Research On Digital Algorithm-assisted RF Self-interference Cancellation In The Optical Domain

With the rapid development of modern mobile communication,a variety of novel wireless communication applications are emerging,which makes the limited spectrum resources more and more crowded.Therefore,how to improve the utilization of spectrum resources has become an urgent problem.To solve this problem,the in-band full-duplex(IBFD)technology has been developed,enabling simultaneous transmission and reception of wireless signals in the same frequency band.Therefore,compared with the well-established frequency-division duplex and time-division duplex communication technologies,the IBFD communication technology can theoretically doubles the efficiency of spectrum usage,and has tremendous application potential in the next generation of wireless communications.However,due to the simultaneous transmission and reception of signals in the same frequency band in IBFD technology,the receiver is inevitably affected by the high-power self-interference signal leaked to the receiving antenna,which makes the reception and demodulation of the signal of interest a huge challenge.Therefore,the application of IBFD communication technology needs to implement self-interference cancellation(SIC)first,which generally includes three different cancellation stages: spatial domain,analog domain,and digital domain.However,traditional electronic SIC(ESIC)is affected by electronic bottlenecks and is limited in terms of SIC bandwidth and reconfigurability.Microwave photonic technology,as a newly emerging technology field in recent years,can provide new solutions for microwave signal processing.Optical SIC(OSIC)based on it can not only break through the limitations of electronic bottlenecks in ESIC,but also have greater operating bandwidth and better reconfigurability.In addition,with the assistance of photonic systems,OSIC can better integrate with optical fiber transmission to meet the needs of long-distance and low-loss optical fiber transmission of wireless received signals in future wireless communication systems.This paper focuses on the research of high-frequency and wide-bandwidth adaptive OSIC technology in IBFD communication systems and presents two digital algorithm-assisted radio frequency OSIC methods.A radio frequency OSIC system based on the recursive least squares algorithm and dual-drive Mach–Zehnder modulator is proposed in the first method.The proposed OSIC method uses a direct reference signal and a constructed multipath reference signal to eliminate the multipath selfinterference signal in the single-input single-output IBFD system,which can alleviate the performance limitation of constructing a single reference signal for OSIC caused by the limited dynamic range of the digital-to-analog converter when the direct-path selfinterference signal is much stronger than the weak reflection-path self-interference signals.To eliminate the more complex multiple-input multiple-output(MIMO)multipath self-interference signal and to set the order of the adaptive algorithm filter more rationally,a radio frequency OSIC system assisted by the least square(LS)algorithm with adaptive order is proposed in the second method.This method achieves better MIMO multipath self-interference channel estimation and OSIC results by adaptively changing the order of the filter by the LS algorithm with adaptive order.At the same time,a reasonable setting of the filter order also reduces the complexity of the digital domain processing and increases the computational speed.