US20200260341A1 - Method and apparatus for indicating two-step random access procedure in wireless communication system - Google Patents

Method and apparatus for indicating two-step random access procedure in wireless communication system Download PDF

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Publication number
US20200260341A1
US20200260341A1 US16/784,550 US202016784550A US2020260341A1 US 20200260341 A1 US20200260341 A1 US 20200260341A1 US 202016784550 A US202016784550 A US 202016784550A US 2020260341 A1 US2020260341 A1 US 2020260341A1
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Prior art keywords
random access
base station
message
preamble
information
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US16/784,550
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English (en)
Inventor
Jaehyuk JANG
Soenghun KIM
Anil Agiwal
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Samsung Electronics Co Ltd
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Samsung Electronics Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0055—Transmission or use of information for re-establishing the radio link
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0833—Random access procedures, e.g. with 4-step access
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/002—Transmission of channel access control information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0055—Transmission or use of information for re-establishing the radio link
    • H04W36/0064—Transmission or use of information for re-establishing the radio link of control information between different access points
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0055—Transmission or use of information for re-establishing the radio link
    • H04W36/0077—Transmission or use of information for re-establishing the radio link of access information of target access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0833—Random access procedures, e.g. with 4-step access
    • H04W74/0841—Random access procedures, e.g. with 4-step access with collision treatment
    • H04W74/085—Random access procedures, e.g. with 4-step access with collision treatment collision avoidance

Definitions

  • the disclosure relates to a method for applying two-step random access in a wireless communication system, specifically when 3rd generation partnership project (3GPP) 5th generation (5G) new radio (NR) technology is used in an unlicensed band. More particularly, the disclosure relates to an apparatus for applying two-step random access in a wireless communication system, specifically when 3GPP 5G new radio (NR) technology is used in an unlicensed band.
  • 3GPP 5G new radio (NR) technology is used in an unlicensed band.
  • the 5G communication system or the pre-5G communication system is called a beyond 4G network communication system or a post long-term evolution (LTE) system.
  • LTE post long-term evolution
  • an implementation of the 5G communication system in a mmWave band for example, 60 GHz band
  • technologies such as beamforming, massive multiple-input and multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, analog beam-forming, and large-scale antenna technologies are being discussed as means to mitigate a propagation path loss in the ultrahigh-frequency band and increase a propagation transmission distance.
  • MIMO massive multiple-input and multiple-output
  • FD-MIMO Full Dimensional MIMO
  • array antenna analog beam-forming
  • large-scale antenna technologies are being discussed as means to mitigate a propagation path loss in the ultrahigh-frequency band and increase a propagation transmission distance.
  • the 5G communication system has developed technologies such as an evolved small cell, an advanced small cell, a cloud Radio Access Network (RAN), an ultra-dense network, Device to Device communication (D2D), a wireless backhaul, a moving network, cooperative communication, Coordinated Multi-Points (CoMP), and received interference cancellation to improve the system network.
  • ACM Advanced Coding Modulation
  • FQAM Hybrid FSK and QAM Modulation
  • SWSC Sliding Window Superposition Coding
  • FBMC Filter Bank Multi Carrier
  • NOMA Non Orthogonal Multiple Access
  • SCMA Sparse Code Multiple Access
  • eMBB ultra wide band mobile communication service
  • URLLC ultra-reliable and low latency communication
  • mMTC massive device-to-device communication service
  • eMBMS next-generation broadcast service
  • URLLC ultra wide band mobile communication service
  • mMTC massive device-to-device communication service
  • eMBMS next-generation broadcast service
  • a system providing the URLLC service may be referred to as a URLLC system
  • a system providing the eMBB service may be referred to as an eMBB system.
  • the terms “service” and “system” may be interchangeably used.
  • the URLLC service that is a new service under consideration in the 5G system in contrast to the existing 4G system requires to meet ultrahigh reliability (e.g., packet error rate of about 10-5) and low latency (e.g., about 0.5 msec) conditions as compared to the other services.
  • ultrahigh reliability e.g., packet error rate of about 10-5
  • low latency e.g., about 0.5 msec
  • the URLLC service may need to apply a shorter transmission time interval (TTI) than the eMBB service, and various operating scheme employing the same are now under consideration.
  • TTI transmission time interval
  • IoT Internet of Things
  • M2M Machine-to-Machine
  • MTC Machine-Type Communication
  • an intelligent Internet Technology (IT) service to create a new value for peoples' lives may be provided.
  • the IoT may be applied to fields such as those of a smart home, a smart building, a smart city, a smart car, a connected car, a smart grid, health care, a smart home appliance, or high-tech medical services through the convergence of the Information Technology (IT) of the related art and various industries.
  • IT Information Technology
  • the 5G communication technology such as a sensor network, machine-to-machine (M2M) communication, and machine-type communication (MTC)
  • M2M machine-to-machine
  • MTC machine-type communication
  • the application of a cloud RAN as the big data processing technology may be an example of convergence of the 5G technology and the IoT technology.
  • an aspect of the disclosure is to provide a method for reducing a collision due to contention when two-step random access is applied in an unlicensed band.
  • Another aspect of the disclosure is to provide an apparatus for reducing a collision due to contention when two-step random access is applied in an unlicensed band.
  • a method for performing random access (RA) by a user equipment (UE) in a wireless communication system includes receiving a handover indication message including preamble indication information about the UE and RA resource information from a first base station, and transmitting a message A (Msg A) for a handover to a second base station, based on the preamble indication information about the UE and the RA resource information included in the handover indication message.
  • a handover indication message including preamble indication information about the UE and RA resource information from a first base station
  • Msg A message A
  • a method for a first base station in a wireless communication system includes generating a handover indication message including preamble indication information and RA resource information for a handover of a UE, and transmitting the generated handover indication message to the UE, the preamble indication information about the UE and the RA resource information included in the handover indication message being for transmitting a message A (Msg A) for the handover of the UE to a second base station.
  • Msg A message A
  • a UE in a wireless communication system includes a transceiver configured to transmit and receive a signal to and from a base station, and a processor configured to receive a handover indication message including preamble indication information about the UE and RA resource information from a first base station and to transmit a message A (Msg A) for a handover to a second base station, based on the preamble indication information about the UE and the RA resource information included in the handover indication message.
  • Msg A message A
  • a first base station in a wireless communication system includes a transceiver configured to transmit and receive a signal to and from a UE, and a processor configured to generate a handover indication message including preamble indication information and RA resource information for a handover and to transmit the generated handover indication message to the UE, wherein the preamble indication information about the UE and the RA resource information included in the handover indication message is for transmitting a message A (Msg A) for the handover of the UE to a second base station.
  • Msg A message A
  • FIG. 1A illustrates the structure of a long-term evolution (LTE) system for reference to describe the disclosure according to an embodiment of the disclosure
  • FIG. 1B illustrates the structure of wireless protocols for an LTE system and a new radio (NR) system for reference to describe the disclosure according to an embodiment of the disclosure
  • FIG. 1C illustrates the structure of downlink and uplink channel frames for beam-based communication in an NR system according to an embodiment of the disclosure
  • FIG. 1D illustrates a procedure in which a user equipment (UE) performs contention-based four-step random access to a base station according to an embodiment of the disclosure
  • FIG. 1E illustrates a procedure in which a UE performs two-step random access to a base station according to an embodiment of the disclosure
  • FIG. 1F illustrates a procedure in which a UE performs random access to a base station according to an embodiment of the disclosure
  • FIG. 1G illustrates an operation sequence in which a UE selects random access according to an embodiment of the disclosure
  • FIG. 1H is a block diagram illustrating the configuration of a UE in a wireless communication system according to an embodiment of the disclosure
  • FIG. 1I is a block diagram illustrating the configuration of a base station in a wireless communication system according to an embodiment of the disclosure
  • FIG. 2A illustrates the structure of an LTE system for reference to describe the disclosure according to an embodiment of the disclosure
  • FIG. 2B illustrates the structure of wireless protocols for an LTE system and an NR system for reference to describe the disclosure according to an embodiment of the disclosure
  • FIG. 2C illustrates the structure of downlink and uplink channel frames for beam-based communication in an NR system according to an embodiment of the disclosure
  • FIG. 2D illustrates a procedure in which a UE performs contention-based four-step random access to a base station according to an embodiment of the disclosure
  • FIG. 2E illustrates a procedure in which a UE performs two-step random access to a base station according to an embodiment of the disclosure
  • FIG. 2F illustrates the necessity and the role of an uplink timing synchronization procedure in a system employing orthogonal frequency-division multiplexing (OFDM) according to an embodiment of the disclosure
  • FIG. 2G illustrates an operation sequence in which a UE determines uplink transmission timing when performing two-step random access according to an embodiment of the disclosure
  • FIG. 2H is a block diagram illustrating the configuration of a UE in a wireless communication system according to an embodiment of the disclosure.
  • FIG. 2I is a block diagram illustrating the configuration of a base station in a wireless communication system according to an embodiment of the disclosure.
  • the disclosure uses terms and names defined in long-term evolution (LTE) and new radio (NR) standards, which are the latest standards among the existing communication standards defined by 3rd-generation partnership project (3GPP) organization.
  • LTE long-term evolution
  • NR new radio
  • 3GPP 3rd-generation partnership project
  • the disclosure is not limited by the terms and names, and may be equally applied to a system that is based on another standard.
  • the disclosure may be applied to 3GPP NR (5th generation mobile communication standards).
  • FIG. 1A illustrates the structure of an LTE system for reference to describe the disclosure according to an embodiment of the disclosure.
  • An NR system also has substantially the same structure.
  • the wireless communication system includes a plurality of base stations 1 a - 05 , 1 a - 10 , 1 a - 15 , and 1 a - 20 , a mobility management entity (MME) 1 a - 25 , and a serving-gateway (S-GW) 1 a - 30 .
  • a user equipment (hereinafter, “UE” or “terminal”) 1 a - 35 is connected to an external network through the base stations 1 a - 05 , 1 a - 10 , 1 a - 15 , and 1 a - 20 and the S-GW 1 a - 30 .
  • the base stations 1 a - 05 , 1 a - 10 , 1 a - 15 , and 1 a - 20 are access nodes of a cellular network and provide wireless connection for UEs connected to the network. That is, in order to serve traffic of users, the base stations 1 a - 05 , 1 a - 10 , 1 a - 15 , and 1 a - 20 performs scheduling by collecting state information on UEs, such as a buffer state, an available transmission power state, and a channel state and supports connection between the UEs and a core network (CN).
  • state information on UEs such as a buffer state, an available transmission power state, and a channel state
  • CN core network
  • the MME 1 a - 25 is a device that performs not only a mobility management function for a UE but also various control functions and is connected to a plurality of base stations.
