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visible light coomunication

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(joined June 2014)
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i try this project visible light communication using OFDM with QAM scheme. for that i have designed all the blocks and and using LED as transmitting source but the problem i am getting is that the system is not able to detect the transmitted data and the min BER is 1. and when i use directly modulated laser in analog mode i am getting the exact data that i have transmitted.
but the same i result i want using LED at visible frequency that is at 700nm..can somebody help me with that??

Responses (9):

    • #11955
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      saharsh singh
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      i try this project visible light communication using OFDM with QAM scheme. for that i have designed all the blocks and and using LED as transmitting source but the problem i am getting is that the system is not able to detect the transmitted data and the min BER is 1. and when i use directly modulated laser in analog mode i am getting the exact data that i have transmitted.
      but the same i result i want using LED at visible frequency that is at 700nm..can somebody help me with that??

    • #11970
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      Damian Marek
      Participant

      Hi,

      For QAM type modulation, and also including more advanced modulation schemes, it is more appropriate to use a BER Test Set. The BER Analyzer calculates the BER from the eye diagram. However, it expects a binary signal and not an m-ary signal you might be using for you QAM scheme.

      If this is not the problem, please send over your project file and I’ll take a look at it.

      Cheers!

    • #13942
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      moso.dodo
      Participant

      Hi;
      How can i get the eye diagram for 16QAM cause when i use BER analyzer tester the eye digram not opened? i use 4 channel (WDM) then transmit it throe FSO but at out put the eye diagram is closed? as attached

    • #13955
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      moso.dodo
      Participant

      attached please

      Attachments:
    • #13957
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      moso.dodo
      Participant
    • #13968
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      Damian Marek
      Participant

      The project file is working correctly, but I’ll try and explain what is happening to the Eye Diagrams. To put it simply I don’t think you should be using eye diagrams to calculate the BER for this system. Since QAM is a amplitude-phase modulation it’s going to be multi-levelled. You also need to create a NRZ signal and electrical signal that is a copy of the QAM transmitters you have to setup the BER Visualizer correctly. Finally, the BER calculation assumes a NRZ (RZ) modulation scheme and calculates the BER from the noise, decision time etc. I think the BER test set is a better way to calculate the BER as it sends bit sequences down the transmission link and directly compares the detected output.

      Using LED’s (or even Lasers) as a modulator at those bit rates is well beyond their limits, especially LED’s for a coherent system. The LED’s will include a lot of phase noise and their large line width will make it difficult. I think it is realistic to expect very high BER for LED’s in this current system.

      Cheers

    • #13970
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      moso.dodo
      Participant

      thanks, when i use BER test for 400m their is no result in BER but when i use 1000km we can see that their result acceptable?whey?

      • #13972
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        Damian Marek
        Participant

        In the BER Test Set? I’m getting BER of around 0 for the 400 m case, since there is low loss and ~0.5 for the 1000 km since there is high loss. Seems to be working for me.

        Regards

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