In a communication system, activity of a transmitter, e.g., a UE, is controlled in response to a deactivation command. The transmitter receives data on at least one transmission carrier and, if a received transmission of data is found to be defective, may send a repeat request to trigger a retransmission of the data. In response to receiving the deactivation command, the transmitter performs a check whether a retransmission is expected on the at least one transmission carrier. If a retransmission is expected, execution of the deactivation command to deactivate the transmission carrier is delayed until the retransmission is received or a timer has expired.