A method of performing, by a user equipment (UE), wireless communication using a serving cell in a wireless communication system is provided. The method includes: starting a deactivation timer associated with the serving cell, the deactivation timer relating to a duration of time after which the serving cell is deactivated; determining whether there is an uplink (UL) grant or a downlink (DL) assignment for the serving cell in a time unit; based on a determination that there is an UL grant or a DL assignment, determining whether a data unit is transmitted on the UL grant or is received on the DL assignment; based on a determination that the data unit is transmitted on the UL grant or is received on the DL assignment: restarting the deactivation timer associated with the serving cell; and transmitting the data unit on the UL grant or receiving the data unit on the DL assignment.