Effects of Receiver Input Impedance on Nonlinear Distortion in Full-duplex Radios

This paper explores and models the generation of nonlinearities arising from common- and differential-mode transmitter (TX) self-interference (SI) at the input of full-duplex (FD) radio receivers (RX). The analysis reveals the impact of residual TX-SI which drives the RX input impedance(Z(rx)), generating distortion products that degrade the RX linearity. Circuit simulation results confirm a nonlinear Z(rx) introduces non-negligible distortion at the RX input from the residual TX-SI. To suppress the total distortion below the RX noise floor, SI mitigation circuits at RF front-end must provide at least 60dB SI suppression and 50dB common-mode isolation to achieve sufficient RX linearity performance. This paper draws conclusions with respect to strategies that allow a reduction in the nonlinearities generated at the RX input due to residual TX-SI as would be found in FD transceivers.