Home Forums SYSTEM QAM Transmitter and Receiver

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    • #27687
      Sasha
      Participant

      Hi all,

      I am trying to connect the optical fiber between QAM modulator and demodulator. Can anyone please help me out, what components should I use to connect optical fiber between them?

      I tried to implement the QAM sample file given in optiwave tutorial.

      Digital modulation – QAM

      At the transmitter side, the constellation diagram is good as shown in the tutorial. I tried connecting the constellation diagram in the receiver side. I will attach the output screenshot. Please help me out whether it is right or not.

      Thanks in advance.

    • #27690
      alistu
      Participant

      Hi Sasha,

      Can you please upload your implementation osd file if it is possible? Thank you.

    • #27691
      Sasha
      Participant

      Hi Alitsu,

      I am working in Optisystem version4 and it is available in my school. You can find the file QAM – Transmitter and Receiver.osd in samples library. I will upload the file when I am in school.

      Thanks in advance.

    • #27798
      Sasha
      Participant

      Hello all,

      I attached a file here. Please take a look at it.

      Thanks in advance.

    • #27804
      Sasha
      Participant

      Hello all,

      I implemented the Coherent Optical Transmission Optical System given in optiwave tutorial.

      Coherent Optical Transmission

      I got the different constellation diagram at the receiver.

      Can anyone please help me out.

      Thanks in advance.

    • #27817
      Participant

      There is always some issue if you simulate system designed in older version in a newer version. So what you can do is install the newer version and try it. If the problem still exists please do share.

      Regards.

    • #27825
      alistu
      Participant

      Hi Sasha,

      I checked it by comparing it to the OptiSystem sample coherent 4-QAM and I must say I got really different constellations by the changes I applied to the implementations. By changing M-ary pulse generators bias and gain (gain=-2, bias=2) which were the main problem I think, I managed to get the constellation you can see. It was the best I could achieve although I tried make changes exactly according to the QAM sample. Here I have used coherent receiver component, even though yours was all right.

      Regards

      • #27849
        Dr. Dhiman Kakati
        Participant

        Hi Alistu,
        I have seen in many cases that the constellation points gets elongated in a circular fashion as that you have attached in the comment above #27825, So can you tell me the reason for waht it happens so ??

        in some another cases I have seen that if we do not connect the fiber the constellation comes quite good and clear points at the receiver side but when we add a fiber (Standard single mode fiber) the constellation points are shifted (not elongated) in anticlockwise direction. What may be the cause for this? Please anyone make me clear.

        I need to mention that I don’t want to use DSP in this case as using DSP we can correct this. I don’t have the design file with me now, If anyone has faced the same problem as me please answer here.

        With regards,
        Dhiman

        • #27877
          alistu
          Participant

          Hi Dhiman,

          I really don’t know the problem with the above simulation, as I tried to change it according to the sample file but did not manage to get the proper result. As for the rotation, you can refer to the below topic which I had started a while ago to read a whole discussion:

          Symbol Rotation in OFDM

          Regards

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