The Research Of RF Self-interference Cancellation In Full-duplex Communication

Full-duplex communication is a signal transmission and reception method at the same frequency simultaneously.Compared to current frequency-division duplex and time-division duplex communication,full duplex can double the spectrum efficiency in theory.However,to achieve full-duplex communication we must cancel the selfinterference(SI)at the receiver end caused by the transmitter.To solve this problem,the RF self-interference cancellation(SIC)technology is quite important,because it relates to the functionality of the low-noise amplifier(LNA)and analog-to-digital converter(ADC)at receiver.In this thesis,we focus on the causes which can affect the ability of RF SIC and the methods which can improve the cancellation performance and bandwidth.The major contributions are listed as follows:Firstly,we compare three classic methods of RF SIC.According to the simulation results,it is concluded that the method of rebuilding self-interference using adjustable attenuator and phase shifter is applicable.Then we analyze the key factors to SIC performance,and it is found that the performance can be improved by control the amplitude,phase and delay errors.The above observations provide a sound basis for the following cancellation design.Secondly,based on the aforementioned method,broadband RF SIC circuits are designed using a single-loop.A phase-frequency slope adjuster is added following the attenuator,and it makes reconstructed signals and received interferences possess the same amplitude and opposite phase within the designed frequency band.The proposed method,with a slope-adjuster,is verified to be effective for broadband signal.The simulation results show that the self-interference cancellation is 32 ~ 58 dB at 2.35 GHz ~ 2.45 GHz for single tone test.Thirdly,a multi-paths self-interference cancellation method is analyzed and designed.Considering the self-interferences in the practical scenario,we analyze the multipath effects of self-interferences and a dual-paths RF SIC circuits are designed as an example.The simulation results show that it can achieve 40 dB~60 dB self-interference cancellation for single tone test,it is found that the cancellation performance is a bit higher than the single-loop circuits.Fourthly,single-path and dual-paths cancellation circuits are fabricated and measured,and the corresponding optimization algorithms are coded and implemented to control system variables.The variables are induced by attenuators,phase shifters and phase-frequency slope adjusters.The optimization algorithm should achieve a global optimal self-interference cancellation performance.Two adaptive algorithms are used: local search and gradient descent.The experimental results show that 1)for the singletone signal,the SIC of single-path design is 60.92 dB;2)for the 20 MHz signal,the SIC performance of single-path and dual-paths design is 41.09 dB and 44.63 dB respectively;3)for the 60 MHz signal,the SIC performance is 32 dB and 36.16 dB respectively.