  • the S-GW 1 a - 30 is a device that provides a data bearer.
  • the MME 1 a - 25 and the S-GW 1 a - 30 may further perform authentication and bearer management for a UE connected to the network and processes a packet transmitted from the base stations 1 a - 05 , 1 a - 10 , 1 a - 15 , and 1 a - 20 or a packet to be transmitted to the base stations 1 a - 05 , 1 a - 10 , 1 a - 15 , and 1 a - 20 .
  • FIG. 1B illustrates the structure of wireless protocols for an LTE system and an NR system for reference to describe the disclosure according to an embodiment of the disclosure.
  • the wireless protocols for the LTE system include a packet data convergence protocol (PDCP) 1 b - 05 and 1 b - 40 , a radio link control (RLC) 1 b - 10 and 1 b - 35 , and a medium access control (MAC) 1 b - 15 and 1 b - 30 for each of a UE and an eNB.
  • the packet data convergence protocol (PDCP) 1 b - 05 and 1 b - 40 is responsible for IP header compression/decompression operations, and the radio link control (hereinafter, “RLC”) 1 b - 10 and 1 b - 35 reconfigures a PDCP packet data unit (PDU) into an appropriate size.
  • PDCP packet data convergence protocol
  • RLC radio link control
  • the MAC 1 b - 15 and 1 b - 30 is connected to a plurality of RLC layer devices configured in one UE, multiplexes RLC PDUs to an MAC PDU, and demultiplexes RLC PDUs from an MAC PDU.
  • a physical layer 1 b - 20 and 1 b - 25 performs channel coding and modulation of upper-layer data and makes the upper-layer data into an orthogonal frequency-division multiplexing (OFDM) symbol to thereby transmit the OFDM symbol data via a radio channel or performs demodulation and channel decoding of an OFDM symbol received through a radio channel to thereby transmit the OFDM symbol to an upper layer.
  • OFDM orthogonal frequency-division multiplexing
  • the physical layer also uses hybrid automatic repeat query (HARQ) for additional error correction, in which a reception terminal transmits one bit to indicate whether a packet transmitted from a transmission terminal is received.
  • HARQ ACK/NACK information In LTE, downlink HARQ ACK/NACK information in response to uplink data transmission may be transmitted through a physical channel, such as a physical hybrid-ARQ indicator channel (PHICH).
  • PHICH physical hybrid-ARQ indicator channel
  • it may be determined through scheduling information about the UE in a physical dedicated control channel (PDCCH), which is a channel for transmitting downlink/uplink resource allocation, whether downlink HARQ ACK/NACK information in response to uplink transmission needs retransmitting or is newly transmitted, because asynchronous HARQ is applied in NR.
  • PDCCH physical dedicated control channel
  • Uplink HARQ ACK/NACK information in response to downlink transmission may be transmitted through a physical channel, such as a physical uplink control channel (PUCCH) or physical uplink shared channel (PUSCH).
  • the PUCCH is generally transmitted in an uplink of a PCell to be described.
  • a base station may additionally transmit the PUCCH to the UE in a SCell to be described, which is referred to as a PUCCH SCell.
  • a radio resource control (RRC) layer exists above the PDCP layer of each of the UE and the base station.
  • the RRC layer may exchange connection and measurement-related setup control messages for radio resource control.
  • the physical layer may include one frequency/carrier or a plurality of frequencies/carriers, and a technology of simultaneously configuring and using a plurality of frequencies is referred to as carrier aggregation (hereinafter, “CA”).
  • CA carrier aggregation
  • a main carrier and one additional subcarrier or a plurality of additional subcarriers are used for communication between a terminal (or UE) and a base station E-UTRAN NodeB (eNB), thereby dramatically increasing the transmission amount as much as the number of subcarriers.
  • eNB E-UTRAN NodeB
  • LTE a cell of a base station using a main carrier is referred to as a primary cell (PCell), and a cell using a subcarrier is referred to as a secondary cell (SCell).
  • PCell primary cell
  • SCell secondary cell
  • FIG. 1C illustrates the structure of downlink and uplink channel frames for beam-based communication in an NR system according to an embodiment of the disclosure.
  • a base station 1 c - 01 transmits a signal in the form of a beam to increase coverage or to transmit a stronger signal ( 1 c - 11 , 1 c - 13 , 1 c - 15 , and 1 c - 17 ). Accordingly, a UE 1 c - 03 in a cell needs to transmit and receive data using a particular beam (beam #1 1 c - 13 in this example) transmitted by the base station 1 c - 01 .
  • the state of the UE 1 c - 03 is divided into an RRC Integrated Development and Learning Environment (IDLE) state and an RRC_CONNECTED state depending on whether the UE 1 c - 03 is connected to the base station 1 c - 01 .
  • the base station 1 c - 01 does not know the position of the UE 1 c - 03 in the RRC_IDLE state.
  • the UE 1 c - 03 receives synchronization signal blocks (SSBs) 1 c - 21 , 1 c - 23 , 1 c - 25 , and 1 c - 27 transmitted by the base station 1 c - 01 .
  • the SSBs are SSB signals periodically transmitted according to a period set by the base station 1 c - 01 , and each SSB is divided into a primary synchronization signal (PSS) 1 c - 41 , a secondary synchronization signal (SSS) 1 c - 43 , and a physical broadcast channel (PBCH) 1 c - 45 .
  • PSS primary synchronization signal
  • SSS secondary synchronization signal
  • PBCH physical broadcast channel
  • an SSB is transmitted per beam.
  • SSB #0 1 c - 21 is transmitted using beam #0 1 c - 11
  • SSB #1 1 c - 23 is transmitted using beam #1 1 c - 13
  • SSB #2 1 c - 25 is transmitted using beam #2 1 c - 15
  • SSB #3 1 c - 27 is transmitted using beam #3 1 c - 17 .
  • the UE 1 c - 03 in the RRC_IDLE state is positioned on beam #1 1 c - 13 .
  • the UE 1 c - 03 in the RRC_CONNECTED state performs random access, the UE 1 c - 03 selects an SSB received at the time of performing the random access.
  • the UE 1 c - 03 receives SSB #1 1 c - 23 transmitted via beam #1 1 c - 13 .
  • the UE 1 c - 03 may obtain a physical cell identifier (PCI) of the base station 1 c - 01 through a PSS and an SSS and may identify the identifier (that is, #1) of the currently received SSB, a position where the current SSB is received in a 10-ms frame, and a system frame number (SFN) corresponding to the received SSB among SFNs a period of 10.24 seconds through a PBCH.
  • PCI physical cell identifier
  • SFN system frame number
  • the PBCH includes a master information block (MIB), and the MIB indicates a position for receiving system information block type 1 (SIB1) broadcasting detailed configuration information about the cell.
  • SIB1 system information block type 1
  • the UE 1 c - 03 may know the total number of SSBs transmitted by the base station 1 c - 01 and may identify the position ( 1 c - 30 to 1 c - 39 assuming that allocation is performed every 1 ms in this illustrated drawing) of a physical random access channel (PRACH) occasion for performing random access to transition to the RRC_CONNECTED state (specifically for transmitting a preamble as a physical signal specially designed for uplink synchronization).
  • PRACH physical random access channel
  • the UE 1 c - 03 may identify which PRACH occasions among the PRACH occasions is mapped to which SSB index based on this information. For example, in this illustrated drawing, it is assumed that allocation is performed every 1 ms and that a 1/2 SSB per PRACH occasion (that is, two PRACH occasions per SSB) is allocated. Accordingly, two PRACH occasions are allocated for each SSB from the start of a PRACH occasion starting according to the SFN. That is, 1 c - 30 and 1 c - 31 are allocated for SSB #0 1 c - 21 , 1 c - 32 and 1 c - 33 are allocated for SSB #1 1 c - 23 , and the like. After configuring PRACH occasions for all the SSBs, PRACH occasions are allocated again for the first SSB ( 1 c - 38 and 1 c - 39 ).
  • the UE 1 c - 03 recognizes the positions of the PRACH occasions 1 c - 32 and 1 c - 33 for SSB #1 1 c - 23 and transmits a random access preamble via the earliest PRACH occasion (for example, 1 c - 32 ) of the PRACH occasions 1 c - 32 and 1 c - 33 corresponding to SSB #1 1 c - 23 . Since receiving the preamble in the PRACH occasion 1 c - 32 , the base station 1 c - 01 can recognize that the UE 1 c - 03 has selected SSB #1 1 c - 23 to transmit the preamble and accordingly transmits and receives data through the corresponding beam in subsequent random access.
  • the UE 1 c - 03 When the UE 1 c - 03 in the RRC_CONNECTED state moves from a current (source) base station to a destination (target) base station due to a handover or the like, the UE 1 c - 03 performs random access in the target base station and performs an operation of selecting an SSB and transmitting a random access preamble.
  • a handover command is transmitted to the UE 1 c - 03 to move from the source base station to the target base station.
  • a random access preamble index dedicated to the UE may be allocated per SSB of the target base station so as to be used when performing random access in the target base station.
  • the base station may not allocate a dedicated random access preamble index for all beams (depending on the current position of the UE or the like), and thus some SSBs may not be allocated a dedicated random access preamble (for example, a dedicated random access preamble is allocated only to beam #2 and beam #3).
  • a dedicated random access preamble is allocated only to beam #2 and beam #3.
  • the UE randomly selects a contention-based random access preamble to perform random access.
  • the UE 1 c - 03 may transmit a dedicated preamble at beam #3 1 c - 17 when transmitting a random access preamble again. That is, even in one random access procedure, when preamble retransmission is performed, a contention-based random access procedure and a contention-free random access procedure may be mixed according to whether a dedicated random access preamble is allocated in a selected SSB for each preamble transmission.
  • FIG. 1D illustrates a contention-based four-step random access procedure performed by a UE in initial connection to a base station, reconnection to a base station, a handover to a base station, or other cases where random access is required according to an embodiment of the disclosure.
  • a UE 1 d - 01 selects a PRACH according to FIG. 1C and transmits a random access preamble via the PRACH ( 1 d - 11 ).
  • One or more UEs may simultaneously transmit a random access preamble through the PRACH resource.
  • the PRACH resource may span one subframe or may occupy only some symbols in one subframe.
  • Information about the PRACH resource is included in system information broadcasted by the base station 1 d - 03 and indicates a time-frequency resource to be used to transmit a preamble.
  • the random access preamble is a specific sequence specially designed to be received even though transmitted before synchronization with the base station 1 d - 03 is completely achieved, and may have a plurality of preamble indexes according to a standard.
  • the preamble transmitted by the UE 1 d - 01 may be a preamble randomly selected by the UE 1 d - 01 or may be a specific preamble designated by the base station 1 d - 03 .
  • the base station 1 d - 03 Upon receiving the preamble, the base station 1 d - 03 transmits a random access response (RAR) message to the UE 1 d - 01 in response ( 1 d - 21 ).
  • the RAR message includes identifier information about the preamble used in operation 1 d - 11 , uplink transmission timing correction information, allocation information about an uplink resource to be used in a subsequent operation (that is, operation 1 d - 31 ), and temporary UE identifier information.
  • the identifier information about the preamble is transmitted to indicate to which preamble the RAR message is a response message, for example, when a plurality of UEs attempts random access by transmitting different preambles in operation 1 d - 11 .
  • the allocation information about the uplink resource is specific information about the resource to be used by the UE 1 d - 01 in operation 1 d - 31 and includes physical position and size of the resource, a modulation and coding scheme (MCS) used for transmission, power adjustment information for transmission, or the like.
  • MCS modulation and coding scheme
  • the temporary UE identifier information is a value transmitted for the case where the UE does not have an identifier allocated by the base station for communication with the base station when the UE transmits the preamble for initial connection.
  • the RAR message needs to be transmitted within a predetermined period starting after a predetermined time from the time the preamble is transmitted, and this period is referred to as an RAR window 1 d - 23 .
  • the RAR window starts after the predetermined time from the time the first preamble is transmitted.
  • the predetermined time may have a subframe unit (1 ms) or shorter.
  • the length of the RAR window may be a predetermined value set by the base station 1 d - 03 for each PRACH resource or for one or more PRACH resource sets in a system information message broadcast by the base station 1 d - 03 .
  • the base station 1 d - 03 schedules the RAR message through a PDCCH, and scheduling information is scrambled using a random access-radio network temporary identifier (RA-RNTI).
  • RA-RNTI random access-radio network temporary identifier
  • the RA-RNTI is mapped to the PRACH resource used to transmit the message in operation 1 d - 11 , and the UE 1 d - 01 having transmitted the preamble via the specific PRACH resource attempts to receive a PDCCH based on the RA-RNTI and determines whether there is a corresponding RAR message.
  • the RA-RNTI used for the scheduling information about the RAR message includes information about the transmission in operation 1 d - 11 .
  • the RA-RNTI may be calculated by the following equation:
  • RA -RNTI 1+ s _ id+ 14 ⁇ t _ id+ 14 ⁇ 80 ⁇ f _ id+ 14 ⁇ 80 ⁇ 8 ⁇ ul _carrier_ id
  • s_id is an index corresponding to the first OFDM symbol in which transmission of the preamble transmitted in operation 1 d - 11 starts and has a value satisfying 0 ⁇ s_id ⁇ 14 (that is, the maximum number of OFDM symbols in one slot);
  • t_id is an index corresponding to the first slot in which transmission of the preamble transmitted in operation 1 d - 11 starts and has a value satisfying 0 ⁇ t_id ⁇ 80 (that is, the maximum number of slots in one system frame (10 ms));
  • the f_id indicates a PRACH resource used to transmit the preamble transmitted in operation 1 d - 11 on the frequency and has a value satisfying 0 ⁇ f_id ⁇ 8 (that is, the maximum number of PRACHs on the frequency within the same time);
  • ul_carrier_id is a factor for distinguishing whether the preamble is transmitted in a normal uplink (NUL) (0 in this case) or in a supplementary uplink (SUL) (1 in this case
  • the UE 1 d - 01 Upon receiving the RAR message, the UE 1 d - 01 transmits different messages via a resource allocated through the RAR message depending on the foregoing various purposes ( 1 d - 31 ).
  • the third transmitted message is also referred to as Msg 3 (that is, the preamble in operation 1 d - 11 or 1 d - 13 is also referred to as Msg 1 , and the RAR in operation 1 d - 21 is also referred to as Msg 2 ).
  • an RRCConnectionRequest message which is a message of an RRC layer, is transmitted for initial connection, an RRCConnectionReestablishmentRequest message is transmitted for reconnection, and an RRCConnectionReconfigurationComplete message is transmitted for a handover. Further, a buffer status report (BSR) message for a resource request may be transmitted.
  • BSR buffer status report
  • the UE 1 d - 01 receives a contention resolution message from the base station 1 d - 03 ( 1 d - 41 ), and the contention resolution message includes the same information as transmitted by the UE 1 d - 01 via Msg 3 , thus indicating to which UE the response corresponds when there is a plurality of UEs selecting the same preamble in operation 1 d - 11 or 1 d - 13 .
  • FIG. 1E illustrates a procedure in which a UE performs two-step random access to a base station according to an embodiment of the disclosure.
  • general contention-based random access involves at least four operations. If an error occurs in one operation, the procedure may be further delayed. Accordingly, it may be considered to reduce the random access procedure to a two-step procedure.
  • a UE 1 e - 01 may transmit MsgA 1 e - 25 of consecutively transmitting preambles Msg 1 ( 1 e - 11 corresponding to 1 d - 11 ) and Msg 3 ( 1 e - 13 corresponding to 1 d - 31 ) of a four-step random access procedure to a base station 1 e - 03 ( 1 e - 15 ), and the base station 1 e - 03 receiving MsgA may transmit MsgB 1 e - 19 including information of Msg 2 (RAR corresponding to 1 d - 21 ) and Msg 4 (corresponding to 1 d - 41 ) of the four-step random access procedure to the UE 2 e - 01 , thereby reducing a random access procedure.
  • MsgA may include a PRACH resource 1 e - 21 for transmitting Msg 1 , a PUSCH resource 1 e - 23 for transmitting Msg 3 , and a gap resource 1 e - 22 for resolving interference that may occur in transmission via the PUSCH resource.
  • the UE 1 e - 01 performs random access for various purposes.
  • the UE 1 e - 01 may perform random access in order to transmit a message for connection when not yet connected to the base station 1 e - 03 or in order to transmit a message for recovering connection when disconnected from the base station 1 e - 03 due to an error, and these messages belong to a common control channel (CCCH).
  • CCCH common control channel
  • Control messages belonging to the CCCH include RRCSetupRequest (for transition from RRC_IDLE to RRC_CONNECTED), RRCResumeRequest (for transition from RRC_INACTIVE to RRC_CONNECTED), RRCReestablishmentRequest (for reestablishing connection), and RRCSystemInfoRequest (upon request for system information broadcast by the base station).
  • RRCSetupRequest for transition from RRC_IDLE to RRC_CONNECTED
  • RRCResumeRequest for transition from RRC_INACTIVE to RRC_CONNECTED
  • RRCReestablishmentRequest for reestablishing connection
  • RRCSystemInfoRequest upon request for system information broadcast by the base station.
  • RRCReestablishmentRequest transmitted for connection recovery or RRCResumeRequest used in transition from RRC_INACTIVE to RRC_CONNECTED is a high-priority message
  • two-step random access may be performed for these messages when random access is required.
  • four-step random access described above may be performed to transmit this message instead of two-step random access.
  • CCCH messages may be determined to have a higher priority than that of messages of other dedicated control channels and dedicated traffic channels, which will be described later, and may be transmitted using two-step random access.
  • the UE 1 e - 01 may transmit and receive a message belonging to a dedicated control channel (DCCH) and a dedicated traffic channel (DTCH) in RRC_CONNECTED.
  • DCCH dedicated control channel
  • DTCH dedicated traffic channel
  • the UE 1 e - 01 needs to transmit a buffer status report (BSR) message indicating that the UE 1 e - 01 has data to transmit via an uplink to the base station 1 e - 03 , thereby requesting uplink resource allocation.
  • BSR buffer status report
  • the base station 1 e - 03 may allocate a dedicated PUCCH resource for transmitting a scheduling request (SR) for a specific logical channel to the UE 1 e - 01 . Accordingly, when receiving an SR from the UE 1 e - 01 via a PUCCH, the base station 1 e - 03 allocates an uplink resource for transmitting a BSR. When the UE 1 e - 01 transmits a BSR via the uplink resource, the base station 1 e - 03 may identify the buffer state of the UE 1 e - 01 and may allocate an uplink resource for data.
  • SR scheduling request
  • the UE 1 e - 01 may perform random access to transmit a BSR to the base station 1 e - 03 via Msg 3 .
  • the UE 1 e - 01 when the UE 1 e - 01 is connected to the base station 1 e - 03 and then configures a logical channel for transmitting data belonging to each of a dedicated control channel (DCCH) and a dedicated traffic channel (DTCH), the UE 1 e - 01 may set whether two-step random access can be performed when performing random access for transmitting the logical channel.
  • the base station 1 e - 03 may configure two-step random access to be enabled for a logical channel for a DCCH (for example, control radio bearer 1 , control radio bearer 2 , and control radio bearer 3 ) and a logical channel for traffic having a high priority.
  • DCCH dedicated control channel
  • DTCH dedicated traffic channel
  • two-step random access may be performed or four-step random access may be performed depending on whether two-step random access is allowed for a logical channel triggering the random access.
  • FIG. 1F illustrates a procedure in which a UE performs random access to a base station according to an embodiment of the disclosure.
  • a UE 1 f - 01 is in the RRC_IDLE state.
  • the UE 1 f - 01 cannot transmit or receive data but can select (or reselect) a specific base station/cell to camp on the cell and can periodically receive a paging message indicating the presence of downlink data from the cell.
  • the UE 1 f - 01 may transmit an RRCSetupRequest message to a base station 1 f - 03 in order to connect to the base station 1 f - 03 , to establish a connection, and to transition to the RRC_CONNECTED state.
  • the UE 1 f - 01 receives system information broadcast by a cell on which the UE 1 f - 01 is currently camping ( 1 f - 11 ).
  • the system information may be transmitted, being divided into various messages according to the type of information transmitted by a SystemInformationBlock (SIB) message.
  • SIB SystemInformationBlock
  • SIB1 SystemInformationBlock
  • the detailed configuration information about the PRACH includes the resource positions and periods of a resource (PRACH information) for four-step random access and a resource (for example, resources for a PRACH, a GAP, and a PUSCH in FIG. 1E ) for two-step random access and a modulation and coding scheme (MCS) used for transmission in the case of a PUSCH.
  • PRACH information for four-step random access
  • a resource for example, resources for a PRACH, a GAP, and a PUSCH in FIG. 1E
  • MCS modulation and coding scheme
  • an indicator indicating which CCCH message the resource for two-step random access can be used to transmit among the aforementioned CCCHs may be included. Accordingly, the UE 1 f - 01 may determine whether to use a corresponding resource according to the type of a CCCH to be transmitted ( 1 f - 13 ).
