On Tue, May 31, 2011 at 2:13 AM, Colby Boyer <[email protected]> wrote:
> Hi All, > > Recently I've been using the MMSE interp filter. I found that when I shift > a signal by a fractional amount of 0 (or anything really), the signal goes > way off! I would expect SOME difference, but not this much... > > Some example output. > > Mu:0 In:(-1.67869,0.480381) Out:(0.0418351,-0.16734) > > Mu:0 In:(-1.23772,-0.104519) Out:(0.16003,-0.115883) > > Mu:0 In:(-1.7598,-0.0618457) Out:(0.0986395,-0.33428) > > On the imgur links are two Re-Im scatter plots of a bpsk signal, one with > the fractional shift of 0 and the other with a fractional shift of 0.1 The > points with 'x' are the resampled points and points with 'o' is the original > signal. As you can see, the mmse fractional interp more or less destroys the > signal! Unless I'm using it wrong!? > > Any comments? > > imgur: http://imgur.com/a/w98SX top picture is 0 delay, bottom is 0.1 > delay. > > Thanks! > Colby Colby, This block has been around for years without any changes, and I and others have been successfully using it in various projects, so my guess is that you have some misconception about what it's doing or what the parameters are. You can see how it's used to simulate a timing offset in gnuradio-core/src/lib/hier/gr_channel_model.cc where it's used inside of the gr_fractional_interpolator_cc block. We also use it in the gr_clock_recovery_mm_XX and gr_mpsk_receiver_cc. Tom
_______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
