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

[George Nychis]

On Tue, Apr 6, 2010 at 5:35 PM, Jeff Brower <address@hidden> wrote:

Philip-

> 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]

I think you're touching on an underlying, basic point:  Matt et. al. have spent years developing an RF + server
architecture that both works and is inexpensive.  Those two things are very difficult to integrate.  Many tradeoffs
and compromises must be made carefully, with a lot of painstaking trial and error.  Matt's followers recognized this
some time ago, more recently NI has recognized this.  The Sora team may find it difficult -- and likely expensive --
to reliably move very high rate ADC data over some distance, external to the PC.  PCIe-over-cable is one way, but
again, not cheap.

SORA is quiet right now because the boards are not public.  To my understanding, they are providing dozens to research institutions for research purposes, and then after this phase pushing them public.  But, I'm not sure.  That's just my impression.

Their original proposed price range of the SORA board was $2k.  I'm not sure it will hit that price, and you're right, they're using a WARP daughterboard which is pricey.  Luckily, in the academic world we can get our hands on some of these.  CMU was awarded 6 of the SORA boards (which I'm assuming will come with daughterboards?) for research.  Our plan is to connect them to our wireless emulator  (http://www.cs.cmu.edu/~emulator/) which is accessible to *anyone*.  That would allow both us, and anyone who wanted to, to use the SORA boards.  But, we need to change some of the infrastructure to support the PCI-E boards.

I definitely agree with you on the tradeoffs there.  There is a pure tradeoff between cost and performance, and Matt and the USRP hit a great point for flexibility at the PHY and low cost radios.  This to me, is sufficient for a lot of PHY-level research.  As we go up the protocol stack, it's just not sufficient enough.  I'm not saying it's a bad SDR solution, it's just insufficient to work our way up the protocol stack and have an effective, high throughput, radio.  I'm not sure what the answer is to this... but I'm hoping there is one in the future that facilitates MAC development at a low cost :)