Patent Description:
Therefore, the <NUM> or pre-<NUM> communication system is also called a "Beyond <NUM> Network" or a "Post LTE System". In the <NUM> system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have also been developed.

<NPL> (<NUM>-<NUM>-<NUM>), provides a discussion on a procedure for two-step RACH. <NPL>, discusses pocedures and mgsB content. <NPL> (<NUM>-<NUM>-<NUM>), discusses the <NUM>-step Random Access procedure. <NPL> (<NUM>-<NUM>-<NUM>), discusses back-off for <NUM>-step RA. <NPL> (<NUM>-<NUM>-<NUM>), provides consideration on <NUM>-step RACH procedure. <NPL> (<NUM>-<NUM>-<NUM>), provides perspectives on Operation of Two-Step RACH.

It is an aspect of the disclosure to provide a method for indicating a backoff when a base station has received an entire MsgA in connection with a two-step random access, and when a part (Msg1) of the MsgA has been received.

According to an embodiment of the disclosure, a base station may differently indicate a backoff according to which channel of the MsgA has undergone a collision when a two-step random access is performed, thereby effectively controlling collisions.

In the following description of the disclosure, a detailed description of known functions or configurations incorporated herein will be omitted when it may make the subject matter of the disclosure unnecessarily unclear. The terms which will be described below are terms defined in consideration of the functions in the disclosure, and may be different according to users, intentions of the users, or customs. Therefore, the definitions of the terms should be made based on the contents throughout the specification.

In the following description, terms for identifying access nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, terms referring to various identification information, and the like are illustratively used for the sake of convenience. Therefore, the disclosure is not limited by the terms as used below, and other terms referring to subjects having equivalent technical meanings may be used.

In the following description, the disclosure will be described using terms and names defined in LTE and NR standards, which are the latest standards specified by the 3rd generation partnership project (3GPP) group among existing communication standards, for the convenience of description. However, the disclosure is not limited by these terms and names, and may be applied in the same way to systems that conform other standards. In particular, the disclosure may be applied to the 3GPP NR (5th generation mobile communication standard).

<FIG> illustrates the structure of an LTE system according to the disclosure. An NR system also has a similar structure.

Referring to <FIG>, a wireless communication system includes a plurality of eNBs 1a-<NUM>, 1a-<NUM>, 1a-<NUM>, and 1a-<NUM>, a mobility management entity (MME) 1a-<NUM>, and a serving-gateway (S-GW) 1a-<NUM>. A user equipment (hereinafter, a UE or terminal) 1a-<NUM> accesses an external network through the eNBs 1a-<NUM>, 1a-<NUM>, 1a-<NUM>, and 1a-<NUM> and the S-GW 1a-<NUM>.

The eNBs 1a-<NUM>, 1a-<NUM>, 1a-<NUM>, and 1a-<NUM> are access nodes of a cellular network and provide a wireless connection to UEs accessing the network. That is, the eNBs 1a-<NUM>, 1a-<NUM>, 1a-<NUM>, and 1a-<NUM> perform scheduling by collecting state information, such as buffer states of the UEs, available transmission power states, and channel states, in order to service traffic of users, and support connection between the UEs and a core network (CN). The MME 1a-<NUM> corresponds to a device which is responsible for various control functions including a mobility management function for a UE and is connected to a plurality of eNBs, and the S-GW 1a-<NUM> corresponds to a device which provides a data bearer. In addition, the MME 1a-<NUM> and the S-GW 1a-<NUM> may further perform authentication, bearer management, and the like for a UE accessing a network, and processes a packet arrived from the eNBs 1a-<NUM>, 1a-<NUM>, 1a-<NUM>, and 1a-<NUM> or a packet to be transferred to the eNBs 1a-<NUM>, 1a-<NUM>, 1a-<NUM>, and 1a-<NUM>.

<FIG> illustrates a wireless protocol structure in LTE and NR systems according to the disclosure.

Referring to <FIG>, in relation to a wireless protocol structure of an LTE system, each of a LTE and an eNB includes a packet data convergence protocol (PDCP) layer 1b-<NUM> or 1b-<NUM>, a radio link control (RLC) layer 1b-<NUM> or 1b-<NUM>, and a medium access control (MAC) layer 1b-<NUM> or 1b-<NUM>. The packet data convergence protocol (PDCP) layer 1b-<NUM> or 1b-<NUM> is responsible for IP header compression/decompression, and the radio link control (hereinafter, referred to as RLC) 1b-<NUM> or 1b-<NUM> reconfigures PDCP packet data units (PDCP PDUs) to a proper size. The MAC layer 1b-<NUM> or 1b-<NUM> is connected to several RLC-layer devices configured in one UE, and performs an operation of multiplexing RLC PDUs to a MAC PDU and demultiplexing RLC PDUs from the MAC PDU. Physical layers 1b-<NUM> and 1b-<NUM> channel-code and modulate higher layer data into OFDM symbols and transmit the OFDM symbols through a wireless channel, or demodulate and channel-decode OFDM symbols received through the wireless channel to transfer the OFDM symbols to a higher layer. In addition, for additional error correction, hybrid ARQ (HARQ) is used in the physical layers, and a receiver side transmits <NUM>-bit information indicating whether a packet transmitted by a transmitter side is received. This information is referred to as HARQ ACK/NACK information. Downlink HARQ ACK/NACK information for uplink data transmission may be transmitted through a physical hybrid-ARQ indicator channel (PHICH) in case of the LTE system. In case of an NR system, it can be determined whether retransmission is required or retransmission is enough, through scheduling information of a corresponding UE in a physical downlink control channel (PDCCH) which is a channel through which downlink/uplink resource allocation is transmitted. This is because asynchronous HARQ is applied in the NR system. Uplink HARQ ACK/NACK information for downlink data transmission may be transmitted through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH) physical channel. The PUCCH is generally transmitted through an uplink of a primary cell (PCell) which is to be described later. However, if there is a support by a UE, an eNB may additionally transmit the PUCCH to the corresponding LTE through a secondary cell (SCell) which is to be described later. This SCell is referred to as a PUCCH SCell.

