KR20100061334A - Method of mitigating interference in mixed frequency - Google Patents

Abstract

PURPOSE: A method of mitigating interference in a mixed frequency is provided to improve the UL(UpLink) quality of a corresponding base station cell by preventing the influence over the target cell resulting from an access limit of the target cell. CONSTITUTION: If a terminal is a member of a CSG(Closed Subscriber Group) of a target cell, the terminal recognizes the target cell as the CSG cell. If the terminal is not the member of the CSG of the target cell, the terminal inspects the wireless conditions of the target cell for the confirmation of the interference status over the target cell. If the wireless conditions are satisfied, the terminal recognizes the target cell as an accessible cell. If the wireless conditions are not satisfied, the terminal recognizes the target cell as the access-limited cell.

Description

Interference Mitigation Method at Mixed Frequency with Cells Restricting Access {METHOD OF MITIGATING INTERFERENCE IN MIXED FREQUENCY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system and a terminal for providing a wireless communication service, and to an Evolved Universal Mobile Telecommunications System (E-UMTS) or a Long Term Evolution System (LTE), which is evolved from a Universal Mobile Telecommunications System (UMTS). The terminal allows the base station to release the access restriction according to the configuration and the interference situation measured by the terminal. Accordingly, the present invention relates to a method for improving the quality of service of cells which limit the terminal and access at a mixed frequency by avoiding a situation in which the terminal stays in the existing cell due to the access restriction to the target cell and greatly affects the target cell. will be.

1 is a diagram illustrating a network structure of an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) which is a mobile communication system to which the present invention and the present invention are applied. The E-UTRAN system is an evolution from the existing UTRAN system and is currently undergoing basic standardization work in 3GPP. The E-UTRAN system is also called a Long Term Evolution (LTE) system.

The E-UTRAN is composed of eNBs (e-NodeBs, hereinafter referred to as base stations), and are connected between eNBs through an X2 interface. The eNB is connected to a user equipment (hereinafter abbreviated terminal) through a wireless interface and is connected to an Evolved Packet Core (EPC) through an S1 interface.

The EPC includes a mobility management entity (MME), a serving-gateway (S-GW), and a packet data network-gateway (PDN-GW). The MME has information about the access information of the terminal or the capability of the terminal, and this information is mainly used for mobility management of the terminal. S-GW is a gateway having an E-UTRAN as an endpoint, and PDN-GW is a gateway having a PDN as an endpoint.

Layers of the radio interface protocol between the terminal and the network are based on the lower three layers of the Open System Interconnection (OSI) reference model, which is widely known in communication systems. (Second layer) and L3 (third layer), wherein a physical layer belonging to the first layer provides an information transfer service using a physical channel, and a third layer. The radio resource control layer (hereinafter referred to as RRC) layer located in the layer plays a role of controlling radio resources between the terminal and the network. To this end, the RRC layer exchanges an RRC message between the terminal and the base station.

2 and 3 illustrate a structure of a radio interface protocol between a UE and an E-UTRAN based on the 3GPP radio access network standard. The wireless interface protocol consists of a physical layer, a data link layer, and a network layer horizontally, and vertically, a user plane for transmitting data information (user plane, u-plane). ) And control plane (C-plane) for transmitting signaling. The protocol layers of FIGS. 2 and 3 are based on the lower three layers of the Open System Interconnection (OSI) reference model, which are well known in communication systems, and include L1 (first layer), L2 (second layer), L3 (third layer) can be divided. These radio protocol layers exist in pairs in the UE and the E-UTRAN, and are responsible for data transmission in the radio section.

Hereinafter, each layer of the wireless protocol control plane of FIG. 2 and the wireless protocol user plane of FIG. 3 will be described.

The physical layer, which is the first layer, provides an information transfer service to an upper layer by using a physical channel. The physical layer is connected to the upper medium access control layer through a transport channel, and data between the medium access control layer and the physical layer moves through the transport channel. Then, data is moved between different physical layers, that is, between physical layers of a transmitting side and a receiving side through physical channels. The physical channel is modulated by an orthogonal frequency division multiplexing (OFDM) scheme and utilizes time and frequency as radio resources.

Medium access control (hereinafter referred to as MAC) of the second layer provides a service to a radio link control layer, which is a higher layer, through a logical channel. The radio link control layer (hereinafter referred to as RLC) layer of the second layer supports reliable data transmission. The functionality of the RLC layer may be implemented as a functional block inside the MAC. In this case, the RLC layer may not exist. The PDCP layer of the second layer is a header compression that reduces the IP packet header size, which is relatively large and contains unnecessary control information, for efficient transmission in a low bandwidth wireless section when transmitting an IP packet such as IPv4 or IPv6. Compression) function.

The radio resource control layer (hereinafter abbreviated as RRC) layer located at the top of the third layer is defined only in the control plane, and the configuration and reset of the radio bearer (abbreviated as RB) are performed. It is responsible for the control of logical channels, transport channels and physical channels in relation to configuration and release. In this case, RB means a service provided by the second layer for data transmission between the terminal and the UTRAN. When there is an RRC connection (RRC Connection) between the RRC of the terminal and the RRC layer of the radio network, the terminal is in the RRC_CONNECTED state, otherwise it is in the RRC idle state (RRC_IDLE).

