Abstract:
In a wireless communication system a control channel is required in order to use limited resources effectively. However, the control channel resource is part of the system overhead, and thus reduces the data channel resource used for data transmission. In the long term evolution (LTE) system based on OFDM, one sub frame the consists of fourteen OFDM symbols wherein a maximum of three OFDM symbols are used for the control channel resource and remaining eleven OFDM symbols are used for the data channel resource. Therefore, the quantity of energy that can be transmitted for the control channel resource is extremely limited compared to the data channel resource. For this reason, the coverage of the control channel becomes less than that &amp;; of the data channel, and even if a user can successfully receive the data channel, reception failure of a control channel sometimes˜results in failure of data recovery. In the present invention, in order to expand the coverage of the control channel to at least the coverage of the data channel, the time resource of the transmission resource wherein the control channel is transmitted is expanded and allocated for sending and receiving the control channel. By way of methods for extending the time resource are provided a method wherein a plurality of sub frames are used to transmit one control channel, and a method wherein a part of a data channel is used for the control channel.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a control channel transmission/reception method and apparatus in a wireless communication system and, in particular, to a method and apparatus for transmitting/receiving downlink control channel for increasing the coverage of the control channel of a wireless communication system. 
         [0003]    2. Description of the Related Art 
         [0004]    Mobile communication systems are currently evolving from basic communication devices into high-speed, high-quality wireless packet data communication systems that provide data services and multimedia services beyond the early voice-oriented services. Recently, various mobile communication standards, such as High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), both defined by 3 rd  Generation Partnership Project (3GPP), High Rate Packet Data (HRPD) defined by 3 rd  Generation Partnership Project-2 (3GPP2), and Institute of Electrical and Electronics Engineers (IEEE) 802.16, have been developed to support the high-speed, high-quality wireless packet data services. 
         [0005]    The existing 3 rd  generation wireless packet data communication system, such as HSDPA, HSUPA and HRPD, uses such technologies as an Adaptive Modulation and Coding (AMC) method and a channel-sensitive scheduling method in order to improve transmission efficiency. With the use of the AMC method, a transmitter can adjust the amount of transmission data according to the channel state. For example, when the channel state is not good, the transmitter reduces the amount of transmission data to match a reception error probability to a desired level, and when the channel state is good, the transmitter increases the amount of transmission data to efficiently transmit a large volume of information while matching the reception error probability to the desired level. Using the channel-sensitive scheduling resource management method, the transmitter, since it selectively services a user having a superior channel state among several users, can increase in the system capacity, as compared with a transmitter that allocates a channel to one user and services the user with the allocated channel. Such capacity increase is commonly referred to as a multi-user diversity gain. In brief, the AMC method and the channel-sensitive scheduling method are methods for receiving partial channel state information being fed back from a receiver, and applying an appropriate modulation and coding technique at the most efficient time determined depending on the received partial channel state information. 
         [0006]    Recently, intensive research is being conducted to replace Code Division Multiple Access (CDMA), which is the multiple access scheme used in the 2 nd  and 3 rd  generation mobile communication systems, with Orthogonal Frequency Division Multiple Access (OFDMA) in the next generation mobile communication system. 3GPP and 3GPP2 have started standardization work on evolved systems based on OFDMA. 
         [0007]    With the implementation of the ACM and channel-sensitive scheduling schemes, the base station is capable of allocating radio resource including frequency, timing, and power in adaptation to the user-specific channel condition. The base station notifies the user of the resource allocated in adaptation to the channel condition via Physical Downlink Control Channel (PDCCH) such that the user can be aware of the radio resource allocated to itself. 
         [0008]    The radio resource allocations can be categorized into downlink resource allocation for the transmission from the base station to the user equipment and uplink resource allocation form the transmission from the user equipment to the base station. The downlink resource allocation is performed in adaptation to the channel condition reported by the user and the information amount of the data to be transmitted to the user, it is notified of the resource allocated to a certain user for transmitting data and modulation and coding scheme to be used for the data transmission via a control channel. The user equipment can recognize whether there is the resource allocated to itself and, if so, how to receive the data on the corresponding resource, based on the control information received on the control channel. The uplink resource allocation is performed in adaptation t the channel condition reported by the user and the information amount of the data to be transmitted and notifies the user of the resource allocated to the user and the transmission scheme to be used for the data transmission on the allocated resource. The user equipment can recognize the uplink resource allocated to itself and transmission scheme to be used for data transmission. 
         [0009]    The information transmitted on the control channel for downlink resource allocation, i.e. Downlink Control Information, includes a User Equipment Identification (UE ID), a Down Link Resource Block (DL RB), a Transport Format (TF), and a Hybrid Automatic Repeat Request (HARQ). 
         [0010]    The UE ID is the information transmitted for identifying whether there is the signal destined to the UE itself. Typically, a Cyclic Redundancy Check (CRC) associated with a certain UE ID is inserted to the DL control information such that if the UE decodes the DL control information successfully this means that the control information is transmitted to the UE. 
         [0011]    If the UE decodes the DL control information successfully, the UE can locate the resource blocks on which the data destined to the UE are transmitted, based on the DL RB allocation information. 
         [0012]    TF indicates the modulation and coding scheme of the transmitted signal. If AMC is adopted, the UE should know TF for performing the modulation and coding correctly. 
         [0013]    HARQ is the process for the receiver to notify the transmitter of whether the transmission packet is received successfully so as to, if so, transmit the next packet and, otherwise, retransmit the lost packet. The HARQ-related information is the information whether the transmission signal is initial transmission or retransmission in HARQ process and the HARQ process number such that the UE determines whether to decode the currently received packet in combination with the previously received packet or perform new decoding operation based on the HARQ-related information. 
         [0014]    The control information carried on the control channel for the downlink resource allocation can further include the information on multiple antenna transmission information, power control, and whether the distributed transmission is applied. 
         [0015]    The information included in the control channel for uplink resource allocation, i.e. the control information, includes the UE ID, Uplink Resource Block (UL RB) allocation information, Transport Format (TF), and Hybrid Automatic Repeat Request (HARQ) related information. 
         [0016]    The control information included in the control channel for uplink resource allocation can further include the information on the uplink reference signal for supporting Space Domain Multiple Access, the information on whether the distributed transmission is applied, and the information whether the channel condition report is requested. 
         [0017]    If the control information is decoded successfully, the UE recognizes the resource blocks to be used for data transmission based on the UL RB information. 
         [0018]    The UE should know the TF to recover the transmitted signal with the demodulation and decoding schemes requested by the base station. 
         [0019]    The HARQ-related information has been described above. 
