A novel low-complexity two-stage digital feed-forward carrier phase estimation algorithm based on the rotation of constellation points to remove phase modulation for a 64-ary quadrature amplitude modulation (QAM) system is proposed and analyzed both experimentally and through numerical simulations. The first stage is composed of a Viterbi and Viterbi (V&V) block, based on either the standard quadrature phase shift keying (QPSK) partitioning algorithm using only Class-1 symbols or a modified QPSK partitioning scheme utilizing both Class-1 and outer most triangle-edge (TE) symbols. The second stage applies the V&V algorithm after the removal of phase modulation through rotation of constellation points. Comparison of the proposed scheme with constellation transformation, blind phase search (BPS) and BPS+MLE (maximum likelihood estimation) algorithm is also shown. For an OSNR penalty of 1 dB at bit error rate of 10-2, the proposed scheme can tolerate a linewidth times symbol duration product (Δv• Ts) equal to 3.7 times 10-5, making it possible to operate 32-GBd optical 64-QAM systems with current commercial tunable lasers.
- Bit error rate (BER)
- carrier phase recovery
- quadrature amplitude modulation (QAM)
- triangle edge (TE)
- Viterbi & Viterbi algorithm
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics