64-QAM OFDM constellation left-shifted

Dear all,

I am working on a project with M-QAM OFDM signals and RoF.
My current problem is with 64QAM signal. I get the constellation, which looks like very good, but it is not ok when I compute the EVM by MatLab. The EVM is higher than 30%!
To compute the EVM on MatLab I use to rescale the constellation. For 4, 16QAM signals work super great. The EVM is always as I expected. However, I cannot know what happen with 64QAM. The constellation, after signal processing on MatLab, looks like a left-shifted. I know that the rotation appears with fiber… but there is no fiber! I have also checked the signal at baseband and I found a peak in the center of data band… I also do not know why it is there… because when I use 4 or 16QAM the baseband data is great.

I know that I have to move OFDM OS12 to new OFDM component, but I need some results now and I do not have lot of time to change everything. I will do it very soon.

Could anyone help me?

Best regards,

Luis