KR102382911B1 - Method and apparatus for initial access in mobile communication system - Google Patents

Abstract

The terminal receives access priority information on a plurality of sub-beams constituting a beam from the base station, selects one beam from among the plurality of beams, and selects one sub-beam from among the plurality of sub-beams of the selected beam based on access priority information. A random access is performed by selecting a beam.

Description

Initial access method and apparatus in a mobile communication system

The present invention relates to a method and apparatus for initial access in a mobile communication system, and more particularly, to a method and apparatus for initial access in a millimeter wave-based mobile communication system.

Current 4G mobile communication systems can support data transmission capacity up to 1 Gbps using carrier aggregation technology in multiple frequency bands below 6 GHz. In this carrier aggregation technique, a plurality of frequency bands are divided into a plurality of carrier components (CC), and data transmission is possible using the plurality of CCs at the same time, thereby increasing data transmission capability.

The UE establishes a connection with a base station by performing initial access to one CC among a plurality of CCs, and this CC becomes a Primary Carrier Component (PCC). A UE may have one PCC and multiple secondary carrier components (SCCs). The UE transmits and receives a control message using the PCC and also transmits control signals such as a scheduling request, HARQ feedback, and CQI feedback through an uplink. If the PCC is to be changed, a handover procedure is used.

A millimeter wave-based mobile communication system of 6 GHz or higher uses a wider frequency band in a high frequency band. And because the frequency characteristic is very straight-forward, beamforming technology is used.

In consideration of the linearity of the millimeter wave frequency, one cell is composed of a plurality of beams, and each beam supports a service using the entire frequency bandwidth of the base station. In this environment, since the frequency bandwidth of each beam is wide, it is divided into a plurality of frequency allocation bands (Frequency Allocation, FA) of a small frequency bandwidth, and each FA is used as a subbeam (SB) to perform a service. That is, the base station consists of a plurality of beams, and each beam is divided into a plurality of SBs.

In the above millimeter wave-based mobile communication system, the terminal selects a beam with the best signal in the initial access process for establishing a connection with the base station, selects a random SB from among a plurality of SBs in the selected beam, and performs initial access with the base station . An SB having a connection with the base station by performing initial access becomes a primary subbeam, and after the initial access procedure is successfully performed, the base station may allocate a plurality of secondary subbeams to the terminal. . Therefore, it is necessary for the base station to efficiently use resources by arranging the terminals well among a plurality of SBs.

In the existing carrier aggregation technology, a handover procedure is used to change the PCC. Since this is performed after the UE arbitrarily selects a main subbeam, performs an initial access procedure, and is allocated a dedicated resource for the PSB, signal complexity and service delay may occur. In particular, the mmWave-based mobile communication system divides a wide bandwidth into a plurality of SBs, and the terminal selects a random SB from among the plurality of SBs and performs an initial access procedure, which may cause a problem that the terminal's access to a specific SB is concentrated. there is.

An object of the present invention is to provide an initial access method and apparatus in a mobile communication system that can effectively control subbeam selection and subbeam resource allocation for initial access of a terminal in a millimeter wave-based mobile communication system.

According to an embodiment of the present invention, an initial access method of a terminal is provided. The initial access method includes the steps of selecting one beam from among a plurality of beams, receiving access priority information for a plurality of sub-beams constituting the beam from a base station, and the access priority among a plurality of sub-beams of the selected beam selecting one subbeam based on the priority information, and performing random access by setting the selected subbeam as a main subbeam.

The receiving may include receiving type 1 of a system information block (SIB) in a subbeam arbitrarily selected from among a plurality of subbeams of the selected beam, wherein type 1 of the SIB includes the access priority information can

The initial access method may further include receiving an instruction to change the main subbeam from the base station, and changing the main subbeam to another subbeam according to the change instruction.

Receiving the change indication of the main subbeam includes transmitting a radio resource control (RRC) connection request message to the base station in the selected subbeam, and index information of a subbeam to be used as the main subbeam and the main subbeam. It may include receiving an RRC connection establishment message including radio resource allocation information in the beam.

The selecting of the single beam may include measuring the quality of signals received from the plurality of beams, and selecting a beam having the best signal quality based on the measurement result.

The initial access method may include transmitting an RRC connection request message to the base station in the selected subbeam, and receiving an RRC connection establishment message including radio resource allocation information in the selected beam.