A downlink transmission channel for transmitting data from a network to a UE includes a broadcast channel (BCH) for transmitting system information and a downlink shared channel (SCH) for transmitting user traffic or control messages. Traffic or control messages of a downlink multicast or broadcast service may be transmitted through a downlink SCH or may be transmitted through a separate downlink multicast channel (MCH). Meanwhile, the uplink transmission channel for transmitting data from the terminal to the network includes a random access channel (RAC) for transmitting an initial control message and an uplink shared channel (SCH) for transmitting user traffic or control messages.

It is located above the transport channel, and the logical channel mapped to the transport channel is a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and a multicast traffic (MTCH). Channel).

The physical channel is composed of several subframes on the time axis and several subcarriers on the frequency axis. Here, one sub-frame consists of a plurality of symbols on the time axis. One subframe consists of a plurality of resource blocks, and one resource block consists of a plurality of symbols and a plurality of sub-carriers. In addition, each subframe may use specific subcarriers of specific symbols (eg, the first symbol) of the corresponding subframe for a physical downlink control channel (PDCCH), that is, an L1 / L2 control channel. One subframe is 0.5 ms, and a transmission time interval (TTI), which is a unit time for transmitting data, is 1 ms corresponding to two subframes.

Hereinafter, the RRC state and the RRC connection method of the UE will be described in detail. The RRC state refers to whether or not the RRC of the UE is in a logical connection with the RRC of the E-UTRAN. If connected, the RRC connected state (RRC_CONNECTED state), and if not connected, the RRC idle state (RRC_IDLE). state). Since the UE of the RRC_CONNECTED state has an RRC connection, the E-UTRAN can grasp the existence of the UE in units of cells, and thus can effectively control the UE. On the other hand, the UE of the RRC_IDLE state cannot be grasped by the E-UTRAN and managed by the core network in units of a tracking area that is a larger area than the cell. That is, the RRC_IDLE state terminal is identified only in a large area unit, and must move to the RRC_CONNECTED state in order to receive a normal mobile communication service such as voice or data.

When the user first powers on the terminal, the terminal first searches for an appropriate cell and then stays in the RRC Idle state in the cell. When the UE staying in the RRC_IDLE state needs to establish an RRC connection, the UE establishes an RRC connection with the RRC of the E-UTRAN through an RRC connection procedure and transitions to the RRC_CONNECTED state. There are several cases in which the UE in the idle state needs to establish an RRC connection. For example, an uplink data transmission is necessary due to a user's call attempt, or a paging message is received from the E-UTRAN. In one case, the response message may be transmitted.

The NAS (Non-Access Stratum) layer located above the RRC layer performs functions such as session management and mobility management.

In order to manage mobility of the UE in the NAS layer, two states of EMM-REGISTERED (EPS Mobility Management-REGISTERED) and EMM-DEREGISTERED are defined, and these two states are applied to the UE and the MME. The initial terminal is in the EMM-DEREGISTERED state, and the terminal performs a process of registering with the corresponding network through an initial attach procedure to access the network. If the attach procedure is successfully performed, the UE and the MME are in an EMM REGISTERED state.

In order to manage a signaling connection between the UE and the EPC, two states are defined, ECM-IDLE (EPS Connection Management) and ECM_CONNECTED, and these two states are applied to the UE and the MME. When the UE in the ECM-IDLE state establishes the RRC connection with the E-UTRAN, the UE enters the ECM-CONNECTED state. The MME in the ECM-IDLE state becomes the ECM-CONNECTED state when it establishes an S1 connection with the E-UTRAN. When the terminal is in the ECM-IDLE state, the E-UTRAN does not have context information of the terminal. Accordingly, the UE in the ECM-IDLE state performs a UE-based mobility related procedure such as cell selection or reselection without receiving a command from the network. On the other hand, when the terminal is in ECM-CONNECTED, the mobility of the terminal is managed by the command of the network. In the ECM-IDLE state, if the position of the terminal is different from the position known by the network, the terminal informs the network of the corresponding position of the terminal through a tracking area update procedure.

The following is a description of system information. The system information includes essential information that the terminal needs to know in order to access the base station. Therefore, the terminal must receive all system information before accessing the base station, and must always have the latest system information. In addition, since the system information is information that all terminals in a cell should know, the base station periodically transmits the system information.

The system information is divided into MIB, SB, and SIB. The master information block (MIB) allows the terminal to know the physical configuration of the cell, for example, bandwidth. SB (Scheduling Block) informs the transmission information of the SIBs, for example, the transmission period. SIB (System Information Block) is a collection of system information related to each other. For example, some SIBs contain only information of neighboring cells, and some SIBs contain only information of uplink radio channels used by the terminal.

In the prior art, when there is a cell allowing only access of a general cell and a specific subscriber group at the same frequency, such as a mixed frequency, an interference problem due to access restriction greatly affects the quality of service of the terminal and the base station. For example, if the terminal is connected to a general cell while approaching a cell with restricted access, the terminal has a great interference with a cell with limited access. The terminal also has a problem in that the quality of service of the terminal is also worsened to receive a greater interference from the cell is limited access.

