On Thu, Mar 1, 2012 at 10:23 AM, Nowlan, Sean <sean.now...@gtri.gatech.edu>wrote:
> That makes sense, but what about in a case like MSK? It looks like the > GMSK example in gr-digital requires an integer for samples_per_symbol due > to the Gaussian pre-filter. In that case, aren’t possible data rates > limited to those that will result in a USRP sample rate that is supported > exactly?**** > > ** ** > > (Also, is my understanding correct about what the possible USRP rates are? > Must be an integer division of DSP clock rate?)**** > > ** ** > > Thanks,**** > > Sean > I tried to do the same with the GMSK, but I screwed up the filter definition and it didn't work at all. So I went back to the old way because at the time, I didn't have time to make it work correctly. And yes, you are correct about the rates of the USRP with the UHD. I don't know the current setup with the UHD implementation, but there used to be restrictions on the filters that were used based on using different decimations/interpolations. Tom *From:* trond...@trondeau.com [mailto:trond...@trondeau.com] *On Behalf Of *Tom > Rondeau > *Sent:* Wednesday, February 29, 2012 9:00 PM > *To:* Nowlan, Sean > *Cc:* discuss-gnuradio@gnu.org > *Subject:* Re: [Discuss-gnuradio] gr-digital and USRP sample rate**** > > ** ** > > On Wed, Feb 29, 2012 at 10:33 AM, Nowlan, Sean < > sean.now...@gtri.gatech.edu> wrote:**** > > I noticed that the generic_mod_demod.py script in gr-digital uses a > root-raised cosine filter taps and the polyphase filterbank arbitrary > resampler block. I want to resample so that I can exactly hit a supported > USRP transmit sample rate. What kind of issues will I encounter trying to > do this? My understanding is that the USRP can only sample at integer > divisions of the DSP rate (100MSPS for N200/210)., and that if a requested > sample rate doesn’t hit a supported rate exactly, it picks the nearest > faster one. Is this correct?**** > > **** > > Thanks,**** > > Sean**** > > ** ** > > The benchmark scripts take care of this, if I understand your question. We > try to set the sample rate through the UHD interface, then ask for the > actual sample rate it set. This is done in benchmark_tx where we use this > info to set the actual samples per symbol (a real number) based on the the > difference between the asked for and actual sample rate. It's this number > that is then used in the generic_mod_demod code to set the sample rate in > the pfb_arb_resampler to match the sample rates.**** > > ** ** > > Tom**** > > ** ** >
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