Abstract:
When downlink data allocation is indicated in an ePDCCH, this terminal device can determine PUCCH resources to be used in notification of response signals indicating results of error detection of downlink data without imposing scheduling restrictions on future DL subframes. In this device, an extraction unit ( 204 ) receives downlink data on multiple unit bands. A CRC unit ( 211 ) detects errors in the downlink data. A response signal generation unit ( 212 ) generates a response signal by using the results of error detection of the downlink data obtained by the CRC unit ( 211 ). The control unit ( 208 ) arranges the response signal in the PUCCH resources corresponding to the current DL subframe.

Description:
TECHNICAL FIELD 
     The present invention relates to a terminal apparatus, a base station apparatus and a transmission method. 
     BACKGROUND ART 
     3GPP LTE employs Orthogonal Frequency Division Multiple Access (OFDMA) as a downlink communication scheme. In radio communication systems to which 3GPP LTE is applied, base stations transmit synchronization signals (i.e., Synchronization Channel: SCH) and broadcast signals (i.e., Broadcast Channel: BCH) using predetermined communication resources. Meanwhile, each terminal finds an SCH first and thereby ensures synchronization with the base station. Subsequently, the terminal reads BCH information to acquire base station-specific parameters (e.g., frequency bandwidth) (see, Non-Patent Literature (hereinafter, abbreviated as NPL) 1, 2 and 3). 
     In addition, upon completion of the acquisition of the base station-specific parameters, each terminal sends a connection request to the base station to thereby establish a communication link with the base station. The base station transmits control information via Physical Downlink Control CHannel (PDCCH) as appropriate to the terminal with which a communication link has been established via a downlink control channel or the like. 
     The terminal performs “blind-determination” on each of a plurality of pieces of control information included in the received PDCCH signal (i.e., Downlink (DL) Assignment Control Information: also referred to as Downlink Control Information (DCI)). More specifically, each piece of the control information includes a Cyclic Redundancy Check (CRC) part and the base station masks this CRC part using the terminal ID of the transmission target terminal. Accordingly, until the terminal demasks the CRC part of the received piece of control information with its own terminal ID, the terminal cannot determine whether or not the piece of control information is intended for the terminal. In this blind-determination, if the result of demasking the CRC part indicates that the CRC operation is OK, the piece of control information is determined as being intended for the terminal. 
     Moreover, in 3GPP LTE, Automatic Repeat Request (ARQ) is applied to downlink data to terminals from a base station. More specifically, each terminal feeds back a response signal indicating the result of error detection on the downlink data to the base station. Each terminal performs a CRC on the downlink data and feeds back Acknowledgment (ACK) when CRC=OK (no error) or Negative Acknowledgment (NACK) when CRC=Not OK (error) to the base station as a response signal. An uplink control channel such as Physical Uplink Control Channel (PUCCH) is used to feed back the response signals (i.e., ACK/NACK signals (hereinafter, may be referred to as “A/N,” simply)). 
     The control information to be transmitted from a base station herein includes resource assignment information including information on resources assigned to the terminal by the base station. As described above, PDCCH is used to transmit this control information. This PDCCH includes one or more L1/L2 control channels (L1/L2 CCH). Each L1/L2 CCH consists of one or more Control Channel Elements (CCE). More specifically, a CCE is the basic unit used to map the control information to PDCCH. Moreover, when a single L1/L2 CCH consists of a plurality of CCEs (2, 4 or 8), a plurality of contiguous CCEs starting from a CCE having an even index are assigned to the L1/L2 CCH. The base station assigns the L1/L2 CCH to the resource assignment target terminal in accordance with the number of CCEs required for indicating the control information to the resource assignment target terminal. The base station maps the control information to physical resources corresponding to the CCEs of the L1/L2 CCH and transmits the mapped control information. 
     In addition, CCEs are associated with component resources of PUCCH (hereinafter, may be referred to as “PUCCH resource”) in a one-to-one correspondence. Accordingly, a terminal that has received an L1/L2 CCH identifies the component resources of PUCCH that correspond to the CCEs forming the L1/L2 CCH and transmits a response signal to the base station using the identified resources. However, when the L1/L2 CCH occupies a plurality of contiguous CCEs, the terminal transmits the response signal to the base station using a PUCCH component resource corresponding to a CCE having a smallest index among the plurality of PUCCH component resources respectively corresponding to the plurality of CCEs (i.e., PUCCH component resource associated with a CCE having an even numbered CCE index). In this manner, the downlink communication resources are efficiently used. 
     As illustrated in  FIG. 1 , a plurality of response signals transmitted from a plurality of terminals are spread using a Zero Auto-correlation (ZAC) sequence having the characteristic of zero autocorrelation in time-domain, a Walsh sequence and a discrete Fourier transform (DFT) sequence, and are code-multiplexed in a PUCCH. In  FIG. 1 , (W 0 , W 1 , W 2 , W 3 ) represent a length-4 Walsh sequence and (F 0 , F 1 , F 2 ) represent a length-3 DFT sequence. As illustrated in  FIG. 1 , ACK or NACK response signals are primary-spread over frequency components corresponding to 1 SC-FDMA symbol by a ZAC sequence (length-12) in frequency-domain. More specifically, the length-12 ZAC sequence is multiplied by a response signal component represented by a complex number. Subsequently, the ZAC sequence serving as the response signals and reference signals after the primary-spread is secondary-spread in association with each of a Walsh sequence (length-4: W 0 -W 3  (may be referred to as Walsh Code Sequence)) and a DFT sequence (length-3: F 0 -F 2 ). More specifically, each component of the signals of length-12 (i.e., response signals after primary-spread or ZAC sequence serving as reference signals (i.e., Reference Signal Sequence) is multiplied by each component of an orthogonal code sequence (i.e., orthogonal sequence: Walsh sequence or DFT sequence). Moreover, the secondary-spread signals are transformed into signals of length-12 in the time-domain by inverse fast Fourier transform (IFFT). A CP is added to each signal obtained by IFFT processing, and the signals of one slot consisting of seven SC-FDMA symbols are thus formed. 
     The response signals from different terminals are spread using ZAC sequences each corresponding to a different cyclic shift value (i.e., index) or orthogonal code sequences each corresponding to a different sequence number (i.e., orthogonal cover index (OC index)). An orthogonal code sequence is a combination of a Walsh sequence and a DFT sequence. In addition, an orthogonal code sequence is referred to as a block-wise spreading code in some cases. Thus, base stations can demultiplex the code-multiplexed plurality of response signals using the related art despreading and correlation processing (see, NPL 4). 
     However, it is not necessarily true that each terminal succeeds in receiving a downlink assignment control signal because the terminal performs blind-determination in each subframe to find a downlink assignment control signal intended for the terminal. When the terminal fails to receive the downlink assignment control signal intended for the terminal on a certain downlink component carrier, the terminal would not even know whether or not there is downlink data intended for the terminal on the downlink component carrier. Accordingly, when a terminal fails to receive the downlink assignment control signal intended for the terminal on a certain downlink component carrier, the terminal generates no response signals for the downlink data on the downlink component carrier. This error case is defined as discontinuous transmission of ACK/NACK signals (DTX of response signals) in the sense that the terminal transmits no response signals. 
     In 3GPP LTE systems (may be referred to as “LTE system,” hereinafter), base stations assign resources to uplink data and downlink data, independently. For this reason, in the 3GPP LTE system, terminals (i.e., terminals compliant with LTE system (hereinafter, referred to as “LTE terminal”)) encounter a situation where the terminals need to transmit uplink data and response signals for downlink data simultaneously in the uplink. In this situation, the response signals and uplink data from the terminals are transmitted using time-division multiplexing (TDM). As described above, the single carrier properties of transmission waveforms of the terminals are maintained by the simultaneous transmission of response signals and uplink data using TDM. 
     In addition, as illustrated in  FIG. 2 , the response signals (i.e., “A/N”) transmitted from each terminal partially occupy the resources assigned to uplink data (i.e., Physical Uplink Shared CHannel (PUSCH) resources) (i.e., response signals occupy some SC-FDMA symbols adjacent to SC-FDMA symbols to which reference signals (RS) are mapped) and are thereby transmitted to a base station in time-division multiplexing (TDM). However, “subcarriers” in the vertical axis in  FIG. 2  are also termed as “virtual subcarriers” or “time contiguous signals,” and “time contiguous signals” that are collectively inputted to a discrete Fourier transform (DFT) circuit in a SC-FDMA transmitter are represented as “subcarriers” for convenience. More specifically, optional data of the uplink data is punctured due to the response signals in the PUSCH resources. Accordingly, the quality of uplink data (e.g., coding gain) is significantly reduced due to the punctured bits of the coded uplink data. For this reason, base stations instruct the terminals to use a very low coding rate and/or to use very large transmission power so as to compensate for the reduced quality of the uplink data due to the puncturing. 
     Meanwhile, the standardization of 3GPP LTE-Advanced for realizing faster communication than 3GPP LTE is in progress. 3GPP LTE-Advanced systems (may be referred to as “LTE-A system,” hereinafter) follow LTE systems. 3GPP LTE-Advanced will introduce base stations and terminals capable of communicating with each other using a wideband frequency of 40 MHz or greater to realize a downlink transmission rate of up to 1 Gbps or above. 
     In the LTE-A system, in order to simultaneously achieve backward compatibility with the LTE system and ultra-high-speed communication several times faster than transmission rates in the LTE system, the LTE-A system band is divided into “component carriers” of 20 MHz or below, which is the bandwidth supported by the LTE system. In other words, the “component carrier” is defined herein as a band having a maximum width of 20 MHz and as the basic unit of communication band. In the Frequency Division Duplex (FDD) system, moreover, “component carrier” in downlink (hereinafter, referred to as “downlink component carrier”) is defined as a band obtained by dividing a band according to downlink frequency bandwidth information in a BCH broadcasted from a base station or as a band defined by a distribution width when a downlink control channel (PDCCH) is distributed in the frequency domain. In addition, “component carrier” in uplink (hereinafter, referred to as “uplink component carrier”) may be defined as a band obtained by dividing a band according to uplink frequency band information in a BCH broadcasted from a base station or as the basic unit of a communication band of 20 MHz or below including a Physical Uplink Shared CHannel (PUSCH) in the vicinity of the center of the bandwidth and PUCCH s for LTE on both ends of the band. In addition, the term “component carrier” may be also referred to as “cell” in English in 3GPP LTE-Advanced. Furthermore, “component carrier” may also be abbreviated as CC(s). 
     In the Time Division Duplex (TDD) system, a downlink component carrier and an uplink component carrier have the same frequency band, and downlink communication and uplink communication are realized by switching between the downlink and uplink on a time division basis. For this reason, in the case of the TDD system, the downlink component carrier can also be expressed as “downlink communication timing in a component carrier.” The uplink component carrier can also be expressed as “uplink communication timing in a component carrier.” The downlink component carrier and the uplink component carrier are switched based on a UL-DL configuration as shown in  FIG. 3 . In the UL-DL configuration shown in  FIG. 3 , timings are configured in subframe units (that is, 1 msec units) for downlink communication (DL) and uplink communication (UL) per frame (10 msec). The UL-DL configuration can construct a communication system capable of flexibly meeting a downlink communication throughput requirement and an uplink communication throughput requirement by changing a subframe ratio between downlink communication and uplink communication. For example,  FIG. 3  illustrates UL-DL configurations (Config 0 to 6) having different subframe ratios between downlink communication and uplink communication. In addition, in  FIG. 3 , a downlink communication subframe is represented by “D,” an uplink communication subframe is represented by “U” and a special subframe is represented by “S.” Here, the special subframe is a subframe at the time of switchover from a downlink communication subframe to an uplink communication subframe. In the special subframe, downlink data communication may be performed as in the case of the downlink communication subframe. In each UL-DL configuration shown in  FIG. 3 , subframes (20 subframes) corresponding to 2 frames are expressed in two stages: subframes (“D” and “S” in the upper row) used for downlink communication and subframes (“U” in the lower row) used for uplink communication. 
     Furthermore, as shown in  FIG. 3 , an error detection result corresponding to downlink data (ACK/NACK) is indicated in the fourth uplink communication subframe or an uplink communication subframe after the fourth subframe from the subframe to which the downlink data is assigned. In the TDD system, it is necessary to transmit response signals indicating error detection results corresponding to downlink data which has been indicated in a plurality of downlink communication subframes collectively in one uplink communication subframe. The number of downlink communication subframes at this time (which may also be called “bundling window”) is represented by M and an index of a downlink communication subframe corresponding to one uplink communication subframe is represented by m. For example, in UL-DL Configuration#2, error detection results on downlink data in four downlink communication subframes SF#4, 5, 6 and 8 of a first frame are indicated in uplink communication subframe SF#3 of a second frame. In this case, M=4, and SF#4, 5, 6 and 8 of the first frame correspond to m=0, 1, 2 and 3 respectively. 
     In TDD in an LTE-A system, a terminal receives downlink assignment control information via PDCCH and transmits a response signal over an uplink upon receiving downlink data. The following two methods are adopted as the method of transmitting the response signals. 
     Method 1 is a method (implicit signaling) whereby a terminal transmits a response signal using a PUCCH resource associated, in a one-to-one correspondence, with leading CCE index n CCE  of CCE (Control Channel Element) occupied by PDCCH and index m of a downlink communication subframe corresponding to one uplink communication subframe (see PTL 1). Note that m is indexed in time sequence. 
     More specifically, the terminal first calculates parameter c={0, 1, 2, 3} that satisfies equation 1 in a magnitude relationship between leading CCE index n CCE  occupied by PDCCH intended for the terminal (DL assignment) and N c  for each DL subframe m. Note that Nc in equation 1 is calculated according to equation 2. N DL   RB  in equation 2 is the number of downlink resource blocks and N RB   SC  is the number of subcarriers per resource block. The terminal then determines PUCCH resources n (1)   PUCCH  based on DL subframe m and calculated c according to equation 3 (see NPL 3). Note that N (1)   PUCCH  in equation 3 is an offset value for all PUCCH resources and is a value set in the terminal in advance.
 
