Improving hierarchical 8PSK performance
A method and receiver systems for demodulating and decoding a hierarchically modulated signal, e.g. an 8 PSK signal, are disclosed. An exemplary method includes demodulating and processing ( 502 ) the hierarchically modulated signal ( 202 ) to produce symbols ( 212 ) from the first modulation at the first hierarchical level, applying information ( 504 ) from a plurality of the symbols from the first modulation at the first hierarchical level in subtracting ( 214 ) from the demodulated hierarchically modulated signal to obtain the second modulation at the second hierarchical level and processing ( 506 ) the second modulation at the second hierarchical level to produce second symbols ( 222 ) from the demodulated second signal. The hierarchically modulated signal comprises a non-uniform 8 PSK signal. Applying the information from the plurality of the symbols from the first modulation can be achieved by applying the symbols after error correction. A decision-directed demodulation of the first modulation can also be used to further improve performance.
1. A receiver system for demodulating and decoding a hierarchically modulated signal having a first modulation at a first hierarchical level and a second modulation at a second hierarchical level, comprising:
a first demodulator for demodulating the first modulation of the hierarchically modulated signal;
a symbol decoder, communicatively coupled to the first demodulator, for producing symbols from the demodulated first signal;
an error decoder, communicatively coupled to the symbol decoder, for producing an error corrected symbol stream front the symbols from the demodulated first signal;
a re-encoder for re-encoding the error corrected symbol stream;
an error correcting demodulator, communicatively coupled to the re-encoder for demodulating the hierarchical signal using the error corrected and re-encoded symbols from the demodulated first signal;
a subtractor, communicatively coupled to the re-encoder and the an error correcting demodulator, for subtracting the re-encoded symbol stream from the error correcting demodulated hierarchically modulated signal to produce a second signal; and
a second symbol decoder, communicatively coupled to the subtractor for producing second symbols from the second signal.
2. The receiver system of claim 1 , further comprising;
a second level demodulator, communicatively coupled between the subtractor and the second symbol decoder for demodulating the second signal from the subtractor and providing the demodulated second signal to the second symbol decoder;
wherein the hierarchically modulated signal is non-coherent.
3. The receiver system of claim 1 , wherein the hierarchically modulated signal is coherent.
4. The receiver system of claim 1 , wherein the error decoder comprises a forward error correction decoder.
5. The receiver system of claim 1 , wherein the hierarchically modulated signal comprises a non-uniform eight phase shift keyed signal.