| Microwave photonics,as an emerging interdisciplinary subject that combines microwave technology and photonic technology,mainly studies the conversion of microwave signal and optical signal and the processing of optical domain.With the development of information technology,higher requirements are put forward for the bandwidth and information transmission rate of the communication frequency band signal.Compared with the traditional frequency division duplex and time division duplex technology,the simultaneous frequency full duplex technology can double the information transmission rate,which is expected to solve the problems of spectrum resource utilization and information transmission rate.However,due to the short distance between the transmitting antenna and the receiving antenna in the full-duplex technology,the transmitted signal with strong power will leak directly to the receiving end,causing system self-interference.Compared with traditional electrical methods,radio frequency self-interference elimination based on microwave photonic technology has the advantages of large bandwidth,high precision,low loss and anti-electromagnetic interference,and has received extensive attention from the academic community.This paper first briefly introduces the development and application of microwave photonic technology,and elaborates the research status of radio frequency self-interference cancellation technology in detail.Then,the principle and performance evaluation parameters of the microwave photonic RF self-interference cancellation system are analyzed.Subsequently,the optical domain RF self-interference cancellation method based on microwave photons is studied for full-duplex communication systems,and the functional integration of self-interference cancellation and down-conversion,and the functional integration of self-interference cancellation and up-conversion are respectively realized.The principle of the above self-interference elimination method is theoretically analyzed,the experimental system is built and the performance test is completed.Finally,the whole paper is summarized and the prospect of microwave photonic RF self-interference cancellation technology is prospected.The main research work of this thesis is as follows:1.For distributed full-duplex communication system,a method for eliminating self-interference in optical domain based on cascade modulation is studied.A Mach-Zehnder（MZM）modulator is used to modulate the local oscillator signal,and a dual-parallel Mach-Zehnder（DPMZM）modulator is used to modulate the received signal and the reference signal,and to achieve self-interference signal cancellation in the optical domain.The unwanted sidebands are filtered out by an optical bandpass filter,and only the+1-order sidebands of the useful signal and the local oscillator signal are retained.After being amplified by an optical amplifier,photoelectric conversion is performed by a photodetector to obtain a down-conversion frequency that eliminates self-interference.Signal.The cancellation depth of the system for single-frequency signals is more than 37 d B,and the cancellation depth for wideband signals is more than 21 d B,and the recovery of useful signals is obtained.The system adopts the cascade modulation method,the isolation of LO and RF signals is high,and it is suitable for distributed full-duplex communication systems where the local oscillator and RF signals are located in two places.2.An optical-domain RF self-interference cancellation method based on Sagnac ring is proposed.The counterclockwise Mach-Zehnder（MZM）modulator in the Sagnac ring is used to modulate the local oscillator signal,and the clockwise dual parallel Mach-Zehnder（DPMZM）modulator is used as a self-interference canceler to modulate the received signal（including the desired signal）.and self-interfering signals)and reference signals.The+1-order sidebands of the useful signal and the local oscillator signal are retained by the optical band-pass filter.After being amplified by the optical amplifier,the photoelectric detector is used for photoelectric conversion to obtain a down-conversion signal that eliminates self-interference.The cancellation depth of the system for single-frequency self-interference signals is better than 50 d B,and the cancellation depth for wideband signals with bandwidths of 20MHz and 100 MHz is more than 19 d B.The method utilizes the Sagnac loop to realize down-conversion and self-interference cancellation at the same time,and has a higher cancellation depth than the cascade structure.3.A microwave photonic in-band full-duplex system that can simultaneously realize up-conversion,down-conversion and radio frequency（RF）self-interference cancellation（SIC）is proposed,and the link is built and verified by experiments.The X-DPMZM modulator in the integrated dual-polarization dual-parallel Mach-Zehnder modulator（DP-DPMZM）is used to simultaneously generate carrier-suppressed single-sideband for both local oscillator（LO）signals and intermediate frequency（IF）signals.The Y-DPMZM in the DP-DPMZM modulator is used as an optical self-interference canceler to suppress the self-interference signal（Si）from the received signal,and to achieve carrier-suppressed double-sideband modulation of Si and the wanted signal（SOI）.The optical signal output by the DP-DPMZM modulator is divided into two parts by a 50:50 optical coupler（OC）.One part selects the X polarization state and uses photodetectors for photoelectric conversion to obtain up-converted signals for signal transmission;the other part is used to filter the signals that have achieved SIC,select the required sidebands,and then use photodetectors to shoot frequency to obtain a down-converted signal.The experimental results show that the spurious-free dynamic range（SFDR）of the up-conversion frequency is 102.6d B/Hz2/3,the cancellation depth of single-frequency and broadband self-interference exceeds 50 d B and 22 d B,respectively,and the useful signal is recovered.The method can realize not only the elimination of self-interference signals,but also the transmission and reception of signals simultaneously by means of the shared local oscillator signal. |
