Demonstration of a carrier frequency offset estimator for 16-/32-QAM coherent receivers: a hardware perspective.

We propose and implement a hardware-efficient frequency offset estimator (FOE) optimized for 16- and 32-QAM coherent optical receivers with low hardware cost and high estimation accuracy. The proposed FOE combines a wide-range coarse estimator and a narrow-range highly accurate estimator in a feedforward architecture. We numerically and experimentally investigate the performance of the proposed estimator by using a field-programmable-logic-array (FPGA) based real-time coherent receiver. Compared with other state-of-the-art estimators in literature, the proposed method reduces over 40% of hardware utilizations while maintaining the same level of estimation accuracy in terms of mean-squared-error (MSE) and optical signal-to-noise ratio (OSNR) sensitivity. These results enable the development of next generation DSP circuit capable of supporting high capacity coherent optical communication link with advanced modulation formats.