Difference between Eye Diagrams

[Sasha]

Hi all,

What is the difference between Digital Modulation – QAM and LED Modulation Response Eye diagram Patterns?

Digital Modulation – QAM link

Digital modulation – QAM

LED Modulation Response

LED Modulation Response

And in the text book they have given eye diagram pattern with upper and lower bounds to determine the logic ‘0’ and logic ‘1’ levels. Is it possible to set those bounds in BER analyzer in Optisystem?

Thanks in advance

[alistu]

Hi Sanjeetha,

The digital modulation (QAM) you are referring to is a type of “digital” modulation; the digital data is “coded” by a coding scheme to enter the channel (in the example provided in the link, the system even works in electrical domain). For example by QAM modulation in your case. In the case of LED modulation, “modulation” refers to the modulation of electrical signal into optical signal. So they are completely different from one another and different methods of each modulation should be compared with the other method of its own modulation type (optical or digital).

There are two major groups of optical modulations: Direct modulation and external modulation. The one provided in the link is direct optical modulation. This is not directly related to your question, but If you need to know more, please let me know.

Regards

[Sasha]

Hi Alistu,

I understand that what you are saying. Thanks for your reply. I tried implementing 4-QAM and got the eye diagram pattern like this. Can you please explain that? Here I have attached the pic.

I gave user defined bit sequence – 8bits ( 01100110)

Thanks in advance

[alistu]

You’re welcome. You haven’t attached any file(s) for me to be able to analyze, though.

[Sasha]

I attached file here.

[alistu]

Can you also attach the osd file?

[Sasha]

I am sorry, I changed some parameter in that file. But still I need to know about eye pattern.

Thanks in advance

[alistu]

The file seems to be belonging to the 64-QAm example you mentioned and the threshold detectors are set to that, while “bits per symbol value” of the QAM coder is set to 2 instead of 6. Also, you haven’t used the same bit sequence in all PRBS generators. I couldn’t find the original file in Optisystem samples. Can you please upload that for me? Thank you.

[Sasha]

Hello Alitsu,
Now I changed user defined sequence in whole system. Now I am attaching the file again. I am trying to get 4-QAM but its constellation diagram shows only two points but I am getting the proper output what I have given as input. For 64 QAM, they QAM sequence generator bits/per symbol =6.( i.e h=6 and M=8) that’s why In 4 QAM I changed bits/per symbol = 2(i.e h=2 and M=2).
I have attached 64 QAM and 4QAM files.

Thanks in advance.

[alistu]

Thank you for the file. For 4-QAm, you need to set the threshold detector accordingly. And there you go! Please refer to the attached modified osd file.

If you wish to see the eye more like the one in the link you have given, you need to increase the bit rate. For this purpose, I have used non-user-defined PRBS generators as the ones in the OptiSystem sample. Please see my attached modified2 osd file.

Regards

[Sasha]

I am not able to open the file. what should I do?

[Sasha]

I am getting an error message like this.

[alistu]

I haven’t seen this error before. It somehow says something about another application being open and so on. However, the file runs well in my computer. You can restart the computer and try again. In the meanwhile, may I ask which exact Optisystem version you are currently using?

[Abhishek Shrama]

Kindly run the file by closing other application .Since the error which screenshot you have attached shows that file is used at multiple programs.In another case sometimes file not downloaded completely and we start running it ,this may be the case here.Rest let me know if it than also exits.Then optiwave or Damian will address you.

[Sasha]

Thanks for your reply.

[alistu]

Is your problem hopefully over now?

[Sasha]

Hi all,

I tried implementing a 4 QAM Coherent Optical transmission system (using optical fiber). I am not getting a proper constellation diagram. What change should I do?

Thanks in advance

[alistu]

Hi Sasha,

The problem in your 4-QAM system is the fact that you have not set the M-ary threshold detectors parameters according toa 4-QAM system. I believe you have copied these components from an implementation of 64-QAM. Please take a look at OptiSystem coherent 4-QAM sample to see they should be set for your system.

Regards

[Author]

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