A novel approach to self-interference cancellation for energy-saving full-duplex systems

Performance of in-band full-duplex (FD) radios is typically hindered by practical hardware limitations of the circulator, whose signal leakage may cause the presence of very large self-interference (SI) in the receiver (RX) chain. This causes both spectral and energy efficiency reduction for the FD radio. In this work, a novel energy-recycling single-antenna FD architecture, in which an energy harvester (EH) is added between the circulator and the RX chain of the FD radio, is designed to address these issues. The presence of the EH brings a two-fold benefit. Firstly, it allows to recycle a portion of the radio frequency (RF) energy leaked through the non-ideal circulator. Secondly, it implicitly provides a tunable attenuation of the received signal that can increase the effectiveness of the subsequently adopted state-of-the-art self-interference cancellation techniques. The performance of the proposed architecture is analyzed in a scenario in which 2 FD access points (APs) serve two half-duplex (HD) user equipments (UEs), while continuously exchanging signaling over a wireless backhaul (WB). Both the achievable rate over the WB and the energy recycled by the FD APs is derived analytically by means of suitable approximations. The accuracy of these derivations is confirmed by numerical simulations. The proposed FD architecture is shown to be able to recycle up to 50% of the leaked energy at the circulator, i.e., 5% of the energy of the transmitted signal. Furthermore, achievable rate gains up to 70%, as compared to state-of-the-art alternatives, are obtained for the considered scenario.