Systems and methods for providing an efficient mechanism for transmitting encoded downlink assignment index (DAI) and for signaling the ACK/NAK information corresponding to downlink grant allocations in an over the air radio telecommunications network with time division duplex (TDD) capability, where aggregation of component carriers (CCs) is used. Downlink control messages containing encoded DAI information are transmitted with downlink allocation grants. A receiver observes the encoded DAI and the downlink allocation grants and forms corresponding ACK/NAK signals. Method embodiments for forming the ACK/NAK signals for CC groups and frames or subframes are provided. The ACK/NAK signals are then encoded using method embodiments and transmitted over parallel channels for each CC group to the transmitter. By using method embodiments for selecting resources for use in the transmission, the last observed DL grant can be identified by the transmitter and the transmitter can detect an error at the receiver.