Microwave Photonic Adaptive Complex Wideband Self-Interference Cancellation Enabled by Digital Pre-Modeling Search and Two-Tap Delay Adjustment

A photonics-assisted adaptive analog self-interference cancellation (SIC) approach for complex wideband self-interference (SI) signals in in-band full-duplex (IBFD) systems is proposed. The least-squares (LS) algorithm is utilized to estimate the complex self-interference signal and construct a total reference signal for SIC. The amplitude and delay of the constructed analog reference signal are searched by using a novel pre-modeling search method. By matching the SIC depth obtained from different reference signals with different delays and amplitudes with the pre-modeling results, the delay and amplitude of the complex SI signal can be obtained in a very short time using our previously proposed segmented search method. The accuracy of the delay setting is significantly enhanced via a two-tap delay adjustment method without upsampling. An experiment is performed by employing the direct path SI signal in IBFD single-input single-output systems and the more complex multipath SI signals in IBFD multiple-input multiple-output systems. An analog SIC depth of around 24 dB can be achieved when the SI signal has a center frequency of 1 GHz and a baud rate of 1 Gbaud. In addition, the acquisition of search results is completed in a very short time using a search signal of 1.28 μs.