  • the UE 1 f - 01 when receiving SIB1 indicating that two-step random access is available for RRCSetupRequest transmission, the UE 1 f - 01 transmits MsgA including an RRCSetupRequest message to the base station 1 f - 03 ( 1 f - 15 ). When successfully receiving the message, the base station 1 f - 03 transmits MsgB to the UE 1 f - 01 in response ( 1 f - 17 ). When the UE 1 f - 01 successfully receives the message, a random access procedure successfully terminates.
  • the base station 1 f - 03 transmits an RRCSetup message to the UE 1 f - 01 at the same time as or after transmitting MsgB, and the UE 1 f - 01 transitions to the RRC_CONNECTED state and transmits an RRCSetupComplete message to the base station 1 f - 03 in response, thereby completing a connection procedure. Accordingly, the UE 1 f - 01 may transmit and receive data to and from the base station 1 f - 03 .
  • the UE 1 f - 01 may receive more detailed configuration information from the base station 1 f - 03 ( 1 f - 21 ).
  • This configuration information may be transmitted through an RRCReconfiguration message and may include, for example, configuration information related to beam failure recovery for quick recovery of a beam when a beam for transmission reception cannot be used due to a sudden movement of the UE 1 f - 01 or the like.
  • the beam failure recovery may be performed by selecting a beam to be recovered after beam failure occurs and transmitting a random access preamble corresponding to the selected beam, and the configuration information may further indicate whether a two-step random access procedure is available for a beam failure recovery procedure when performing the recovery procedure.
  • the UE 1 f - 01 may be configured to transmit a scheduling request (SR) signal via a PUCCH Resource per specific traffic type (or logical channel) in order to report a buffer status report (BSR).
  • SR scheduling request
  • BSR buffer status report
  • FIG. 1F shows a case where a beam failure occurs while the UE 1 f - 01 is communicating with the base station 1 f - 03 ( 1 f - 23 ) and the use of a two-step random access procedure is additionally indicated for quick recovery.
  • the UE 1 f - 01 selects a beam available for communication in the current situation, selects a resource for transmitting a random access preamble corresponding to the beam, and transmits a preamble along with a MAC-layer message control element (CE) including an identifier of the UE 1 f - 01 performing this procedure to the base station 1 f - 03 through the resource ( 1 f - 25 ).
  • CE MAC-layer message control element
  • a scenario in which the UE 1 f - 01 may needs to change a connection to another base station 1 f - 05 due to a movement of the UE 1 f - 01 may be further considered.
  • the current base station 1 f - 03 may configure a measurement for the UE 1 f - 01 to measure the neighboring base station 1 f - 05 , and the UE 1 f - 01 reports a measurement result to the base station 1 f - 03 when a report condition is satisfied according to a measurement configuration. Accordingly, the current base station 1 f - 03 may determine to move the UE 1 f - 01 to one of reported base stations.
  • the current base station 1 f - 03 transmits a handover request message to the target base station 1 f - 05
  • the target base station 1 f - 05 transmits a handover acceptance message to the current base station 1 f - 03
  • the handover acceptance message includes various kinds of configuration information to be used by the UE 1 f - 01 in the target base station 1 f - 05 .
  • the current base station 1 f - 03 transmits these kinds of configuration information to the UE 1 f - 01 , thus commanding the UE 1 f - 01 to hand over to the target base station 1 f - 05 ( 1 f - 31 ).
  • an RRCReconfiguration message including an information element of reconfigurationWithSync may be transmitted to the UE 1 f - 01 , thereby commanding the UE 1 f - 01 to perform a corresponding operation.
  • a message may be transmitted to indicate a handover to the UE 1 f - 01 to instruct the handover ( 1 f - 31 ).
  • the UE 1 f - 01 needs to transmit an RRCReconfigurationComplete message to the target base station 1 f - 05 in order to indicate the completion of a handover.
  • the UE 1 f - 01 needs to perform random access. Therefore, the target base station 1 f - 05 may allocate a dedicated two-step random access resource via a configuration message for indicating the handover so that the UE 1 f - 01 may transmit the RRCReconfigurationComplete message, which is for allocating the transmission resource only for the UE 1 f - 01 , preventing a different UE from using the resource for transmission, thus quickly completing the handover without any collision.
  • the UE 1 f - 01 may transmit not only a preamble allocated in MsgA transmission but also the RRCReconfigurationComplete message to the target base station 1 f - 05 in operation 1 f - 33 , thus completing a handover procedure.
  • the UE 1 f - 01 may receive MsgB from the target base station 1 f - 05 , thus completing a random access procedure in the target base station 1 f - 05 ( 1 f - 35 ).
  • the target base station 1 f - 05 may allocate only a dedicated preamble to the UE 1 f - 01 .
  • the UE 1 f - 01 may transmit an RRCReconfigurationComplete message according to an existing random access procedure in which only a preamble is transmitted even though there is a two-step random access resource in the target base station 1 f - 05 , and may use the two-step random access resource after the RRCReconfigurationComplete message is transmitted or after a timer T 304 used to determine the completion of a handover expires or is suspended.
  • FIG. 1G illustrates an operation sequence in which a UE selects random access according to an embodiment.
  • the UE receives configuration information related to random access from a base station ( 1 g - 03 ).
  • the configuration information may be received via a system information block (SIB) message broadcast by the base station or may be received by the UE via a dedicated RRC message.
  • SIB system information block
  • CCCH transmission-related information may be included in a SIB message.
  • the configuration information may be received by the UE via a dedicated RRC message transmitted only to the UE.
  • the UE triggers a random access procedure ( 1 g - 05 ).
  • the random access procedure may be triggered to transmit a CCCH for a transition from the RRC_IDLE state to the RRC_CONNECTED state as described in FIG. 1F , may be triggered for beam failure recovery, or may be triggered in handover/SCG addition scenarios.
  • the UE determines whether a resource for two-step random access is configured and the type of a CCCH to be transmitted for which two-step random access is allowed from information received from the base station (information received via an SIB) in operation 1 g - 07 . Accordingly, when two-step random access is configured and is allowed according to the type of a CCCH to be transmitted by the UE, the UE performs two-step random access; otherwise, the UE performs four-step random access ( 1 g - 11 and 1 g - 21 ).
  • the UE determines whether the base station configures whether a two-step random access procedure recovery procedure is available for a beam failure recovery procedure. When it is configured that a two-step random access procedure recovery procedure is available for a recovery procedure, the UE performs a beam failure recovery procedure using a two-step random access procedure; otherwise, the UE performs four-step random access ( 1 g - 13 and 1 g - 21 ).
  • a BSR may be triggered for the UE to transmit a regular BSR, in which when random access is triggered for BSR transmission, the UE determines whether the base station configures whether a two-step random access procedure is available for BSR transmission. When it is configured that a two-step random access procedure is available for BSR transmission, the UE transmits the BSR using a two-step random access procedure; otherwise, the UE performs four-step random access ( 1 g - 15 and 1 g - 21 ).
  • FIG. 1H is a block diagram illustrating the configuration of a UE in a wireless communication system according to an embodiment of the disclosure.
  • the UE includes a radio frequency (RF) processor 1 h - 10 , a baseband processor 1 h - 20 , a storage unit 1 h - 30 , and a controller 1 h - 40 .
  • RF radio frequency
  • the RF processor 1 h - 10 performs a function for transmitting or receiving a signal through a wireless channel, such as band conversion and amplification of a signal. That is, the RF processor 1 h - 10 upconverts a baseband signal, provided from the baseband processor 1 h - 20 , into an RF band signal to transmit the RF band signal through an antenna and downconverts an RF band signal, received through the antenna, into a baseband signal.
  • the RF processor 1 h - 10 may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC).
  • the UE may include a plurality of antennas.
  • the RF processor 1 h - 10 may include a plurality of RF chains. Further, the RF processor 1 h - 10 may perform beamforming. For beamforming, the RF processor 1 h - 10 may adjust the phase and strength of each of signals transmitted and received through a plurality of antennas or antenna elements.
  • the baseband processor 1 h - 20 performs a function of converting a baseband signal and a bit stream according to the physical-layer specification of a system. For example, in data transmission, the baseband processor 1 h - 20 encodes and modulates a transmission bit stream, thereby generating complex symbols. In data reception, the baseband processor 1 h - 20 demodulates and decodes a baseband signal, provided from the RF processor 1 h - 10 , thereby reconstructing a reception bit stream.
  • the baseband processor 1 h - 20 in data transmission, the baseband processor 1 h - 20 generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and constructs OFDM symbols through an inverse fast Fourier transform (IFFT) and cyclic prefix (CP) insertion.
  • IFFT inverse fast Fourier transform
  • CP cyclic prefix
  • the baseband processor 1 h - 20 divides a baseband signal, provided from the RF processor 1 h - 10 , into OFDM symbols, reconstructs signals mapped to subcarriers through a fast Fourier transform (FFT), and reconstructs a reception bit stream through demodulation and decoding.
  • FFT fast Fourier transform
  • the baseband processor 1 h - 20 and the RF processor 1 h - 10 transmit and receive signals. Accordingly, the baseband processor 1 h - 20 and the RF processor 1 h - 10 may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. At least one of the baseband processor 1 h - 20 and the RF processor 1 h - 10 may include a plurality of communication modules to support a plurality of different radio access technologies. Further, at least one of the baseband processor 1 h - 20 and the RF processor 1 h - 10 may include different communication modules for processing signals in different frequency bands.
  • the different radio access technologies may include a wireless LAN (for example, IEEE 802.11), a cellular network (for example, an LTE network), and the like.
  • the different frequency bands may include a super high frequency (SHF) band (for example, 2.5 GHz or 5 GHz) and a millimeter wave band (for example, 60 GHz).
  • SHF super high frequency
  • the storage unit 1 h - 30 stores data, such as a default program, an application, and configuration information for operating the UE.
  • the storage unit 1 h - 30 may store information about a wireless local-area network (WLAN) node performing wireless communication using a WLAN access technology.
  • the storage unit 1 h - 30 provides stored data upon request from the controller 1 h - 40 .
  • WLAN wireless local-area network
  • the controller 1 h - 40 controls overall operations of the UE.
  • the controller 1 h - 40 transmits and receives signals through the baseband processor 1 h - 20 and the RF processor 1 h - 10 .
  • the controller 1 h - 40 records and reads data in the storage unit 1 h - 30 .
  • the controller 1 h - 40 may include at least one processor.
  • the controller 1 h - 40 may include a communication processor (CP) to perform control for communication and an application processor (AP) to control an upper layer, such as an application.
