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Re: [Discuss-gnuradio] MAC layer development and USRP2


From: Philip Balister
Subject: Re: [Discuss-gnuradio] MAC layer development and USRP2
Date: Tue, 06 Apr 2010 16:42:03 -0400
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc11 Thunderbird/3.0.4

On 04/06/2010 04:19 PM, George Nychis wrote:
Jeff, I definitely agree that buffering also adds significant latency.  How
much of the MAC can you get around?  I just think that, there are a number
of people who want the flexibility of the SDR, but want to do MAC research,
and current common SDR architecture is just not good enough.  We need lower
latency between the hardware and the host.

Microsoft Research recently built up a new SDR which uses PCI-E to address
the latency issue:
http://research.microsoft.com/en-us/projects/sora/

Is Sora active? The forum seems really quiet. Also they say there is a strict non-commercial use use license. Also, it seems like they are using the RF front ends from WARP, a look at the Warp site suggests the radio board is 2K. Also, they estimate the board price at "several K$", so it is not quite WARP prices, but looks to be closing in on it rapidly. [1]

Philip

[1] http://social.microsoft.com/Forums/en-US/sora/thread/2701a49b-2ea1-4df6-a85c-d5d01b4ea77c



Their whitepaper is here:
http://research.microsoft.com/apps/pubs/default.aspx?id=79927

I had a paper in the same conference which used several techniques to split
common MAC functionality between the USRP and the host to reduce the latency
of time-critical functions (e.g., carrier sense):
http://www.andrew.cmu.edu/user/gnychis/nychis_nsdi09.pdf

I of course believe in my own work, but I also believe that it is not
sufficient to cover all MAC implementations and future novel MACs ;)  PS. it
also has architectural latency measurements (e.g., host ->  kernel, kernel ->
USRP, USRP ->  kernel, etc.)... and I posted the code for these measurements
on CGRAN, for those interested.  This is why you have the problems you have
Veljko, the turnaround time is extremely high.  We came up with the approach
of "fast-ACKs" which are generated from the USRP itself.

This all said... I really think we need a better interface to reduce
latency.  Some platforms take the: run on the board approach, such as WARP
which puts the MAC on a core on the board.  Good luck conjuring up $10-15k
just for a single WARP board plus frontends though :P

- George




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