KR20170017307A - Method for cell selection in wireless communication system and apparatus therefor - Google Patents

Abstract

The present invention relates to a method for selecting a cell in a wireless communication system. The method for selecting the cell determines whether a cell before the determination of compatibility of the cell is a CSG member cell. When the cell is the CSG member cell, a corresponding cell can be added to a CSG fingerprint regardless of whether to be suitable for the cell.

Description

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

The present invention relates to a cell selection method in a wireless communication system and an apparatus therefor.

As an example of a wireless communication system to which the present invention can be applied, a 3GPP LTE (Third Generation Partnership Project) Long Term Evolution (LTE) communication system will be schematically described.

1 is a diagram schematically showing an E-UMTS network structure as an example of a wireless communication system. The Evolved Universal Mobile Telecommunications System (E-UMTS) system evolved from the existing Universal Mobile Telecommunications System (UMTS), and is currently undergoing basic standardization work in 3GPP. In general, E-UMTS may be referred to as an LTE (Long Term Evolution) system. For details of the technical specifications of UMTS and E-UMTS, refer to the standard documents of the " 3rd Generation Partnership Project (Technical Specification Group Radio Access Network ").

1, an E-UMTS includes an Access Gateway (AG) located at the end of a User Equipment (UE), a Node B (eNode B), and a network (E-UTRAN) . The base station may simultaneously transmit multiple data streams for broadcast services, multicast services, and / or unicast services.

One base station has more than one cell. The cell is set to one of the bandwidths of 1.25, 2.5, 5, 10, 15, 20Mhz and the like to provide downlink or uplink transmission service to a plurality of UEs. Different cells may be set up to provide different bandwidths. The base station controls data transmission / reception for a plurality of terminals. The base station transmits downlink scheduling information for downlink (DL) data, and notifies the UE of time / frequency region, coding, data size, and HARQ related information to be transmitted to the UE. In addition, the base station transmits uplink scheduling information to uplink (UL) data, and notifies the UE of time / frequency domain, coding, data size, and HARQ related information that the UE can use. An interface for transmitting user traffic or control traffic may be used between the base stations. The Core Network (CN) can be composed of an AG and a network node for user registration of the UE. The AG manages the mobility of the terminal in units of TA (Tracking Area) composed of a plurality of cells.

Wireless communication technologies have been developed from WCDMA to LTE and LTE-Advanced (LTE-Advanced), but the demands and expectations of users and operators are steadily increasing. In addition, since other wireless access technologies are continuously being developed, new technology evolution is required to be competitive in the future. Cost reduction per bit, increased service availability, use of flexible frequency band, simple structure and open interface, and proper power consumption of terminal.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the related art as described above, and it is an object of the present invention to provide a CSG service improved by managing a CSG member cell list.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the precise form disclosed. Lt; / RTI >

According to an aspect of the present invention, there is provided a method of selecting a cell in a wireless communication system, the method comprising: measuring received power for all frequencies supported by the terminal; Detecting one or more cells based on the measurements; Generating a list by sorting the detected one or more cells according to received power; Obtaining System Information Block Type 1 (SIB1) of the first cell of the list; Adding the first cell to a CSG fingerprint and determining the suitability of the first cell if the first cell is determined as a CSG (Closed Subscriber Group) cell based on the SIB1; And deleting the first cell from the list if it is determined that the first cell is not a CSG (Closed Subscriber Group) cell based on the SIB1.

Also, a terminal for performing cell selection in a wireless communication system according to an exemplary embodiment includes a radio frequency unit; And a processor configured to measure received power for all frequencies supported by the terminal, detect one or more cells based on the measurements, sort the detected one or more cells according to received power And acquires system information block type 1 (SIB1) of the first cell of the list. If the first cell is determined as a CSG (Closed Subscriber Group) cell based on SIB1 , Adds the first cell to the CSG fingerprint and determines the suitability of the first cell, and if it is determined that the first cell is not a CSG (Closed Subscriber Group) cell based on the SIB1, And delete the first cell from the list.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. And can be understood and understood.

According to the embodiments of the present invention, the following effects are obtained.

Embodiments of the present disclosure may increase the probability of receiving a CSG service using an extended CSG member cell.

