Gnuradio RRC filter

Hi guys,

Here we are trying to develop a standalone USRP2 system which means we
don’t use host PC and wonderful Gnuradio. We are planning to modify the
USRP2’s RTL code. We are studying Gnuradio’s frequency sync and symbol
sync, so that we can implement them in RTL.

I’m using benchmark_tx/rx as a reference design. And for dqpsk, i come
across this RRC filter. I have gone through RRC filter’s C++ code but i
have difficulty understanding this filter’s Tap equation. Can someone
point out if there is any related paper to this Gnuradio’s RRC filter?
Many thanks.

PN