Scrambling algorithms for peak-to-average power ratio reduction in long haul coherent optical OFDM systems

Recently, Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) has been seen as a potential candidate for long haul optical transmission. It is due to OFDM technique that was proved as an effective solution for mitigating chromatic dispersion (CD) effects in optical communication systems. However, a very basic drawback of OFDM technique is large peak-to-average power ratio (PAPR) problem which requires large scale linear power amplifier and optical external modulator. The large PAPR leads to the increase of nonlinearity of optical fiber which depends on instantaneous signal power. So, the performance of CO-OFDM system is degraded. Several approaches were studied and applied in wireless communication. Among all techniques of PAPR reduction, Selected Mapping (SLM) and Partial Transmit Sequence (PTS) are considered as two better methods because of their distortionless characteristics. It is also known as a kind of scrambling technique. But the efficiency of these algorithms in long haul optical communication application is still an open issue. In this paper, we study both PTS and SLM technique to reduce the influence of optics nonlinear effects. The Simulink simulation results are presented and discussed.