Research And Implementation Of Synchronization Technology In Real-time IM/DDO-OFDM System

With the increasing demand of communication band,width,Optical Orthogonal Frequency Division Multiplexing(OOFDM)has attracted much attention because of its high spectrum utilization and flexible dynamic bandwidth allocation.Synchronization technology is a key technology of OOFDM system.Small synchronization error may cause inter-symbol interference and inter-carrier interference,resulting in system performance degradation.However,the traditional and mature synchronization algorithm in wireless OFDM system is not suitable for OOFDM system.Most of the synchronization studies on OOFDM system do not consider the algorithm complexity and synchronization accuracy under noise interference in the process of hardware implementation.Based on Intensity Modulation/Direct Detection OOFDM(IM/DDO-OFDM)system,this paper proposes a symbol synchronization algorithm with low complexity and high accuracy based on a single training sequence.In addition,based on FPGA,the relevant DSP algorithm of baseband OFDM transceiver is designed and implemented,and the transmission performance of real-time IM/DDO-OFDM system is studied.The main research contents of this paper are as follows:First,the basic principle and synchronization technology of IM/DDO-OFDM system are theoretically deduced and analyzed.The differences in implementation modes and application scenarios of the two types of IM/DDO-OFDM systems are analyzed,and the effects of different timing synchronization positions on system performance are analyzed theoretically.Secondly,a new symbol timing synchronization algorithm based on a single training sequence is proposed.The algorithm uses the cross correlation between the sign bits of received data and the training sequence and the symmetry of the training sequence itself to realize The timing metric.The symbol timing synchr-onization algorithm achieves high synchronization accuracy with low computational complexity.When the signal to noise ratio(SNR)is 20db and the data is transmitted through 100km single-mode fiber,the variance value of timing deviation is stable within 10-2.Thirdly,the real-time IM/DDO-OFDM system is designed and implemented,and the transmission performance of the system is experimentally verified.The overall design scheme of real-time IM/DDO-OFDM system based on FPGA is studied.In addition,the key DSP module composition of baseband OFDM system transmitter and receiver and the indirect port logic functions of each module are described in detail.The reliability of the system is verified by experiment the symbol synchronization,sampling frequency synchronization and bit error rate.