A method for extracting a message from a received signal frame is provided. The method includes: receiving a signal frame having N parts which are modulated with different power levels, where N is an integer equal to or greater than 2; demodulating and decoding the received signal frame to obtain N bit sequences which correspond to the N parts respectively; and forming a message based on the N bit sequences and a partition scheme according to which the message is partitioned into N message parts corresponding to the N bit sequences respectively.