KR101962143B1 - Method and apparatus for scanning a cell frequency in wireless communication system - Google Patents

Abstract

A method for searching a frequency of a cell in a wireless communication system and a terminal device therefor are disclosed. A method for a mobile station to search for a frequency of a cell in a wireless communication system includes: measuring a first signal strength of each of blocks obtained by dividing an operating band into a predetermined bandwidth; Measuring a second signal strength in a predetermined frequency unit in a block in the order of strong first signal strength and detecting a frequency having a signal intensity of a threshold value or more; Obtaining information about the cell based on the detected frequency to determine whether the detected frequency is available; And performing the measurement of the second signal strength again if the detected frequency is not available, wherein performing the measurement of the second signal strength again comprises measuring a frequency within the system bandwidth around the detected frequency Can be performed in the frequency domain excluding the frequency domain.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and apparatus for searching for a cell frequency in a wireless communication system,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to wireless communication, and more particularly, to a method of searching for a cell frequency in a wireless communication system and a terminal device therefor.

When the terminal is powered on or searches for a new cell or a base station out of the cell or base station range, the terminal must perform a frequency search to attempt to camp on. A cell is a zone that can be covered by one base station.

In a cellular communication system, a UE receives a cell synchronization signal through a frequency search, secures time and frequency synchronization of a cell, and obtains cell common control information including a cell number (i.e., a physical cell ID) .

At this time, when the terminal performs frequency search in all the operating bands, a frequency search speed may be slowed down. Therefore, there is a need for a scheme capable of efficiently searching frequencies.

It is an object of the present invention to provide a method and apparatus for searching a cell frequency in a wireless communication system.

According to one aspect, a method for a mobile station to search for a frequency of a cell in a wireless communication system includes: measuring a first signal strength of each of blocks obtained by dividing an operating band into a predetermined bandwidth; Measuring a second signal strength in a predetermined frequency unit in a block in the order of strong first signal strength and detecting a frequency having a signal intensity of a threshold value or more; Obtaining information about the cell based on the detected frequency to determine whether the detected frequency is available; And performing the measurement of the second signal strength again if the detected frequency is not available, wherein performing the measurement of the second signal strength again comprises measuring a frequency within the system bandwidth around the detected frequency But may be performed in the frequency domain excluding the frequency domain.

According to another aspect, a terminal for searching a frequency of a cell in a wireless communication system includes a transmitting and receiving unit; And a processor coupled to the transmitter and receiver, wherein the processor measures a first signal strength of each of the blocks obtained by dividing the operating band into a predetermined bandwidth, Measuring a second signal strength in frequency units to detect a frequency having a signal intensity greater than or equal to a threshold value; acquiring information about the cell based on the detected frequency to determine whether the detected frequency is available; If not available, the measurement of the second signal strength can be performed again, but the measurement of the second signal strength can be performed again in the frequency domain excluding frequencies within the system bandwidth around the detected frequency.

If the system bandwidth is outside the range of the second signal strength of the measured block, it is possible to perform the measurement of the second signal strength again within the block of the next order of the first signal strength.

When the system bandwidth includes one or more blocks, a measurement of the second signal strength may be performed again in the next block of the first one of the blocks except for one or more blocks included in the system bandwidth.

The system bandwidth may be any of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz.

The predetermined bandwidth may be determined based on the system bandwidth.

The predetermined bandwidth may be 1.4 MHz.

The first signal strength can be measured based on the center frequency of the block.

The detected frequency may be the center frequency of the system bandwidth.

The first signal strength and the second signal strength may be Received Signal Strength Indicator (RSSI).

In the case of performing the method of searching for the cell frequency according to an embodiment of the present invention, the terminal can obtain the effect of increasing the frequency search speed.

1 is a diagram conceptually showing a network structure of an E-UMTS.
2 is a conceptual diagram illustrating a network structure of an evolved universal terrestrial radio access network (E-UTRAN).
5 is a system configuration diagram for frequency search according to an embodiment of the present invention.
6 is a frequency search flowchart according to an embodiment of the present invention.
7 is a diagram for explaining a frequency search method according to an embodiment of the present invention.
8 is a frequency search flowchart according to another embodiment of the present invention.
9 to 10 are views for explaining a frequency search method according to another embodiment of the present invention.
11 is a diagram showing a configuration of a base station apparatus and a terminal apparatus according to an embodiment of the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will recognize that the present invention may be practiced without these specific details. For example, the following detailed description assumes that the mobile communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 system or a 3GPP (3rd Generation Partnership Project). However, the IEEE 802.16 system, The present invention is applicable to any other mobile communication system.

