Hello Sam Sung,
You’re right and I think the better results obtained from optisystem 13 are due to the fact that it makes use of pilot signals in the OFDM block. About what you mentioned earlier about your constellation diagram and how it was different from mine, I think the reason is that I am using a Matlab program for the OFDM block, and not the Optisystem block. And although my program is probably correct, in every Optisystem version it gives a different constellation diagram! Si I think it’s a bug related to Optisystem and its co-simulation with Matlab.