Hierarchical modulation system and transmitter and method thereof

A hierarchical modulation system, comprising:

• a transmitter, comprising:
• a hierarchical modulator, for receiving a high-priority bit stream signal and a low-priority bit stream signal, and for performing a joint encoding and a hierarchical modulation on the high-priority bit stream signal and a low-priority bit stream signal, so as to generate a plurality of mapping signals, wherein each mapping signal is the summation of a high-priority mapping signal and a low-priority mapping signal, the high-priority mapping signal is a complex number signal on the frequency domain to which part bits of the encoded high-priority bit stream signal are mapped, the low-priority mapping signal is a complex number signal on the frequency domain to which part bits of the encoded low-priority bit stream signal are mapped, wherein the pth low-priority mapping signal of the low-priority mapping signals is related to (p+1)th low-priority mapping signal of the low-priority mapping signals, and p is an even number or an odd number;
• and
• an orthogonal frequency division multiplexing (OFDM) modulator, for receiving the mapping signals, and for performing an OFDM modulation on the mapping signals, so as to generate a time domain OFDM signal;
• and
• a receiver, for receiving the time domain OFDM signal, and for performing an OFDM demodulation, a hierarchical demodulation, and a joint decoding on the time domain OFDM signal, so as to obtain the high-priority bit stream signal and the low-priority bit stream signal.