Almost-Blind Frequency Offset Estimation Method With Wide Range for Discrete Spectrum Modulated NFDM Systems

As a potential way for surpassing the Kerr nonlinearity limit, nonlinear frequency division multiplexing (NFDM) transmission scheme has attracted much attention in fiber-optic communication systems. For the discrete spectrum (DS) modulated NFDM systems, due to the mismatch of the transmitter and local oscillation lasers, frequency offset estimation (FOE) and compensation would be an indispensable step. In this paper, we propose an almost-blind FOE method with wide range for DS-NFDM systems, which can achieve high estimation accuracy with only two training symbols (TSs). In this method, the eigenvalue-shift (ES) method is used to get a shortened search interval of frequency offset (FO) firstly, and then the optimal FOE of which is found based on the minimum phase correction error principle without need of any TSs. At last, a FO decision criterion aided by only two TSs is proposed to eliminate estimation range constraint. The reliability and effectiveness of the proposed almost-blind FOE approach have been experimentally demonstrated, and the results reveal that the proposed method is robust to the amplified spontaneous emission (ASE) noise and phase noise, as well as has the wide FOE range with high estimation accuracy. Furthermore, with a comparison of the hybrid methods based on ES and angle search (AS) or ES and angle difference (AD) operations, the proposed method can save at least 99% and 94% TS overheads, respectively. Thus, this method shows the potential in the field of high-speed DS-NFDM systems.