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From: | Landsman, Arik |
Subject: | Re: [Discuss-gnuradio] costas ambiguity and correlate-and-sync block in qpsk |
Date: | Sun, 3 Apr 2016 20:24:36 +0000 |
Hi Andy,
So now that the Thrift issue is resolved (separate thread, thank you!), had a few follow up questions on the actual corr_est implementation and placement of tags: >> ./Rx_syncd.py | grep -v volk | sed -e 's/(//g' -e 's/)//g' > foo.txt this doesn't want to port the samples; it does however add a header with something to the likes of "Volk machine: sse4_1_64". Tried as sudo as well, still no go.. I also couldn't find setup_env.sh, searched the whole folder structure. so didn't run >>source <etc>. maybe that's part of the problem? Any other way to send the raw samples into a file from GRC? otherwise going the python route.. ) btw, played with tag delay manually, this has an immense effect on costas rotation once fading model is added to channel. Thanks, Arik From: Andy Walls address@hidden
Sent: Saturday, April 02, 2016 8:11 PM To: Landsman, Arik Cc: address@hidden Subject: Re: [Discuss-gnuradio] costas ambiguity and correlate-and-sync block in qpsk Hi Arik:
On Sat, Apr 2, 2016 at 7:41 PM, Landsman, Arik
<address@hidden> wrote:
Hi Andy, It looks like a GNURadio ControlPort / Apache Thrift error.
I took your flowgraph and modified it slightly, only adding a few blocks:
-modulate_vector
-skip_head
-keep_1_in_n
-qt_time_sink
-feedforward_agc
-multiply const
-qt gui range
One of those might be doing it. Disable skip_head, keep_1_in_n, and the constellation sink they connect to. Hopefully it's one of them.
Otherwise, you didn't drop a control port related block on the flowgraph did you?
FWIW, I also modified the Polyphase clock sync filter taps, the Corr_Est symbols, and changed a few 3.14's to math.pi.
If you build GNURadio with the PyBOMBS build system and install in a target directory somewhere, PyBOMBS generates this environment file which is essential to run GNURadio Companion and gnuradio scripts properly. If you are using the GNURadio supplied
by your distribution, then sourcing a setup_env.sh file is not necessary.
. wondering what <path_to_target> may be. Yes, I just have it emit the complex samples vector that the modulate_vector block creates, and then inspect the samples in octave. You can do it in MatLab or Python or Excel, or whatever.
going to try it if I find setup_env.sh on my end. and once I can run Rx_syncd.py... ) And another, "Oh by the way" for when things are working. In the flowgraph I sent, I mark the phase correction on the last symbol of the preamble - where the phase correction was measured. This means, that the previous symbols in the preamble, if they
suffered a phase rotation, may not get corrected by the costas loop. You can "fix" that by setting the corr_est tag marking delay to 0, to mark the first symbol in the preamble with the phase correction. This is OK as long as you are very close to the correct
center frequency. The measured phase rotation will become less correct the farther you move from the measurement point at the peak of the correlation, if you don't have good frequency lock when performing the correlation.
Regards,
Andy
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