On Tue, May 31, 2011 at 4:37 PM, Colby Boyer <[email protected]> wrote:
> Related. It seems that this delay is not taking in account for the MM clock > recovery block? It some cases, this delay will not matter (2 or 4 samples > per symbol), but for other rates it will. > > --Colby That's an excellent point. Any chance for a patch? :) Tom > On Tue, May 31, 2011 at 1:29 PM, Tom Rondeau <[email protected]>wrote: > >> On Tue, May 31, 2011 at 4:25 PM, Colby Boyer <[email protected]>wrote: >> >>> >>> >>> On Tue, May 31, 2011 at 5:59 AM, Tom Rondeau <[email protected]>wrote: >>> >>>> 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 >>>> >>>> >>> >>> Hi Tom, >>> >>> I looked at the issue again and I was not taking in account the group >>> delay of the interp filter (its 5 taps into the future or 3 in the past), so >>> I was sampling a few taps out of phase! After a time shift, it passes the >>> sanity check of '0.0' delay. Thanks for the response! >>> >>> --Colby >>> >> >> Excellent, glad that worked out. I was pretty sure it works, but you never >> know... good to have extra confirmation. >> >> Tom >> >> >> >> >
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