High-Precision and Low-Complexity Symbol Synchronization Algorithm Based on Dual-threshold Amplitude Decision for Real-time IMDD OFDM-PON

We propose a low-complexity and high-precision symbol synchronization algorithm based on dual-threshold amplitude decision for FPGA-based real-time Intensity Modulation Direct Detection (IMDD) OFDM-PON system. In addition, a new criterion to judge symbol synchronization accuracy is proposed firstly based on bipolar non-return-to-zero (NRZ) codes in time domain. Experimental results show that 95% synchronization precision rate can be achieved after 25km standard single-mode fiber (SSMF) transmission with the received optical power as low as -21dBm.Compared with the previously proposed one threshold symbol synchronization algorithm, the synchronization performance has been greatly improved which brings a maximum signal bit rate gain of 35% when the received optical power is lower than -16dBm.Furthermore, it is verified that the proposed algorithm is robust. It has wide transmission range which is applicable for OFDM-PON optical access networks within 100km and has good sampling frequency offset (SFO) tolerance which can cover the SFO up to 500ppm without any discard on synchronization precision rate. Finally, complexity analysis shows that our algorithm has the lowest computational complexity and hardware resource consumption which accounting for only 0.9% of system resources without any multipliers.