Research On Key Technologies Of Real Time Adaptive Optical Self-interference Cancellation System

With the coming era of Internet of Everything,numerous interconnection services are emerging,thus the users' demand for the transmission rate and capacity of the wireless communication system is constantly increasing.In-band full-duplex(IBFD)communication can support simultaneously bidirectional RF transmission within the same frequency band.Compared to frequency-division duplex(FDD)and timedivision duplex(TDD)schemes,IBFD can double the spectral efficiency and makes the spectrum allocation more flexible.Self-interference cancellation(SIC)is the key technique in IBFD communications.Normally,the SIC schemes are divided into electrical self-interference cancellation(ESIC)and optical self-interference cancellation(OSIC).The key goal of studying IBFD communication is to achieve commercialization.The key to commercialization of IBFD technology is to design a real-time self-interference cancellation system.The real-time SIC systems are divided into real-time ESIC systems and real-time OSIC systems.Field-Programmable Gate Array(FPGA)or other real-time processors are used as adaptive control devices in ESIC systems.Compared to ESIC systems,wider cancellation bandwidth and higher radio frequency band are achieved in OSIC systems.To our best knowledge,the existing real-time OSIC system costs a long time for adaptive adjustment,and isn't suitable for commercialization.In this paper,a real-time adaptive OSIC(RTA-OSIC)system for inband full-duplex transmission is proposed and demonstrated for the first time.The RTA-OSIC system contains hardware components and adaptive algorithms.For the hardware components,the power circuit and temperature control circuit of some OSIC system devices are designed to ensure the proper operation of the OSIC system device.Meanwhile,in order to reduce the system size and improve system stability,these circuits are integrated onto a circuit board.The SIC performance of the RTA-OSIC system is tested.Experimental results show that the RTA-OSIC system achieves more than 22 dB cancellation depth within 0-700 MHz frequency band.Experimental results also testified the bandwidth advantage of OSIC systems.As for the adaptive algorithm,a modified Hooke-Jeeves(MHJ)algorithm is proposed to achieve fast adaption of the RTA-OSIC system.The MHJ algorithm runs on the real-time microcontroller STM32.The tunable optical delay line and variable optical attenuator are controlled by the STM32,for the purpose that the SI signal and reference signal are precisely matched both in amplitude and phase to achieve the optimal cancellation depth of the RTA-OSIC system.Experimental results show that the MHJ algorithm requires only 15-25 samples to achieve the optimal performance of the RTA-OSIC system.Compared with the existing adaptive OSIC system using other algorithms,the RTA-OSIC system using MHJ algorithm has obvious advantages which requires fewer samples and shorter adaptive time.