| In order to meet the demand of the large increase of communication capacity at present,the signal carrier frequency of wireless communication system is developing to high frequency band.When the radio frequency signal propagates in the medium,the power of the radio frequency signal decreases rapidly with the increase of frequency,which leads to the reduction of its transmission distance.In order to achieve seamless coverage of RF signals,the current development trend is to adopt Radio-over-Fiber(RoF)links.The externally modulated RoF link has the advantages of high electro-optical conversion efficiency and wide modulation bandwidth.However,when the RF vector signals generated by double sideband modulation and single sideband modulation are transmitted in the RoF link,distortion will be introduced,resulting in the inability to recover data information.Therefore,this thesis will focus on the dispersion power fading and phase change caused by long-distance optical fiber transmission of RF vector signals,and the specific work is as follows:(1)The communication requirements for the next generation wireless access network at this stage are analyzed,and the current research status at home and abroad is summarized.Starting from QAM(Quadrature Amplitude Modulation)signal modulation,link parameters and modulation methods,the signal transmission process of RoF external modulation link is analyzed theoretically,which lays a theoretical foundation for subsequent experiments and simulations.(2)A dispersion compensation technology of RoF link based on stimulated Brillouin scattering effect is proposed.Aiming at the power fading problem of the double sideband modulated signal in the RoF link,the Error Vector Magnitude(EVM)of the compensated system is increased from 18.23% to 1.71% due to the influence of power fading caused by fiber dispersion in the transmission process of the double sideband modulated signal in the central station,and the transmission in the frequency range of 10 MHz-10 GHz is realized.(3)The dispersion compensation technology of RoF link based on digital signal processing(DSP)is verified,and the dispersion compensation technology of RoF link based on digital signal processing is proposed to solve the phase change problem of single sideband modulation signal transmission in RoF link.The simulation verifies the RoF link dispersion compensation technology,and corrects the influence of the phase change of single sideband modulation signal caused by fiber dispersion on the demodulated signal constellation.In addition,the influence of laser parameters on link signal transmission is studied based on the Optisystem simulation platform. |
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