I am curious if anything like this is available for the USRP version 1,
for anyone who might know.
As a random side note, it would be interesting if future versions of the
USRP contained off-board RAM chips for data buffering for just this
purpose. The reason I suggest this is for making the USRP more usable
in RADAR applications. Universal RADAR Peripheral, anyone?
On 3/18/2011 3:09 PM, Marc Epard wrote:
I posted this to the USRP users list since we're not using GNU Radio
proper for this project, but Devin's questions about spectrum sensing
make me think it could be useful for GNU USRP users, too. Although we
did this on the N210, it might be possible to do something similar on
the USRP2.
We've customized an FPGA image for the N210 that lets us grab batches
of 256K complex samples (one SRAM full) at 100 Msps with no
decimation, scaling, or downconversion. It works by filling the SRAM
with samples at full rate, then dribbling them out the Ethernet in the
normal fashion. I posted the ISE project, Verilog code, and a built
image at https://public.me.com/mepard. You'll also find some examples
of visualizing the spectrum data there. I'm particularly fond of the
movie.
Some things you should know:
* It cannot be used to transmit. Transmit support used the SRAM, which
I needed to buffer the received samples.
* It works with the current UHD firmware and host code.
* When you issue_stream_cmd, request no more than 2^18 samples, the
size of the SRAM. You can issue another stream command later to get
another batch, but you can't get more than 256K contiguous samples.
* The rx sample rate is ignored. For good measure, I set it to the
usual maximum of 25 Msps.
* Since there's no downconversion, you'll only get whatever center
frequencies the daughterboard supports and you can't use LO offsets.
The uhd_streamer.cpp app, also posted, is what we've used to do our
testing.
Enjoy.
-Marc
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