Residual self-interference after cancellation in full-duplex systems

We investigate the signal-to-residual-interference ratio (SIR_out) in a full-duplex transceiver with analog self-interference cancellation in consideration of three major sources of imperfection: (i) self-interference channel estimation error, (ii) quantization error in the receiver analog-to-digital converter (ADC), and (iii) quantization error in the digital-to-analog converter (DAC) used to generate the self-interference replica. In particular, we first derive the Cramér-Rao lower bound on the variance of the self-interference channel estimation error, and use it to further develop a closed-form expression of the SIR_out. The resulting SIR_out expression facilitates a study of the limit of a full-duplex system and determines the minimum required resolution for the ADC and DAC in order to meet a given performance. The expression reveals that, with a sufficiently high number of bits, the effects of ADC and DAC are negligible, but the cancellation performance is limited by the thermal noise and, in the best case, we can obtain a SIR_out equal to the received signal-to-thermal-noise ratio (SNR).