Low-complexity time synchronization algorithm for optical OFDM PON system using a directly modulated DFB laser

In this paper a low-complexity time synchronization algorithm for optical orthogonal frequency division multiplexing (OFDM) is proposed. The algorithm is based on a repetitive preamble that allows the use of a short cross correlator with an exponential average filter for postprocessing before a threshold detection. The signals in the correlation have been quantized with 1 bit, and the correlations have been implemented as a hard-wired tree adder to reduce the hardware cost. This solution has been verified in a passive optical network (PON) system using a directly modulated distributed feedback (DFB) laser achieving excellent performance with low computing processing complexity even in low signal-to-noise ratio scenarios. Finally, a parallel hardware architecture has been proposed for this time synchronization algorithm, and it has been implemented in a field programmable gate array device reaching a sample rate throughput up to 7.4 Gs/s.