Transmitting an acknowledgement/negative acknowledgement (ACK/NACK) signal in association with a packet transmitted on an uplink is disclosed. The method includes the steps of receiving a packet transmitted from a user equipment, decoding the packet, and determining whether the packet has been successfully decoded, transmitting an ACK signal or a NACK signal, based on the decoding result. Different transmission powers are allocated for the ACK signal and the NACK signal. Alternatively, the transmission power for the NACK signal selectively has an OFF level. The present invention optimizes the transmission powers for downlink ACK/NACK signals in accordance with the required reception quality of each of the ACK/NACK signals, and thus, enables the system to operate efficiently.