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[Discuss-gnuradio] supporting carrier sense

From: George Nychis
Subject: [Discuss-gnuradio] supporting carrier sense
Date: Fri, 03 Aug 2007 02:11:44 -0400
User-agent: Thunderbird (X11/20070604)

It's MAC discussion time :)

So, I was thinking about the plan for supporting carrier sense, as its probably the most concrete and widely used functionality of MAC protocols.

I can imagine two common carrier sense situations, one is where the MAC simply wants to know if the channel is idle to perform some action, such as entering a new state. The other situation is to carrier sense before a transmission.

The first situation does not require an extremely low latency. I can imagine that the MAC could just read the RSSI level from the RX side and compare it to some threshold to determine if the channel is idle.

In the second situation, tighter timing might be required/desired. If you rely on reading the RSSI from the RX side, this is at least some amount of time old, and then by the time the decision is made and the frame is passed down, the channel may be busy now. Of course, this can still happen if the functionality is built in the FPGA, but the timing can be much tighter.

But of course, everything could be built in the FPGA.

So I'm wondering what other peoples opinions are. Most of the MAC should be in GNU Radio, but there are some things we might want to push to the FPGA for tighter timing.

I'd imagine we can have some packet or flag which says to carrier sense before the given transmission. It would need to specify the threshold and time to sense.

In GNU Radio, or in the FPGA with control from GNU Radio?

- George

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