According to one embodiment, a method for switching operating carrier at a user equipment (UE) includes receiving a message including a carrier index of a target carrier for a current primary carrier change from a base station. The message further includes action time information indicating a start time in which the mobile station switches from the current primary carrier to the target carrier. The UE may switch from a current operating carrier to the indicated target carrier based on the received action time information and the carrier index of the target carrier.