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Re: [Discuss-gnuradio] 8b/10b for GMSK

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] 8b/10b for GMSK
Date: Sun, 4 Feb 2007 11:27:36 -0800
User-agent: Mutt/1.5.9i

On Sun, Feb 04, 2007 at 02:32:30AM -0800, Brett Trotter wrote:
> After coming up with some scripts to generate thousands of 200-byte random
> files and attempt to transfer them over a GMSK link, I isolated 5 of 10,000
> 'files' that cause the packet to be dropped (when the MTU is big enough to
> hold the entire 200 bytes- which should be all the time)- most likely due to
> repeated zeros or ones that cause a loss of sync. Upon debugging the output
> after the whitener, it does appear that there are instances of around
> 12-zeros in the packets that don't work.

What's the maximum run length that you see in packets that _do_ work?
My understanding from talking to Johnathan is that he has some
packets that work that have 17-bit runs in them (post-whitener).
(Not sure if they're ones or zeros.)

This makes me think that the 8b/10b "solution" is premature, given
that the problematic symptom is not yet nailed-down.

In summary, create the smallest test case you can that reproduces the
problem.  When you've got that under control, figure out the next

I suspect that some adjusting of control loop constants may be in order.


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