Photonically And Digitally Assisted RF Self-Interference Cancellation

In-band full duplex(IBFD)wireless communication systems can double the radio spectrum utilization by simultaneously transmitting and receiving radio signals at the same frequency.However,since the high-power transmitted signal can crosstalk to the receiving antenna at the same time as the signal of interest,this crosstalk signal can seriously affect the correct demodulation of the signal of interest and needs to be deeply eliminated,which is also known as self-interference signal.In addition to the IBFD wireless communication system,frequency-modulated continuous-wave(FMCW)radar due to the continuous emission of detection signals,its detection signals will also be crosstalked to the receiver and received together with the target echo signal of the same frequency simultaneously,affecting the correct detection of the target,the selfinterference signal also needs to be deeply eliminated.However,the above selfinterference signal cannot be filtered out by a bandpass filter,bandstop filter,or time slot,and it needs to be suppressed by using a specially designed self-interference cancellation(SIC)link.With the gradual increase of radio system working frequency and bandwidth,the traditional bandwidth-limited electrical domain SIC methods cannot meet the development needs of radio applications with high frequency and large bandwidth.Different from traditional electric domain methods,microwave photonic technology has the advantage of large bandwidth and high-frequency microwave signal processing,which can be used to solve the problem of bandwidth limitation of traditional electrical domain methods,and is widely studied for the large bandwidth SIC.This dissertation focuses on photonically and digitally assisted RF SIC.The dissertation first introduces the research background and significance of SIC,then photonics-assisted SIC methods are summarized and categorized,and the key research points of photonics-assisted SIC are elaborated.Furthermore,the SIC for IBFD radioover-fiber(ROF)systems,adaptive control of delay and amplitude of SIC,and SIC and de-chirping processing conjunction are investigated in this dissertation.The details are as follows:1.Two photonics-assisted SIC schemes for IBFD ROF systems are proposed and experimentally investigated to achieve broadband RF SIC and avoid the effect of fiber dispersion on optical signal transmission.The first scheme achieves optical domain SIC at the base station and digital domain SIC at the central office,this scheme also allows for multi-channel multiplexed fiber transmission,and the spectral efficiency of fiber transmission is significantly improved,for a 500-Mbaud quadrature phase-shift keying(QPSK)modulated signal,the analog cancellation depth is about 20 dB.The second scheme achieves the SIC in the central office so that the base station is simplified,and frequency up-conversion and down-conversion functions are also achieved to further simplify the whole system,the SIC depth for a 20-Mbaud 16 quadrature amplitude modulation(QAM)signal is about 22 dB.2.A photonics-assisted analog domain SIC method based on digital domain adjustment of delay and amplitude is proposed and experimentally verified.The reference signal amplitude is set according to the self-interference signal power,and the reference signal delay can be accurately searched using the cross-correlation process combined with the bisection or segmented search method.The problem of the slow speed of motor-based delay adjustment in the analog domain is avoided.The analog cancellation depth for a 2-Gbaud QPSK modulated signal is approximately 20 dB when the sampling rate is 64 GSa/s.In addition,the digital domain upsampling method is proposed to solve the problem of the limited accuracy of digital domain delay adjustment.By combining the digital domain upsampling method and segmented search method,the best delay can be found quickly and accurately in the experiment,and the search efficiency of SIC adaptive control is greatly improved.For a 16 QAM orthogonal frequency division multiplexing(OFDM)signal with a center frequency of 2 GHz and a baud rate of 1 Gbaud,the SIC depth is only about 4 dB at a sampling rate of 10 GSa/s.The SIC depth can be increased to 25 dB by digitally upsampling the sampling rate to 1000 GSa/s.3.Building upon the first two studies,a photonics-assisted SIC and frequency down-conversion method for IBFD multiple-input multiple-output(MIMO)systems is proposed,and two schemes of SIC delay and amplitude adaptive control for IBFD MIMO systems with different data streams from transmitting antennas are designed and experimentally verified.The first scheme achieves multidimensional delay and amplitude adaptive adjustment using a genetic algorithm combined with the segmented search method,and the second scheme reduces multidimensional adaptive adjustment to two-dimensional adaptive adjustment using the least-squares(LS)estimation method combined with the segmented search method.These methods can all achieve SIC depths of more than 19 dB for 1-Gbaud 16 QAM OFDM signals and provide simple and efficient ideas for adaptive analog domain cancellation of complex self-interference signals in IBFD MIMO systems.4.A photonics-assisted SIC and echo signal de-chirping system of FMCW radar based on a dual-drive Mach-Zehnder modulator(DD-MZM)is proposed and experimentally verified,the SIC and echo signal de-chirping of FMCW radar are implemented simultaneously in the proposed system,and the designed system is studied and discussed in conjunction with the functions of radar system such as distance measurement and imaging.When the center frequency and bandwidth of the linearly frequency-modulated signal are 11.5 and 2 GHz,the cancellation depth of the dechirped self-interference signal is about 23 dB.The imaging performance,ranging accuracy,and system dynamic range are significantly improved after SIC.