         [0020]    The UE performs blind decoding of available candidate group to search for the downlink control channel destined to itself among plural downlink control channels. Here, the blind decoding is to perform decoding control channel candidates to find its own control channel without information on which control channel is used for the transmission of the control channel information when the base station has transmitted the control channel among the control channel candidates defined in a group of control channel candidates. 
         [0021]      FIG. 1  is a diagram illustrating a control channel candidate group configuration method in the conventional wireless communication system. 
         [0022]    In  FIG. 1 , Control Channel Element (CCE) is a unit of logical channel constituting the control channel. CCE corresponds to a group of Resource Elements (RE) as a unit of physical channel. 
         [0023]    How many CCEs constitute a control channel is referred to as Aggregation Level (AL). If a control channel is composed of N CCEs, AL is N; and  FIG. 1  is depicted in consideration of examples of AL=1 111, AL=2 112, AL=4 113, and AL=8 114. 
         [0024]    In the exemplary case of  FIG. 1 , it is assumed that the control channel uses one modulation scheme. In this case, as AL increases, a number of coded bits decreases. This means that the code rate of the control channel decreases. That is, the lower AL is, the fewer the resource for transmission of the control information is; however, the UE can receive the control information successfully under good channel condition. As AL increases, the more resources are used, but, in such as case, even the user equipment experiencing bad channel condition can successfully receive the control information. In order to improve resource usage efficiency, it is preferred to configure the control channel with low AL for the user equipment having good channel condition and with high AL for the user equipment having bad channel condition. 
         [0025]    A number of information bits constituting the control information (DCI) can be changed depending on the type of the control information. For example, the number of bits can be increased to increase degree of freedom or decreased with the cost of reduction of degree of freedom for indicating the resource block allocation information. The number of bits of the control information can be changed according to the information to be added. In case that the control information changes in length due to different numbers of bits, the lengths of the control information can be discriminated by DCI format. Since the user equipment does not know which DCI format is used for transmitting the control information, blind decoding is applied. Although transmitted in the same channel condition, it is preferred to transmit the control channel carrying the control information in DCI format of a large number of bits with a high AL as compared to the control channel carrying the control information in DCI format of a small number of bits. 
         [0026]    Referring to  FIG. 1 ,  8  CCEs  100  to  107  are given. This is just for the convenience sake, but a number of CCEs can be changed at any time. The number of CCEs can be influenced by constant values such as downlink system bandwidth, a number of base station transmit antennas, and a number of downlink ACK/NACK channels for supporting uplink HARQ, and the control region information in which the values change every subframe as unit of time for scheduling. 
         [0027]    In the exemplary case of  FIG. 1 , there are the control channel candidates  120  to  127  corresponding to AL=1 as denoted by reference number  111 . Reference number  120  denotes the control channel configured with a CCE  0   100 , and reference number  127  denotes the control channel configured with a CCE  7   107 . There are control channel candidates  128  and  129  corresponding to AL=2 as denoted by reference number  112 . Reference number  128  denotes the control channel configured with CCE  0   128  and CCE  3   103 . There is the control channel candidate  132  corresponding to AL=4 as denoted by reference number  113 . Reference number  132  denotes the control channel configured with CCE  0   101  to CCE  3   103 . There is the control channel candidate  134  corresponding to AL=8 as denoted by reference number  114 , and reference number  134  denotes the control channel configured with  8  CCEs of CCE  0   100  to CCE  7   108 . 
         [0028]    The method for configuring the control channel candidate per AL in  FIG. 1  is based on the tree structure. The control channel candidates of AL=2 includes a set of control channel candidates corresponding to AL=1, the control channel candidates of AL=4 include a set of control channel candidates corresponding to AL=2, and the control channel candidates of AL=8 include a set of control channel candidates corresponding to AL=4. 
         [0029]    For example, reference number  132  is PDCCH composed of 4 CCEs  0  to  3  corresponding to the control channel candidate  128  including a set of CCEs  0  and  1  and the control channel candidate  129  including a set of CCEs  2  and  3  at AL=2. According to such a tree structure, when the total number of CCEs is N_CCE, a number of control channels that can be configured at an AL is floor(N_CCE/AL). Here, floor(x) is the floor function expressing the maximum integer equal to or less than x. 
         [0030]      FIG. 2  is a diagram illustrating a structure of a downlink subframe in a conventional OFDM-based Long Term Evolution (LTE) system. 
         [0031]    In  FIG. 2 , a subframe is composed of 14 OFDM symbols  200  to  213 , the three OFDM symbols  200  to  202  at the beginning of the subframe are assigned for the control channel (PDCCH), and the rest OFDM symbols  203  to  213  assigned for the data channel (Physical Downlink Data Channel (PDDCH)). The control channel region is positioned at the beginning of the subframe such that the UE can check whether the subframe carries no data destined to itself and, if so, enters micro sleep mode to reduce power consumption in the data channel region. 
         [0032]    In case that the same amount of bit information is transmitted in the control channel and the data channel in the subframe structure as shown in  FIG. 2 , the energy per bit on the control channel is less than that on the data channel at the limited transmit power. This is because the resource allocated for the control channel is less than the resource allocated for the data channel in time domain such that the more frequency resource is used for control channel as compared to the data channel in the same OFDM symbol and thus the energy amount per bit decreases in the limited transmit power. After all, this means that the actual coverage of the transmitted signal of the control channel is less that of the data channel. Accordingly, although the data channel is received successfully, the user terminal may fail to receive the control channel, resulting in failure of data channel decoding. There is therefore a need of a method for increasing the coverage of the control channel to become larger than that of the data channel to overcome the aforementioned problem. 
       SUMMARY OF THE INVENTION 
     Problem to be Solved 
       [0033]    In order to solve the above problems, it is an objective of the present invention to provide a control channel transmission/reception method and apparatus that is cable of increasing the coverage of the control channel by increasing the resource amount in time domain when transmitting the control channel. 
       Means for Solving the Problem 
       [0034]    In order to achieve the above objective, a control channel transmission method of a base station in a wireless communication system according to a preferred embodiment of the present invention includes steps of generating control information for a terminal scheduled, generating a control channel having the control information, and transmitting the control channel through transmission resource of time resource longer than the time resource of a control channel region of a subframe. 
         [0035]    In order to achieve the above objective, a control channel reception method of a terminal in a wireless communication system according to a preferred embodiment of the present invention includes steps of receiving at least one subframe having a control channel mapped to transmission resource of time resource longer than the time resource or control channel region of a subframe, extracting the control channel and control information from the at least one subframe through a blind decoding method, and transmitting/receiving data through the transmission resource indicated by the control information. 
