Hello, I have recently been doing some tests, simulating QPSK-modulated transmissions and studying Costas loop performance. When doing this, I noticed a problem related to gr_mpsk_receiver_cc’s costas loop NCO frequency as I already mentioned in post [1].
I have created two test files: Testfile.py and Tesfile_modified.py. I have basically been working with Testfile.py but in order to better analyse output (in text file) I have created Testfile_modified.py where I have removed simple_framer and simple_correlator part which conditioned output (there is no output as long as simple_correlator doesn’t identify “a frame”). I have also slightly modified dqpsk.py file, gr_mpsk_receiver_cc.cc file (to print Costas loop NCO frequency for every iteration of the loop) and gr_simple_correlator.cc (just to space display). Please find terminal display in attached files: terminal_display_1, 2 and 3. I have configured different values of frequency_offset (channel_model block parameter). I have had no answer to my questions concerning this parameter in post [1] so I have taken this parameter to represent a slight deviation between theoretical transmission frequency and the real frequency at which the signal is sent (in Hz). “terminal_display” result files prove NCO’s frequency isn’t adapted to frequency_offset correction (even for small values of frequency deviation). [1] http://www.nabble.com/Trace-mpsk_receiver_cc%28%29-td17605464.html http://www.nabble.com/file/p17757609/dqpsk.py dqpsk.py http://www.nabble.com/file/p17757609/gr_mpsk_receiver_cc.cc gr_mpsk_receiver_cc.cc http://www.nabble.com/file/p17757609/gr_simple_correlator.cc gr_simple_correlator.cc http://www.nabble.com/file/p17757609/terminal_display_1.txt terminal_display_1.txt http://www.nabble.com/file/p17757609/terminal_display_2.txt terminal_display_2.txt http://www.nabble.com/file/p17757609/terminal_display_3.txt terminal_display_3.txt http://www.nabble.com/file/p17757609/Testfile.py Testfile.py http://www.nabble.com/file/p17757609/Testfile_modified.py Testfile_modified.py -- View this message in context: http://www.nabble.com/Gr_mpsk_receiver_cc%E2%80%99s-costas-loop-issue-tp17757609p17757609.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
