  A photonics-based digital and analog self-interference cancellation approach
for in-band full-duplex communication systems and frequency-modulated
continuous-wave radar systems is reported. One dual-drive Mach-Zehnder
modulator is used to implement the analog self-interference cancellation by
pre-adjusting the delay and amplitude of the reference signal applied to the
dual-drive Mach-Zehnder modulator in the digital domain. The amplitude is
determined via the received signal power, while the delay is searched by the
cross-correlation and bisection methods. Furthermore, recursive least squared
or normalized least mean square algorithms are used to suppress the residual
self-interference in the digital domain. Quadrature phase-shift keying
modulated signals and linearly frequency-modulated signals are used to
experimentally verify the proposed method. The analog cancellation depth is
around 20 dB, and the total cancellation depth is more than 36 dB for the
2-Gbaud quadrature phase-shift keying modulated signals. For the linearly
frequency-modulated signals, the analog and total cancellation depths are
around 19 dB and 34 dB, respectively.