  • the controller 1 h - 40 includes a multi-connection processor 1 h - 42 to perform processing for an operation in a multi-connection mode.
  • the controller 1 h - 40 may control the UE to perform the procedure of operations of the UE illustrated in FIG. 1E .
  • the controller 1 h - 40 When random access is triggered according to configuration information indicated by a base station, the controller 1 h - 40 according to the embodiment may indicate the UE to perform two-step random access or four-step random access.
  • FIG. 1I is a block diagram illustrating the configuration of a base station in a wireless communication system according to an embodiment of the disclosure.
  • the base station includes an RF processor 1 i - 10 , a baseband processor 1 i - 20 , a backhaul communication unit 1 i - 30 , a storage unit 1 i - 40 , and a controller 1 i - 50 .
  • the RF processor 1 i - 10 performs a function for transmitting or receiving a signal through a wireless channel, such as band conversion and amplification of a signal. That is, the RF processor 1 i - 10 upconverts a baseband signal, provided from the baseband processor 1 i - 20 , into an RF band signal to transmit the RF band signal through an antenna and downconverts an RF band signal, received through the antenna, into a baseband signal.
  • the RF processor 1 i - 10 may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, and an ADC.
  • FIG. 1I shows only one antenna, the base station may include a plurality of antennas.
  • the RF processor 1 i - 10 may include a plurality of RF chains. Further, the RF processor 1 i - 10 may perform beamforming. For beamforming, the RF processor 1 i - 10 may adjust the phase and strength of each of signals transmitted and received through a plurality of antennas or antenna elements. The RF processor may transmit one or more layers, thereby performing downlink MIMO.
  • the baseband processor 1 i - 20 performs a function of converting a baseband signal and a bit stream according to the physical-layer specification of a first radio access technology. For example, in data transmission, the baseband processor 1 i - 20 encodes and modulates a transmission bit stream, thereby generating complex symbols. In data reception, the baseband processor 1 i - 20 demodulates and decodes a baseband signal, provided from the RF processor 1 i - 10 , thereby reconstructing a reception bit stream.
  • the baseband processor 1 i - 20 in data transmission, the baseband processor 1 i - 20 generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and constructs OFDM symbols through an IFFT and CP insertion.
  • the baseband processor 1 i - 20 divides a baseband signal, provided from the RF processor 1 i - 10 , into OFDM symbols, reconstructs signals mapped to subcarriers through an FFT, and reconstructs a reception bit stream through demodulation and decoding.
  • the baseband processor 1 i - 20 and the RF processor 1 i - 10 transmit and receive signals. Accordingly, the baseband processor 1 i - 20 and the RF processor 1 i - 10 may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.
  • the backhaul communication unit 1 i - 30 provides an interface for performing communication with other nodes in a network. That is, the backhaul communication unit 1 i - 30 converts a bit stream, transmitted from the main base station to another node, for example, a secondary base station or a core network, into a physical signal and converts a physical signal, received from the other node, into a bit stream.
  • the storage unit 1 i - 40 stores data, such as a default program, an application, and configuration information for operating the main base station.
  • the storage unit 1 i - 40 may store information on a bearer allocated to a connected UE, a measurement result reported from a connected UE, and the like.
  • the storage unit 1 i - 40 provides stored data upon request from the controller 1 i - 50 .
  • the controller 1 i - 50 controls overall operations of the main base station. For example, the controller 1 i - 50 transmits and receives signals through the baseband processor 1 i - 20 and the RF processor 1 i - 10 or through the backhaul communication unit 1 i - 30 . Further, the controller 1 i - 50 records and reads data in the storage unit 1 i - 40 . To this end, the controller 1 i - 50 may include at least one processor (e.g., multi-connection processor 1 i - 52 ).
  • a computer-readable storage medium storing one or more programs (software modules) may be provided.
  • One or more programs stored in the computer-readable storage medium are configured for execution by one or more processors in an electronic device.
  • the one or more programs include instructions that enable the electronic device to execute the methods according to the embodiments illustrated in the claims or specification.
  • These programs may be stored in a random-access memory, a nonvolatile memory including a flash memory, a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), a magnetic disc storage device, a compact disc ROM (CD-ROM), digital versatile discs (DVDs), an optical storage device in a different form, a magnetic cassette, or a memory configured in a combination of some or all thereof.
  • a nonvolatile memory including a flash memory, a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), a magnetic disc storage device, a compact disc ROM (CD-ROM), digital versatile discs (DVDs), an optical storage device in a different form, a magnetic cassette, or a memory configured in a combination of some or all thereof.
  • ROM read-only memory
  • EEPROM electrically erasable programmable ROM
  • CD-ROM compact disc ROM
  • DVDs digital versatile discs
  • each constituent memory may be included
  • the programs may be stored in an attachable storage device which is accessible through a communication network, such as the Internet, an intranet, a local area network (LAN), a wide area network (WLAN), or a storage area network (SAN), or a communication network configured in a combination thereof.
  • a communication network such as the Internet, an intranet, a local area network (LAN), a wide area network (WLAN), or a storage area network (SAN), or a communication network configured in a combination thereof.
  • This storage device may be connected to a device for performing an embodiment through an external port.
  • a separate storage device on a communication network may be connected to a device for performing an embodiment.
  • FIG. 2A illustrates the structure of an LTE system for reference to describe the disclosure according to the embodiment of the disclosure.
  • An NR system also has substantially the same structure.
  • the wireless communication system includes a plurality of base stations 2 a - 05 , 2 a - 10 , 2 a - 15 , and 2 a - 20 , a mobility management entity (MME) 2 a - 25 , and a serving-gateway (S-GW) 2 a - 30 .
  • a user equipment (hereinafter, “UE” or “terminal”) 2 a - 35 is connected to an external network through the base stations 2 a - 05 , 2 a - 10 , 2 a - 15 , and 2 a - 20 and the S-GW 2 a - 30 .
  • the base stations 2 a - 05 , 2 a - 10 , 2 a - 15 , and 2 a - 20 are access nodes of a cellular network and provide wireless connection for UEs connected to the network. That is, in order to serve traffic of users, the base stations 2 a - 05 , 2 a - 10 , 2 a - 15 , and 2 a - 20 performs scheduling by collecting state information on UEs, such as a buffer state, an available transmission power state, and a channel state and supports connection between the UEs and a core network (CN).
  • state information on UEs such as a buffer state, an available transmission power state, and a channel state
  • the MME 2 a - 25 is a device that performs not only a mobility management function for a UE but also various control functions and is connected to a plurality of base stations.
  • the S-GW 2 a - 30 is a device that provides a data bearer.
  • the MME 2 a - 25 and the S-GW 2 a - 30 may further perform authentication and bearer management for a UE connected to the network and processes a packet transmitted from the base stations 2 a - 05 , 2 a - 10 , 2 a - 15 , and 2 a - 20 or a packet to be transmitted to the base stations 2 a - 05 , 2 a - 10 , 2 a - 15 , and 2 a - 20 .
  • FIG. 2B illustrates the structure of wireless protocols for an LTE system and an NR system for reference to describe the disclosure according to an embodiment of the disclosure.
  • the wireless protocols for the LTE system include a packet data convergence protocol (PDCP) 2 b - 05 and 2 b - 40 , a radio link control (RLC) 2 b - 10 and 2 b - 35 , and a medium access control (MAC) 2 b - 15 and 2 b - 30 for each of a UE and an eNB.
  • the packet data convergence protocol (PDCP) 2 b - 05 and 2 b - 40 is responsible for IP header compression/decompression operations, and the radio link control (hereinafter, “RLC”) 2 b - 10 and 2 b - 35 reconfigures a PDCP packet data unit (PDU) into an appropriate size.
  • PDCP packet data convergence protocol
  • RLC radio link control
  • the MAC 2 b - 15 and 2 b - 30 is connected to a plurality of RLC layer devices configured in one UE, multiplexes RLC PDUs to an MAC PDU, and demultiplexes RLC PDUs from an MAC PDU.
  • a physical layer 2 b - 20 and 2 b - 25 performs channel coding and modulation of upper-layer data and makes the upper-layer data into an OFDM symbol to thereby transmit the OFDM symbol data via a radio channel or performs demodulation and channel decoding of an OFDM symbol received through a radio channel to thereby transmit the OFDM symbol to an upper layer.
  • the physical layer also uses hybrid ARQ (HARQ) for additional error correction, in which a reception terminal transmits one bit to indicate whether a packet transmitted from a transmission terminal is received.
  • HARQ ACK/NACK information In LTE, downlink HARQ ACK/NACK information in response to uplink transmission may be transmitted through a physical channel, such as a physical hybrid-ARQ indicator channel (PHICH).
  • PHICH physical hybrid-ARQ indicator channel
  • it may be determined through scheduling information about the UE in a physical dedicated control channel (PDCCH), which is a channel for transmitting downlink/uplink resource allocation, whether downlink HARQ ACK/NACK information in response to uplink transmission needs retransmitting or is newly transmitted, because asynchronous HARQ is applied in NR.
  • PDCCH physical dedicated control channel
  • Uplink HARQ ACK/NACK information in response to downlink transmission may be transmitted through a physical channel, such as a physical uplink control channel (PUCCH) or physical uplink shared channel (PUSCH).
  • the PUCCH is generally transmitted in an uplink of a PCell to be described.
  • a base station may additionally transmit the PUCCH to the UE in a SCell to be described, which is referred to as a PUCCH SCell.
  • a radio resource control (RRC) layer exists above the PDCP layer of each of the UE and the base station.
  • the RRC layer may exchange connection and measurement-related setup control messages for radio resource control.
  • the physical layer may include one frequency/carrier or a plurality of frequencies/carriers, and a technology of simultaneously configuring and using a plurality of frequencies is referred to as carrier aggregation (hereinafter, “CA”).
  • CA carrier aggregation
  • a main carrier and one additional subcarrier or a plurality of additional subcarriers are used for communication between a terminal (or UE) and a base station E-UTRAN NodeB (eNB), thereby dramatically increasing the transmission amount as much as the number of subcarriers.
  • eNB E-UTRAN NodeB
  • LTE a cell of a base station using a main carrier is referred to as a primary cell (PCell), and a cell using a subcarrier is referred to as a secondary cell (SCell).
  • PCell primary cell
  • SCell secondary cell
  • FIG. 2C illustrates the structure of downlink and uplink channel frames for beam-based communication in an NR system according to an embodiment of the disclosure.
