Works with GR 3.6, breaks with 3.7

GNU Radio
21

Thanks Andy! Good catch - I made the changes you suggested. I was just
doing a simple back of the envelope calculation to come up with channel
size. It does look like cleans things up and adding the waterfall graphs
does make it easier to see. Unfortunately, it does seem to change the
decoding. I am still getting the same amount of CRC errors.

Did the overall signal look right, like something that should be
decodable?

Anything else I should try?

  • Luke
22

On Mon, 2014-11-03 at 22:13 -0500, Luke B. wrote:

Thanks Andy! Good catch - I made the changes you suggested. I was just
doing a simple back of the envelope calculation to come up with
channel size. It does look like cleans things up and adding the
waterfall graphs does make it easier to see. Unfortunately, it does
seem to change the decoding. I am still getting the same amount of CRC
errors.

Did the overall signal look right, like something that should be decodable?

So I put the output of the FLL into a quad demod block and compared its
output to the PLL Freq det output. They are pretty much in line, except
the quadrature demod block output shows occasional burst of noise for a
few symbol times where the transmission must have stopped and restarted.
The PLL freq detect block just makes something up during these times.
So that seems generally OK.

Anything else I should try?

Your PLL freq detector block output is swinging between -2 and 2. You
might want to reduce the max and min freq by a factor of 2, so that the
clock recovery block sees inputs limited to +/- 1.0. See Nick’s
recommendation here:
http://lists.gnu.org/archive/html/discuss-gnuradio/2014-10/msg00473.html

So after i did that, what I really noticed is that the correlator is
just not marking preambles properly. See the top plot of the attached
to window shots: Preamble_marked_late_twice.png and
Preamble_marked_early.png

If the deinterleaver and/or crc block isn’t searching around for where
the preamble really is, well that would explain it.

Regards,
Andy

23

This is awesome! I just pulled master and I am recompiling it right now.
Thanks you both so much for the help.

I clearly still have some tuning work to do either way, but it would be
great to get move up to 3.7. I will let you know if this clears it up. I
have my fingers crossed that it will.

24

That fixed it!!

Nick & Andy - thank you both so much for looking into it. Without your
help, there is no way I would have fixed this… and without Nick’s code I
couldn’t have built it in the first place.

  • Luke
25

Red face over here.

There was a bug in correlate_access_code_tag – which only gr-smartnet
and
gr-ais use, so far as I know. The fix was pulled into master a couple of
days ago. This could explain the discrepancy you’re seeing in the
preamble
mark.

Pull latest GR master, build, and see if it fixes what you’re seeing.

–n

On Tue, Nov 4, 2014 at 5:19 PM, Andy W. [email protected]