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Re: [Discuss-gnuradio] in-band signaling & dependent packets (i.e., ACK


From: George Nychis
Subject: Re: [Discuss-gnuradio] in-band signaling & dependent packets (i.e., ACK generation)
Date: Tue, 04 Dec 2007 12:49:44 -0500
User-agent: Thunderbird 2.0.0.6 (X11/20071022)



I don't think I understand what you're trying to do here.  What frames
were you transmitting?  What pattern are you looking for?  Do you hope
on performing this operation in the FPGA or on the host?

Sorry for my confusion.


No problem, I don't mind trying to be clear :)

Here's an *example* of what I want to overcome: latency between the USRP and host when ACK'ing a DATA frame in _any_ CSMA type protocol.

The frames I was transmitting are home-made frames that just so happen to use the same sync bits as the GNU Radio GMSK frames. It's not really important, but the pattern I am looking for is the start of frame in sample space.

The "in sample space" is what's important, because I can obviously find the framing bit sequence by decoding the samples using the PHY layer... but this incurs the latency over the bus. What I'm trying to do is detect the start of frame sequence without using the PHY layer to avoid this latency.

So as a first experiment I would mark what samples were needed to actually decode the frame bits, and was trying to see if I could pattern match these raw samples. If there was a high correlation between the samples, I could simply implement some functionality in the FPGA to look for this pattern. This would hopefully be independent of the PHY layer used.

- George




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