Research Of Phase Noise Compensation Algorithm Based On RF-pilot In Wide Linewidth CO-OFDM System

The CO-OFDM system is very sensitive to the phase noise caused by the laser linewidth.Phase noise can be divided into two types:common phase error(CPE)and inter-carrier interference(ICI),which can destroy the orthogonality between subcarriers and seriously deteriorate the system performance.At present,the narrow linewidth external cavity laser is expensive,so it is important to improve the tolerance of laser linewidth to reduce the cost of the system.The main contents of this paper are as follows:1.This paper briefly introduces the research background,significance of CO-OFDM technology,the current situation of development,as well as the research status of phase noise compensation algorithm in CO-OFDM system.Based on the analysis of CO-OFDM technology principle and key technology,a complete Optisystem and Matlab simulation platform is established.2.The paper focuses on the phase noise of CO-OFDM system,and mainly introduces the phase noise compensation algorithm based on RF pilot.The RF-Pilot can track the changes of phase well while compensating for signal impairments caused by CPE and ICI.This method can support longer symbol durations and higher QAM modulation formats,and improving the spectral efficiency of the system.In this paper,based on the traditional time-domain RFP algorithm,channel estimation is performed,and the channel response function is optimized by using Kalman filter and ISFA to further enhance the compensation effect.In the algorithm,the low-pass extraction of the RF pilot is performed by using a cascaded move average filter(MAF2)which with stronger sidelobe attenuation instead of a single move average filter(MAF1),to reduces the bit error rate of the system.The key factors such as the number of taps in the filter,the amplitude of the pilot signal,the transmit power of the laser,the modulation method and so on are discussed and optimized later to improve the tolerance of the system to the linewidth as much as possible.The compesated frequency domain data are predetermined and converted to the time domain.Combined with the time domain data of IFFT conversion after channel equalization of the receiving terminal,the Extended Calman filter is used in time domain to achieve the final compensation of the signal.For 50Gb/s CO-OFDM system with 100km transmission distance.Under the circle 16QAM modulation,the performance of bit error rate(BER)after phase noise compensation reaches the upper limit of forward error correction(FEC)in the CO-OFDM system with a laser linewidth of 2.2MHz and a circular modulation of 16QAM.