According to another embodiment of the present invention, there is provided a terminal initial access method in a base station operating a plurality of beams. The initial access method includes, for each of a plurality of sub-beams constituting the beam, setting each sub-beam as a main sub-beam to measure the number of terminals in service and a resource utilization rate, and access to the plurality of sub-beams based on the measurement result calculating the priority, transmitting the access priority in each of the plurality of subbeams, receiving a preamble for random access in the subbeam selected based on the access priority by the terminal, and the preamble and transmitting a response to the amble to the terminal.

The initial access method includes receiving a radio resource control (RRC) connection request message in a subbeam selected by the terminal, determining whether to set the subbeam receiving the RRC connection request message as a main subbeam of the terminal; The method may further include transmitting an RRC connection establishment message including radio resource allocation information in the main subbeam to the terminal.

In the step of transmitting the RRC connection establishment message to the terminal, when the terminal determines to change the main subbeam to another subbeam, adding index information of a subbeam to be used as the main subbeam to the RRC connection establishment message. may include

The calculating may include setting the access priority to be high in the order of the number of terminals and the sub-beam having a low resource utilization rate.

According to another embodiment of the present invention, an initial access device for a terminal is provided. The initial access device includes a transceiver and a processor. The transceiver receives access priority information for a plurality of sub-beams constituting each beam from the base station. And the processor selects one beam based on the quality of signals received from the plurality of beams, and selects one subbeam to be used as the main subbeam from among the plurality of subbeams of the selected beam based on the access priority information, , random access is performed through the selected subbeam.

The access priority information is calculated based on the number of service terminals and the resource utilization rate by setting each subbeam as a main subbeam by the base station, and the transceiver is configured to use an arbitrary subbeam from among a plurality of subbeams of the selected beam. Type 1 of a System Information Block (SIB) including the access priority may be received.

The processor may change the main sub-beam according to a change instruction of the main sub-beam from the base station.

The transceiver receives an RRC connection establishment message including index information of a subbeam to be used as the main subbeam and radio resource allocation information in the main subbeam, and the processor receives index information of a subbeam to be used as the main subbeam. Based on this, the main sub-beam may be changed.

The processor performs an RRC connection request from the selected subbeam to the base station, determines the selected subbeam as a main subbeam according to an RRC connection establishment message received from the base station through the transceiver, and configures radio resources; The RRC connection establishment message may include radio resource allocation information in the selected subbeam.

According to an embodiment of the present invention, it is possible to effectively control sub-beam selection and sub-beam resource allocation for initial access of a terminal in a millimeter wave-based mobile communication system.

1 is a diagram showing the configuration of one cell in a millimeter wave-based mobile communication system according to an embodiment of the present invention.
2 is a diagram illustrating an initial access procedure of a terminal according to an embodiment of the present invention.
3 is a flowchart illustrating a procedure for evenly distributing the PSB of a terminal to each subbeam in a base station according to an embodiment of the present invention.
4 is a flowchart illustrating an initial access procedure of a terminal according to an embodiment of the present invention.
5 is a diagram illustrating a base station according to an embodiment of the present invention.
6 is a diagram illustrating a terminal according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be implemented in several different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification and claims, when a part "includes" a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated.

Throughout the specification, a terminal is a mobile terminal (MT), a mobile station (MS), an advanced mobile station (AMS), a high reliability mobile station (HR-MS) , a subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), user equipment (UE), etc. may refer to, and the like, MT, MS, AMS , HR-MS, SS, PSS, AT, UE, etc. may include all or some functions.

In addition, the base station (base station, BS) is an advanced base station (advanced base station, ABS), a high reliability base station (high reliability base station, HR-BS), a Node B (node B), an advanced node B (evolved node B, eNodeB), an access point (AP), a radio access station (RAS), a base transceiver station (BTS), a mobile multihop relay (MMR)-BS, a relay serving as a base station station (RS), a relay node (RN) serving as a base station, an advanced relay station (ARS) serving as a base station, high reliability relay station (HR) serving as a base station -RS), small base station [femto base station (femoto BS), home node B (home node B, HNB), home eNodeB (HeNB), pico base station (pico BS), metro base station (metro BS), micro base station (micro BS) ), etc.], etc., may include all or some functions of ABS, NodeB, eNodeB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, etc. there is.

