Hi Marvi Grover
Well a number of discussions have already been held on to how this is supposed to be done.
you need to add a MATLAB component to your layout. Turn off intensity scintillation in FSO channel. Load your MATLAB component by program of the corresponding fading model you want to employ. You would need to mention the path of your program in MATLAB component as well.
i am posting link to a beneficial post. Here it goes : https://optiwave.com/forums/topic/log-normal-channel-in-fso