Method and apparatus for cell selection in a wireless communication system

The present invention relates to a method for cell selection in a wireless communication system. The method for cell selection by a terminal according to one embodiment of the present invention may comprise the following steps: measuring the channel quality of a first cell; measuring the channel quality of a second cell; determining whether the value obtained by applying an offset to the result of the measurement of the channel quality of the second cell is better than the result of the measurement of the channel quality of the first cell; if the value obtained by applying an offset to the result of the measurement of the channel quality of the second cell is better than the result of the measurement of the channel quality of the first cell, determining whether the value obtained by applying no offset to the result of the measurement of the channel quality of the second cell is better than a preset reference value; and, if the value obtained by applying no offset to the result of the measurement of the channel quality of the second cell is better than the preset reference value, selecting the second cell. According to one embodiment of the present invention, an operable cell can be selected to prevent malfunctions, and interference from a CSG cell may be reduced.

TECHNICAL FIELD

The present invention relates to a wireless communication system and, in particular, to a cell reselection method and a method for reporting interference of non-Closed Subscriber Group (non-CSG) cells in a Long Term Evolution (LTE) system.

BACKGROUND ART

Recently, the wireless communication technology has developed rapidly along with the advance of communication system technology, and the LTE system is one of the prominent 4thGeneration mobile communication systems.

The LTE system adopts various advanced functions. For example, the LTE system supports heterogeneous network (hereinafter, referred to as HetNet) capable of accommodating the situation where the macro eNBs having relatively large coverage for dynamic eNB/cell deployment adoptive to various situation and supporting CSG cells for providing service to the restricted users.

In order to support the HetNet structure, the current standard is designed to select a pico cell with priority, even when the signal quality of the pico cell is bad, by ignoring the difference as much as the offset/bias applied to the pico cell in cell reselection. However, although the pico cell is selected with the offset/bias, if the pico cell of which signal is too bad to perform communication is selected, this causes problem. That is, the pico cell which selected with the advantage of the offset/bias value but of which signal strength is too bad to perform communication causes problem.

In the situation where the CSG cell and other cells coexist in the network, if the UE is not a member of the CSG cell, it may detects the signal of the CSG cell which is storing enough but cannot connects the corresponding cell.

FIG. 1is diagram illustrating a heterogeneous network structure. InFIG. 1, the UE305cannot communicate with the CSG cell303although it is close to the CSG cell303physically. In this case, the UE305has to attempt connection to the macro eNB301but it is difficult to communicate with the macro eNB301due to the strong interference signal from the CSG cell303.

DISCLOSURE OF INVENTION

Technical Problem

The present invention has been conceived to solve the above problem and aims to provide a method for selecting a best cell in the HetNet scenario and a method for a UE which is not a member of the CSG cell to report interference of the CSG cell in the situation where the CSG and other cells in a wireless mobile communication system.

Solution to Problem

In accordance with an aspect of the present invention, a cell selection method of a terminal includes measuring channel quality of a first cell,

measuring channel quality of a second cell, determining whether a value obtained by applying an offset to the channel quality of the second cell is greater than the channel quality of the first cell, determining, when the value obtained by applying an offset to the channel quality of the second cell is greater than the channel quality of the first cell, the channel quality of the second cell without application of the offset is greater than a predetermined threshold, and selecting, when the channel quality of the second cell without application of the offset is greater than a predetermined threshold, the second cell.

In accordance with another aspect of the present invention, a scheduling method of a base station includes receiving a connection setup message or a connection reestablishment message from a terminal, determining whether the connection setup message or the connection reestablishment message includes an indicator notifying of existence of interference from other cell, and scheduling, when the connection setup message or the connection reestablishment message includes an indicator, resource for the terminal in consideration of the interference.

In accordance with another aspect of the present invention, a terminal includes a controller which measures channel qualities of a first and second cells and determines whether a value obtained by applying an offset to the channel quality of the second cell is greater than the channel quality of the first cell. The controller determines, when the value obtained by applying an offset to the channel quality of the second cell is greater than the channel quality of the first cell, the channel quality of the second cell without application of the offset is greater than a predetermined threshold. The controller selects, when the channel quality of the second cell without application of the offset is greater than a predetermined threshold, the second cell.

