# Patent

## Title
Method of mitigating interference in mixed frequency

## Abstract

Disclosed is the radio (wireless) communication system providing a radio communication service and the terminal, and more particularly, to a method of releasing a restricted-access based on a network's setting and an interference situation measured by the terminal in an Evolved Universal Mobile Telecommunications System (E-UMTS) evolved from the Universal Mobile Telecommunications System (UMTS) or a Long Term Evolution (LTE) system.

## Background
RELATED APPLICATION
This application claims the benefit of and right of priority to U.S. Provisional Application No. 61/118,469, filed on Nov. 27, 2008, and Korean Application No. 10-2009-0104520, filed on Oct. 30, 2009, which is herein expressly incorporated by reference in its entirety.


TECHNICAL FIELD
The present invention relates to a radio (wireless) communication system providing a radio communication service and a terminal, and more particularly, to a method of releasing a restricted-access based on a network's setting and an interference situation measured by the terminal in an Evolved Universal Mobile Telecommunications System (E-UMTS) or a Long Term Evolution (LTE) system.
BACKGROUND ART
FIG. 1 is a view illustrating a network architecture of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), which is a mobile communication system to which the related art and the present invention are applied. The E-UTRAN system has evolved from the existing UTRAN system, and a basic standardization work thereof is currently going on in 3GPP. The E-UMTS system may be also referred to as a Long Term Evolution (LTE) system.
The E-UTRAN includes a plurality of e-NBs (e-NodeB; hereinafter, referred to as “base station”), and the plurality of eNBs are connected to one another through an X2 interface. The eNB is connected to user equipment (hereinafter, referred to as “UE”) via a wireless interface, and connected to an Evolved Packet Core (EPC) through an S1 interface.
The EPC may include a Mobility Management Entity (MME), a Serving-Gateway (S-GW), and a Packet Data Network-Gateway (PDN-GW). The MME has information on the connection of UE or the capability of UE, and such information is primarily used for the mobility management of the UE. The S-GW is a gateway having E-UTRAN as an end point, and the PDN-GW is a gateway having PDN as an end point.
The radio interface protocol layers between UE and a network can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based on three lower layers of an Open System Interconnection (OSI) reference model widely known in communications systems. A physical layer belonging to the first layer provides information transfer services using a physical channel, and a radio resource control (hereinafter, referred to as “RRC”) layer located at the third layer plays a role of controlling radio resources between UE and a network. For the purpose of this, the RRC layer exchanges RRC messages between UE and a network.
FIGS. 2 and 3 are views illustrating an architecture of a radio interface protocol between UE and a base station based on the 3GPP radio access network standard. The radio interface protocol horizontally includes a physical layer, a data link layer, and a network layer, and vertically divided into a user plane (U-plane) for transmitting data information and a control plane (C-plane) for transferring a control signaling. The protocol layers of FIGS. 2 and 3 can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based on three lower layers of an Open System Interconnection (OSI) reference model widely known in communications systems. Those radio protocol layers exist as a pair in the UE and the E-UTRAN to perform a data transmission for the radio section.
Hereinafter, each layer in a radio protocol control plane of FIG. 2 and a radio protocol user plane of FIG. 3 will be described.
The first layer as a physical layer provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to its upper layer, called a Medium Access Control (MAC) layer, via a transport channel, and data is transferred between the MAC layer and the physical layer via the transport channel. Furthermore, data is transferred via a physical channel between different physical layers, in other words, between the physical layer of a transmitting side and the physical layer of a receiving side. The physical channel is modulated by an Orthogonal Frequency Division Multiplexing (OFDM) scheme and time and frequency are used as radio resources for the channel.
The Medium Access Control (hereinafter, referred to as “MAC”) layer located at the second layer provides a service to its upper layer, called a Radio Link Control (hereinafter, referred to as “RLC”) layer, via a logical channel. The RLC layer of the second layer supports reliable data transmissions. The function of the RLC layer may be implemented as a functional block in the MAC layer. In this case, the RLC layer may not exist. A Packet Data Convergence Protocol (PDCP) layer of the second layer is used to efficiently transmit IP packets, such as IPv4 or IPv6, in the radio section having a relatively small bandwidth. For this purpose, the PDCP layer performs a header compression function for reducing the size of an IP packet header, which is relatively large in size and includes unnecessary control information.
A Radio Resource Control (hereinafter, referred to as “RRC”) layer located at the uppermost portion of the third layer is only defined in the control plane. The RRC layer takes charge of controlling logical channels, transport channels and physical channels in relation to the configuration, re-configuration and release of Radio Bearers (RBs). Here, the RB denotes a service provided by the second layer to perform a data transmission between the UE and the UTRAN. If an RRC connection is established between a RRC layer of the UE and a RRC layer of the UTRAN, then the UE is in an RRC_CONNECTED state. Otherwise, the UE is in an RRC_IDLE state.
Downlink transport channels for transmitting data from a network to UE may include a Broadcast Channel (BCH) for transmitting system information, and a downlink Shared Channel (SCH) for transmitting other user traffic or control messages. In case of traffic or control messages of a downlink multicast or broadcast service, they may be transmitted either via a downlink SCH, or via a separate downlink Multicast Channel (MCH). On the other hand, uplink transport channels for transmitting data from UE to a network may include a Random Access Channel (RACH) for transmitting an initial control message and an uplink Shared Channel (SCH) for transmitting user traffic or control messages.
