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Re: [Discuss-gnuradio] regarding fft-ifft processing

From: Kuntal Majumdar
Subject: Re: [Discuss-gnuradio] regarding fft-ifft processing
Date: Wed, 7 Mar 2007 06:17:04 -0800 (PST)

Well, thats good enough. But then, I havent still got the relevant documentation on this anywhere on the trac. I mean, I want to know how does the host side handle all the related (I)FFT stuff.
Please help me in this regard.
Maybe some USRP documentation on OFDM might suffice.

Thanks a lot.


Trond Danielsen wrote:

> I read in an earlier thread that you want to do the (I)FFT processing
> in the FPGA. This is not how it is intended to be used. GNU Radio is a
> software radio framework, and the goal is to move as much of the
> signal processing as possible onto the host computer. Moving the FFT
> back to the FPGA would therefore be a step backward in the software
> approach. This is just my personal opinion, so feel free to spank me
> with a 10 foot monopole if your view is different :)

An interesting debate. FPGA is indeed hardware, but I'd argue that if
the (I)FFT can be done faster on the FPGA and can use the appropriate
window sizes, etc (eg on-the-fly reconfigurable) that it would still
technically meet the definition of 'software'. If it frees up USB
bandwidth somehow or frees up host-CPU and lets the host have more
resources left to do its job and we're not really doing a mode-specific
function that locks us into MIMO or GMSK or OFDM, etc that it would be
OK by me as a consumer.

That Cyclone FPGA was awfully full last I checked- I don't know enough
about this type of thing to say it wouldn't fit, but it seems at least
possible that the amount of real-estate required to do the FFT might be
more than the current generation USRP could handle?

IANAE (expert), but I thought the debate was interesting enough to risk
embarassment :)

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