Cost-effective SFO compensation scheme based on TSs for OFDM-PON

A cost-effective sampling frequency offset (SFO) compensation scheme based on a simple training symbol (TS) is proposed and experimentally demonstrated in an orthogonal frequency-division multiplexing passive optical network (OFDM-PON) downlink transmission system. For SFO estimation and compensation, two TSs are used, while one of them is also used for timing synchronization and channel estimation. In addition, the performance of the SFO compensation scheme is investigated using four optical network units (ONUs) and one optical line terminal in an asynchronous intensity-modulated and direct-detection OFDM system. Moreover, the error vector magnitude (EVM) performance with respect to the SFO error is evaluated. The experimental results indicate that the SFO estimation accuracy of the proposed scheme is within ±2 ppm under an SFO ranging from −200 ppm to +200 ppm. When the SFO error is 2 ppm, the EVM penalties for ONU1-ONU4 are all below 1 dB. In addition, aided by the proposed scheme, up to ±200 ppm SFO can be successfully compensated with an EVM penalty under 1 dB.