Re: [Discuss-gnuradio] Re: in-band signaling project overview

[Brian Padalino]

On 10/12/07, Jeff Brower <address@hidden> wrote:
> ...
> 2) Does your new FPGA code require the next-gen USRP, with Spartan 3 FPGA?  
> My understanding is that capacity is very
> limited in the Cyclone, which is an old FPGA (around yr 2002 time-frame).

If you have a single, specific application in mind, you should be able
to reduce down the size taken in the USRP FPGA significantly.

The original USRP FPGA was designed to be able to handle the most
minimal decimation (4 by the CIC and 2 by the halfband FIR filter, I
believe) which has the FIR computing every 8 clock cycles and an
effective bandwidth of 8MHz.

It was also designed for the CIC to handle large decimation rates
which increases the "bit growth" of that filter.  If you specifically
have a bandwidth and decimation rate you're interested in (or even a
small range of decimation rates) then you should be able to change the
CIC filter to use significantly less space.  Moreover, if you're
decimating more than 4 at the CIC, you can use more clock cycles and
less instantiated soft multipliers for the FIR filter in the FPGA.

Just curious, what are you specifically looking to do?  Do you need
the ranges for the CIC decimation, or just a few select values?  Can
you handle having less CIC decimation and more FIR decimation?  What
waveforms are you looking at which causes latency to be so tight?

Brian