Research On PAPR Reduction In Nonlinear Channel OFDM Optical Access System

Optical orthogonal frequency division multiplexing(OFDM)has been widely used in optical access networks because of its high spectral efficiency,dispersion tolerance and dynamic bandwidth allocation.One drawback of OFDM is that the transmitted signal has high peak-to-average power ratio(PAPR).High PAPR requires a large linear range for linear power amplifier and fiber,and it will lead to nonlinear distortion of the transmitted signal and affect system performance.In this paper,we analyze the basic theory and key technologies of OFDM.Subsequently,The PAPR performance and the computational complexity for DCT precoding and probabilistic techniques have been studied.Moreover,a millimeter-wave optical OFDM access-wave system is designed and simulated in nonlinear channel.Finally,we propose two types of novel schemes for reducation PAPR and analyse their performance.Simulation result show that both novel schemes can effectively reduce PAPR and provide a good trade-off between computational complexity and PAPR performance.Firstly,the basic principles and key technologies of OFDM,which includes parallel transmission and serial transmission,DFT/IDFT implementation and cyclic prefix are studied.Then,we analyze the basic classification of OFDM system in optical communication,including Intensity modulation and linear field modulation.Intensity modulated applications are divided into two general categories:asymmetrically clipped optical OFDM(ACO-OFDM)and DC bias optical OFDM(DCO-OFDM)and linear field modulated applications fall into two major categories:direct detection optical OFDM(DDO-OFDM)and coherent optical OFDM(CO-OFDM).Secondly,the definition of PAPR and its impact for OFDM system are analyzed.Furthermore,we briefly introduce common techniques for reducing PAPR,including pre-distorting technology,coding technology and probabilistic technology.We focus on the computational complexity of probabilistic technologies.Thirdly,we research the key technologies of common optical OFDM system,which contain Hermitian symmetry,zero-clipped,quadrature modulation and demodulation,RF to optical up conversion and optical to RF down conversion.Moreover,the principle of reducing PAPR using discrete cosine transform(DCT)precoding is studied.Eventually,we research three kinds of segmentation methods and the optimization scheme of partial transmit sequence technique.At least,we build a millimeter-wave OFDM optical access system in nonlinear channel using Optisystem and Matlab,and study two novel hybrid schemes applicable to different optical access system for reducing PAPR.Simulation result show that both hybrid schemes can effectively improve the PAPR performance and provide a good trade off between computational complexity and PAPR performance.