Accordingly, the present invention is to provide a method for mitigating interference generated in the prior art at a mixed frequency in which cells restricting access in a wireless communication system more effectively than in the prior art.

In order to solve the above problems of the present invention, a method of connecting a cell to a cell in a wireless communication system, the method comprising: determining whether a terminal is allowed to access a specific cell; If it is determined that the terminal is not allowed to access the specific cell, checking the radio signal quality with respect to the specific cell; If the radio signal quality for the specific cell satisfies a specific radio condition, considering the specific cell as an accessible cell; And accessing the specific cell by the terminal even if the terminal is not previously allowed to access the specific cell.

Preferably, the radio signal quality is characterized in that the downlink path loss value (downlink path loss value) for the particular cell measured by the terminal.

Preferably, when the downlink loss value is larger than a threshold, the specific radio condition is satisfied.

Preferably, when the difference between the downlink loss value for the specific cell and the downlink loss value for the currently connected cell is greater than a threshold, the specific radio condition is satisfied.

Preferably, the threshold value is received through system information (system information) transmitted from a network managing the particular cell.

Preferably, the threshold value is received through system information (system information) transmitted from the network managing the particular cell or the cell currently connected.

Preferably, if the terminal is not a member of a closed subscriber group (CSG), it is characterized in that the connection of the terminal is not allowed to the specific cell.

Preferably, the method further comprises the step of receiving a CSG indicator and a CSG identifier from the network.

Preferably, the connection of the specific cell is characterized by determining the received CSG indicator and the CSG identifier.

Preferably, all the above steps are performed during the cell reselection process.

Preferably, all of the above steps are performed during the handover process.

According to the present invention, when the UE approaches close to a cell to which access is restricted, such as a CSG cell in which the UE does not belong to a member, the UE stays in an existing cell due to access restriction to the target cell and has a great interference with the target cell. I can solve it. This improves the uplink quality of the cell of the base station. Further, according to the present invention, since the terminal also stays in the service area of the cell where the access is restricted, it can escape from a situation where the interference is severely received from the cell where the access is limited, so that the quality of service of the terminal is also improved.

The present invention is applied to 3GPP communication technology, in particular, a Universal Mobile Telecommunications System (UMTS) system or a Long Term Evolution (LTE) system, a communication device, and a communication method. However, the present invention is not limited thereto and may be applied to all wired and wireless communication to which the technical spirit of the present invention can be applied.

A basic concept of the present invention is a method of a terminal accessing a cell in a wireless communication system, comprising: determining whether a terminal is allowed to access a specific cell; If it is determined that the terminal is not allowed to access the specific cell, checking the radio signal quality with respect to the specific cell; If the radio signal quality for the specific cell satisfies a specific radio condition, considering the specific cell as an accessible cell; And even if the connection of the terminal to the specific cell was not previously allowed, the method comprising the step of accessing the terminal to the specific cell characterized in that it proposes a cell access method of the terminal in a wireless communication system and to perform such a method We propose a wireless mobile communication terminal.

Hereinafter, the configuration and operation of the embodiments according to the present invention will be described with reference to the accompanying drawings.

In general, services provided by a network to a terminal can be classified into three types as follows. In addition, the terminal also recognizes the cell type differently according to which service can be provided. The following describes the service type first, followed by the cell type.

1) Limited service This service provides Emergency Call and Tsunami Warning System (ETWS), which can be provided by an acceptable cell.

2) Normal service This service is a general purpose public service, and can be provided in a normal cell.

3) Operator service This service means service for network operator. This cell can be used only by network operator and not by general users.

In relation to the service type provided by the cell, the cell types may be classified as follows.

1) Acceptable cell A cell in which the terminal can receive limited service. This cell is a cell that is not barred from the viewpoint of the terminal and satisfies the cell selection criteria of the terminal.

2) Suitable cell A cell where the terminal can receive normal service. This cell satisfies the conditions of an acceptable cell and at the same time satisfies additional conditions. As an additional condition, this cell must belong to a PLMN to which the terminal can access and must be a cell which is not prohibited from performing a tracking area update procedure of the terminal. If the cell is a CSG cell, the terminal should be a cell that can be connected to the cell as a CSG member.

3) Barred cell A cell that broadcasts information indicating that the cell is a barred cell through system information.

4) Reserved cell A cell that broadcasts information indicating that a cell is a reserved cell through system information.

4 is an exemplary diagram illustrating a procedure for UE operation of selecting a cell in an idle mode.

In the first step, the terminal selects a radio access technology (hereinafter, abbreviated as RAT) for communicating with a network (public land mobile network; hereinafter abbreviated as PLMN) that it wants to receive. The PLMN and RAT information may be selected by the user of the terminal, or may be stored in the USIM.

In a second step, the terminal selects a cell having the largest value among the measured base station and a cell whose signal strength or quality is greater than a specific value (Cell Selection). Then, the base station periodically receives the SI. The above specific value refers to a value defined in the system in order to ensure the quality of the physical signal in data transmission / reception. Therefore, the value may vary depending on the RAT applied.

