In a communication system using HARQ, the problem of false ACK detection when no ACK/NACK feedback is transmitted is solved sent by varying the reliability of the scheduling information transmitted to the user terminal on a downlink control channel depending on whether the user terminal is expected to use a first or second uplink channel for sending ACK/NACK feedback. When the user terminal is expected to use the first channel to send ACK/NACK feedback, the base station transmits scheduling information to the user terminal with normal reliability. When the user terminal is expected to send ACK/NACK feedback on the second uplink channel, the base station transmits the signaling information to the user terminal with enhanced reliability. The reliability of the signaling information can be increased, for example, by increasing the transmit power on the downlink control channel, increasing the aggregation level, or a combination thereof.