These are special fpga firmwares for the USRP to enable high-bitrate qpsk transmitting.
The firmware has a built-in RRCfilter, fractional interpolator and qpsk modulator.
It can be used with rfx and basic TX daughterboards.

The easiest way to get going is:
unpack and install gnuradio-3.qpsk4.tar.gz:
tar zxvf gnuradio-3.qpsk4.tar.gz
cd gnuradio-3.qpsk4
./configure
make 
sudo make install

Now gnuradio is installed and the special fpga firmware should be in /usr/local/share/usrp/rev2 and /usr/local/share/usrp/rev4
to try it out:
cd gnuradio-examples/python/qpsk_fpga
tar zxvf commandline examples.tar.gz

use commandline examples

The examples are explained in gnuradio-examples/python/qpsk_fpga/README.txt


What is here:
README.txt  		this file
README_examples.txt	explanation of example python scripts to test qpsk with special qpsk fpga firmware
gnuradio-3.qpsk4.tar.gz	The source of the modified gnuradio distribution, includes special fpga firmware and qpsk_fpga examples
gnuradio-3.0svn_gnuradio3.qpsk4.diff	diff between original gnuradio distribution and this one with special qpsk fpga firmware
usrp-3.qpsk4.tar.gz	The source of the special usrp fpga firmware and driver (is subset of gnuradio-3.qpsk4.tar.gz)
usrp-3.0svn_usrp3.qpsk4.diff	diff between original usrp sourcecode and this one with special qpsk fpga firmware

qpsk_fpga_examples_4.tar.gz	Examples on how to use the special qpsk fpga firmware using gnuradio

The special qpsk fpga firmwares: (these should be in /usr/local/share/usrp/rev2 and /usr/local/share/usrp/rev4)
usrp_frac_interp_2rxhb_2tx_alpha0.2_int16_dec10_DACint4X.rbf	bitrate= 40Mbit/sec, alpha=0.2
usrp_frac_interp_2rxhb_2tx_alpha0.2_int16_dec1_DACint4X.rbf     bitrate= 4 Mbit/sec, alpha=0.2
usrp_frac_interp_2rxhb_2tx_alpha0.35_int16_dec10_DACint4X.rbf   bitrate= 40 Mbit/sec, alpha=0.35
usrp_frac_interp_2rxhb_2tx_alpha0.35_int16_dec1_DACint4X.rbf    bitrate= 4 Mbit/sec, alpha=0.35