Although not illustrated, a radio resource control (RRC) layer exists above a PDCP layer of each of a UE and an eNB, and the RRC layer may transmit or receive an access- and measurement-related configuration control message in order to control radio resources.

Meanwhile, the PHY layer may include one or a plurality of frequencies/carriers, and a technology of simultaneously configuring and using a plurality of frequencies is called a carrier aggregation technology (hereinafter, referred to as CA). Only one carrier has been used for communication between a terminal (or user equipment (UE)) and a base station (E-UTRAN nodeB (eNB)) in the past, but the CA technology can significantly increase the transmission amount as much as the number of subcarriers by additionally using a main carrier and one or more subcarriers. Meanwhile, in the LTE system, a cell in an eNB using a main carrier is referred to as a main cell or a primary cell (PCell), and a cell in an eNB using a subcarrier is referred to as a sub-cell or a secondary cell (SCell).

<FIG> illustrates an example of downlink and uplink channel frame structures in beam-based communication of an NR system according to the disclosure.

In <FIG>, an eNB 1c-<NUM> transmits a signal in the form of beams 1c-<NUM>, 1c-<NUM>, 1c-<NUM>, and 1c-<NUM> in order to transmit wider coverage or a stronger signal. Accordingly, a LTE 1c-<NUM> in a cell is required to transmit or receive data by using a specific beam (beam #<NUM>1c-<NUM> in this exemplary drawing) transmitted by the eNB.

Meanwhile, depending on whether the UE is connected to the eNB, the state of the UE is divided into an idle mode (RRC _IDLE) and a connected mode (RRC_CONNECTED). Accordingly, the eNB does not recognize location of the UE in the idle mode.

If the UE in the idle mode is to be shifted to the connected mode, the UE may receive synchronization signal blocks (SSBs) 1c-<NUM>, 1c-<NUM>, 1c-<NUM>, and 1c-<NUM> transmitted by the eNB. The SSBs are transmitted periodically according to a cycle configured by the eNB, and each of the SSBs may include a primary synchronization signal (PSS) 1c-<NUM>, a secondary synchronization signal (SSS) 1c-<NUM>, and a physical broadcast channel (PBCH).

In this exemplary drawing, a scenario in which an SSB is transmitted for each beam is assumed. For example, it is assumed that SSB #<NUM>1c-<NUM> is transmitted using beam #<NUM>1c-<NUM>, SSB #<NUM>1c-<NUM> is transmitted using beam #<NUM>1c-<NUM>, SSB #<NUM>1c-<NUM> is transmitted using beam #<NUM>1c-<NUM>, and SSB #<NUM>1c-<NUM> is transmitted using beam #<NUM>1c-<NUM>. In this drawing, it is assumed that the UE in the idle mode is located in beam #<NUM>. However, if the UE in the connected mode performs random access, the LTE selects an SSB received at the time of performing random access.

Accordingly, in <FIG>, the UE receives SSB #<NUM> transmitted using beam #<NUM>. If SSB #<NUM> is received, the LTE acquires a physical cell identifier (PCI) of the eNB through a PSS and an SSS, and receives a PBCH, so that the UE may identify an identifier (i.e., #<NUM>) of the currently received SSB, a location at which the SSB is currently received within a <NUM> frame, and a system frame number (SFN) having a cycle of <NUM> seconds in which the SSB is located. In addition, the PBCH may include a master information block (MIB), and the MIB may include information indicating a location on which system information block type <NUM> (SIB1) for broadcasting more detailed configuration information of the cell is received. If the SIB1 is received, the UE may identify the total number of SSBs transmitted by the eNB and may identify location (assuming a scenario in which a PRACH occasion is allocated every <NUM> in this exemplary drawing: indicated by reference numerals 1c-<NUM> to 1c-<NUM>) of physical random access channel (PRACH) occasions in which the UE may perform random access to be shifted to the connected mode (more precisely, capable of transmitting a preamble which is a physical signal specifically designed for uplink synchronization). In addition, the UE may identify that a PRACH occasion, among the PRACH occasions, is mapped to an SSB index, based on the information. For example, in this exemplary drawing, a scenario in which a PRACH occasion is allocated every <NUM> and a scenario in which a half of an SSB is allocated per PRACH occasion (that is, two PRACH occasions per SSB) are assumed. Accordingly, a scenario in which two PRACH occasions are allocated for each SSB from a PRACH occasion starting according to an SFN value is illustrated. That is, according to the scenario, 1c-<NUM> and 1c-<NUM> are allocated for SSB #<NUM>, and 1c-<NUM> and 1c-<NUM> are allocated for SSB #<NUM>. After configurations are made for all SSBs, PRACH occasions are allocated again for the first SSB (indicated by reference numerals 1c-<NUM> and 1c-<NUM>).

