1) can determine the message format and processing method by checking this field. The Frequency Domain Resource Assignment can define the frequency resources that the terminal (120-1) will use for UL transmission. Through this field, the network can assign the frequency bandwidth to the terminal (120-1) to be utilized when performing random access. The Random Access Preamble Index can indicate the index of the random access preamble that the terminal (120-1) must use. Through this value, the network can reduce collisions between terminals and identify the random access of a specific terminal. The UL / SUL Indicator can determine whether the terminal (120-1) will use the uplink or the Supplementary Uplink (SUL). This field can optimize the resource usage of the terminal (120-1) according to the network settings. The SS / PBCH Index can instruct the terminal (120-1) to refer to a specific Synchronization Signal / Physical Broadcast Channel (SS / PBCH) block. The network can utilize this value to support the initial synchronization required for the corresponding random access procedure. The PRACH Mask Index can specify the mask value of the PRACH resource to be used by the terminal (120-1). Through this, the network restricts the terminal (120-1) to use a specific PRACH resource when attempting a random access.

[0244] The Random access occasion type can be used to specify the RO type in a wireless communication system using SBFD. This field can specify the RO type to the terminal (120-1) for a CFRA triggered by a PDCCH instruction, allowing the terminal (120-1) to select the RO type as intended by the base station. This field can be composed of 1 bit. This field can represent an additional RO or a legacy RO through 0 and 1. Through this field, the terminal (120-1) can recognize which RO the resource and index indicated in the remaining fields correspond to.

[0245] Reserved Bits are fields reserved for future scalability or specific network requirements. Even if they are not currently in use, the consistency of the message structure can be maintained. In the case of DCI format 1_0 for instructions via the existing PDCCH, there were 10 reserved bits, but according to the embodiment with reference to FIG. 24, 1 bit is allocated to the random access occasion type, leaving 9 reserved bits.

[0246] If the base station (110-1) does not allow random access in additional ROs, or if the base station does not operate SBFD, the base station may use the existing standard DCI 1_0 format without adding a random access occasion type field to DCI 1_0 for CFRA triggered by the PDCCH instruction.

[0247] FIG. 26 is a conceptual diagram exemplifying the start time of a random access procedure according to RO coordination in a random access procedure.

[0248] In Fig. 26, "D" represents the DL slot, "U" represents the UL slot, and "S" represents the special slot.

[0249] This description is based on CFRA triggered by the PDCCH instruction, but is not limited to this case and can be applied equally to the msg1 and msgA transmission steps in contention-based 4-level random access and 2-level random access, respectively.

[0250] Referring to FIG. 26, the terminal (120-1) can receive DCI transmitted by the base station (110-1) via PDCCH in the first time interval (12). The terminal (120-1) can transmit msg1 using the UL subband in the second time interval (14). Of course, the terminal (120-1) can also transmit msg1 using the UL subband in the third time interval (16).

[0251] Since the UL resource allocation required for the terminal (120-1) to transmit msg1 is performed flexibly and quickly through the UL subband, the terminal (120-1) can transmit msg1 without waiting until the UL time interval. Therefore, the time required to reconnect to the base station (110-1) can be shortened by the third time interval (16). Thus, the delay occurring in the contention-based random access process triggered by the PDCCH instruction can be reduced.

[0252] A random access method and apparatus according to exemplary embodiments have been described above with reference to FIGS. 1 to 26.

[0253] According to at least one embodiment, the selection of additional ROs can be performed appropriately and efficiently. According to at least one embodiment, additional ROs can be appropriately selected to increase the probability of random access success and reduce the delay time required for the random access procedure.

[0254] According to at least one embodiment, the conditions for selecting additional RO are shared between the terminal and the base station and are appropriately reflected, thereby increasing the efficiency of using the UL subband.

[0255] According to at least one embodiment, if the uplink data transmission rate is important, information prohibiting the use of additional RO may be included in the broadcasting message. This prevents terminals from using additional RO in advance, thereby increasing the uplink data transmission rate. On the other hand, if the improvement of random access performance is important, allowing the terminal (120-1) to use additional RO can prevent collisions occurring during the random access process and reduce the delay time.

[0256] According to at least one embodiment, the effect of interference can be reduced by selecting an additional RO based on the RSRP of the reference signal.

[0257] According to at least one embodiment, flexible communication system operation may be possible by selecting an additional RO based on at least one of a preamble format and a preamble repeat transmission configuration.

[0258] According to at least one embodiment, interference effects or random access latency can be reduced by adjusting additional RO selection probability according to the PRACH resource configuration ratio.

[0259] According to at least one embodiment, the signaling overhead and delay time required for a random access procedure can be efficiently managed by redoing the RO selection when a message transmission fails in a random access procedure.

[0260] According to at least one embodiment, in contention-based random access, a base station uses DCI to indicate the RO type, so that a terminal can use an appropriate type of RO according to network conditions.