In addition, embodiments of the present disclosure may add a CSG member cell to a CSG fingerprint, irrespective of suitability, to generate a more extended CSG fingerprint.

Additional advantages, objects, and features of the present invention will become readily apparent as the invention proceeds through the following description or on the basis of the following description by those skilled in the art. Further, the present invention may have unexpected advantages as one of ordinary skill in the art may implement the present invention based on the following description.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. It is to be understood, however, that the technical features of the present invention are not limited to the specific drawings, and the features disclosed in the drawings may be combined with each other to constitute a new embodiment.
1 schematically shows an E-UMTS network structure as an example of a wireless communication system.
2 conceptually illustrates a network structure of an evolved universal terrestrial radio access network (E-UTRAN).
3 shows a control plane and a user plane structure of a radio interface protocol between a UE and an E-UTRAN based on the 3GPP radio access network standard.
4 shows the physical channels used in the 3GPP system and a general signal transmission method using them.
5 shows a structure of a radio frame used in an LTE system.
6 is a flowchart of a cell selection method according to a conventional embodiment.
7 is a flowchart of a cell selection method according to an embodiment.
8 is a flowchart of a PLMN and CSG list retrieval method according to an embodiment.
9 is a flowchart of a cell reselection method according to an embodiment.
10 shows an example of the structure of a terminal and a base station according to the embodiment described in this specification.

Hereinafter, the structure, operation and other features of the present invention will be readily understood by the embodiments of the present invention described with reference to the accompanying drawings. The embodiments described below are examples in which technical features of the present invention are applied to a 3GPP system.

Although the present specification describes an embodiment of the present invention using an LTE system and an LTE-A system, embodiments of the present invention may be applied to any communication system corresponding to the above definition. In addition, although the present invention is described with reference to the FDD scheme, the embodiments of the present invention can be easily modified to the H-FDD scheme or the TDD scheme.

2 is a conceptual diagram illustrating a network structure of an evolved universal terrestrial radio access network (E-UTRAN). Especially, the E-UTRAN system is an evolved system in the 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 is a diagram showing a control plane and a user plane structure of a radio interface protocol between a UE and an E-UTRAN based on the 3GPP radio access network standard. The control plane refers to a path through which control messages used by a UE and a network are transferred. The user plane means a path through which data generated in the application layer, for example, voice data or Internet packet data, is transmitted.

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 a medium access control layer (upper layer) through a transport channel. Data moves between the MAC layer and the physical layer over the transport channel. Data is transferred between the transmitting side and the receiving side physical layer through the physical channel. The physical channel utilizes time and frequency as radio resources. Specifically, the physical channel is modulated in an OFDMA (Orthogonal Frequency Division Multiple Access) scheme in a downlink, and is modulated in an SC-FDMA (Single Carrier Frequency Division Multiple Access) scheme in an uplink.

The Medium Access Control (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 functional block in the MAC. The Packet Data Convergence Protocol (PDCP) layer of the second layer performs a header compression function to reduce unnecessary control information in order to efficiently transmit IP packets such as IPv4 and IPv6 in a wireless interface with a narrow bandwidth.

The Radio Resource Control (RRC) layer located at the bottom of the third layer is defined only in the control plane. The RRC layer is responsible for the control of logical channels, transport channels and physical channels in connection with the configuration, re-configuration and release of radio bearers (RBs). RB denotes a service provided by the second layer for data transmission between the UE and the network. To this end, the terminal and the RRC layer of the network exchange RRC messages with each other.

Hereinafter, the RRC state of the UE and the RRC connection method will be described. The RRC state refers to whether or not the RRC of the UE is a logical connection with the RRC of the E-UTRAN. If the RRC is connected, the RRC connection state (RRC_CONNECTED) is established. If not, the RRC idle state (RRC_IDLE) .

Since the E-UTRAN can grasp the presence of the UE in the RRC-connected state on a cell-by-cell basis, the E-UTRAN can effectively control the UE. On the other hand, the E-UTRAN can not grasp the RRC idle terminal in the cell unit, and the CN manages the TA unit, which is a larger area unit than the cell. That is, in order for the UE in the RRC idle state to receive services such as voice or data from the cell, the UE must transition to the RRC connected state.