Accordingly, the UE recognizes locations of the PRACH occasions 1c-<NUM> and 1c-<NUM> for SSB #<NUM>, and transmits a random access preamble at the currently earliest PRACH occasion among the PRACH occasions 1c-<NUM> and 1c-<NUM> corresponding to SSB #<NUM> (for example, 1c-<NUM>). Since the eNB has received the preamble at the PRACH occasion 1c-<NUM>, it can be seen that the corresponding LTE has transmitted the preamble by selecting SSB #<NUM>. Accordingly, data may be transmitted or received through the corresponding beam when subsequent random access is performed.

Meanwhile, when the UE in the connected mode moves from the current (source) eNB to a target eNB due to handover, etc., the UE performs random access at the target eNB and selects an SSB as described above to perform an operation of transmitting a random access preamble. In addition, during handover, a handover command is transmitted to the UE to allow the UE to move from the source eNB to the target eNB. Here, the message may include a corresponding UE dedicated random access preamble identifier allocated to each SSB of the target eNB to enable use of the identifier at the time of performing random access at the target eNB. The eNB may not allocate a dedicated random access preamble identifier for all beams (depending on the current location of the UE, etc.), and some SSBs may not be allocated with a dedicated random access preamble (for example, allocation of a dedicated random access preamble to beam #<NUM> and beam #<NUM> only may occur). If a dedicated random access preamble is not allocated to an SSB selected by the LTE for preamble transmission, the LTE randomly selects a contention-based random access preamble to perform random access. For example, in this drawing, after the UE is located in beam #<NUM> and first performs random access but fails, the LTE may be located in beam #<NUM> to transmit a dedicated preamble when transmitting a random access preamble again. That is, even in one random access procedure, if preamble retransmission occurs, a contention-based random access procedure and a contention-free random access procedure may be mixed depending on whether a dedicated random access preamble is allocated to a selected SSB for each preamble transmission.

<FIG> illustrates a contention-based four-step random access procedure in which a UE performs, with respect to a base station, a contention-based four-step random access procedure that may be performed in initial access, re-access, handover, and other various cases where random access is required according to the disclosure.

In order to perform access to a base station 1d-<NUM>, a UE 1d-<NUM> selects a PRACH according to <FIG> described above and transmits a random access preamble through the corresponding PRACH (operation 1d-<NUM>). A case in which one or more UEs simultaneously transmit the random access preamble through the PRACH resources may occur. The PRACH resources may span over one subframe or only some of the symbols in one subframe may be used. Information about the PRACH resource is included in system information broadcast by a base station, and accordingly, the LTE may identify time/frequency resources used for transmission of a preamble. In addition, the random access preamble is a particular sequence specially designed to be receivable even when transmitted before being completely synchronized with the base station, and there may be a plurality of preamble identifiers (indexes) according to standards. If there is a plurality of preamble identifiers, the preamble transmitted by the UE may be a preamble randomly selected by the UE or may be a particular preamble designated by the base station.

Upon receiving the preamble, the base station may transmit a random access response (hereinafter, "RAR") message (this is also referred to as Msg2) to the UE in response to the preamble (operation 1d-<NUM>). The RAR message includes identifier information of the preamble used in operation 1d-<NUM>, uplink transmission timing correction information, uplink resource allocation information to be used for a subsequent operation (that is, operation 1d-<NUM>), and temporary UE identifier information. The identifier information of the preamble is transmitted to notify that the RAR message may include responses to respective preambles and which preamble the RAR message is transmitted in response to, for example, when a plurality of UEs transmit different preambles to attempt random access in operation 1d-<NUM>. The uplink resource allocation information, which is included in responses to respective preambles, is detailed information about resources to be used by the UE in operation 1d-<NUM>, and includes physical locations and sizes of the resources, a modulation and coding scheme used during transmission, and power adjustment information during transmission. The temporary UE identifier information is a value transmitted for use since the UE does not include an identifier allocated by the base station for communication with the base station if the UE having transmitted a preamble performs initial access.

Meanwhile, the RAR message may include not only the response(s) to each of the preambles, but also optionally include a backoff indicator (BI). The backoff indicator indicates a value transmitted to delay transmission randomly according to the value of the backoff indicator, rather than immediately retransmitting the preamble when the random access preamble needs to be retransmitted because random access is not successfully performed. More specifically, if the UE does not properly receive the RAR, or if contention resolution, which will be described later, is not properly achieved, the random access preamble should be retransmitted. Here, the value indicated by the back-off indicator may be indicated by the index values of the following table (Table <NUM>), and the LTE selects a random value from among <NUM> to the values indicated by the index values, and after a period of time equal to the value, the UE retransmits the random access preamble. For example, if the base station indicates <NUM> (that is, <NUM>) as the BI value and the UE randomly selects a value of <NUM> among <NUM> to <NUM>, the selected value is stored in a parameter called PREAMBLE_BACKOFF, and the LTE performs a procedure of retransmitting the preamble after a <NUM> period of time. If the backoff indicator is not transmitted, and if random access is not successfully performed and thus the random access preamble needs to be retransmitted, the LTE immediately transmits the random access preamble.