In accordance with still another aspect of the present invention, a base station includes a transceiver which receives a connection setup message or a connection reestablishment message from a terminal, a controller which determines whether the connection setup message or the connection reestablishment message includes an indicator notifying of existence of interference from other cell, and a scheduler which schedules, when the connection setup message or the connection reestablishment message includes an indicator, resource for the terminal in consideration of the interference.

Advantageous Effects of Invention

The cell selection method and apparatus of the present invention is capable of selecting a communication-available cell in the situation where the offset/bias is applied in the HetNet situation to as to continue communication and controlling interference of the corresponding CSG efficiently by reporting the interference from the non-CSG cell

MODE FOR THE INVENTION

Detailed description of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention. Exemplary embodiments of the present invention are described with reference to the accompanying drawings in detail.

FIG. 2is a diagram illustrating the architecture of an LTE system to which the present invention is applied.

Referring toFIG. 2, the radio access network of the mobile communication system includes evolved Node Bs (eNBs)105,110,115, and120, a Mobility Management Entity (MME)125, and a Serving-Gateway (S-GW)130. The User Equipment (hereinafter, referred to as UE)135connects to an external network via eNBs105,110,115, and120and the S-GW130.

InFIG. 2, the eNBs105,110,115, and120corresponds to the legacy node Bs of the UMTS system. The eNBs105,110,115, and120allow the UE to establish a radio link and are responsible for complicated functions as compared to the legacy node B. In the LTE system, all the user traffic including real time services such as Voice over Internet Protocol (VoIP) are provided through a shared channel and thus there is a need of a device which is located in the eNB to schedule data based on the state information such as UE buffer conditions, power headroom state, and channel state. Typically, one eNB controls a plurality of cells. In order to secure the data rate of up to 100 Mbps, the LTE system adopts Orthogonal Frequency Division Multiplexing (OFDM) as a radio access technology. Also, the LTE system adopts Adaptive Modulation and Coding (AMC) to determine the modulation scheme and channel coding rate in adaptation to the channel condition of the UE. The S-GW130is an entity to provide data bearers so as to establish and release data bearers under the control of the MME125. MME125is the entity responsible for various control functions as well as UE mobility management and connected to a plurality of eNBs.

FIG. 3is a diagram illustrating a protocol stack of the LTE system to which the present invention is applied.

Referring toFIG. 3, the protocol stack of the LTE system includes Packet Data Convergence Protocol (PDCP)205and240, Radio Link Control (RLC)210and235, Medium Access Control (MAC)215and230, and Physical (PHY)220and225. The PDCP205and240is responsible for IP header compression/decompression, and the RLC210and235is responsible for segmenting the PDCP Protocol Data Unit (PDU) into segments in an appropriate size. The MAC215and230is responsible for establishing connection to a plurality of RLC entities so as to multiplex the RLC PDUs into MAC PDUs and demultiplex the MAC PDUs into RLC PDUs. The PHY220and225performs channel coding on the MAC PDU and modulates the MAC PDU into OFDM symbols to transmit over radio channel or performs demodulating and channel-decoding on the received OFDM symbols and delivers the decoded data to the higher layer. Also, the PHY layer uses Hybrid ARQ (HARQ) for additional error correction by transmitting 1 bit information indicating for positive or negative acknowledgement from the receiver to the transmitter. This is referred to as HARQ ACK/NACK information. The downlink HARQ ACK/NACK corresponding to the uplink transmission is carried by Physical Hybrid-ARQ Indicator Channel (PHICH), and the uplink HARQ ACK/NACK corresponding to downlink transmission is carried Physical Uplink Control Channel (PUCCH) or Physical Uplink Shared Channel (PUSCH).

FIG. 4is a signal flow diagram illustrating a cell reselection procedure according to an embodiment of the present invention.

Referring toFIG. 4, it is assumed that the UE401is in the state of monitoring the signal of the macro cell403, i.e. camped on the macro cell403, before step411. Also, it is assumed that one or more pico cells405are deployed within the macro cell403in the similar way toFIG. 1. That is, the picocell405is installed instead of the CSG cell303ofFIG. 1.

