|From:||Marcus D. Leech|
|Subject:||Re: [Discuss-gnuradio] Newbie question on USRP2, synchronization done by the FPGA?|
|Date:||Wed, 01 Sep 2010 19:57:06 -0400|
|User-agent:||Mozilla/5.0 (X11; U; Linux i686; en-US; rv:220.127.116.11) Gecko/20100720 Fedora/3.0.6-1.fc12 Thunderbird/3.0.6|
On 09/01/2010 06:47 PM, Sam Keene wrote:
I'm not sure what you're asking for, but I'll take a stab at guessing :-)
I'll describe what the USRP2 does on the receiver side:
o Complex samples the input (which is complex, that is I + Q, baseband, typically) at 100Msps
o Filters and decimates that complex sample stream down to whatever sample rate/bandwidth you wish to appear across the
1GiGe interface (and hence into your Gnu Radio application). Your Gnu Radio application then does whatever it does with
than complex-sampled stream. That stream is a time-series with fixed and uniform timing, so any discrete-time-series "math"
you want to do on that stream will "work".
o Both the sample clock and synthesizer clocks can be synchronized to an external source, via the 10MHz SMA inputs, or via
the so-called "mimo bus".
o The FPGA "assists" in the programming of the various daughter-cards programmable elements, like the PLL synthesizers and
variable-gain elements in the gain chain.
The transmit side is the logical reverse, with the D/A sampling at 200Msps, and the FPGA interpolating your application data stream
as appropriate, and presenting it as a complex sampled baseband stream to the D/A. From there, it is presented to complex mixers
on the daughtercard to produce the desired final RF signal.
I don't know if this even comes close to answering your question.
-- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org
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