Robust Frequency Offset Estimation for Coherent DSCM Systems Under Severe Bandwidth Limitation

Since digital subcarrier multiplexing (DSCM) signals require frequency offset estimation (FOE) and compensation before demultiplexing, we propose a robust FOE scheme for DSCM systems that estimates the frequency offset (FO) by calculating the magnitude sum of spectral components within a specified range centered at zero frequency. The scheme remains effective even under severe bandwidth limitation conditions. The experimental results show that with FFT sizes of 2048, the maximum FOE errors are 119 MHz, 123 MHz, and 87 MHz for the 4, 6, and 8 subcarrier DSCM signals, respectively. Additionally, the cumulative distribution functions (CDF) of the FOE error less than 50 MHz are 0.79, 0.81, and 0.82, respectively. Furthermore, the proposed scheme demonstrates stable performance across a wide range of FO and received optical power (ROP). Therefore, the proposed scheme can achieve high FOE accuracy in the presence of severe bandwidth limitation for coherent DSCM systems.