The invention provides a wireless communication system. In one embodiment, the wireless communication system comprises a base station and user equipment. The base station transmits data to user equipment via a plurality of the component carriers comprising a series of data transmission cycles, interleaves starting time of a plurality of active periods of the component carriers in each data transmission cycle in an order, and sends control data to the user equipment via the component carriers during the active periods of the component carriers. The user equipment receives the control data via the component carriers during the active periods of the component carriers.