A method is presented for transmitting signals at a User Equipment (UE) in a multi-antenna wireless communication system. Acknowledgment (ACK)/negative ACK (NACK) information is received from a base station (BS). At least one transport block negatively acknowledged by the ACK/NACK information is retransmitted to the BS. An uplink grant for retransmitting the at least one transport block is not detected. If a number of the at least one transport block is not equal to a number of transport blocks indicated by a most recent uplink grant, cyclic shift values and orthogonal cover codes (OCCs) of a demodulation reference signal (DMRS) for the at least one transport block are configured based on a cyclic shift field included in the most recent uplink grant and a number of layers corresponding to the at least one transport block.