Wouldn't one normally use differential encoding to avoid this problem? Maybe I'm missing something important.
Ben On Thu, May 19, 2011 at 12:21 PM, Robert McGwier <rwmcgw...@gmail.com> wrote: > Vlad > It is apparent to me that you did not understand Josh's explanation. > Possibly he was not forceful enough. ;-). > This is not an error. It is the mathematical consequence of doing QAM with > rotational symmetries. YOU MUST provide your OWN synchronization to remove > the phase ambiguity. It is not a bug or an error. It is a feature. It is > the mathematical nature of the beast. > Bob > > On Thu, May 19, 2011 at 7:55 AM, Vlad Stoianovici > <stoianovici_v...@yahoo.com> wrote: >> >> Dear list and Josh, >> I'm still getting this error when using the QAM Demod block (qamX_demod is >> not connected internally). >> Are there any new developments concerning these blocks? >> >> Vlad. >> >> >> Josh Blum-2 wrote: >> > >> > Well, when you receive a qam signal, and lock to it, you still have some >> > unknown phase offset. Lets suppose qam8 has two possible phases: 0 and >> > 180 degrees. Since you don't know which phase is correct, you can look >> > for the packet header in the received signal at 0 degrees and >> > simultaneously at 180 degrees. Whichever phase offset yields a valid >> > packet is the winner. Of course, this all assumes that you are framing >> > your data with some kind of packet headers. >> > >> > Anyone else have some qam demodulation ideas to share? >> > >> > -josh >> > _______________________________________________ >> > Discuss-gnuradio mailing list >> > Discuss-gnuradio@gnu.org >> > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> > >> >> -- >> View this message in context: >> http://old.nabble.com/QAM-demod-Error-in-GRC-tp23722153p31655276.html >> Sent from the GnuRadio mailing list archive at Nabble.com. >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > -- > Bob McGwier > rwmcgw...@gmail.com > Amateur Radio Station: N4HY > Engineer, Mathematician (Ph.D Brown University) > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