In a third step, the terminal registers its information (eg IMSI) to receive a service (eg paging) from the network. In this case, the terminal does not register with the accessing network every time the cell is selected, and information of the network (eg, Tracking Area Identity (TAI)) received from the SI and information of the network known to the UE are not registered. In other cases, register on the network.

In a fourth step, if the value of the strength and quality of the signal measured from the base station being serviced is lower than the value measured from the base station of the adjacent cell, the terminal has better signal characteristics than the cell of the base station to which the terminal is connected. Select one of the other cells providing. This process is called cell re-selection, which is distinguished from initial cell selection of the second step. In this case, in order to prevent the cell from being frequently reselected according to the change of the signal characteristic, a time constraint may be provided.

Next, a procedure of selecting a cell by the terminal will be described in detail. When the terminal is powered on, the terminal should perform a preparation procedure for receiving a service by selecting a cell of a suitable quality.

A UE in an RRC idle (RRC_IDLE) state should always be prepared to select a cell of appropriate quality and to receive service through this cell. For example, a terminal that has just been powered on must select a cell of appropriate quality to register with the network. When the UE in the RRC_CONNECTED state enters RRC_IDLE, the UE should select a cell to stay in RRC_IDLE. As such, the process of selecting a cell that satisfies a certain condition in order for the terminal to stay in a service standby state such as an RRC_IDLE state is called cell selection. Importantly, since the cell selection is performed in a state in which the UE does not currently determine a cell to stay in the RRC_IDLE state, it is most important to select a cell as soon as possible. Therefore, if the cell provides a radio signal quality of a predetermined criterion or more, even if this cell is not the cell providing the best radio signal quality to the terminal, it may be selected during the cell selection process of the terminal.

Hereinafter, a method and procedure for selecting a cell by an LTE terminal will be described in detail. When the terminal is initially powered on, the terminal searches for an available PLMN and selects an appropriate PLMN for receiving a service. Subsequently, the UE selects a cell having a signal quality and characteristics capable of receiving an appropriate service from among cells provided by the selected PLMN. Here, the cell selection process is largely divided into two types. First, an initial cell selection process, in which the terminal does not have prior information on the radio channel. Accordingly, the terminal searches all radio channels to find an appropriate cell. The terminal finds the strongest cell in each channel. Thereafter, the terminal selects a corresponding cell if it finds a suitable cell that satisfies the cell selection criteria. The following is a cell selection process using stored information. In this process, a cell selection is performed by using information stored in the terminal for a wireless channel or by using information broadcast in a cell. Therefore, the cell selection may be faster than the initial cell selection process. If the terminal only finds a cell that satisfies a cell selection criterion, the terminal selects the cell. If a suitable cell that satisfies the cell selection criteria is not found through this process, the UE performs an initial cell selection process.

The cell selection criteria used by the terminal in the cell selection process may be as shown in the formula in Table 1 below.

The factors used in the above cell selection criteria are as follows.

-Q _rxlevmeas Receive Level (RSRP) of the measured cell.

Minimum required receive level (dBm) in Q _rxlevmin cells

Q _{rxlevminoffset} Offset to _Qrxlevmin

-Pcompensation max (P _EMAX -P _UMAX , 0) (dB)

_-Maximum transmit power (dBm) that P _EMAX terminal can transmit in the cell

-P _UMAX Maximum transmit power (dBm) of the terminal radio transmitter (RF) according to the performance of the terminal

In Table 1, the UE can know that the strength of the measured signal selects a cell whose strength and quality are greater than a specific value determined by the cell providing the service. In addition, the parameters used in Table 1 are broadcast through system information, and the terminal receives these parameter values and uses them in cell selection criteria.

When the terminal selects a cell that satisfies a cell selection criterion, the terminal receives information necessary for the RRC_IDLE mode operation of the terminal in the cell from the system information of the cell. After the UE receives all the information necessary for the RRC_IDLE mode operation, the UE waits in the idle mode to request a service (eg, an originating call) or to receive a service (eg, a terminating call) from the network.

After the terminal selects a cell through a cell selection process, the strength or quality of a signal between the terminal and the base station may change due to a change in mobility or a wireless environment of the terminal. Therefore, if the quality of the selected cell is degraded, the terminal may select another cell that provides better quality. When reselecting a cell in this way, a cell that generally provides better signal quality than the currently selected cell is selected. This process is called cell reselection. The cell reselection process has a basic purpose in selecting a cell that generally provides the best quality to a terminal in view of the quality of a radio signal. In addition to the quality of the wireless signal, the network may determine the priority for each frequency and notify the terminal. Upon receiving this priority, the UE considers this priority prior to the radio signal quality criteria in the cell reselection process.

As described above, there is a method of selecting or reselecting a cell according to a signal characteristic of a wireless environment, and in selecting a cell for reselection when the cell is reselected, a radio access technology of the cell (abbreviated as RAT). There may be the following cell reselection method according to the and frequency characteristics.

Intra-frequency cell reselection Reselects a cell having the same center-frequency as the radio technology (RAT) same as the cell being used by the UE.

Inter-frequency cell reselection Reselects a cell having a center-frequency different from a radio technology (RAT) such as a cell being used by the UE

Inter-RAT cell reselection Reselects a cell using a radio technology (RAT) different from the radio technology being used by the terminal

Meanwhile, 3G or EPS (Evolved Packet System) service may be provided through a base station owned by an individual or a specific operator or a group other than a mobile communication network operator. Such a base station is called a Home Node B (HNB) or a (Home eNB; HeNB). Hereinafter, both the HNB and the HeNB are collectively referred to as H (e) NB. The H (e) NB basically aims to provide a specialized service only to a specific user group (Closed Subscriber Group, CSG). However, the service may be provided to other users in addition to the CSG according to the operation mode setting of the H (e) NB.

5 is an exemplary diagram illustrating a network structure of an E-UTRAN operating an H (e) NB using an H (e) NB gateway (GW).

As shown in FIG. 5, the HeNBs are connected to the EPC or directly to the EPC via the HeNB GW. Here, the HeNB GW looks like a normal eNB to the MME. The HeNB GW also looks like the MME to the HeNB. Therefore, the HeNB GW and the EPC are connected through the S1 interface between the HeNB and the HeNB GW. In addition, when the HeNB and the EPC are directly connected, they are connected to the S1 interface. The function of HeNB is mostly the same as that of general eNB.

In general, the H (e) NB has a lower radio transmission power than the (e) NB owned by the mobile network operator. Therefore, the coverage provided by the H (e) NB is generally smaller than the coverage provided by the (e) NB. Due to this characteristic, a cell provided by an H (e) NB is often classified as a femto cell in comparison with a macro cell provided by (e) NB from a service area perspective. On the other hand, in terms of the service provided, when the H (e) NB provides a service only to the CSG group, the cell provided by the H (e) NB is called a CSG cell.

Each CSG has its own unique identification number, which is called a CSG identity (CSG identity). The terminal may have a list of CSGs belonging to the member, and the CSG list may be changed by a request of the terminal or a command of the network. In general, one H (e) NB may support one CSG.

H (e) The NB transmits the CSG ID of the CSG supported by itself to the member terminal of the corresponding CSG through the system information. When the UE finds a CSG cell, it can check which CSG the CSG cell supports by reading the CSG ID included in the system information. The terminal reading the CSG ID is regarded as a cell to which the cell can be accessed only when the UE is a member of the CSG cell.

H (e) NB does not always need to allow access to the CSG terminal. Depending on the configuration of the H (e) NB, it is also possible to allow connection of a terminal other than the CSG member. Which terminal is allowed to access is changed according to the configuration of H (e) NB, where the configuration setting means the setting of the operation mode of H (e) NB. The operation mode of the H (e) NB is divided into three types according to which UE provides a service.

1) Closed access mode A mode that provides services only to specific CSG members. H (e) NB provides the CSG cell.

2) Open access mode General (e) Mode that provides service without restriction of specific CSG member like NB. H (e) NB provides a general cell that is not a CSG cell.

3) Hybrid access mode A mode in which a CSG service can be provided to a specific CSG member and a service is provided to a non-CSG member like a normal cell. CSG member UEs are recognized as CSG cells, and non-CSG member UEs are recognized as normal cells. These cells are called hybrid cells.

The H (e) NB informs the UE whether the cell it serves is a general cell, which is a CSG cell, so as to know whether the UE can access the cell. The H (e) NB operating in the closed access mode broadcasts that it is a CSG cell through system information. The H (e) NB operating in the open access mode broadcasts that it is not a CSG cell through the system information. As such, the H (e) NB includes a 1-bit CSG indicator in the system information indicating whether or not the cell it serves is a CSG cell. For example, the CSG cell broadcasts by setting the CSG indicator to TRUE. If the serving cell is not a CSG cell, the CSG indicator may be set to FALSE or a method of omitting CSG indicator transmission may be used. Since the UE should be able to distinguish the general cell provided by the (e) NB from the CSG cell, the general (e) NB also sends a CSG indicator (eg, FALSE) so that the UE knows that the cell type provided by the UE is the general cell. can do. In addition, the general (e) NB may not let the UE know that the cell type provided by the UE is a general cell by not transmitting the CSG indicator. Table 2 shows CSG related parameters transmitted by a corresponding cell for each cell type. Table 3 then allows connection by cell type [[Table 3]

The type of terminal used is shown.

TABLE 2

[Table 3]

6 is a first exemplary diagram illustrating a method of confirming an access mode of a base station by a terminal according to the present invention.

In a first step, the terminal first checks the CSG indicator in the system information of the target cell to determine what type of cell the target cell is. After confirming the CSG indicator, in a second step, if the CSG indicator indicates that the target cell is a CSG cell, the UE recognizes the cell as a CSG cell. Thereafter, the terminal checks the CSG identity (CSG identity or CSG identifier) in the system information to determine whether the UE is a CSG member of the target cell. When the terminal determines that the UE is a CSG member of the target cell from the CSG identifier, the terminal recognizes the cell as an accessible CSG cell.