[1]
 
 N   c   ≦n   CCE   &lt;N   c+1   (Equation 1)
 
[2]
 
 N   c =max{0,└[ N   RB   DL ·( N   sc   RB   ·c− 4)]/36┘}  (Equation 2)
 
[3]
 
 n   PUCCH,j   (1) =( M−m− 1)· N   c   +m·N   c+1   +n   CCE,m   +N   PUCCH   (1)   (Equation 3)
 
     As shown in  FIG. 4 , in TDD, PUCCH resource region  10  corresponding to PDCCH is divided for each c and each partial region corresponding to c is divided for each m. PUCCH resources for each c and each m are arranged from a frequency end direction toward the center direction of a component carrier in ascending order of m and in ascending order of c. 
     In the example of  FIG. 4 , when transmitting a response signal indicating an error detection result corresponding to downlink data indicated in a subframe with m=2, the terminal first calculates c from a magnitude relationship between leading CCE index n CCE  occupied by PDCCH (DL assignment) intended for the terminal and N c  in virtual PUCCH resource region  50  that collects PUCCH resources corresponding to the subframe with m=2 (equation 1). 
     Next, the terminal arranges the response signal in PUCCH resource n (1)   PUCCH  (reference numeral  11  in  FIG. 4 ) in actual PUCCH resource region  10  for the acquired c (c=0 in  FIG. 4 ) (equation 3). 
     The range of c used here extends as the CCE index increases. A maximum value of the CCE index increases as the scale of the PDCCH region increases. Therefore, the greater the range of c used, the greater the PDCCH region becomes. The scale of the PDCCH region is defined by CFI (Control Format Indicator). For example, the PDCCH region is composed of three OFDM symbols when CFI=3, and it is therefore largest, whereas when CFI=1, the PDCCH region is composed of one OFDM symbol, and it is therefore smallest. Furthermore, CFI is dynamically indicated to the terminal for every subframe. Therefore, the PUCCH resource region is used more frequently when c is smaller. For this reason, the occupancy of control information in the PUCCH resource region increases as c decreases and decreases as c increases. 
     In the LTE-A system, a control signal may be transmitted using a plurality of PUCCH resources by applying transmission diversity or applying channel selection during carrier aggregation. In this case, as shown in equation 4 and  FIG. 5 , method 1 uses a predetermined PUCCH resource (reference numeral  11  in  FIG. 5 ) and a PUCCH resource (reference numeral  12  in  FIG. 5 ) adjacent to the PUCCH resource (which becomes n CCE +1 with respect to n CCE ) in the actual PUCCH resource region. In other words, in the LTE-A system, an offset of +1 is added to the CCE index in the actual PUCCH resource region.
 
[4]
 
 n   PUCCH,j+1   (1) =( M−m− 1)· N   c   +m·N   c+1   +n   CCE,m +1+ N   PUCCH   (1)   (Equation 4)
 
     Method 2 is a method (explicit signaling) whereby a base station indicates PUCCH resources to a terminal in advance and the terminal transmits a response signal using the PUCCH resources indicated in advance from the base station. 
     According to method 2, the base station can dynamically indicate to the terminal, information (ARI (Ack/Nack Resource Indicator)) indicating one PUCCH resource from among a plurality of PUCCH resources through DL assignment in advance. This makes it possible to dynamically switch between quasi-static PUCCH resources with a small number of bits. For example, when ARI has 2 bits, the base station can select one of four PUCCH resources. 
     In the LTE-A system, various devices are introduced as radio communication terminals such as M2M (Machine to Machine) communication, and the number of multiplexed terminals tends to increase by MIMO transmission techniques, and therefore the number of control signals transmitted from a base station to a terminal is considered to increase. For this reason, there may not be enough PDCCH regions which are regions in which PDCCHs used for control signals are mapped. When the base station cannot transmit control signals due to this shortage of resources, the base station can no longer assign data to the terminal. For this reason, the terminal can no longer use a PUSCH region to be used for data even if the PUSCH region is free and the system throughput may deteriorate. 
     As a method of solving this shortage of resources, studies are being carried out on the possibility of mapping control signals intended for terminals under a base station to a PDSCH region as well. This region in which control signals intended for terminals under the base station are mapped, that is, a region available to both control signals and data is called “enhanced PDCCH (ePDCCH) region.” Thus, the base station can transmit more control signals to terminals by providing ePDCCHs, and can thereby realize various kinds of control. For example, the base station can perform transmission power control on control signals transmitted to a terminal located near a cell edge or control of interference of transmitted control signals with another cell or control of interference of another cell with the cell formed by the base station. 
     In LTE, DL assignment instructing downlink data assignment (PDSCH) and UL grant instructing uplink data assignment are transmitted using PDCCH. 
     In LTE-Advanced, DL assignment and UL grant are transmitted also using ePDCCH in the same way as PDCCH. Studies are being carried out on the possibility that resources to which DL assignment is mapped and resources to which UL grant is mapped will be divided on the frequency axis in an ePDCCH region. 
     Methods 1 and 2 described above are defined as the method of determining PUCCH resources in a PUCCH resource region when DL assignment is indicated in a PDCCH region (hereinafter referred to as “PDCCH-PUCCH resource region”). Furthermore, in method 2, it is defined that a preset PUCCH resource is selected by dynamic ARI. 
     Here, when a PUCCH resource region in the case where DL assignment is indicated in an ePDCCH region (hereinafter referred to as “ePDCCH-PUCCH resource region”) is secured aside from a PDCCH-PUCCH resource region, the total amount of the PUCCH resource region increases. Especially when carrier aggregation is applied, PUCCH is transmitted using only one cell to avoid PAPR (Peak-to-Average Power Ratio) of the terminal from increasing. The cell is always PCell. PCell is generally a macro cell having a large coverage and high mobility is secured by a macro cell transmitting PUCCH. The capacity of PUCCH resources may be tight in the future due to not only introduction of ePDCCH but also introduction of carrier aggregation or introduction of M2M whereby many terminals perform data communication. Thus, in the LTE-A system, studies are being carried out on operation of causing ePDCCH-PUCCH resource regions to overlap with PDCCH-PUCCH resource regions. 
     As a method of determining ePDCCH-PUCCH resources, a method of instructing a preset offset value for an eCCE index using ARI or a method of defining a fixed value (equation 5) (see NPL 5). According to these methods, the base station first determines whether or not ePDCCH-PUCCH resources with offset value 0, that is, through implicit signaling, collide with PDCCH-PUCCH resources. When no collision occurs, the base station indicates ARI=0 to the terminal so as to use the ePDCCH-PUCCH resources. On the other hand, when collision occurs, the base station sequentially determines collision or no collision using ePDCCH-PUCCH resources with other offset values added thereto and indicates ARI or a fixed value corresponding to a non-colliding ePDCCH-PUCCH resource to the terminal.
 
[5]
 
 n   PUCCH   E   =n   E-CCE   +N   PUCCH   (1) +ARI  (Equation 5)
 
     In ePDCCH, values such as 4, 8, 16, 32 are taken as scale N eCCE  of one ePDCCH search space. However, values such as 2, 4, 8, 16 are taken as N eCCE  in the case of a special subframe where the number of OFDM symbols to be used for the downlink is small (that is, the case where a configuration with a small number of OFDM symbols to be used for the downlink is set as a special subframe configuration in which the number of OFDM symbols to be used for downlink communication in a special subframe, a gap (downlink/uplink switching period) and a ratio of the number of OFDM symbols to be used for uplink communication are set). Furthermore, the base station can set ePDCCH search space sets which are different between terminals and these ePDCCH search space sets may have different sizes. The base station can further set a plurality of ePDCCH search space sets in one terminal and these ePDCCH search space sets may have different scales. The base station can further set N (1)   PUCCH  as start positions of different PUCCH resources for the respective ePDCCH search space sets. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1 
         Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-507704 
       
