Method and apparatus for transmitting ack/nack in a tdd-based wireless communication system

A wireless device for configuring a positive acknowledgement or negative acknowledgement (ACK/NACK) in a wireless communication system based on time division duplex (TDD) in which M, M=4, downlink subframes are associated with an uplink subframe, the wireless device receiving a physical downlink shared channel (PDSCH) and a physical downlink control channel (PDCCH), comprising:

• a radio frequency unit configured to transmit radio signals;
• and
• a processor operatively coupled with the radio frequency unit and configured to
• receive at least one downlink transport block in the M downlink subframes from a first serving cell;
• determine ACK/NACK states {HARQ-ACK(1), HARQ-ACK(2), HARQ-ACK(3), HARQ-ACK(4)} for the first serving cell;
• and
• determine an ACK/NACK response based on the ACK/NACK states,
• wherein the PDCCH carries a downlink grant including a downlink assignment index (DAT) which indicates an accumulative number of PDCCHs with assigned PDSCH transmission
• wherein the ACK/NACK states {HARQ-ACK(1), HARQ-ACK(2), HARQ-ACK(3), HARQ-ACK(4)} are determined among possible ACK/NACK states, the possible ACK/NACK states comprising at least six states of (A, A, A, N/D), (A, A, N/D, any), (A, D, D, D), (A, A, A, A), (N/D, any, any, any) and (A, N/D, any, any) except for (A, D, D, D), where ‘A’ indicates an ACK, ‘N’ indicates a NACK, ‘D’ indicates discontinuous transmission (DTX), and ‘any’ indicates any of ACK, NACK and DTX,
• wherein the ACK/NACK states {(A, D, D, D), (A, A, A, A)} are mapped to a first state associated with ACK/NACK resources, the ACK/NACK states {(N/D, any, any, any) and (A, N/D, any, any) except for (A, D, D, D)} are mapped to a second state associated with ACK/NACK resources, and the first state is different from the second state, and
• wherein HARQ-ACK(j), j=1, 2, 3, 4, is ACK/NACK/DTX for a corresponding downlink transport block on the PDSCH with a DAT value j in a corresponding PDCCH.