Thanks Alistu for the effort, what i tried doing is connecting directly without optics, and the time window for its calculation is longer. when you run the simulation, it takes more time for its calculation. And i dont want to use 256 subcarriers out of 512. I want to use just 256 subcarriers out of 256.. is it possible to do that in the OFDM blocks… i have connected directly without optics it takes more time for its calculation. I attached the file below.