The RAR message needs to be transmitted within a predetermined period starting from a predetermined period time after the preamble is transmitted, and the period is referred to as a "RAR window". The RAR window 1d-<NUM> starts from a time point at which a predetermined period of time has passed after the first preamble is transmitted. The predetermined period of time may have a subframe unit (<NUM>) or a smaller value than thereof. In addition, the length of the RAR window 1d-<NUM> may be a predetermined value set by the base station for each PRACH resource or for at least one PRACH resource set within a system information message broadcast by the base station. Meanwhile, when the RAR message is transmitted, the base station schedules the RAR message through a PDCCH, and the corresponding scheduling information is scrambled using a random access-radio network temporary identifier (RA-RNTI). The RA-RNTI is mapped to a PRACH resource used for transmission of the message 1d-<NUM>, the UE having transmitted a preamble via a specific PRACH resource attempts to receive a PDCCH based on a corresponding RA-RNTI and determines whether there is a corresponding RAR message. That is, if the RAR message is a response to the preamble transmitted by the UE in operation 1d-<NUM> as shown in this exemplary drawing, the RA-RNTI used for the scheduling information of the RAR message may include information about transmission performed in operation 1d-<NUM>. To this end, the RA-RNTI is calculated according to the equation as follows:
<MAT>.

Here, s_id denotes an index corresponding to a first OFDM symbol from which the preamble transmission occasion in operation 1d-<NUM> is started, and has a value of <NUM> ≤ s_id < <NUM> (that is, the maximum number of OFDMs in one slot). Further, t_id denotes an index corresponding to a first slot in which preamble transmission occasion in operation 1d-<NUM> is started, and has a value of <NUM> ≤ t_id < <NUM> (that is, the maximum number of slots in one system frame (<NUM>)). Furthermore, f_id indicates the sequential position of a PRACH resource in a frequency domain through which the preamble transmission occasion in operation 1d-<NUM> is transmitted, and has a value of <NUM> ≤ f_id < <NUM> (that is, the maximum number of PRACHs in the frequency domain within the same period of time). In addition, ul_carrier_id is a factor used to distinguish, if two carriers are used as uplink in connection with one cell, whether uplink through which the preamble is transmitted is a normal uplink (NUL) (in this case, ul_carrier_id has a value of <NUM>) or a supplementary uplink (SUL) (in this case, ul_carrier_id has a value of <NUM>).

Upon receiving the RAR message, the UE transmits a different message via a resource allocated through the RAR message according to various purposes described above (operation 1d-<NUM>). Here, the third transmitted message in this exemplary drawing may be referred to as Msg3 (that is, the preamble in operation 1d-<NUM> is also referred to as Msg1, and the RAR in operation 1d-<NUM> is also referred to as Msg2). Examples of Msg3 transmitted by the UE may include an RRCSetupRequest message, which is an RRC layer message, in case of initial access, an RRCReestablishmentRequest message in case of re-access, and an RRCReconfigurationComplete message in case of handover. Alternatively, a buffer status report (BSR) message for a resource request may be transmitted.

Thereafter, in a case of initial transmission (that is, in case that Msg3 does not include base station identifier information previously allocated to the UE, etc.), the UE may receive a contention resolution message from the base station (operation 1d-<NUM>). The content resolution message includes the same content as that transmitted by the UE through Msg3. Thus, even if a plurality of UEs select the same preamble in operation 1d-<NUM>, it is possible to notify of which UE the contention resolution message is transmitted in response to.

<FIG> illustrates a procedure in which a UE performs a two-step random access procedure to a base station.

As described above in <FIG>, general contention-based random access is performed through at least four steps, and if an error occurs in one step, the procedure may be further delayed. Accordingly, a scenario in which the random access procedure is reduced to a two-step procedure can be considered.

To this end, the LTE successively transmits preamble Msg1 1e-<NUM> (corresponding to 1d-<NUM>) and Msg3 1e-<NUM> (corresponding to 1d-<NUM>) in a four-step random access procedure, thereby transmitting MsgA 1e-<NUM>. Thereafter, the base station having received the MsgA transmits MsgB 1e-<NUM> including information of Msg2 (RAR) (corresponding to 1d-<NUM>) and Msg4 (corresponding to 1d-<NUM>) in the four-step random access procedure. Thus, the random access procedure can be reduced.

Here, when the MsgA is shown in a time domain, the MsgA 1e-<NUM> may include a PRACH resource 1e-<NUM> for transmission of Msgl, a PUSCH resource 1e-<NUM> for transmission of Msg3, and a gap resource 1e-<NUM> for resolving interference problem that may occur during transmission to the PUSCH resource. In addition, Msg3 includes information related to Msg1, and thus it can be seen that Msg3 is transmitted by a UE having transmitted a predetermined preamble (Msgl).

Upon receiving both Msg1 and Msg3 included in MsgA, the base station transmits MsgB to the UE (operation 1e-<NUM>). Here, the MsgB may include the BI described above.

Meanwhile, if collision occurs due to transmission of several MsgAs in operation 1e-<NUM>, a case that the base station receives only Msg1(s) included in MsgA and cannot receive Msg3 may occur. Here, the base station may transmit, to the UE, aforementioned Msg2 (operation 1e-<NUM>) instead of MsgB (operation 1e-<NUM>), may change the procedure to the four-step random access procedure described in <FIG>, and thus performs the remaining random access procedure.

In addition, in case in which the base station receives the MsgA, multiple Msg1 receptions and only one Msg3 reception may occur. Here, the base station may transmit, to the UE, a response (i.e., MsgB) (operation 1e-<NUM>) to the LTE from which both Msg1 and Msg3 have been received and a response (i.e., Msg2) (operation 1e-<NUM>) to only Msg1. Different responses can be included in the same message or in different messages (operation 1e-<NUM>) (operation 1e-<NUM>). In case of responding with different messages as shown in this drawing, the base station enables an indicator to be included in the PDCCH (operation 1e-<NUM>) (operation 1e-<NUM>) for scheduling the MsgB or Msg2, notifies the UE of whether the scheduled message is MsgB or Msg2, and enables the UE to correctly perform decoding. Alternatively, the RA-RNTI value for scrambling the PDCCH may be distinguished by using a different value. Here, an identifier for determining whether MsgB is included is added in calculation of the RA-RNTI. Each of the MsgB or Msg2 messages may include the BI value described above. Thereafter, if random access is not successful, the UE needs to determine, using the BI value included in a message, whether to delay the preamble transmission.

