Nonlinear Signal Correction For Wireless Full-Duplex Communications

Full duplex(FD)technology which enables a transceiver to transmit and receive signals simultaneously at the same frequency,shows the potential to double the spectrum efficiency.Recently,both academia and industry are attempting to solve key problems within FD.As the strong self-interference(SI)signal from the local transmitter and the weak signal-of-interest from the remote transmitter arrive at the FD receiver simultaneously,the detection performance of the signal-of-interest is deteriorated by the strong SI signal.In practice,the transfer functions of the analog instruments are nonlinear,which make the detection performance even worse.In this paper,the impacts of the oscillator phase noise and the nonlinear radio frequency(RF)chains on the SI cancellation capability are analyzed.The main contributions of this paper are summarized as follows:Firstly,the impacts of the phase noise on digital cancellation capability are analyzed.The closed-form expression for digital cancellation capability is derived with the presence of both transmitter and receiver phase noises.Subsequently,the upper bound of the digital cancellation capability is proposed.Analytical results show that,for the FD transceiver adopting separate transmitter and receiver oscillators,the upper bound of the digital cancellation capability is 22 dB with the signal bandwidth,subcarrier spacing,and 3-dB coherence bandwidth of phase noise being 20 MHz,15 kHz,and 15 Hz,respectively.Secondly,a method is proposed to minimize the impacts of the phase noise on FD transceiver.By adjusting the delay of the receiver oscillator signal according to the transmitter oscillator signal,the digital cancellation capability is maximized.Analytical results demonstrate that,in the Rice fading SI channel with the delay of the line-of-sight path being 33 ns and K-factor being 35 dB,the improvement of the digital cancellation capability is 2.5 dB with the signal bandwidth,subcarrier spacing,and 3-dB coherence bandwidth of phase noise being 20 MHz,15 kHz,and 15 Hz,respectively.Thirdly,a digital-domain-aided analog domain nonlinear correction method is proposed to mitigate the impacts of the nonlinearity of the transmitter and the receiver.With the precision of the analog-to-digital converter limited,the linear and the nonlinear SI signals are reconstructed at the digital domain,and cancel the received SI signals at the analog domain after passing through the digital-to-analog converter.Experimental results show that the analog nonlinear SI cancellation capability improvement is 14 dB with the LTE signal bandwidth being 20 MHz and the transmission power being 27 dBm.Fourthly,a nonlinear cancellation method is proposed to correct the nonlinearity of the analog canceller.By adopting an extra analog canceller,the nonlinearity of the main analog canceller can be captured.Experimental results show that the cancellation capability is improved by 15 dB with the LTE signal bandwidth being 20 MHz and the transmission power being 24 dBm.The conclusions and methods can be applied to wireless communications,microwave relay communications,wireless data links,satellite communications,radar systems,and electronic warfare.