Sampling frequency offset estimation and compensation for asynchronous optical IMDD FBMC systems

Filter bank multi-carrier (FBMC) can provide higher spectral efficiency and lower out-of-band spectrum leakages than orthogonal frequency division multiplexing (OFDM) or discrete multi-tone (DMT). Due to a crystal or oscillator usually having a frequency tolerance and stability of a few tens of parts per million (ppm), the sampling frequency offset (SFO) between digital-to-analog converter and analog-to-digital converter in the transceiver will seriously degrade the performance of these asynchronous optical multi-carrier communication systems. The SFO-induced impairments and their estimation and compensation methods have been widely studied in optical OFDM/DMT systems. However, the SFO problem is rarely investigated in the optical fiber FBMC system. In this work, the SFO-induced impairments in the asynchronous optical FBMC system are first theoretically analyzed, and then we propose an inter-symbol guard (ISG) and training symbol (TS)-aided SFO estimation method and compare two commonly used SFO compensation methods, i.e., phase compensation (PC) and digital interpolation (DI) regarding estimation accuracy and bit error rate (BER) or error vector magnitude performance by both numerical simulation and offline experiment. The results exhibit that an SFO estimation accuracy of less than ±1 ppm is achieved in the intensity modulation and direct detection FMBC system with a 20-km single-mode fiber link under initial SFOs up to ±200 ppm. Besides, FBMC can afford a similar BER performance with DMT with PC or DI methods in the presence of SFO up to ±100 ppm, and achieve a negligible power penalty at the BER of 3.8e-3, compared to the SFO-free cases. Moreover, FBMC is more robust to SFO estimation errors than DMT.