The present invention relates to a scheduling unit in a wireless communication system. For sequentially receiving a plurality of Protocol Data Units (PDUs) in a plurality of communication sessions, accumulate and schedule the plurality of PDUs during a predetermined time frame, and transmit the PDUs based on a maximum power-strength of the wireless communication system. The scheduling unit comprises a time-based scheduler and a power-based scheduler. When the power-based scheduler schedules the PDUs, if the total sum of the required power of the PDUs exceeds the maximum power-strength of the wireless communication system, the power-based scheduler sends back to the time-based scheduler the PDUs whose power amounts to the exceeding of the maximum power-strength of the wireless communication system according to the corresponding priority values of the PDUs, so that the wireless communication system transmits all at a time the remaining PDUs whose total power remains within the maximum power-strength.