Hi David, Thanks for the answer! I have just simulated a 2FSK modem on AWGN channel, but this time without using FM demodulation. It performs just like you said, ~2 dB worse than QPSK (at 5% frames dropped). This means that the FM demodulator I used for 2400A must be introducing some symbol errors.
What I can't figure out is the 10 dB difference to analog FM. My experimental results (test in urban environment, with distances between 500 meters and 1 km between sender and receiver) show ~6 dB between QPSK and analog FM (with 2.5 kHz deviation) and no more than 4 dB between 4FSK and FM. Could the non-coherent demodulation explain this? I know I can obtain up to 6 dB SNR improvement by going to Codec2 700 bits/sec and using Viterbi soft symbol decoding, but I'd like to get the optimal results before. Would convolutional encoding in 2400A be worth considering? Thanks, Adrian ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
