Research On Symbol Timing Synchronization In Real-time Optical IM/DD-OFDM System

Optical Orthogonal Frequency Division Multiplexing(OOFDM)has widely attached researchers' attention in optical communication field due to the advantages of high spectral efficiency and high tolerance of chromatic dispersion.Although the theoretical researches and offline experiments on OOFDM have been reported successively,they do not fully take a variety of hardware implementation constraints into account,such as hardware resource consumption,hardware precision and the highest supporting operating speed.This thesis mainly gives research on real-time optical Intensity Modulated Directed Detected OFDM(IM/DD-OFDM)system and focuses on study of the key processing:symbol timing synchronization technology.Two algorithms have been proposed which are based on Cyclic Prefix(CP)and one novel preamble symbol respectively.Meanwhile,the algorithm based on CP has been implemented via Field Programmable logic Gate Array(FPGA)and verified in a real-time optical IM/DD-OFDM testing system.Finally,the transmission of the optical IM/DD-OFDM system over 80km fiber link has been demonstrated successfully.The main work and innovations of this thesis are as follows:(1)The effect of symbol timing synchronization offset on IM/DD-OFDM system has been analyzed through theoretical derivation and numerical simulation.Numerical simulation result shows that the received constellation points are chaotic drastically and can not be decided correctly when timing synchronization offset exceeds the length of CP.(2)Two symbol timing synchronization algorithms are proposed which are based on CP and one novel preamble consisting of Zero Correlation Zone(ZCZ)sequence respectively.Numerical simulation results indicate that in optical IM/DD-OFDM system the former can keep well performance with zero multiplier consumption,the latter achieves a sharper timing metric peak and better stability than S&C,Minn and Park's algorithms.(3)The symbol timing synchronization algorithm based on CP is realized on FPGA hardware platform,and development work has been done to build the optical IM/DD-OFDM system with the transmission rate of 1.2Gb/s.Finally,the whole system has been tested over 80km fiber link,experiment results prove that the realized symbol timing synchronization module performs correctly and the system achieves zero Bit Error Rate(BER)performance.