[Discuss-gnuradio] Gr_mpsk_re ceiver_cc’s costas loop issue

[irene159]

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 
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