Patent ID: 8599702

Claim:
A method of transmitting data in a time division duplex (TDD) system, the method comprising: transmitting downlink data in a plurality of downlink subframes to a user equipment, each transmitted downlink subframe corresponding to a different constellation point set of a plurality of constellation point sets, wherein acknowledgement/negative acknowledgement (ACK/NACK) signals of each transmitted downlink subframe are mapped to constellation points included in the constellation point set corresponding to the transmitted downlink subframe, and wherein a last downlink subframe of the transmitted downlink subframes includes an indicator that indicates a number of the transmitted downlink subframes; receiving an uplink subframe including one or more ACK/NACK signals, each ACK/NACK signal at the constellation point of the constellation point set determined by the user equipment to correspond to one of the transmitted downlink subframes that was received by the user equipment, wherein the determination by the user equipment is based on the indicator; determining that one of the constellation point sets does not include the ACK/NACK signal; determining that the transmitted downlink subframe corresponding to the constellation point set that does not include the ACK/NACK signal is a failed downlink subframe that failed to transmit downlink data; and re-transmitting the downlink data that failed to transmit via the failed downlink subframe.