Frequency Offset Estimation Based on Improved Concavity Positioning for Digital Subcarrier Multiplexing Systems

We propose a frequency offset estimation (FOE) scheme for digital subcarrier multiplexing (DSCM) system. Firstly, a smoothing filter with a length of 5 points is used to smooth the received spectrum. Subsequently, the concavity position is located by searching for local extrema. Finally, the power corresponding to the located point is elevated by 3 dB. Among these points within the 3 dB range, the point located in the middle is selected for frequency offset estimation. The simulation results for 64 GBaud polarization division multiplexing (PDM)-16/64QAM DSCM system demonstrate that, compared to the Dip-FOE scheme that detects the spectral concavity, our scheme is applicable to a wider range of roll-off factors. Besides that, the frequency offset estimation error of our scheme is only half that of the Dip-FOE scheme at the same level of complexity.