    
     Non-Patent Literature 
     
         
         NPL 1 
         3GPP TS 36.211 V10.1.0, “Physical Channels and Modulation (Release 10),” March 2011 
         NPL 2 
         3GPP TS 36.212 V10.1.0, “Multiplexing and channel coding (Release 10),” March 2011 
         NPL 3 
         3GPP TS 36.213 V10.1.0, “Physical layer procedures (Release 10),” March 2011 
         NPL 4 
         Seigo Nakao, Tomofumi Takata, Daichi Imamura, and Katsuhiko Hiramatsu, “Performance enhancement of E-UTRA uplink control channel in fast fading environments,” Proceeding of IEEE VTC 2009 spring, April. 2009 
         NPL 5 
         Samsung, 3GPP RAN1 meeting #68bis, R1-121647, “HARQ-ACK PUCCH Resources in Response to E-PDCCH Detections,” March 2012 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     As shown in  FIG. 6 , ePDCCH-PUCCH resource region  20  may be divided for each c′ and each m as in the case of PDCCH-PUCCH resource region  10  shown in  FIGS. 4 and 5 . At this time, PUCCH resources are arranged in ascending order of m and in ascending order of c′ from the frequency end direction to center direction of a component carrier. When ARI has 2 bits, one of four different offset values δ 0 (=0), δ 1 , δ 2  and δ 3  is indicated to the terminal. At least two offset values are greater than “+1.” For this reason, when m for a DL subframe at certain timing is assumed to be m current , the possibility that a PUCCH resource as the offset destination may become m&gt;m current  is higher than “+1” which is the offset value applicable in the PDCCH-PUCCH resource region. 
     For example, in  FIG. 6 , when m=1, suppose ePDCCH-PUCCH resource  21  with offset value δ 0 =0 in terminal A to which ePDCCH is indicated with eCCE index n eCCE  collides with a PDCCH-PUCCH resource in another terminal B to which PDCCH is indicated with CCE index n CCE . In this case, the base station determines collision or no collision regarding PUCCH resources  22 ,  23  and  24  which correspond to PUCCH resource  21  with offset values δ 1 , δ 2  and δ 3  added thereto respectively to avoid collision. The base station then indicates to terminal A, one of ARI=1, 2 and 3 corresponding to a resource among PUCCH resources  22 ,  23  and  24  in which no collision has occurred. However, in the example of  FIG. 6 , PUCCH resource  23  which is the destination of a shift corresponding to δ 2  becomes a PUCCH resource corresponding to m=2 and PUCCH resource  24  which is the destination of a shift corresponding to δ 3  becomes a PUCCH resource corresponding to m=3. This means that at a point in time of DL subframe m=1, control information mapped to an ePDCCH-PUCCH resource will occupy PUCCH resources when m=2 and m=3 which are future DL subframes. Since PUCCH resources are associated with PDCCH and ePDCCH respectively in a one-to-one correspondence, this means that the base station cannot perform scheduling on the PDCCH and ePDCCH when m=2 and m=3 which are future DL subframes. 
     Thus, the prior art imposes constraints on scheduling for future DL subframes when downlink data assignment is instructed by ePDCCH. The constraints increase as the value of m increases. Therefore, it is more likely that the base station cannot assign control information to an optimum terminal regarding large m. The base station may need scheduling taking into account an interval between subframes, which may cause a base station scheduler to be more complicated. 
     An object of the present invention is to provide a method of determining a PUCCH resource to be used to indicate a response signal indicating an error detection result of downlink data without imposing constraints on scheduling for future DL subframes when downlink data assignment is indicated by ePDCCH. 
     Solution to Problem 
     As described above, a terminal apparatus according to an aspect of the present invention is a terminal apparatus including: a control section that arranges a response signal on a predetermined PUCCH resource in an uplink control channel (PUCCH) resource region corresponding to an enhanced downlink control channel (ePDCCH); and a transmitting section that transmits the response signal arranged on the PUCCH resource, in which the PUCCH resource region is divided into a plurality of partial regions, and each of the partial regions is divided into a number of downlink communication subframes, PUCCH resources for each index c′ of the partial region and each index m indicating a time-sequential order of the downlink communication subframe are arranged in the PUCCH resource region in ascending order of indices m and in ascending order of indices c′, and the control section arranges a response signal corresponding to an m-th downlink communication subframe in a PUCCH resource selected from among the PUCCH resources corresponding to the indices in and below. 
     A transmission method according to an aspect of the present invention is a transmission method including: making a control to arrange a response signal on a predetermined PUCCH resource in an uplink control channel (PUCCH) resource region corresponding to an enhanced downlink control channel (ePDCCH); and transmitting the response signal arranged on the PUCCH resource, in which: the PUCCH resource region is divided into a plurality of partial regions, and each of the partial regions is divided into a number of downlink communication subframes, PUCCH resources for each index c′ of the partial region and each index m indicating a time-sequential order of the downlink communication subframe are arranged in the PUCCH resource region in ascending order of m and in ascending order of c′, and in the making a control, a response signal corresponding to an m-th downlink communication subframe is arranged in a PUCCH resource selected from among the PUCCH resources corresponding to the indices m and below. 
     Advantageous Effects of Invention 
     According to the present invention, when downlink data assignment is indicated by ePDCCH, it is possible to determine a PUCCH resource to be used to indicate a response signal indicating an error detection result of downlink data without imposing constraints on scheduling for future DL subframes. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a method of spreading response signals and reference signals; 
         FIG. 2  is a diagram illustrating an operation related to a case where TDM is applied to response signals and uplink data on PUSCH resources; 
         FIG. 3  is a diagram provided for describing a UL-DL configuration in TDD; 
         FIG. 4  is a diagram provided for describing a PDCCH-PUCCH resource region; 
         FIG. 5  is a diagram provided for describing an offset value in the PDCCH-PUCCH resource region; 
         FIG. 6  is a diagram provided for describing problems in the method of determining ePDCCH-PUCCH resources; 
         FIG. 7  is a block diagram illustrating a main configuration of a base station according to Embodiment 1 of the present invention; 
         FIG. 8  is a block diagram illustrating a main configuration of a terminal according to Embodiment 1 of the present invention; 
         FIG. 9  is a block diagram illustrating a configuration of the base station according to Embodiment 1 of the present invention; 
         FIG. 10  is a block diagram illustrating a configuration of the terminal according to Embodiment 1 of the present invention; 
         FIG. 11  is a diagram provided for describing a method of determining ePDCCH-PUCCH resources according to Embodiment 1 of the present invention; 
         FIG. 12  is a diagram provided for describing a method of determining ePDCCH-PUCCH resources according to Embodiment 2 of the present invention; 
         FIG. 13  is a first diagram provided for describing variation 1 according to Embodiment 2 of the present invention; 
         FIG. 14  is a second diagram provided for describing variation 1 according to Embodiment 2 of the present invention; 
         FIG. 15  is a diagram provided for describing variation 2 according to Embodiment 2 of the present invention; 
         FIG. 16  is a diagram provided for describing variation 3 according to Embodiment 2 of the present invention; 
         FIG. 17  is a first diagram provided for describing variation 4 according to Embodiment 2 of the present invention; 
         FIG. 18  is a second diagram provided for describing variation 4 according to Embodiment 2 of the present invention; 
         FIG. 19  is a diagram provided for describing variation 6 according to Embodiment 2 of the present invention; 
         FIG. 20  is a method of determining ePDCCH-PUCCH resources according to Embodiment 3 of the present invention; 
         FIG. 21  is a method of determining ePDCCH-PUCCH resources according to Embodiment 4 of the present invention; 
         FIG. 22  is a diagram provided for describing problems and a solution thereof when an ePDCCH terminal and a UL CoMP terminal exist; 
         FIG. 23  is a first diagram provided for describing variation 7 according to Embodiment 2 of the present invention; 
         FIG. 24  is a second diagram provided for describing variation 7 according to Embodiment 2 of the present invention; 
         FIG. 25  is a third diagram provided for describing variation 7 according to Embodiment 2 of the present invention; 
         FIG. 26  is a first diagram provided for describing a method of dividing a PUCCH resource region of variation 7 according to Embodiment 2 of the present invention; 
         FIG. 27  is a second diagram provided for describing a method of dividing a PUCCH resource region of variation 7 according to Embodiment 2 of the present invention; 
         FIG. 28  is a third diagram provided for describing a method of dividing a PUCCH resource region of variation 7 according to Embodiment 2 of the present invention; 
         FIG. 29  is a first diagram provided for describing a size of dividing a PUCCH resource region of variation 7 according to Embodiment 2 of the present invention; 
         FIG. 30  is a second diagram provided for describing a size of dividing a PUCCH resource region of variation 7 according to Embodiment 2 of the present invention; and 
         FIG. 31  is a third diagram provided for describing a size of dividing a PUCCH resource region of variation 7 according to Embodiment 2 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Throughout the embodiments, the same elements as those already described are assigned the same reference numerals and any detailed description of the elements is omitted. 
     Embodiment 1 
       FIG. 7  is a block diagram illustrating a main configuration of base station  100  according to the present embodiment.  FIG. 8  is a block diagram illustrating a main configuration of terminal  200  according to Embodiment 1 of the present invention. Terminal  200  communicates with base station  100  using a plurality of component carriers including a first component carrier and a second component carrier. A subframe configuration pattern making up one frame, which is a configuration pattern (DL-UL Configuration) including a downlink communication subframe (DL subframe) used for downlink communication and an uplink communication subframe (UL subframe) used for uplink communication is set in each component carrier set in terminal  200 . 
     In base station  100 , control section  101  determines collision or no collision between ePDCCH-PUCCH resources and PDCCH-PUCCH resources. Control information generating section  102  indicates ARI corresponding to non-colliding ePDCCH-PUCCH resources to terminal  200 . 
     In terminal  200 , extraction section  204  receives downlink data using a plurality of component carriers. Decoding section  210  decodes downlink data. CRC section  211  detects an error of decoded downlink data. Response signal generating section  212  generates response signals using error detection result of the downlink data obtained in CRC section  211 . Control section  208  arranges response signals in predetermined PUCCH resources and transmits the response signals to base station  100 . 
     [Configuration of Base Station] 
       FIG. 9  is a configuration diagram of base station  100  according to Embodiment 1 of the present invention. In  FIG. 9 , base station  100  includes control section  101 , control information generating section  102 , coding section  103 , modulation section  104 , coding section  105 , data transmission controlling section  106 , modulation section  107 , mapping section  108 , inverse fast Fourier transform (IFFT) section  109 , CP adding section  110 , radio transmitting section  111 , radio receiving section  112 , CP removing section  113 , PUCCH extracting section  114 , despreading section  115 , sequence controlling section  116 , correlation processing section  117 , A/N determining section  118 , bundled A/N despreading section  119 , inverse discrete Fourier transform (IDFT) section  120 , bundled A/N determining section  121  and retransmission control signal generating section  122 . 
     Control section  101  assigns a downlink resource for transmitting control information (i.e., downlink control information assignment resource) and a downlink resource for transmitting downlink data (i.e., downlink data assignment resource) for a resource assignment target terminal (hereinafter, referred to as “destination terminal” or simply “terminal”)  200 . This resource assignment is performed in a downlink component carrier included in a component carrier group configured for resource assignment target terminal  200 . In addition, the downlink control information assignment resource is selected from among the resources corresponding to downlink control channel (i.e., PDCCH or ePDCCH) in each downlink component carrier. Moreover, the downlink data assignment resource is selected from among the resources corresponding to downlink data channel (i.e., PDCCH) in each downlink component carrier. In addition, when there are a plurality of resource assignment target terminals  200 , control section  101  assigns different resources to terminals  200 , respectively. 
     The downlink control information assignment resources are equivalent to L1/L2 CCH described above. More specifically, the downlink control information assignment resources are each formed of one or a plurality of CCEs or eCCEs. 
     Control section  101  determines whether or not ePDCCH-PUCCH resources collide with PDCCH-PUCCH resources and controls control information generating section  102  so as to generate ARI based on the determination result. 
     Control section  101  determines the coding rate used for transmitting control information to resource assignment target terminal  200 . The data size of the control information varies depending on the coding rate. Thus, control section  101  assigns a downlink control information assignment resource having the number of CCEs or eCCEs that allows the control information having this data size to be mapped to the resource. 
     Control section  101  outputs information on the downlink data assignment resource to control information generating section  102 . Moreover, control section  101  outputs information on the coding rate to coding section  103 . In addition, control section  101  determines and outputs the coding rate of transmission data (i.e., downlink data) to coding section  105 . Moreover, control section  101  outputs information on the downlink data assignment resource and downlink control information assignment resource to mapping section  108 . However, control section  101  controls the assignment in such a way that the downlink data and downlink control information for the downlink data are mapped to the same downlink component carrier. 
     Control information generating section  102  generates and outputs control information including the information on the downlink data assignment resource and ARI to coding section  103 . This control information is generated for each downlink component carrier. In addition, when there are a plurality of resource assignment target terminals  200 , the control information includes the terminal ID of each destination terminal  200  in order to distinguish resource assignment target terminals  200  from one another. For example, the control information includes CRC bits masked by the terminal ID of destination terminal  200 . This control information may be referred to as “control information carrying downlink assignment” or “downlink control information (DCI).” 
     Coding section  103  encodes the control information using the coding rate received from control section  101  and outputs the coded control information to modulation section  104 . 
     Modulation section  104  modulates the coded control information and outputs the resultant modulation signals to mapping section  108 . 
     Coding section  105  inserts the coding rate information from control section  101  into transmission data (downlink data) for each destination terminal  200  and encodes and outputs the transmission data after the insertion to data transmission controlling section  106 . However, when a plurality of downlink component carriers are assigned to destination terminal  200 , coding section  105  encodes transmission data to be transmitted by each downlink component carrier. 
     Data transmission controlling section  106  outputs the coded transmission data to modulation section  107  and also keeps the coded transmission data at the initial transmission. The coded transmission data is kept for each destination terminal  200 . Transmission data to one destination terminal  200  is kept for each downlink component carrier for transmission. This makes it possible to perform not only retransmission control of the entire data transmitted to destination terminal  200  but also retransmission control for each downlink component carrier. 
     Furthermore, upon reception of a NACK or DTX for downlink data transmitted on a predetermined downlink component carrier from retransmission control signal generating section  122 , data transmission controlling section  106  outputs the data kept in the manner described above and corresponding to this downlink component carrier to modulation section  107 . Upon reception of an ACK for the downlink data transmitted on a certain downlink component carrier from retransmission control signal generating section  122 , data transmission controlling section  106  deletes the data kept in the manner described above and corresponding to this downlink component carrier. 
     Modulation section  107  modulates the coded transmission data received from data transmission controlling section  106  and outputs the resultant modulation signals to mapping section  108 . 
     Mapping section  108  maps the modulation signals of the control information received from modulation section  104  to the resource (PDCCH) indicated by the downlink control information assignment resource received from control section  101  and outputs the resultant modulation signals to IFFT section  109 . 
     Mapping section  108  maps the modulation signals of the transmission data received from modulation section  107  to the resource (i.e., PDSCH (i.e., downlink data channel)) indicated by the downlink data assignment resource received from control section  101  (i.e., information included in the control information) and outputs the resultant modulation signals to IFFT section  109 . 
     IFFT section  109  performs IFFT processing on the modulation signals mapped in mapping section  108  and outputs the modulation signals to CP adding section  110 . This causes the modulation signals to be transformed from frequency-domain to time-domain signals. 
     CP adding section  110  adds the same signal as that of the tail portion after IFFT to the leading part thereof as a CP to form an OFDM signal and outputs the OFDM signal to radio transmitting section  111 . 
     Radio transmitting section  111  performs transmission processing such as D/A (digital to analog) conversion, amplification and up-conversion on the OFDM signal and transmits the OFDM signal to terminal  200  via an antenna. 
     Radio receiving section  112  receives uplink response signals or reference signals transmitted from terminal  200  via the antenna, performs reception processing such as down-conversion, A/D conversion on the uplink response signals or reference signals and outputs the signals to CP removing section  113 . 
     CP removing section  113  removes a CP added to the uplink response signals or reference signals after the reception processing and outputs the signals to PUCCH extracting section  114 . 
     PUCCH extracting section  114  extracts, from the PUCCH signals included in the received signals, the signals in the PUCCH region corresponding to the bundled ACK/NACK resource previously indicated to terminal  200 . Here, the bundled ACK/NACK resource is a PUCCH resource by which a bundled ACK/NACK signal should be transmitted as described above and a resource that adopts a DFT-S-OFDM format configuration. More specifically, PUCCH extracting section  114  extracts the data part of the PUCCH region corresponding to the bundled ACK/NACK resource (i.e., SC-FDMA symbols on which the bundled ACK/NACK resource is assigned) and the reference signal part of the PUCCH region (i.e., SC-FDMA symbols on which the reference signals for demodulating the bundled ACK/NACK signals are assigned). PUCCH extracting section  114  outputs the extracted data part to bundled A/N despreading section  119  and outputs the reference signal part to despreading section  115 - 1 . 
     PUCCH extracting section  114  extracts, from the PUCCH signals included in the received signals, a plurality of PUCCH regions corresponding to A/N resources associated with CCEs occupied by PDCCH used for transmission of downlink assignment control information (DCI), A/N resources associated with eCCEs occupied by ePDCCH used for transmission of downlink assignment control information (DCI) and a plurality of A/N resources previously indicated to terminal  200 . The A/N resource herein refers to the resource to be used for transmission of an A/N. More specifically, PUCCH extracting section  114  extracts the data part of the PUCCH region corresponding to the A/N resource (i.e., SC-FDMA symbols on which the uplink control signals are assigned) and the reference signal part of the PUCCH region (i.e., SC-FDMA symbols on which the reference signals for demodulating the uplink control signals are assigned). PUCCH extracting section  114  outputs both of the extracted data part and reference signal part to despreading section  115 - 2 . In this manner, the response signals are received on the resource selected from the PUCCH resource associated with the CCE or eCCE and the specific PUCCH resource previously indicated to terminal  200 . Note that the method of determining A/N resources (PUCCH resources to which response signals are mapped) will be described later. 
