The Research Of PAPR Reduction Techniques In The CO-OFDM System

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) is a new type of optical communication technology, which combines the advantages of OFDM and coherent optical communication technology. CO-OFDM system has good prospects in high-speed, high-capacity, long-distance optical fiber communication systems due to its high efficiency spectrum, low loss and can be effective against dispersion. High peak-to-average power ration (PAPR) of OFDM signals not only result in the power amplifiers, ADCs, DACs, Mach-Zehnder modulator (MZM) and other optoelectronic devices beyond their linear ranges, but also bring fiber nonlinearity. This paper deals with the methods on how to reduce the PAPR of CO-OFDM system. The main contents are as follows:1) Introduce the principle and system structure of CO-OFDM. Analysis RF to optical modulation module and coherent demodulation module emphatically. Using Matlab and Optisystem software built a CO-OFDM communication system.2) Describe the peak to average power ratio is defined and analyzed the peak to average power ratio signal generating reasons, introduction three main types technology to suppress PAPR, then analysis some main algorithms for PAPR reduction, such as Clipping, Selective Mapping (SLM), Partial Transmit Sequence (PTS).3) An improved tone reservation method based on FFT/IFFT is proposed. The reserved subcarrier’s peak cancelling signal is multiplied by different correction phase sequences and the signal with the minimum PAPR among these alternative signals is selected to transmit. Simulation results show that, compared with the original algorithm, our proposed method can get about 3dB PAPR performance gains with low computational complexity.4) An improved tone reservation method based on FFT/IFFT algorithm is applied in 10 Gbit/s,300km single-mode optical fiber CO-OFDM system. The simulation results show that the improved algorithms can well suppress PAPR, while also improving the error performance over long distances CO-OFDM system.