Re: [Discuss-gnuradio] AWAL root raised cosine filter in the GRC trunk?

[Glenn Richardson]

Johnathan Corgan wrote:
> On Fri, Dec 12, 2008 at 1:47 PM, Josh Blum <address@hidden> wrote:
>
>   
> > However, I would like to make these convenience blocks for some of the
> > combinations. Would RRC FIR be useful? Any other suggestions for some
> > practical combinations?
> >     
>
> A rational resampler that used RRC taps would be useful as a transmit
> side RRC interpolator.
>
> A common MPSK transmitter chain is to create a symbol stream at a
> particular number of samples per symbol (related to your input data),
> perform RRC filtering, then resample to meet the rate expected by the
> USRP at some particular hardware interpolation rate.
>
> You can economize CPU cycles by merging the RRC and resampling filter
> stages, that is, by using properly calculated RRC taps in the place of
> the resampler lowpass filter.
>   
Our transmit chain indeed follows this exact pattern.  The RRC was/is 
used to shape the data stream, and then we resampled in a second block.

I would be interested to measure the performance gain by eliminating the 
extra block(s).  (There is a constant gain block as well, to bring the 
level up to the USRP's expectations.)  However, I'm still back working 
on understanding how all these taps are "properly created".  :)