In some instances, well-known structures and devices may be omitted or may be shown in block diagram form, centering on the core functionality of each structure and device, to avoid obscuring the concepts of the present invention. In the following description, the same components are denoted by the same reference numerals throughout the specification.

In the following description, it is assumed that the UE collectively refers to a mobile stationary or stationary user equipment such as a UE (User Equipment), an MS (Mobile Station), and an AMS (Advanced Mobile Station). It is also assumed that the base station collectively refers to any node at a network end that communicates with a terminal such as a Node B, an eNode B, a BS (Base Station), and an AP (Access Point).

In a mobile communication system, a mobile station can receive information from a base station through a downlink, and the mobile station can also transmit information through an uplink. The information transmitted or received by the terminal includes data and various control information, and various physical channels exist depending on the type of information transmitted or received by the terminal.

Prior to describing the present invention, the Evolved Universal Mobile Telecommunications System (E-UMTS), which is a technical field to which the present invention is applied, and related technical features will be described below.

1 is a diagram conceptually showing a network structure of an E-UMTS. In particular, the E-UMTS system has evolved from the existing WCDMA UMTS system, and is currently undergoing basic standardization work in the 3rd Generation Partnership Project (3GPP). E-UMTS is also called Long Term Evolution (LTE) system. For details of the technical specifications of UMTS and E-UMTS, refer to Release 7 and Release 8 of "3rd Generation Partnership Project (Technical Specification Group Radio Access Network)" respectively.

Referring to FIG. 1, an E-UMTS is an Access Gateway (hereinafter referred to as AG) located at the end of a UE, a cell (eNB), and a network (E-UTRAN) . Typically, an eNB may simultaneously transmit multiple data streams for broadcast services, multicast services, and / or unicast services. An interface for transmitting user traffic or control traffic may be used between eNBs.

The AG may be divided into a part for handling user traffic and a part for processing control traffic. At this time, a new interface between the AG for processing new user traffic and the AG for processing control traffic can be communicated with each other. Also, the AG manages the mobility of the UE in a TA (Tracking Area) unit, and the TA is composed of a plurality of cells. If the terminal moves from one TA to another TA, it informs AG that the TA where it is located has changed.

The CN (Core Network) can be configured as a network node for user registration of AG and UE. An interface for distinguishing E-UTRAN and CN may be used.

2 is a conceptual diagram illustrating a network structure of an evolved universal terrestrial radio access network (E-UTRAN).

Referring to FIG. 2, the E-UTRAN system is an evolved system in an existing UTRAN system. The E-UTRAN is composed of cells (eNBs), and the cells are connected via the X2 interface. The cell is connected to the terminal through the air interface, and is connected to the EPC (Evolved Packet Core) through the S1 interface.

EPC is composed of MME (Mobility Management Entity), S-GW (Serving-Gateway) and PDN-GW (Packet Data Network-Gateway). The MME has information on the access information of the terminal or the capability of the terminal, and this information is mainly used for managing the mobility of the terminal. The S-GW is a gateway having an E-UTRAN as an end point, and the PDN-GW is a gateway having a PDN (Packet Data Network) as an end point.

3 and 4 illustrate a control plane and a U-Plane (User-Plane) structure of a radio interface protocol between a UE and an E-UTRAN based on the 3GPP radio access network standard Fig.

In particular, the wireless interface protocol consists of a physical layer, a data link layer, and a network layer vertically, and horizontally includes a user plane for data information transmission and a control plane And a control plane for signal transmission.

The protocol layers of FIGS. 3 and 4 are based on an Open System Interconnection (OSI) reference model widely known in communication systems. The lower three layers are referred to as L1 (first layer), L2 (second layer) , And L3 (third layer).

The control plane is a path through which control messages used by the UE and the network to manage calls are transmitted. The user plane means a path through which data generated in the application layer, for example, voice data or Internet packet data, is transmitted. Hereinafter, the layers of the control plane and the user plane of the wireless protocol will be described.

