Synchronization And Phase Noise Compensation Scheme For Coherent Optical OFDM Systems

With the development of communication technology,a lot of new business emerge constantly,especially the rise of IP services,a lot of information needs to be transmitted.Communication change from the traditional phone business to a high-speed IP data and multimedia services.The communication network requires high capacity and bandwidth.In order to meet user requirements for communication's rate and make full use of the enormous bandwidth of optical fiber to achieve high-capacity and long-distance transmission,the international raise to combine OFDM with coherent optical communication technology.It offers the advantages of high electrical and optical spectral efficiency,dispersion insensitivity and high optical signal-to-noise(OSNR)sensitivity.However,the CO-OFDM system suffers from frequency offset and phase noise sensitivity,which make it more sensitive to synchronization.Therefore details of synchronization of CO-OFDM signals deserve careful perusal,including timing synchronization,frequency synchronization and phase noise estimation.So,this paper research on synchronization and phase noise compensation scheme for coherent optical OFDM systems.This paper introduces OOFDM system,then timing and frequency synchronization and phase noise estimation algorithm are presented respectively.We set up CO-OFDM system,and the simulation algorithm mentioned earlier is completed in the Optisystem communication simulation software and Matlab software.The main works in this study are as follow:(1)The research and simulation analysis of timing and frequency synchronization algorithm based on chaos sequence in CO-OFDM system are completed.The method combing chaos sequences with timing and frequency synchronization has more advantages such as more accurate and sharp timing curve with smaller sidelobes compared with the classical synchronization algorithm.(2)Having a research on phase noise estimation based on chaos sequences,the comb pilot inserted into the OFDM symbols is generated by chaos sequences instead of the traditional pseudo-random sequence.The impact of linewidth,modulation factor and the number of subcarriers on phase noise estimation is demonstrated.The results show that the algorithm is effective only in the case of narrow linewidth,the case of wide width needing for further research.(3)The method combing randomized PTS algorithm based on chaos sequences with adaptive compression and expansion techniques effectively reduce the PAPR and improve the performance of the system.PTS algorithm adopts processed Lorenz chaos sequences because of its fairly uniform distribution,enhancing the system security.Finally,the three algorithms based on chaos sequences are simulated together to enhance the physical layer security.Algorithm based on chaos sequences has more advantages by three algorithms simulation aforementioned.It can provide more reliable information transmission and further improve the physical layer security.