Abstract
Optical signal-to-noise ratio (OSNR) is an important parameter in coherent optical communication systems to monitor the quality of the received signal and the transmission-link fault. The OSNR monitoring technique based on the moments of the received signals is simply and blind, where no extra training sequence is required. The moments-based method works well with QPSK signals with constant modulus constellations but has degraded performance for 16-QAM and 64-QAM signals with multilevel constellations. Instead of calculating higher-order moments, we proposed an accurate second- and fourth-order moments-based OSNR monitoring scheme, where the clock recovery of the M-QAM signal is first implemented and then the inner amplitude level is extracted to estimate the OSNR values. The proposed method has been verified and evaluated in QPSK, 16-QAM and 64-QAM simulations and experiments.
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