Re: [Discuss-gnuradio] Newbie question on USRP2, synchronization done by the FPGA?

[Marcus D. Leech]

On 09/01/2010 06:47 PM, Sam Keene wrote:

 Hi,

Sorry if this is a simple question. I'm trying to figure out what synchronization is done by the FPGA on the USRP2. Does it perform both phase and freq synch? If I want to implement a simple digital modulation tx-rx, do I just need to do timing synchronization? Is there a simple example of basic digital modulation that is a good reference?

thanks,

-Sam

P.S. Sorry if this is a re-post, I can't tell if the other email went thru

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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