Frequency Offset Estimation for Optical Coherent M-QAM Detection Using Chirp z-Transform

The chirp z-Transform (CZT) is introduced to replace the traditional gradient descent (GD) in frequency offset estimation for digital coherent quadrature amplitude modulation reception. Different from GD, CZT is not sensitive to the changes of the parameters and is free of uncertain latency that GD suffers. The implementation of frequency offset estimator based on CZT is presented and numeric simulations demonstrate that CZT can reach the same accuracy as GD. The computation complexity of CZT is analyzed and is roughly equivalent to GD with three iterations.