[0261] Based on the foregoing description of various embodiments of this disclosure, a person skilled in the art will clearly understand that the methods and / or processes of the present invention and the steps thereof may be realized in hardware, software, or any combination of hardware and software suitable for a particular use case. The hardware may include a general-purpose computer and / or a dedicated computing device or a specific computing device or a particular form or component of a specific computing device. The processes may be realized by one or more processors having internal and / or external memory, such as a microprocessor, a controller, such as a microcontroller, an embedded microcontroller, a microcomputer, an arithmetic logic unit (ALU), a digital signal processor, such as a programmable digital signal processor, or other programmable device. In addition, or as an alternative, the above processes may be carried out by an application-specific integrated circuit (ASIC), a programmable gate array, such as a field programmable gate array (FPGA), a programmable logic unit (PLU), or a programmable array logic (PAL), or any other device capable of executing and responding to instructions, any other device or combination of devices that may be configured to process electronic signals. The processing unit may execute an operating system (OS) and one or more software applications executed on said operating system. Additionally, the processing unit may access, store, manipulate, process, and generate data in response to the execution of the software.For ease of understanding, the processing unit may be described as being used as a single unit, but a person of ordinary skill in the art will understand that the processing unit may include multiple processing elements and / or multiple types of processing elements. For example, the processing unit may include multiple processors or one processor and one controller. In addition, other processing configurations, such as parallel processors, are also possible.

[0262] Software may include computer programs, code, instructions, or a combination of one or more of these, and may configure a processing unit to operate as desired or command the processing unit independently or collectively. Software and / or data may be permanently or temporarily embodied in any type of machine, component, physical device, virtual equipment, computer storage medium or device, or transmitted signal wave in order to be interpreted by the processing unit or to provide instructions or data to the processing unit. Software may be distributed over networked computer systems and may be stored or executed in a distributed manner. Software and data may be stored on one or more machine-readable recording media.

[0263] Furthermore, parts contributing to the objects of the technical solution of the present invention or to the prior art may be implemented in the form of program instructions that can be executed through various computer components and recorded on a machine-readable medium. The machine-readable medium may include program instructions, data files, data structures, etc., either alone or in combination. The program instructions recorded on the machine-readable recording medium may be those specifically designed and configured for the embodiments, or they may be those known and available to a person skilled in the art of computer software. Examples of machine-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes; optical recording media such as CD-ROMs, DVDs, and Blu-rays; magneto-optical media such as floptical disks; and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, and flash memory. Examples of program instructions include machine code, bytecode, as well as high-level language code that can be executed by a computer using an interpreter, etc., which can be created using a structured programming language such as C, an object-oriented programming language such as C++, or high-level or low-level programming languages ​​(assembly language, hardware description languages, and database programming languages ​​and technologies), which can be stored and compiled or interpreted to be executed on a machine capable of executing any of the aforementioned devices, as well as a processor, a processor architecture, or a heterogeneous combination of different hardware and software combinations.

[0264] Accordingly, in one embodiment according to the present invention, when the methods and combinations thereof described above are performed by one or more computing devices, the methods and combinations thereof may be implemented as executable code that performs each step. In another embodiment, the methods may be implemented as systems that perform the steps, and the methods may be distributed in various ways across devices, or all functions may be integrated into a single dedicated, standalone device or other hardware. In yet another embodiment, the means for performing the steps associated with the processes described above may include any of the hardware and / or software described above. All such sequential combinations and combinations are intended to fall within the scope of this disclosure.

[0265] For example, the above-described hardware device may be configured to operate as one or more software modules to perform the operation of the embodiment, and vice versa. The hardware device may include a processor such as an MPU, CPU, GPU, or TPU that is combined with memory such as ROM / RAM for storing program instructions and configured to execute instructions stored in said memory, and may include a communication unit capable of exchanging signals with an external device. Additionally, the hardware device may include a keyboard, mouse, or other external input device for receiving instructions written by developers.

[0266] Although the present invention has been described above with specific details such as specific components, limited embodiments, and drawings, this is provided only to aid in a more comprehensive understanding of the invention, and the invention is not limited to the above embodiments, and a person skilled in the art to which the invention belongs can make various modifications and variations from this description.

[0267] Accordingly, the scope of the present invention is not limited to the embodiments described above, and all modifications equivalent to or equivalent to the claims attached to this disclosure, as well as the claims attached to this disclosure, shall be considered to be within the scope of the scope of the concept of the present invention. For example, appropriate results may be achieved even if the described techniques are performed in a different order than the described method, and / or the components of the described system, structure, device, circuit, etc. are combined or assembled in a form different from the described method, or are replaced or substituted by other components or equivalents.

[0268] Such equivalent or equivalent modifications may include, for example, logically equivalent methods capable of producing the same result as carrying out the method according to the present invention; the true meaning and scope of the present invention shall not be limited by the examples described above, but shall be understood in the broadest sense permissible by law.