If the terminal confirms that it is not a CSG member of the target cell from the CSG identifier, the terminal regards the cell as a cell that is not accessible. In the first step, if the CSG indicator indicates that the target cell is not a CSG cell, the terminal recognizes the target cell as a general cell. In addition, if the CSG indicator is not transmitted in the first step, the terminal recognizes the target cell as a general cell.

In general, a CSG cell and a macro cell may be operated simultaneously at a specific frequency. This frequency is called the mixed carrier frequency. The network may reserve specific physical layer cell identifiers for the CSG cell separately at the mixed carrier frequency. The physical layer cell identifier is called PCI (Physical Cell Identity) in the E-UTRAN system, and PSC (Physical Scrambling Code) in the UTRAN. For convenience of description, the physical layer identifier is expressed in PCI. At the mixed carrier frequency, the CSG cell informs the system information about the PCIs reserved for CSG at the current frequency. Upon receiving this information, the UE can determine whether a cell is a CSG cell or not a CSG cell from PCI of this cell when it discovers a cell at a corresponding frequency. The following describes how two terminals use this information.

First, in case of a UE that does not support CSG-related functions or does not have a CSG list as a member thereof, the UE does not need to consider the CSG cell as a selectable cell during cell selection / reselection. In this case, the terminal checks only the PCI of the cell, and if the PCI is a PCI reserved by the CSG, the cell can be immediately excluded from the cell selection / reselection process. In general, the PCI of a cell can be known immediately at the terminal when the physical layer confirms the existence of the cell.

Second, in case of a UE having a CSG list of which the UE is a member, when the UE wants to know a list of neighboring CSG cells at the mixed carrier frequency, the CSG identifier of the system information of all cells found in the entire PCI range. Instead of verifying, we only find a cell with a PCI reserved for CSG and we know that the cell is a CSG cell.

In general, when a macro cell and a CSG cell exist together at the same frequency as a mixed frequency, signal interference becomes a big problem in terms of quality of service of the terminal and the base station. For example, when the UE accesses a CSG cell with limited access while the UE is connected to the macro cell, the UE has a greater interference with the CSG cell. That is, when the access restricted terminal approaches the CSG cell closer and closer, the uplink quality of the cell becomes worse due to interference from the access restricted terminal. In addition, even when the terminal is approached to the cell with limited access, the terminal receives a greater interference from the restricted CSG cell, thereby deteriorating the service quality of the terminal.

In some cases, when the terminal comes closer to the CSG cell with the access of the terminal limited, the terminal will no longer be capable of normal communication communication with the existing macro cell that was being served by the terminal. In this case, the communication link of the terminal is broken. As such, when a network operates a mixed frequency and there are a large number of cells in the macro cell that restrict access to the UE, such as the CSG cell, the quality of the UE decreases whenever the UE enters the service area of the cell to which the access restriction applies. In addition, the cell that restricts access is also frequently interrupted by the terminal subject to access restriction, thereby deteriorating uplink received signal quality, which degrades the performance of the cell.

Accordingly, in the present invention, when the terminal satisfies a specific condition in a situation in which the terminal is approaching an area of a cell where access is restricted, the cell is transmitted to the terminal in order to eliminate interference that the terminal has on the cell where access is restricted. We propose a way to allow access. Here, the radio condition may be that a downlink (DL) path loss value measured for a cell in which the access of the terminal is limited exceeds a certain threshold value. In addition, the radio condition may be a difference between a DL path loss value measured for a cell of which the access of the terminal is restricted and a DL path loss value measured for a cell to which the terminal is currently connected exceeds a certain threshold. The threshold value in the radio condition may be broadcasted through system information or transmitted to the terminal by a base station restricting access of the terminal. In addition, the threshold value in the radio condition may be broadcasted through system information or transmitted to the terminal by the base station to which the terminal is currently connected.

In addition, the base station for restricting the access of the terminal may transmit an access indicator, so if the base station transmits the access indicator, the terminal may recognize the cell of the base station that satisfies the radio condition as an accessible cell. have. If the base station transmits this access indicator and this value is set such that access restriction can be ignored according to a radio condition, the terminal may recognize a cell of the base station satisfying the radio condition as an accessible cell. . If the base station does not transmit the access indicator, the terminal may follow the access restriction of the base station regardless of the radio condition. If the base station transmits this access indicator and this value is set that the access restriction should not be ignored, the terminal may follow the access restriction of the base station regardless of the radio condition. Here, the access indicator may be the threshold value.

The access restriction applied to the terminal may be an access restriction applied to the terminal that is not a member of the CSG cell. When a terminal satisfying the radio condition is connected to a cell in which the access is restricted, the terminal notifies the network that the radio condition is satisfied (or has been connected), so that the network is exceptional in accessing the terminal. You can allow it. The above processes may be used in a cell reselection process or a handover process of the UE.

7 illustrates an operation of a terminal according to the present invention when a terminal connected to a specific cell approaches a cell capable of suggesting connection of the terminal.

