Research On Key Technologies Of Radio Frequency Self-Interference Cancellation In Co-Time Co-Frequency Full-Duplex Radios

In the past twenty years,the contradiction between explosively growing wireless communication services and increasingly scarce electromagnetic spectrum drives the revolution of theories and technologies of wireless communications.Co-time co-frequency full-duplex(CCFD)transmits and receives electromagnetic wave signals simultaneously at the same frequency band,and is able to double theoretically spectrum efficiency.The prerequisite of normal operation of CCFD devices is that the strong self-interference(SI)from transmitted signal to received signal is canceled sufficiently.SI cancellation(SIC)can be decomposed into spatial SIC,radio frequency(RF)SIC,and digital SIC.This thesis focuses on RF SIC,and the research perspectives are about the architecture and performance of RF SIC and the dynamic range of receive chain,which are detailed as follows.Firstly,this thesis proposes self-mixed SIC architecture.Breaking through existing addition-based SIC architectures,this proposed architecture adapts multiplication based method by multiplying SI and transmitted signal to eliminate the phase of SI and then only cancels the envelope of SI,which solves the issue that the SIC performance of existing architectures is sensitive to phase alignment error.Analysis and simulation results show that,in case of 20 MHz SI and timing error of 0.5 ns,the SIC performance of this proposed architecture is able to achieve 36 dB.Secondly,this thesis proposes shared-phase-shifter-constrained multi-tap architecture.By analyzing multi-path SI channel,we found that the phase offset of SI channel is dominated by the strongest path.By the way of sharing one single variable phase shifter by all taps,this proposed architecture makes tradeoff between SIC performance and quantity of phase shifters.Analysis and simulation results show that,in case of exponential fading SI channel with fading factor of 3,this proposed architecture is able to cancel a 100 MHz SI by 33 dB with 6 taps.Thirdly,this thesis proposes infinite impulse response(IIR)filtering SIC architecture.By analyzing RF SIC in case of large delay spread SI channel,we found that,with finite number of taps,existing finite impulse response(FIR)filtering SIC architectures are hard to cancel the large delayed components of SI.This proposed architecture adapts feedback branches to realize large delay function,then reconstructs and cancels the large delayed components of SI,and finally improves SIC performance.Analysis and simulation results show that,in case of exponential fading SI channel with fading factor of 2,5-order IIR filtering architecture is able to cancel a 20 MHz SI by 50.7 dB.Fourthly,this thesis proposes SIC-advanced high dynamic range receive chain architecture.In present of strong SI,limited dynamic range analog-to-digital convertor(ADC)is saturated,and thus restricts the dynamic range of receive chain.Adapting this proposed architecture to degrade SI down to noise floor avoids the saturation of ADC,and in turn improve the dynamic range of receive chain.For a full-duplex prototype in which the power of SI,the RF SIC performance,and the digital SIC performance are-20 dBm,16 dB,and 48 dB,respectively,the dynamic range of receive chain is improved by 37 d B in experiments.This thesis researches the SIC performance and engineering feasibility of RF SIC and the dynamic range of receive chain in CCFD.The research conclusions can be applied to CCFD wireless communications to improve spectrum efficiency.