Claims

1. A method for performing random access performed by a terminal comprising at least one processor, wherein Step of receiving a reference signal; Step of receiving a broadcasting message; A step of obtaining information for determining the type of Random Access Occasion (RO) from the above broadcasting message; A step of selecting either an additional RO or a legacy RO based on information for determining the type of the above RO; and A method for performing random access including the step of performing random access using a selected RO.

2. In Paragraph 1, A random access execution method in which the above additional RO is placed in an SBFD time interval and the above legacy RO is placed in a non-SBFD time interval.

3. In Paragraph 2, The above broadcasting message includes information regarding whether the above additional RO can be used, and A random access method for selecting a type of RO based on information regarding the availability of use of the additional RO in the step of selecting either an additional RO or a legacy RO.

4. In Paragraph 2, The above broadcasting message includes information on the RSRP threshold value for the Reference Signal Received Power (RSRP) of the above reference signal, and A random access method for selecting a type of RO based on the comparison result between the RSRP of the reference signal and the RSRP threshold value in the step of selecting either an additional RO or a legacy RO.

5. In Paragraph 4, A random access method for selecting an additional RO when the RSRP of the above reference signal is greater than the RSRP threshold value.

6. In Paragraph 2, The above broadcasting message includes information about the preamble format used in the random access procedure, and A random access method for selecting a type of RO based on information about the preamble format in the step of selecting either an additional RO or a legacy RO.

7. In Paragraph 6, A method for performing random access to select additional ROs when the above preamble format is a long preamble format.

8. In Paragraph 2, The above broadcasting message includes preamble repeat transmission configuration information, and A random access method for selecting a type of RO based on the preamble iteration transmission configuration in the step of selecting either an additional RO or a legacy RO.

9. In Paragraph 2, The above broadcasting message includes information related to the composition ratio of physical random access channel (PRACH) resources, and The step of selecting either Additional RO or Legacy RO is, A method for performing random access comprising the steps of determining a resource allocation ratio of an additional RO based on information related to the above-mentioned PRACH resource composition ratio, determining a selection probability of an additional RO based on the above-mentioned resource allocation ratio of an additional RO, and selecting an additional RO or a legacy RO based on the additional RO selection probability.

10. In Paragraph 1, The step of performing random access using the selected RO is, A step of transmitting a preamble using the selected RO above; If the above preamble transmission fails, a step of counting the number of preamble transmission failures; A method for performing random access, comprising the step of resetting the type of RO when the number of preamble transmission failures reaches a preset maximum number of transmissions.

11. In Paragraph 1, In the step of performing random access using a selected RO, if random access is performed based on a 2-step method, the step of performing random access using the selected RO is: A step of transmitting a preamble using the selected RO above; If the above preamble transmission fails, a step of counting the number of preamble transmission failures; When the number of preamble transmission failures reaches a preset maximum number of transmissions, a step of comparing the RSRP of the reference signal with a first threshold value; A method for performing random access, comprising the step of switching to a 4-step method to perform random access when the RSRP of the reference signal is smaller than a first threshold value.

12. In Paragraph 11, The step of performing random access using the selected RO above is, If the RSRP of the reference signal is greater than a first threshold value, a step of comparing the RSRP of the reference signal with a second threshold value; and A random access execution method comprising the step of performing random access in a 2-step manner using an additional RO when the RSRP of the above reference signal is greater than a second threshold value.

13. In Paragraph 1, In the step of performing random access using a selected RO, if random access is performed based on a 2-step method, the step of performing random access using the selected RO is: A step of transmitting a preamble using the selected RO above; If the above preamble transmission fails, a step of comparing the number of preamble transmission failures with at least one of a first threshold number and a second threshold number; and A random access method comprising the step of resetting the type of RO based on the result of comparing the number of preamble transmission failures with at least one of a first threshold number and a second threshold number.

14. In Paragraph 13, A random access execution method that performs random access by switching to a 4-step method when the number of preamble transmission failures is greater than the first threshold number.

15. In Paragraph 13, A random access execution method that performs random access in a 2-step manner using legacy RO when the number of preamble transmission failures is less than the first threshold number and greater than the second threshold number.

16. A method for performing random access performed by a base station comprising at least one processor, wherein A step of obtaining RSRP information of a reference signal measured by the terminal from the terminal; A step of selecting an RO type based on the RSRP information of the above reference signal; A step of configuring downlink control information including information on the selected RO type; and A method for performing random access comprising the step of transmitting downlink control information including information about the selected RO type.

17. In Paragraph 16, A random access method comprising information regarding the selected RO type, including information indicating either an additional RO or a legacy RO.

18. In Paragraph 17, A random access method for selecting an RO type based on at least one of the comparison result between the RSRP of the reference signal and the RSRP threshold value, a preamble format, a preamble repeat transmission configuration, and a PRACH resource configuration ratio in the step of selecting the RO type.

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