     Sequence controlling section  116  generates a base sequence that may be used for spreading each of the A/N indicated from terminal  200 , the reference signals for the A/N, and the reference signals for the bundled ACK/NACK signals (i.e., length-12 ZAC sequence). In addition, sequence controlling section  116  identifies a correlation window corresponding to a resource on which the reference signals may be assigned (hereinafter, referred to as “reference signal resource”) in PUCCH resources that may be used by terminal  200 . Sequence controlling section  116  outputs the information indicating the correlation window corresponding to the reference signal resource on which the reference signals may be assigned in bundled ACK/NACK resources and the base sequence to correlation processing section  117 - 1 . Sequence controlling section  116  outputs the information indicating the correlation window corresponding to the reference signal resource and the base sequence to correlation processing section  117 - 1 . In addition, sequence controlling section  116  outputs the information indicating the correlation window corresponding to the A/N resources on which an A/N and the reference signals for the A/N are assigned and the base sequence to correlation processing section  117 - 2 . 
     Despreading section  115 - 1  and correlation processing section  117 - 1  perform processing on the reference signals extracted from the PUCCH region corresponding to the bundled ACK/NACK resource. 
     More specifically, despreading section  115 - 1  despreads the reference signal part using a Walsh sequence to be used in secondary-spreading for the reference signals of the bundled ACK/NACK resource by terminal  200  and outputs the despread signals to correlation processing section  117 - 1 . 
     Correlation processing section  117 - 1  uses the information indicating the correlation window corresponding to the reference signal resource and the base sequence and thereby finds a correlation value between the signals received from despreading section  115 - 1  and the base sequence that may be used in primary-spreading in terminal  200 . Correlation processing section  117 - 1  outputs the correlation value to bundled A/N determining section  121 . 
     Despreading section  115 - 2  and correlation processing section  117 - 2  perform processing on the reference signals and A/Ns extracted from the plurality of PUCCH regions corresponding to the plurality of A/N resources. 
     More specifically, despreading section  115 - 2  despreads the data part and reference signal part using a Walsh sequence and a DFT sequence to be used in secondary-spreading for the data part and reference signal part of each of the A/N resources by terminal  200 , and outputs the despread signals to correlation processing section  117 - 2 . 
     Correlation processing section  117 - 2  uses the information indicating the correlation window corresponding to each of the A/N resources and the base sequence and thereby finds a correlation value between the signals received from despreading section  115 - 2  and a base sequence that may be used in primary-spreading by terminal  200 . Correlation processing section  117 - 2  outputs each correlation value to A/N determining section  118 . 
     A/N determining section  118  determines, on the basis of the plurality of correlation values received from correlation processing section  117 - 2 , which of the A/N resources is used to transmit the signals from terminal  200  or none of the A/N resources is used. When determining that the signals are transmitted using one of the A/N resources from terminal  200 , A/N determining section  118  performs coherent detection using a component corresponding to the reference signals and a component corresponding to the A/N and outputs the result of coherent detection to retransmission control signal generating section  122 . Meanwhile, when determining that terminal  200  uses none of the A/N resources, A/N determining section  118  outputs the determination result indicating that none of the A/N resources is used to retransmission control signal generating section  122 . 
     Bundled A/N despreading section  119  despreads, using a DFT sequence, the bundled ACK/NACK signals corresponding to the data part of the bundled ACK/NACK resource received from PUCCH extracting section  114  and outputs the despread signals to IDFT section  120 . 
     IDFT section  120  transforms the bundled ACK/NACK signals in the frequency-domain received from bundled A/N despreading section  119  into time-domain signals by IDFT processing and outputs the bundled ACK/NACK signals in the time-domain to bundled A/N determining section  121 . 
     Bundled A/N determining section  121  demodulates the bundled ACK/NACK signals corresponding to the data part of the bundled ACK/NACK resource received from IDFT section  120 , using the reference signal information on the bundled ACK/NACK signals that is received from correlation processing section  117 - 1 . In addition, bundled A/N determination section  121  decodes the demodulated bundled ACK/NACK signals and outputs the result of decoding to retransmission control signal generating section  122  as the bundled A/N information. However, when the correlation value received from correlation processing section  117 - 1  is smaller than a threshold, and bundled A/N determining section  121  thus determines that terminal  200  does not use any bundled A/N resource to transmit the signals, bundled A/N determining section  121  outputs the result of determination to retransmission control signal generating section  122 . 
     Retransmission control signal generating section  122  determines whether or not to retransmit the data transmitted on the downlink component carrier (i.e., downlink data) on the basis of the information inputted from bundled A/N determining section  121  and the information inputted from A/N determining section  118  and generates retransmission control signals based on the result of determination. More specifically, when determining that downlink data transmitted on a certain downlink component carrier needs to be retransmitted, retransmission control signal generating section  122  generates retransmission control signals indicating a retransmission command for the downlink data and outputs the retransmission control signals to data transmission controlling section  106 . In addition, when determining that the downlink data transmitted on a certain downlink component carrier does not need to be retransmitted, retransmission control signal generating section  122  generates retransmission control signals indicating not to retransmit the downlink data transmitted on the downlink component carrier and outputs the retransmission control signals to data transmission controlling section  106 . 
     (Configuration of Terminal) 
       FIG. 10  is a block diagram illustrating a configuration of terminal  200  according to Embodiment 1. In  FIG. 10 , terminal  200  includes radio receiving section  201 , CP removing section  202 , fast Fourier transform (FFT) section  203 , extraction section  204 , demodulation section  205 , decoding section  206 , determination section  207 , control section  208 , demodulation section  209 , decoding section  210 , CRC section  211 , response signal generating section  212 , coding and modulation section  213 , primary-spreading sections  214 - 1  and  214 - 2 , secondary-spreading sections  215 - 1  and  215 - 2 , DFT section  216 , spreading section  217 , IFFT sections  218 - 1 ,  218 - 2  and  218 - 3 , CP adding sections  219 - 1 ,  219 - 2  and  219 - 3 , time-multiplexing section  220 , selection section  221  and radio transmitting section  222 . 
     Radio receiving section  201  receives, via an antenna, an OFDM signal transmitted from base station  100 , performs reception processing such as down-conversion, A/D conversion and/or the like on the received OFDM signal and outputs the OFDM signal to CP removing section  202 . It should be noted that the received OFDM signal includes a PDSCH signal assigned to a resource in a PDSCH (i.e., downlink data), PDCCH signal assigned to a resource in a PDCCH signal or ePDCCH signal assigned to a resource in an ePDCCH. 
     CP removing section  202  removes a CP that has been added to the OFDM signal from the OFDM signal that have undergone the reception processing and outputs the OFDM signal to FFT section  203 . 
     FFT section  203  transforms the received OFDM signal from which the CP has been removed into a frequency-domain signal by FFT processing and outputs the resultant received signal to extraction section  204 . 
     Extraction section  204  extracts, from the received signal to be received from FFT section  203 , a downlink control channel signal (i.e., PDCCH signal or ePDCCH signal) in accordance with coding rate information to be received. That is, since the number of CCEs or eCCEs forming a downlink control information assignment resource varies depending on the coding rate, extraction section  204  uses the number of CCEs or eCCEs that corresponds to the coding rate as units of extraction processing, and extracts a downlink control channel signal and outputs the downlink control channel signal to demodulation section  205 . Note that the downlink control channel signal is extracted for each downlink component carrier. 
     Extraction section  204  extracts downlink data (i.e., downlink data channel signal (i.e., PDSCH signal)) from the received signals on the basis of information on the downlink data assignment resource intended for terminal  200  to be received from determination section  207  to be described, hereinafter, and outputs the downlink data to demodulation section  209 . As described above, extraction section  204  receives the downlink assignment control information (i.e., DCI) mapped to the PDCCH or ePDCCH and receives the downlink data on the PDSCH. 
     Demodulation section  205  demodulates the downlink control channel signal received from extraction section  204  and outputs the obtained result of demodulation to decoding section  206 . 
     Decoding section  206  decodes the result of demodulation received from demodulation section  205  in accordance with the received coding rate information and outputs the obtained result of decoding to determination section  207 . 
     Determination section  207  performs blind-determination (i.e., monitoring) to find out whether or not the control information included in the result of decoding received from decoding section  206  is the control information intended for terminal  200 . This determination is made in units of decoding results corresponding to the units of extraction processing. For example, determination section  207  demasks the CRC bits by the terminal ID of terminal  200  and determines that the control information resulted in CRC=OK (no error) as the control information intended for terminal  200 . Determination section  207  outputs information on the downlink data assignment resource intended for terminal  200 , which is included in the control information intended for terminal  200 , to extraction section  204 . 
     In addition, when detecting the control information (i.e., downlink assignment control information) intended for terminal  200 , determination section  207  informs control section  208  that an ACK/NACK signal will be generated (or is present). Moreover, when detecting the control information intended for terminal  200  from a PDCCH signal or ePDCCH signal, determination section  207  outputs information on a CCE that has been occupied by the PDCCH or information on an eCCE that has been occupied by the ePDCCH to control section  208 . 
     Control section  208  identifies the A/N resource associated with the CCE or the eCCE on the basis of the information on the CCE or the eCCE received from determination section  207 . Control section  208  outputs the A/N resource associated with the CCE, the A/N resource associated with the eCCE or base sequence and cyclic shift amount corresponding to the A/N resource indicated in advance from base station  100  to primary-spreading section  214 - 1  and outputs a Walsh sequence and a DFT sequence corresponding to the A/N resource to secondary-spreading section  215 - 1 . In addition, control section  208  outputs the frequency resource information on the A/N resource to IFFT section  218 - 1 . Note that the method of determining A/N resources (PUCCH resources to which response signals are mapped) will be described later. 
     When determining to transmit a bundled ACK/NACK signal using a bundled ACK/NACK resource, control section  208  outputs the base sequence and cyclic shift value corresponding to the reference signal part (i.e., reference signal resource) of the bundled ACK/NACK resource previously indicated by base station  100  to primary-despreading section  214 - 2  and outputs a Walsh sequence to secondary-despreading section  215 - 2 . In addition, control section  208  outputs the frequency resource information on the bundled ACK/NACK resource to IFFT section  218 - 2 . 
     Control section  208  outputs a DFT sequence used for spreading the data part of the bundled ACK/NACK resource to spreading section  217  and outputs the frequency resource information on the bundled ACK/NACK resource to IFFT section  218 - 3 . 
     Control section  208  selects the bundled ACK/NACK resource or the A/N resource and instructs selection section  221  to output the selected resource to radio transmitting section  222 . Moreover, control section  208  instructs response signal generating section  212  to generate the bundled ACK/NACK signal or the ACK/NACK signal in accordance with the selected resource. 
     Demodulation section  209  demodulates the downlink data received from extraction section  204  and outputs the demodulated downlink data to decoding section  210 . 
     CRC section  211  performs error detection on the decoded downlink data received from decoding section  210 , for each downlink component carrier using CRC and outputs an ACK when CRC=OK (no error) or outputs a NACK when CRC=Not OK (error) to response signal generating section  212 . Moreover, CRC section  211  outputs the decoded downlink data as the received data when CRC=OK (no error). 
     Response signal generating section  212  generates response signals on the basis of the reception condition of downlink data (i.e., result of error detection on downlink data) on each downlink component carrier inputted from CRC section  211  and information indicating a predetermined group number. More specifically, when instructed to generate the bundled ACK/NACK signal from control section  208 , response signal generating section  212  generates the bundled ACK/NACK signals including the results of error detection for the respective component carriers as individual pieces of data. Meanwhile, when instructed to generate ACK/NACK signals from control section  208 , response signal generating section  212  generates an ACK/NACK signal of one symbol. Response signal generating section  212  outputs the generated response signal to coding and modulation section  213 . 
     Upon reception of the bundled ACK/NACK signal, coding and modulation section  213  encodes and modulates the received bundled ACK/NACK signal to generate the modulation signal of 12 symbols and outputs the modulation signal to DFT section  216 . In addition, upon reception of the ACK/NACK signal of one symbol, coding and modulation section  213  modulates the ACK/NACK signal and outputs the modulation signal to primary-spreading section  214 - 1 . 
     Primary-spreading sections  214 - 1  and  214 - 2  corresponding to the A/N resources and reference signal resources of the bundled ACK/NACK resources spread the ACK/NACK signals or reference signals using the base sequence corresponding to the resources in accordance with the instruction from control section  208  and output the spread signals to secondary-spreading sections  215 - 1  and  215 - 2 . 
     Secondary-spreading sections  215 - 1  and  215 - 2  spread the received primary-spread signals using a Walsh sequence or a DFT sequence in accordance with an instruction from control section  208  and outputs the spread signals to IFFT sections  218 - 1  and  218 - 2 . 
     DFT section  216  performs DFT processing on 12 time-series sets of received bundled ACK/NACK signals to obtain 12 signal components in the frequency-domain. DFT section  216  outputs the 12 signal components to spreading section  217 . 
     Spreading section  217  spreads the 12 signal components received from DFT section  216  using a DFT sequence indicated by control section  208  and outputs the spread signal components to IFFT section  218 - 3 . 
     IFFT sections  218 - 1 ,  218 - 2  and  218 - 3  perform IFFT processing on the received signals in association with the frequency positions where the signals are to be allocated, in accordance with an instruction from control section  208 . Accordingly, the signals inputted to IFFT sections  218 - 1 ,  218 - 2  and  218 - 3  (i.e., ACK/NACK signals, the reference signals of A/N resource, the reference signals of bundled ACK/NACK resource and bundled ACK/NACK signals) are transformed into time-domain signals. 
     CP adding sections  219 - 1 ,  219 - 2  and  219 - 3  add the same signals as the last part of the signals obtained by IFFT processing to the beginning of the signals as a CP. 
     Time-multiplexing section  220  time-multiplexes the bundled ACK/NACK signals received from CP adding section  219 - 3  (i.e., signals transmitted using the data part of the bundled ACK/NACK resource) and the reference signals of the bundled ACK/NACK resource to be received from CP adding section  219 - 2  on the bundled ACK/NACK resource and outputs the multiplexed signals to selection section  221 . 
     According to the instruction from control section  208 , selection section  221  selects one of the bundled ACK/NACK resource received from time-multiplexing section  220  and the A/N resource received from CP adding section  219 - 1  and outputs the signals assigned to the selected resource to radio transmitting section  222 . 
     Radio transmitting section  222  performs transmission processing such as D/A conversion, amplification and up-conversion on the signals received from selection section  221  and transmits the signals to base station  100  from the antenna. 
     [Method of Determining ePDCCH-PUCCH R Resources] 
     Next, the method of determining ePDCCH-PUCCH resources in base station  100  and terminal  200  configured as described above will be described. 
       FIG. 11  is a diagram provided for describing the method of determining ePDCCH-PUCCH resources according to the present embodiment. As shown in  FIG. 11 , ePDCCH-PUCCH resource region  300  is divided for each c′ and each in and the resultant portions are arranged from the frequency end direction to center direction of the component carrier in ascending order of m and in ascending order of c′. 
     In the present embodiment, base station  100  sets offset values (δ 1 , δ 2 , δ 3 ) for shifts made in a virtual PUCCH resource region corresponding to current DL subframe m current . 
     Base station  100  first determines whether or not ePDCCH-PUCCH resource  310  with offset value 0, that is, by implicit signaling collides with a PDCCH-PUCCH resource. In the case of no collision, base station  100  indicates ARI=0 to terminal  200  so as to use ePDCCH-PUCCH resources  310 . On the other hand, in the case of collision, base station  100  sequentially determines collision or no collision in ePDCCH-PUCCH resources  311 ,  312  and  313  to which other offset values are added and indicates ARI corresponding to non-colliding ePDCCH-PUCCH resources to terminal  200 . 
     Terminal  200  obtains c′ based on eCCE index n eCCE  and offset value δ ARI  in a virtual PUCCH resource region corresponding to the indicated ARI and determines PUCCH resources to be used to indicate response signals indicating error detection results of downlink data from the PUCCH resource region corresponding to current DL subframe m current . 
     [Effects] 
     Thus, according to the present embodiment, since a shift by an offset value indicated by ARI is made only within PUCCH resources associated with m=m current , that is, the current DL subframe, no constraint is imposed on DL scheduling in future DL subframes. 
     Embodiment 2 
     In Embodiment 2, terminal  200  obtains c′ based on eCCE index n eCCE  and offset value δ ARI  corresponding to indicated ARI in a virtual PUCCH resource region which combines PUCCH resources corresponding to m= current . Next, terminal  200  determines PUCCH resources to be used to indicate response signals indicating error detection results of downlink data in an ePDCCH-PUCCH resource region which is actually used. 
       FIG. 12  is a diagram provided for describing a method of determining ePDCCH-PUCCH resources according to the present embodiment. In the example in  FIG. 12 , suppose m current =2. In  FIG. 12 , PUCCH resource region  350  is a virtual PUCCH resource region combining PUCCH resources with m=m current =2. PUCCH resource region  350  is divided for each c′ and resultant portions are arranged from the frequency end direction to center direction of a component carrier in ascending order of c′. 
     Base station  100  calculates c′ to which n eCCE +δ ARI  belongs in virtual PUCCH resource region  350  according to equation 6. Base station  100  determines one of PUCCH resources ( 360 ,  361 ,  362 ,  363 ) based on the calculated c′ according to equation 7.
 
