Research On Blind Equalization Algorithm Of Optical OFDM System

With the rising of the new concept of the internet,such as the internet of things and the internet plus,the future demand of network bandwidth will be further improved.So the requirement for large capacity,high speed,and long distance information transmission has become a hot research topic.There are obviously two research directions in today's optical fiber transmission system,(1)improve the transmission rate of a single channel;(2)multi-channel transmission technology.Optical orthogonal frequency division multiplexing(O-OFDM)is a kind of orthogonal multi carrier frequency division multiplexing technology with high spectral efficiency and resistance to fiber chromatic dispersion(CD)and polarization mode dispersion(PMD).However,the coherent optical orthogonal frequency division multiplexing(CO-OFDM),which combines the advantages of O-OFDM technology and the characteristics of coherent optical communication,has further improved the receiver sensitivity and data throughput of the system.Due to the effect of optical fiber dispersion,the CO-OFDM signal will suffer the amplitude distortion and phase shift.Therefore,the mature and respectively low cost adaptive blind equalization technique can be used as one of the important channel equalization algorithms.The adaptive blind equalization technique overcomes the training sequence requirement which is need by conventional channel equalization algorithms,thus effectively improves the bandwidth utilization and data throughput.In addition,the adaptive blind equalization technique can make a timely response to the channel characteristics,and more effectively compensate the random phase shift and amplitude distortion of signal in the transmission process.In this paper,the adaptive blind equalization technology in CO-OFDM system is studied,and the work is organized as follows:Firstly,the basic theory of CO-OFDM is introduced,and the CO-OFDM system model is designed by Optisystem and Matlab.The CO-OFDM experimental system is constructed by AWG,I/Q modulator,90 degree hybrid and so on.Secondly,the availability of blind adaptive technique for CO-OFDM system is demonstrated in the experiment.A new algorithm for blind equalization,which is based on singum function,is used to reduce the computational complexity and improve the convergence rate.The algorithm modifies the cost function of the traditional blind equalization algorithm,and solves the problem of phase blind of constant modulus algorithm(CMA).By constructing CO-OFDM simulation and experiment systems,the BER and MSE performance of the algorithm is evaluated.Lastly,according to the DD-OFDM and CO-OFDM system,the BER performance of the blind equalization algorithms is verified in each system.The analysis and simulation results show that the CO-OFDM system has a higher sensitivity than DD-OFDM.Moreover,IM-DD-OFDM system is proved to be phase blind.