Research On Coherent Optical Orthogonal Frequency Division Multiplexing System Based On Wavelet Packet Transform

As a novel multi-carrier modulation technology,optical orthogonal frequency division multiplexing(OOFDM)has become a popular research in optical communication field in recent years because of its special advantages.Coherent optical orthogonal frequency division multiplexing(CO-OFDM)system is considered as the important solution for large-capacity high-speed,and long-haul fiber communications for its superior performance in spectral efficiency,receiver sensitivity,and polarization-dispersion resilience.High peak-to-average power ratio(PAPR)is one of the major drawbacks,which will increase the complexity and cost of system,and affect the nonlinearity of fiber.Therefore,how to reduce the PAPR effectively is the key for CO-OFDM system to become practical.Due to the high peak to average power ratio in CO-OFDM,in this paper,a novel CO-OFDM using wavelet packet transform instead of the traditional fast Fourier transform is proposed.Simulation results show that the novel transformation has obvious inhibiting effect on peak to average power ratio and gets better bit error rate performance than the traditional system using FFT.WPT combined with peak to average power ratio reduction algorithm is proposed.The paper is organized as follows:1.The research background,development situation,and existing problems of OOFDM system are introduced.The basic principle and key technology of CO-OFDM system are depicted.Then the reasons why PAPR is high and the negative influences of PAPR on the performance of system are discussed primarily.In addition,CO-OFDM system is built with matlab and optisystem software.2.A novel CO-OFDM using the wavelet packet transform(WPT)instead of the traditional fast Fourier transform is proposed.The PAPR reduction performance of different wavelet functions are compared by using of complementary cumulative distribution function(CCDF)curves and signal power figures in optical domain.Furthermore,on the basis of research,with the simpler algorithm structure,lifting wavelet transform instead of Mallat algorithm is proposed to apply to the CO-OFDM and the inhibition PAPR and BER performance is researched.3.Due to the high peak to average power ratio,combined with peak to average power ratio reduction algorithm,WPT using in CO-OFDM system is proposed.Combined with single algorithm and joint algorithm respectively,the simulation analyses the degradation of transmission performance in CO-OFDM system using WPT compared with those of the traditional fast Fourier transform(FFT).Compared with those of FFT,WPT combined with peak to average power ratio reduction algorithm can not only improve the degradation of transmission performance,but also reduce the peak to average power ratio further.