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[Discuss-gnuradio] building carrier sense in the FPGA and UHD

From: George Nychis
Subject: [Discuss-gnuradio] building carrier sense in the FPGA and UHD
Date: Sat, 3 Mar 2012 18:51:18 -0500

Hi all,

I'm going to be hacking carrier sense in to the FPGA on the USRP2 very soon.  Basically, taking what I did with the "in-band" project from the USRP1 with carrier sense, and moving it forward to USRP2. 

The idea is, just like you can set a timestamp to "gate" a packet on its way out: only transmit it at time X, you can do something similar with carrier sense.  If the burst has the carrier sense flag set, then you wait for the carrier to become idle, then transmit the packet.

For the in-band implementation, I had a command to set the value at which the carrier is determined to be busy/idle.  This was stored in memory in the FPGA.  Then, when bursts came with a carrier sense bit set, that value is used.

OK:  so I'd like to re-do this implementation to keep this kind of stuff alive, and I will use it myself.  But in doing so, I'd like to implement it in a way that jives well with the higher ups.  If I'm going to do it, I'd like to do it right so that it lives on through future versions of GNU Radio.  So that means doing it using UHD.

For the life of me, I can't find the UHD header spec.  But I imagine somewhere in there we can fit a bit to gate based on carrier sense, and a new command to set the carrier sense threshold.

If you have any advice/guidance on how you'd like to see this implemented, let me know.  I sincerely would like this to live long and prosper in GNU Radio and the USRPs.

- George

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