Wireless communication base station equipment, wireless communication terminal device and search space setting method

An integrated circuit comprising:

• at least one input;
• and
• circuitry coupled to the at least one input, wherein the circuitry, in operation:
• controls reception of a downlink control channel transmitted on a control channel element (CCE) in a first search space that is comprised of a plurality of CCEs, wherein the downlink control channel includes resource assignment information indicating a resource allocated to a terminal apparatus in a component carrier n (CCn) out of one or multiple component carrier(s) (CC(s)) that are configured to the terminal apparatus;
• and
• controls transmission of a ACK/NACK signal on an uplink control channel, an index of which is associated with a CCE number of the CCE on which the downlink control channel is transmitted,
• wherein the first search space, in which the downlink control channel including the resource assignment information indicating the resource allocated in the CCn is transmitted, is comprised of the plurality of CCEs depending on the value of n, and
• wherein a CCE number that defines an end position of the first search space for the CCn and a CCE number that defines a start position of a second search space for a component carrier n+1 (CCn+1) are consecutive, the second search space being different from the first search space.