Self-interference Cancellation Circuit Based On Asymmetric Power Divider

In modern wireless communication,radar and other fields,the transmitted signal leaks to the receiver due to insufficient isolation between transceivers.Thereby forming radio frequency self-interference.Radio frequency self-interference leads to a decrease in its own signal-to-noise ratio,even saturates the low-noise amplifier at the front end of the receiver and blocks communication,which is also a key challenge for simultaneous co-frequency fullduplex communication in the future.This thesis mainly focuses on the transmission and reception leakage of the circulator in the simultaneous co-frequency full-duplex transceiver architecture.And designed a self-interference cancellation circuit based on an asymmetric power divider and an RF tap filter,which improves the transmission efficiency.The RF tap filter control module is designed.Bas899 on the software radio platform,the instantaneous gradient descent control algorithm is developed,and the closed-loop automatic control of the self-interference cancellation circuit is realized.The main research contents and results of this thesis are as follows:(1)The RF self-interference cancellation circuit based on asymmetric power divider is designed.The mechanism of RF self-interference cancellation is studied,and the design method of self-interference cancellation circuit for specific leakage channel is established.A four-way tap filter is designed and implemented,and the amplitude and phase regulation of the cancellation signal is realized.A method of using an asymmetrical power divider in the front stage of the four-way tap filter circuit is proposed to improve the transmission efficiency.The relationship between the power distribution ratio of the power divider and the transmission efficiency is discussed.A comparative analysis of three commonly used asymmetric power dividers is carried out,taking into account the output phase difference,insertion loss,and distribution flatness in the target frequency band.Finally,the architecture of Gysel asymmetric power divider and tap filter circuit is selected,and a microwave hybrid circuit is designed to integrate it on a RF board.The actual circuit test shows that: in the range of ISM frequency band 915～926MHz,the isolation of the circulator transceiver channel increases by 37 d B;the transmission efficiency is increased from the previous 42.5%(power divider power distribution ratio 1:1)to 69.1%(power splitter power distribution ratio 1:1).divider power distribution ratio 1:4).Related research results have been published in an EI conference paper.(2)The closed-loop automatic control prototype of the RF self-interference cancellation circuit is designed and realized.The hardware control circuit of RF self-interference cancellation is designed and implemented,and the general software radio platform B210 is used to realize the transmission and reception of RF signals.An instantaneous gradient descent algorithm was developed based on Gnuradio.The residual self-interference signal energy is detected in real time,and the attenuation coefficient of the four-way tap under the specific suppression requirement is obtained iteratively,which realizes the closed-loop automatic regulation of RF cancellation.The verification results of the automatic control prototype show that 52 d B of isolation is achieved in the target frequency band 915-927 MHz.