Research On Digital Domain Interference Cancellation Technology Of Simultaneous Transceiver System

With the development of wireless communication technology,spectrum resources have become increasingly tense.The Co-frequency and Co-time Full Duplex(CCFD)technology can theoretically double the spectrum efficiency and has received extensive attention and research.However,due to the short distance between the transmitting and receiving antennas and the high transmission signal power,there is a serious self-interference(SI)problem in the system,which poses a severe challenge to the normal operation of transceivers.In response to this problem,this paper studies the digital domain interference cancellation in the selfinterference cancellation technology.Digital domain interference cancellation technology is mainly divided into linear interference cancellation and nonlinear interference cancellation.Firstly,aiming at the disadvantages of LMS algorithms in digital domain linear interference cancellation,such as slow convergence speed,large influence of gradient noise,and sensitivity to the eigenvalue dispersion of the input signal,this paper proposes a variable step size affine projection(VSSAP)algorithm.Compared with the time-varying step size LMS(TVSSLMS)algorithm,the VSSAP algorithm has faster convergence speed,lower steady-state error,and the interference cancellation ratio is about 10 d B higher than TVSSLMS.In the application of the DRFM repeater jammer,it is further verified that the interference cancellation system based on the VSSAP algorithm can effectively suppress deceptive interference and suppress interference.When the interference-to-noise ratio(INR)is 40 d B,the cancellation ratio can reach 37.6d B and 35.5d B respectively,which solves the problem of self-interference cancellation in radar jammers,and has good application value.Secondly,in the actual simultaneous receiving and sending system,only linear interference cancellation can not realize the complete elimination of self-interference,and there are many nonlinear factors in the receiving and sending link.This paper considers the nonlinear distortion caused by the power amplifiers(PA),uses a memory polynomial(MP)to model the power amplifier,analyzes and derives the principle of nonlinear self-interference cancellation in the digital domain.The experimental results show that the digital domain cancellation technical scheme in this paper is effective and feasible for the performance improvement of the cancellation system.Finally,this paper studies the digital domain nonlinear interference cancellation technology that considers the power amplifiers nonlinearity,IQ imbalance and PA-IQ cascade nonlinearities,and uses the digital domain joint cancellation nonlinear model to reconstruct the nonlinear interference existing in the transceiver link.In the simulation experiment,it is verified that when the image rejection ratio(IRR)is 30 d B,for a signal with a bandwidth of 20 MHz,the self-interference signal can be suppressed near the noise floor after using the proposed nonlinear model in this paper,and the in-band cancellation ratio of the system is better than that of the improved widely-linear model,as well as the in-band cancellation ratio is improved by 8.89 dB on average.