A mobile communication device including a Baseband processor is provided. The Baseband processor determines an ending period of time of a Transmission Time Interval (TTI) for processing one or more first Service Data Units (SDUs) in a first protocol layer, and prior to the ending period of time, pre-processes one or more second SDUs, which are received during the remaining period of time of the TTI, and re-processes the pre-processed second SDUs in a second protocol layer to generate the first SDUs. Particularly, the second protocol layer is hierarchically higher than the first protocol layer in a communication protocol stack.