| In recent years,with the rise of Internet of Things applications,the popularity of smart terminal devices and high-speed broadband access,as well as the growing demand for high-speed streaming media by users.New requirements for simultaneous transmission of analog signals are put forward in access network,vehicle networking,indoor light access,and optical home.Multimode optical fibers are suitable for short-distance optical access network transmission.Therefore,it is necessary to study the transmission scheme of multimode optical fibers in the field of optical wireless.In this thesis,the transmission of high-speed digital and analog RF signals in optical wireless systems is studied first.A method of overlay transmission of digital and analog signals based on spectral zero overlay is presented.This method can realize the overlay transmission of two signals at a single wave-length.The simulation and experimental results show that this method can achieve the overlay transmission of digital and analog signals with high spectral utilization and low mutual interference.Then,based on the transmission characteristics of special optical fibers such as multimode optical fibers,the overlay transmission of digital and analog signals in optical wireless systems in multimode optical fibers is studied.Based on the above theoretical basis,the following work has been completed:(1)For the requirement of simultaneous transmission of digital and analog signals,the transmission scheme in optical wireless system is studied and analyzed,and several digital and analog signal overlay transmission schemes for simultaneous transmission of signals are proposed,and the digital simulation validation and experimental scheme design are carried out.The parameter design of digital and analog signal transmission system is completed through experimental research.The scheme can be used in home network and vehicle network.The transmission performance of 2.6 Gbps high speed baseband signal and 64QAM radio frequency signal overlay scheme at 100 MHz are tested.The experimental results show that the overlay transmission scheme can transmit both digital and analog signals at the same time with lower performance loss in back-to-back system experiments.(2)The characteristics of multimode optical fibers are studied,and a scheme for overlay transmission of nonzero OOK baseband signal with 2.6 GHz main valve width and 5.2 GHz orthogonal frequency division multiplexing(OFDM)analog signal is proposed.The baseband signal can be automatically filtered by the circuit at the receiving end.The analog signal is decoded after the band-pass filter.Both the baseband signal and the analog signal can meet the requirements of the transmission error rate for the service,and the interference between the signals is low.The transmission performance of special multimode optical fibers is evaluated and compared through experiments.The multimode optical fibers mainly include plastic optical fibers,bend resistant optical fibers and other multimode optical fibers.Transmission experiments were carried out at 1550 and 1310 nm laser,respectively.In plastic optical channel,the power cost of non-zero OOK signal is lower than that of bend-resistant optical fiber.When transmitting RF signals in bend-resistant optical fibers,there is a larger dynamic range of input signal power.Each kind of optical fiber has its own advantages and disadvantages in transmitting baseband and analog signals.(3)A hybrid overlay transmission scheme of frequency division multi-plexed digital-analog signals with good spectral efficiency is proposed,which can improve the transmission capacity.The scheme first filters and shifts several NRZ-OOK signals,then superimposes them with the analog signals.This scheme improves the spectral efficiency.The transmission performance of multimode optical fiber including POF,BIPOF and MMF is experimented.The system transmission performance is evaluated using performance parameters such as bit error rate and EVM. |
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