For 100Gbit/s（or above）Polarization Multiplexed-Quadrature Phase Shift Keying（PM-QPSK）optical coherent transmission systems

we propose an improved statistical moment-based intraband Optical-Signal-Noise-Ratio（OSNR）monitoring method and carry out its numerical simulation in such an established system.The results show that when this method is used

all the monitoring errors of RZ code modulated signals with different duty cycles are smaller than 0.5dB in the OSNR range of 5

2

5dB and in line with the requirement of the commercially available coherent receivers for the OSNR at the receiver end

taking the reference value of 14 dB

the system Chromatic Dispersion（CD）tolerance is 2 400ps/nm and that for the 1storder Polarization Mode Dispersion（PMD）

i.e.Differential Group Delay（DGD）

is 62ps/nm in the monitoring range of0.5dB.