Now, an initial access method and apparatus in a mobile communication system according to an embodiment of the present invention will be described in detail with reference to the drawings.

1 is a diagram illustrating one cell configuration in a millimeter wave-based mobile communication system according to an embodiment of the present invention.

Referring to FIG. 1 , a millimeter wave-based mobile communication system includes a base station 100 and a terminal 200 .

The base station 100 operates the multi-beams B1 to B9 in the cell. Each of the multiple beams B1 to B9 has a unique identifier, and each beam B1 to B9 may overlap an adjacent beam with a partial region.

The base station 100 uses a millimeter wave frequency band of 10 GHz or more for communication with the terminal 200 , and the service radius of each beam B1 to B9 is several tens of m, and thus a 1 GHz bandwidth can be used. In addition, each beam divides the entire frequency band into a plurality of frequency allocation bands (FA0 ~ FAK), and performs a service by using each FA (FA0 ~ FAk) as a subbeam (SB0 ~ SBK). . That is, each of the beams B1 to B9 may include a plurality of sub-beams SB0 to SBK.

The terminal 200 performs an initial connection to establish a connection with the base station 100 .

In the initial access process, the terminal 200 selects a beam having the best signal from among the multiple beams B1 to B9 and selects an arbitrary subbeam from among a plurality of subbeams in the selected beam to perform initial access with the base station. A subbeam having a connection to the base station 100 through initial access becomes a primary subbeam (PSB).

After the initial access procedure is successfully performed, the base station 100 may allocate a plurality of secondary subbeams (SSBs) to the terminal.

The terminal 200 performs transmission and reception of a control message, reception of downlink control information, an uplink scheduling request, and transmission of CQI feedback and HARQ feedback using the PSB.

2 is a diagram illustrating an initial access procedure of a terminal according to an embodiment of the present invention.

Referring to FIG. 2 , the base station 100 determines an access priority for each subbeam based on the number of terminals serving in each subbeam or the amount of uplink traffic. That is, the base station 100 may measure the number of terminals serving as PSBs in each subbeam, the utilization rates of the uplink control channel and the uplink shared channel, and determine the access priority for each subbeam based on this.

The base station 100 includes information on the determined access priority of each subbeam in type 1 of a system information block (SIB) and broadcasts it in all subbeams.

The base station 100 may periodically determine an access priority for each subbeam, and broadcast SIB type 1 information on the changed access priority of each subbeam in all subbeams ( S202 to S206 ).

The terminal 200 determines a subbeam to access the base station 100 as a PSB by using the information on the access priority of each subbeam obtained through type 1 of the SIB, and performs an initial access process through this. The base station 100 determines whether to set a subbeam accessed by the terminal 200 as a PSB when the terminal 200 performs initial access. If the base station 100 wants to change the PSB of the terminal 200 to another subbeam in the initial access procedure, a change procedure is performed.

Specifically, the terminal 200 receives the type 1 of the SIB and retrieves the access priority of each SB. A random subbeam is selected from among the subbeams having high priority, and a random access procedure is performed with the selected subbeam. 2 shows that the sub-beam SB0 is selected for convenience of description.

For the random access procedure, the terminal 200 transmits a preamble to the selected subbeam SB0 (S208), and receives a random access response (RAR) response from the base station 100 to the preamble. Receive (S210).

In this way, when the random access procedure is successfully completed, the terminal 200 transmits a Radio Resource Control (RRC) connection request message (RRCConnectionRequest) to the base station 100 through the selected subbeam SB0 (S212).

The base station 100 determines whether to set the subbeam SB0 to which the terminal 200 is currently connected as the PSB of the terminal 200 .

When the base station 100 determines that the subbeam SB0 to which the terminal 200 is currently connected is the PSB of the terminal 200, the base station 100 allocates a dedicated radio resource to be used by the terminal 200 in the current subbeam SB0, and allocates a dedicated radio The resource allocation information is included in the RRC connection setup message (RRCConnectionSetup) and transmitted to the terminal 200 (S214).

If the base station 100 determines to set a subbeam different from the subbeam SB0 to which the terminal 200 is currently connected as the PSB of the terminal 200, it determines a subbeam to be used as the PSB, and a dedicated subbeam to be used in the PSB. Allocate radio resources. In addition, the base station 100 transmits an RRC connection setup message (RRCConnectionSetup) including sub-beam change information and dedicated radio resource allocation information to be used in the PSB to the terminal 200 (S214). In this case, the subbeam change information may include index information of a subbeam to be used as a PSB. That is, by setting the index information of the subbeam to be used as the PSB in the RRC Connection Setup message (RRCConnectionSetup), it is possible to instruct the terminal 200 to change the subbeam.

Upon receiving the RRC connection establishment message (RRCConnectionSetup), the terminal 200 sets a dedicated radio resource allocated to the PSB, and transmits an RRC connection establishment completion message (RRCConnectionSetupComplete) from the PSB to the base station 100 (S216).

For example, when the index information of the subbeam SB1 is included in the RRC connection setup message (RRCConnectionSetup) as subbeam change information, the terminal 200 determines the subbeam SB1 as the PSB, and a dedicated radio resource can be set. In addition, the terminal 200 transmits an RRC connection setup completion message (RRCConnectionSetupComplete) to the base station 100 in the subbeam SB1 (S216).

3 is a flowchart illustrating a procedure for evenly distributing the PSB of a terminal to each subbeam in a base station according to an embodiment of the present invention.

Referring to FIG. 3 , the base station 100 measures the number of terminals currently serving as PSBs for each SB, and calculates the utilization rate of the uplink control channel allocated for these terminals and the utilization rate of the uplink shared channel used for data transmission. By measuring, the connection priority of each SB is calculated (S300). Information on the access priority of each SB is periodically measured and updated. The base station 100 may calculate the PSB of the terminal in each subbeam so as to evenly distribute the PSB of the terminal in each subbeam. For example, the base station 100 may set the access priority to be high in the order of the number of terminals currently serving as a PSB, the usage rate of the uplink control channel, and the usage rate of the uplink shared channel.

The base station 100 includes information on the access priority of each SB in type 1 of the SIB and broadcasts it in all SBs (S310).

When the base station 100 receives the RRC connection request message (RRCConnectionRequest) from the terminal 200 (S320), the base station 100 determines whether to set the subbeam receiving the RRC connection request message (RRCConnectionRequest) as the PSB of the terminal 200 (S330) ).

When the base station 100 intends to change the subbeam different from the subbeam that has received the RRC connection request message (RRCConnectionRequest) to the PSB (S340), it determines a subbeam to be used as the PSB (S350).

The base station 100 allocates a dedicated radio resource to be used by the terminal 200 in the determined subbeam (S360).

The base station 100 includes the determined subbeam index information and dedicated radio resource allocation information in an RRC connection setup message (RRCConnectionSetup) and transmits it to the terminal 200 (S380).

On the other hand, when the base station 100 determines that the subbeam receiving the RRC connection request message (RRCConnectionRequest) is the PSB of the terminal 200, it allocates a dedicated radio resource to be used by the terminal 200 in this subbeam (S370), The dedicated radio resource allocation information is included in the RRC connection setup message (RRCConnectionSetup) and transmitted to the terminal 200 (S380). At this time, the RRC connection establishment message (RRCConnectionSetup) is transmitted through the subbeam included in the RRC connection request message (RRCConnectionRequest).

And when the RRC connection setup completion message (RRCConnectionSetupComplete) is received through the PSB of the terminal 200 ( S390 ), the base station 100 determines that the PSB setup for the terminal 200 is complete.

4 is a flowchart illustrating an initial access procedure of a terminal according to an embodiment of the present invention.

Referring to FIG. 4 , the base station 100 sets a plurality of beams in its coverage area, and transmits signals to each of the plurality of beam areas.

The terminal 200 measures the quality of a signal received from a plurality of beams of the base station 100, and selects a beam having the best signal quality based on the measurement result (S402).

The terminal 200 selects an arbitrary subbeam from among a plurality of subbeams existing in the selected beam, and receives the SIB type 1 broadcast by the base station 100 in the selected subbeam (S404).

The terminal 200 checks the access priority of each subbeam through the received SIB type 1, and based on the access priority of each subbeam, any one subbeam from among a predetermined number of subbeams having the highest access priority. is selected (S406).

The terminal 200 performs random access for initial access through the selected subbeam (S408).

When the random access is successfully performed, the terminal 200 transmits an RRC connection request message (RRCConnectionRequest) to the base station 100 (S410).

Next, the terminal 200 receives the RRC connection establishment message (RRCConnectionSetup) from the base station 100 (S412), and whether to change the subbeam to be set as the PSB through the subbeam change information included in the RRC connection establishment message (RRCConnectionSetup) It is decided (S414).

When subbeam change information is included in the RRC connection setup message (RRCConnectionSetup), the terminal 200 changes the subbeam according to the subbeam change information (S416), and determines the changed subbeam as the PSB.

The terminal 200 sets the radio dedicated resource to be used in the PSB determined based on the dedicated radio resource allocation information included in the RRC connection setup message (RRCConnectionSetup) (S418).

On the other hand, when there is no subbeam change information in the RRC connection setup message (RRCConnectionSetup), the terminal 200 determines the previously selected subbeam as the PSB, and determined based on the dedicated radio resource allocation information included in the RRC connection setup message (RRCConnectionSetup). A radio dedicated resource to be used in the PSB is set (S420).

The terminal 200 transmits an RRC connection setup completion message (RRCConnectionSetupComplete) to the base station by using the dedicated radio resource information of the established PSB (S422).

5 is a diagram illustrating a base station according to an embodiment of the present invention.

Referring to FIG. 5 , the initial access device 500 of the base station 100 includes a processor 510 , a transceiver 520 , and a memory 530 .

The processor 510 performs an initial access procedure of the terminal 200 by performing the procedures described with reference to FIG. 3 . The processor 510 measures the number of terminals currently serving as PSBs for each SB and measures the utilization rate of an uplink control channel allocated for these terminals and the utilization of an uplink shared channel used for data transmission, The access priority is calculated, and type 1 of the SIB including information on the access priority of each SB is generated. In addition, the processor 510 determines whether to set the determined subbeam of the terminal 200 as the PSB of the terminal 200 , and, when the PSB of the terminal 200 is to be changed to another subbeam, changes the subbeam to the terminal 200 . ) is indicated.

The transceiver 520 periodically broadcasts type 1 of the SIB, and transmits and receives the messages described with reference to FIG. 3 .

The memory 530 stores instructions for execution by the processor 510 or loads and temporarily stores instructions from a storage device (not shown), and the processor 510 is stored in the memory 530 or Executes the loaded command.

The processor 510 and the memory 530 are connected to each other through a bus (not shown), and an input/output interface (not shown) may also be connected to the bus. In this case, the transceiver 520 is connected to the input/output interface, and peripheral devices such as an input device, a display, a speaker, and a storage device may be connected.

6 is a diagram illustrating a terminal according to an embodiment of the present invention.

Referring to FIG. 6 , the initial access device 600 of the terminal 200 includes a processor 610 , a transceiver 620 , and a memory 630 .

The processor 610 performs an initial access procedure of the terminal 200 by performing the procedures described with reference to FIG. 4 . The processor 610 measures the quality of a signal received from a plurality of beams, and selects a beam having the best signal quality based on the measurement result. The processor 610 selects an arbitrary subbeam from among a plurality of subbeams existing in the selected beam, and checks the access priority of each subbeam through type 1 of the SIB received from the selected subbeam. The processor 610 performs a random access procedure by selecting an arbitrary subbeam from among a predetermined number of subbeams having the highest access priority based on the access priority of each subbeam. In addition, the processor 610 determines the selected sub-beam or the sub-beam determined by the base station 100 as the PSB, and configures a dedicated radio resource.

The transceiver 620 receives type 1 of the SIB in the subbeam selected by the processor 610 . Also, the transceiver 620 may transmit/receive the messages described with reference to FIG. 4 through the PSB.

The memory 630 stores instructions for execution by the processor 610 or loads and temporarily stores instructions from a storage device (not shown), and the processor 610 is stored in the memory 630 or Executes the loaded command.

The processor 610 and the memory 630 are connected to each other through a bus (not shown), and an input/output interface (not shown) may also be connected to the bus. In this case, the transceiver 620 is connected to the input/output interface, and peripheral devices such as an input device, a display, a speaker, and a storage device may be connected.

An embodiment of the present invention is not implemented only through the apparatus and/or method described above, and a program for realizing a function corresponding to the configuration of an embodiment of the present invention or a recording medium in which the program is recorded may be implemented. This implementation can be easily implemented by an expert in the technical field to which the present invention pertains from the description of the above-described embodiments.

Although the embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the right.

Claims (15)

As an initial access method of a terminal,
selecting one beam from among a plurality of beams;
Receiving access priority information on a plurality of sub-beams constituting the one beam selected from the base station;
selecting one subbeam from among a plurality of subbeams of the one beam based on the access priority information; and
performing random access by setting the selected subbeam as a main subbeam
includes,
The access priority information for the plurality of subbeams includes access priorities of the plurality of subbeams, and the access priorities of the plurality of subbeams depend on the number of serviced terminals in each subbeam and the serviced terminals. The initial access method determined based on the utilization rate of the allocated resource. In claim 1,
The receiving includes receiving type 1 of a System Information Block (SIB) in a subbeam arbitrarily selected from among a plurality of subbeams of the selected beam,
The type 1 of the SIB is an initial access method including the access priority information. In claim 1,
Receiving a change indication of the main subbeam from the base station, and
changing the main subbeam to another subbeam according to the change instruction
An initial access method further comprising a. In claim 3,
Receiving the change instruction of the main sub-beam comprises:
transmitting a radio resource control (RRC) connection request message to the base station in the selected subbeam; and
and receiving an RRC connection establishment message including index information of a subbeam to be used as the main subbeam and radio resource allocation information in the main subbeam. In claim 1,
The step of selecting one beam is
measuring the quality of signals received in the plurality of beams; and
An initial access method comprising selecting a beam having the best signal quality based on a measurement result. In claim 1,
transmitting an RRC connection request message to the base station in the selected subbeam, and
Receiving an RRC connection establishment message including radio resource allocation information in the selected beam
An initial access method further comprising a. As a terminal initial access method in a base station operating a plurality of beams,
For each of a plurality of sub-beams constituting one beam selected by the terminal, setting each sub-beam as a main sub-beam to measure the number of service terminals and the utilization rate of resources allocated to the service terminals;
determining an access priority for the plurality of sub-beams based on the number of service terminals and the resource utilization rate measured for each of the plurality of sub-beams;
transmitting information on the access priority in each of the plurality of subbeams;
receiving, by the terminal, a preamble for random access in a subbeam selected based on the access priority from the terminal; and
Transmitting a response to the preamble to the terminal
An initial access method comprising a. In claim 7,
Receiving a radio resource control (RRC) connection request message in the subbeam selected by the terminal;
determining whether to set the subbeam receiving the RRC connection request message as the primary subbeam of the terminal; and
Transmitting an RRC connection establishment message including radio resource allocation information in the main subbeam to the terminal
An initial access method further comprising a. In claim 8,
In the step of transmitting the RRC connection establishment message to the terminal, if the terminal determines to change the main subbeam to another subbeam, adding index information of a subbeam to be used as the main subbeam to the RRC connection establishment message. Initial access method including. In claim 7,
The determining includes setting the access priority to be high in the order of the number of terminals and the sub-beam having a low resource utilization rate. As an initial access device of a terminal,
A transceiver for receiving access priority information for a plurality of sub-beams constituting each beam from the base station, and
Selecting one beam based on the quality of a signal received from a plurality of beams, selecting one subbeam to be used as a main subbeam from among a plurality of subbeams of the selected beam based on the access priority information, the selected subbeam A processor that performs random access through
includes,
The access priority information for the plurality of subbeams includes access priorities of the plurality of subbeams, and the access priorities of the plurality of subbeams depend on the number of serviced terminals in each subbeam and the serviced terminals. Initial access device determined based on the utilization rate of the allocated resource. In claim 11,
The access priority information is calculated based on the number of terminals in service and resource utilization rate by setting each subbeam as a main subbeam by the base station,
The transceiver receives the type 1 of a System Information Block (SIB) including the access priority through an arbitrary subbeam among a plurality of subbeams of the selected beam. In claim 11,
The processor is configured to change the main sub-beam according to an instruction to change the main sub-beam from the base station. In claim 13,
The transceiver receives an RRC (Radio Resource Control) connection establishment message including index information of a subbeam to be used as the main subbeam and radio resource allocation information in the main subbeam,
The processor is configured to change the main subbeam based on index information of a subbeam to be used as the main subbeam. In claim 11,
The processor performs an RRC connection request from the selected subbeam to the base station, determines the selected subbeam as a main subbeam according to an RRC connection establishment message received from the base station through the transceiver, and configures radio resources;
The RRC connection establishment message is an initial access device including radio resource allocation information in the selected subbeam.

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