Active self-interference cancellation of passband signals using gradient descent

Recent interest in same-frequency/same-time full-duplex radio frequency communication has led to the study of self-interference cancellation methods for a co-located transmitter and receiver pair. So far, important practical aspects of self-interference cancellation have not been considered, such as receiver amplifier saturation and dynamic range, which extend the minimum distance between transmit and receive antennas without sufficient interference isolation. Further, current solutions lack significant self-interference attenuation for wideband signals. In this paper, a method for canceling a passband self-interference signal using adaptive filtering in the digital domain is presented. Based on acoustic active noise cancellation foundations, a cancellation signal is created that destructively combines with the undesired self-interference signal in the passband, taking into account differences in the complex passband nature of RF signals versus the baseband nature of acoustic signals. The efficacy of this interference cancellation scheme is compared to other self-interference cancellation architectures in the literature including digital as well as other active passband approaches. It is shown that for high-power wideband transmission signals, this adaptive active analog cancellation method effectively reduces the self-interference signal while satisfying practical constraints set by transceiver hardware. It is also shown that this approach decreases the minimum distance between the transmit and receive antennas or allows higher transmission power, thereby extending the range of a full-duplex device.