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LMS adaptive equalizer problem

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    • July 3, 2015 at 7:41 pm #22153
      mai fouad
      Participant

      I used a Matlab code of LMS (least mean square algorithm) to equalize the effect of the channel, it is working for a tapped delay channel generated in MATLAB but for optical fiber channel using optisystem, it doesn’t work well, i think the problem is in optical fiber impulse response, as it is not finite impulse response and the algorithm needs a finite impulse response but how to solve this problem? also i try to use electronic equalizer in receiver library but it also doesn’t work!

      attached the constellation of MATLAB channel and optical fiber channel.

    • July 6, 2015 at 2:10 pm #22218
      Damian Marek
      Participant

      There might be other sources of noise that your code cannot account for, like perhaps self phase modulation? What does your project look like?

      Regards

    • July 6, 2015 at 11:50 pm #22222
      Ravil
      Participant

      Hi mai fouad,

      In general, I am agree with you that proper equalizing or filtering should help in your situation with a finite impulse response. However, as Damian mentioned before, the other ideas about your question can come up after looking at your project channel layout or the screen shots of it…

    • July 7, 2015 at 12:14 pm #22226
      mai fouad
      Participant

      I agree with you that the problem in the noise of the system, as when i test LMS algorithm by just adding noise to the modulated signal (without optical fiber channel), it couldn’t compensate its effect, does this problem usually occur with LMS algorithm?

      • July 7, 2015 at 1:34 pm #22229
        Damian Marek
        Participant

        From my understanding of the LMS algorithm it can only compensate for dispersion effects from fibers. Have you tried disabling all of the other nonlinear effects? And even attenuation?

        Furthermore, the signal generated by the Matlab link creates a very structured constellation diagram. It seems like every point is on some sort of grid. The signal does not look truly random.

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