Method and apparatus for making harqs in carrier aggregation systems

An apparatus for performing hybrid automatic repeat request (HARQ) in a carrier aggregation system, the apparatus comprising:

• a radio frequency (RF) unit that transmits and receives a radio signal;
• and
• a processor connected with the RF unit,
• wherein the process is configured to perform,
• receiving downlink data through a first subframe of a first carrier;
• transmitting acknowledgement/not-acknowledgement (ACK/NACK) for the downlink data through a second subframe of a second carrier;
• and
• receiving the downlink data again through a third subframe of the first carrier,
• wherein the first carrier is a carrier which s comprised of downlink subframe only, and wherein the second carrier includes the uplink subframe and the downlink subframe.