Research On Radio Frequency Interference Elimination Technology Based On Optical Method

With the development of new generation wireless communication technology,smart city,networking,virtual reality and Unmanned Aerial Vehicle?UAV?technology is increasingly widespread in our daily life.It requires that the wireless communication technology should have high bandwidth,high rate and low delay performance.Wireless communication technology is mainly divided into three kinds: frequency division duplex,time division duplex and full duplex.Compared with frequency division duplex and time division,full duplex has much better advantages,such as frequency resource utilization,transmission rate and delay,which may meet with the need of new wireless communication technology.However full duplex communication has the inherent problem of self interference during transmitting and receiving at the same time and with the same frequency.In this thesis,the radio frequency?RF?interference cancellation technique based on optical methods is investigated for full-duplex communication.Two optical methods for implementing RF self-interference cancellation are proposed and demonstrated experimentally.The first method is to utilize two intensity modulators and polarization multiplexing.With the two Mach-Zehnder modulators biased at inverted quadrature points,the antiphase relationship between the recovered interference signal and the reference signal is obtained.By tuning the amplitude and delay time of the reference path in optical domain,the matching condition for the RF self-interference cancellation is realized.The interference branch and reference branch are combined by polarization multiplexing,which avoids the optical interference due to the same laser source.A cancellation depth larger than 73 dB is obtained for the single frequency signal of 2.4,5,10 and 15 GHz.For the bandwidth of 10 MHz,a cancellation depth as high as 34.4,29.2,32.7 ? 31.8dB are realized at frequencies of 2.4,5,10 and 15 GHz,respectively.The elimination depth of different bandwidth and different power,as well as the change of cancellation depth of with time are measured and analyzed.Finally,spurious-free dynamic range of the interference cancellation system is analyzed,with the average value of 64.5 dB·Hz^2/3.The second method is to utilize an integrated dual-parallel Mach-Zehnder modulator?DP-MZM?.The received signals and the reference signal are converted into optical domain via the sub-MZMs?MZM1 and MZM2?in the DP-MZM,which are biased at the quadrature point and the minimum point with the output of double sideband with carrier?DSB+C?signal and double sideband with carrier-suppressed?DSB-CS?signal,respectively.It avoids the optical interference at the combining Y branch waveguide.The time and the amplitude matching conditions for cancellation between the reference signal and the interference signal are completed by the electrical tunable time delay line and the phase shifter in the MZM2 path.A cancellation depth larger than 80 dB is obtained for the single frequency signal of 2.4,5,8 and 10 GHz.For the bandwidth of 100 MHz,a cancellation depth as high as 37.6,35.8,33.1 and 38.3dB are realized at frequencies of 2.4,5,8 and 10 GHz,respectively.For WiFi standard frequency of 2.4GHz,the elimination depth with 10MHz-100 MHz bandwidth,with input power from-5dBm to 15 dBm and stability with time at 100 MHz bandwidth are measured.Finally,spurious-free dynamic range of the interference cancellation system is analyzed with,the average value of 54.2 dB·Hz^2/3.