Hi Dani and Gerhard, Nice work with your 8PSK modem Dani! There are high rate LDPC codes in codec2 that might be useful.
The current FreeDV 2020 waveform is described here: https://github.com/drowe67/codec2/blob/master/octave/modem_codec_frame_design.ods With FEC it's about 3000 bits/s, so about half that in RF bandwidth using unfiltered QPSK. I'd suggest using unfiltered QPSK then let your SSB radio (is it a SSB TX Gerhard?) do the filtering. If you are interested in using the codec2/src/ofdm.c modem, the work would involve modifying it to run as a single carrier modem. It already has variables for many modem parameters (number of carriers, pilot insertion rate etc), but there are some edge conditions that would need tweaking for one carrier. If the phase noise bandwidth is 50Hz, suggest a pilot insertion rate of 100 or 200 Hz, so at 1500 symbols/s 1:15 or 1:10. With minor changes that would connect to the existing freedv_api.c 2020 code that integrates the modem with the FEC and the LPCnet codec. On a AWGN (satellite) channel it will run happily down to 3dB SNR == 3dB Eb/No (as the 3000 Hz noise bandwidth == bit rate, so Eb/No == SNR). Cheers, David > Hi David and all, > > I'm interested in working with this. I'm currently playing with a 2ksps > 8PSK signal, designed to fit in 2700Hz and be as strong as the beacon: > > https://twitter.com/ea4gpz/status/1119364156715618306 > > I'm getting a good constellation (after all, we have around 14dB Eb/N0), > so with a light FEC (maybe 8/9), achieving 5kbps is perfectly possible. > > Still a work in progress, but it would be good to get interest or input > from other people. > > 73, > > Dani. > > > > > > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