The UE401receives the system information broadcast by the macro cell403at step411. In the LTE system, the system information is broadcast through Master Information Block (MIB) and System Information Block (SIB), and SIB is classified into one of SIB1, SIB2, and SIB3depending on the contained information. Among them, the cell reselection-related parameter is included in the SIB3, and the information on the neighbor cells of the same frequency band is included in the SIB4. The UE401receives the cell reselection parameters of the same frequency band through SIB3and SIB4. The macro cell403transmits S-intrasearch information capable of determining whether to perform cell reselection according to the signal strength and quality in the SIB3and the offset/bias values to be applied to the respective pico cells for rang expansion in the SIB4.

The range expansion aims to avoid failing selection of a pico cell405due to the interference from the macro cell403in the situation where the macro and pico cells403and405coexist. If the macro cell403sends the UE the offset/bias information to be applied for the neighbor pico cells405in the UE's cell reselection procedure, the UE401selects the corresponding pico cell405, as far as possible, using the offset/bias value although the received signal quality of the corresponding pico cell405is low.

That is, the UE401operates as follows according to the S-intrasearch field value and offset/bias value information received through the SIB3and SIB4. The UE401applies the offset/bias value, i.e. used the value obtained by adding the offset/bias value to the channel measurement value of the corresponding cell in prioritizing the cells, to determine for cell reselection. If the S-intrasearch field is omitted doe to the absence of S-intrasearch field value, the UE401performs measurement to the corresponding cell regardless of the channel quality of the serving cell (i.e. always) to perform the cell reselection. In another method, the eNB may provide the individual cells with respective S-intrasearch values. If S-intrasearch value y is given to a certain cell x and if the channel quality of the cell x becomes lower than y, the UE401starts measurement for the cell x and, if the channel quality of the cell x (by taking notice of the offset) is better than that of the serving cell, reselects the cell x.

At step413, the UE401performs cell reselection procedure using the information of step411. The UE401performs neighbor cell measurement and, if there is any cell better than the serving cell in channel quality, receives the system information from the corresponding cell to determine whether it can reselect the cell. If the cell is in the barred state or a non-member CSG cell to which the UE has no access right, the UE401cannot reselect the cell. Here, the non-member CSG cell denotes the cell to which the UE401has not subscribed.

The UE401operates as follows in selecting a pico cell. For explanation convenience, a description is made with a pico cell as an example of the cell for which a negative offset value (i.e. the measurement value of the corresponding cell is biased as much as the offset) is designated. However, the same method may be applied to the other cell having a negative offset value than the pico cell. Although the channel quality of the pico cell405to which the offset is applied is higher than that of the serving cell, if the channel quality without application of the offset is lower than a predetermined threshold, the UE401does not select the pico cell405. That is, the UE401selects the pico cell405, only when both the following two conditions are fulfilled.
Rn>Rs; here,Rs=Qmeas,s+QHyst, Rn=Qmeas,n−QoffsetCondition 1
Rn>Threshold−QoffsetCondition 2

Here, Rndenotes the measurement result to the neighbor cell for which the offset is applied, i.e. the measurement result to the pico cell for which the offset is applied. Rnis obtained by adding a hysteresis value (QHyst) to the measurement value of the serving cell (Qmeas,s). The threshold indicates the minimum channel quality allowing the UE401to operate normally, and the S-criteria calculated using the information received through the SIB3may be used as the threshold value. The S-criteria may be calculated using the following formula.
Srxlev>0 AND Squal>0

Qrxlevmeasdenotes the measured received signal strength, and Qqualmeasdenotes the measured received signal quality. Qrxlevmindenotes the minimum power value required for operation, and Qqualmindenotes minimum quality required for operation. Qrxlevminoffsetdenotes the offset of the power for the eNBs having priority, Qqualminoffsetdenotes the offset of the quality for the eNBs having priority, and Pcompensationdenotes a compensation parameter matching the uplink transmit power of the UE.

As described above, only when the channel quality of the pico cell405fulfills the S-criteria of the pico cell405, the UE401reselects the pico cell405. At this time, the values received through the SIB3of the current cell are used as Qrxlevminand Qqualminof the pico cell405.

