Simple Wide Range Carrier Frequency Offset Estimator for Coherent Optical OFDM

Abstract

Coherent optical orthogonal frequency division multiplexing systems have a wide carrier frequency offset (CFO) range due to the frequency inaccuracy of lasers. In this letter, a simple wide range CFO estimator is proposed. In the proposed algorithm, wide estimation range and high accuracy are achieved by using a combination of the Chinese remainder theorem (CRT) for the integer part of CFO and fine estimation for the fractional part of CFO. For the proposed estimator, a training symbol structure consisting of two identical symbols is also suggested. The sizes of subsymbols of the training symbols are relatively prime to apply CRT. Simulations verify the validity of the proposed algorithm. The results indicate that the range of estimator is as large as the sampling frequency.