         [0036]    In order to achieve the above objective, a control channel transmission apparatus of a base station in a wireless communication system according to a preferred embodiment of the present invention includes a control information generator which generates control information of a terminal scheduled; a CCE mapper which maps a control channel having the control information to transmission resource; a controller which controls the CCE mapper to maps the control channel to the transmission resource of time resource longer than the time resource or control channel region of a subframe; and a transmitter which transmits the control information through the allocated transmission resource. 
         [0037]    In order to achieve the above objective, a control channel reception apparatus of a terminal in a wireless communication system according to a preferred embodiment of the present invention includes a receiver which receives at least one subframe having a control channel mapped to transmission resource of time resource longer than the time resource or control channel region of a subframe; a CCE de-mapper which de-maps the control channel from the at least one subframe according to the transmission resource; a control channel decoder/demodulator which perform blind decoding on the control channel; a controller which recognizes data channel allocated to the terminal by referencing the control information of the control channel; and a data channel decoder/demodulator which decodes the data channel under the control of the controller. 
       Advantageous Effects 
       [0038]    The method and apparatus according to an embodiment of the present invention is capable of obtain high energy using the additional time domain resource for transmitting a control channel so as to increases the coverage of the control channel. Accordingly, it is possible to avoid data channel decoding failure caused by the control channel reception failure, resulting in reduction of probability of outage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]      FIG. 1  is a diagram illustrating a control channel candidate group configuration method in the conventional wireless communication system. 
           [0040]      FIG. 2  is a diagram illustrating a structure of a downlink subframe in a conventional OFDM-based Long Term Evolution (LTE) system. 
           [0041]      FIG. 3  is a diagram illustrating a control channel candidate group configuration method as control channel signal according to an embodiment of the present invention. 
           [0042]      FIG. 4  is a diagram illustrating a method for transmitting the control channel repeatedly in the control channel regions of plural subframes according to an embodiment of the present invention. 
           [0043]      FIG. 5  is a flowchart illustrating a method for transmitting the control channel repeatedly in the control channel regions of plural subframes according to an embodiment of the present invention. 
           [0044]      FIG. 6  is a flowchart illustrating a method for receiving the control channel transmitted repeatedly in plural subframes according to an embodiment of the present invention. 
           [0045]      FIG. 7  is a diagram illustrating a method for transmitting a control channel using the control channel candidates distributed over the control channel regions of plural subframes according to an embodiment of the present invention. 
           [0046]      FIG. 8  is a flowchart illustrating a method for transmitting the control channel using the control channel candidates group extended over the control channel regions of plural subframes according to an embodiment of the present invention. 
           [0047]      FIG. 9  is a flowchart illustrating a method for receiving the control channel using the control channel candidates group distributed over plural subframes according to an exemplary embodiment of the present invention. 
           [0048]      FIG. 10  is a diagram illustrating a method for transmitting/receiving control channel signal using a part of the data channel region of a subframe according to an embodiment of the present invention. 
           [0049]      FIG. 11  is a diagram illustrating a method for transmitting/receiving the control channel using a part of the data channel region in a subframe according to another embodiment of the present invention. 
           [0050]      FIG. 12  is a flowchart illustrating a method for transmitting control channel using the data channel region according to an embodiment of the present invention. 
           [0051]      FIG. 13  is a flowchart illustrating a method for the user equipment to receive the control channel transmitted in data channel region according to an embodiment of the present invention. 
           [0052]      FIG. 14  is a diagram illustrating a method for transmitting/receiving control channel using both the control and data channel regions according to an embodiment of the present invention. 
           [0053]      FIG. 15  is a diagram illustrating a method for transmitting/receiving control channel using both the control and data channel regions according to another embodiment of the present invention. 
           [0054]      FIG. 16  is a flowchart illustrating a method for transmitting control channel using both the control and data channel regions according to an embodiment of the present invention. 
           [0055]      FIG. 17  is a flowchart illustrating a method for a user equipment to receive the control channel transmitted in both the control and data channel regions using the extended control channel candidate group according to an embodiment of the present invention. 
           [0056]      FIG. 18  is a block diagram illustrating a configuration of a base station for transmitting control channel in a wireless communication system according to an embodiment of the present invention. 
           [0057]      FIG. 19  is a block diagram illustrating a configuration of a user equipment for receiving control channel in a wireless communication according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0058]    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. 
         [0059]    The transmission resources include time resource and frequency resource. For example, the unit of the time resource can be OFDM symbol, and the unit of the frequency resource can be subcarrier (or tone). 
         [0060]    The present invention is to increase the coverage of the control channel transmitted to a certain user equipment. For this purpose, the more time resource is assigned for the transmission of the control channel as compared to the conventional control channel transmission. As a result, the energy per bit in transmit power increases so as to extend the actual cell coverage of the control channel transmission. 
         [0061]    That is, the present invention uses additional time resource to transmit the control channel for a certain user equipment. In order to increase the amount of time resource for control channel, it is proposed first to use the control channel resource of multiple subframes and second to borrow the data channel resource in the one subframe. 
         [0062]    Here, the control channel resource is Packet Data Control Channel (PDCCH) region, and the data channel resource is Physical Downlink Shared Channel (PDSCH) region. The user equipment can discriminate the control channel and data channel regions by receiving PCFICH. PCFICH is the physical channel for transmitting Control Channel Format Indicator (CCFI) information. CCFI is the information composed of 2 bits indicating the control channel allocation indicator, i.e. “L.” The user equipment should receive the CCFI first to know a number of symbols allocated for the control channel, such that the PCFICH should be received first in the subframe by all the user equipments except for the fixedly allocated downlink resource. The control channel region is the region determined by a number of symbols which the base station informs to the user equipment by means of PCFICH in the downlink frame, and the rest region becomes the data region. 
         [0063]    Typically, the control channel for a certain user equipment is transmitted in the control channel region of a subframe. As aforementioned, the control channel region uses up to 3 symbols at the beginning of a subframe in time domain. In an embodiment of the present invention, the time resource allocated for the control channel is extended such that the control channel is transmitted on the transmission resource having the extended time resource. According to an embodiment of the present invention, the region on which the control channels are transmitted can be distributed to the control channel regions of a plurality of subframes or across the control channel and data channel regions or formed in the data channel region. 
         [0064]    In order to transmit the control information using the transmission resource extended in time resource, two methods are proposed, i.e. first to increase the maximum Aggregation Level (AL) and second to repeat the conventional control channel candidate group according to the extended time resource. 
         [0065]    The information used for transmitting a control channel signal required for use of the additional time domain resource can include a number of subframes, control channel candidates group of increased AL, and information on the data channel region allocated in advance for control channel transmission. Such information can be shared by a certain user equipment and base station via higher layer signaling. For example, the higher layer signaling can be the system information, i.e. SIB 1 . 
