Research On The Synchronization Algorithm And Channel Estimation Algorithm Of Coherent Optical Orthogonal Frequency Division Multiplexing System

In recent years,with the expediting step of the Internet,data services demand for a substantial increase in transmission speed and bandwidth.It is an inevitable choice to establish a transmission network with super high speed and super large capacity.Coherent optical orthogonal frequency division multiplexing(CO-OFDM)technology has the advantages of high sensitivity,large channel capacity,high dispersion tolerance and high spectrum efficiency,which has drawn wide attention.It soon has become a research hotspot of the future optical transmission technology.Timing synchronization is the technical support of all communication systems.Due to the own characteristics of CO-OFDM system,it has very low tolerance to frequency offset.So frequency synchronization further needs to be carried out.Channel estimation must be carried out after the above synchronization process,because the effect of fiber channel damage on high speed signal can not be ignored.The process of synchronization and channel estimation play a decisive role in the realization of CO-OFDM system.Therefore this study focuses on the time-frequency synchronization algorithm and channel estimation algorithm,which are used in those key processes.The principles and the key technologies of CO-OFDM system were studied,including the principles of orthogonal frequency division multiplexing(OFDM)modulation/demodulation and up/down frequency conversion technologies.Based on those principles and technologies,a CO-OFDM simulation platform was established.The synchronization error and channel damage were theoretically studied and simulated.The influences of them on the signal were analyzed through the simulation results.The classical time-frequency synchronization algorithms were studied and simulated.The existing problems of the classical algorithms were analyzed on principle and performance.An improved synchronization algorithm based on Zadoff-Chu(ZC)sequences was studied in this research.Compared with the classical algorithms,the improved ZC algorithm had solved the problems of the classical algorithms in the process of timing synchronization.In this study,periodogram method used in wireless communication was proposed for the integer part frequency synchronization.The improved ZC algorithm had achieved a good accuracy,a wide estimation range and a low complexity.Only one training symbol(TS)was used in the improved ZC algorithm,which had reduced the system overhead.It had a good applicability in CO-OFDM system.The existing channel estimation algorithms were studied and analyzed.We found that there were constraint relationships among accuracy,system overhead and complexity.In order to better balance the relationships,an improved algorithm based on scattered pilot was proposed in this study.The performance of the improved algorithm was tested through simulation and comparison.Compared with the traditional algorithm based on scattered pilot,the improved algorithm had improved the accuracy.Compared with the intra-symbol frequency-domain averaging(ISFA)algorithm,the improved algorithm sacrificed a small part of accuracy in exchange for the reduction of system overhead,which had improved the communication efficiency.The complexity of the improved algorithm was relatively moderate.We had demonstrated that the improved algorithm was suitable for local area network transmission.