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Re: [Discuss-gnuradio] Weird behavior of the correlate_and_sync block

From: Richard Bell
Subject: Re: [Discuss-gnuradio] Weird behavior of the correlate_and_sync block
Date: Sat, 28 Mar 2015 23:22:28 -0700

I was seeing results with amplitudes like that as well, but I didn't trust myself. I didn't push hard enough to get it working. I let it go. I'm still need to get it working, for the same reason as you, but I can't say when I will be able to put the time in. I'll let you know what happens when I do, if no one else comments on this.


On Sat, Mar 28, 2015 at 6:19 PM, Karl Koscher <address@hidden> wrote:
I'm trying to use the correlate_and_sync block to get an initial timing estimate from a packet radio, but it doesn't seem to work at all. I decided to dig a bit deeper and try to figure out what it was doing. As it turns out, the sequence it correlates against seems to be completely wrong. Here's a simple test script to demonstrate the problem:


from gnuradio import digital
from gnuradio.filter import firdes
from pylab import *

preamble = [1,1,-1,-1] * 10
taps = firdes.root_raised_cosine(32, 32, 1, 0.35, 11*4*32)
corr_and_sync = digital.correlate_and_sync_cc(preamble, taps, 8, 32)

This produces a non-deterministic graph, but will often show wildly oscillating samples, with an amplitude as high as 1e31. Clearly something is amiss. 

When I extend the preamble to be 64 symbols long, everything seems to work. However, when I change the filter it uses, it breaks again.

Any ideas what's going on?

- Karl

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