USRP: FFT on FPGA?

GNU Radio
1

Hi,

is it feasible to implement an FFT directly on the
FPGA in the USRP?

I would like to use the USRP for spectral analysis,
a 512-point FFT (and windowing) would greatly reduce
CPU load. A “hardware” FFT would also be a great plus
for OFDM waveforms.

I don’t have any experience in FPGA programming,
just wondering if it’s possible.

Best regards,
Jens

2

Go to Altera.com and enter “FFT” in the search box. This will probably
work:
http://www.altera.com/cgi-bin/devsearch.pl?
searchText=&docsetConstraints=&col=corp&qt=FFT&scope=0&submit.x=30&submi
t.y=11&submit=Search

Steve

3

Jens E. wrote:

is it feasible to implement an FFT directly on the
FPGA in the USRP?

Possible, yes, but the FPGA does not have any “hard” multipliers, so
you’ll need to use logic cells for that. But I don’t think it is
necessary.

I would like to use the USRP for spectral analysis,
a 512-point FFT (and windowing) would greatly reduce
CPU load. A “hardware” FFT would also be a great plus
for OFDM waveforms.

The CPU on the host machine is very capable of high-speed FFTs. We can
easily do thousand point FFTs on 8 MS/s data streams.

4

Matt,

thanks for your reply.

The CPU on the host machine is very capable of high-speed FFTs. We can
easily do thousand point FFTs on 8 MS/s data streams.

I would like to localize signals in time and frequency in real time.
My CPU can handle the FFT in real time, but additional (and not
optimized) tasks like segmentation and classification take up a fair
share of CPU time as well.

It would just be nice to have a “switch” that tells the USRP to give
frequency domain data, maybe even averaging internally. I understand
that this is a step away from “Software Radio”, but this seems to be
necessary with my standard hardware. Once I get to the point I need
optimization, I’ll consider this again. Buying a new PC might be
easier. :slight_smile:

Regards,
Jens