El 16/5/19 a las 22:37, David Rowe escribió: > 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.
Hi David, I did a real world test of the 8PSK modem the other day and got 7e-4 BER without FEC. I'm thinking about adding a very light FEC (very high rate, higher than 9/10) to correct the few errors that appear. Are there such very high rate LDPC codes in codec2? What I've seen is more reasonable and conventional, on the order of 8/9. If not, I'm thinking of adding something more simple, such as a Reed-Solomon code with only a few parity check bytes. The idea is not only to be able to transmit codec2 through this modem (it is clear that this is very easy, since there is more than enough Eb/N0 on this channel), but also other kinds of data, such as images (people are using some old Japanese 1k2 GMSK modem to send digital SSTV, and this could be improved a lot in terms of speed with this modem). The fun thing is that the channel of the QO-100 narrowband transponder is bandwidth limited rather than SNR limited. According to the "rules" we can use up to 2.7kHz and 52dB CN0. 73, Dani.
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