On Sun, Jan 16, 2011 at 2:52 PM, Tom Rondeau <trondeau1...@gmail.com> wrote: > On Sat, Jan 15, 2011 at 1:40 AM, Ben Reynwar <b...@reynwar.net> wrote: >> Hi all, >> >> What do people think of introducing a constellation object into gnuradio? >> >> It would hold the constellation points and also a decision-making function. >> New modulations could then be easily created by subclassing a constellation. >> >> It would also mean that the decision-making function for a given >> modulation could >> easily be used by different receivers (i.e. the standard receiver and >> the ofdm receiver would >> both use the same decision making code for a given modulation). >> >> I've already had a go at implementing this on my repo. >> >> https://github.com/benreynwar/gnuradio/blob/master/gnuradio-core/src/lib/general/gr_constellation.h >> https://github.com/benreynwar/gnuradio/blob/master/gnuradio-core/src/lib/general/gr_constellation_receiver_cb.h >> https://github.com/benreynwar/gnuradio/blob/master/gnuradio-core/src/python/gnuradio/blks2impl/qam.py >> https://github.com/benreynwar/gnuradio/blob/master/gnuradio-core/src/python/gnuradio/blks2impl/generic_mod_demod.py >> >> Cheers, >> Ben > > > Ben, > Are you talking about something different than > gr_constellation_decoder_cb? I haven't looked at your code, but it > strikes me that what you want is similar to that decoder code (you can > find its use in dbpsk.py and dbpsk2.py in > gnuradio-core/src/python/gnuradio/blks2impl). > > My only suggestion for this part is to have a constellation_decoder_cf > that would output soft symbols instead of hard symbols. > > Let me know if I've missed something in what you are asking. > > Thanks, > Tom >
gr_constellation_decoder_cb uses minimum distance to determine the correct symbol. I would guess this would become a bottleneck for large constellations. My suggestion was to create c++ classes representing constellations which would contain both the constellation points and a function to determine what point a given complex number corresponded to. This way different decision making functions could be written for each modulation (e.g. for PSK you just bin based on the phase, for QAM you bin based on the real and imag components.) These classes would not be signal-processing blocks, but rather would be passed to blocks as arguments. Separating out this code from the receivers would mean that it didn't have to be implemented separately for each receiver. This would effect gr_constellation_decoder_cb in that it would take a constellation object when initialized, e.g. gr_constellation_decoder_cb::gr_constellation_decoder(const gr_constellation_sptr constell) and would use constell.decision_maker to determine what symbol value to return. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
