When I set the receive gain 20dB, and the power of air signal at antenna is -40dBm， the amplitude of digital signals on chipscope is about 100~110, which is too little. Because the amplitude of the noise is about 10, resulting in poor signal to noise ratio， so our project of lte uplink receive can not work well and cannot decode signal correctly.
That I use the USRP to send data with 20dB's send gain, and the distance betweent USRP and the fmcomms1-ebz is about 90cm, not even 1m. When I use the same USRP to send, and use another USRP to receive at 20dB's receive gain at the position of above fmcomms1-ebz, the amplitude of receive data is 1500. By the way, when the distance between fmcomms1 and USRP(sending data) is short to about 30cm, our uplink receive project can decode correctly, so the project should be no problem.
What I want to ask is how can I am able to increase the amplitude of the received signal so that our project can work well when increase the distance between send and receive ?
(In the attached diagram, I see there is an -9dB gain π-type circuit at RFin, is it a must ? )