On Thursday 05 March 2009 19:12:15 Eric Blossom wrote: > On Thu, Mar 05, 2009 at 05:37:00PM +0100, Dimitris Symeonidis wrote: > > Hi List, > > I was reading through the dbpsk.py block in blks2impl, and found > > something that doesn't seem to make much sense (to me). > > Lines 272-273 read: > > rot = 1 > > rotated_const = map(lambda pt: pt * rot, > > psk.constellation[arity]) Is this not equivalent to: > > rotated_const = psk.constellation[arity] > > ??? I mean, it's just multiplying each output item of > > psk.constellation with the number 1, or am I mis-reading something? > > > > Thanx for looking at this... > > I'm guessing that it's in there because at sometime someone wanted to > rotate the constellation. (If rot were a suitable complex value, the > multiplication by rot would rotate it.) rot = 1 means "don't rotate"
This may be needed based on the type of mpsk decoder in the chain. As currently there is a differential decoder, sybols will always be on positions (theta + i * 2pi/M; i=[1..M]; theta=0). With no differential decoder, it depends on the carrier tracking loops view of 'zero phase (theta)'. For the mspk_receiver_cc, the constellation points will be the same as stated for the diff. encoding. In general theta can have any value, and for the qpsk _encoder_ is set to 45 degrees. Stefan -- Stefan Brüns / Bergstraße 21 / 52062 Aachen mailto:lurch at gmx.li http://www.kawo1.rwth-aachen.de/~lurchi/ phone: +49 241 53809034 mobile: +49 151 50412019 _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