In particular, when the user first turns on the power of the UE, the UE first searches for an appropriate cell and stays in the RRC idle state in the cell. The UE which has stayed in the RRC idle state performs the RRC connection establishment process with the RRC of the E-UTRAN only when it is necessary to establish the RRC connection, and transits to the RRC connection state. Here, the case where the RRC connection needs to be established means that uplink data transmission is required due to a user's call attempt or the like, or when a paging message is received from the E-UTRAN, a response message should be transmitted.

Meanwhile, the non-access stratum (NAS) layer at the top of the RRC layer performs functions such as session management and mobility management. 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 to manage a signaling connection between a terminal and an EPC. . When the UE in the ECM idle state establishes the RRC connection with the E-UTRAN, the UE enters the ECM connected state. ECM The MME in the idle state is connected to the ECM when it makes an S1 connection with the E-UTRAN.

When the UE is in the ECM idle state, the E-UTRAN does not have a context of the UE. Therefore, the terminal in the ECM idle state performs terminal-based mobility-related procedures such as cell selection or cell re-selection procedure without receiving commands from 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 position of the terminal differs from the position known to the network in the ECM idle state, the terminal informs the network of the corresponding position of the terminal through a TA update (Tracking Area Update) procedure.

In the LTE system, one cell constituting the base station (eNB) is set to one of the bandwidths of 1.25, 2.5, 5, 10, 15, and 20 MHz to provide downlink or uplink services to a plurality of terminals. Different cells may be set up to provide different bandwidths.

A downlink transmission channel for transmitting data from a network to a terminal includes a BCH (Broadcast Channel) for transmitting system information, a PCH (Paging Channel) for transmitting a paging message, a downlink SCH (Shared Channel) for transmitting user traffic or control messages, have. In case of a traffic or control message of a downlink multicast or broadcast service, it may be transmitted through a downlink SCH, or may be transmitted via a separate downlink multicast channel (MCH).

Meanwhile, the uplink transmission channel for transmitting data from the UE to the network includes a random access channel (RACH) for transmitting an initial control message and an uplink SCH (shared channel) for transmitting user traffic or control messages. A logical channel mapped to a transport channel is a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH) Traffic Channel).

4 is a view for explaining a physical channel used in a 3GPP system and a general signal transmission method using the same.

The terminal performs an initial cell search operation such as synchronizing with a base station when the power is turned on or a new cell is entered (S401). To this end, the terminal receives a primary synchronization channel (P-SCH) and a secondary synchronization channel (S-SCH) from a base station and synchronizes with the base station and acquires information such as a cell ID have. Then, the terminal can receive the physical broadcast channel from the base station and acquire the in-cell broadcast information. Meanwhile, the UE can receive the downlink reference signal (DL RS) in the initial cell search step to check the downlink channel state.

Upon completion of the initial cell search, the UE receives more detailed system information by receiving a Physical Downlink Control Channel (PDCCH) and a Physical Downlink Control Channel (PDSCH) according to the information on the PDCCH (S402).

On the other hand, if the base station is initially connected or there is no radio resource for signal transmission, the mobile station can perform a random access procedure (RACH) on the base station (steps S403 to S406). To this end, the UE transmits a specific sequence through a Physical Random Access Channel (PRACH) as a preamble (S403), and receives a response message for the preamble on the PDCCH and the corresponding PDSCH (S404) . In case of the contention-based RACH, a contention resolution procedure can be additionally performed.

The UE having performed the above procedure performs PDCCH / PDSCH reception (S407) and physical uplink shared channel (PUSCH) / physical uplink control channel Control Channel (PUCCH) transmission (S408). In particular, the UE receives downlink control information (DCI) through the PDCCH. Here, the DCI includes control information such as resource allocation information for the UE, and formats are different according to the purpose of use.

Meanwhile, the control information that the UE transmits to the base station through the uplink or receives from the base station includes a downlink / uplink ACK / NACK signal, a channel quality indicator (CQI), a precoding matrix index (PMI) ) And the like. In the case of the 3GPP LTE system, the UE can transmit control information such as CQI / PMI / RI as described above through PUSCH and / or PUCCH.

