Dual stage carrier phase estimation for 16-QAM systems based on a modified QPSK-partitioning algorithm

Coherent optical communications based on higher order modulation formats are severely affected by the phase noise of transmitter and receiver lasers. In this work, a novel yet simple scheme is presented for carrier phase estimation (CPE) of 16-ary Quadrature Amplitude Modulation (16- QAM) formats, based on a modified QPSK-partitioning algorithm. The proposed algorithm can tolerate a linewidth times symbol duration product (Δv · T_s) of the order of 10^-4, with 1 dB penalty at a bit error rate (BER) of 10^-3. Tolerance can be further improved by introducing a maximum likelihood estimation (MLE) stage (Δv · T_s ≈ 1.432×10^-4). Comparison of the scheme with other proposed algorithms is shown. The obtained results indicate that the presented approach can be used with the commercially available state of the art lasers for 16-ary Quadrature Amplitude Modulation (16- QAM) transmission at 100 Gbps.