  • a base station 2 c - 01 transmits a signal in the form of a beam to increase coverage or to transmit a stronger signal ( 2 c - 11 , 2 c - 13 , 2 c - 15 , and 2 c - 17 ). Accordingly, a UE 2 c - 03 in a cell needs to transmit and receive data using a particular beam (beam #1 2 c - 13 in this example) transmitted by the base station 2 c - 01 .
  • the state of the UE 2 c - 03 is divided into an RRC_IDLE state and an RRC_CONNECTED state depending on whether the UE 2 c - 03 is connected to the base station 2 c - 01 .
  • the base station 2 c - 01 does not know the position of the UE 2 c - 03 in the RRC_IDLE state.
  • the UE 2 c - 03 receives synchronization signal blocks (SSBs) 2 c - 21 , 2 c - 23 , 2 c - 25 , and 2 c - 27 transmitted by the base station 2 c - 01 .
  • the SSBs are SSB signals periodically transmitted according to a period set by the base station 2 c - 01 , and each SSB is divided into a primary synchronization signal (PSS) 2 c - 41 , a secondary synchronization signal (SSS) 2 c - 43 , and a physical broadcast channel (PBCH) 2 c - 45 .
  • PSS primary synchronization signal
  • SSS secondary synchronization signal
  • PBCH physical broadcast channel
  • an SSB is transmitted per beam.
  • SSB #0 2 c - 21 is transmitted using beam #0 2 c - 11
  • SSB #1 2 c - 23 is transmitted using beam #1 2 c - 13
  • SSB #2 2 c - 25 is transmitted using beam #2 2 c - 15
  • SSB #3 2 c - 27 is transmitted using beam #3 2 c - 17 .
  • the UE 2 c - 03 in the RRC_IDLE state is positioned on beam #1 2 c - 13 .
  • the UE 2 c - 03 in the RRC_CONNECTED state performs random access, the UE 2 c - 03 selects an SSB received at the time of performing the random access.
  • the UE 2 c - 03 receive SSB #1 2 c - 23 transmitted via beam #1 2 c - 13 .
  • the UE 2 c - 03 may obtain a physical cell identifier (PCI) of the base station 2 c - 01 through a PSS and an SSS and may identify the identifier (that is, #1) of the currently received SSB, a position where the current SSB is received in a 10-ms frame, and a system frame number (SFN) corresponding to the received SSB among SFNs a period of 10.24 seconds through a PBCH.
  • PCI physical cell identifier
  • SFN system frame number
  • the PBCH includes a master information block (MIB), and the MIB indicates a position for receiving system information block type 1 (SIB1) broadcasting detailed configuration information about the cell.
  • SIB1 system information block type 1
  • the UE 2 c - 03 may know the total number of SSBs transmitted by the base station 2 c - 01 and may identify the position ( 2 c - 30 to 2 c - 39 assuming that allocation is performed every 1 ms in this illustrated drawing) of a physical random access channel (PRACH) occasion for performing random access to transition to the RRC_CONNECTED state (specifically for transmitting a preamble as a physical signal specially designed for uplink synchronization).
  • PRACH physical random access channel
  • the UE 2 c - 03 may identify which PRACH occasions among the PRACH occasions is mapped to which SSB index based on this information. For example, in this illustrated drawing, it is assumed that allocation is performed every 1 ms and that a 1/2 SSB per PRACH occasion (that is, two PRACH occasions per SSB) is allocated. Accordingly, two PRACH occasions are allocated for each SSB from the start of a PRACH occasion starting according to the SFN. That is, 2 c - 30 and 2 c - 31 are allocated for SSB #0 2 c - 21 , 2 c - 32 and 2 c - 33 are allocated for SSB #1 2 c - 23 , and the like. After configuring PRACH occasions for all the SSBs, PRACH occasions are allocated again for the first SSB ( 2 c - 38 and 2 c - 39 ).
  • the UE 2 c - 03 recognizes the positions of the PRACH occasions 2 c - 32 and 2 c - 33 for SSB #1 2 c - 23 and transmits a random access preamble via the earliest PRACH occasion (for example, 2 c - 32 ) of the PRACH occasions 2 c - 32 and 2 c - 33 corresponding to SSB #1 2 c - 23 . Since receiving the preamble in the PRACH occasion 2 c - 32 , the base station 2 c - 01 can recognize that the UE 2 c - 03 has selected SSB #1 2 c - 23 to transmit the preamble and accordingly transmits and receives data through the corresponding beam in subsequent random access.
  • the UE 2 c - 03 When the UE 2 c - 03 in the RRC_CONNECTED state moves from a current (source) base station to a destination (target) base station due to a handover or the like, the UE 2 c - 03 performs random access in the target base station and performs an operation of selecting an SSB and transmitting a random access preamble.
  • a handover command is transmitted to the UE 2 c - 03 to move from the source base station to the target base station.
  • a random access preamble index dedicated to the UE may be allocated per SSB of the target base station so as to be used when performing random access in the target base station.
  • the base station may not allocate a dedicated random access preamble index for all beams (depending on the current position of the UE or the like), and thus some SSBs may not be allocated a dedicated random access preamble (for example, a dedicated random access preamble is allocated only to beam #2 and beam #3).
  • a dedicated random access preamble is allocated only to beam #2 and beam #3.
  • the UE randomly selects a contention-based random access preamble to perform random access.
  • the UE 2 c - 03 may transmit a dedicated preamble at beam #3 2 c - 17 when transmitting a random access preamble again. That is, even in one random access procedure, when preamble retransmission is performed, a contention-based random access procedure and a contention-free random access procedure may be mixed according to whether a dedicated random access preamble is allocated in a selected SSB for each preamble transmission.
  • FIG. 2D illustrates a contention-based four-step random access procedure performed by a UE in initial connection to a base station, reconnection to a base station, a handover to a base station, or other cases where random access is required according to an embodiment of the disclosure.
  • a UE 2 d - 01 selects a PRACH according to FIG. 2C and transmits a random access preamble via the PRACH ( 2 d - 11 ).
  • One or more UEs may simultaneously transmit a random access preamble through the PRACH resource.
  • the PRACH resource may span one subframe or may occupy only some symbols in one subframe.
  • Information about the PRACH resource is included in system information broadcasted by the base station 2 d - 03 and indicates a time-frequency resource to be used to transmit a preamble.
  • the random access preamble is a specific sequence specially designed to be received even though transmitted before synchronization with the base station 2 d - 03 is completely achieved, and may have a plurality of preamble indexes according to a standard.
  • the preamble transmitted by the UE 2 d - 01 may be a preamble randomly selected by the UE 2 d - 01 or may be a specific preamble designated by the base station 2 d - 03 .
  • the base station 2 d - 03 Upon receiving the preamble, the base station 2 d - 03 transmits a random access response (hereinafter, “RAW”) message to the UE 2 d - 01 in response ( 2 d - 21 ).
  • the RAR message includes identifier information about the preamble used in operation 2 d - 11 , uplink transmission timing correction information, allocation information about an uplink resource to be used in a subsequent operation (that is, operation 2 d - 31 ), and temporary UE identifier information.
  • the identifier information about the preamble is transmitted to indicate to which preamble the RAR message is a response message, for example, when a plurality of UEs attempts random access by transmitting different preambles in operation 2 d - 11 .
  • the allocation information about the uplink resource is specific information about the resource to be used by the UE 2 d - 01 in operation 2 d - 31 and includes physical position and size of the resource, a modulation and coding scheme (MCS) used for transmission, power adjustment information for transmission, or the like.
  • MCS modulation and coding scheme
  • the temporary UE identifier information is a value transmitted for the case where the UE does not have an identifier allocated by the base station for communication with the base station when the UE transmits the preamble for initial connection.
  • the RAR message needs to be transmitted within a predetermined period starting after a predetermined time from the time the preamble is transmitted, and this period is referred to as an RAR window 2 d - 23 .
  • the RAR window starts after the predetermined time from the time the first preamble is transmitted.
  • the predetermined time may have a subframe unit (2 ms) or shorter.
  • the length of the RAR window may be a predetermined value set by the base station 2 d - 03 for each PRACH resource or for one or more PRACH resource sets in a system information message broadcast by the base station 2 d - 03 .
  • the base station 2 d - 03 schedules the RAR message through a PDCCH, and scheduling information is scrambled using a random access-radio network temporary identifier (RA-RNTI).
  • RA-RNTI random access-radio network temporary identifier
  • the RA-RNTI is mapped to the PRACH resource used to transmit the message 2 d - 11 , and the UE 2 d - 01 having transmitted the preamble via the specific PRACH resource attempts to receive a PDCCH based on the RA-RNTI and determines whether there is a corresponding RAR message.
  • the RA-RNTI used for the scheduling information about the RAR message includes information about the transmission in operation 2 d - 11 .
  • the RA-RNTI may be calculated by the following equation:
  • RA -RNTI 1+ s _ id+ 14 ⁇ t _ id+ 14 ⁇ 80 ⁇ f _ id+ 14 ⁇ 80 ⁇ 8 ⁇ ul _carrier_ id
  • s_id is an index corresponding to the first OFDM symbol in which transmission of the preamble transmitted in operation 2 d - 11 starts and has a value satisfying 0 ⁇ s_id ⁇ 14 (that is, the maximum number of OFDM symbols in one slot);
  • t_id is an index corresponding to the first slot in which transmission of the preamble transmitted in operation 2 d - 11 starts and has a value satisfying 0 ⁇ t_id ⁇ 80 (that is, the maximum number of slots in one system frame (20 ms));
  • the f_id indicates a PRACH resource used to transmit the preamble transmitted in operation 2 d - 11 on the frequency and has a value satisfying 0 ⁇ f_id ⁇ 8 (that is, the maximum number of PRACHs on the frequency within the same time);
  • ul_carrier_id is a factor for distinguishing whether the preamble is transmitted in a normal uplink (NUL) (0 in this case) or in a supplementary uplink (SUL) (1 in this case
  • the UE 2 d - 01 Upon receiving the RAR message, the UE 2 d - 01 transmits different messages via a resource allocated through the RAR message depending on the foregoing various purposes ( 2 d - 31 ).
  • the third transmitted message is also referred to as Msg 3 (that is, the preamble in operation 2 d - 11 or 2 d - 13 is also referred to as Msg 1 , and the RAR in operation 2 d - 21 is also referred to as Msg 2 ).
  • an RRCConnectionRequest message which is a message of an RRC layer, is transmitted for initial connection, an RRCConnectionReestablishmentRequest message is transmitted for reconnection, and an RRCConnectionReconfigurationComplete message is transmitted for a handover. Further, a buffer status report (BSR) message for a resource request may be transmitted.
