Research On CLPS Precoding Technology For Bandwidth-constrained ACO-OFDM Optical Systems

With the rapid development of the Internet,the demand for communication bandwidth and transmission rate of terminal services has exploded,which makes short-distance communication systems such as access networks and Data Centers(DC)continuously enhance the requirements for communication quality.Intensity Modulation and Direct Detection(IM/DD)technology is widely used in short-distance optical communication systems because of the advantages of low power consumption and low cost.Because Orthogonal FrequencyDivision Multiplexing(OFDM)technology has the advantages of high Spectral Efficiency(SE)and excellent dispersion robustness,it has become an indispensable modulation format in shortdistance communication systems.In the IM/DD system,only non-negative real signals can be transmitted.Asymmetrically Clipped Optical OFDM ACO-OFDM(ACO-OFDM)has the characteristics of being able to transmit unipolar signals,high power efficiency,strong resistance to transmission damage and high receiving sensitivity,and can be a promising solution for access and DC network communication systems.This paper is based on the ACOOFDM IM/DD system,and propose to use the circulant matrix generated by Chirp-Like Polyphase Sequences(CLPS)to precode the OFDM signal.By using the proposed design and relevant digital signal processing technology at the receiver,the transmission performance of the ACO-OFDM system is greatly improved.We compare different precoding schemes in simulations and experiments and verify the advantage of the proposed CLPS precoding.The innovations of this paper are summarized as follows: For the first time,we propose to use the circulant matrix generated by CLPS as the precoding matrix in bandwidth-limited optical ACOOFDM IM/DD system.The precoding matrix generated by CLPS can effectively control the power distribution of inter-symbol interference and inter-carrier interference(ISI/ICI)over subcarriers by adjusting the coefficient of CLPS.When the ISI/ICI power is more evenly distributed over subcarriers,the Signal-to-Noise Ratio(SNR)curve of the transmission system is flatter and the overall SNR is higher,which improves the performance of bandwidth-limited optical ACO-OFDM system.We also investigate the distribution of the normalized ISI/ICI power and SNR of the system over subcarriers,as well as the influence of the received power and the length of the cyclic prefix/postfix on the system's bit error rate.Experimental results show that in a 34.4Gbit/s IM/DD ACO-OFDM optical communication system with a system bandwidth of 10 GHz and a transmission distance of 10 kilometers,the proposed CLPS precoding ACO-OFDM achieve better performance than the traditional DFT-spread ACOOFDM system and OCT precoded ACO-OFDM system.