[6]
 
 N   c′   ≦n   eCCE +δ ARI   &lt;N   c′+1   (Equation 6)
 
[7]
 
 n   PUCCH,j   (1) =( M−m− 1)· N   c′   +m·N   c′+1   +n   eCCE,m +δ ARI   +N   PUCCH   (1) ′  (Equation 7)
 
     In equation 6, c′ need not always be the same value as c or within a range of the same value in PDCCH-PUCCH. In equation 7, N (1)   PUCCH ′ is an offset value corresponding to all ePDCCH-PUCCH resources previously set in terminal  200 , but may also be a value different from offset value N (1)   PUCCH  corresponding to all PDCCH-PUCCH resources. 
     As described above, in a special subframe in which the number of OFDM symbols used for the downlink is small, the size of an ePDCCH search space set is half the size of a normal subframe. Thus, while an offset value for a normal subframe is δ, an offset value for a special subframe may be δ/2. 
     [Effects] 
     Thus, according to the present embodiment, a shift by an offset value indicated by ARI is made in a virtual PUCCH resource region. Furthermore, for a virtual PUCCH resource, only a PUCCH resource associated with m=m current , that is, a current DL subframe is used, and no constraint is imposed on DL scheduling in future DL subframes. Even an offset value of a small absolute value can indicate an ePDCCH-PUCCH resource corresponding to the same m and different c′, and therefore when a positive offset value is given, it is possible to make a shift to an ePDCCH-PUCCH resource region having a lower probability of collision with PDCCH-PUCCH resources. Furthermore, these effects can be obtained even when the same offset value is set with different c′ and m. 
     In  FIG. 12 , the virtual PUCCH resource region includes, except the ePDCCH-PUCCH resource region corresponding to m=2, resources outside the ePDCCH-PUCCH resource region (e.g., PUSCH region). The present embodiment may operate PUCCH resources shifted by an offset so as to be able to (1) indicate resources outside the ePDCCH-PUCCH resource region or (2) always indicate only resources inside the ePDCCH-PUCCH resource region. 
     Hereinafter, (1) a case where PUCCH resources are not limited to within the ePDCCH-PUCCH resource region and (2) a case where PUCCH resources are limited to within the ePDCCH-PUCCH resource region will be described. 
     (Variation 1) 
     Variation 1 is (1) a case where PUCCH resources are not limited to within the ePDCCH-PUCCH resource region. 
       FIG. 13  and  FIG. 14  illustrate an operation method when the virtual PUCCH resource region is not limited to within the ePDCCH-PUCCH resource region. 
     In the operation method shown in  FIG. 13 , resources outside the ePDCCH-PUCCH resource region are also divided for each c′ and each in (that is, according to the same rule as that of ePDCCH-PUCCH) in actual ePDCCH-PUCCH resource region  300 . In  FIG. 13 , an ePDCCH-PUCCH resource region is defined by c′=0, 1, 2, 3 and resources outside the ePDCCH-PUCCH resource region (e.g., PUSCH region) are defined by c′=4, . . . . In virtual PUCCH resource region  350 , PUCCH resources are shifted based on offset values indicated by ARI in the ePDCCH-PUCCH resource region when m=m current  and in the resource region outside the ePDCCH-PUCCH resource region. Note that equation 6 and equation 7 follow the present operation method. 
     On the other hand, in the operation method shown in  FIG. 14 , in actual ePDCCH-PUCCH resource region  300 , resources outside the ePDCCH-PUCCH resource region are not divided for each c′ and each m. In the virtual PUCCH resource region, resources outside the ePDCCH-PUCCH resource region in addition to the ePDCCH-PUCCH resource region when m=m current  are added in the same way as in the actual resource region. In this resource region, PUCCH resources are shifted based on offset values indicated by ARI. In the present operation method, when c′ that satisfies equation 6 is a maximum value of c′ defined as the ePDCCH-PUCCH resource region (defined as c′ max ) (c′ max =3 in the example of  FIG. 14 ) or below, PUCCH resources are calculated according to equation 6 and equation 7, and when c′ is greater than the maximum value of c′ defined as the ePDCCH-PUCCH resource region, PUCCH resources are calculated according to equation 8.
 
[8]
 
 n   PUCCH,j   (1) =( M− 1)· N   c′     max     +1 +( n   eCCE,m +δ ARI   −N   c′     max     +1 )+ N   PUCCH   (1) ′  (Equation 8)
 
     In the operation method shown in  FIG. 13  above, since the resource region outside the ePDCCH-PUCCH resource region is divided for each m, no collision of PUCCH resources indicated by ePDCCH occurs between different m&#39;s even outside the ePDCCH-PUCCH resource region. Therefore, this operation method is useful when the ePDCCH-PUCCH resource region is small, when the absolute value of an offset value is large or the like, that is, when many shift destinations by an offset go out of the ePDCCH-PUCCH resource region. 
     On the other hand, in the operation method shown in  FIG. 14  above, the resource region outside the ePDCCH-PUCCH resource region is not divided for each m. For this reason, this operation method is useful when the ePDCCH-PUCCH resource region is large, when the absolute value of an offset value is small or the like, that is, when many shift destinations by an offset are included in the ePDCCH-PUCCH resource region. 
     (Variation 2) 
     Variation 2 corresponds to (2) a case where PUCCH resources are limited to within the ePDCCH-PUCCH resource region. 
       FIG. 15  illustrates an operation method when PUCCH resources in a virtual PUCCH resource region are limited to within the ePDCCH-PUCCH resource region. 
     In the operation method (method 1) shown in  FIG. 15 , an ePDCCH-PUCCH resource region in the virtual PUCCH resource region when m=m current  is rotated. In this rotating resource region, PUCCH resources are shifted based on an offset value indicated by ARI. In the present operation method, the entire virtual PUCCH resource region is rotated so that c′ that satisfies equation 9 becomes a maximum value of c′ or below, c′ being defined as the ePDCCH-PUCCH resource region (defined as c′ max ) (c′ max =3 in the example of  FIG. 15 ). PUCCH resources are calculated from c′ obtained according to equation 10.
 
[9]
 
 N   c′ ≦( n   eCCE +δ ARI )mod  N   c′     max     +1   &lt;N   c′+1   (Equation 9)
 
[10]
 
 n   PUCCH,j   (1) =( M−m− 1)· N   c′   +m·N   c′+1 +( n   eCCE,m +δ ARI )mod  N   c′     max     +1   +N   PUCCH   (1) ′  (Equation 10)
 