  • BSR buffer status report
  • the UE 2 d - 01 receives a contention resolution message from the base station 2 d - 03 ( 2 d - 41 ), and the contention resolution message includes the same information as transmitted by the UE 2 d - 01 via Msg 3 , thus indicating to which UE the response corresponds when there is a plurality of UEs selecting the same preamble in operation 2 d - 11 or 2 d - 13 .
  • FIG. 2E illustrates a procedure in which a UE performs two-step random access to a base station according to an embodiment of the disclosure.
  • general contention-based random access involves at least four operations. If an error occurs in one operation, the procedure may be further delayed. Accordingly, it may be considered to reduce the random access procedure to a two-step procedure.
  • a UE 2 e - 01 may transmit MsgA of consecutively transmitting preambles Msg 1 ( 2 e - 11 corresponding to 2 d - 11 ) and Msg 3 ( 2 e - 13 corresponding to 2 d - 31 ) of a four-step random access procedure to a base station 2 e - 03 ( 2 e - 15 ), and the base station 2 e - 03 receiving MsgA may transmit MsgB 2 e - 19 including information of Msg 2 (RAR corresponding to 2 d - 21 ) and Msg 4 (corresponding to 2 d - 41 ) of the four-step random access procedure to the UE 2 e - 01 , thereby reducing a random access procedure.
  • MsgA may include a PRACH resource 2 e - 21 for transmitting Msg 1 , a PUSCH resource 2 e - 23 for transmitting Msg 3 , and a gap resource 2 e - 22 for resolving interference that may occur in transmission via the PUSCH resource.
  • the UE 2 e - 01 performs random access for various purposes.
  • the UE 2 e - 01 may perform random access in order to transmit a message for connection when not yet connected to the base station 2 e - 03 or in order to transmit a message for recovering connection when disconnected from the base station 2 e - 03 due to an error, and these messages belong to a common control channel (CCCH).
  • CCCH common control channel
  • Control messages belonging to the CCCH include RRCSetupRequest (for transition from RRC_IDLE to RRC_CONNECTED), RRCResumeRequest (for transition from RRC_INACTIVE to RRC_CONNECTED), RRCReestablishmentRequest (for reestablishing connection), and RRCSystemInfoRequest (upon request for system information broadcast by the base station).
  • RRCSetupRequest for transition from RRC_IDLE to RRC_CONNECTED
  • RRCResumeRequest for transition from RRC_INACTIVE to RRC_CONNECTED
  • RRCReestablishmentRequest for reestablishing connection
  • RRCSystemInfoRequest upon request for system information broadcast by the base station.
  • RRCReestablishmentRequest transmitted for connection recovery or RRCResumeRequest used in transition from RRC_INACTIVE to RRC_CONNECTED is a high-priority message
  • two-step random access may be performed for these messages when random access is required.
  • four-step random access described above may be performed to transmit this message instead of two-step random access.
  • CCCH messages may be determined to have a higher priority than that of messages of other dedicated control channels and dedicated traffic channels, which will be described later, and may be transmitted using two-step random access.
  • the UE 2 e - 01 may transmit and receive a message belonging to a dedicated control channel (DCCH) and a dedicated traffic channel (DTCH) in RRC_CONNECTED.
  • DCCH dedicated control channel
  • DTCH dedicated traffic channel
  • the UE 2 e - 01 needs to transmit a buffer status report (BSR) message indicating that the UE 2 e - 01 has data to transmit via an uplink to the base station 2 e - 03 , thereby requesting uplink resource allocation.
  • BSR buffer status report
  • the base station 2 e - 03 may allocate a dedicated PUCCH resource for transmitting a scheduling request (SR) for a specific logical channel to the UE 2 e - 01 . Accordingly, when receiving an SR from the UE 2 e - 01 via a PUCCH, the base station 2 e - 03 allocates an uplink resource for transmitting a BSR. When the UE 2 e - 01 transmits a BSR via the uplink resource, the base station 2 e - 03 may identify the buffer state of the UE 2 e - 01 and may allocate an uplink resource for data.
  • SR scheduling request
  • the UE 2 e - 01 may perform random access to transmit a BSR to the base station 2 e - 03 via Msg 3 .
  • the UE 2 e - 01 when the UE 2 e - 01 is connected to the base station 2 e - 03 and then configures a logical channel for transmitting data belonging to each of a dedicated control channel (DCCH) and a dedicated traffic channel (DTCH), the UE 2 e - 01 may set whether two-step random access can be performed when performing random access for transmitting the logical channel.
  • the base station 2 e - 03 may configure two-step random access to be enabled for a logical channel for a DCCH (for example, control radio bearer 1 , control radio bearer 2 , and control radio bearer 3 ) and a logical channel for traffic having a high priority.
  • DCCH dedicated control channel
  • DTCH dedicated traffic channel
  • two-step random access may be performed or four-step random access may be performed depending on whether two-step random access is allowed for a logical channel triggering the random access.
  • FIG. 2F illustrates the necessity and the role of an uplink timing synchronization procedure in a system employing OFDM according to an embodiment of the disclosure.
  • terminal 1 refers to a terminal positioned close to a gNB (base station), and UE 2 (hereinafter, “terminal 2 ”) refers to a terminal far from the gNB.
  • a first propagation delay time (hereinafter, “T_pro 1 ”) refers to a propagation delay time in radio transmission to terminal 1
  • a second propagation delay time (hereinafter, “T_pro 2 ”) refers to a propagation delay time in radio transmission to terminal 2 .
  • terminal 1 is positioned closer to the gNB than terminal 2 and thus has a relatively short propagation delay time (in FIG. 2F , T_pro 1 is 0.333 us, and T_pro 2 is 3.33 us).
  • terminal 1 and terminal 2 are powered on in one cell of the gNB of FIG. 2F or when terminal 1 and terminal 2 are in the idle mode, the uplink timing of terminal 1 , the uplink timing of terminal 2 , and the uplink timings of terminals in the cell detected by the gNB are not synchronized.
  • 2 f - 01 indicates the timing synchronization of terminal 1 for uplink transmission of an OFDM symbol
  • 2 f - 03 indicates the timing synchronization of terminal 2 for uplink transmission of an OFDM symbol.
  • the gNB receives the uplink OFDM symbols at timings 2 f - 05 , 2 f - 07 , and 2 f - 09 . That is, the uplink symbol of terminal 1 of 2 f - 01 is received at the gNB at the timing 2 f - 07 with a propagation delay time, and the uplink symbol of terminal 2 of 2 f - 03 is received at the gNB at the timing 2 f - 09 with a propagation delay time.
  • the start timing 2 f - 05 at which the gNB receives and decodes an uplink OFDM symbol, the timing 2 f - 07 for receiving the OFDM symbol from terminal 1 , and the timing 2 f - 09 for receiving the OFDM symbol from terminal 2 are different.
  • the uplink symbols transmitted from terminal 1 and terminal 2 do not have orthogonality and thus act as interference with each other, and the gNB cannot successfully decode the uplink symbols transmitted from terminal 1 of 2 f - 01 and terminal 2 of 2 f - 03 due to the interference and the timings 2 f - 07 and 2 f - 09 for receiving the uplink symbols not synchronized with 2 f - 05 .
  • An uplink timing synchronization procedure is a process for synchronizing the uplink symbol reception timings of terminal 1 , terminal 2 , and the gNB.
  • the start timing at which the gNB receives and decodes an uplink OFDM symbol the timing for receiving an uplink OFDM symbol from terminal 1 , and the timing for receiving an uplink OFDM symbol from terminal 2 are synchronized as indicated by 2 f - 11 , 2 f - 13 , and 2 f - 15 .
  • the uplink symbol reception timings are aligned with an error within the length of a cyclic prefix (CP) to be synchronized, thus enabling the base station to perform decoding.
  • CP cyclic prefix
  • the base station transmits timing advance (TA) information to the terminals to provide information about how much the timings are adjusted. Specifically, based on a predetermined downlink 2 f - 21 , the base station provides information about how early transmission needs to be performed compared to the downlink.
  • TA timing advance
  • the base station may transmit the TA information through a timing advance command MAC control element (TAC MAC CE) or also through a random access response (RAR) to a random access preamble transmitted by a terminal when performing random access to be described below, which applies to both LTE and NR.
  • TAC MAC CE timing advance command MAC control element
  • RAR random access response
  • N TA,new N TA,old +(TA ⁇ 31)*16.
  • an uplink transmission time is (N TA *N TA_offset )*T s earlier than the downlink ( 2 f - 23 ), where N TA_offset is 0 in an FDD system and is 624 in a TDD system, and T s is 1/(3048*subcarrier spacing).
  • the terminal may adjust an uplink transmission time using the TA information.
  • the terminal receiving the TA information starts a time alignment timer (TAT).
  • TAT is a timer indicating whether a TA is valid. That is, the TA is determined to be valid in an interval in which the TAT operates, but the TA cannot be guaranteed to be valid after the operation of the TAT expires.
  • the terminal restarts the TAT when subsequently receiving additional TA information.
  • the terminal determines that the TA information received from the base station is no longer valid and stops uplink communication with the gNB.
  • the uplink symbols transmitted from terminal 1 and terminal 2 can maintain orthogonality, and the gNB can successfully decode uplink symbols transmitted from terminal 1 of 2 f -Oland terminal 2 of 2 f - 03 .
  • the preamble signal is a signal designed to be decoded even when deviating from an arrival time as described above.
  • PUSCH preamble but also data
  • FIG. 2G illustrates an operation sequence in which a UE determines uplink transmission timing when performing two-step random access according to an embodiment.
  • the UE receives configuration information related to random access from a base station ( 2 g - 03 ).
  • the configuration information may be received via an SIB message broadcast by the base station or may be received by the UE via a dedicated RRC message.
  • CCCH transmission-related information may be included in a SIB message.
  • the configuration information may be received by the UE via a dedicated RRC message transmitted only to the UE.
  • the configuration information may include not only a random access-related configuration for four-step random access but also configuration information for two-step random access and may further include information indicating in which case two-step random access can be used.
  • the UE triggers a random access procedure ( 2 g - 05 ).
  • the random access procedure may be triggered to transmit a CCCH for a transition from the RRC_IDLE state to the RRC_CONNECTED state, may be triggered for beam failure recovery, or may be triggered in handover/SCG addition scenarios.
  • the UE determines whether to perform two-step random access or four-step random access according to the configuration information from the base station ( 2 g - 07 ).
  • the UE transmits a preamble via a corresponding PRACH resource to perform a four-step random access procedure ( 2 g - 17 ).