         [0066]      FIG. 3  is a diagram illustrating a control channel candidate group configuration method as control channel signal according to an embodiment of the present invention. 
         [0067]    Referring to  FIG. 3 , the AL of the extended control channel candidate group can increase by square of 2. Accordingly, the maximum AL of the extended channel candidate group can be determined according to the resource amount of the added time region. That is, the maximum AL can be determined according to the number of subframes in the method using the control channel resources of multiple subframes and the available data channel resource amount in the method using the data channel resource in the same subframe. 
         [0068]    The extended channel candidate group to be transmitted as the control channel signal can be used across the control channel region and the additional time region in the above two methods. 
         [0069]    Suppose a case where a control channel is transmitted across two subframe, AL=4 as denoted by reference number  341 , and CCEs  16  to  19  denoted by reference numbers  316  to  319 . In this case, CCE  16   316  and CCE  17   317  can be transmitted in the first subframe while CCE  18   318  and CCE  19   319  are transmitted in the second subframe. 
         [0070]    A description is made of the method for transmitting a control channel for a certain user equipment using the control channel resource of plural subframes according to an embodiment of the present invention. This includes the first method transmitting the conventional control channel candidates repeatedly in the plural subframes and the second method transmitting the extended control channel candidates across the plural subframes. In the method for transmitting the control channel using the plural subframes, the data channel is transmitted in the last subframe among the plural subframes. 
       First Embodiment 
     Transmit the Control Channel in the Control Channel Regions of Plural Subframes Repeatedly 
       [0071]      FIG. 4  is a diagram illustrating a method for transmitting the control channel repeatedly in the control channel regions of plural subframes according to an embodiment of the present invention. 
         [0072]    In  FIG. 4  two subframes (subframe 0 , subframe 1 ) are depicted. The base station transmits the control channel (PDCCH)  428  in the control channel regions of the individual subframes repeatedly. Here, the control channel is composed of 8 CCEs. That is, the control channel  428  is transmitted on a part of the 3 OFDM symbols  400  to  402  at the beginning of the first subframe (subframe 0 ) and on a part of the 3 OFDM symbols  414  to  416  at the beginning of the second subframe (subframe 1 ) again. 
         [0073]    A number of subframes used for transmitting the designation information of certain user equipments receiving the control channel and the number of subframes used for transmitting a control channel with this method is notified to the user equipment receiving such control channel via higher layer signaling. In the example of  FIG. 4 , the number of subframes used for transmitting one control channel and the number of CCEs constituting the control channel can be changed. 
         [0074]      FIG. 5  is a flowchart illustrating a method for transmitting the control channel repeatedly in the control channel regions of plural subframes according to an embodiment of the present invention. 
         [0075]    Referring to  FIG. 5 , the base station determines priorities of the users to be scheduled at step  500 . Next, the base station determines the control information (DCI) and control information format (DCI format) of the users to be scheduled in order of priority at step  502 . Next, the base station calculates a number of CCEs available in the corresponding subframe at step  504 . The number of available CCEs is determined based on the constant value such as the downlink system bandwidth, a number of base station transmit antennas, a number of downlink ACK/NACK channels for supporting uplink HARQ, and the control region information of which value varies in every subframe as time unit of scheduling. 
         [0076]    Afterward, the base station determines a number of control channel candidates per AL at step  506 . Once the number of control channel candidates are determined, the base station determines the control channel candidates group by applying the determined value to a hash function at step  508 . 
         [0077]    Next, the base station selects the control channel candidate which is not occupied by the user (user equipment) having the highest priority at step  510 . The base station determines the selected control channel candidate as the control channel candidate of the corresponding user. Next, the base station performs channel coding on the control information (DCI) determined (at step  502 ) suitable for the DCI format and performs scrambling on the control information with the index of the subframe in which the user data is transmitted at step  512 . For example, referring to  FIG. 4 , since the control channel is transmitted in the first subframe (subframe 0 ) and the second subframe (subframe 1 ), the control information is scrambled with the identifier of the second subframe (subframe 1 ). This means that, when the control channel is transmitted in at least two subframes, the control information is scrambled using the identity number of the last subframe. This method of scrambling the control information using the index of the subframe to transmit data can prevent the user equipment from decoding the control channel successfully due to the error occurred before the last subframe carrying the data among the plural subframes carrying the control channel. 
         [0078]    Next, the base station modulates the symbols of the scrambled control information and maps the modulated symbol stream to the selected control channel. 
         [0079]    The base station maps the control channel to the control channel regions of a predetermined number of subframes at step  516 . For example, referring to  FIG. 4 , the symbol stream constituting the control channel (PDCCH)  428  composed of 8 CCEs is mapped is mapped to the control channel regions (PDCCH regions) of the two subframes (subframe 0 , subframe 1 ), repeatedly. 
         [0080]    Next, the base station repeats steps  504  to  516  for the user to be scheduled in the next priority to map the control channel of the users to be scheduled at step  518 . The base station transmits the control channel after multiplexing with the downlink data signal. 
         [0081]    A description is made of the method for receiving control channel transmitted repeatedly in the plural subframes according to the aforementioned method.  FIG. 6  is a flowchart illustrating a method for receiving the control channel transmitted repeatedly in plural subframes according to an embodiment of the present invention. 
         [0082]    If a signal is received from the base station, the user equipment checks the control information format receivable at step  600  and calculates the number of available CCEs. As aforementioned, the receivable control information format is preset via the higher layer signaling. As shown in the transmission method of the base station that is described with reference to  FIG. 5 , the number of available CCEs is determined based on the constant value such as the downlink system bandwidth, a number of base station transmit antennas, a number of downlink ACK/NACK channels for supporting uplink HARQ, and the control region information of which value varies in every subframe as time unit of scheduling, such that the user terminal should know all these values. 
         [0083]    Next, the user equipment determines a number of the control channel candidates per AL at step  604  and determines the control channel candidates group per AL by applying the previously determined values (the number of control channel candidates) to the hash function at step  606 . 
         [0084]    The user equipment combines the predetermined plural subframes per control channel candidate and performs descrambling with the corresponding subframe number. Here, the corresponding subframe number is the number of the subframe carrying the control channel including the control information of the user equipment itself. For example, referring to  FIG. 4 , since the control channel is transmitted in the first subframe (subframe 0 ) and the second subframe (subframe 1 ), the user equipment performs descrambling on the control channel with the identifier of the second subframe (subframe 1 ). This means that, when the control channel is transmitted in at least two subframes, the descrambling is performed with the identity number of the last subframe. 
