Analysis On The CO-OFDM Transmission Performance And Simulation Flatform Design

The next generation network has turned to broadband network since the development of the information society. The demand of bandwidth is increasing dramatically, and the capacity of the backbone network is going up with 50%～80% per year. As a result, high speed, huge capacity and high efficiency are desiracle currently. Orthogonal Frequency Division Multiplexing(OFDM) is a multi-carrier transmission technology, which the channel is divided into several orthogonal sub-carriers and the high-speed data stream are transmitted onto the low-speed sub-carriers,so that the transmission speed, the spectral efficiency and the ability of anti-interfere are improved. The coherent optical communication enjoys the advantages of huge capacity, long transmission and high signal quality. Coherent Optical OFDM (CO-OFDM) combines the advantages of OFDM and the coherent optical communication, and features for high spectral efficiency and low losts.So that it becomes a potential technology for 100Gbit/s ultra-long optical transmission network.The design of the CO-OFDM simulation platform is discussed specifically, including the function orientation, framework design,data formation and working processes.Modeling and coding processes are implemented to several models by MATLAB.The principle and the key technologies of CO-OFDM are summarized, and then quantitative analysis is done to Four Wave Mix (FWM) phenomenon and fiber dispersion in CO-OFDM.Finally some solutions are provided and simulations are given respectively. As for FWM,a fact that the FWM noises are closely related with the serial correlation among OFDM sub-carriers is given;so that the PTS algorithms are adopted to reduce FWM noises by reducing the correlation between sub-carriers with the help of phase factors;result shows that the signal performance improves obviously according to constellation map.As for optical dispersion, the dispersion noises in CO-OFDM system are derived;cycle prefix and channel estimations are taken for dispersion equalization.Channel estimation algorithms based on LS and LMMSE rules are discussed and implemented, and simulation result shows that channel estimation can compensate the distortion induced by dispersion. LMMSE algorithm enjoys 2dB gains compared with LS algorithm, when bit error rate is 10-4.