The system information may include essential information that the terminal should know in order to access the base station. Therefore, the terminal must receive all the system information before connecting to the base station, and always have the latest system information. In addition, the system information is periodically transmitted to all terminals within one cell. The system information may consist of MIB (Master Information Block), SB (Scheduling Block) and SIB (System Information Block). The MIB contains information about the physical configuration (e.g., bandwidth) of the cell in question. The SB may include transmission information (e.g., transmission period, etc.) of the SIBs. SIB is a collection of system information related to each other. For example, the SIB may include only information of neighboring cells or only information of an uplink radio channel used by the UE.

Generally, a service provided by a network to a terminal can be classified into three types. Also, the terminal can recognize the cell type differently depending on what service can be provided. The limited service may provide an emergency call and an earthquake and tsunami warning system (ETWS), and a limited service may be provided in an acceptable cell. A normal service means a general service of a public use, and may be provided in a suitable cell. Operator service refers to a service for a network operator. Only communication users can use the cell, and ordinary users can not use it.

With respect to the service type provided by the cell, the type of the cell can be divided as follows. An acceptable cell is a cell in which a terminal can receive a limited service. A terminal is not barred in an acceptable cell, and an acceptable cell is a cell satisfying a cell selection criterion of the terminal. A suitable cell is a cell in which a terminal can receive a normal service. A suitable cell satisfies the conditions of the acceptable cell while satisfying the additional conditions. As an additional condition, a suitable cell is a cell belonging to the PLMN to which the corresponding terminal can access and is not prohibited from performing the tracking area (TA) update procedure of the terminal. If the corresponding cell is a CSG cell, the corresponding cell must be a cell that the UE can access as a CSG member. Also, a barred cell is a cell broadcasted as a cell prohibited by system information. A reserved cell is a cell broadcast as a cell reserved by the system information.

5 is a diagram illustrating a structure of a radio frame used in an LTE system.

Referring to FIG. 5, a radio frame has a length of 10 ms (327200 × Ts) and is composed of 10 equal sized subframes. Each subframe has a length of 1 ms and is composed of two slots. Each slot has a length of 0.5 ms (15360 x Ts). Here, Ts represents the sampling time, and is represented by Ts = 1 / (15 kHz x 2048) = 3.2552 x 10 ^-8 (about 33 ns). A slot includes a plurality of OFDM symbols in a time domain and a plurality of resource blocks (RB) in a frequency domain. In the LTE system, one resource block includes 12 subcarriers x 7 (6) OFDM symbols. A transmission time interval (TTI), which is a unit time at which data is transmitted, may be determined in units of one or more subframes. The structure of the radio frame is merely an example, and the number of subframes included in a radio frame, the number of slots included in a subframe, and the number of OFDM symbols included in a slot can be variously changed.

Hereinafter, procedures for selecting a cell by a terminal will be described.

The terminal in the RRC idle state should always select a cell of appropriate quality and prepare to receive the service through the selected cell. For example, a powered down terminal may select a cell of appropriate quality to register with the network. When the UE in the RRC connection state enters the RRC idle state, the UE must select a cell to camp on in the RRC idle state. The process of selecting a cell satisfying a predetermined condition to stay in a service waiting state such as the RRC idle state is referred to as a cell selection. For rapid cell selection, the cell may be selected in the cell selection process if the cell meets a predetermined criterion even though it does not provide the best radio signal quality.

The terminal shall perform measurements for cell selection and reselection. For example, by displaying a Radio Access Technology (RAT) associated with a selected PLMN (Public Land Mobile Network) and maintaining a list of PLMNs equivalent to the forbidden registration area, the NAS (Non Access Stratum) RAT can be controlled. The terminal can select a suitable cell based on the idle mode measurement and the cell selection criterion.

When camped on a cell, the terminal should periodically search for a better cell according to the cell reselection criterion. If a better cell is found, a good cell is selected. A change in the cell may mean a change in the RAT.

In the case of a normal service, the terminal camps on a suitable cell, receives system information from the PLMN by tuning to the control channel of the cell, receives registration information from the PLMN (e.g., Tracking area information), and may receive other AS (Access Stratum) and NAS information. In addition, if the terminal is registered, the terminal can receive a paging and notification message from the PLMN and start switching to the connected mode.