     In method 1 shown in  FIG. 15 , c′ having a high occupancy of PDCCH-PUCCH is returned to the ePDCCH-PUCCH resource region due to the rotation of the entire virtual PUCCH resource region (at the time of δ 3  shift in  FIG. 15 ). Since the ePDCCH-PUCCH resources which are shift destinations are more likely to have been occupied by PDCCH-PUCCH resources, there is a high possibility that the shift destinations may not be used. Thus, as shown in method 2 or method 3 shown in  FIG. 15 , a rotation or loopback method may be used so that greater c′ is used preferentially. More specifically, according to method 2, rotation is made within the ePDCCH-PUCCH resource region corresponding to c′ greater than a predetermined threshold (2&lt;c′ in  FIG. 15 ). According to method 3, a loopback is made (a negative offset value is used) after a lowest end of the ePDCCH-PUCCH resource region corresponding to a maximum value of c′ defined as the ePDCCH-PUCCH resource region (direction toward the center of the component carrier is defined as down). 
     (Variation 3) 
     The present embodiment has been described based on a positive offset value which is a direction in which c′ and m increase as a premise, but the present invention is not limited to this, and a negative offset value may be used and PUCCH resources closer to the end of the component carrier may be used as well. For PUCCH, frequency hopping is performed symmetrically with respect to the center frequency of each component carrier for each slot, and therefore the possibility that resources outside the system band may be used increases by positively using a negative offset value, and a large frequency diversity effect is thereby obtained. However, the smaller the value of c′, the higher the probability that ePDCCH-PUCCH resources will collide with PDCCH-PUCCH resources becomes. For that reason, for example, as shown in  FIG. 16 , an operation may be adopted such that collision is avoided using a positive offset for c′ smaller than a predetermined threshold (e.g., 1.5) and a frequency diversity effect is increased using a negative offset for c′ greater than the predetermined threshold. That is, in the present embodiment, the offset value can take any one of positive and negative values. The present embodiment does not limit all c′ and m values to the same offset value. 
     (Variation 4) 
     As described above, c′ in ePDCCH-PUCCH resources need not always have the same value and the same range of values as those of PDCCH-PUCCH.  FIG. 17  and  FIG. 18  illustrate a case where the present embodiment is applied when c′={0}.  FIG. 17  illustrates an example of a case where the ePDCCH-PUCCH resource region is shared with the PDCCH-PUCCH resource region corresponding to c=1.  FIG. 18  illustrates an example of a case where the ePDCCH-PUCCH resource region is not shared with the PDCCH-PUCCH resource region. 
     As shown in  FIG. 17 , when the ePDCCH-PUCCH resource region is shared with the PDCCH-PUCCH resource region, the scale of the PUCCH resource region for each c and each m is equalized to the scale of the PUCCH resource region for each c′ and each in between the shared PDCCH-PUCCH resource region (c=1) and ePDCCH-PUCCH resource region (c′=0). That is, in  FIG. 17 , the PDCCH-PUCCH resource region for each m when c=1 and the ePDCCH-PUCCH resource region for each m when c′=0 have the same scale. By this means, since PDCCH-PUCCH and ePDCCH-PUCCH can use a PUCCH region corresponding to the same m with an actual PUCCH resource number, the one control channel (PDCCH or ePDCCH) in a current DL subframe will not impose constraints on scheduling of the other control channel (ePDCCH or PDCCH) in future DL subframes. 
     As described above, the scale of the PDCCH region is defined by CFI (Control Format Indicator). Therefore, the maximum value that c indicating the scale of the PDCCH-PUCCH resource region can take depends on the magnitude of CFI. 
     CFI is intended to indicate the scale of the PDCCH region. Therefore, if the OFDM symbol from which assignment of ePDCCH (and PDSCH) is started is assigned from a fixed OFDM symbol (or OFDM symbol preset by base station  100 ) independent of the scale of the PDCCH region, terminal  200  that receives ePDCCH but does not receive PDCCH need not receive CFI. That is, terminal  200  that receives ePDCCH but does not receive PDCCH may be operated assuming that without receiving CFI, for example, CFI=3 (that is, the PDCCH region occupies the first to third OFDM symbols) is fixedly set and assignment of ePDCCH starts from the fourth OFDM symbol. However, in this case, terminal  200  does not know the scale of the actual PDCCH region. Thus, terminal  200  does not know the maximum value that c can take either. In such a case, terminal  200  may calculate the maximum value that c can take assuming CFI=3 which is the value assumed above. Base station  100  may preset the maximum value that c can take or information pursuant thereto (e.g., CFI value) in terminal  200 . 
     As shown in  FIG. 18 , when not shared with the PDCCH-PUCCH resource region, the design of the ePDCCH-PUCCH resource region is not constrained by the design of the PDCCH-PUCCH resource region. For that reason, the method of calculating the scale of the ePDCCH-PUCCH resource region for each c′ and each m is not constrained by the method (N c+1 −N c ) of calculating the scale of the PDCCH-PUCCH resource region for each c and each m. The present embodiment may adopt an operation such that the ePDCCH-PUCCH resource region overlaps with the PDCCH-PUCCH resource region (e.g., δ 3  in  FIG. 18 ) by a shift based on the offset value indicated by ARI. Alternatively, the present embodiment may also adopt an operation such that the resources are arranged outside the PDCCH-PUCCH resource region and outside the ePDCCH-PUCCH resource region (e.g., δ 1  and δ 2  in  FIG. 18 ). If an operation is positively adopted such that the ePDCCH-PUCCH resource region overlaps with the PDCCH-PUCCH resource region, it is possible to reduce the overhead of total PUCCH resources. 
     (Variation 5) 
     A case has been described in the present embodiment where an eCCE index is used as an implicit parameter, but the present invention is not limited to this. In addition to the eCCE index, the implicit parameter may also be an index of resource element group (REG) eREG in the ePDCCH region, PRB (Physical Resource Block) number of PDSCH or antenna port number with which ePDCCH is indicated. A plurality of ePDCCH search space sets may be defined, and which search space set is used to indicate ePDCCH can also be said to be an implicit parameter. Some of these parameters or a combination of these parameters are also implicit parameters. In short, when DL assignment and PDSCH are assigned to terminal  200 , the implicit parameter can be any parameter that is at least implicitly determined. 
     (Variation 6) 
     Furthermore, the present invention is not necessarily applied to only the method of indicating PUCCH resources based on an implicit parameter and an offset value (relative value) from the implicit parameter indicated by ARI, and as shown in  FIG. 19 , terminal  200  may also obtain c′ based on an “explicit resource (absolute value) in a virtual PUCCH resource region” indicated by ARI in the virtual PUCCH resource region corresponding to m=m current  and then identify a PUCCH resource in the actual PUCCH resource region. In this case, as shown in  FIG. 19 , even when the explicit resources (absolute values) in the virtual PUCCH resource region are the same between different m&#39;s, those fitting to each m are used in the actual PUCCH resource region. Note that the “explicit resource (absolute value) in the virtual PUCCH resource region” may also be expressed as an “offset value (absolute value) from a fixed position (e.g., frequency end of a component carrier) in the virtual PUCCH resource region.” 
     That is, when ARI indicates the “explicit resource (absolute value) in the virtual PUCCH resource region,” an ePDCCH-PUCCH resource corresponding to m=m current  is indicated within the PDCCH-PUCCH resource region or within the ePDCCH-PUCCH resource region, which will impose no scheduling constraint in future DL subframes. 
     (Variation 7) 
     A shift by an offset value is made in the virtual PUCCH resource region in the above description, and the following description will show that a shift by an offset can be realized without imposing any constraint on DL scheduling in future DL subframes by imposing constraints on the method of dividing the PUCCH resource region for each c′ and each m, and an offset value. However, the following is not intended to avoid collision between PDCCH-PUCCH resources and ePDCCH-PUCCH resources but collision between ePDCCH-PUCCH resources. 
     According to the present variation, base station  100  sets different ePDCCH search space sets between terminals. In this case, the scale (N in  FIG. 23 ) of the PUCCH resource region for each c′ and each m is set to a fixed value irrespective of the ePDCCH search space. However, in special subframes in which the number of OFDM symbols used for the downlink is small, the scale of the PUCCH resource region for each c′ and each m may be set to N/2. According to  FIG. 23 , suppose ePDCCH search space set A having a scale of N eCCE (=N) and ePDCCH search space set B having a scale of N eCCE ′ (=2N) are set, and leading eCCE indices n eCCE  and n eCCE ′ to which DL assignment is assigned in the respective ePDCCH search spaces indicate the same PUCCH resource. In this case, since collision between PUCCH resources occurs, it is possible to avoid collision by adding an offset having at least a scale of N eCCE  or N eCCE ′ or more of the ePDCCH search space set to the one PUCCH resource. However, it is not desirable to impose scheduling constraints in future DL subframes as described above. 
     Thus, in the present variation, as shown in  FIG. 24 , offset value S is assumed to be MN for ePDCCH search space set A having a scale of N eCCE =N in a physical PUCCH resource region. Here, N is the scale of a PUCCH resource region for each c′ and each in common among different search space sets. By setting scale N of the PUCCH resource region for each c′ and each m to a fixed value irrespective of the ePDCCH search space, it is possible to avoid collision between ePDCCH-PUCCH resources also in the physical PUCCH resource region without imposing constraints on future scheduling. 
     In order to avoid collision between PUCCH resources in  FIG. 23 , terminal  200  having ePDCCH search space set B of N eCCE ′=2N in scale as shown in  FIG. 25  may make a shift by an offset. In this case, offset value δ is assumed to be 2MN. This can avoid collision between ePDCCH-PUCCH resources without imposing constraints on future scheduling. 
     In the example of  FIG. 25 , although it is possible to avoid collision of PUCCH resources by setting offset value δ to MN, a shift by offset value δ=MN may be made by another terminal having ePDCCH search space set A of N eCCE =N in scale. Therefore, the shift by offset may be determined based on the scale of the ePDCCH search space whereby DL assignment intended for the terminal is indicated. An example of N eCCE =N and N eCCE ′=2N has been shown above, and generally, the value of offset δ may be MN in a range of N eCCE ≦N and the value of offset δ may be 2MN in a range of N&lt;N eCCE ≦2N. When these are expressed in a generalized manner, offset value δ (δ ARI ) may be set as shown in equation 11. Here, N eCCE  represents the scale of the ePDCCH search space set whereby DL assignment is indicated in terminal  200  that makes a shift by offset. M represents a bundling window.
 
[11]
 
δ ARI   =┌N   eCCE   /N┐·M·N   (Equation 11)
 
     As described above, the scale of the ePDCCH search space set in a special subframe in which the number of OFDM symbols used for the downlink is small is half the scale of a normal subframe. Thus, while scale N Normal  of the PUCCH resource region for each c′ and each m for a normal subframe is set to N, scale N Special  of the PUCCH resource region for each c′ and each m for a special subframe may be set to N/2. At this time, the offset value in  FIG. 23  according to the description of the present variation is (3+½)N when bundling window M includes a special subframe in which the number of OFDM symbols used for the downlink is small and is 4N when bundling window M does not include any special subframe in which the number of OFDM symbols used for the downlink is small. The offset value in  FIG. 24  is 2×(3+½)N when bundling window M includes a special subframe in which the number of OFDM symbols used for the downlink is small and is 2×4N when bundling window M does not include any special subframe in which the number of OFDM symbols used for the downlink is small. That is, the offset value at this time is as shown in equation 12 when bundling window M includes a special subframe in which the number of OFDM symbols used for the downlink is small and as shown in equation 13 when bundling window M does not include any special subframe in which the number of OFDM symbols used for the downlink is small.
 
[12]
 
δ ARI   =┌N   eCCE,m   /N ┐·(( M− 1)· N   Normal   +N   special )  (Equation 12)
 
[13]
 
δ ARI   =┌N   eCCE,m   /N┐·M·N   Normal   (Equation 13)
 
     Although the present invention relates to TDD, if the present invention is applied to FDD, M=1 is assumed and the PUCCH resource region for each c′ and each m need not be considered, and therefore N need not be considered. That is, offset value δ (δ ARI ) is the scale of the ePDCCH search space set to which DL assignment intended for the terminal is assigned in terminal  200  as shown in equation 14.
 
[14]
 
δ ARI   =N   eCCE   (Equation 14)
 
     Since the scale of the ePDCCH search space set is an even number irrespective of FDD or TDD and the aggregation level of ePDCCH is an even number except 1, PUCCH resources corresponding to even-numbered eCCE indices are likely to be occupied. 
     Based on this, when the offset value shown in equation 11 and equation 14 is an even number, an offset value obtained by adding +1 or −1 to the offset value may be used. 
     Based on the above description, the method of determining PUCCH resources according to the present variation will be described using equations. 
     Terminal  200  calculates c′ to which leading eCCE index n eCCE  belongs according to equation 15, DL assignment intended for the terminal being assigned to leading eCCE index n eCCE . Terminal  200  determines PUCCH resources according to equation 16 based on the calculated c′.
 
[15]
 
 c′·N≦n   eCCE &lt;( c′+ 1)· N   (Equation 15)
 
[16]
 
 n   PUCCH,j   (1) =( M−m− 1)· c′N+m ·( c′+ 1) N+n   eCCE,m   +N   PUCCH   (1) ′  (Equation 16)
 
     N (1)   PUCCH ′ is an offset value preset in terminal  200  for all ePDCCH-PUCCH resources and may also take a value which varies from one ePDCCH search space set to another. 
     When a PUCCH resource determined according to equation 16 collides with a PUCCH resource used by another terminal, base station  100  may instruct terminal  200  to make a shift of the PUCCH resource by dynamic offset δ ARI  using ARI indicated by DL assignment intended for terminal  200 . At this time, terminal  200  determines a PUCCH resource after the shift using equation 17. The value of c′ in equation 17 is the same as the value of equation 16. The value of δ ARI  in equation 17 is determined according to equation 11.
 
[17]
 
 n   PUCCH,j   (1) =( M−m− 1)· c′N+m ·( c′+ 1) N+n   eCCE,m +δ ARI   +N   PUCCH   (1) ′  (Equation 17)
 
