Photonics-based RF self-interference cancellation for distributed systems

A photonics-based scheme to realize RF self-interference cancellation for distributed systems is proposed and demonstrated. By introducing photonic polarization multiplexing, the intermediate frequency (IF) signal and the local oscillator (LO) signal are modulated onto the orthogonally polarized optical carriers. The optical signal is transmitted over a long fiber to the remote base station, and then divided into two parts through a polarization beam splitter (PBS) following a polarization controller (PC). After photodetection, the two outputs are served as the transmitted signal and the reference signal for self-interference cancellation, respectively. The frequency up-conversion for transmitting, and the self-interference cancellation with high cancellation depth over a wide bandwidth for receiving are both achieved in the optical domain simultaneously. The independent photonic system for self-interference cancellation is avoided, guaranteeing the simplicity of the remote base station. The experimental results show that the cancellation depths of 30 dB over a 1-GHz bandwidth, and 26 dB over a 2-GHz bandwidth are realized.