Logical channels which are located at an upper level of transport channels and mapped to the transport channels may include a Broadcast Control Channel (BCCH), a Paging Control Channel (PCCH), a Common Control Channel (CCCH), a Multicast Control Channel (MCCH), a Multicast Traffic Channel (MTCH), and the like.
A physical channel includes multiple sub-frames arranged on a time axis and multiple sub-carriers arranged on a frequency axis. Here, a sub-frame includes a plurality of symbols on the time axis. A sub-frame includes a plurality of resource blocks each including a plurality of symbols and a plurality of sub-carriers. Also, each sub-frame can use particular sub-carriers of particular symbols (e.g., a first symbol) in the relevant sub-frame for a Physical Downlink Control Channel (PDCCH), that is, a L1/L2 control channel. A sub-frame has a time duration of 0.5 ms. A Transmission Time Interval (TTI) as a unit time for transmitting data is 1 ms, corresponding to two sub-frames.
Hereinafter, an RRC state and an RRC connection method of UE will be described in detail. The RRC state refers to whether or not the RRC of the UE is logically connected to the RRC of an E-UTRAN. If connected, then it is called an RRC_CONNECTED state, and otherwise it is called an TTC_IDLE state. For the UE in an RRC_CONNECTED state, the E-UTRAN can recognize the existence of the relevant UE in a cell unit because there exists an RRC connection thereof, and thus the E-UTRAN can effectively control the UE. On the contrary, for the UE in RRC_IDLE state, the E-UTRAN cannot recognize the relevant UE, and therefore, it is managed by a core network in a tracking area unit, which is a unit larger than a cell. In other words, the existence of the UE in an RRC_IDLE state is only recognized in a large area unit, and therefore, it should be changed to an RRC_CONNECTED state in order to receive typical mobile communication services such as voice or data.
When the UE is initially turned on by a user, the UE first searches for a suitable cell and then is camped in an RRC_IDLE state in the relevant cell. The UE camped in an RRC_IDLE state makes an RRC connection with the RRC of the E-UTRAN through an RRC connection procedure when it is required to make an RRC connection, thereby changing the state to an RRC_CONNECTED state. There are several cases when the UE in an idle state is required to make an RRC connection. For example, an uplink data transmission may be required due to a phone call attempt by the user, or the like, or the transmission of a response message may be required in response to a paging message received from the E-UTRAN.
The Non-Access Stratum (NAS) layer located at an upper level of the RRC performs a function such as session management, mobility management, and the like.
In order to manage the mobility of the UE at the NAS layer, both an EPS Mobility Management-REGISTERED (EMM-REGISTERED) state and an EMM-DEREGISTERED state are defined, and both states will be applied to the UE and a Mobility Management Entity (MME). The UE is initially in an EMM-DEREGISTERED state, and carries out a process of registering it into the relevant network through an ‘Initial Attach’ procedure in order to access a network. If this ‘Attach’ procedure has been successfully carried out, then the UE and the MME will be in an EMM-REGISTERED state.
In order to manage a signaling connection between the UE and the EPC, both an EPS Connection Management (ECM)-IDLE state and an ECM-CONNECTED state are defined, and the both states will be applied to the UE and the MME. If the UE in an ECM-IDLE state makes an RRC connection with E-UTRAN, then it will be in an ECM-CONNECTED state. If the MME in an ECM-IDLE state makes an S1 connection with E-UTRAN, then it will be in an ECM-CONNECTED state. When the UE is in an ECM-IDLE state, the E-UTRAN has no context information of the UE. Therefore, the UE in an ECM-IDLE state carries out a UE-based mobility procedure such as a cell selection or reselection without receiving a command from the network. On the contrary, when the UE is in an ECM-CONNECTED state, the mobility of the UE is managed by a command of the network. If the location of the UE in an ECM-IDLE state is changed from the location that has been recognized by the network, the UE performs a Tracking Area Update procedure to notify the network of the relevant location of the UE.
Next, system information will be described. The system information includes essential information for the UE to know in order to access a base station. Therefore, the UE should have received all of the system information prior to accessing the base station, and also should have the latest system information all the time. Furthermore, the base station periodically transmits the system information because the system information should be notified to every UE in a cell.
The system information can be divided into MIB, SB, SIB, and the like. The Master Information Block (MIB) allows the UE to be notified of a physical architecture of the relevant cell, for example, a bandwidth, and the like. The Scheduling Block (SB) notifies of the transmission information of SIBs, for example, transmission period, and the like. The System Information Block (SIB) is a set of mutually-related system information. For example, a certain SIB includes only the information of neighboring cells, and another certain SIB includes only the information of uplink radio channels used by the UE.
In the related art, if both a typical (or general) cell and a CSG (Closed Subscriber Group) cell, which allows to be accessed only for a particular subscriber group, are existed in a same frequency, an interference problem due to a restricted-access causes a great drawback for a service quality of both terminal (UE) and network (base station). For example, if the UE approaches to an access-restricted cell while the UE camps on the typical cell, the UE affects a great amount of interference to the access-restricted cell. Also, in this situation, the service quality of the UE is degraded due to the interferences caused by the access-restricted cell.
DISCLOSURE OF THE INVENTION
Therefore, an object of the present invention is to provide a method of releasing a restricted-access based on a network's setting and an interference situation measured by a terminal.
To achieve this and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a method of accessing a cell in wireless communication system, the method comprising: determining whether a particular cell is allowed to be accessed or not; checking a radio signal quality with respect to the particular cell if it is determined that the particular cell is not allowed to be accessed; considering the particular cell as an accessible cell if the radio signal quality with respect to the particular cell satisfies a certain radio condition; and accessing to the particular cell even if the particular cell was not previously allowed to be accessed.



