A first system receives N data transmissions from a second system. The first system combines N ACK/NACK responses, corresponding to the N data transmissions received, and encodes the combined N ACK/NACK responses by selecting a position of a communication channel over which the first system sends ACK/NACK transmissions to the second system and setting a value for each bit sent during each ACK/NACK transmission based on the combined N ACK/NACK responses. The first system sends the bits at the selected position of the communication channel. The second system, upon receiving the bits sent at the selected position of the communication channel, decodes the N ACK/NACK responses based on the position at which the bits are sent and the bits.