In addition, if the UE does not establish a connection with the base station (for example, in order to shift from IDLE to CONNECTED) and thus the MsgA includes a common control channel (CCCH)-related message (e.g., messages such as RRCSetupRequest, RRCResumeRequest, RRCReestablishmentRequest, RRCSystemInfoRequest, etc. of the RRC layer), the contents in the MsgB include uplink transmission timing information (timing advance command (TAC)) transmitted through the above-described Msg2, temporary identifier (temporary C-RNTI) of a UE to be used in a base station by the UE in the future, and contention resolution related information (UE contention resolution identity) transmitted through Msg4. In addition, if the UE is already connected to the base station and thus the C-RNTI MAC CE including the identifier information of the UE has been transmitted through the MsgA, the MsgB is a message through which the base station transmits resource allocation to the UE using the identifier (C-RNTI) of the corresponding UE via the PDCCH.

Meanwhile, as described above in <FIG>, the UE performs random access for various purposes. For example, the UE may perform random access in order to transmit a message for establishing a connection while the LTE is not yet connected to the base station, or to transmit a message for recovering connection in a case in which the UE and base station were connected but a connection failure occurs due to an error. The above message is a message belonging to a common control channel (CCCH). Control messages belonging to the CCCH include RRCSetupRequest (when shifting from idle mode (RRC _IDLE) to connected mode), RRCResumeRequest (when shifting from inactive mode (RRC_INACTIVE) to connected mode), RRCReestablishmentRequest (when recovering connection), RRCSystemInfoRequest (when requesting system information broadcasted by a base station), and the like. As described above, if the UE is not connected to the base station and thus the CCCH is included in MsgA as described above, the contents in the MsgB include uplink transmission timing information (timing advance command (TAC)) transmitted through Msg2 described above, a temporary identifier (temporary C-RNTI) of a UE, to be used by the UE in the base station in the future, and contention resolution-related information (UE contention resolution identity) transmitted through Msg4.

Meanwhile, when the UE normally accesses the base station, the UE may transmit or receive messages belonging to a dedicated control channel (DCCH) and a dedicated traffic channel (DTCH) in a connected mode (RRC_CONNECTED). In connection with the message transmitted by the UE, the UE transmits a "buffer status report (BSR)" message notifying that the UE currently includes data to be transmitted through uplink to the base station so as to request uplink resource allocation. To this end, the base station may allocate a dedicated PUCCH resource for transmission of a "scheduling request (SR)" with respect to a specific logical channel to the UE. Accordingly, when receiving the SR from the LTE through the PUCCH, the base station may allocate an uplink resource to be used for transmission of the BSR, and when transmitting the BSR through the corresponding uplink resource, the base station may identify the buffer state of the LTE and provide allocation of uplink resources for data.

On the other hand, if the base station does not allocate the SR to a specific logical channel (a logical concept that is divided according to the types of control and general data), or if the BSR cannot be transmitted because there is no uplink resource even if the base station performs allocation of the SR and the SR has been transmitted as many as the maximum number of SR transmissions, the LTE may perform random access and transmit the BSR through Msg3.

Accordingly, when the UE accesses the base station and then configures each logical channel for transmission of data belonging to a logical channel dedicated control channel (DCCH) and a dedicated traffic channel (DTCH), if the UE performs random access to perform transmission for the corresponding logical channel, the UE transmits the C-RNTI MAC CE including the identifier information of the UE through MsgA so as to notify that the subject performing the random access is the UE. In this case, the MsgB is a message through which the base station transmits resource allocation to the corresponding UE by using the identifier (C-RNTI) of the corresponding UE via the PDCCH.

<FIG> illustrates embodiment <NUM> relating to a method for determining whether to use BI information, which is included in a message (Msg2 or MsgB), when a UE performs two-step random access according to an embodiment of the disclosure.

At operation 1f-<NUM>, the method starts. The UE receives random access related configuration information from a base station, which is currently camped on or being accessed, through an RRC layer message (operation 1f-<NUM>). The RRC layer message may be transmitted as a system information message (SIB) that the base station broadcasts to all UEs in a cell, or may be transmitted, in connection with connected LTEs, only to the corresponding LTE through an RRCReconfiguration message. The random access-related configuration information includes configuration information for a PRACH capable of transmitting a random access preamble (Msg1) (i.e., a resource for a four-step random access procedure) and configuration information for a channel capable of transmitting MsgA (i.e., a resource for a two-step random access procedure), and the PRACH resource for the four-step random access procedure and the PRACH resource among MsgA for the two-step random access procedure may be configured independently each other or configured to be shared. The configuration of sharing the PRACH resources denotes that a UE for performing the four-step random access procedure and a UE for performing the two-step random access procedure can transmit the random access preamble to the same PRACH resource. However, in this case, since the UE randomly selects the random access preamble within a predetermined configuration, a preamble index to be used may be the same or different.

