Forwarding a signal from RX to TX using a USRP with FPGA
I'm not familiar with that bit of kit (though it looks really tasty and I wish I had one), but I'd suggest breaking it down into steps and confirm each one.  

First just try and receive a signal without forwarding it - make sure that side of it is working fine and your receiver configuration / code is correct.

When you have confirmed reception, create a basic transmit bit of code.  Even if it's just transmitting a set sequence of digits or something so you can confirm you're configuring the transmitter correctly.

Then finally weld the two together - feed the output of the receiver into the input of the transmitter.

It certainly looks like what you want to do should be perfectly feasible using that device.

Be warned though that the signals must be separate - i.e., contained within a separate medium, like coaxial cable.  Wireless transmission would just cause interference between what is transmitted and what is received, basically creating feedback between the two - unless you transmitted on a different carrier frequency to the receiver...