Large EVM of OFDM 64-QAM signal when the constellation is super good

[Luis Vallejo]

Hello,

I am working with M-QAM and OFDM signals. However, I have some errors in 64-QAM signals. For simplicity, I started to work with electrical back-to-back (EB2B).

The project has fourth layouts: 1. EB2B 16-QAM, 2. EB2B 64-QAM, 3. EB2B 16-QAM BER and 4. EB2B 64-QAM BER.
The 16-QAM (EB2B) works fine, but the 64-QAM does not work good. Althought the received constellation is ok, the EVM is not ok.
The EB2B 16-QAM signal works fine. The EVM (proccessed by MatLab) is below 1%, which is good. However, the EB2B 64-QAM EVM is quite high. It is larger than 16% and it must not be like that. According to the received constellation, it should be less than 1%. I have checked the transmitted and received constellation and it looks like ok. I checked where the symbols are located and they look like that they are in the correct quadrant. Nevertheless, it looks like that some symbols are not correct.

I attach a brief MatLab file which proccess the trasmitted and received constellation and give us the EVM.
I also show you a sample result which the constellation is super ok, but the EVM is not… Of course, I have checked my MatLab file with 4 and 16-QAM signals and the EVM is good.

Finally, I also ask you help about the BER. The BER for 16-QAM (and 64-QAM) is quite high, i.e. 0.5. With the constellation (16-QAM), the BER should be lower than 1e-5… Are there anything which it is not ok? I am not sure if it is working correctly…

Best regards,

Luis

PD. My optisystem is v17

[Ahmad Atieh]

Dear Luis,
I’ve sent you by email an edited version of your project which resolved the issue. It must be calculated using OptiSystem version 17.1 because there is a bug in earlier versions, which is fixed. As a result, you may get zero BER as shown in the attached image.
Regards,
Ahmad

[Sher Afraz]

(Awaiting moderation)

[Sher Afraz]

(Awaiting moderation)

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