A method and system for measuring chromatic dispersion, experienced by ASK/PSK modulated optical signals, are provided. Dispersion measurement is enabled either by encoding an additional overhead at lower baud rate or by monitoring signal SOP or RF spectrum of signal SOP. The bulk chromatic dispersion of the link is measured by analyzing the dispersion broadening of the overhead constellation or signal temporal diagram, or time-overlapped signal diagram, or overhead spectrum. This information is used to reduce the computation time required for electronic recovery of a highly dispersed signal.