[Patch-gnuradio] QAM receiver modules

[Mason]

Hello,
   So I've been working on writing the QAM demodulation blocks.
   What I have so far works in a simulation, but fails between two 
actual USRPs: the constellation spins and spins, occasionally locking 
when the frequencies get close enough and then breaking again.
   I was wondering if anyone knew better constants to use for the 
alpha/beta/mu/omega greek alphabet soup, because otherwise it's pretty 
much a six-dimensional optimization problem.

The latest version of the patch is available at 
http://www.cae.wisc.edu/~masond/gr-qam-patch-rev3.diff
(the changes I made to gr_feedforward_agc.cc *may* affect other blocks, 
but the way it was working before was too much like hard compression.)

--Mason