On Tue, May 31, 2011 at 1:46 PM, Tom Rondeau <[email protected]> wrote:
> 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 >>> >>> >>> >>> >> > Sure thing, perhaps later this week? I can submit all my patches at once (this fix, gardner algorithm, multi-order loopfilter). --Colby
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