I am doing the QPSK transciever transmission with two USRPs NI-2920. As I check from the datasheet, the maximum gain for the transmitter usrp is 31 dB. When I set the transmitter gain at 27dB, it gets the minimum BER. However, when I turn the gain to higher values below the maximum, the BER gets worse. I wonder why this happens. Is it due to higher SNR leading to more packets drop?Does anyone know the answer? Many thanks.