Bits for acknowledgement (ACK) and/or negative acknowledgement (NAK) may be allocated based on whether a special subframe configuration in a TDD configuration permits downlink transmission. For carrier aggregation, ACK/NAK bits may be allocated only to special subframes in component carriers (CCs) which permit downlink transmission. Also, for example, ACK/NAK bits may be allocated to all CC special subframes if a single CC is configured to allow downlink transmission on one of its special subframes. ACK/NAK bits may also be allocated to all special subframes.