[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] USRP hardware purchase

From: George Nychis
Subject: Re: [Discuss-gnuradio] USRP hardware purchase
Date: Thu, 16 Aug 2007 04:33:52 -0400
User-agent: Thunderbird (X11/20070604)

I've got to go with Dan on this one, there is no chance of 802.11 with the USRP and GNU Radio. However, we are working on something 802.11-like with the in-band signaling work and the MAC we are building.

I think a big first step for the platform is getting a solid contention based MAC protocol, which the platform lacks as a whole. From this, some 802.11-like MAC can be built, and other protocols.

To give you a heads up Dan, we are working on doing carrier sense in the FPGA and supporting it with the in-band signaling work. It's actually what we're working on at this second. Building it in the FPGA avoids the FPGA->host->FPGA latency. The FPGA is going to read carrier sense related parameters from registers, and the host will set a flag in the packet if it wants the FPGA to carrier sense before transmitting it. I think very time sensitive functionalities like this need to be pushed in the FPGA.... though we're also considering building it in the host too so we can evaluate the tradeoffs.

- George

Dan Halperin wrote:
Hash: SHA1

The USRP has a maximum bandwidth of about 16 MHz (using 8-bit samples
instead of the usual 16), which is not even enough to cover one
802.11b/g channel (22 MHz Nyquist). Thus you'll have a hard time
decoding b/g packets at faster than 1,2 Mbit rates (BBN has done some
work facilitating the recovery of these packets).

On top of that, an (extremely, I think) optimistic lower bound for
latency in a GNU radio system is over 1 millisecond from the RX antenna
through the FPGA over the USB to the computer to your software back over
the USB and out the TX antenna. This makes it _reallllllly_ hard to get
the 10 _microsecond_ turnaround required for an 802.11b ACK, and carrier
sense is meaningless with such a latency.

Also, see Tom Rondeau's email of 12/05/2006 for more comments, but the
short of it is that you're unlikely to be able to get any sort of
reasonable interoperation between the USRP and commercial 802.11b/g

- -Dan
Version: GnuPG v1.4.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org


Discuss-gnuradio mailing list

reply via email to

[Prev in Thread] Current Thread [Next in Thread]