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.
In the drawings:
FIG. 1 shows an exemplary network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as a mobile communication system to which a related art and the present invention are applied;
FIG. 2 shows an exemplary view of related art control plane architecture of a radio interface protocol between a terminal and an E-UTRAN;
FIG. 3 shows an exemplary view of related art user plane architecture of a radio interface protocol between a terminal and an E-UTRAN;
FIG. 4 is an exemplary view illustrating a procedure for the operation of UE selecting a cell in the idle mode;
FIG. 5 is an exemplary view illustrating a network architecture of E-UTRAN for managing H(e)NB by using an H(e)NB gateway (GW);
FIG. 6 is an exemplary view of checking an access mode of a base station according to the present invention;
FIG. 7 is an exemplary view illustrating a procedure performed by a terminal within an access-restricted cell according to the present invention;
FIG. 8 is an exemplary view illustrating a procedure performed by a terminal within a closed subscriber group (CSG) cell, which restricts an access for non-CSG member, according to the present invention;
FIG. 9 is an exemplary view illustrating an access procedure between a terminal and a base station when the terminal accesses to a non-CSG member cell during a cell selection or a cell reselection, according to the present invention; and
FIG. 10 is an exemplary view illustrating an access procedure between a terminal and a base station when the terminal accesses to a non-CSG member cell during a handover, according to the present invention.



MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS
One aspect of this disclosure relates to the recognition by the present inventors about the problems of the related art as described above, and further explained hereafter. Based upon this recognition, the features of this disclosure have been developed.
Although this disclosure is shown to be implemented in a mobile communication system, such as a UMTS developed under 3GPP specifications, this disclosure may also be applied to other communication systems operating in conformity with different standards and specifications.
Hereinafter, description of structures and operations of the preferred embodiments according to the present invention will be given with reference to the accompanying drawings.
One aspect of this disclosure relates to the recognition by the present inventors about the problems of the related art as described above, and further explained hereafter. Based upon this recognition, the features of this disclosure have been developed.
Although this disclosure is shown to be implemented in a mobile communication system, such as a UMTS developed under 3GPP specifications, this disclosure may also be applied to other communication systems operating in conformity with different standards and specifications.
The present invention may be applied to a 3GPP communication technology, particularly to a Universal Mobile Telecommunications System (UMTS), system, and a communication device and method thereof. However, the present invention is not limited to this, but may be applied to every wire/wireless communication to which technical spirit of the present invention can be applied.
According to a basic concept of the present invention, there is proposed a method of determining an access mode of a cell in a wireless communication and proposed a wireless mobile communication UE (or terminal) capable of performing such a method, which is characterized by including the steps of determining whether the access mode of the cell is a first mode, wherein one or more UEs in a particular subscriber group are only allowed to be accessed in the first mode; checking an existence of a subscriber group identity, if it is determined that the access mode of the cell is not the first mode; and considering the access mode of the cell as a second mode, if the subscriber group identity exists, wherein the one or more UEs in the particular subscriber group or all UEs in the cell are selectively allowed to be accessed in the second mode.
According to the present invention, furthermore, there is proposed a method of determining an access mode of a cell in a wireless communication and proposed a wireless mobile communication UE capable of performing such a method, which is characterized by including the steps of determining whether UE supports a particular access mode of the cell, wherein one or more UEs in a particular subscriber group or all UEs in the cell are selectively allowed to be accessed in the particular access mode; checking a subscriber group identity, if it is determined that the UE supports the particular access mode; and checking a subscriber group indicator in order to determine the access mode of the cell, if it is determined that the UE does not support the particular access mode.
According to the present invention, furthermore, there is proposed a method of determining an access mode of a cell in a wireless communication and proposed a network capable of performing such a method, which is characterized by including the steps of providing information and a subscriber group identity to the UE in order to determine the access mode of the cell, wherein the information indicates that the UE is not in a particular access mode, and the particular access mode only allows one or more UEs in a particular subscriber group to be accessed.
Hereinafter, the configuration and operation of preferred embodiments according to the present invention will be described with reference to the accompanying drawings.
In general, network services provided to UE can be divided into three types as follows. Furthermore, the UE may recognize the type of a cell differently based on which service can be received. First, the type of services will be described, and then the type of a cell will be described below.
1) Limited service: This service provides an emergency call and an earthquake and tsunami warning system (ETWS), and may be provided in an acceptable cell.
2) Normal service: This service denotes a public use with general purposes, and may be provided in a suitable or normal cell.
3) Operator service: This service denotes a service for communication network service providers, and this cell can be only used by communication network service providers but cannot be used by typical users.
With regard to the service types provided by a cell, the type of a cell can be divided as follows.
1) Acceptable cell: A cell in which the UE can receive a limited service. This cell is not barred and satisfies the cell selection criteria of the UE from a standpoint of the corresponding UE.
2) Suitable cell: A cell in which the UE can receive a normal service. This cell satisfies the condition of an acceptable cell, and at the same time satisfies additional conditions. For additional conditions, the cell should be attached to PLMN to which the corresponding UE can be accessed, and it should be a cell in which the implementation of a tracking area update procedure by the UE is not barred. If the relevant (or corresponding) cell is a CSG cell, then it should be a cell that can be accessed by the UE as a CSG member.
3) Barred cell: A cell broadcasting information that it is a barred cell through the system information.
4) Reserved cell: A cell broadcasting that it is a reserved cell through the system information.
FIG. 4 is an exemplary view illustrating the operation of UE selecting a cell in the idle mode.
In the first step, the UE selects a Radio Access Technology (hereinafter, referred to as “RAT”) for communicating with a Public Land Mobile Network (hereinafter, referred to as “PLMN”) from which the UE itself desires to receive a service. The information of PLMN and RAT may be selected by the user of the UE, and what is stored in the USIM may be also used.
In the second step, the UE selects a cell having the largest value among the cells that the measured base station has a value greater than a particular value in the signal intensity and quality (cell selection). Then, it receives SI being sent by the base station. The particular value denotes a value defined by a system to guarantee the quality of physical signals in the data transmission and/or reception. Accordingly, the value may vary based on the RAT to be applied.
In the third step, the UE registers its own information (for example, IMSI) for receiving a service (for example, paging) from a network. Here, the UE is not registered into a network to be accessed whenever selecting a cell but registered into a network in case when network information received from SI (for example, Tracking Area Identity (TAI)) is different from network information that the UE itself knows.
In the fourth step, if a value of the signal intensity and quality measured by the base station from which the UE receives a service is less than a value measured by the base station of the neighboring cell, then the UE selects one of the other cells providing signals having better characteristics than those of the cell of the base station being accessed by the UE. This process is called a cell reselection to distinguish it from an initial cell selection in the second step. At this time, a time restriction condition may be specified in order to prevent a cell from being frequently reselected based on the change of the signal characteristics.
Next, a procedure for selecting a cell by the UE will be described in detail. If the UE is turned on, then the UE should perform preparation procedures for selecting a cell having a suitable quality in order to receive a service.
The UE in a RRC_IDLE state should select a cell having a suitable quality all the time, and thus be prepared to receive a service through the cell. For example, the UE that has been just turned on should select a cell having a suitable quality to be registered into a network. If the UE that has been in a RRC_CONNECTED state enters into an RRC_IDLE state, then the UE should select a cell in which the UE itself is camped on. In this manner, a process of selecting a cell satisfying a predetermined condition by the UE in order to be camped in a service waiting state such as the RRC_IDLE state, is called a cell selection. The cell selection is performed in a state that the UE does not currently determine a cell in which the UE itself is camped in the RRC_IDLE state, and thus it is very important to select the cell as quickly as possible. Therefore, if it is a cell providing a radio signal quality greater than a predetermined level, then it may be selected during a cell selection process by the UE even though the cell is not a cell providing best radio signal quality.
Hereinafter, a method and procedure for selecting a cell by LTE UE will be described in detail. If power is initially turned on, the UE searches for available PLMNs and selects a suitable PLMN to receive a service. Subsequently, the UE selects a cell having a signal quality and characteristic capable of receiving a suitable service among the cells being provided by the selected PLMN. Here, the cell selection process can be largely divided into two types. One type is an initial cell selection process, and in this process, the UE does not have previous information on radio channels. Therefore, the UE searches for all the radio channels to find a suitable cell. In each channel, the UE searches for the strongest cell. Subsequently, if a suitable cell satisfying the cell selection criteria is found, then the UE selects the corresponding cell. The other type is a cell selection process using the stored information, and in this process, the UE uses information on radio channel stored in the UE, or selects a cell by using information being broadcasted from the cell. Accordingly, a cell may be quickly selected compared to an initial cell selection process. If a cell satisfying the cell selection criteria is found, then the UE selects the corresponding cell. If a cell satisfying the cell selection criteria is not found, then the UE performs an initial cell selection process.
The cell selection criteria used by the UE in the cell selection process may be represented by the formula in the following Table 1.







