I know this image so much coz i saw it alot while my gradutaion project...
Look to calc. SNR from PSD figure..it is 99.99% that u create this image by using Matlab or simulink anyway
u will going to create a func. which 1'st search for the max. in the BW of interest and then store the its value (and the value of 2 or 3 points left & right from the peak)
then u sum all the values from 0 to the end of BW (without taking the points of the peak)
So u now got the signal power value and the noise power..