The disclosed systems and methods for monitoring, by a coherent optical monitor (OPM), generalized optical signal-to-noise ratio (gOSNR) of an optical channel, the method comprising: i) receiving, by an input port of the coherent OPM, a first signal and a second signal, wherein: the first signal and the second signal include same data, the first signal is an optical signal received from the optical channel, and the first signal is affected by a noise; ii) processing, by a digital signal processor (DSP) of the coherent OPM, the first signal and the second signal and extract the data from the first signal and the second signal; iii) computing, by the DSP, a first correlation between the data from the first signal and the data from the second digital signal; and iv) computing, by the DSP, a first gOSNR based on the first correlation.