TABLE 1





Criteria for selecting a cell by the UE in LTE.















Cell selection criteria: Srxlev > 0


Here, Srxlev = Qrxlevmeas − (Qrxlevmin + Qrxlevminoffset) − Pcompensation









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

    
    
        Qrxlevmeas Measured cell received level (RSRP)
        Qrxlevmin Minimum required received level in the cell (dBm)
        Qrxlevminoffset Offset to Qrxievmin (offset)
        Pcompensation max(PEMAX−PUMAX, 0) (dB)
        PEMAX Maximum transmission power allowed for the UE in the corresponding cell (dBm)
        PUMAX Maximum transmission power of the UE radio transmission unit (RF) based on the performance of the UE (dBm)
    
    


In the above Table 1, it may be seen that UE selects a cell having a value of the measured signal intensity and quality greater than a particular value specified by the cell providing a service. Furthermore, the parameters used in the above Table 1 are broadcasted via the system information, and the UE receives those parameter values to use them for the cell selection criteria.
If the UE selects a cell satisfying the cell selection criteria, then the UE receives the information required for the RRC_IDLE mode operation of the UE in the corresponding cell from the system information of the corresponding cell. The UE receives all the information required for the RRC_IDLE mode operation, and then waits in an idle mode to request a service (for example, originating call) to a network or receive a service (for example, terminating call) from a network.
After the UE selects a certain cell via a cell selection process, the signal intensity and quality between the UE and the base station may be changed due to the change of the UE mobility and wireless environment. Therefore, if the quality of the selected cell is deteriorated, then the UE may select another cell providing better quality. In this manner, if a cell is reselected, then a cell providing signal quality better than that of a currently selected cell is typically selected. This process is called a cell reselection. A basic object of the cell reselection process is typically to select a cell providing best quality to the UE from a standpoint of the radio signal quality. In addition to the standpoint of the radio signal quality, the network may notify the UE of its priority by determining it for each frequency. The UE that has received the priority may consider this priority in the first place than the radio signal quality criteria during the cell reselection process.
As described above, there is a method of selecting or reselecting a cell based on the signal characteristics of wireless environment. When reselecting a cell, in selecting a cell for the reselection, there may be cell reselection methods as described below, based on the radio access technology (hereinafter, referred to as “RAT”) and frequency characteristics of a cell.