         [0085]    Next, the base station performs channel decoding per receivable control information format at step  610 . Next, the user equipment performs CRC test to determine whether the control channel is decoded successfully at step  612 . If it is determined that the control channel decoding is failed, the user equipment repeats steps  608  and  610  to other control channel candidates acquired through step  606 . If the control channel decoding has failed for all the control channel candidates, this means that there is no control channel transmitted to the corresponding user. Otherwise, if the control channel decoding is successful at step  612 , the user equipment locates the transmission resource allocate to itself according to the control information (DCI) received through the control channel decoded successfully (passed the CRC test) and performs transmission/reception operation using the transmission resource allocate to itself at step  614 . 
       Second Embodiment 
     Control Channel Transmission Using Control Channel Candidates Extended Over the Control Channel Regions of Plural Subframes 
       [0086]      FIG. 7  is a diagram illustrating a method for transmitting a control channel using the control channel candidates distributed over the control channel regions of plural subframes according to an embodiment of the present invention. 
         [0087]    In  FIG. 7 , two subframes (subframe 0 , subframe 1 ) are depicted. The base station transmits the extended control channel in the subframes in divided manner. Here, the extended control channel is composed of 16 CCEs. That is, the first 8 CCEs  729  of the extended control channel  728  carries a part of the three OFDM symbols  700  to  702  placed at the beginning of the first subframe (subframe 0 ), and the last 8 CCEs  730  of the extended control channel  728  carries a part of the three OFDM symbols  714  to  716  at the beginning of the second subframe (subframe 1 ). 
         [0088]    The base station notifies the corresponding user equipment with the designation information of specific user equipment receiving the control channel using the above described method, information on the extended control channel candidate group, and the number of subframes used for transmitting the extended control channel via higher layer signaling. In  FIG. 7 , the number of subframes used for transmitting an extended control channel and the number of CCEs constituting the control channel can be changed. 
         [0089]      FIG. 8  is a flowchart illustrating a method for transmitting the control channel using the control channel candidates group extended over the control channel regions of plural subframes according to an embodiment of the present invention. 
         [0090]    Referring to  FIG. 8 , the base station determines the priority of the user to be scheduled at step  800  and then determines the control information and the control information format for the user to be scheduled in order of priority at step  802 . 
         [0091]    In order to transmit the control channel using plural subframes as proposed in the present invention, the base station calculates a number of the CCEs available in the plural subframes determined in advance by higher layer signaling at step  804  and determines a number of control channel candidates per extended AL at step  806 . At this time, the maximum AL is determined based on the predetermined number of subframes. Next, the base station determines extended control channel candidates group by applying the predetermined number of candidates (at step  806 ) to the hash function at step  808 . 
         [0092]    The base statin selects the control channel candidate which is not preoccupied by the user (equipment) having higher priority at step  810 . That is, the base station determines the selected control channel candidate as the control channel candidate of the corresponding user. 
         [0093]    Next, the base station performs channel encoding on the control information into the control information format and performs scrambling on the control information using the number of subframe carrying the data signal of the user at step  812 , as step  512  of  FIG. 5 . For example, referring to  FIG. 7 , since the extended control channel is transmitted as distributed in the first subframe (subframe 0 ) and the second subframe (subframe 1 ), the control information is scrambled with the identifier of the second subframe (subframe 1 ). This means that, when the control channel is transmitted in at least two subframes, the control information is scrambled using the identity number of the last subframe. This method of scrambling the control information using the index of the subframe to transmit data can prevent the user equipment from decoding the control channel successfully due to the error occurred before the last subframe carrying the data among the plural subframes carrying the control channel. 
         [0094]    Next, the base station modulates the scrambled signal and maps the modulated symbol stream to the control channel regions of the plural subframes. For example, referring to  FIG. 7 , the symbol stream constituting the control channel composed of 16 CCEs are mapped in unit of 8 CCEs for the respective subframes (subframe 0 , subframe 1 ). 
         [0095]    Next, the base station repeats steps  804  to  814  for the user to be scheduled in the order of next priority until the control channels of all the users to be scheduled are mapped at step  816 . Next, the base station transmits the control channel as multiplexed with the downlink data signal. 
         [0096]    A description is made of the method for receiving the control channel distributed over plural subframes as described above.  FIG. 9  is a flowchart illustrating a method for receiving the control channel using the control channel candidates group distributed over plural subframes according to an exemplary embodiment of the present invention. 
         [0097]    Referring to  FIG. 9 , the user equipment checks the receivable control information formats at step  900 . The receivable control information formats are preset via higher layer signaling. The user equipment calculates a number of the CCEs of the predetermined number of plural subframes at step  902  and determines the number of control channel candidates per extended AL at step  904 . Next, the user equipment determines the control channel candidates group per extended AL by applying the value (number of control channel candidates) to the hash function. 
         [0098]    Next, the user equipment performs demodulation on individual control channel candidates for the predetermined number of previous subframes and performs descrambling with the corresponding subframe numbers as the method for receiving base station transmission proposed in  FIG. 8  according to the present invention, at step  908 . For example, referring to  FIG. 7 , since the control channels are transmitted in the first subframe (subframe 0 ) and the second subframe (subframe 1 ), the control information is descrambled with the identifier of the second subframe (subframe 1 ). This means that, when the control channel is transmitted in at least two subframes, the descrambling is performed with the identity number of the last subframe. 
         [0099]    The user equipment performs channel decoding on the individual receivable control information formats. The user equipment performs CRC to determine whether the control channel is decoded successfully at step  912 . If the CRC fails, the user equipment repeats steps  908  to  910  on other remained control channel candidates. If the decoding attempts on all of the control channel candidates have failed, this means that there is no control channel transmitted to the corresponding user. If the control channel decoding is successful at step  912 , the user equipment locates the transmission resource allocated to itself based on the control information received through the successfully decoded control channel (successful CRC test result) and performs transmission/reception operation on the transmission resource allocate to itself at step  914 . 
         [0100]    In the present invention, two methods are proposed for transmitting a control channel for a specific user equipment with a part of the data channel resource. The first method is to transmit/receive the control channel in a predetermined data channel region without using the control channel, and the second method is to transmit/receive the extended control channel candidates in the convention control channel region and a part of the data channel region. 
       Third Embodiment 
     Control Channel Transmission Using a Part of Data Channel Region 
       [0101]      FIG. 10  is a diagram illustrating a method for transmitting/receiving control channel signal using a part of the data channel region of a subframe according to an embodiment of the present invention. 
         [0102]    In  FIG. 10 , the downlink subframe includes the control channel region composed of three symbols  1000  to  1002  at the beginning of the subframe and the data region composed of the rest 11 symbols  1003  to  1013 . 