     [Effect by Setting N to Fixed Value] 
     Here, the effect of setting scale N of the PUCCH resource region for each c′ and each m to a fixed value irrespective of the ePDCCH search space will be described with reference to  FIG. 26 ,  FIG. 27  and  FIG. 28 . 
     When base station  100  sets different ePDCCH search space sets (set A and set B) between terminals, the following two methods can be considered as operation methods available to base station  100 . 
     (1) Scheduled to only one ePDCCH search space set 
     (2) Simultaneously scheduled (in the same subframe) to both ePDCCH search space sets 
     (1) When scheduled to only one ePDCCH search space set, PUCCH resources as shown in 
       FIG. 26  are shared to reduce the overhead of PUCCH resources corresponding to each ePDCCH search space set. Here,  FIG. 26  illustrates indication of assignment of downlink data by ePDCCH and a corresponding PUCCH resource in subframe #5 of UL-DL Configuration#2 shown in  FIG. 3 . In  FIG. 26 , only ePDCCH search space set A is scheduled. Although the same PUCCH resource region as that of ePDCCH search space set A is associated with ePDCCH search space set B, no collision of PUCCH resources occurs between both sets because ePDCCH search space set B is not scheduled. 
     On the other hand, (2) when both ePDCCH search space sets are simultaneously scheduled, collision of PUCCH resources occurs between both sets, and it is therefore preferable not to share the PUCCH resource region. 
     Here, a case will be considered where the base station performs operation by dynamically switching between the two operation methods above, that is, (1) only one ePDCCH search space set is scheduled and (2) both ePDCCH search space sets are simultaneously (in the same subframe) scheduled. At this time, when PUCCH resources are shared between the sets, overhead of the PUCCH resources can be reduced, but on the other hand, collision of PUCCH resources occurs between the sets. In order to avoid collision, an offset value greater than the scale of the ePDCCH search space set needs to be used, and the value is 4, 8, 16, 32 or the like as described above, that is, greater than 1. 
     For this reason, even when different ePDCCH search space sets are set between the terminals, the possibility that the offset destination PUCCH resource will become m&gt;m current  when m corresponding to a DL subframe at certain timing is assumed to be m current  becomes higher than the case with “+1” which is the offset value applied in the PDCCH-PUCCH resource region. Therefore, when downlink data assignment is indicated by ePDCCH, constraints are imposed on scheduling for future DL subframes. The constraints become bigger as the value of m increases. Therefore, the base station is more likely not to be able to assign control information to an optimum terminal. Moreover, the base station requires scheduling taking into account a relationship between subframes and the base station scheduler becomes more complicated. 
     As described above, the base station may set different ePDCCH search space sets between terminals and these ePDCCH search space sets may be different in scale. In addition, the base station can set different start positions N (1)   PUCCH  of PUCCH resources for the respective ePDCCH search space sets.  FIG. 27  illustrates PUCCH resources when the scale of ePDCCH search space set A is N eCCE , the corresponding start position of the PUCCH resource is N (1)   PUCCH , the scale of ePDCCH search space set B is N eCCE ′(≠N eCCE ) and the corresponding start position of the PUCCH resource is N (1)   PUCCH ′. Here, in  FIG. 27 , PUCCH resources for ePDCCH are calculated based on equation 1, equation 2 and equation 3 as in the case of PUCCH resources for PDCCH. Scales N 1-0 , N 2-1  and N 3-2  of the PUCCH resource region for each c and each m are calculated by N 1 −N 0 , N 2 −N 1  and N 3 −N 2  using equation 2 and these scales take different values. That is, the scale of the PUCCH resource region for each c and each m varies for each c. As shown in  FIG. 27 , when start position N (1)   PUCCH  of PUCCH of ePDCCH search space set A coincides with the start of c=1 of the PUCCH resource of ePDCCH search space set B, the PUCCH resource corresponding to m=0 of ePDCCH search space set A coincides with the PUCCH resource corresponding to m=0 of ePDCCH search space set B, but the leading part of the PUCCH resource corresponding to m=1 of ePDCCH search space set A coincides with the PUCCH resource corresponding to m=0 of ePDCCH search space set B (shaded part (A) in  FIG. 27 ). At this time, when m=0 of ePDCCH search space set B, if the PUCCH resource of shaded part (A) in  FIG. 27  is used, ePDCCH search space set A cannot use the PUCCH resource when m=1 which is a future subframe for m=0. The same applies to shaded parts (B) and (C) in  FIG. 27 . Therefore, when the scale of the ePDCCH search space and the start position of a PUCCH corresponding to the ePDCCH search space are different among a plurality of ePDCCH search spaces, constraints are also imposed on scheduling for future DL subframes. 
     Thus, as shown in  FIG. 28 , by dividing the PUCCH regions for ePDCCH search space set A and ePDCCH search space set B by the same scale N respectively, the same value of m is always associated by PUCCH resources between the sets, and it is thereby possible to avoid constraints on future scheduling due to the difference in scale of the ePDCCH search space as shown in  FIG. 27 . 
     The effect of setting scale N of the PUCCH resource region for each c′ and each m to a fixed value irrespective of the ePDCCH search space has been described so far. 
     [Value of N] 
     N according to the present variation needs only to have a common scale when a PUCCH resource region is shared among a plurality of ePDCCH search space sets, and a more specific example of the setting method of N is shown below though this does not necessarily limit the value or range of values thereof. Note that when the PUCCH resource region is shared among a plurality of ePDCCH search space sets, the value of N needs to have a scale common among the plurality of ePDCCH search space sets as described above, but if the PUCCH resource region is not shared among the plurality of ePDCCH search space sets, the value of N may have a scale common among a plurality of ePDCCH search space sets or the value of N may have a different scale. 
     (Method 1) 
       FIG. 29  illustrates a specific example of a case where a PUCCH resource region is shared among a plurality of ePDCCH search space sets, N eCCE =8 as the scale of ePDCCH search space set A, N eCCE =32 as the scale of ePDCCH search space set B and N=32 as the scale of N. When the PUCCH resource region is assigned to only ePDCCH search space set A, corresponding PUCCH resources are 8 PUCCH resources (shaded parts in  FIG. 29 ) of each PUCCH resource region for each m and each c′ of N=32 and the remaining 24 resources are not used as the PUCCH resources corresponding to search space set A. Since PUCCH resources used are dispersed within the PUCCH resource region, when the PUCCH resource region is shared among a plurality of ePDCCH search space sets, if the PUCCH resource region is assigned to only ePDCCH search space set A, it is obvious that setting N=32 causes overhead of PUCCH to increase. 
     Next,  FIG. 30  illustrates a specific example of a case where N=32 in  FIG. 29  is changed to N=8. When the PUCCH resource region is assigned to only ePDCCH search space set A, the corresponding PUCCH resources (shaded parts in  FIG. 30 ) are arranged tightly close to each other within the PUCCH resource region. Thus, when the PUCCH resource region is shared among a plurality of ePDCCH search space sets, if the PUCCH resource region is assigned to only ePDCCH search space set A, setting N=8 makes it possible to reduce the overhead of PUCCH compared to setting N=32. 
     As described above, the scale of each ePDCCH search space set is 4, 8, 16, 32 or the like. Furthermore, the value of N is preferably divisible among a plurality of ePDCCH search space sets because PUCCH resources are never dispersed and PUCCH resources can be efficiently used in this way. As such, when the PUCCH resource region is shared among a plurality of ePDCCH search space sets of different scales, the value of N may be set to a smaller ePDCCH search space set. That is, as shown in  FIG. 29  and  FIG. 30 , when the scale of ePDCCH search space set A is N eCCE =8 and the scale of ePDCCH search space set B is N eCCE ′=32, N=8 is set. However, since terminal  200  does not recognize any ePDCCH search space other than ePDCCH search space sets intended for the terminal, it is the premise that the scales of ePDCCH search space set A and ePDCCH search space set B should be indicated to terminal  200 . 
     When the PUCCH resource region is shared among a plurality of ePDCCH search space sets of different scales, overhead of PUCCH can be reduced by setting the value of N to a smaller ePDCCH search space set. 
     From the above, the method of determining N in terminal  200  according to method 1 is as follows. 
     When PUCCH resources are shared among a plurality of ePDCCH search space sets set in terminal  200 , terminal  200  sets as the value of N, the scale of the smallest ePDCCH search space among the plurality of ePDCCH search space sets set in the terminal among which the PUCCH resources are shared. This can reduce the overhead of PUCCH. 
     Here, the decision as to whether or not to share PUCCH resources is determined as follows. When it is assumed that the start positions of PUCCH resources relating to ePDCCH search space set A and ePDCCH search space set B set in terminal  200  are N (1)   PUCCH  and N (1)   PUCCH ′ (N (1)   PUCCH ≦N (1)   PUCCH ′) respectively, and when equation 18 is satisfied regarding scale N eCCE  of ePDCCH search space set A, ePDCCH search space set A and ePDCCH search space set B share the PUCCH resources. The PUCCH resources are not shared when equation 18 is not satisfied.
 
[8]
 
 N   PUCCH   (1)   +M·N   eCCE   &gt;N   PUCCH   (1) ′  (Equation 18)
 
     When the PUCCH resource region is not shared among a plurality of ePDCCH search space sets set in terminal  200 , the scale of ePDCCH search space sets may be set to the value of N for the ePDCCH search space sets. Alternatively, the scale of ePDCCH search space sets may be set to the smallest among the scales of ePDCCH search space sets set in terminal  200  for simplicity. 
     To put it more simply, even when the scale of ePDCCH search space sets which becomes the smallest among all ePDCCH search space sets set in terminal  200  is set to the value of N, it is likewise possible to reduce the overhead of PUCCH. 
     (Method 2) 
       FIG. 31  illustrates a PUCCH resource region when N=4. PUCCHs can be multiplexed with one PRB (Physical Resource Block) by a maximum of 36 PUCCHs/Δ PUCCH   _   OFFSET  in ascending order of PUCCH resource indices. Here, Δ PUCCH   _   OFFSET  represents the amount of offset of PUCCHs mapped within one PRB and is generally Δ PUCCH   _   OFFSET =2 or 3. That is, when Δ PUCCH   _   OFFSET =2, 3, a maximum 18 and 12 PUCCHs can be multiplexed with one PRB. However, in reality, interference between PUCCHs within the PRB increases as the multiplexing number increases, and therefore the number of PUCCHs that can be multiplexed with one PRB is smaller than the maximum multiplexing number. As shown in the shaded part in  FIG. 31 , PUCCHs corresponding to m=0, 1, 2, 3 (4 m&#39;s) are multiplexed with one PRB when N=4 (note that Δ PUCCH   _   OFFSET =2 in  FIG. 31 ). As the value of m increases, the number of PUCCHs arranged in the PRB increases and interference increases correspondingly. Thus, the greater the value of m, the fewer PUCCHs can be arranged in the PRB. This imposes constraints on scheduling for future subframes. 
     When the PUCCH resource region is shared among a plurality of ePDCCH search space sets in different scales, setting the value of N to the larger of the ePDCCH search space sets makes it possible to reduce constraints on scheduling for future subframes due to the multiplexing of PUCCHs with many DL subframes within one PRB. 
     From the above, the method of determining N in terminal  200  according to method 2 is as follows. 
     When PUCCH resources are shared among a plurality of ePDCCH search space sets set in terminal  200 , terminal  200  sets as the value of N, the scale of the largest ePDCCH search space among the plurality of ePDCCH search space sets set in the terminal among which the PUCCH resources are shared. This can reduce constraints on scheduling for future subframes due to the multiplexing of PUCCHs with many DL subframes within one PRB. 
     Here, the decision as to whether or not to share PUCCH resources is determined according to equation 18 as in the case of method 1. 
     When method 2 is applied, since the scale of the largest ePDCCH search space among a plurality of ePDCCH search space sets set in the terminal is assumed to be the value of N, the value of c′ is always 0. That is, parameter c′ need not be taken into account in this case. 
     Note that when PUCCH resources are not shared among a plurality of ePDCCH search space sets set in terminal  200 , the scales of the ePDCCH search space sets may be set to the value of N for the respective ePDCCH search space sets. Alternatively, the scales of ePDCCH search space sets may be set to the largest among the scales of ePDCCH search space sets set in terminal  200  for simplicity. 
     To put it more simply, even when the scale of an ePDCCH search space set which becomes the largest among all ePDCCH search space sets set in terminal  200  is set to the value of N, it is likewise possible to reduce constraints on scheduling for future subframes due to the multiplexing of PUCCHs with many DL subframes within one PRB. 
     (Method 3) 
     Method 1 and method 2 are in a trade-off relationship and the degree of importance to be attached to effects obtained from method 1 and method 2 varies depending on how the system that applies the present variation is operated. In a system that attaches importance to downlink communication, a UL-DL configuration having a high DL subframe ratio such as UL-DL Configuration  2  is used. In this case, method 1 that can reduce the overhead of PUCCH is effective since it is necessary to indicate HARQ-ACK for downlink data in a plurality of DL subframes collectively in one UL subframe. Method 2 is effective when attaching importance to a simpler base station configuration by reducing the complexity of the base station scheduler. To make the most of the effects of both method 1 and method 2, the method of determining N in terminal  200  according to method 3 may be configured as follows. 
     After setting a static or quasi-static lower limit value to a possible value of N, when PUCCH resources are shared among a plurality of ePDCCH search space sets set in the terminal, terminal  200  designates the scale of the smallest ePDCCH search space among a plurality of ePDCCH search space sets set in the terminal sharing the PUCCH resources as the value of N. However, when this value falls below a lower limit value, the value of N is set to the lower limit value. It is thereby possible to reduce the overhead of PUCCH while reducing constraints on scheduling for future subframes due to the multiplexing of PUCCH with many DL subframes within one PRB. 
     (Method 4) 
     According to method 4 in contrast to method 3, when sharing PUCCH resources among a plurality of ePDCCH search space sets after setting an upper limit value, terminal  200  designates the scale of the largest ePDCCH search space among a plurality of ePDCCH search space sets set in the terminal sharing PUCCH resources as the value of N. That is, the method of determining N in terminal  200  according to method 4 is as follows. 
     After setting a static or quasi-static upper limit value to a possible value of N, when PUCCH resources are shared among a plurality of ePDCCH search space sets set in the terminal, terminal  200  designates the scale of the largest ePDCCH search space among a plurality of ePDCCH search space sets set in the terminal sharing the PUCCH resources as the value of N. However, when this value exceeds an upper limit value, the value of N is set to the upper limit value. It is thereby possible to reduce constraints on scheduling for future subframes due to the multiplexing of PUCCH with many DL subframes within one PRB while reducing the overhead of PUCCH. 
     (Method 5) 
     According to method 5 in association with method 2, the value of N is set to a maximum value of PUCCH that can be multiplexed with one PRB. That is, terminal  200  sets the value of N based on equation 19. Here, Δ PUCCH   _   OFFSET  represents the amount of offset of PUCCH to be mapped within one PRB and is a value set in advance by base station  100 . Since HARQ-ACKs arranged on PUCCHs in one PRB correspond to only downlink data in one DL subframe, it is possible to avoid constraints on scheduling for future subframes due to the multiplexing of PUCCHs with many DL subframes within one PRB.
 