First, the terminal checks whether the target cell can restrict the access of the terminal through system information of the target cell. Subsequently, when the terminal determines that the target cell does not restrict the access of the terminal, the terminal recognizes the target cell as an accessible cell. However, if it is confirmed that the target cell restricts the access of the terminal, the terminal checks a radio condition for the target cell in order to confirm an interference situation for the target cell. If the radio condition for the target cell is satisfied, the terminal ignores the access restriction applied to the terminal and recognizes the target cell as an accessible cell. On the other hand, if the radio condition for the target cell is not satisfied, the terminal accepts the access restriction that the target cell imposes on the terminal, recognizes the target cell as a connection restricted cell, and does not attempt to access the target cell. .

Here, if the process is a terminal occurring during the cell (re) selection process, after recognizing the target cell as a connectable cell, the terminal is connected to the connection (re) setup request message The mobile station may inform the network by including information indicating that the terminal transmits the mobile station by satisfying the radio condition.

In addition, if the process is a terminal occurring during the handover process, after recognizing the target cell as an accessible cell, the terminal itself satisfies the radio condition in a handover complete message. The network may be informed by including information on the transmitting terminal.

8 illustrates an operation of a terminal according to the present invention as an embodiment of the present invention in which a terminal connected to a specific cell approaches a CSG cell.

As shown in FIG. 8, the terminal first checks the CSG indicator in the system information of the target cell in order to identify what type of cell the target cell is. If the CSG indicator indicates that the target cell is a CSG cell, the terminal recognizes the cell as a CSG cell, and the terminal identifies a CSG identifier (CSG) in the system information to determine whether the target cell is a CSG member of the target cell. Check identity. When the terminal confirms that it is a CSG member of the target cell from the CSG identifier, the terminal recognizes the corresponding cell as a member CSG cell. If the terminal confirms that it is not a CSG member of the target cell from the CSG identifier, according to the present invention, the terminal checks a radio condition for the target cell to confirm the interference situation for the target cell. . If the radio condition is satisfied, the terminal recognizes the target cell as an accessible cell even though it is not a CSG member of the target cell. On the other hand, if the radio condition is not satisfied, the terminal recognizes the target cell as a cell that is not accessible. In the process, if the CSG indicator indicates that the target cell is not a CSG cell, the terminal recognizes the target cell as a general cell. In addition, if the CSG indicator is detected by the terminal that it is not being transmitted (eg, timeout), the terminal may recognize the target cell as a general cell.

Here, if the process is a terminal occurring during the cell (re) selection process, after recognizing the target cell as a connectable cell, the terminal is connected to the connection (re) setup request message The mobile station may inform the network by including information indicating that the terminal transmits the mobile station by satisfying the radio condition.

In addition, if the process is a terminal occurring during the handover process, after recognizing the target cell as an accessible cell, the terminal itself satisfies the radio condition in a handover complete message. The network may be informed by including information on the transmitting terminal.

According to the present invention, when the UE approaches close to a cell to which access is restricted, such as a CSG cell that is not a member of the UE, the UE stays in an existing cell due to access restriction to the target cell and has a large interference with the target cell. You can solve the situation. This improves the uplink quality of the cell of the base station. Further, according to the present invention, since the terminal also stays in the service area of the cell where the access is restricted, it can escape from a situation where the interference is severely received from the cell where the access is limited, and the quality of service of the terminal is also improved.

The base station allowing only the access of the terminal having a large interference may induce the mobility of the terminal so that the terminal stays according to the network operation policy or if the terminal has another frequency available, the terminal accesses a cell of another frequency. Can be.

The present invention does not exclude a scenario in which the base station can strictly apply the access restriction rule regardless of the interference of the terminal. When the terminal checks a radio condition that can ignore the access restriction, the base station transmits an indication that the base station does not transmit the parameter used for the condition or the terminal must follow the access restriction, so that the base station must comply with the access restriction. The UE may control cell connection related behavior of the UE.

FIG. 9 is an exemplary diagram illustrating a base station access process of a terminal accessing a CSG (Closed Subscriber Group) cell that is not a member of a cell (re) selection process according to the present invention.

First, the terminal receives system information including the CSG indicator and the CSG identifier from the base station. Thereafter, the terminal additionally receives information such as a radio condition parameter or an access indicator from the base station. Here, the additionally received information of the radio condition parameter or the access indicator may be provided to the terminal included with the system information including the CSG indicator and the CSG identifier, or included in another system information broadcasted to the terminal. It may be provided, or may be provided to each terminal through a dedicated message. The radio condition parameter may be the same as or different from the access indicator. Thereafter, the terminal checks the received CSG indicator and the CSG identifier to determine whether the corresponding cell is a cell to which it can access. If it is determined that access to the cell is impossible, the terminal checks the received access indicator to determine whether to allow access if the cell satisfies a radio condition. If the access indicator indicates that the connection can be allowed, the terminal performs a radio condition check to confirm the interference situation. If the radio condition check is satisfied, the terminal ignores the access limitation of the base station and considers the cell as an accessible cell and then starts accessing the cell.