         [0103]    According to an embodiment of the present invention, the base station can transmit the control channel  1014  in the data channel region  1003  to  1013  but not the control channel region  1000  to  1002  so as to increase the transmission resource in time domain as compared to the case using the control channel region. Here, the control channel  1014  is composed of 8 CCEs. 
         [0104]    The base station notifies the corresponding user equipment with the designation information of specific user equipments receiving the control channel using the above described method, information on the extended control channel candidate group, and the number of subframes used for transmitting the extended control channel via higher layer signaling. In  FIG. 10 , the number of subframes used for transmitting an extended control channel and the number of CCEs constituting the control channel can be changed. 
         [0105]      FIG. 11  is a diagram illustrating a method for transmitting/receiving the control channel using a part of the data channel region in a subframe according to another embodiment of the present invention. 
         [0106]      FIG. 11  shows another exemplary case of transmitting control channel using a part of the data channel region, and the base station transmits the control channel  1114  on the 5 OFDM symbols  1103  to  1107  at the beginning of the data channel region. 
         [0107]    In order to receive control channel, the user equipment checks the first 5 symbols of the data channel region to determine whether the control channel  1114  destined to itself is carried therein. If there is not data allocation information, the user equipment enters the micro sleep mode for the rest 5 OFDM symbols  1108  to  1113  to reduce the power consumption. Here, the number of OFDM symbols of the data channel region that are allocated for transmitting the control channel can be changed. The base station notifies the corresponding user equipment of the information on the data channel region for transmitting the control channel via higher layer signaling. 
         [0108]      FIG. 12  is a flowchart illustrating a method for transmitting control channel using the data channel region according to an embodiment of the present invention. 
         [0109]    Referring to  FIG. 12 , the base station determines the priorities of the users to be scheduled at step  1200 . Next, the base station determines the control information and the control information formats of the users scheduled in order of priority at step  1202 . In order to implement the method for transmitting the control channel using a part of the data channel region, the base station calculates a number of CCEs available as a part of the predetermined dada channel region at step  1204 . Next, the base station determines a number of control channel candidate per AL at step  1206  and then determines the control channel candidates group by applying the value (number of control channel candidates) to the hash function at step  1208 . Once the control channel candidates group is determined, the base station selects the control channel candidate which is not preoccupied by the user having a higher priority as the control channel candidate of the corresponding user at step  1210 . Next, the base station performs channel coding and modulation on the control information into a symbol stream using the previously (step  1208 ) selected control channel candidate and maps the symbol stream to the predetermined data channel region at step  1212 . At this time, the predetermined data channel region can be formed on all or some of the symbols in the data channel region. This is the same as described with reference to  FIGS. 10 and 11 . That is, the control channel can be transmitted using all or some of the symbols of the data channel region. 
         [0110]    According to an embodiment of the present invention, the base station can map the control information to the data channel region in distributed type at step  1212  so as to obtain frequency diversity gain. 
         [0111]    The base station repeats steps  1204  to  1212  to the users scheduled in order of priority so as to map the control channels of the scheduled users to transmission resources. Next, the base station transmits the control channel as multiplexed with the downlink data signal at step  1216 . 
         [0112]    A description is made of the method for the user equipment to receive the control channel transmitted over all or some of the symbols of the data channel region as described above.  FIG. 13  is a flowchart illustrating a method for the user equipment to receive the control channel transmitted in data channel region according to an embodiment of the present invention. 
         [0113]    Referring to  FIG. 13 , each user equipment checks the receivable control information formats at step  1300 . The receivable control information formats are preset via higher layer signaling. 
         [0114]    Next, the user equipment calculates a number of CCEs available for transmitting the control channel in some of the predetermined data channel region at step  1204 . Next, the user equipment determines a number of control channel candidates per AL at step  1304  and then determines the control channel candidates group per AL by applying the value (number of control channel candidates) to the hash function at step  1306 . 
         [0115]    Next, the user equipment performs demodulation on the control channel candidates in the predetermined data channel region and then performs channel decoding with receivable control information formats at step  1308 . The user equipment performs CRC to determine whether the decoding is successfully, at step  1310 . If the decoding fails, the user equipment repeats steps  1308  and  1310  on the other control channel candidates determined at step  1306 . If the decoding fails to all of the control channel candidates, this means that there is not control channel transmitted to the corresponding user. If the decoding is successful at step  1310 , the user equipment locates the transmission resource allocated itself by referencing the control information acquired on the control channel decoded successfully (successful CRC operation) and performs transmission/reception operating on the transmission resource allocated to itself. 
       Fourth Embodiment 
     Control Channel Transmission Using Control Channel Candidate Group Extended Over the Control Channel Region and Data Channel Region 
       [0116]      FIG. 14  is a diagram illustrating a method for transmitting/receiving control channel using both the control and data channel regions according to an embodiment of the present invention. 
         [0117]    In  FIG. 14 , the transmission resource is divided into the control channel region composed of 3 symbols  1400  to  1402  and the data channel region composed of 11 symbols  1403  to  1413  in time domain. 
         [0118]    Referring to  FIG. 14 , the base station transmits the extended control channel  1414  on the control channel region of the symbols  1400  to  1402  and the data channel region of symbols  1403  to  1413  in a subframe. Here, the extended control channel  1414  is composed of 16 CCEs. 
         [0119]    The eight CCEs  1415  at the first half of the extended control channel  1414  is transmitted in parts of three OFDM symbols  1400  to  1402  at the beginning of the subframe. Also, the eight CCEs  1416  at the last half of the extended control channel  1414  is transmitted on predetermined frequency region (subcarriers) in the rest 11 OFDM symbols  1403  to  1413  of the subframe. The base station notifies the corresponding user equipment with the designation information of specific user equipments receiving the control channel using the above described method, information on the extended control channel candidate group, and the number of subframes used for transmitting the extended control channel via higher layer signaling. In  FIG. 14 , the number of CCEs constituting an extended control channel can be changed. 
         [0120]      FIG. 15  is a diagram illustrating a method for transmitting/receiving control channel using both the control and data channel regions according to another embodiment of the present invention. 
         [0121]    In  FIG. 15 , the transmission resource is divided into the control channel region composed of 3 symbols  1500  to  1502  and the data channel region composed of 11 symbols  1503  to  1513  in time domain. 
         [0122]    Referring to  FIG. 15 , the base station transmits the extended PDCCH  1514  on the conventional control channel region of the symbols  1500  to  1502  and some parts of the data channel region of symbols  1503  to  1513  in a subframe. Here, the extended control channel  1514  is composed of 16 CCEs. 
