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Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise

From: Matthew J. Brandsema
Subject: Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise
Date: Tue, 20 Nov 2018 16:01:18 +0000

So I got the BER to drop by aligning the two streams, but when I look at both bit streams on the scope they do not look aligned.  So I am confused!  See attached images.

It is working, I am able to adjust the noise level now and watch the BER drop.  But I do not understand this.  Can anyone shed some light on this?

Thanks so much for the help so far!!

From: Achilleas Anastasopoulos address@hidden
Sent: Tuesday, November 20, 2018 9:10 AM
To: Matthew J. Brandsema
Cc: address@hidden
Subject: Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise

It is important that you have a time scope where you compare the initial bit stream with the output of the demodulator.
These are NOT synchronized.
Unless you do that you cannot get any meaningful measurement of the BER!

You can substitute the Qt blocks with WX blocks. This is easy.


On Tue, Nov 20, 2018 at 7:36 AM Matthew J. Brandsema <address@hidden> wrote:

I don't have QT gui so I had to convert to WX blocks (how do I install QT?). I cannot get the BER to change appreciably, no matter what delay I set.  The best I can get it to is only about -1 dB.  I will keep playing with it.

From: Achilleas Anastasopoulos [address@hidden]
Sent: Monday, November 19, 2018 5:37 PM
To: Matthew J. Brandsema; address@hidden
Subject: Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise

I attach a simple grc file that works for me.

Using the delay10/delay sliders try to align the input/output bit stream.
(in this example this happens at delay=12, but it may be different for you...)

Then play with the noise variance; you will see the BER changing slowly as you go around values = -6,-5,-4

let me know if this works for you,

Attachment: qam_working_flowchart.png
Description: qam_working_flowchart.png

Attachment: qam_aligned_plots.png
Description: qam_aligned_plots.png

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