The physical layer as the first layer provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to the upper layer of Medium Access Control (MAC) layer through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. Data is transferred between the transmitting side and the receiving side physical layer through the physical channel. The physical channel is modulated by an Orthogonal Frequency Division Multiplexing (OFDM) scheme, and uses time and frequency as radio resources.

The MAC layer of the second layer provides a service to a radio link control (RLC) layer, which is an upper layer, through a logical channel. The RLC layer of the second layer supports reliable data transmission. The function of the RLC layer may be implemented as a function block inside the MAC. In this case, the RLC layer may not exist. The Packet Data Convergence Protocol (PDCP) layer of the second layer performs a header compression function to reduce unnecessary control information for efficient transmission in an air interface having a narrow bandwidth when transmitting IP packets such as IPv4 or IPv6 .

A Radio Resource Control (RRC) layer located at the bottom of the third layer is defined only on the control plane and includes a configuration, reconfiguration, and release of radio bearers (RBs) And controls the logical channels, the transport channels, and the physical channels. The radio bearer means a service provided by the second layer for data transmission between the UE and the E-UTRAN. To this end, the RRC layer exchanges RRC messages between the UE and the network.

In FIG. 3, the Non-Access Stratum (NAS) layer at the top of the RRC layer performs functions such as session management and mobility management. The NAS layer exists in the Mobility Management Entity (MME) of the UE and the network.

The MME is a key control-node in an LTE access network. The MME is responsible for the tracking and paging procedures for the idle terminal. In addition, the MME participates in the radio bearer activation / deactivation process and is responsible for selecting a Serving Gateway (SGW) at the time of 'Initial Attach' or during an intra-LTE handover including a core network relocation. do. The MME takes charge of terminal authentication through interaction with a Home Subscriber Server (HSS). The NAS signaling is terminated at the MME, and the MME is responsible for creating and assigning a temporary identifier to the terminal. The MME verifies that the terminal has the authority to camp-on the service provider's PLMN (Public Land Mobile Network). MME is the endpoint for encryption / integrity protection for NAS signaling in the network and is responsible for security key management. The MME provides a control plane function for mobility between LTE and 2G / 3G access networks.

In the NAS layer, two states of EMM (EPS Mobility Management) registration state (EMM-REGISTERED) and EMM unregistered state (EMM-UNREGISTERED state) are defined for terminal mobility management, and these states are applied to the terminal and the MME. The initial terminal is an EMM unregistered state, and the terminal performs a process of registering with the network through an initial attach procedure to access the network. When the contact procedure is successfully performed, the terminal and the MME are in the EMM registration state.

In the NAS layer, two types of ECM (EPS Connection Management) idle state (ECM_IDLE) and ECM connection state (ECM_CONNECTED) are defined in order to manage signaling connection between the terminal and the EPC, . When an ECM idle terminal establishes an RRC connection with an E-UTRAN, the UE becomes an ECM connected state. ECM An idle MME becomes an ECM connection when it makes an S1 connection with an E-UTRAN. When the UE is in the ECM idle state, the E-UTRAN has no context of the UE. Therefore, the UE in the idle state of the ECM performs a mobility-related procedure based on a terminal such as a cell selection or a cell reselection procedure without receiving a command of the network. On the other hand, when the terminal is in the ECM connection state, the mobility of the terminal is managed by a command of the network. If the location of the terminal is different from the location known by the network in the ECM idle state, the terminal notifies the network of the corresponding location of the terminal through a TA (Tracking Area Update) procedure.

5 is a system configuration diagram for frequency search according to an embodiment of the present invention.

Referring to FIG. 5, a UE may include an RRC layer and a physical layer, as illustrated in FIGS. When the terminal first turns on the power or searches for a new cell or a base station out of the range of the cell or the base station, the terminal can not know on what frequency it should try to camp on. Accordingly, the terminal must search for frequencies that it can use.