    
    
        Intra-frequency reselection: A cell having a center-frequency similar to the RAT similar to the cell currently being used by the UE is reselected.
        Inter-frequency reselection: A cell having a center-frequency different from the RAT similar to the cell currently being used by the UE is reselected.
        Inter-REAT cell reselection: A cell using a different RAT from the RAT currently being used by the UE is reselected.
    
    


On the other hand, 3G or Evolved Packet System (EPS) services may be provided via a base station owned by a private person, particular service provider, or group in addition to a mobile communication service provider. Such a base station is called a Home Node B (HNB) or Home eNB (HeNB). Hereinafter, both the HNB and HeNB are commonly designated as an H(e)NB. An object of the H(e)NB is basically to provide specialized services only to a Closed Subscriber Group (CSG). However, those services may be provided to other users in addition to the CSG based on the operation mode setting of the H(e)NB.
FIG. 5 is an exemplary view illustrating a network architecture of E-UTRAN for managing an H(e)NB by using an H(e)NB gateway (GW).
As illustrated in FIG. 5, HeNBs may be connected to EPC via HeNB GW or directly connected to EPC. Here, the HeNB GW is regarded as a typical eNB to MME. Also, the HeNB GW is regarded as the MME to the HeNB. Therefore, an Si interface is connected between HeNB and HeNB GW, and also an Si interface is connected between the HeNB GW and the EPC. Furthermore, even in case of directly connecting between HeNB and EPC, it is connected via an Si interface. The function of HeNB is almost similar to the function of a typical eNB.
In general, H(e)NB has a low radio transmission output power compared to (e)NB owned by mobile communication service providers. Therefore, the service coverage provided by H(e)NB is typically smaller than the service coverage provided by (e)NB. Due to such characteristics, the cell provided by H(e)NB is classified as a femto cell in contrast to a macro cell provided by (e)NB from a standpoint of the service coverage. On the other hand, from a standpoint of provided services, when H(e)NB provides those services only to a CSG group, the cell provided by this H(e)NB is referred to as a CSG cell.
Each CSG has its own identification number, and this identification number is called a CSG ID (CSG identity). The UE may have a CSG list to which the UE itself belongs as a member thereof, and this CSG list may be changed by a request of the UE or a command of the network. Typically, one H(e)NB may support one CSG.
H(e)NB delivers the CSG ID of the CSG being supported by itself through the system information, thereby allowing only the corresponding CSG member UE to be accessed. When a CSG cell is found by the UE, what type of CSG being supported by this CSG cell can be checked by reading the CSG ID included in the system information. The UE that has read the CSG ID regards the corresponding cell as an accessible cell only if the UE itself is a member of the corresponding CSG cell.
It is not always required for H(e)NB to allow only the CSG UE to be accessed. Based on the configuration setting of H(e)NB, non-CSG member UE may be allowed to be accessed. The type of UE allowed to be accessed may be changed based on the configuration setting of H(e)NB. Here, the configuration setting denotes the setting of the operation mode of H(e)NB. The operation mode of H(e)NB can be divided into three types as follows based on the type of UE.
1) Closed access mode: A mode in which services are provided to particular CSG members only. A CSG cell is provided by H(e)NB.
2) Open access mode: A mode in which services are provided without any restriction of particular CSG members like typical (e)NB.
3) Hybrid access mode: A mode in which CSG services are provided to particular CSG members and also services are provided to non-CSG members like a typical cell. It is recognized as a CSG cell for the CSG member UE, and recognized as a typical cell for the non-CSG member UE. This cell is called a hybrid cell.
H(e)NB notifies the UE that the cell being serviced by itself is a CSG cell or typical cell, allowing the UE to know whether or not it can be accessed to the corresponding cell. H(e)NB being managed in a closed access mode broadcasts via the system information that it is a CSG cell. In this manner, H(e)NB allows the system information to include an one-bit CSG indicator indicating whether or not the cell being serviced by itself is a CSG cell in the system information. For example, the CSG cell broadcasts by setting the CSG indicator to TRUE. If the cell being serviced is not a CSG cell, then it may be used a method that the CSG indicator may be set to FALSE or the transmission of the CSG indicator is omitted. The UE should distinguish a typical cell provided by (e)NB from a CSG cell, and thus a typical (e)NB may also transmit the CSG indicator (for example, FALSE), thereby allowing the UE to know that the cell type provided by itself is a typical cell. Furthermore, the typical (e)NB may not transmit the CSG indicator, thereby allowing the UE to know that the cell type provided by itself is a typical cell, too. The CSG-related parameters transmitted by the corresponding cell for each cell type are represented in Table 2. Subsequently, the types of UE allowed to be accessed for each cell type are represented in Table 3.







