I resampled all the data to do a proof-of-concept. The frames are only a small part of the "chunk" variable. What I am getting is a fairly nice pi/4 DPSK. Only that in between OFDM Symbols (there are 76 in a frame) there is some sort of random phase jitter. And I am clueless what it could be. Frequency offset is compensated, the channel doesnt vary that fast.
Jens 4/1/2006, "Clark Pope" <[EMAIL PROTECTED]> вы писали: >Resample is okay, but beware of any other filter operations you are doing on >the data in a block-wise manner, e.g. chunks. You have to remember to save >the initial conditions: > >[chunk_filt, z] = filter(b,a,chunk,z); > >This would cause phase discontinuities at the edges of each block. > >-Clark > >>From: Jens Elsner <[EMAIL PROTECTED]> >>To: discuss-gnuradio@gnu.org >>Subject: Re: [Discuss-gnuradio] OFDM / DAB demodulation >>Date: Sat, 1 Apr 2006 10:48:29 +0200 >> >>To resample, I used the Matlab "resample" function >> >>chunk_resamp = resample(chunk, 2048, 2000); >> >>It's basically an FIR low-pass - phase is linear. >> >>I'll try again today without resampling, but then the timing is >>pretty much screwed up. >> >>Jens >> >>On Fri, Mar 31, 2006 at 04:28:14PM -0800, Eric Blossom wrote: >> > On Fri, Mar 31, 2006 at 05:10:40PM -0500, Clark Pope wrote: >> > > I would doubt that unless your USRP is defective. The phase noise >>should >> > > only become a major factor at baud rates below about 10 kbaud. >> > > >> > > What's the actual bandwidth of the DAB signal? Did you try collecting >>at 4 >> > > MSPS and then downsampling to the FFT sample rate? Maybe the CIC or >> > > compensation filter transition are distorting the final result. >> > > >> > > -Clark >> > > >> > > >> >> > > >> DAB is using COFDM with pi/4-DPSK on 1536 subcarriers (see >>www.etsi.com, >> > > >standard >> > > >> EN300401 for details). I wrote some Matlab code to demodulate the >> > > >> signal. The data is resampled from 2 MHz (URSP) to 2.048 MHz (DAB >> > > >Standard). >> > > >> A frequency offset is compensated manually. >> > >> > How did you resample from 2.000MHz to 2.048 MHz? >> > >> > Eric >> >> >>_______________________________________________ >>Discuss-gnuradio mailing list >>Discuss-gnuradio@gnu.org >>http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >_________________________________________________________________ >Express yourself instantly with MSN Messenger! Download today - it's FREE! >http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
