Dear Alistu,
The process that is used is as follow.
You set the maximum possible subcarriers and the number of used carriers at the port. As a result, the number of bit in the sequence used in BERT will be a fraction of the Sequence length (Bit rate *80/128) set in the Layout Parameters “Sequence length”.
This number will be used in QAM Sequence Generator as it groups each four bits into a symbol.
Please use the example (OFDM Coherent Detection Single Port Single Polarization 16QAM.osd) in OptiSystem 17 that describes properly the setting of each component. The number of FFT points in the OFDM Modulator has to be larger than the number of subcarriers. This is only used in an old obsolete component. A replacement component is created in newer versions of OptiSystem that doesn’t set the FFT points.
Please send me an email at ahmad.atieh@optiwave.com for further discussions.
Regards,
Ahmad