Thereafter, the UE triggers a random access procedure (operation 1f-<NUM>). The triggering of the random access procedure may occur in order to transmit the CCCH for the purpose of shifting from the idle mode to the connected mode as described above, may occur for beam failure recovery, or may occur in a scenario such as handover. Here, if the base station provides the two-step random access resource and the LTE supports the two-step random access, the UE may determine whether to perform the two-step random access or the four-step random access according to a predetermined condition (operation 1f-<NUM>). That is, if the UE determines to perform two-step random access, in order to perform MsgA transmission, the PRACH and PUSCH transmission to a resource capable of transmitting MsgA is performed, and if the LTE determines to perform four-step random access, in order to perform Msg1 transmission, preamble transmission to the PRACH resource capable of transmitting Msg1 is performed. The predetermined condition may be exemplified by, for example, performing a two-step random access procedure when the strength of a received signal from the base station is greater than a threshold value indicated by the base station.

Accordingly, if the UE determines to perform four-step random access, the UE receives only Msg2 (operation 1f-<NUM>). If the base station transmits Msg2 by including the BI value therein, the PREAMBLE_BACKOFF value is determined according to the corresponding value (operation 1f-<NUM>). Thereafter, the above-described Msg3 transmission and Msg4 reception are performed (operation 1f-<NUM>), and if the random access is not successfully completed (operation 1f-<NUM>), the UE determines whether to attempt retransmission of the preamble, and after a delay time equal to the determined PREAMBLE_BACKOFF value, performs the random access preamble transmission again (operation 1f-<NUM>).

If the UE determines to perform two-step random access, the UE may receive Msg2 and/or MsgB after transmission of MsgA (operation 1f-<NUM>). This is because, as in the above example, when multiple UEs transmit MsgA, if a scenario occurs in which the base station receives only the PRACH due to collision in PUSCH transmission, the base station may response to the reception through Msg2. Accordingly, a scenario in which the base station transmits both Msg2 and MsgB may occur, and here, a scenario in which the BI is included in both Msg2 and MsgB and transmitted may also be considered. This may occur in a scenario in which the PRACH resource is shared in the four-step random access and the two-step random access. That is, in this scenario, BI transmitted through Msg2 is for UEs performing four-step random access, and BI transmitted through MsgB is for UEs performing two-step random access. Accordingly, if the LTE transmits MsgA, and then if the LTE receives both MsgB and Msg2 in response to the corresponding MsgA transmission, the UE determines the PREAMBLE _BACKOFF value according to the BI value included in MsgB (operation 1f-<NUM>). In addition, if the UE receives only Msg2, the UE configures the PREAMBLE _BACKOFF value to be <NUM> even if the BI is included in the message.

Thereafter, the above-described Msg3 transmission and Msg4 reception are performed (operation 1f-<NUM>) and if the random access is not successfully completed, the UE determines whether to attempt retransmission of the preamble, and after a delay time equal to the determined PREAMBLE_BACKOFF value, performs the random access preamble transmission again (operation 1f-<NUM>).

At operation <NUM>-<NUM>, the method starts. The UE receives random access related configuration information from a base station, which is currently camped on or being accessed, through an RRC layer message (operation <NUM>-<NUM>). The RRC layer message may be transmitted as a system information message (SIB) that the base station broadcasts to all UEs in a cell, or may be transmitted, in connection with connected LTEs, only to the corresponding UE through an RRCReconfiguration message. The random access-related configuration information includes configuration information for a PRACH capable of transmitting a random access preamble (Msg1) (i.e., a resource for a four-step random access procedure), configuration information for a channel capable of transmitting MsgA (i.e., a resource for a two-step random access procedure), and the like, wherein the PRACH resource for the four-step random access procedure and the PRACH resource among MsgA for the two-step random access procedure may be configured independently each other or configured to be shared. The configuration of sharing the PRACH resources denotes that a UE for performing the four-step random access procedure and a UE for performing the two-step random access procedure can transmit the random access preamble to the same PRACH resource. However, in this case, since the UE randomly selects the random access preamble within a predetermined configuration, the used preamble index may be the same or different.

Thereafter, the UE triggers a random access procedure (operation <NUM>-<NUM>). The triggering of the random access procedure may occur in order to transmit the CCCH for the purpose of shifting from the idle mode to the connected mode as described above, may occur for beam failure recovery, or may occur in a scenario such as handover. Here, if the base station provides the two-step random access resource and the LTE supports the two-step random access, the UE may determine whether to perform the two-step random access or the four-step random access according to a predetermined condition (operation <NUM>-<NUM>). That is, if the UE determines to perform two-step random access, the PRACH and PUSCH transmission to a resource capable of transmitting MsgA is performed for MsgA transmission, and if the UE determines to perform four-step random access, preamble transmission to the PRACH resource capable of transmitting Msg1 is performed for Msg1 transmission. The predetermined condition may be exemplified by, for example, performing a two-step random access procedure when the strength of a received signal from the base station is greater than a threshold value indicated by the base station.

Accordingly, if the UE determines to perform four-step random access, the UE receives only Msg2 (operation <NUM>-<NUM>). If the base station transmits Msg2 by including the BI value therein, the PREAMBLE_BACKOFF value is determined according to the corresponding value (operation <NUM>-<NUM>). Thereafter, the above-described Msg3 transmission and Msg4 reception are performed (operation <NUM>-<NUM>), and if the random access is not successfully completed (operation <NUM>-<NUM>), the UE determines whether to attempt retransmission of the preamble, and after a delay time equal to the determined PREAMBLE _BACKOFF value, performs the random access preamble transmission again (operation <NUM>-<NUM>).

