1. A method for a User Equipment (UE) operating in a wireless communication system, the method comprising:receiving an uplink grant from an eNodeB (eNB) when there is no uplink data to be generated, wherein the uplink grant is valid during a specific time duration;
transmitting data using the uplink grant when the data is generated during the specific time duration; and
discarding the uplink grant when the specific time duration is passed when the data has not been generated during the specific time duration,
wherein the uplink grant includes an indication that the uplink grant is for data which the UE expects to be generated.