I am investigating Meteor M2 decoding. So far I had tackled BPSK decoding (RDS, GPS) and it is the first time I analyze QPSK signals. Based on github.com/otti-soft/meteor-m2-lrpt.git, decoding works fantastically well, but I don't understand why. Costas and MM Clock recovery are understood, but it is the first time I meet the Constellation Soft Decoder. I am unable to find any information on its output and operating principle, but most worrying to me is that I believed that the real output would exhibit four levels following the decision of which bit pair was the most probable, but when displaying on a scope the output of the Constellation Soft Decoder I only see two well defined levels. Can anyone bring some insight on this processing block, which would help me understand the structure of the resulting file and hence start tackling the digital decoding part of the protocol. The flowgraph I use in this investigation is visible at http://jmfriedt.sequanux.org/airspy_m2_lrpt_rxtest.png with an input file containing complex I/Q samples collected during a Meteor M2 pass.
Thanks, JM _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