The terminal may perform initial cell selection and stored information cell selection. The initial cell selection does not require prior knowledge of which RF channels are E-UTRA carriers. The UE can search for RF channels in all E-UTRA bands according to the capability of the UE to search for a suitable cell. On each carrier frequency, the terminal can only search for the strongest cell. If a suitable cell is found, the found cell is selected. In addition, cell selection of stored information may be performed based on information of the stored carrier frequency and information of additional cell parameters. Such information may be obtained from previously received measurement control information elements or previously detected cells. Once the terminal finds a suitable cell, the terminal selects the found cell. If no suitable cell is found, an initial cell selection procedure may be initiated. The criteria for specific cell selection can be referenced in accordance with 5.2.3.2 of the 3GPP standard document TS 36.304.

Once the UE has selected a cell through the cell selection process, the strength or quality of the signal between the UE and the BS may be changed due to mobility of the UE or change of the radio environment. Thus, if the quality of the selected cell degrades, the terminal may select another cell that provides better quality. When the cell is reselected in this way, a cell is selected that generally provides better signal quality than the currently selected cell. This process is called cell reselection. The cell reselection process is basically aimed at selecting a cell that provides the best quality to the UE in terms of the quality of the radio signal.

In addition to the quality of the radio signal, the network can determine the priority for each frequency and notify the terminal. The MS receiving the priority order takes priority over the radio signal quality reference in the cell reselection process.

In order to select a cell for reselection in the cell reselection, there is a method of selecting or reselecting a cell according to the signal characteristics of the wireless environment, There may be a choice.

- Intra-frequency cell reselection: reselects cells with the same center-frequency as the RAT such as the cell in which the terminal is camping (camping)

Inter-frequency cell reselection: reselects a cell with a center frequency different from the RAT of the cell the terminal is camping on

- Inter-RAT (Inter-RAT) cell reselection: Reselect a cell that uses a different RAT than the RAT the terminal is camping on

The principle of the cell reselection process is as follows

First, the UE measures the quality of a serving cell and a neighboring cell for cell reselection.

Second, cell reselection is performed based on cell reselection criteria. The cell reselection criterion has the following characteristics with respect to the serving cell and the neighbor cell measurement.

Intra-frequency cell reselection is basically based on ranking. Ranking is the task of defining the index values for the cell reselection evaluation and ordering the cells by the index value size using the index values. A cell with the best indicator is often called the best ranked cell. The cell index value is a value obtained by applying a frequency offset or a cell offset as necessary based on a value measured by the terminal for the corresponding cell.

Inter-frequency cell reselection is based on the frequency priorities provided by the network. The terminal attempts to camp on the frequency with the highest frequency priority. The network may provide frequency priority for each UE through signaling (dedicated signaling), or may provide common frequency priority or frequency priority to UEs in a cell through broadcast signaling. The cell reselection priority provided through broadcast signaling may be referred to as a common priority, and the cell reselection priority set by the network for each terminal may be referred to as a dedicated priority. When the terminal receives the dedicated priority, it can receive the validity time associated with the dedicated priority. Upon receiving the dedicated priority, the UE starts a validity timer set to the validity time received together. The terminal applies the dedicated priority in the RRC idle mode while the validity timer is operating. When the validity timer expires, the terminal discards the dedicated priority and applies the public priority again.

For inter-frequency cell reselection, the network may provide the terminal with parameters (e.g., frequency-specific offset) used for cell reselection on a frequency-by-frequency basis.

For intra-frequency cell reselection or inter-frequency cell reselection, the network may provide the terminal with a Neighboring Cell List (NCL) used for cell reselection. This NCL includes cell-specific parameters (e.g., cell-specific offsets) used for cell reselection

For intra-frequency or inter-frequency cell reselection, the network may provide the terminal with a cell blacklist, which is used for cell reselection. The UE does not perform cell reselection for cells included in the forbidden list.

Hereinafter, selection of a manual CSG (closed subscriber group) as an operation in the idle mode will be described. At the requesting terminal of the NAS, the Access Stratum (AS) can search all the RF channels in the E-UTRA according to the capability of the terminal to search for possible CSGs. For each carrier, the terminal can at least search the strongest cell, read the system information of the searched cell, and report the possible CSG ID (s) to the NAS along with the "HNB name" and the PLMN. The search for available CSGs can be stopped at the request of the NAS. If the NAS selects the CSG and provides this selection to an Access Stratum (AS), the terminal may search for an acceptable or suitable cell belonging to the CSG selected to camp on.