 10 is an exemplary diagram illustrating a base station access process of a terminal accessing a CSG (Closed Subscriber Group) cell, which is not a member, during the handover process according to the present invention.

First, a terminal receives system information including a CSG indicator and a CSG identifier from an existing source base station. Thereafter, the terminal additionally receives information such as a radio condition parameter or an access indicator from a target base station to be handed over. Herein, the additionally received radio condition parameter or access indicator information may be included in the system information broadcast to the terminal and provided to the terminal, or may be provided to each terminal through a dedicated message. The radio condition parameter may be the same as or different from the access indicator. Thereafter, the terminal checks the received CSG indicator and the CSG identifier to determine whether the corresponding cell is a cell to which it can access. If it is determined that access to the cell is impossible, the terminal checks the received access indicator to determine whether to allow access if the cell satisfies a radio condition. If the access indicator indicates that the connection can be allowed, the terminal performs a radio condition check to confirm the interference situation. If the radio condition check is satisfied, the terminal ignores the access impossibility constraint of the base station and considers the corresponding cell as an accessible cell. Thereafter, after the additional messaging process for handover, the terminal starts accessing the corresponding cell.

Hereinafter, a terminal according to the present invention will be described.

The terminal according to the present invention includes all types of terminals that can use a service that can exchange data with each other over the air. That is, the terminal according to the present invention is a mobile communication terminal capable of using a wireless communication service (for example, user equipment (UE), mobile phone, cellular phone, DMB phone, DVB-H phone, PDA phone, and PTT phone, etc.) It is a comprehensive meaning including laptops, laptops, laptops, digital TVs, GPS navigation, handheld game consoles, MP3s, and other consumer electronics.

The terminal according to the present invention may include a basic hardware configuration (transmitter / receiver, processor or controller, storage, etc.) required to perform functions and operations for efficient system information reception illustrated in the present invention.

The method according to the invention described thus far can be implemented in software, hardware, or a combination thereof. For example, the method according to the present invention may be stored in a storage medium (eg, internal memory of a mobile terminal or base station, flash memory, hard disk, etc.), and may be stored in a processor (eg, mobile terminal or base station). Code or instructions within a software program that can be executed by an internal microprocessor).

In the above, the present invention has been described with reference to the embodiments shown in the drawings, which are merely exemplary and will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. . Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a network structure of E-UTRAN, which is a mobile communication system to which the present invention and the present invention are applied.

Figure 2 is an exemplary view showing a control plane structure of a radio interface protocol between the terminal and the E-UTRAN in the prior art.

3 is an exemplary diagram illustrating a user plane structure of a radio interface protocol between a terminal and an E-UTRAN in the prior art.

4 is an exemplary diagram illustrating a procedure for UE operation of selecting a cell in an idle mode.

 5 is an exemplary diagram illustrating a network structure of an E-UTRAN operating an H (e) NB using an H (e) NB gateway (GW).

6 is an exemplary view illustrating a method of confirming an access mode of a base station by a terminal according to the present invention.

7 is an exemplary diagram illustrating a procedure performed by a terminal in a cell in which access may be restricted according to the present invention.

8 is an exemplary view illustrating a procedure performed by a terminal in a closed subscriber group (CSG) cell in which access of a terminal other than a member may be restricted according to the present invention.

FIG. 9 is an exemplary diagram illustrating a base station access process of a terminal accessing a CSG (Closed Subscriber Group) cell that is not a member of a cell (re) selection process according to the present invention.

 10 is an exemplary diagram illustrating a base station access procedure of a terminal accessing a CSG (Closed Subscriber Group) cell, which is not a member, during the handover process according to the present invention.

Claims (11)

A method in which a terminal connects a cell in a wireless communication system, Determining whether access of the terminal to a specific cell is permitted or not; If it is determined that the terminal is not allowed to access the specific cell, checking the radio signal quality with respect to the specific cell; If the radio signal quality for the specific cell satisfies a specific radio condition, considering the specific cell as an accessible cell; And And connecting the terminal to the specific cell even if the terminal is not previously permitted to access the specific cell. The method of claim 1, wherein the radio signal quality is a downlink path loss value for the specific cell measured by the terminal. 3. The method of claim 2, wherein the specific radio condition is satisfied when the downlink loss value is larger than a threshold value. The wireless communication system of claim 2, wherein the specific radio condition is satisfied when a difference between the downlink loss value for the specific cell and the downlink loss value for the currently connected cell is greater than a threshold. Cell access method of a terminal on a mobile station. 3. The method of claim 2, wherein the threshold value is received through system information transmitted from a network managing the specific cell. 5. The method of claim 4, wherein the threshold is received through system information transmitted from a network managing the specific cell or the currently connected cell. The method of claim 1, wherein if the terminal is not a member of a closed subscriber group (CSG), the terminal is not allowed to access the specific cell. The method of claim 1, further comprising the step of receiving a CSG indicator and a CSG identifier from a network. The method of claim 8, wherein the connection of the specific cell is determined by checking the received CSG indicator and the CSG identifier. The method of claim 1, wherein all the steps are performed during a cell reselection process. The method of claim 1, wherein all the steps are performed during a handover process.

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