Research On A Technology Of Self-interference Radio Frequency Suppression In Single-Input Single-Out Co-Time Co-Frequency Full Duplex

With the advent of the era of 5G mobile communication,the co-time co-frequency full duplex(CCFD)technology,as one of the important technologies to improve spectrum utilization,has increasingly become the focus of the researchers.However,due to the close distance between the transmitting and receiving antennas and the huge power difference between the transmitted and received signals,strong self-interference(SI)signals will be generated at the receiver,which will seriously affect the reception of useful signals at the far end.This is the main challenge for the wide application of full duplex technology.As one of the key technologies of full duplex SI suppression,radio frequency(RF)SI suppression aims to suppress the SI signal at the RF front end of the receiver,so as to prevent the analog to digital convert(ADC)saturation blocking of the receiver and ensure the correct reception of useful signals.In this thesis,the direct coupling RF SI suppression method is studied on the basis of the single-input single-out(SISO)CCFD system,and the structure and performance of SI suppression in different bandwidth scenarios are discussed.In addition,a method to effectively suppress wideband linear frequency modulation SI is proposed.Specific contributions are as follows:Firstly,the method of RF SI suppression under narrowband SI is studied.Based on the analysis of the SI channel in the narrowband scenario,the method of RF single-tap SI suppression should be chosen.The system structure of single-tap SI suppression is introduced in detail,and the closed expression of SI suppression performance is derived.In addition,the effects of the device errors of adjustable delayer,adjustable attenuator and adjustable phase shifter on the performance of SI suppression are discussed.Numerical and simulation results show that when there is no device error and the delay,amplitude and phase of the SI reconstruction channel are theoretically optimal,the maximum SI suppression ratio is equal to the interference to noise ratio(INR)of the received signal;When there is device error,the increase of signal bandwidth or the increase of device error will lead to the decrease of SI suppression performance.Secondly,the method of RF SI suppression under broadband SI is studied.Based on the analysis of the SI channel in the broadband scenario,the method of RF multi-tap SI suppression should be chosen.The system structure of multi-tap SI suppression is introduced in detail,and the analytic expression of SI suppression performance is derived.In addition,the effects of the device precision of adjustable attenuator and adjustable phase shifter on the performance of SI suppression is discussed.Numerical and simulation results show that the increase in the number of taps,the increase in the INR of the receiving channel or the improvement in the device precision will increase the SI suppression performance.In particular,when the signal bandwidth is too large,the increase in the number of taps will not improve the SI suppression performance.Finally,a RF SI piecewise suppression method is proposed for broadband linear frequency modulation(LFM)SI signals.Based on the time-frequency piecewise equivalent characteristics of LFM signals,the SI signals is segmented in the time domain,and then the SI signals are reconstructed and suppressed by the same SI reconstruction channel.This method transforms the broadband SI suppression into several narrowband SI suppression and improves the performance of SI suppression without increasing the hardware complexity.The experimental data test results show that when the signal bandwidth is 300 MHz and the INR of the received signal is 46 dB,the performance of SI piecewise suppression method can reach 40 dB with 4 taps,which is 14 dB higher than the traditional multi-tap SI suppression method with 32 taps.This thesis researches the method of RF SI suppression under different bandwidths.The research results can provide a theoretical reference for the scheme design and performance evaluation of CCFD RF SI suppression.