Re: [Discuss-gnuradio] CQPSK and raised cosine filters

[Eric Blossom]

On Wed, Oct 27, 2004 at 09:33:56PM -0500, Rick Parrish wrote:
> Is anyone out there working one these?
> 
> 1. CQPSK

No, but we'd love it if you did!

> 2. raised cosine (or root-raised cosine) filters

We've got root raised cosine.  I though we had raised cosine too, but
apparently we haven't needed it yet.  In any event, you determine the
taps using :

  taps = gr.firdes.root_raised_cosine (gain, sampling_freq, symbol_rate,
                                       alpha, ntaps)

then use

  filter = gr.fir_filter_fff (decim, taps)

to instantiate the signal processing block.


See http://www.gnu.org/software/gnuradio/doc/classgr__firdes.html

> I've got a working clock pulse recovery PLL for CQPSK but I'm wondering 
> if running the data through a raised cosine filter will improve S/N for 
> the final decoded result. The application is APCO Project 25 two-way 
> voice communications.

It's been a while since I looked at the specs, but a matching filter
on each end wouldn't be a surprise.

Eric