In one embodiment, the RRC layer may request a frequency search to the physical layer (S510). At this time, the RRC layer can transmit parameters required for frequency search to the physical layer. For example, the RRC layer may transmit information on an operating band to the physical layer. In another example, the RRC layer may send information about the operating band and information about the system bandwidth to the physical layer. Thereafter, the physical layer may perform frequency search for the corresponding operation band (S520). A specific embodiment for performing frequency search will be described with reference to Figs. 6 to 10 below. If the frequency search result indicates that a frequency satisfying a predetermined condition is detected, the physical layer may notify the RRC layer of the frequency search result (S530). The RRC layer can determine whether the corresponding frequency is available by using the search result received from the physical layer (S540). If the frequency is available, the terminal may attempt to camp on the cell or base station based on the frequency. On the other hand, if the corresponding frequency is not available, the RRC layer may re-request the physical layer for frequency search (S550). At this time, the RRC layer can transmit information on the operating band and system bandwidth to the physical layer.

6 is a frequency search flowchart according to an embodiment of the present invention.

Referring to FIG. 6, the terminal may divide an operation band into blocks having a predetermined bandwidth to perform frequency search (S610). Here, the operating band can be defined as in section 5.5 of 3GPP standard document TS 36.101. For example, the operating band may consist of one band with a bandwidth of 60 MHz. As another example, the operating band may consist of two or more bands with a bandwidth of 60 MHz. Thus, the operating band may be 60 MHz, 120 MHz, and so on. This is an example for explanation of the invention and the operating band may be defined differently as needed.

As an example, the predetermined bandwidth may be determined based on the system bandwidth. Here, the system bandwidth may be the channel bandwidth of 3GPP TS 36.521 section 5.4.2. For example, the system bandwidth can be any one of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. As an example, the bandwidth of the block may be 1.4 MHz. For example, if the operating bandwidth is 60 MHz, the block can be divided by 1.4 MHz.

Thereafter, the terminal may measure the first signal strength for each of the divided blocks (S620). At this time, the first signal strength may be Received Signal Strength Indicator (RSSI). For example, the terminal can measure the RSSI of each block based on the center frequency of each block. Here, the process of measuring the first signal strength for each block can be referred to as an RSSI coarse scan process. The terminal can make a list of the blocks in the order of the measured first signal strength.

Thereafter, the terminal can select the block having the largest first signal strength (S630) and measure the second signal strength in the selected block (S640). At this time, the second signal strength may be Received Signal Strength Indicator (RSSI). Here, the process of measuring the second signal strength in the block can be referred to as an RSSI fine scan process. Specifically, the terminal can measure the second signal strength in a predetermined frequency unit in the selected block. For example, if the block size is 1.4 MHz, the terminal can measure the second signal strength in units of 100 kHz. Further, a frequency at which the measured result has a signal intensity of a threshold value or more can be detected (S650). If the measured result is equal to or less than the threshold value, the UE can sequentially measure the second signal strength in the corresponding block. If it is determined that a frequency higher than a threshold value is not detected in the corresponding block, the second signal strength may be measured by taking a block having the next first signal strength (S660).

If a frequency having a signal strength higher than the threshold value is detected, the terminal can determine whether the frequency is available (S670). For example, the terminal performs at least one of a common pilot channel (CPICH) decoding, a physical cell ID detection, a master information block (MIB) decoding, and a system information block (SIB) And determine whether or not the corresponding frequency is available. If it is determined that the frequency is available, the terminal ends the frequency search (S680). At this time, the frequency may be the center frequency of the system bandwidth. On the other hand, if the frequency is not an available frequency, the terminal continues to measure the second signal strength in the block.

FIG. 7 is a diagram for explaining a frequency search method according to an embodiment of the present invention.

Referring to FIG. 7, the terminal can divide the operating band into four blocks and measure the signal strength of each block. In one example, the height of each block represents signal strength, and block 1 may have the largest signal strength, as shown in the figure. The terminal may then measure the second signal strength for each frequency according to a predetermined frequency unit, a second signal strength measurement unit displayed in the figure. At this time, the second signal strength can be measured by moving in the high frequency direction (or the opposite direction) from the low frequency of the block.

The terminal measures the second signal for each frequency and can determine whether each signal is above a threshold value. At this time, when detecting a frequency having a signal strength of a threshold value or more, the terminal can judge whether or not the frequency is available. For example, when the frequency indicated by (A) in the drawing has a signal intensity of a threshold value or more, information on the frequency may be used to determine whether or not it is available. As a result, if the frequency is not available, the terminal can again measure the second signal strength from the next frequency (the frequency indicated by (B) in the figure). According to the above embodiment, the UE must measure all frequencies until the available frequency is searched, which may lead to an increase in the search time by searching for unnecessary frequencies. Therefore, in the process of measuring the second signal strength again, it is necessary to prevent the signal intensity of the unnecessary frequency from being measured by using the specific condition. For example, if the terminal knows the system bandwidth, it can use it to reduce unnecessary frequency signal strength measurements. Specific examples of this will be described later.