The case where the cell reselection is performed in the CSG cells will be described. In addition to normal cell reselection, if at least one CSG ID associated with the PLMN identification is included in the CSG whitelist of the terminal, the terminal shall include the inter-RAT frequencies in accordance with the performance requirements defined in 3GPP TS 36.133 An autonomous search function should be used to detect previous visited CSG member cells on non-serving frequencies. The CSG member cell may be a cell broadcasting an identifier of a selected PLMN, a registered PLMN or an equivalent PLMN, and may include a cell including a CSG ID of the cell and a corresponding PLMN identification in the CSG whitelist of the UE.

The terminal may also use an automatic search function for the serving frequency. The terminal may disable the automatic search function when the CSG whitelist of the terminal is empty. Also, depending on the implementation of the terminal, the automatic search function of the terminal may determine when and / or where to search for CSG member cells.

If a terminal discovers one or more suitable CSG cells on different frequencies, if the cell is the highest ranked cell at that frequency, the terminal determines whether the current terminal is to detect, Lt; / RTI > cells. If the terminal finds a suitable CSG cell on the same frequency, the terminal may reselect a suitable cell according to normal reselection rules. If the terminal detects one or more suitable CSG cells on another RAT, the terminal may select one of the detected cells according to 3GPP TS 25.304.

While camping on a suitable CSG cell, the terminal may apply a normal cell reselection procedure. To search for suitable CSG cells on non-serving frequencies, the terminal may utilize an automatic search function. When the CSG cell on the non-serving frequency is detected, the UE can reselect the highest ranked cell on the frequency. If the terminal detects one or more suitable CSG cells on another RAT, the terminal may reselect one of the detected cells according to 3GPP TS 25.304.

In addition to the normal cell reselection rules, the terminal may, in accordance with the performance requirements defined in 3GPP TS 36.133, include a CSG whitelist of non-serving frequencies on the non-serving frequencies, including inter- An autonomous search function should be used to detect previously visited hybrid cells containing ID and associated PLMN identification.

Accordingly, the UE must perform an automatic search function to search for CSG member cells in the idle state. When the automatic search function is performed, the UE searches for a previously visited CSG member cell to determine whether the re-selection condition is satisfied. If the re-selection condition is satisfied, the UE must perform a re-selection.

Accordingly, the UE may not be able to detect a CSG member cell other than the previously visited (or selected) CSG cell, and in this case, the UE may not be able to provide the CSG service to the user.

6 is a flowchart of a cell selection method according to a conventional embodiment.

The terminal performs frequency measurement for each carrier (S6-10). The terminal may perform frequency measurement by measuring the received power. The UE may perform frequency measurement on all frequencies supported by the UE. This frequency measurement may be performed at a predetermined period or may be performed based on a signal from an upper layer. Further, the frequency measurement may be performed based on predetermined conditions. For example, frequency measurement may be performed when the signal strength of the currently camped cell is less than or equal to a predetermined value. Based on the frequency measurement result, the terminal performs cell detection (S6-20).

In addition, the terminal can sort the detected cells in the order of received power (S6-30). The terminal may generate a list according to the sorted cells. If there is not more than one cell in the list of sorted cells, the terminal determines whether cell detection has been performed for all the frequencies (S6-50). If no cell detection is performed for all frequencies, Detection (S6-20) procedure can be performed. On the other hand, when one or more cells exist in the list of sorted cells (S6-40), the UE transmits a System Information Block Type 1 (System Information Block Type 1) of the first cell (S6-60). The terminal can judge the conformity of the cell based on the SIB1 (S6-70), and repeat the procedure of S6-60 and S6-70 for the next cell on the sorted list if the cell is not suitable. If the cell is not suitable, the cell may be deleted from the list of sorted cells. On the other hand, if the cell is suitable, the UE may determine whether the corresponding cell is a CSG member cell (S6-80). If the corresponding cell is a CSG member cell, the terminal may add the selected cell to the CSG fingerprint (S6-90). The CSG fingerprint is a list of CSG member cells that the terminal has visited in the past and may include information related to previously visited CSG member cells.

