Dear Hidayah,
please refer to the examples in OptiSystem Example Library located at the following link for more information and guidance. If you still have the problem, please email the project as a zip file to ahmad.atieh@optiwaave.com and I’ll check it for you and try to provide feedback.
C:\Users\USER NAME\Documents\OptiSystem 17.0 Samples\Advanced modulation systems\OFDM systems
Regards,
Ahmad