Laser Linewidth Tolerance of Decision-Aided Maximum Likelihood Phase Estimation in Coherent Optical M-ary PSK and QAM Systems

This letter extends the decision-aided (DA) maximum likelihood (ML) phase estimation in anM-ary phase-shift keying (PSK) system to quadrature amplitude modulation (QAM) signals. The block length effect is simulated for bothM-ary PSK and QAM systems, and also investigated inM-ary PSK systems through analysis. Our results show that the tolerance of DA ML to laser linewidth for square 16-QAM can be increased by$>$10 times compared to the blockMth power scheme.