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Modulation format

(joined August 2015)
Participant

Hi all,
I have tried many advanced modulation format to implement such as 4-QAM, 16-QAM, QPSK, DQPSK and find good result for all of them. So my question is is there any limit in terms of bit error rate (BER) and transmission distance for these modulation schemes.

Regards,
Dhiman Kakati

Responses (11):

    • #27846

      Hi all,
      I have tried many advanced modulation format to implement such as 4-QAM, 16-QAM, QPSK, DQPSK and find good result for all of them. So my question is is there any limit in terms of bit error rate (BER) and transmission distance for these modulation schemes.

      Regards,
      Dhiman Kakati

    • #27847
      Profile Photo
      Abdallah Ismail
      Participant

      Sure, It is very nice to increase the constellation level to increase the data rate or the transmission rate. However, as you are increasing the constellation level, you will use much power and hence the non-linearity will appear in long haul.
      DP-QPSK is the most common used one.
      DQPSK is used to ease the detection without LO.

      • #27850

        Hi abdallah,
        I am asking about modulation format comparison, i.e. I want to know about the limitation of the modulation formats I have mentioned, I agree to you that differential modulation scheme is used for making the system cost lower i.e. at the receiver side no laser source is needed and the receiver is also simplified in comparison to that of coherent detection. Thanks for the reply.

        Regards,
        Dhiman

        +2
        • #27887
          Profile Photo
          alistu
          Participant

          In your examples of advanced modulations, there was no mention of optical OFDM. If you want to also consider that, I think in terms of tackling channel dispersion, OFDM has better performance than the aforementioned (and of course, is more complex). However, the high PAPR may cause problems regarding nonlinearities.

        • #27901

          Hi Alistu,
          I agree that using OFDM we can achieve higher bit rate as multiplexing is done here, The reason I didn’t mention about OFDM is inside OFDM also i have seen that some modulation technique is used such as 16-QAM etc. so i asked the question in the very basic level. Thanks Alistu for the reply.

          Regards,
          Dhiman

        • #27908
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          alistu
          Participant

          You’re welcome Dhiman. By the way, I don’t think some modulation formats such as 4-QAM (or even QPSK in their basic form) can be considered as “advanced” modulation formats. I suggest you consider the paper “advanced optical modulation formats” by Peter Winzer, and also visit the page below:

          Advanced Modulation Formats

          Kind regards

        • #27909

          Thanks Alistu for attaching the paper, I will definite go through it.

          Regards,
          Dhiman

    • #27848
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      alistu
      Participant

      Hi Dhiman,

      If by limit you mean Shannon channel limit, I don’t know how much has Shannon theory regarding channel capacity been applied to optical fiber channel and systems (which has nonlinear effect for high powers) and I assume it is complicated (I have read some papers in this regard two years ago and the limits for some constellations were rather experimental than theoretical). However, researchers are constantly trying to achieve higher bit rate-distance product using methods such as channel estimation and equalizers.

      Regards

      • #27852

        Hi Alistu,
        I am not asking about the shannon channel limit for a optical fiber system, I want to compare the above modulation format in terms of bit rate, so can you tell me what are the factors that governs the bit rate in any of the modulation scheme, taking same input bit pattern. I agree to you that u mentioned “Researchers are constantly trying to achieve higher bit rate-distance product using methods such as channel estimation and equalizers.”. Thanks for the reply.

        Regards,
        Dhiman

        • #27886
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          alistu
          Participant

          If you are not referring to Shannon limit (which I don’t know if actually can show the limit), then I don’t think there is any way to determine any limits for this. Of course, you can find papers regarding comparison of these modulations performances in different systems, but this doesn’t mean limit I think.

          Regards

        • #27900

          Thank you so much Alisu for your kind reply. I also believe that using different techniques such as channel estimation and equalizers as you mentioned in reply #27848 the bit rate can be increased. I will look into this as my next area to study.

          Regards,
          Dhiman

        • #27907
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          alistu
          Participant

          You’re welcome. It is more a question of which modulation format gives a better performance under a certain condition (such as a channel with low/high noise, etc). I believe comparing all the modulations in terms of performance in a certain system can even be a good subject for a paper and many papers can be found doing this.

          Regards

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