Joint Timing and Frequency Synchronization for Coherent Optical SEFDM Systems

In this paper, we propose a joint timing and frequency synchronization algorithm for spectrally efficient frequency-division multiplexing (SEFDM) systems by utilizing a training symbol composed of a conjugate symmetric sequence. The timing metric is designed to be the multiplication of two timing metrics which aims to reduce the amplitude of sidelobes, thus ensuring the timing synchronization performance. In addition, according to the phase relationship between the four halves in the designed training symbol, we then derive a closed form expression of the the carrier frequency offset (CFO) estimate. Simulation results verify the superior timing and frequency synchronization accuracy of the proposed method compared with the existing synchronization algorithms.