[Discuss-gnuradio] DVB-S2 Physical Layer Framer: Why outputs a zero after each sample?

[Francisco Albani]

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

Relevant lines: 80, 684, 704 and 727.

Bye and thanks!

dvbs2-phy-layer-framer-output.png
Description: PNG image