Realization And Research On PAPR Reduction In OOFDM System

Orthogonal frequency-division multiplexing(OFDM)technology has attracted much attention in recent years,owing to numerous advantages such as high spectral efficiency,high data rate,and exibility to dynamic bandwidth.However,the drawback of the OFDM signal is the high PAPR.High PAPR prevents the modulator from operating within its linear region,causes additional interference.Moreover,it demands a wider dynamic range in digital-to-analog converter/analog-to-digital converter(DAC/ADC)to accommodate the large peaks of the OFDM signal.In addition,the BER performance will deterioration because of the non-linear effects of the transmission fiber if the launched power is relatively high.To overcome those shortcomes,we propose a novel hybrid scheme which combines the Huffman coding and DFT-spread,for OOFDM signal.There are some highlights below:Firstly,theoretical analysis of the hybrid scheme.Huffman coding can improve the system throughput,DFT-Spread can reduce the correlation among the encoded symbols.Thus,the hybrid scheme can reduce the PAPR as well as increase the data throughput.The theoretical analysis provide a cornerstone for subsequent simulation and experiment research.Secondly,the intensity-modulated and direct-detection optical orthogonal frequency division multiplexing(IMDD-OOFDM)system with hybrid scheme is investigated by experiment.The experimental results displayed that our hybrid scheme can suppress the PAPR by about 6 dB when the CCDF is 10-3 and achieve 3 dB receiver sensitivity improvement compared to original OFDM signal,at an error vector magnitude(EVM)of-10 dB after 20 km standard single-mode fiber(SSMF)transmission.Furthermore,the throughput gain can be of the order of 30%by using the hybrid scheme compared with the cases of without applying the Huffman coding.Thirdly,a 120° phase modulation OFDM-ROF system based on hybrid scheme was proposed and demonstrated.The outcomes of the simulation indicatied that the +2nd-order sideband is 24.62 dB lower than the conventional 90° phase modulation by employing the proposed scheme.In addition,the 15 Gbit/s OFDM signal can reduce the PAPR by about 6 dB,and achieve 12 dB receiver sensitivity improvements than the conventional 90° phase modulation when transmitted over 50 km SSMF at an EVM of-14.5 dB.