TABLE 2







CSG-related parameters included in the system information for each


cell type










CSG Cell
Typical Cell















CSG Indicator
‘CSG Cell’ is indicated
‘Non-CSG cell’ is





indicated, or not





transmitted



CSG Identity
Supported CSG identity
Not transmitted




is transmitted

















TABLE 3







Type of UE allowed to be accessed for each cell type










CSG Cell
Typical Cell















UE not supporting CSG
Access disabled
Access enabled



Non-CSG member UE
Access disabled
Access enabled



CSG member UE
Access enabled
Access enabled










FIG. 6 is a first exemplary view illustrating a method of checking the access mode of a base station by the UE according to the present invention.
In the first step, the UE first checks the CSG indicator in the system information of the object cell in order to check the type of the object cell. After checking the CSG indicator, and then in the second step, if the CSG indicator indicates that the object cell is a CSG cell, then the UE recognizes the corresponding cell as a CSG cell. Subsequently, the UE checks the CSG identity or CSG identifier in the system information in order to check whether or not the UE itself is a CSG member of the object cell. If it is checked from the CSG identity that the UE is a CSG member of the object cell, then the corresponding cell will be recognized as an accessible CSG cell.
If it is checked from the CSG identity that the UE is not a CSG member of the object cell, then the corresponding cell will be recognized as an inaccessible CSG cell. If the CSG indicator indicates that the object cell is not a CSG cell in the first step, then the UE recognizes the object cell as a typical cell. Furthermore, if the CSG indicator is not transmitted in the first step, the UE recognizes the object cell as a typical cell.
In general, CSG cells and macro cells may be concurrently managed at a particular frequency. This frequency is called a mixed carrier frequency. The network may reserve particular physical layer CSG identities in a mixed carrier frequency for CSG cells. The physical layer CSG identity is called a Physical Cell Identity (PCI) in E-UTRAN, and called a Physical Scrambling Code (PSC) in UTRAN. For the sake of convenience of explanation, the physical layer CSG identity will be expressed by PCI. In a mixed carrier frequency, the CSG cell notifies information on the PCIs reserved for CSG at a current frequency via the system information. The UE received this information can determine whether or not this cell is a CSG cell from the PCI of the cell when a certain cell is found at the corresponding frequency. How this information being used by the UE will be illustrated below in case of two types of UE.
First, in case of the UE, not supporting the CSG-related function or having no CSG list to which the UE itself belongs, the UE does not need to regard a CSG cell as a selectable cell during the cell selection/reselection process. In this case, the UE checks only the PCI of the cell, and then the UE may immediately eliminate the corresponding cell during the cell selection/reselection process if the PCI is a reserved PCI for CSG. Typically, the PCI of a certain cell may be immediately known during a process of checking the existence of the corresponding cell in a physical layer by the UE.
Second, in case of the UE having a CSG list to which the UE itself belongs, when the UE wants to know a list of the neighboring CSG cells at a mixed carrier frequency it may be known that the corresponding cell is a CSG cell if only a cell having the PCI reserved for CSG is found, instead of individually checking the CSG identity of the system information of every cell found in the whole PCI range.
In general, if a macro cell and a CSG cell are existed in same frequency such as a mixed frequency, signal interference may cause a great problem for a service quality of both a terminal and a base station. For example, if the terminal approaches to a restricted-access CSG cell while the terminal is connected with the macro cell, the terminal affects a great interference to a corresponding CSG cell. Namely, if the access restricted terminal is approaching to the corresponding CSG cell step by step, an uplink quality of the corresponding cell is getting worst due to the interference by the access restricted terminal. Also, a service quality of terminal itself is getting worst due to interference by the corresponding CSG cell. Under a certain circumstance, if the terminal keeps approaching to the CSG cell while the access to the CSG cell is still restricted, a communication link of the terminal may be terminated because the terminal is no longer able to receive a proper service data from the macro cell.
Namely, if there are many CSG cell, which restricts an access of the terminal (i.e., non-CSG member terminal), within the macro cell, the service quality of terminal may be degraded whenever the terminal approaches to the CSG cell. The quality of the corresponding CSG cell may also be degraded because the uplink reception signal quality becomes bad due to the interference by the terminal.
Therefore, the present invention may propose to permit or release a terminal's restricted-access if the terminal satisfies a certain radio condition, thereby minimizing or eliminating the interference effect on the corresponding cell by the terminal. Here, the certain radio condition may be satisfied when a downlink path loss value, which measured with respect to the terminal's access-restricted cell, is greater than a certain threshold value. In addition, the certain radio condition may be satisfied when an offset value between the downlink path loss value measured with respect to the terminal's access-restricted cell and a downlink path loss value measure with respect to terminal's current access cell, is greater than a certain threshold value. The above certain threshold value may be broadcasted to all terminals via system information or may be transmitted to each individual terminal respectively. Here, the above certain threshold value may be transmitted from a base station that restricts the access of the terminal or may be transmitted from a base station that currently accesses with the terminal.
Also, the base station restricting the access of the terminal, may transmit an access indicator to the terminal such that the terminal may identify a corresponding cell satisfying the certain radio condition as an access enabled cell if the access indicator is transmitted. If the base station transmits the access indicator and a value of the access indicator is set to ignore the restricted-access based on the certain radio condition, the terminal may identify a corresponding cell satisfying the certain radio condition as an access enabled cell. If the base station does not transmit the access indicator, the terminal may be not accessed to the corresponding cell regardless of the certain radio condition. If the base station transmits the access indicator and a value of the access indicator is set to restrict the terminal's access, the terminal may be not accessed to the corresponding cell regardless of the certain radio condition. Here, the access indicator may be the threshold value.
The access restriction applied to the terminal may be a restricted-access to a non-CSG member terminal. If the terminal satisfying the certain radio condition is accessing to the access-restricted cell, the network (base station) may allow an access of the corresponding terminal exceptionally. The above procedure may be applied during a cell (re)selection or a handover of the terminal.
FIG. 7 is an exemplary view illustrating a procedure performed by a terminal within an access-restricted cell according to the present invention.

