Research On The Synchronization Algorithm Of Direct Detection Optical FOFDM System

FOFDM,proves as a promising candidate for digital signal processing,which uses only half of the conventional OFDM subcarrier spacing and more simple modulation formats just based on real number.The FOFDM architectural design reduces hardware and software engineering effort,as well as reducing complexity by using real operations without sacrificing performance.In addition,due to its simplicity,FOFDM offers not only simple computations but also a corresponding decrease of processing power.In contrast to conventional OFDM,which uses real-valued fast Fourier transform(FFT)and inverse FFT(IFFT),FOFDM takes advantages of half of the subcarrier spacing with single-dimensional modulation formats where only in-phase constellation points are considered.The subcarrier multiplexing/demultiplexing can be implemented by using a discrete cosine transform(DCT)pair.In the intensity-modulated and direct-detected(IMDD)FOFDM system,the timing error cann't be solved by the existing algorithm.In this paper,the modulation and demodulation mechanisms of the discrete Fourier transform-based optical fast orthogonal frequency-division multiplexing(F-OFDM)scheme have been examined.Analysis shows that the timing error brings severe impact on this F-OFDM system while the conventional OFDM system can be well recovered through equalizers,through the training sequence cross-correlation synchronization algorithm to determine the correct timing position(pointer)for the DCT window,when the timing error changes in the decimal sacle over [-4/24 Ts,3/24Ts],still have a bad impact on the system,the ber is less than FEC threshold value.Two kinds of accurate symbol synchronization algorithm is proposed.Optical DDO-FOFDM system is established.And one is proved by simulation which is very close to the theoretical value,another experiment verified,the results show that the algorithm can improve the performance of the system very well.