  • the UE determines whether the TATs of cells timing advance group (TAG) using the same TA as a cell performing the random access are running ( 2 g - 09 ). For example, in a transition from the RRC_IDLE state to the RRC_CONNECTED state, the TAG of a connected PCell (PTAG) is not running. In addition, for example, when the UE has already transitioned to the RRC_CONNECTED state once, the UE receives TA information through an RAR and runs a TAT while performing the random access to transition to the RRC_CONNECTED state, and thus the TAT is running before expiring. When the TAT expires, the TAT is no longer running.
  • TAG timing advance group
  • the UE determines that N TA calculated using a TA value previously received through an RAR or a TAC MAC CE is valid and performs the random access procedure by transmitting a PUSCH of MsgA using N TA in the two-step random access ( 2 g - 13 ).
  • a first method is setting N TA always to a predetermined value (e.g., 0).
  • This method is simple but requires the gap 2 e - 22 illustrated in FIG. 2E to have a sufficiently large size in order to solve the problem described in FIG. 2F . That is, the gap is not a resource used to actually transmit and receive data, and when MsgA resources are allocated according to beams, waste of resources for the gap is also increased according to the number of supported beams.
  • a second method is determining whether a UE has existing N TA received from a cell to which the UE currently performs random access. That is, the UE may be connected to the cell by accessing the cell, may thus has a previously used N TA value, and may maintain the existing N TA value even though a TAT expires. Accordingly, when the TAT is not running but the existing N TA value is maintained, the UE performs the random access procedure by transmitting a PUSCH of MsgA using the N TA value in the two-step random access ( 2 g - 13 ).
  • the UE when the UE does not maintain N TA (e.g., when performing random access to transition from the RRC_IDLE state to the RRC_CONNECTED state), the UE performs the random access procedure by transmitting a PUSCH of MsgA using a predetermined N TA value in the two-step random access ( 2 g - 15 ).
  • FIG. 2H is a block diagram illustrating the configuration of a UE in a wireless communication system according to an embodiment of the disclosure.
  • the UE includes a radio frequency (RF) processor 2 h - 10 , a baseband processor 2 h - 20 , a storage unit 2 h - 30 , and a controller 2 h - 40 .
  • RF radio frequency
  • the RF processor 2 h - 10 performs a function for transmitting or receiving a signal through a wireless channel, such as band conversion and amplification of a signal. That is, the RF processor 2 h - 10 upconverts a baseband signal, provided from the baseband processor 2 h - 20 , into an RF band signal to transmit the RF band signal through an antenna and downconverts an RF band signal, received through the antenna, into a baseband signal.
  • the RF processor 2 h - 10 may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC).
  • the UE may include a plurality of antennas.
  • the RF processor 2 h - 10 may include a plurality of RF chains. Further, the RF processor 2 h - 10 may perform beamforming. For beamforming, the RF processor 2 h - 10 may adjust the phase and strength of each of signals transmitted and received through a plurality of antennas or antenna elements.
  • the baseband processor 2 h - 20 performs a function of converting a baseband signal and a bit stream according to the physical-layer specification of a system. For example, in data transmission, the baseband processor 2 h - 20 encodes and modulates a transmission bit stream, thereby generating complex symbols. In data reception, the baseband processor 2 h - 20 demodulates and decodes a baseband signal, provided from the RF processor 2 h - 10 , thereby reconstructing a reception bit stream.
  • the baseband processor 2 h - 20 in data transmission, the baseband processor 2 h - 20 generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and constructs OFDM symbols through an inverse fast Fourier transform (IFFT) and cyclic prefix (CP) insertion.
  • IFFT inverse fast Fourier transform
  • CP cyclic prefix
  • the baseband processor 2 h - 20 divides a baseband signal, provided from the RF processor 2 h - 10 , into OFDM symbols, reconstructs signals mapped to subcarriers through a fast Fourier transform (FFT), and reconstructs a reception bit stream through demodulation and decoding.
  • FFT fast Fourier transform
  • the baseband processor 2 h - 20 and the RF processor 2 h - 10 transmit and receive signals. Accordingly, the baseband processor 2 h - 20 and the RF processor 2 h - 10 may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. At least one of the baseband processor 2 h - 20 and the RF processor 2 h - 10 may include a plurality of communication modules to support a plurality of different radio access technologies. Further, at least one of the baseband processor 2 h - 20 and the RF processor 2 h - 10 may include different communication modules for processing signals in different frequency bands.
  • the different radio access technologies may include a wireless LAN (for example, IEEE 802.11), a cellular network (for example, an LTE network), and the like.
  • the different frequency bands may include a super high frequency (SHF) band (for example, 2.5 GHz or 5 GHz) and a millimeter wave band (for example, 60 GHz).
  • SHF super high frequency
  • the storage unit 2 h - 30 stores data, such as a default program, an application, and configuration information for operating the UE.
  • the storage unit 2 h - 30 may store information about a WLAN node performing wireless communication using a WLAN access technology.
  • the storage unit 2 h - 30 provides stored data upon request from the controller 2 h - 40 .
  • the controller 2 h - 40 controls overall operations of the UE.
  • the controller 2 h - 40 transmits and receives signals through the baseband processor 2 h - 20 and the RF processor 2 h - 10 .
  • the controller 2 h - 40 records and reads data in the storage unit 2 h - 30 .
  • the controller 2 h - 40 may include at least one processor.
  • the controller 2 h - 40 may include a communication processor (CP) to perform control for communication and an application processor (AP) to control an upper layer, such as an application.
  • the controller 2 h - 40 includes a multi-connection processor 2 h - 42 to perform processing for an operation in a multi-connection mode.
  • the controller 2 h - 40 may control the UE to perform the procedure of operations of the UE illustrated in FIG. 2E .
  • the controller 2 h - 40 When random access is triggered according to configuration information indicated by a base station, the controller 2 h - 40 according to the embodiment may indicate the UE to perform two-step random access or four-step random access. When two-step random access is performed, the controller 2 h - 40 indicates the value of N TA to be used for transmitting a PUSCH of MsgA.
  • FIG. 2I is a block diagram illustrating the configuration of a base station in a wireless communication system according to an embodiment of the disclosure.
  • the base station includes an RF processor 2 i - 10 , a baseband processor 2 i - 20 , a backhaul communication unit 2 i - 30 , a storage unit 2 i - 40 , and a controller 2 i - 50 .
  • the RF processor 2 i - 10 performs a function for transmitting or receiving a signal through a wireless channel, such as band conversion and amplification of a signal. That is, the RF processor 2 i - 10 upconverts a baseband signal, provided from the baseband processor 2 i - 20 , into an RF band signal to transmit the RF band signal through an antenna and downconverts an RF band signal, received through the antenna, into a baseband signal.
  • the RF processor 2 i - 10 may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, and an ADC.
  • FIG. 2I shows only one antenna, the base station may include a plurality of antennas.
  • the RF processor 2 i - 10 may include a plurality of RF chains. Further, the RF processor 2 i - 10 may perform beamforming. For beamforming, the RF processor 2 i - 10 may adjust the phase and strength of each of signals transmitted and received through a plurality of antennas or antenna elements. The RF processor may transmit one or more layers, thereby performing downlink MIMO.
  • the baseband processor 2 i - 20 performs a function of converting a baseband signal and a bit stream according to the physical-layer specification of a first radio access technology. For example, in data transmission, the baseband processor 2 i - 20 encodes and modulates a transmission bit stream, thereby generating complex symbols. In data reception, the baseband processor 2 i - 20 demodulates and decodes a baseband signal, provided from the RF processor 2 i - 10 , thereby reconstructing a reception bit stream.
  • the baseband processor 2 i - 20 in data transmission, the baseband processor 2 i - 20 generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and constructs OFDM symbols through an IFFT and CP insertion.
  • the baseband processor 2 i - 20 divides a baseband signal, provided from the RF processor 2 i - 10 , into OFDM symbols, reconstructs signals mapped to subcarriers through an FFT, and reconstructs a reception bit stream through demodulation and decoding.
  • the baseband processor 2 i - 20 and the RF processor 2 i - 10 transmit and receive signals. Accordingly, the baseband processor 2 i - 20 and the RF processor 2 i - 10 may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.
  • the backhaul communication unit 2 i - 30 provides an interface for performing communication with other nodes in a network. That is, the backhaul communication unit 2 i - 30 converts a bit stream, transmitted from the main base station to another node, for example, a secondary base station or a core network, into a physical signal and converts a physical signal, received from the other node, into a bit stream.
  • the storage unit 2 i - 40 stores data, such as a default program, an application, and configuration information for operating the main base station.
  • the storage unit 2 i - 40 may store information on a bearer allocated to a connected UE, a measurement result reported from a connected UE, and the like.
  • the storage unit 2 i - 40 provides stored data upon request from the controller 2 i - 50 .
  • the controller 2 i - 50 controls overall operations of the main base station. For example, the controller 2 i - 50 transmits and receives signals through the baseband processor 2 i - 20 and the RF processor 2 i - 10 or through the backhaul communication unit 2 i - 30 . Further, the controller 2 i - 50 records and reads data in the storage unit 2 i - 40 . To this end, the controller 2 i - 50 may include at least one processor (e.g., multi-connection processor 2 i - 52 ).
  • a computer-readable storage medium for storing one or more programs (software modules) may be provided.
  • the one or more programs stored in the computer-readable storage medium may be configured for execution by one or more processors within the electronic device.
  • the at least one program may include instructions that cause the electronic device to perform the methods according to various embodiments of the disclosure as defined by the appended claims and/or disclosed herein.
  • the programs may be stored in non-volatile memories including a random access memory and a flash memory, a Read Only Memory (ROM), an Electrically Erasable Programmable Read Only Memory (EEPROM), a magnetic disc storage device, a Compact Disc-ROM (CD-ROM), Digital Versatile Discs (DVDs), or other type optical storage devices, or a magnetic cassette.
  • ROM Read Only Memory
  • EEPROM Electrically Erasable Programmable Read Only Memory
  • CD-ROM Compact Disc-ROM
  • DVDs Digital Versatile Discs
  • any combination of some or all of them may form a memory in which the program is stored.
  • a plurality of such memories may be included in the electronic device.
  • the programs may be stored in an attachable storage device which may access the electronic device through communication networks such as the Internet, Intranet, Local Area Network (LAN), Wide LAN (WLAN), and Storage Area Network (SAN) or a combination thereof.
  • a storage device may access the electronic device via an external port.
  • a separate storage device on the communication network may access a portable electronic device.
  • a component included in the disclosure is expressed in the singular or the plural according to a presented detailed embodiment.
  • the singular or plural expressions are selected to be suitable for proposed situations for convenience of description, and the disclosure is not limited to the singular or plural elements.
  • An element expressed in a plural form may be configured in singular, or an element expressed in a singular form may be configured in plural.

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