You’re right. I was merely suggesting that it seems your implementation of the system is different from that of the sample. For example, I have used your channel in optisystem sample CO-OFDM (see the attached file) and you can see that the error is near to the error given by optisystem sample for a back-to back system. You get BER=0.008 for the system attached below, while the BER for the implementation attached in your post is always around 0.5.