If the UE determines to perform two-step random access, the UE may receive Msg2 and/or MsgB after transmission of MsgA (operation <NUM>-<NUM>). This is because, as in the above example, when multiple UEs transmit MsgA, if a scenario occurs in which the base station receives only the PRACH due to collision in PUSCH transmission, the base station may response to the reception through Msg2. Accordingly, a scenario in which the base station transmits both Msg2 and MsgB may occur, and here, a scenario in which the BI is included in both Msg2 and MsgB and transmitted may also be considered. This may occur in a scenario in which the PRACH resource is shared in the four-step random access and the two-step random access. Accordingly, if the PRACH resource is shared in the four-step random access procedure and the two-step random access procedure, the Msg2 response is transmitted to both the UE that has performed the two-step random access and the UE that has performed the four-step random access. Thus, if the base station wants to transmit the BI value to the UE that has performed the two-step random access, the BI value transmission is performed through MsgB, and even if the UE receives both Msg2 and MsgB, the PREAMBLE _BACKOFF value is determined according to the BI value included in MsgB (operation <NUM>-<NUM>). In addition, if the UE receives only Msg2, the UE configures the PREAMBLE _BACKOFF value to be <NUM> even if the BI is included in the message.

However, if the PRACH resource is not shared in the four-step random access procedure and the two-step random access procedure and is configured only for the two-step random access, both Msg2 and MsgB with respect to transmission of the corresponding MsgA are used for UEs that have performed the two-step random access. Therefore, the UE determines the PREAMBLE _BACKOFF value according to the last received BI value from either Msg2 or MsgB (operation <NUM>-<NUM>).

Thereafter, the above-described Msg3 transmission and Msg4 reception are performed (operation <NUM>-<NUM>), and if the random access is not successfully completed, the UE determines whether to attempt retransmission of the preamble, and after a delay time equal to the determined PREAMBLE_BACKOFF value, performs the random access preamble transmission again (operation <NUM>-<NUM>).

Accordingly, if the UE determines to perform four-step random access, the UE receives only Msg2 (operation <NUM>-<NUM>). If the base station transmits Msg2 by including the BI value therein, the PREAMBLE_BACKOFF value is determined according to the corresponding value (operation <NUM>-<NUM>). Thereafter, the above-described Msg3 transmission and Msg4 reception are performed (operation <NUM>-<NUM>), and if the random access is not successfully completed, the UE determines whether to attempt retransmission of the preamble, and after a delay time equal to the determined PREAMBLE _BACKOFF value, performs the random access preamble transmission again (operation <NUM>-<NUM>).

If the UE determines to perform two-step random access, the UE may receive Msg2 and/or MsgB after transmission of MsgA (operation <NUM>-<NUM>). This is because, as in the above example, when multiple UEs transmit MsgA, if a scenario occurs in which the base station receives only the PRACH due to collision in PUSCH transmission, the base station may response to the reception through Msg2. Accordingly, a scenario in which the base station transmits both Msg2 and MsgB may occur, and here, a scenario in which the BI is included in both Msg2 and MsgB and transmitted may also be considered. Accordingly, if the UE transmits MsgA, and then if the UE receives both MsgB and Msg2 in response to the corresponding MsgA transmission, the UE determines the PREAMBLE _BACKOFF value according to the last received BI value from either Msg2 or MsgB (operation <NUM>-<NUM>). Here, it is assumed that the base station configures the BI values, which are included in Msg2 and MsgB transmitted in response to the corresponding MsgA transmission, to be identical value, and transmits the same.

Thereafter, the above-described Msg3 transmission and Msg4 reception are performed (operation <NUM>-<NUM>), and if the random access is not successfully completed (operation <NUM>-<NUM>), the UE determines whether to attempt retransmission of the preamble, and after a delay time equal to the determined PREAMBLE _BACKOFF value, performs the random access preamble transmission again (operation <NUM>-<NUM>). The method ends at operation <NUM>-<NUM>.

<FIG> illustrates a block configuration of a UE according to the disclosure.

Referring to <FIG>, the UE includes a radio frequency (RF) processor 1i-<NUM>, a baseband processor 1i-<NUM>, a storage 1i-<NUM>, and a controller 1i-<NUM>.

The RF processor 1i-<NUM> performs functions for transmission/reception of signals through a wireless channel, such as signal band conversion, amplification, and the like. That is, the RF processor 1i-<NUM> up-converts a baseband signal provided from the baseband processor 1i-<NUM> into an RF band signal, transmits the same through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 1i-<NUM> may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), and the like. Although only one antenna is illustrated in <FIG>, the UE may include multiple antennas. In addition, the RF processor 1i-<NUM> may include multiple RF chains. Moreover, the RF processor 1i-<NUM> may perform beamforming. For the sake of the beamforming, the RF processor 1i-<NUM> may adjust the phase and magnitude of each of signals transmitted/received through multiple antennas or antenna elements.

