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

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    • #67711
      Luis Vallejo
      Participant

      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

      Problems

    • #67961
      Ahmad Atieh
      Moderator

      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

      Attachments:
      +1
    • #68788
      Sher Afraz
      Participant

      (Awaiting moderation)

    • #68789
      Sher Afraz
      Participant

      (Awaiting moderation)

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