Duobinary Shaping and Phase Correction Algorithm for Faster-than-Nyquist Coherent Optical Transmission Systems

摘要

The increasing shortage of spectrum resources makes researchers pay much attention to how to improve the spectral efficiency. Faster-than-Nyquist (FTN) coherent optical transmission is one of the most promising techniques to improve the spectral efficiency achieved by duobinary shaping. In this work, a FTN coherent optical transmission system is constructed containing transmitting side and receiving side. On the transmitting side, signals are transmitted after QPSK or 16QAM modulation with duobinary shaping. On the receiving side, the laser phase noise is eliminated by a pilot aided blind phase search (BPS) algorithm. Then the duobinary-shaped 16QAM or QPSK signal is processed by the maximum likelihood sequence estimation (MLSE). The constellation diagrams prove the effectiveness and convergence of the proposed algorithms. Moreover, the numerical results verify the relationship between the optical signal to noise ratio (OSNR) and the bit error rate (BER). Meanwhile, it is obvious that the FTN coherent optical transmission with duobinary shaping can improve the spectral efficiency effectively for signals of different modulation formats.