RF Vector-Multiplier Compensation for Self-Interference Cancellation in Full-Duplex Radios

Full-duplex radios have been receiving considerable attention due to their ability to simultaneously transmit and receive signals. However, the main challenge in full-duplex radio is the elimination of the self-interference (SI) signal, which is a transmission signal that leaks to the receiver. In this paper, we investigate the effect of the imperfection of the radio frequency vector multiplier (RF-VM) used for removing the SI signal in a full-duplex radio on the SI cancellation performance, and propose a compensation method. The RF-VM has mismatch between the inphase and quadrature paths of the internal hybrid coupler, and imperfections, such as gain and phase mismatch, between the baseband control lines. We derive the equation for the received signal after SI removal using the channel responses of the SI and cancellation paths, and the filter response for RF-VM impairment modeling in a full-duplex radio transceiver. Based on this, we propose a method for obtaining the RF-VM baseband control signal, which compensates the RF-VM impairment and maximizes the SI cancellation performance. The proposed scheme is verified by simulation, through which the effect of RF-VM impairment on the SI cancellation performance is investigated and confirmed to be effectively compensated by the proposed method.