Wide-range frequency offset estimation method for a DD-OFDM-PON downstream system

We propose a wide-range frequency offset estimation algorithm used in a direct detection orthogonal frequency division multiplexing passive optical network (DD-OFDM-PON) downstream system. Using this method, frequency offset is estimated according to the spectrum of the received DD-OFDM signal. The estimated frequency offset is used for frequency down-conversion in the digital domain to obtain the baseband OFDM signal. With this method, all data-bearing subcarriers should fall into the OFDM bandwidth after frequency down-conversion. The validity of the method is confirmed by an experiment with 20 Gb/s OFDM-PON downstream transmission.