8 is a frequency search flowchart according to another embodiment of the present invention. Referring to FIG. 8, a specific method for solving the problems described in FIGS. 6 to 7 is described.

For example, the terminal may divide the operating band into blocks having a predetermined bandwidth, and measure a second signal strength to determine whether the detected frequency is available (S810 to S870). A detailed description thereof will be omitted since it is the same as in Fig.

Thereafter, if the detected frequency is not available, the terminal can again measure the second signal strength. However, the UE can measure the second signal strength in a frequency region excluding a frequency within a system bandwidth around the detected frequency. According to an example, the RRC layer of the UE may attempt to receive a broadcast channel (BCH) based on the frequency search result, and determine whether the cell found by the received information is a cell with which the UE can communicate You can see the system bandwidth through the process.

Referring to FIG. 9, if the frequency A having a signal strength higher than the threshold value is not available, the signal strength with respect to the frequency within the system bandwidth around the frequency A may not be measured. In other words, in the case of the frequency indicated by (X) in the drawing, the second signal strength for the frequency may not be measured, which is a frequency included within the system bandwidth. Instead, the second signal strength can be measured from a frequency outside the system bandwidth.

In one example, if the system bandwidth is outside the range of block 1, the terminal may no longer measure the second signal strength in block 1. Therefore, the terminal can measure the second signal strength again from the second strongest block in the second signal strength. For example, the terminal can measure the second signal strength again from the frequency (B). As another example, the terminal may measure the second signal strength by omitting the frequency included in the system bandwidth from the frequency of the block 2. That is, the second signal strength can be measured again from the frequency (C).

As another example, if block 2 with the second strongest first signal strength is included in the system bandwidth, the terminal may not have measured the second signal strength for the entire block 2. [ Referring to FIG. 10, the system bandwidth may include block 1 and block 2. In this case, the terminal may not measure the second signal strength not only for block 1 but also for block 2. Instead, the terminal can then measure the second signal strength from the block with the first signal strength being good. For example, the terminal can measure the signal strength from block 3. That is, the signal intensity can be measured from the frequency (B). Alternatively, the terminal can measure the second signal strength from the portion excluding the frequency included in the system bandwidth in Block 3. That is, the signal intensity can be measured from the frequency (C).

According to the above embodiment, the UE may not measure the second signal strength within a range included in the system bandwidth, thereby reducing unnecessary search time. According to an embodiment of the present invention, the frequency search speed of the terminal can be significantly increased. Therefore, when the terminal is located in a moving or inter-country roaming area, a required PLMN (Public Land Mobile Network) The mobile communication service provider can display the mobile communication service provider in a short time.

11 is a diagram showing a configuration of a base station apparatus and a terminal apparatus according to an embodiment of the present invention.

11, a base station apparatus 1110 according to the present invention may include a receiving module 1111, a transmitting module 1112, a processor 1113, a memory 1114, and a plurality of antennas 1115. [ The plurality of antennas 1115 refers to a base station device supporting MIMO transmission / reception. The receiving module 1111 can receive various signals, data, and information on the uplink from the terminal. The transmission module 1112 can transmit various signals, data, and information on the downlink to the terminal. The processor 1113 may control the operation of the base station apparatus 1110 as a whole.

The processor 1113 of the base station apparatus 1110 according to an embodiment of the present invention can process the necessary items in each of the above-described embodiments.

The processor 1113 of the base station apparatus 1110 also performs a function of calculating information received by the base station apparatus 1110 and information to be transmitted to the outside and the memory 1114 stores the processed information and the like at a predetermined time And may be replaced by a component such as a buffer (not shown).

11, the terminal device 1120 according to the present invention may include a receiving module 1121, a transmitting module 1122, a processor 1123, a memory 1124, and a plurality of antennas 1125 have. The plurality of antennas 1125 means a terminal device supporting MIMO transmission / reception. The receiving module 1121 can receive various signals, data, and information on the downlink from the base station. The transmission module 1122 can transmit various signals, data, and information on the uplink to the base station. The processor 1123 can control the operation of the entire terminal device 1120. [

The processor 1123 of the terminal device 1120 according to an embodiment of the present invention can process the necessary items in each of the above-described embodiments.

