On Mon, 2021-08-23 at 10:43 +0930, david wrote: > The BPSK pilot is used for acquisition (e.g. estimating the initial > frequency offset) and frame sync. More power is allocated to the > BPSK > pilot to make those two functions fast and reliable (an important > requirement for PTT digital voice). As there is only one BPSK > carrier, > the overhead in terms of total power is about 1dB IIRC.
Yes, I thought acquisition might be a reason. The 1dB power overhead is not much, but for some other systems using QAM a designer would be told that 1dB is unacceptable. > > The FreeDV 1600 waveform (the FDMDV modem) was an open source > implementation of an earlier waveform (see the History section on > http://freedv.org) that was known to work well for this application. > So it was something of a starting point for FreeDV, and a stepping > stone to later waveforms. > > There are Octave and C versions of the modem ( > https://github.com/drowe67/codec2/blob/master/README_fdmdv.md), plus > various blog posts, if you would like to experiment with the modem or > inspect it's implementation. OK, I now know where to look if I decide to have a play. Thanks for your answer, very illuminating. -- Brian _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