[19]
 
 N= 36/Δ PUCCH   _   OFFSET   (Equation 19)
 
     (Method 6) 
     As described in method 1, the scale of ePDCCH search space sets is 4, 8, 16, 32 or the like, and since PUCCH resources are never dispersed if the value of N is divisible among a plurality of ePDCCH search space sets, PUCCH resources can be efficiently used. Thus, in method 6, the value of N is equalized to the scale of the ePDCCH search space set. The present method can be combined with one of methods 1 to 5. 
     A specific method of setting the value of scale N of a PUCCH resource region for each c′ and each m has been described so far for the case where the PUCCH resource region is shared among a plurality of ePDCCH search space sets. 
     Embodiment 3 
     In Embodiment 2, terminal  200  calculates c′ based on not only eCCE index n eCCE  but also offset value δ ARI  in a virtual PUCCH resource region corresponding to m=m current  and then identifies PUCCH resources in the actual PUCCH resource region. In the present embodiment, terminal  200  includes the ePDCCH-PUCCH resource region corresponding to not only m=m current  but also m&lt;m current  in the virtual PUCCH resource region. 
     As described above, parameter m is an index of a downlink communication subframe for one uplink communication subframe and sequentially numbered. Thus, parameter m corresponding to m&lt;m current  means a past DL subframe. Since DL scheduling in a past DL subframe is determined in the current DL subframe, if there are any free PUCCH resources corresponding to PDCCH or ePDCCH in the past DL subframe, using the free PUCCH resources in the current DL subframe will impose no constraint on scheduling of future DL subframes. 
     In the present embodiment, an ePDCCH-PUCCH resource region when m≦m current  as shown in  FIG. 20  is designated as a virtual PUCCH resource region. 
       FIG. 20  shows an example when m current =2. 
     Here, if m≦m current , since the ePDCCH-PUCCH resource region corresponding to m=0 is most congested, the range of m may be limited such as “m current  and m current −1(m current0 )” instead of “m≦m current .” 
     According to the present embodiment, more ePDCCH-PUCCH resources are included in the virtual PUCCH resource region than in Embodiment 1, and it is thereby possible to lower the possibility that the shifted PUCCH resources will be arranged outside the ePDCCH-PUCCH resource region due to a shift based on an offset value indicated by ARI, and reduce the total PUCCH resource region. 
     Variations 1 to 7 shown in Embodiment 2 are also applicable in the present embodiment. 
     Embodiment 4 
     In Embodiment 2, terminal  200  calculates c′ based on not only eCCE index n eCCE  but also offset value δ ARI  in the virtual PUCCH resource region corresponding to m=m current  and then identifies PUCCH resources in the actual PUCCH resource region. In the present embodiment, terminal  200  includes an ePDCCH-PUCCH resource region corresponding to not only m=m current  but also m=m special  when the occupancy of the PUCCH region is low, in the virtual PUCCH resource region. 
     As shown in  FIG. 3 , there are special subframes indicating switchover from a DL subframe to UL subframe in TDD. A special subframe is composed of several symbols for downlink communication (DwPTS: Downlink Pilot Time Slot), a gap and several symbols for uplink communication (UpPTS: Uplink Pilot Time Slot). In DwPTS, downlink data communication may be performed as in the case of a downlink communication subframe. In UpPTS, SRS (Sounding Reference Signal) transmission or PRACH (Physical Random Access CHannel) transmission may be performed. In a special subframe, available PDCCH region and PDSCH region are smaller than those in other DL subframes. Thus, there are fewer terminals to which PDSCHs are assigned in the subframe. 
     When a HetNet environment combining a macro cell and a pico cell is assumed, ABS (Almost Blank Subframe) is defined in which PDCCH and PDSCH are not assigned in downlink subframes in the macro cell in order to avoid interference from the macro cell to the pico cell. There are no PDCCH-PUCCH resources in the subframe. 
     Thus, in a special subframe or ABS, the occupancy of PUCCH by PDCCH is locally lowered. Therefore, in the present embodiment, ePDCCH-PUCCH resources are positively arranged in the PUCCH region whose occupancy is locally low. This allows free resources to be effectively used. 
       FIG. 21  illustrates a case where m current =2 and special subframe m special =0. Here, m=0, 1 and 2 in  FIG. 21  correspond to SF#1, 5 and 6 in UL-DL Configuration#3 in  FIG. 3 . 
     In this case, an ePDCCH-PUCCH resource region corresponding to m=m current =2 or m special =0 is defined as a virtual PUCCH resource region. 
     Variations 1 to 7 shown in Embodiment 2 are also applicable in the present embodiment. 
     Embodiment 4 may be operated in combination with Embodiment 3. That is, the ePDCCH-PUCCH resource region corresponding to m≦m current  and m=m special  can also be defined as a virtual PUCCH resource region. 
     The embodiments of the present invention have been described so far. 
     The above description has focused on the avoidance of collision between PDCCH-PUCCH and ePDCCH-PUCCH, but the present invention is also applicable for the avoidance of collision between ePDCCH-PUCCH in an ePDCCH terminal and PUCCH in a UL CoMP terminal in addition to the avoidance of collision described above. 
       FIG. 22  illustrates a case where when an ePDCCH terminal and a UL CoMP terminal exist in a HetNet environment, the UL CoMP terminal receives PDCCH (ePDCCH) and PDSCH from macro eNB and transmits PUCCH to pico eNB. When the ePDCCH terminal and UL CoMP terminal transmit PUCCHs using the same PRB, even when PUCCH resources orthogonal to each other within the same PRB are used for PUCCHs, interference due to a difference in reception timing of a plurality of PUCCHs in pico eNB or interference due to a difference in PUCCH receiving power (far-near problem) occurs. This is attributable to the fact that while the UL CoMP terminal performs downlink communication with macro eNB, the UL CoMP terminal performs uplink communication with pico eNB. 
     In order to avoid such interference, PUCCH resources need to be shifted by at least one PRB.  FIG. 22  illustrates method 1 and method 2 as such a method. 
     In method 1, the entire ePDCCH-PUCCH resource region is offset and resources completely different from a PUCCH resource region for CoMP are used to thereby avoid interference. Method 1 can easily avoid interference, but meanwhile, there is a problem that the overhead of PUCCH resources in total is large. 
     Thus, method 2 shares the ePDCCH-PUCCH resource region and the CoMP PUCCH resource region to reduce the overhead of PUCCH resources in total. In this case, in order to avoid interference, a shift is made based on an offset value indicated by ART. Here, in order to realize at least one PRB shift, when the number of PUCCH resources per PRB is 18, the offset value needs to be set to 18 or above. For this reason, the possibility that the offset destination PUCCH resource may become m&gt;m current  is higher than in the case with “+1” which is an offset value applied in the PDCCH-PUCCH resource region. That is, there are problems similar to the problems to be solved in the present invention. That is, constraints are generated on scheduling of future DL subframes and collision between PUCCH resources occurs (however, in the case of  FIG. 22 , collision between ePDCCH-PUCCH resources and CoMP PUCCH resources instead of collision between ePDCCH-PUCCH resources and PDCCH-PUCCH resources). 
     The present invention is applicable not only to a case where collision occurs between ePDCCH-PUCCH resources and PDCCH-PUCCH resources or between ePDCCH-PUCCH resources and UL CoMP PUCCH resources, but also to a case where collision occurs between ePDCCH-PUCCH resources between different ePDCCH terminals. That is, the present invention is applicable to a case where collision occurs between PUCCH resources between different terminals and where ePDCCH-PUCCH resources are used in at least one terminal. 
     Although an antenna has been described in the aforementioned embodiments, the present invention may be similarly applied to an antenna port. 
     The term “antenna port” refers to a logical antenna including one or more physical antennas. In other words, the term “antenna port” does not necessarily refer to a single physical antenna, and may sometimes refer to an antenna array including a plurality of antennas, and/or the like. 
     For example, how many physical antennas are included in the antenna port is not defined in LTE, but the antenna port is defined as the minimum unit allowing the base station to transmit different reference signals in LTE. 
     In addition, an antenna port may be specified as a minimum unit to be multiplied by a precoding vector weighting. 
     In the foregoing embodiments, the present invention is configured with hardware by way of example, but the invention may also be provided by software in cooperation with hardware. 
     In addition, the functional blocks used in the descriptions of the embodiments are typically implemented as LSI devices, which are integrated circuits. The functional blocks may be formed as individual chips, or a part or all of the functional blocks may be integrated into a single chip. The term “LSI” is used herein, but the terms “IC,” “system LSI,” “super LSI” or “ultra LSI” may be used as well depending on the level of integration. 
     In addition, the circuit integration is not limited to LSI and may be achieved by dedicated circuitry or a general-purpose processor other than an LSI. After fabrication of LSI, a field programmable gate array (FPGA), which is programmable, or a reconfigurable processor which allows reconfiguration of connections and settings of circuit cells in LSI may be used. 
     Should a circuit integration technology replacing LSI appear as a result of advancements in semiconductor technology or other technologies derived from the technology, the functional blocks could be integrated using such a technology. Another possibility is the application of biotechnology and/or the like. 
     As described above, a terminal apparatus according to the embodiments described above is a terminal apparatus including: a control section that arranges a response signal on a predetermined PUCCH resource in an uplink control channel (PUCCH) resource region corresponding to an enhanced downlink control channel (ePDCCH); and a transmitting section that transmits the response signal arranged on the PUCCH resource, in which the PUCCH resource region is divided into a plurality of partial regions, and each of the partial regions is divided into a number of downlink communication subframes, PUCCH resources for each index c′ of the partial region and each index m indicating a time-sequential order of the downlink communication subframe are arranged in the PUCCH resource region in ascending order of indices m and in ascending order of indices c′, and the control section arranges a response signal corresponding to an m-th downlink communication subframe in a PUCCH resource selected from among the PUCCH resources corresponding to the indices m and below. 
     The terminal apparatus according to the embodiments described above, further includes: an error detection section that detects an error of downlink data in each downlink communication subframe transmitted from a base station apparatus; and a generating section that generates a response signal indicating the error detection result for each downlink communication subframe, in which the control section arranges a response signal indicating the error detection result in an m-th downlink communication subframe in a PUCCH resource selected from among the PUCCH resources corresponding to the indices m and below. 
     In the terminal apparatus according to the embodiments described above, the control section arranges a response signal corresponding to the m-th downlink communication subframe in a PUCCH resource selected from among the PUCCH resources corresponding to the index m or PUCCH resources corresponding to indices of downlink communication subframes to which fewer ePDCCHs are assigned than to other downlink communication subframes. 
     In the terminal apparatus according to the embodiments described above, the control section calculates the index c′ in a virtual PUCCH resource region in which PUCCH resources corresponding to downlink communication subframes are collected and determines a PUCCH resource on which the response signal is arranged. 
     In the terminal apparatus according to the embodiments described above, the control section calculates the index c′ based on a leading eCCE index occupied by the ePDCCH intended for the terminal and an offset value indicated from base station apparatus and determines a PUCCH resource on which the response signal is arranged. 
     In the terminal apparatus according to the embodiments described above, when the PUCCH resource determined based on the eCCE index and the offset value is not included in the PUCCH resource region, the control section includes a PUCCH resource on which the response signal is arranged in the PUCCH resource region by circulating the PUCCH resource in the virtual PUCCH resource region or inverting the PUCCH resource at an end of the virtual PUCCH resource region. 
     In the terminal apparatus according to the embodiments described above, when the PUCCH resource determined based on the eCCE index and the offset value is not included in the PUCCH resource region, the control section determines a PUCCH resource on which the response signal is arranged in a region other than the virtual PUCCH resource region. 
     In the terminal apparatus according to the embodiments described above, when the index c′ is smaller than a predetermined threshold, the control section determines a PUCCH resource on which the response signal is arranged based on a positive offset value in a direction in which the index m and the index c′ increase, and when the index c′ is greater than the threshold, the control section determines a PUCCH resource on which the response signal is arranged based on a negative offset value in a direction in which the index m and the index c′ decrease. 
     In the terminal apparatus according to the embodiments described above, the control section calculates the index c′ based on a fixed value indicated from the base station apparatus and determines a PUCCH resource on which the response signal is arranged. 
     In addition, a base station apparatus according to the embodiments described above is a base station apparatus including: a control section that determines whether or not a predetermined PUCCH resource in an uplink control channel (PUCCH) resource region corresponding to an enhanced downlink control channel (ePDCCH) collides with another resource; a control information generating section that generates control information for identifying a non-colliding PUCCH resource for a terminal apparatus; and a transmitting section that transmits the control information, in which: the PUCCH resource region is divided into a plurality of partial regions, and each of the partial regions is divided into a number of downlink communication subframes, PUCCH resources for each index c′ of the partial region and each index m indicating a time-sequential order of the downlink communication subframe are arranged in the PUCCH resource region in ascending order of in and in ascending order of c′, and the control section determines collision or no collision with another resource among PUCCH resources corresponding to the indices m and below. 
     A transmission method according to the embodiments described above is transmission method including: making a control to arrange a response signal on a predetermined PUCCH resource in an uplink control channel (PUCCH) resource region corresponding to an enhanced downlink control channel (ePDCCH); and transmitting the response signal arranged on the PUCCH resource, in which: the PUCCH resource region is divided into a plurality of partial regions, and each of the partial regions is divided into a number of downlink communication subframes, PUCCH resources for each index c′ of the partial region and each index m indicating a time-sequential order of the downlink communication subframe are arranged in the PUCCH resource region in ascending order of m and in ascending order of c′, and in the making a control, a response signal corresponding to an m-th downlink communication subframe is arranged in a PUCCH resource selected from among the PUCCH resources corresponding to the indices m and below. 
     The disclosures of the specifications, drawings, and abstracts in Japanese Patent Application No. 2012-172348 filed on Aug. 2, 2012, and Japanese Patent Application No. 2012-209810 filed on Sep. 24, 2012, are incorporated herein by reference in their entireties. 
     INDUSTRIAL APPLICABILITY 
     The present invention is suitable for use in mobile communication systems compliant with LTE-Advanced. 
     REFERENCE SIGNS LIST 
     
         
           100  Base station 
           200  Terminal 
           101 ,  208  Control section 
           102  Control information generating section 
           103 ,  105  Coding section 
           104 ,  107  Modulation section 
           106  Data transmission controlling section 
           108  Mapping section 
           109 ,  218  IFFT section 
           110 ,  219  CP adding section 
           111 ,  222  Radio transmitting section 
           112 ,  201  Radio receiving section 
           113 ,  202  CP removing section 
           114  PUCCH extracting section 
           115  Despreading section 
           116  Sequence controlling section 
           117  Correlation processing section 
           118  A/N determining section 
           119  Bundled A/N despreading section 
           120  IDFT section 
           121  Bundled A/N determining section 
           122  Retransmission control signal generating section 
           203  FFT section 
           204  Extraction section 
           205 ,  209  Demodulation section 
           206 ,  210  Decoding section 
           207  Determination section 
           211  CRC section 
           212  Response signal generating section 
           213  Coding and modulation section 
           214  Primary-spreading section 
           215  Secondary-spreading section 
           216  DFT section 
           217  Spreading section 
           220  Time multiplexing section 
           221  Selection section