         [0123]    The 8 CCEs  1515  at the first half of the extended control channel  1514  is transmitted in some parts of the three OFDM symbols  1500  to  1502  at the beginning of the subframe. Also, the 8 CCEs  1516  at the last half of the extended control channel  1514  is transmitted on the predetermined frequency region (subcarriers) of 5 FODM symbols  1503  to  1507  in the data channel region. 
         [0124]    The base station notifies the corresponding user equipment with the designation information of specific user equipment receiving the control channel using the above described method, information on the extended control channel candidate group, and the number of subframes used for transmitting the extended control channel via higher layer signaling. In  FIG. 15 , the number of CCEs constituting an extended control channel and the number of OFDM symbols used for the control channel transmission can be changed. The reason why only a part at the beginning of the data channel region is used for the control channel transmission is to reduce the power consumption of the user equipment as described above. 
         [0125]      FIG. 16  is a flowchart illustrating a method for transmitting control channel using both the control and data channel regions according to an embodiment of the present invention. 
         [0126]    Referring to  FIG. 16 , the base station determines priorities of the users to be scheduled at step  1600 . Next, the base station determines the control information of the user and the control information format in order of priority of the user at step  1602 . 
         [0127]    In order to implement the method for transmitting the control channel using the extended control channel candidates with a part of the data channel region, the base station calculates a number of CCEs available for transmitting the control channel in further consideration of a part of the predetermined data channel region at step  1604 . The base station determines a number of control channel candidates per extended AL proposed in the present invention at step  1606 . At this time, the maximum AL is determined based on the predetermined amount of data channel resource for transmitting control channel. Next, the base station determines the extended control channel candidate group by applying the number of control channel candidates at step  1608 . Once the control channel candidate group is determined, the base station selects a control channel candidate which is not preoccupied by a user having a higher priority as the control channel candidate of the corresponding user at step  1610 . Next, the base station performs channel coding and modulation on the control information in the control information format into the modulated symbol stream and maps the symbol stream to the control and data channel regions using the selected control channel candidate at step  1612 . At step  1612 , the base station maps the control information to the data channel region such that the resource blocks are transmitted in distributed manner as described with reference to step  1212  of  FIG. 12 . 
         [0128]    At this time, the predetermined data channel region can be a formed across all or some of the symbols of the data channel region. This is the same as described with reference to  FIGS. 14 and 15 . That is, the control channel transmitted in the data channel region can be mapped in all or some of the symbols of the data channel region. 
         [0129]    Next, the base station repeats steps  1604  to  1612  to the user having the next higher priority until the control channels of all the scheduled users are mapped to the transmission resource at step  1614 . Finally, the base station transmits the control channels as multiplexed with the downlink data signals at step  1616 . 
         [0130]    A description is made of a method for receiving the control channel transmitted on both the control and data channel regions as described above.  FIG. 17  is a flowchart illustrating a method for a user equipment to receive the control channel transmitted in both the control and data channel regions using the extended control channel candidate group according to an embodiment of the present invention. 
         [0131]    Referring to  FIG. 17 , each user equipment checks the receivable control information formats at step  1700 . The receivable control information formats are preset via higher layer signaling. Next, the base station calculates a number of CCEs available in the predetermined data channel region as described with reference to step  1606  of  FIG. 16  at step  1702 . Next, the base station determines a number of control channel candidates per extended Al at step  1704  and then determines the control channel candidate group per extended AL by applying the value (number of control channel candidates) to the hash function at step  1706 . Next, the user equipment performs demodulations on the control channel region and a predetermined part of the data channel region channel and then performs decoding for the receivable control channel formats at step  1708 . The user equipment performs CRC to determine whether the decoding is successful at step  1710 . If the decoding fails, the user equipment repeats steps  1708  and  1710  to the other control channel candidates. If the decoding fails on all the control channel candidates, this means that there is no control channel destined to the corresponding user. Otherwise, if the decoding succeeds at step  1710 , the user equipment locates the transmission resource allocated to itself based on the control information obtained by decoding the control channel (successful CRC operation) and performs transmission/reception operation on the transmission resource allocated to itself at step  1712 . 
         [0132]    As described with reference to  FIG. 17 , when it is impossible to use the extended control channel candidate group, the control channel can be transmitted/received repeatedly in a predetermined part of the data channel region using the control channel candidate group. That is, the same control channel can be transmitted in the control and data channel regions repeatedly. In the embodiment of  FIG. 14 , the first 8 CCEs  1415  of the control channel  1414  transmitted in a part of the 3 OFDM symbols  1400  to  1402  at the beginning of the subframe as the control channel region and the last 8 CCEs  1416  transmitted in a predetermined frequency region of the 11 OFDM symbols  1403  to  1413  can be the same control channel. Also, in the embodiment of  FIG. 15 , the first 8 CCEs transmitted at a part of the first 3 OFDM symbols  1500  to  1502  of the subframe as the control channel region and the last 8 CCEs  1516  transmitted on a predetermined frequency region in 5 OFDM symbols  1503  to  1507  as a part of the data channel region can be the same control channel. 
         [0133]    The configurations of the base station and the user equipment for transmitting/receiving control channels according to an embodiment of the present invention are described hereinafter. 
         [0134]    First of all, a description is made of the configuration of a base station for transmitting the control channel in a wireless communication according to an embodiment of the present invention.  FIG. 18  is a block diagram illustrating a configuration of a base station for transmitting control channel in a wireless communication system according to an embodiment of the present invention. 
         [0135]    The base station according to an embodiment of the present invention includes a scheduler  1800 , a controller  1802 , a PDCCH hash function device  1804 , a DCI signal generator  1806 , a scrambler  1808 , a CCE mapper  1810 , a channel encoder/modulator  1812 , a multiplexer  1814 , and a Tx processor  1816 . 
         [0136]    The scheduler  1800  transmits control channel (PDCCH) to a certain user (equipment) to inform of allocation of downlink (DL) resource and uplink (UL resource and performs scheduling by assigning priorities to users. At this time, the scheduler  1800  performs scheduling as described above base on the channel condition reported by each user (equipment). 
         [0137]    The control unit  1802  controls operations of the function blocks  1804  to  1816  according the scheduling of the scheduler  1800 . At this time, the determination of the scheduler  1802  can be updated according to the determination of the controller  1802 . 
         [0138]    The hash function device  1804  receives a number of available CCEs and a number of PDCCHs from the controller  1802 , determines a control channel candidate based on these values, and returns the determined value to the controller  1802 . The controller  1802  selects a control channel candidate which is not occupied by other user equipment having higher priority as the control channel of the corresponding user equipment. 
         [0139]    Meanwhile, the controller  1802  generates DCI of the user equipment according to the scheduling result of the scheduler  1800 . 