The processor 1123 of the terminal device 1120 also performs a function of calculating information received by the terminal device 1120 and information to be transmitted to the outside and the memory 1124 stores the processed information and the like at a predetermined time And may be replaced by a component such as a buffer (not shown).

The specific configuration of the base station apparatus and the terminal apparatus may be implemented such that the above-described embodiments of the present invention are applied independently or two or more embodiments may be simultaneously applied. For the sake of clarity, It is omitted.

The description of the base station apparatus 1110 in the description of FIG. 11 may be similarly applied to a repeater apparatus as a downlink transmission entity or an uplink receiving entity. The description of the terminal apparatus 1120 may be applied to a downlink reception The present invention can be similarly applied to a repeater device as a subject or an uplink transmission entity.

The above-described embodiments of the present invention can be implemented by various means. For example, embodiments of the present invention may be implemented by hardware, firmware, software, or a combination thereof.

In the case of hardware implementation, the method according to embodiments of the present invention may be implemented in one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs) , FPGAs (Field Programmable Gate Arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of an implementation by firmware or software, the method according to embodiments of the present invention may be implemented in the form of a module, a procedure or a function for performing the functions or operations described above. The software code can be stored in a memory unit and driven by the processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor by various well-known means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing description of the preferred embodiments of the invention disclosed herein has been presented to enable any person skilled in the art to make and use the present invention. While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. For example, those skilled in the art can utilize each of the configurations described in the above-described embodiments in a manner of mutually combining them. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the above description should not be construed in a limiting sense in all respects and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention. The present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. In addition, claims that do not have an explicit citation in the claims may be combined to form an embodiment or be included in a new claim by amendment after the filing.

1110: base station apparatus 1120: terminal apparatus
1111, 1121: receiving modules 1112, 1122: transmitting module
1113, 1123: Processor 1114, 1124: Memory
1115, 1125: antenna

Claims (10)

A method for a terminal to search for a frequency of a cell in a wireless communication system,
Measuring a first signal strength of each of the blocks obtained by dividing an operating band into a predetermined bandwidth;
Measuring a second signal strength in a predetermined frequency unit in a block in the order of stronger the first signal strength, and detecting a frequency having a signal intensity of a threshold value or more;
Obtaining information about a cell based on the detected frequency to determine whether the detected frequency is available; And
If the detected frequency is not available, again performing a measurement of the second signal strength,
Wherein the step of performing the measurement of the second signal strength is performed in a frequency domain excluding a frequency within a system bandwidth included in information on the obtained cell. The method according to claim 1,
Wherein the system bandwidth again performs a measurement of a second signal strength within a block of the next order of the first signal strength when the second signal strength is outside the range of the measured block. 3. The method of claim 2,
Wherein the system bandwidth comprises one or more blocks, and wherein, when the system bandwidth includes at least one of the blocks excluding the one or more blocks included in the system bandwidth, To search for the frequency of. The method according to claim 1,
Wherein the system bandwidth is one of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. The method according to claim 1,
Wherein the predetermined bandwidth is determined based on the system bandwidth. 6. The method of claim 5,
Wherein the predetermined bandwidth is 1.4 MHz. The method according to claim 1,
Wherein the first signal strength is measured based on a center frequency of the block. The method according to claim 1,
Wherein the detected frequency is a center frequency of the system bandwidth. The method according to claim 1,
Wherein the first signal strength and the second signal strength are a Received Signal Strength Indicator (RSSI). A terminal for searching a frequency of a cell in a wireless communication system,
A transmission / reception unit; And
And a processor coupled to the transceiver,
The processor
Measuring a first signal strength of each of the blocks obtained by dividing an operating band into a predetermined bandwidth,
Measuring a second signal strength in a predetermined frequency unit in a block in a descending order of the first signal strength, detecting a frequency having a signal strength of a threshold value or more,
Obtaining information about the cell based on the detected frequency to determine whether the detected frequency is available,
If the detected frequency is not available, perform a measurement of the second signal strength again,
And measures a second signal strength in a frequency region excluding a frequency within a system bandwidth included in information on the obtained cell.

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