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[Discuss-gnuradio] Packet Decoder Breaking when adding noise

From: Matthew J. Brandsema
Subject: [Discuss-gnuradio] Packet Decoder Breaking when adding noise
Date: Mon, 19 Nov 2018 13:56:12 +0000


This is my first time emailing to this mailing list.  I am working in GNU radio and I have been having a problem that I just cannot solve.

What I am doing:
Setting up a QAM modulation, adding noise, and then demodulating and looking at the bit error rate. See attached screenshot (qam_gnu.png).

What's the problem?
It works fine with no noise and with SOME noise, but it breaks if I add too much noise.  I have traced the problem down to the packet decoder block.  If there is too much noise it just stops outputting anything.  When there is only some noise, it only outputs sometimes.

What have I done to try and fix this?
I thought the issue had to deal with noise affecting the packet headers and not allowing decoding to occur. So I added in some FEC blocks to try and correct the errors, but it didn't help at all. 

I have also tried removing the packet decoding all together but it doesn't seem to work either (see attached for flow chart).

Does anyone have and ideas that I could try to make this work?  My bit error rates plotted are either all 0, or nothing at all.  If I get any bit errors, the packet decoder breaks!

Attachment: qam_gnu.png
Description: qam_gnu.png

Attachment: qam_gnu_no_packet_encoding.png
Description: qam_gnu_no_packet_encoding.png

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