Thanks! Why not moving the zero stuffing downstream and use a polyphase arbitrary resampler with RRC taps? I'm not familiar with performance comparison between PFAR and FFT FIR Filter.
2016-06-15 19:41 GMT-03:00 Ron Economos <[email protected]>: > The primary design decision was to use the FFT filter instead of the > interpolating FIR filter for performance. The FFT filter is considerably > faster, especially at the 100 taps used in the flow graph. However, (as far > as I know) the FFT filter does not have an interpolation option, just > decimation. So the 2X interpolation is done in the Physical Layer Framer > block instead. > > You can remove the zero stuffing from the Physical Layer Framer and use > the Interpolating FIR Filter block instead of the FFT filter block for RRC > filtering. If you try that, be sure to remove the factor of two in lines > 535, 548 and 680 in the PL framer block. > > Here's a link that explains why zero stuffing is the correct way to do > interpolation. > > http://www.dspguru.com/dsp/faqs/multirate/interpolation > > Ron > > > On 06/15/2016 02:37 PM, Francisco Albani wrote: > > Hi to all! Specially to Ron Economos! (and thanks for sharing your work) > > I was trying to understand the example *dvbs2_tx.grc* and, after putting > graphical sinks after many blocks, I noticed that the one called "Physical > Frame Layer" outputs one complex zero after each constellation point (see > attached screenshot). Moreover, the FFT Filter that gives the RRC shape is > *not* instructed to interpolate to fit any samples_per_symbol > requirement. Moremoreover, the sample rate is hardcoded to symbol_rate*2. > > This makes me think this transmitter can only work for 2 samples per > symbol. (I suppose one can resample to an arbitrary sps value if needed.) > > The point of this message is to confirm my suspicion and to ask why this > was a design decision. I hope to learn some insight. > > Here is the code: * > <https://github.com/gnuradio/gnuradio/blob/master/gr-dtv/lib/dvbs2/dvbs2_physical_cc_impl.cc#L684>https://github.com/gnuradio/gnuradio/blob/master/gr-dtv/lib/dvbs2/dvbs2_physical_cc_impl.cc#L684 > <https://github.com/gnuradio/gnuradio/blob/master/gr-dtv/lib/dvbs2/dvbs2_physical_cc_impl.cc#L684>* > > Relevant lines: 80, 684, 704 and 727. > > Bye and thanks! > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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