Thus, in the case of FIG. 6, if it is determined that the CSG member cell is not a suitable cell, the detected CSG member cell is not added to the CSG fingerprint. That is, when the terminal performs the above-described automatic search function, it is determined whether the re-selection condition is satisfied with respect to the previously visited CSG member cell. Therefore, the CSG member cell not added to the CSG fingerprint is re- . In this case, the CSG member cell may not be reselected even if the state of the cell is suitable for the future.

7 is a flowchart of a cell selection method according to an embodiment.

For the convenience of description, the description of the same procedure as in Fig. 6 is omitted.

7, it is determined whether the selected cell is a CSG member cell (S7-70). If the corresponding cell is not a CSG member cell, the terminal deletes the corresponding cell from the list of sorted cells, and proceeds to S7-40 Can be repeatedly performed. If the corresponding cell is a CSG member cell, the terminal adds the selected cell to the CSG fingerprint (S7-80) and determines the suitability of the selected cell (S7-90). Therefore, unlike FIG. 6, the UE can once add a CSG member cell having a high CSG reception power to the CSG fingerprint. For example, the selected CSG member cell is determined to be an unsuitable cell, and the corresponding cell may not be selected in the cell selection / reselection process. The terminal may also increase the probability of finding CSG member cells by adding unselected CSG member cells to the CSG fingerprint. Also, due to the increased probability of finding a CSG member cell, the opportunity for providing the CSG service to the user may also be increased.

7, the CSG fingerprint can be managed as follows. For example, if the maximum number of CSG member cell stores of a preset CSG fingerprint exceeds the number of stored CSG member cells due to the addition of a new CSG member cell, the oldest found CSG member cell may be deleted from the CSG fingerprint. Also, if an added CSG member cell already exists in the CSG fingerprint, the existing CSG member cell may be deleted. It is also possible to add the CSG member cell as the first term of the new CSG fingerprint and copy the existing CSG fingerprint to the second term of the new CSG fingerprint.

8 is a flowchart of a PLMN and CSG list retrieval method according to an embodiment.

For convenience of explanation, the description of the same procedures as those of Figs. 6 and 7 is omitted.

A similar scheme to that of FIG. 7 may be applied to the retrieval of the PLMN and the CSG list. However, in FIG. 8, the UE determines whether it is a CSG member cell for all terminals in the list (S8-70), and adds all the CSG member cells to the CSG fingerprint (S8-80). That is, if the selected cell is determined to be a CSG member cell based on SIB1 (S8-70), the terminal acquires SIB 1 sequentially in accordance with the received power for the detected cells (S8-60) (S8-80). If it is determined that all the searched cells are CSG member cells (S8-70), the UE can terminate the available PLMN and CSG list search procedure.

9 is a flowchart of a cell reselection method according to an embodiment.

For the sake of convenience of description, description of the same procedures as those of Figs. 6 to 8 will be omitted.

When the UE detects a cell satisfying the cell reselection criterion, it can acquire SIB1 of the cell reselection candidate cell (S9-10). Based on the obtained SIB1, the UE determines whether the corresponding cell is a CSG member cell (S9-20), and adds the selected cell to the CSG fingerprint (S9-30) if the corresponding cell is a CSG member cell. Also, regardless of whether the cell is a CSG member cell, the UE determines whether the cell is suitable (S9-40), moves to a candidate cell if it is a suitable cell (S9-60) (S9-50).

10, in order to perform the above-described methods according to the present invention, a processor unit (not shown), which can access and execute software codes stored in a memory or storage 12, there is provided an apparatus comprising a processing unit (a controller, a central processing unit (CPU), a microprocessor, etc.) 11 and 21 and a radio frequency (RF) unit 13 and 23. The various embodiments and features described herein may be implemented in software, hardware, or a combination thereof. For example, a computer program executing a method and apparatus for performing embodiments of the present invention (executed by a processor, controller, CPU, etc., mobile terminal and / or network device of a computer) And may include at least one program code section or module. Likewise, a software tool that performs methods and apparatus for performing embodiments of the present disclosure (executed by a processor, controller, CPU, etc., mobile terminal and / or network device of a computer) And may include at least one program code section or module for performing the functions described herein.

Methods and apparatus for performing the embodiments of the present disclosure are compatible with various types of techniques and standards. The embodiments described herein relate to standards such as 3GPP (Global System for Mobile Communications (GSM), Wideband Code Division Multiple Access (WCDMA), UMTS, LTE, LTE-Advanced, etc.), IEEE 802, However, the above exemplary standards do not limit other related standards and techniques applicable to the various embodiments and features described herein.