    
    
        First, the terminal may determine whether a corresponding cell is capable to restrict an access of the terminal. Here, such determination may be made by system information of the corresponding cell. Thereafter, the terminal identifies the corresponding cell as an access enabled cell if it is determined that the corresponding cell does not restrict the access of the terminal. However, if it is determined that the corresponding cell does restrict the access of the terminal, the terminal may exam a radio condition with respect to the corresponding cell in order to check an interference situation. If the radio condition with respect to the corresponding cell is satisfied, the terminal identifies the corresponding cell as an access enabled cell. In case that the radio condition with respect to the corresponding cell is not satisfied, the terminal identifies the corresponding cell as an access disabled cell and the terminal does not attempt to make a connection to the corresponding cell.
    
    


Here, if the above procedure is happened by the terminal during a cell (re)selection, after identifying step, the terminal may transmit a certain message or information to notify a network (base station) that the radio condition is satisfied. Here, the certain message or information may be transmitted to the network using a connection (re)setup request message.
Also, if the above procedure is happened by the terminal during a handover process, after identifying step, the terminal may transmit a certain message or information to notify a network (base station) that the radio condition is satisfied. Here, the certain message or information may be transmitted to the network using a handover complete message.
FIG. 8 is an exemplary view illustrating a procedure performed by a terminal within a closed subscriber group (CSG) cell, which restricts an access for non-CSG member, according to the present invention.
As illustrated in FIG. 8, the terminal may check a CSG indicator included in system information of a corresponding cell in order to determine a cell type of the corresponding cell. If the CSG indicator indicates that the corresponding cell is a CSG cell, the terminal identifies the corresponding cell as the CSG cell, and then the terminal may check a CSG identity included in the system information in order to determine whether the terminal is a CSG member of the corresponding cell. After checking of the CSG identity, if it is determined that the terminal is the CSG member of the corresponding cell, the terminal may identifies the corresponding cell as a member CSG cell. If it is determined that the terminal is not the CSG member after checking of the CSG identity, according to the present invention, the terminal may exam a radio condition with respect to the corresponding cell in order to check an interference situation. If the radio condition with respect to the corresponding cell is satisfied, the terminal identifies the corresponding cell as an access enabled cell. In case that the radio condition with respect to the corresponding cell is not satisfied, the terminal identifies the corresponding cell as an access disabled cell. During the above procedure, if the CSG indicator indicates that the corresponding cell is not the CSG cell, the terminal may identify the corresponding cell as a typical cell. Also, if the terminal perceives that the CSG indicator is not being transmitted (i.e., timeout), the terminal may also identify the corresponding cell as the typical cell.
Here, if the above procedure is happened by the terminal during a cell (re)selection, after identifying the corresponding cell as the access enabled cell, the terminal may transmit a certain message or information to notify a network (base station) that the radio condition is satisfied. Here, the certain message or information may be transmitted to the network using a connection (re)setup request message.
Also, if the above procedure is happened by the terminal during a handover process, after identifying the corresponding cell as the access enabled cell, the terminal may transmit a certain message or information to notify a network (base station) that the radio condition is satisfied. Here, the certain message or information may be transmitted to the network using a handover complete message.
FIG. 9 is an exemplary view illustrating an access procedure between a terminal and a base station when the terminal accesses to a non-CSG member cell during a cell selection or a cell reselection, according to the present invention.
Firstly, the terminal may receive system information including a CSG indicator and/or a CSG identity. Thereafter, the terminal may additionally receive information relating to an access indicator and/or radio condition parameter(s). Here, the additionally information may be transmitted to the terminal via same system information including the CSG indicator and/or the CSG identity, or the additionally information may be transmitted to the terminal via different system information or signals. Also, the additional information may be provided to the terminal via a dedicated message from a network (base station). Here, the radio condition parameter(s) may be identical to the access indicator or may be different from the access indicator. The terminal may determine whether or not a corresponding cell is an accessible cell by checking the received CSG indicator and CSG identity. If it is determined that the corresponding is not-accessible cell, by checking the access indicator, the terminal may further determine whether the corresponding cell permits the access of terminal depending upon the radio condition. If the access indicator indicates that the access of the terminal is based on the radio condition, then the terminal may exam the radio condition for checking an interference situation. After the examination of the radio condition, the terminal may identify the corresponding cell as an access enabled cell if the radio condition is satisfied. Thereafter, the terminal may start to perform an access procedure with the base station.
FIG. 10 is an exemplary view illustrating an access procedure between a terminal and a base station when the terminal accesses to a non-CSG member cell during a handover, according to the present invention.
Firstly, the terminal may receive system information including a CSG indicator and/or a CSG identity. Thereafter, the terminal may additionally receive information relating to an access indicator and/or radio condition parameter(s) from a target base station. Here, the additionally information may be transmitted to the terminal via same system information including the CSG indicator and/or the CSG identity, or the additionally information may be transmitted to the terminal via different system information or signals. Also, the additional information may be provided to the terminal via a dedicated message from a network (base station). Here, the radio condition parameter(s) may be identical to the access indicator or may be different from the access indicator. The terminal may determine whether or not a corresponding cell is an accessible cell by checking the received CSG indicator and CSG identity. If it is determined that the corresponding is not-accessible cell, by checking the access indicator, the terminal may further determine whether the corresponding cell permits the access of terminal depending upon the radio condition. If the access indicator indicates that the access of the terminal is based on the radio condition, then the terminal may exam the radio condition for checking an interference situation. After the examination of the radio condition, the terminal may identify the corresponding cell as an access enabled cell if the radio condition is satisfied. Thereafter, the terminal may start to perform an access procedure with the base station after additional messaging procedure for the handover.
Accordingly, the present invention may provide a solution to minimize or eliminate the interference causing by the terminal when the terminal approaches to an access-restricted cell such as a CSG cell that the terminal is not belonged as a CSG member. According to the present invention, an uplink quality of the corresponding cell of the base station and a service quality of the terminal may also be significantly improved. After permitting the access of the terminal by the base station, the base station may continuously allow the access of the terminal or the base station may order the terminal to access into other cell in a different frequency. Further, the base station may control a terminal's performance relating to the access of the cell.
The present invention may provide a method of accessing a cell in wireless communication system, the method comprising: determining whether a particular cell is allowed to be accessed or not; checking a radio signal quality with respect to the particular cell if it is determined that the particular cell is not allowed to be accessed; considering the particular cell as an accessible cell if the radio signal quality with respect to the particular cell satisfies a certain radio condition; accessing to the particular cell even if the particular cell was not previously allowed to be accessed, and receiving a CSG indicator and a CSG identity from a network, wherein the radio signal quality is a downlink path loss value with respect to the particular cell measured by a terminal, the certain radio condition is satisfied if the downlink path loss value is greater than a threshold value, the certain radio condition is satisfied if a difference value between the downlink path loss value with respect to the particular cell and a downlink path loss value with respect to a currently accessed cell is greater than a threshold value, the threshold value is received through system information transmitting from a network that manages the particular cell, the threshold value is received through system information transmitting from a network that manages the particular cell or the currently accessed cell, the particular cell is not allowed to be accessed if a terminal is not a closed subscriber group (CSG) member, the accessibility of the particular cell is determined by checking the received CSG indicator and CSG identity, the all steps are performed during a cell reselection procedure, and the all steps are performed during a handover procedure.
Although the present disclosure is described in the context of mobile communications, the present disclosure may also be used in any wireless communication systems using mobile devices, such as PDAs and laptop computers equipped with wireless communication capabilities (i.e. interface). Moreover, the use of certain terms to describe the present disclosure is not intended to limit the scope of the present disclosure to a certain type of wireless communication system. The present disclosure is also applicable to other wireless communication systems using different air interfaces and/or physical layers, for example, TDMA, CDMA, FDMA, WCDMA, OFDM, EV-DO, Wi-Max, Wi-Bro, etc.
The exemplary embodiments may be implemented as a method, apparatus or article of manufacture using standard programming and/or engineering techniques to produce software, firmware, hardware, or any combination thereof. The term “article of manufacture” as used herein refers to code or logic implemented in hardware logic (e.g., an integrated circuit chip, Field Programmable Gate Array (FPGA), Application Specific Integrated Circuit (ASIC), etc.) or a computer readable medium (e.g., magnetic storage medium (e.g., hard disk drives, floppy disks, tape, etc.), optical storage (CD-ROMs, optical disks, etc.), volatile and non-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs, SRAMs, firmware, programmable logic, etc.).
Code in the computer readable medium may be accessed and executed by a processor. The code in which exemplary embodiments are implemented may further be accessible through a transmission media or from a file server over a network. In such cases, the article of manufacture in which the code is implemented may comprise a transmission media, such as a network transmission line, wireless transmission media, signals propagating through space, radio waves, infrared signals, etc. Of course, those skilled in the art will recognize that many modifications may be made to this configuration without departing from the scope of the present disclosure, and that the article of manufacture may comprise any information bearing medium known in the art.
As the present disclosure may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.

## Claims

1. A method of accessing a cell in a wireless communication system, the method comprising:
receiving a Closed Subscriber Group (CSG) indicator and a CSG identity via first system information from a network;
determining whether a particular cell is allowed to be accessed by checking the received CSG indicator and the CSG identity;
checking a radio signal quality with respect to the particular cell for an interference situation if it is determined that the particular cell is not allowed to be accessed;
considering the particular cell as an accessible cell if the radio signal quality with respect to the particular cell satisfies a certain radio condition; and
accessing the particular cell even if the particular cell was not previously allowed to be accessed,
wherein the radio signal quality is a downlink path loss value with respect to the particular cell measured by a terminal,
wherein the certain radio condition is satisfied if a difference between the downlink path loss value with respect to the particular cell and a downlink path loss value with respect to a currently accessed cell is greater than a threshold value,
wherein the threshold value is received via second system information from a network that manages the particular cell or the currently accessed cell,
wherein the first system information is different from the second system information, and
wherein the particular cell is recognizable by the terminal as a CSG cell if the terminal is a CSG member and is recognizable by the terminal as a typical cell if the terminal is not a CSG member.

2. The method of claim 1, wherein the particular cell is not allowed to be accessed if the terminal is not a CSG member.

3. The method of claim 1, wherein the method is performed during a cell reselection procedure.

4. The method of claim 1, wherein the method is performed during a handover procedure.