  A photonics-assisted analog wideband RF self-interference (SI) cancellation
and frequency downconversion approach for in-band full-duplex (IBFD)
multiple-input multiple-output (MIMO) systems with adaptive digital amplitude
and delay pre-matching is proposed based on a dual-parallel Mach-Zehnder
modulator (DP-MZM). In each MIMO receiving antenna, the received signal,
including different SI signals from different transmitting antennas and the
signal of interest, is applied to one arm of the upper dual-drive Mach-ehnder
modulator (DD-MZM) of the DP-MZM, the reference signal is applied to the other
arm of the upper DD-MZM, and the local oscillator signal is applied to the
lower DD-MZM. The SI signals are canceled in the optical domain in the upper
DD-MZM and the frequency downconversion is achieved after photodetection. To
cancel the SI signals, the reference signal is constructed in the digital
domain, while the amplitude and delay of the constructed reference are adjusted
digitally by upsampling with high accuracy. Experiments are performed when two
different SI signals are employed. The genetic algorithm and least-squares
algorithm are combined with segmented searching respectively for the SI signal
reconstruction and amplitude and delay pre-matching. A cancellation depth of
around 20 dB is achieved for the 1-Gbaud 16 quadrature-amplitude modulation
orthogonal frequency-division multiplexing signal.