According to an embodiment of the present invention, although the channel quality to which the offset has added is higher than the channel quality of the serving cell (although the condition 1 is fulfilled), if it is failed to acquire the essential system information (e.g. MIB/SIB,1/SIB2) of the pico cell405, the UE301may adjust the offset by itself. That is, after the channel condition of the corresponding cell405is recovered to the extent capable of acquiring the essential system information, the UE401may adjust the offset to reselect the cell405. The offset adjustment may be performed according to a predetermined rule. For example, the UE401may increase the offset value as much as a predetermined value. Or, the UE401may decrease the bias level as much as a predetermined value. Or, the UE401may adjust the offset to 0. If the essential system information of the cell405is received normally after adjusting the offset, the adjusted offset may be applied continuously. For example, if the macro cell a instruct the UE to apply offset of −x for the pico cell b but the essential system information is received successfully after self-adjustment of the offset to −x+k, the UE401may use the adjusted offset, i.e. −x+k, in the cell reselection process to the pico cell in the macro cell a afterward. If a cell other than the cell b for which the adjusted offset is applied is reselected, the UE401may recover the original offset value for the corresponding cell.

If the new cell405is selected, the UE401receives the system information and paging information from the selected cell405at step415.

If the raw channel quality (i.e. the channel quality without application of the offset) of the newly selected cell405is lower than the raw channel quality of the serving cell403and if the selected cell405and the old serving cell403are synchronized in System Frame Number (SFN), the UE401attempts receiving the paging message from both the old and new serving cells403and405. If the raw channel quality (without application of the offset) of the newly selected cell405becomes higher than the raw channel quality of the old serving cell403, the UE401stops receiving the paging message from the old cell403and attempts receiving the paging message from the new serving cell405.

According to another embodiment, the following operation is possible. In the case of applying the cell range expansion to the UE401in idle mode, it is advantageous to reduce the battery power consumption in RRC connection establishment for the UE to transition to the connected mode. This is because the uplink transmission power consumption of the UE close to the pico cell405is very low. However, the application of the cell range expansion to the UE401in idle mode has a shortcoming in that the paging message reception failure probability of the UE401increases due to the interference from the macro cell403.

According to another embodiment of the present invention, the UE401operating without application of the range expansion in the normal situation applies the range expansion at an instance when the RRC connection establishment is required in order to mitigate the problem. The UE401in the idle mode receives the paging message from the macro eNB403from which the received signal is strong and, if transitioning to the connected mode, selects the pico cell405using offset for cell reselection to perform the RRC connection establishment with the pico cell405.

In this embodiment, if the downlink channel quality of the pico cell405is equal to or greater than a predetermined threshold value, the UE acquires the MIB, SIB1, and SIB2of the pico cell405. In the state that the channel quality of the pico cell from which the MIB/SIB1/SIB2has been received is equal to or greater than the threshold, the pico cell405is managed as a potential serving cell405. Here, the threshold may be an absolute threshold or a relative threshold indicating the different with the serving cell. The threshold value may be notified through the system information of the macro cell. However, the UE401is in the state of receiving the paging message from the macro cell405yet. Afterward, if it is required to perform RRC connection establishment, e.g. if the UE401receives the paging message or if transmission data occurs at the UE401, the UE401selects the potential serving cell405to perform RRC connection establishment procedure with the serving cell405.

FIG. 5is a flowchart illustrating the cell reselection procedure of the UE401according to the embodiment ofFIG. 4. The UE401receives system information from the macro cell403at step503. The system information includes the information of MIB, SIB1, SIB2, SIB3, SIB4, etc.

Afterward, the UE401performs cell reselection corresponding to step413ofFIG. 4. That is, the UE performs measurement on the neighbor cell405and, if there is any cell superior to the serving cell403in channel condition, receives the system information from the corresponding cell405to determine whether to select the cell405. If the cell405is in the barred (access-barred) state or a non-member CSG cell to which the UE401has no access right, the UE cannot select the cell405.

The UE401determines whether the cell reselection condition is fulfilled at step507. If the cell reselection condition is not fulfilled, the UE waits until the cell reselection condition is fulfilled. If the cell reselection condition is fulfilled, the procedure goes to step509.

The UE401performs cell reselection according to SIB3and SIB values at step509.

The UE401operates as follows in pico cell reselection. For explanation convenience, the description is directed to the case where the pico cell403as the cell for which the negative offset value (i.e. the measurement result of the corresponding cell is biased as much as the offset). Although the channel quality of the pico cell405to which the offset is applied is superior to the channel quality of the serving cell403, if the channel quality with application of the offset is equal to or less than a predetermined threshold, the UE401does not select the pico cell405. That is, the pico cell is selected only when the following two conditions are fulfilled.
Rn>Rs; here,Rs=Qmeas,s+QHyst, Rn=Qmeas,n−QoffsetCondition 1
Rn>Threshold value−QoffsetCondition 2

Here, Rndenotes the measurement result to the neighbor cell for which the offset is applied, i.e. the measurement result to the pico cell for which the offset is applied. Rnis obtained by subtracting Qoffsetfrom the neighbor cell measurement value Qmeas,n. Qmeas,nis obtained by adding the hysteresis value QHystto the serving cell measurement value Qmeas,s. The threshold is the minimum channel quality required for the UE401to operate normally in the corresponding cell, and S-criteria calculated using the information received through SIB3may be used as the threshold value.

After the cell reselection has been performed according to the above method, the UE determines whether a new cell405has been selected at step511. If a new cell405is selected, the procedure goes to step513. If no new cell is selected, the procedure goes to step507. The UE401receives the system information and paging message from the new cell405at step513.

FIG. 6is a signal flow diagram illustrating a procedure for the UE601to report interference from the CSG cell according to an embodiment of the present invention.

InFIG. 6, if the601powers on, it searches for and selects a suitable cell to start a procedure for establishing communication connection or reestablishing the lost communication connection at step611. The UE601may select the cell based on the received signal condition. For example, the UE may select the cell having the best Reference Symbol Received Power (RSRP) or Reference Symbol Received Quality (RSRQ). The UE601also may perform cell selection based on other parameters indicating the signal condition or any combination of RSRP, RSRQ, and other parameters.

After neighbor cell search, the UE601receives the system information of the cell605having the best received signal strength and recognizes that the cell605is a CSG cell usable by members and the UE601has no access right to the CSG cell605at step613. For example, if the CSG indicator (csg-Indication) value in SIB1from the cell605is true and the white list of the UE601includes no CSG identifier (csg-Identity) of the corresponding cell605, the UE has no access right.

Afterward, the UE601searches for other cells with the exception of the CSG cell650in the cell selection or reselection procedure to select the cell having the next highest signal strength at step615. In the cell search process, the UE601continues receipt of the system information of the CSG cell605to acquire the Almost Blank Subframe (ABS) information of the CSG cell650. The ABS pattern is provided in the form of a bitmap to indicate whether the interferer cell605transmits signal at each subframe, i.e. the subframe includes interference signal and, in the present embodiment, it is assumed that the ABS pattern is broadcast through a predetermined SIB within the cell605. The ABS may be provided through a measSubframePatternPCell Information Element. The ABS pattern indicates the subframes at which the CSG cell does perform downlink transmission almost. If almost there is no downlink transmission, this means that the control channel such as CRS is transmitted at the normal transmit power level but PDCCH and PDSCH at a very low transmit power level.

At step617, the UE601selects a cell605having the next best signal strength/quality (second best cell) with the exception of the CSG cell650. In the procedure, the UE601may measure the channel quality of other cells by applying the ABS pattern. After selecting the second best cell603, the UE601receives the system information from the next best cell603to determine whether the corresponding cell603is non-CSG cell or CSG cell to which the UE601has the access right.

If the corresponding cell603is non-CSG cell or CSG cell to which the UE601has the access right, the UE601starts RRC CONNECTION SETUP procedure or RRC CONNECTION RE-ESTABLISHMENT procedure.

The UE601performs random access procedure to transmit a message at step619. The random access procedure is performed in such a way that the UE601transmits a certain preamble at a position of the random access channel and is allocated resource from the eNB603. If uplink resource is allocated through random access procedure, the UE601sends the cell603an RRC CONNECTION REQUEST message or an RRC CONNECTION REESTABLISHMENT REQUEST message for connection request or connection reconfiguration at step621. In the embodiment, the RRC CONNECTION REQUEST message or RRC CONNECTION REESTABLISHMENT REQUEST message may include an indicator indicating that the UE601is interfered significantly by the non-member CSG cell605, i.e. the CSG cell to which the UE601is not allowed for access. The RRC CONNECTION REQUEST message or RRC CONNECTION REESTABLISHMENT REQUEST message also may include an indicator indicating that the channel quality of the non-member CSG cell605is better than the channel quality of the cell603.

If the network of the cell603allows access, the UE601receives a connection setup or connection reestablishment message from the network through the cell603at step623. This message may be any of RRC Connection Setup or RRC Connection Reestablishment message.

