Research On The Key Technology Of Nonlinear Self-interference Suppression For Co-frequency Co-time Full Duplex

Compared to the traditional half-duplex communication mode,the spectral efficiency of the co-frequency co-time full duplex(hereinafter referred to as "full duplex")system can be doubled because it communicates at the same time with the same frequency.Full-duplex communication quality is constrained by strong self-interference signals.Meanwhile,with the increase of the transmit power,the non-linear self-interference problem existing in the radio frequency transmission channel,the radio frequency receiving channel,and the radio frequency interference reconstruction board can not be neglected.The key technology of nonlinear self-interference suppression for full-duplex is researched in this paper,mainly including the nonlinear distortion problem existing in the radio frequency transmission channel and radio frequency interference reconstruction board.The work in this paper is organized as follows.Firstly,the interference cancellation of full-duplex communication is investigated,which is divided into linear self-interference cancellation and nonlinear self-interference cancellation.Non-linear self-interference cancellation includes non-linear self-interference suppression of the transmitter,non-linear self-interference suppression of the receiver,and nonlinear self-interference suppression of radio frequency interference reconstruction board.Secondly,the influence of the nonlinearity of the radio frequency power amplifier on full-duplex self-interference suppression is analyzed.Taking the interference cancellation ratio at the receiving antenna of the local transceiver as the measure,the influence of the amplitude estimation error and the phase estimation error on the interference cancellation ratio is deduced in the case of the ideal power amplifier and the non-ideal power amplifier formula.The simulation results show that the interference cancellation is the same as the interference cancellation ratio of the ideal power amplifier when the reference signal source of the radio frequency interference is derived from the output signal of the amplifier,which is better than the interference cancellation ratio of the reference signal source from the input signal of the amplifier.Thirdly,the nonlinear distortion problem in radio frequency power amplifier and radio frequency interference cancellation is analyzed and reconstructed.The full-duplex nonlinear self-interfering signal is reconstructed by using the memory polynomial model,and the baseband is canceled at the receiver.In this paper,the interference cancellation ratio of the structure and the effect of the memory depth and nonlinear order on the nonlinear self-interference cancellation effect are analyzed.As for bandwidth 20 MHz LTE signal,the results show that the nonlinear cancellation effect is positively correlated with the depth of memory and the nonlinear order,and the nonlinear order only needs to consider the odd term.With the increase of the transmit gain,when the signal is not more than 20 dB,the model can completely cancel the nonlinear self-interference signal.The paper proposes a model to reconstruct the nonlinear self-interference signal,which provides a theoretical basis for the study of full-duplex communication.