Novel baud-rate estimation technique for M-PSK and QAM signals based on the standard deviation of the spectrum

A robust baud-rate estimation technique that is integrated into a coherent receiver prior to digital equalization and intermediate frequency estimation based on the standard deviation of the signal spectrum is presented. It is shown to operate from 4 to 25 GBaud QPSK signals with a maximum estimation error of 2% at the FEC limit of 3.8·10
^-3
.