Accordingly, the UE601transmits a confirmation message to the network at step625. The confirmation message transmitted by the UE601may be the RRC Connection Setup Complete or RRC Connection Reestablishment Complete message. According to an embodiment, the confirmation message of step625may include an indicator indicating that the best cell having the strongest received signal to the UE601is a non-CSG cell. If the indicator indicating that the best cell having the strongest received signal to the UE601is received, the cell603performs scheduling in consideration of ABS by taking of that. The confirmation message of step625may further include the following informations.cell identifier (cell id) and RSRP/RSRQ measurement value of non-member CSG cell605ABS pattern of non-member CSG cell605UE601acquire above information from predetermined SIB of non-member CSG cell605If UE has started RRC CONNECTION SETUP/RRC CONNECTION REESTABLISHMENT procedure before acquiring above information, the corresponding information may not be received.RSRP/RSRQ measurement value of the serving cell, i.e. the cell603performing RRC CONNECTION SETUP procedure or RRC CONECTION RE-ESTABLISHMENT procedure currentlySFN difference between non-member CSG cell605and serving cell603

After completing the RRC CONNECTION SETUP procedure or RRC CONECTION RE-ESTABLISHMENT procedure with the UE601, the eNB603performs resource allocation (scheduling) to the UE601at the ABS subframe having no interference of the CSG cell605at step627in order to prevent the corresponding UE601from experiencing interference problem.

FIG. 7is a flowchart illustrating the interference report procedure of the UE according to the embodiment ofFIG. 6.

Referring toFIG. 7, the UE601selects the cell605having the best received signal strength/quality among the neighbor cells in the cell (re)selection procedure and receives system information of the corresponding cell605at step703. The UE601checks the content of the system information received at step703and determines whether the selected cell605is an access-allowed cell at step705. As described with reference toFIG. 6, the UE may determine whether the cell is the access-allowed cell using the information on the CSG indicator (csg-Indication) value in SIB1from the cell605is true and whether the white list of the UE601includes no CSG identifier (csg-Identity) of the corresponding cell605. If the selected cell is not the access-allowed cell, the UE601performs the cell reselection procedure for selecting the next best cell at step703. If the selected cell603is the access-allowed cell, the UE601performs the random access procedure to the corresponding cell at step707.

If any uplink resource is allocated through the random access procedure, the UE601transmits the RRC CONNECTION REQUEST message or the RRC CONNECTION REESTABLISHMENT REQUEST message for connection request or connection reestablishment at step709. In this embodiment, the RRC CONNECTION REQUEST message or the RRC CONNECTION REESTABLISHMENT REQUEST message may include an indicator indicating that the UE is interfered significantly by the non-member CSG cell605or the channel quality of the non-member CSG cell605is better than the channel quality of the current cell603.

Afterward, the UE601determines whether a connection message (connection setup/connection reestablishment message) is received from the eNB603at step711. If the connection message is not received in a predetermined time, the procedure returns to step703such that the UE601performs the cell reselection procedure again. If the connection message is received from the network, the UE601sends a confirmation message to the cell of the network at step713. The confirmation message transmitted by the UE601may be any of the RRC Connection Setup Complete and RRC Connection Reestablishment Complete messages. The confirmation message transmitted by the UE601may include an indicator indicating that the best cell corresponding to the strongest received signal strength is non-member CSG cell. The confirmation message may further include following informations.cell id of non-member CSG cell605and RSRP/RSRQ measurement valueABS pattern of non-member CSG cell605UE601acquire predetermined SIB of non-member CSG cell605from above information.If UE601has started RRC CONNECTION SETUP/RRC CONNECTION REESTABLISHMENT procedure before acquiring above information, the corresponding information may not be received.RSRP/RSRQ measurement value of the serving cell, i.e. the cell603performing RRC CONNECTION SETUP procedure or RRC CONECTION RE-ESTABLISHMENT procedure currentlySFN difference between non-member CSG cell605and serving cell603

Afterward, the UE601transmits and receives data according to the scheduling information of the eNB603at step715. At this time, the scheduling information may be the scheduling information allocated by the cell603in order to prevent the corresponding UE601from being interfered according to the ABS pattern information transmitted by the UE601in the above procedure.

FIG. 8is a block diagram illustrating the UE according to an embodiment of the present invention. The UE transmits and receives data to and from the higher layer805. The control message processor807transmits and receives control messages. In transmission, the multiplexer803multiplexes data and the transceiver801transmits the multiplexed data under the control of the controller. In reception, the transceiver801receives a physical signal and the demultiplexer803demultiplexes the received signal under the control of the controller809. The demultiplexed signal is delivered to the higher layer device805or the control message processor807according to the message information.

In this embodiment, if the SIB message is received for cell reselection, the control message processor807processes the corresponding information and delivers the information to the cell reselection processor811. In searching for neighbor cell, the UE determines the parameter to be used for cell selection. If it is necessary perform cell reselection afterward, the UE checks the information on the signal strength to determine whether to further read the MIB and SIB information of the corresponding cell. If it is required to read the MIB and SIB information of the corresponding cell, the control unit809receives the MIB and SIBs of the new cell. Afterward, the cell reselection processor811determines whether it is possible to access the corresponding cell and performs additional process or reselection procedure for selecting a new cell according to the determination result.

Afterward, in the case of attempting access to the access-allowed cell, if the control unit809commands for uplink resource allocation, the control message processor generates and transmits the connection request or connection reestablishment request message. This message may include an indicator indicating that the UE is interfered significantly by the non-member CSG cell or the channel quality of the non-member CSG cell is better than the channel quality of the current cell. Afterward, if the connection setup/connection reestablishment message is received from the eNB, the UE sends the eNB a confirmation message. The confirmation message transmitted by the UE may include the information indicating that the best cell having highest received signal strength is the non-member CSG cell as described with reference toFIGS. 6 and 7. The confirmation method may further include following informations.cell id of non-member CSG cell605and RSRP/RSRQ measurement valueABS pattern of non-member CSG cell605UE601acquire predetermined SIB of non-member CSG cell605from above information.If UE601has started RRC CONNECTION SETUP/RRC CONNECTION REESTABLISHMENT procedure before acquiring above information, the corresponding information may not be received.RSRP/RSRQ measurement value of the serving cell, i.e. the cell603performing RRC CONNECTION SETUP procedure or RRC CONECTION RE-ESTABLISHMENT procedure currentlySFN difference between non-member CSG cell605and serving cell603

FIG. 9is a block diagram illustrating the eNB according to an embodiment of the present invention. The eNB includes a transceiver905, a controller910, a multiplexer/demultiplexer920, a control message processor935, higher layer devices925and930, and a scheduler915.

The transceiver905transmits data and control signals on downlink carriers and receives data and control signals on uplink carriers. In the case that a plurality of carriers is configured, the transceiver905may transmit and received data and control signals over a plurality of carriers. The multiplexer/demultiplexer920multiplexes the data generated by higher layer processors925and930and the control message processor935and demultiplexes the data received through the transceiver905and delivers the demultiplexed data to the higher layer processors925and930, control message processor935, and/or the controller910. The control message processor935may takes an action necessary for processing the control message transmitted by the UE and delivers the controls message to be transmitted to the UE to the higher layer. The higher layer processors925and930may be formed per UE per service and processes the data generated in the user service such as FTP and VoIP to transfer the processed data to the multiplexer/demultiplexer920or processes the data output from the multiplexer/demultiplexer920to transfer the processed data to the service applications of the higher layer. The controller910determines the timing of transmitting CSI/SRS and controls the transceiver. The scheduler allocates transmission resource to the UE at an appropriate time in consideration of the buffer state, channel condition, and active time of the UE and controls the transceiver to process the signal transmitted by or to be transmitted to the UE.

In this embodiment, if the information indicating the interference caused by the non-member CSG cell is acquired from the received message in the UE's access attempt, the scheduler915allocates resource to the UE in the frame having low interference.

The proposed method is advantageous in performing the cell reselection procedure without malfunctioning by selecting the cell which is actually accessible even in the case of using the offset for cell reselection in the HetNet situation and in transmitting/receiving data without interference, when there is any non-member CSG cell, by notifying the cell to which the UE connects actually of the information on the interference from the corresponding cell.

Although the description has been made with reference to particular embodiments, the present invention can be implemented with various modifications without departing from the scope of the present invention. Thus, the present invention is not limited to the particular embodiments disclosed but will include the following claims and their equivalents.