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

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This letter extends the decision-aided (DA) maximum likelihood (ML) phase estimation in an <formula formulatype="inline"><tex Notation="TeX">$M$</tex> </formula>-ary phase-shift keying (PSK) system to quadrature amplitude modulation (QAM) signals. The block length effect is simulated for both <formula formulatype="inline"> <tex Notation="TeX">$M$</tex></formula>-ary PSK and QAM systems, and also investigated in <formula formulatype="inline"><tex Notation="TeX">$M$</tex> </formula>-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 <formula formulatype="inline"><tex Notation="TeX">$&gt;$</tex></formula>10 times compared to the block <formula formulatype="inline"><tex Notation="TeX">$M$</tex></formula>th power scheme. </para>