The baseband processor 1i-<NUM> performs a function of conversion between a baseband signal and a bit string according to the physical layer specification of the system. For example, during data transmission, the baseband processor 1i-<NUM> encodes and modulates a transmission bit string, thereby generating complex symbols. In addition, during data reception, the baseband processor 1i-<NUM> demodulates and decodes a baseband signal provided from the RF processor 1i-<NUM>, thereby reconstructing a reception bit string. For example, when an orthogonal frequency division multiplexing (OFDM) scheme is followed, during data transmission, the baseband processor 1i-<NUM> encodes and modulates a transmission bit string so as to generate complex symbols, maps the complex symbols to subcarriers, and then configures OFDM symbols through an inverse fast Fourier transform (IFFT) operation and cyclic prefix (CP) insertion. In addition, during data reception, the baseband processor 1i-<NUM> divides a baseband signal provided from the RF processor 1i-<NUM> in units of OFDM symbols, reconstructs the signals mapped to subcarriers, through a fast Fourier transform (FFT) operation, and then reconstructs the reception bit string through demodulation and decoding.

The baseband processor 1i-<NUM> and the RF processor 1i-<NUM> transmit or receive signals as described above. Accordingly, the baseband processor 1i-<NUM> and the RF processor 1i-<NUM> may be referred to as transmitter, receiver, transceiver, or communication units. In addition, at least one of the baseband processor 1i-<NUM> and the RF processor 1i-<NUM> may include multiple communication modules in order to support multiple different radio access technologies. Furthermore, at least one of the baseband processor 1i-<NUM> and the RF processor 1i-<NUM> may include different communication modules in order to process signals in different frequency bands. For example, the different radio access technologies may include a wireless LAN (for example, IEEE <NUM>), a cellular network (for example, LTE), and the like. In addition, the different frequency bands may include a super high frequency (SHF) (for example, <NUM>, <NUM>) band and a millimeter wave (for example, <NUM>) band.

The storage 1i-<NUM> stores data for operation of the UE, such as a basic program, an application program, and configuration information. Particularly, the storage 1i-<NUM> may store information regarding a wireless LAN node configured to perform wireless communication by using a wireless LAN access technology. In addition, the storage 1i-<NUM> provides stored data at a request of the controller 1i-<NUM>.

The controller 1i-<NUM> controls the overall operations of the UE. For example, the controller 1i-<NUM> transmits/receives signals through the baseband processor 1i-<NUM> and the RF processor 1i-<NUM>. In addition, the controller 1i-<NUM> records and reads data in and from the storage 1i-<NUM>. To this end, the controller 1i-<NUM> may include at least one processor. For example, the controller 1i-<NUM> may include a communication processor (CP) configured to perform control for communication, and an application processor (AP) configured to control the higher layer, such as an application program. According to an embodiment of the disclosure, the controller 1i-<NUM> includes a multi-connection processor 1i-<NUM> configured to perform processing for operating in a multi-connection mode. For example, the controller 1i-<NUM> may control the UE so as to perform the procedure of operations of the UE illustrated in <FIG>.

The controller 1i-<NUM> according to an embodiment of the disclosure determines, if two-step random access is triggered, whether to use the BI which has been received from a message, from among the received BI values, and thus determines the BI value to be used at the time of retransmission of MsgA or Msg1.

<FIG> illustrates the structure of a UE according to an embodiment of the disclosure.

Referring to <FIG>, the UE may include a transceiver <NUM>, a controller <NUM>, and a storage <NUM>. In the disclosure, the controller may be defined as a circuit, an application-specific integrated circuit, or at least one processor.

The transceiver <NUM> may transmit or receive a signal to or from another network. The transceiver <NUM> may receive system information, for example, from a base station, and may receive a synchronization signal or reference signal.

The controller <NUM> may control the overall operation of the UE according to an embodiment proposed in the disclosure. For example, the controller <NUM> may control signal flow between blocks to perform an operation according to the procedures described above by referring to <FIG>. For example, the controller <NUM> may perform a method of applying the backoff when using the two-step random access according to the embodiment of the disclosure.

The storage <NUM> may store at least one of information transmitted or received through the transceiver <NUM> and information generated through the controller <NUM>. For example, the storage <NUM> may store information required to use the two-step random access according to the above-described embodiment.

<FIG> illustrates the structure of a base station according to an embodiment of the disclosure.

Referring to <FIG>, the base station may include a transceiver <NUM>, a controller <NUM>, and a storage <NUM>. In the disclosure, the controller may be defined as a circuit, an application-specific integrated circuit, or at least one processor.

The transceiver <NUM> may transmit or receive a signal to or from another network. The transceiver <NUM> may transmit system information, for example, to a UE, and may transmit a synchronization signal or reference signal.

The controller <NUM> may control the overall operation of the base station according to an embodiment proposed in the disclosure. For example, the controller <NUM> may control signal flow between blocks to perform an operation according to the procedures described above by referring to <FIG>. Specifically, the controller <NUM> may perform a method of applying the backoff when using the two-step random access according to the embodiment of the disclosure.

Claim 1:
A method for random access by a terminal in a wireless communication system, the method comprising:
receiving, from a base station, a threshold value related to determination of a random access type and random access-related information;
determining the random access type as one of a two-step random access type and a four-step random access type based on the threshold value and a strength of a reception signal received from the base station;
transmitting, to the base station, a signal related to a first preamble for random access based on the determined random access type and the random access-related information, wherein the signal related to the first preamble for random access is transmitted based on a common resource for the two-step random access type and the four-step random access type;
in case that the determined random access type is the two-step random access type, identifying, among a message B, Msg B, according to the two-step random access type and a message <NUM>, Msg <NUM>, according to the four-step random access type, a backoff indicator included in the Msg B;
in case that the determined random access type is the four-step random access type, identifying, among the Msg B and the Msg <NUM>, a backoff indicator included in the Msg <NUM>; and
transmitting, to the base station, a signal related to a second preamble based on the identified backoff indicator.