Hi David, Since you mentioned working on a 4FSK modem, I have started to model one using Gnuradio and test it over a noisy channel. My question is: since to maintain a reasonable bandwidth of the signal you have to do heavy pulse shaping and not use orthogonal freqencies, how do you manage a reasonable BER? By my simulations, 4FSK requires orthogonal tones in order to still get a reasonable decode error with a noisy channel. That creates a signal with a huge bandwidth, especially compared with DQPSK which for less bandwidth handles noise a lot better. Of course QPSK requires high linearity of the amplifier, which is why my next step is to investigate PI/4 DQPSK which is used as modulation scheme by the Tetra standard.
>From my experiments so far, given a fixed bandwidth and a noise spectrum with the same power, the ranking from best to worst in BER is: DBPSK > DQPSK > 2FSK, GMSK, 4FSK Can you confirm this using you mathematical knowledge? Cheers, Adrian ------------------------------------------------------------------------------ _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