The embodiments and features described herein may be implemented in various types of user devices (e.g., mobile terminals, handsets, wireless communication devices, etc.) and / or network devices, entities, components that support MTC and / .

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The detailed description above should not be construed as limiting unless expressly specified otherwise, and should be interpreted broadly within the scope of the claims. Accordingly, it is intended that all changes and modifications within the equivalent scope of the invention be included within the scope of the present invention and interpreted within the scope of the claims.

The embodiments described above are those in which the elements and features of the present invention are combined in a predetermined form. Each component or feature shall be considered optional unless otherwise expressly stated. Each component or feature may be implemented in a form that is not combined with other components or features. It is also possible to construct embodiments of the present invention by combining some of the elements and / or features. The order of the operations described in the embodiments of the present invention may be changed. Some configurations or features of certain embodiments may be included in other embodiments, or may be replaced with corresponding configurations or features of other embodiments. It is clear that the claims that are not expressly cited in the claims may be combined to form an embodiment or be included in a new claim by an amendment after the application.

It will be apparent to those skilled in the art that 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.

Claims (14)

A method of selecting a cell of a terminal in a wireless communication system,
Measuring received power for all frequencies supported by the terminal;
Detecting one or more cells based on the measurements;
Generating a list by sorting the detected one or more cells according to received power;
Obtaining System Information Block Type 1 (SIB1) of the first cell of the list;
Adding the first cell to a CSG fingerprint and determining the suitability of the first cell if the first cell is determined as a CSG (Closed Subscriber Group) cell based on the SIB1; And
And deleting the first cell from the list if it is determined that the first cell is not a closed subscriber group (CSG) cell based on the SIB1. The method according to claim 1,
Further comprising camping on the first cell if the first cell is determined to be a suitable cell. 3. The method of claim 2,
Wherein the first cell is a cell included in a Public Land Mobile Network (PLMN) that the terminal can access and is not prohibited from performing a Tracking Area (TA) update procedure of the terminal. The method of claim 3,
Further comprising deleting the first cell from the list if the first cell is determined to be an unsuitable cell. The method according to claim 1,
Wherein the terminal is configured to perform the cell detection to generate a new list if no cell is present in the list. The method according to claim 1,
Wherein the CSG fingerprint is treated as a list of CSG member cells that the terminal visited in the cell reselection procedure. The method according to claim 1,
Further comprising deleting, from the CSG fingerprint, the oldest found CSG member cell if a predetermined maximum number of storable number of the CSG fingerprint is exceeded due to the addition of the first cell. How to choose. 1. A terminal for performing cell selection in a wireless communication system,
A radio frequency unit; And
The processor comprising:
Measures received power for all frequencies supported by the terminal,
Detecting one or more cells based on the measurements,
Generates a list by sorting the detected one or more cells according to the received power,
Acquires System Information Block Type 1 (SIB1) of the first cell of the list,
If it is determined that the first cell is a CSG (Closed Subscriber Group) member cell based on the SIB1, the first cell is added to a CSG fingerprint and the conformity of the first cell is determined
And delete the first cell from the list if it is determined that the first cell is not a closed subscriber group (CSG) cell based on the SIB1. 9. The method of claim 8,
Further comprising: camping on the first cell if the first cell is determined to be a suitable cell. 10. The method of claim 9,
Wherein the first cell is a cell included in a Public Land Mobile Network (PLMN) that the terminal can access and is not prohibited from performing a Tracking Area (TA) update procedure of the terminal. 11. The method of claim 10,
The processor comprising:
And delete the first cell from the list if the first cell is determined to be an unsuitable cell. 9. The method of claim 8,
Wherein the processor is further configured to perform the cell detection to generate a new list if no cell is present in the list. 9. The method of claim 8,
Wherein the CSG fingerprint is treated as a list of CSG member cells that the terminal has visited in the cell reselection procedure. 9. The method of claim 8,
The processor comprising:
Further comprising deleting, from the CSG fingerprint, the oldest CSG member cell if the maximum number of storable number of the CSG fingerprint is exceeded due to the addition of the first cell.

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