Communication apparatus and retransmission control method

An integrated circuit comprising:

• reception circuitry, which, in operation, controls reception of downlink data on a first component carrier and a second component carrier;
• transmission circuitry, which, in operation, controls transmission of a block of ACK/NACK bits that indicates error detection results of the downlink data on the first component carrier and the second component carrier, wherein the block of ACK/NACK bits is mapped, according to a mapping table, to a phase point among phase points on an uplink control channel resource (PUCCH resource) selected from a plurality of PUCCH resources, wherein the mapping rule defines:
• a first number of PUCCH resource(s) respectively associated with set(s) of phase points, wherein all phase points in the set are mapped with acknowledgment (ACK) or all phase points in the set are mapped with negative acknowledgement (NACK)/discontinuous transmission (DTX) in one of the error detection results;
• a second number of PUCCH resource(s) respectively associated with set(s) of phase points, wherein all phase points in the set are mapped with ACK or all phase points in the set are mapped with NACK/DTX in another one of the error detection results;
• and
• a maximum difference between the first number of PUCCH resources and the second number of PUCCH resource(s) is one or zero;
• wherein,
• the reception circuitry, responsive to the block of ACK/NACK bits indicating a retransmission, controls reception of the downlink data in the retransmission.