Experimental demonstration of 30 Gb/s direct-detection optical OFDM transmission with blind symbol synchronisation using virtual subcarriers.

The paper investigates the performance of a blind symbol synchronisation technique for optical OFDM systems based on virtual subcarriers. The test-bed includes a real-time 16-QAM OFDM transmitter operating at a net data rate of 30.65 Gb/s using a single OFDM band with a single FPGA-DAC subsystem and demonstrates transmission over 23.3 km SSMF with direct detection at a BER of 10(-3). By comparing the performance of the proposed synchronisation scheme with that of the Schmidl and Cox algorithm, it was found that the two approaches achieve similar performance for large numbers of averaging symbols, but the performance of the proposed scheme degrades as the number of averaging symbols is reduced. The proposed technique has lower complexity and bandwidth overhead as it does not rely on training sequences. Consequently, it is suitable for implementation in high speed optical OFDM transceivers.