         [0140]    The control information generator  1806  generates the DCI under the control of the controller  1802 . 
         [0141]    The scrambler  1808  performs scrambling on the control information with the identifier of the subframe in which the data channel indicating the control information of the corresponding user equipment is transmitted. That is, when the control channel is transmitted in at least two subframes, the scrambler  1808  performs scrambling the control information using the identifier of the last subframe. 
         [0142]    The CCE mapper  1810  maps the control information to the control channel selected by the controller  1802  among the control channel candidates determined by the hash function device  1804 . 
         [0143]    The controller  1802  controls the CCE mapper  1810  to map the control channel to the control channel transmission region. The control channel can be mapped to the control channel regions of plural subframes as described with reference to  FIG. 4 , an extended control channel is mapped to the control channel regions of plural subframes as described with reference to  FIG. 7 . Also, the control channel can be mapped to the data channel region as described with reference to  FIGS. 10 and 11 . Furthermore, the control channel can be mapped to the control and data channel regions as described with reference to  FIGS. 14 and 15 . 
         [0144]    Meanwhile, the encoder/modulator  1812  performs encoding and modulation on the downlink data to generate data channel. The multiplexer  1814  multiplexes the encoded and modulated data channel and control channel into downlink signals. The transmitter  1816  transmits the downlink signals. 
         [0145]    A procedure proposed in the present invention is performed by the controller  1802 , the hash function device  1804 , the scrambler  1808 , and CCE mapper  1810 . 
         [0146]    The controller  1802  knows the control channel resource or data channel resource of a plurality of subframes as the additional resource for use in control channel transmission in advance and determines whether to configure the extended control channel candidates group or the conventional control channel candidates group according to how to us the additional resource. Once the additional control resource and how to use the control resource are determined, the controller  1802  controls the scheduler  1800  to use the additional resource for control channel transmission and, when using the extended control channel candidate group, provides this information to the hash function device  1804  to determine the extended control channel candidate from the extended control channel candidate group. 
         [0147]    In case of transmitting the control channel using plural subframes, the scrambler  1808  performs scrambling with the number of subframe carrying the corresponding data which is input by the controller  1802 . 
         [0148]    The controller  1802  can provide the CCE mapper  1810  with the information on the control channel region and the data channel region determined for control channel transmission. The CCE mapper  1810  maps the control channel to the corresponding region according to the information received from the controller  1802 . 
         [0149]    A description is made of the configuration of a user equipment for receiving the control channel in a wireless communication system according to an embodiment of the present invention.  FIG. 19  is a block diagram illustrating a configuration of a user equipment for receiving control channel in a wireless communication according to an embodiment of the present invention. 
         [0150]    Referring to  FIG. 19 , the user equipment according to an embodiment of the present invention includes an RX processor  1900 , a de-multiplexer  1902 , a storage  1904 , a CCE de-mapper  1906 , a data channel decoder/demodulator  1908 , a controller  1910 , a hash function device  1912 , and a control channel decoder/demodulator  1914 . 
         [0151]    The receiver  1900  receives the signal transmitted by the base station through an antenna and converts the signal into baseband signal. The de-multiplexer  1902  de-multiplexes the signal received by the means of the receiver into the control channel and the data channel. 
         [0152]    The storage  1904  stores the control channel de-multiplexed from the received signal. This is for the method for transmitting the control channel using a plurality of subframes, and the capacity of the storage  1904  is determined under the control of the controller  1910 . 
         [0153]    The CCE de-mapper  1906  de-maps the control channel received in one or more subframes into control channel candidates. That is, the CCE de-mapper  1906  extracts the control channel from one or more subframes. 
         [0154]    The hash function device  1912  receives information on the number of available CCEs and the number of available control channel candidates input by the controller  1910 , determines the control channel candidate, and returns the determined value to the controller  1910 . The controller  1910  notifies the CCE de-mapper  1906  with the control channel candidates. 
         [0155]    The control channel decoder/demodulator  1908  performs demodulation and decoding on the individual control channel candidates de-multiplexed by the CCE de-mapper  1906  and notifies the controller  1910  whether the decoding succeeds. 
         [0156]    If the decoding on a specific control channel candidate, the control channel decoder/demodulator  1908  performs channel decoding and demodulation on the next control channel candidate de-multiplexed by the CCE mapper  1906  and notifies the controller  1910  whether the decoding succeeds. That is, the control channel decoder/demodulator  1908  performs CRC and notifies whether the blind decoding succeeds. If the CRC succeeds, this means that the decoding is successful. 
         [0157]    If the control channel decoding succeeds, the control channel decoder/demodulator  1908  notifies the controller  1910  of the success of decoding. The controller  1910  determines that where there is the data channel allocated to itself, based on the control information decoded from the control channel. That is, the controller  1910  recognizes the data channel allocated to the user equipment by referencing the control information. If there is the data signal of the corresponding user, the data channel decoder/demodulator  1908  performs demodulation and decoding on the data channel extracted by the de-multiplexer  1902  under the control of the controller  1910 . 
         [0158]    The procedure proposed in the present invention is performed by the controller  1910 , the de-multiplexer  1902 , the storage  1904 , the CCE de-mapper  1906 , the control channel decoder/demodulator  1908 , and the hash function device  1912 . 
         [0159]    The controller  1910  notifies the de-multiplexer  1902  of the resource added for use of transmitting control channel so as to recognize a part of the data channel region that is used for control channel transmission. 
         [0160]    In case of using extended control channel candidate group, the controller  1910  provides the hash function device  1912  with this information such that the hash function device  1912  determines the extended control channel candidate in the extended control channel candidate group. 
         [0161]    In case of using a plurality of subframes for transmitting control channels, the controller  1910  notifies the storage  1904  of the number of subframes used for control channel transmission such that the storage  1904  can store the control channels transmitted in the plural subframes. 
         [0162]    The storage  1904  sends the control channels stored according to the value input by the controller  1910  to the CCE de-mapper  1906 . The CCE de-mapper  1906  and the control channel decoder/demodulator  1908  performs de-multiplexing and decoding and demodulation on the control signal of individual control channel candidates (or extended control channel candidates) input by the controller  1910 . 
         [0163]    As described above, the method according to an embodiment of the present invention secure high energy using the additional time domain resource for transmitting a control channel so as to increases the coverage of the control channel. Accordingly, it is possible to avoid data channel decoding failure caused by the control channel reception failure, resulting in reduction of probability of outage. 
         [0164]    The specification and drawings are to be regarded in an illustrative rather than a restrictive sense in order to help understand the present invention. It is obvious to those skilled in the art that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims.