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This letter extends the decision-aided (DA) maximum likelihood (ML) phase estimation in an M -ary phase-shift keying (PSK) system to quadrature amplitude modulation (QAM) signals. The block length effect is simulated for both M-ary PSK and QAM systems, and also investigated in M -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 block Mth power scheme.
Date of Publication: Aug.1, 2009