Research On Microwave Photonics RF Interference Cancellation Feedback Control Technology

The rapid development of wireless communication technology has made non-renewable spectrum resources extremely scarce.Full-duplex wireless communication technology uses the same frequency to transmit and receive signals at the same time,which overcomes the shortcomings of traditional half-duplex communication technology that can only transmit and receive signals at different frequencies or different time slots,and can double the spectrum utilization rate.However,radio frequency self-interference is a key issue that must be solved in the practical application of full-duplex communication technology.The microwave photonics self-interference cancellation technology has received great attention and significant progress in recent years due to its advantages in processing signal bandwidth and high control precision.In this thesis,the microwave photonics RF self-interference cancellation technology is investigated,and the feedback control technology of self-interference cancellation system is carried out,which mainly includes the following three aspects.A theoretical model of microwave photonics RF self-interference cancellation system based on dual Mach-Zehnder modulator scheme is established.Under the condition of optical amplitude mismatch and time delay mismatch,the RF self-interference suppression expression for the single frequency signal and specific bandwidth are derived respectively.On this basis,the effects of optical amplitude mismatch and time delay mismatch on RF interference suppression performance are simulated and analyzed,which provides a good guiding role for the optimization design and experimental system construction of RF self-interference cancellation system.A microwave interference self-interference cancellation control system for full-duplex communication is designed and developed.It is used to control the amplitude and delay in the optical domain.The feedback control system includes a RF signal down conversion unit,a signal acquisition unit,and an automatic feedback control unit.The automatic feedback control unit uses the gradient descent method to perform two-dimensional search on the delay deviation and the amplitude deviation to obtain the matching delay and amplitude adjustment amount.By using Labview software,it realizes the functions,such as signal acquisition,data processing,logic operation and adjustment control.A microwave photon RF self-interference cancellation experiment link based on the dual Mach-Zehnder modulator scheme is established,and the feasibility of the feedback control algorithm is verified.Experimental results show that the feedback control algorithm can achieve fast automatic search with amplitude in the range of ±5dB and delay in the range of ±200ps and achieve the optimal control state.The 22 dB interference cancellation automatic optimization at 40 MHz is realized.Further,in the full-duplex communication scenario,it is verified that the feedback control algorithm can recover the weak useful signals submerged in the self-interference signal.