Research On ACO-OFDM System Based On OCT Precoding

In recent years,the rapid development of high-speed services such as cloud computing,IPTV,and 4K/8K high-definition television have increased the requirements for access network bandwidth.In Passive Optical Networ k(PON),Intensity Modulation/Direct Detection(IM/DD)system is currently prefered as a common solution in a short-distance optical communication system.The multi-carrier Orthogonal Frequency Division Multiplexing(OFDM)is robust to channel dispersion and has high spectral efficiency.Due to such advantages,OFDM has been considered as one of the powerful optical communication technologies in optical access networks.Because the optical transmission system requires the signal form to be a non-negative real number signal,Asymmetrically Clipped Optical OFDM(ACO-OFDM)is a unipolar OFDM signal with high optical power efficiency and high receiver sensitivity.Therefore,this paper focuses on the ACO-OFDM technology.By the way of the precoding and digital signal processing algorithms,improving the performance of ACOM-OFDM based intensity modulation direct detection system.The main innovations in this article are as follows:First,a scheme combining the orthogonal circulant matrix transform(OCT)precoding and digital clipping technology is proposed in the ACO-OFDM system.The OCT precoding relieves the impairment caused by high-frequency subcarrier fading,and the digital clipping reduces the non-linear effects,the scheme brought about effectively improve the ACO-OFDM signal transmission performance.In addition,Least Square channel estimation is used.And frequency domain equalization for off-line digital signal processing.The distribution of SNR of the signal under different algorithms and the error performance of the system when receiving different optical power are studied.Experimental results show that the performance of OCT precoding scheme is better than that of digital limiting scheme,and the combined performance of OCT precoding scheme is better than that of single scheme.After 20 km of single-mode fiber transmission,the signal can get a bit error rate of 5×10-5,well below the 7% FEC threshold of 3.8×10-3.According to the experimental results,it is verified that the joint scheme of OCT precoding and digital limiting can effectively improve the system transmission performance.Second,a joint scheme of OCT precoding and Discrete Fourier Transform Spread(DFT-Spread)is proposed for direct detection of intensity-modulated ACO-OFDM systems,reducing the peak-to-average power ratio of ACO-OFDM signals.(Peak to Average Power Ratio,PAPR)improves the nonlinear effect of the signal.The BER performance of 16 QAM ACO-OFDM signal was also studied.By comparing the SNR and Error Vector Magnitude(EVM)after transmission between the back-to-back and 20 km single-mode fiber,the experimental results show that the performance of the proposed combined OCT precoding and discrete Fourier transform expansion scheme is better than that of the single scheme.After 20 km single-mode optical fiber transmission,compared with the traditional signal and OCT precoding and digital clipping combined algorithm,the receiver sensitivity of the joint scheme of the ACO-OFDM system increased by 1.3dB and 3.1dB,respectively.