Research On Sampling Frequency Offset Compensation Technologies Of Directly Detecting Optical OFDM System

With the rapid development of cloud computing and big data technology,4k high-definition video,virtual reality,smart medical services and other services have been widely popularized.High-speed,largecapacity,and low-latency optical access networks are the future development trend.Orthogonal Frequency Division Multiplexing(OFDM)is applied to the optical access network to construct a direct detection optical OFDM system,which has technical advantages such as high spectrum utilization,resistance to channel dispersion and fading.However,in an OFDM system,the sampling frequency offset(SFO)of the transmitter and the receiver will cause a decrease in transmission performance.This paper mainly studies the SFO estimation and compensation technology for direct detection of optical OFDM systems to improve system performance.The main work is as follows:1.In this paper,a low-complexity blind estimation and compensation method is proposed for the SFO problem of directly detect fiber-optic OFDM systems.By extracting the modulation symbols in the subcarriers of the received OFDM symbols,the fourth power algorithm is used to estimate the phase offset caused by the SFO,and then the overall SFO of the system is estimated.In order to further improve the estimation accuracy,a subtraction operation of two sub-carrier modulation symbols is used to eliminate the residual phase caused by inaccurate channel equalization.Experimental results show that the maximum SFO estimation range of this method is ±1000ppm,and the estimation error is less than ±3ppm.Since no pilot or training symbols are needed,the system complexity is reduced.2.In this paper,in order to deal with the SFO problem of the directly detect visible light laser OFDM system,a SFO automatic compensation method based on the improved K-means clustering algorithm is proposed,without the need to estimation the phase caused by SFO.K-means clustering is performed by selecting part of the sample data in the receiver,and the centroid of the first generation is corrected by combining the rotation factor.Experimental results show that 1.314 Gb/s visible light OFDM signal is transmitted through 3m free space,and the SFO tolerance range of the system is up to ±120ppm.Compared with the traditional Kmeans algorithm,the improved K-means clustering algorithm proposed in this paper can reduce the computational complexity and data redundancy.