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 field programmable gate array-based real-time intensity modulation direct detection orthogonal frequency division multiplexing-passive optical network (OFDM-PON) system. In addition, a new criterion to judge symbol synchronization accuracy is proposed first based on bipolar non-return-to-zero codes in time domain. Experimental results show that 95% synchronization precision rate can be achieved after 25 km standard single-mode fiber transmission with the received optical power as low as -21 dBm. 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 -16 dBm. 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 100 km and has good sampling frequency offset (SFO) tolerance, which can cover the SFO up to 500 ppm without any discard on synchronization precision rate. Finally, complexity analysis shows that our algorithm has the lowest computational complexity and hardware resource consumption, which account for only 0.9% of system resources without any multipliers.