Improved Pilot-Symbol-Aided Phase Estimation Algorithm in Homodyne Coherent Scheme

Abstract

This paper studies the carrier phase recovery based on pilot symbols in a single carrier system. The system model considered in the paper includes channel additive white noise, phase noise, and device bandwidth limitations. In optical transmission systems based on high-order modulation, the effect of phase noise that affects the phase of the received carrier on system performance may be relevant. We propose an improved pilot symbol aided optical carrier phase recovery (CPR) method, which uses a fixed symbol set for noise suppression in M-QAM. Through the simulation of the 64-QAM system, the performance of this method is studied and compared with the CPR method without a fixed symbol set. The results show that CPR with a fixed symbol set is much better than CPR without a fixed symbol set. In addition, the use of maximum likelihood (ML) phase estimation after pilot symbol assisted CPR can be used to further improve the laser phase noise tolerance. For a dual-polarization system, by inserting pilot symbols in different time slots with different polarization states, the system performance can be further improved.