A wide-range frequency offset correction is an essential function in the coherent-detection optical (CO) orthogonal frequency division multiplexing (OFDM) system. However, unlike conventional radio-frequency OFDM systems, the frequency offsets of CO systems come from the laser instability and bring much higher randomness and uncertainty between the local oscillation source and the incoming signal. Therefore, it is difficult to achieve low complexity and high precision for the frequency offset estimation at the same time. To fulfill the requirement of the CO-OFDM transmission system, we propose a novel algorithm using sample-shifted training symbols for the fast acquisition of the frequency offset in the CO-OFDM system. Based on the characteristics of optical coherency and the CO-OFDM symbol interval, the dynamic tracking of the frequency offset variation can also be simplified by using the OFDM pilot subcarriers.
© 2011 IEEEPDF Article