Frequency offset estimation and carrier phase recovery for high-order QAM constellations using the Viterbi-Viterbi monomial estimator

We present two novel, low-complexity feedforward algorithms for frequency offset estimation (FOE) and carrier phase recovery (CPR) in coherent optical M-QAM systems, employing the Viterbi-Viterbi monomial-based estimator. The FOE scheme is an extension of the phase-increment algorithm used for QPSK, while CPR is achieved with a robust, two-stage algorithm that does not rely on a computationally expensive Blind Phase Search (BPS) stage. Simulations show performance close to that of BPS for square constellations up to 256-QAM, while the penalty when both FOE and CPR are operated together is shown to be negligible.