Research On Papr Reduction Technology In Optical OFDM System

Optical orthogonal frequency division multiplexing system (OOFDM) combines withthe advantages of OFDM technology and optical communication. OOFDM system has highspectrum efficiency and can effectively resist chromatic dispersion and polarization modedispersion in the fiber link. However, the high peak-to-average power ratio (PAPR) is oneof the important disadvantages for OOFDM system. High PAPR will not only make themodulator, amplifier and converter beyond their linear range, can also lead to seriousoptical fiber nonlinear effects. The improved method of mixd the parabolic peakcancellation algorithm (PPC) and the constellation diagram extension algorithm (ACE) wasput forward to reduce the PAPR in optical communication systems.Firstly, based on the study of the basic principle and key technology of OFDMtechnology, the basic principle of optical OFDM system was introduced. The reasons ofsignal distortion caused by the high PAPR in the optical OFDM system are analyzed. Onthe one hand is the nonlinear characteristic of the optical devices such as the amplifier, themodulator and the laser. On the other hand is the nonlinear phenomenon of the fiber linksuch as the self-modulation and the cross phase modulation. In the modeled CO-OFDMsystem, the influence of the fiber optical power and fiber length was simulated. Can be seenfrom the simulation results, the emission of light power can increase the nonlinear problemin fiber link, will make the system performance degradation. Moreover, the longer thetransmit distance, the worse the transmission quality.Secondly, aiming at the shortcomings of the ACE algorithm, such as the peak regrowthphenomenon and the lower speed of convergence, this paper has carried on theimprovement, using the PPC can improve the peak regrowth phenomenon in the process ofiteration, and constellation point pre-adjustment technology can improve the speed ofconvergence. The improved algorithm was simulated in a4-QAM,29Gb/s CO-OFDMsystem, simulation results demonstrate that the method has faster convergence speed, andcan effectively reduce the PAPR of OFDM signals by4.41dB. For CO-OFDM system, theimproved algorithm reduced optical fiber nonlinear effect and increased the tolerance ofoptical power.