BER / Eye Diagram

[Alexandru B]

Hello, i’m kind of new to this, but i have to implement in my thesis an example of an WDM of a fiber.
I’ve looked in your tutorial lesson 3 with the WDM Design. My problem is how do i interpret and what conclussions can i take from the BER Analysis/Eye Diagram: How do i know that the values of Max Q Factor, Min BER, Eye Height, Threshold, Decision Instant are plausible values. What are the tipical values for a practical implementation? For Q factor i think that it should be below 10^-9?

Please, i really need some help. Thank You in Advance!

[Ravil]

Hi Alexandru,

Each type of designed system has its own requirements (defined by recommendations of ITU-T, IEEE, etc.) for BER and, therefore, Q-factor. It is known that these two parameters are related BER=1/2*erfc(Q/sqrt(2)). According to ITU-T recommendations, BER is limited by 10^-12. The Q-factor is usually in the oreder of 10^1 power. Threshold parameter is used to define your decision criteria. By doing that, you can maximize your BER and corresponding Q-factor.

[Ravil]

I am attaching you a good explanation of main terms of eye diagram below. Please, take a look, it should answer most of the questions that you have as a learner. Here is a link for that as well: http://www.onsemi.com/pub_link/Collateral/AND9075-D.PDF

Attachments:

1. AND9075-D.pdf

[Ravil]

I would also recommend you to get more familiar with BER analyzer with OptiSystem manual that can be found on Optiwave website. The links for some forums about work with eye diagram are provided below:
https://optiwave.com/forums/topic/eye-diagram-2/%20
https://optiwave.com/forums/topic/question-about-eye-diagram/%20%20

EYE DIAGRAM

[Alessandro Festa]

I agree with Ravil; typical designs must guarantee BER<10^-12 or 10^-10. Please note that BER Analyzer can give you also BER after FEC correction (more info on FEC for example here http://www.ieee802.org/3/10G_study/public/july99/azadet_1_0799.pdf)

[Ravil]

Hi Alessandro! And thank you for bringing this point about the BER. When I indicated the value of a BER 10^-12, I meant the BER at the receiver terminal input for the group signal. If I am not mistaken, this value is defined in rec. G.941.1 of ITU-T. However, if we are defining a plausible value for BER in a channel that is digital, i.e. Ethernet of SDH hierarchy, it will be equal to 10^-9, in accordance with corresponding recommendations for digital communications.

[Alessandro Festa]

Yes Ravil, I usually work with SDH signals (STM-1…to OTU4) and typically we refer our systems for BER<1E-10

[Ravil]

Yes, Alessandro. You are right about SDH. I understand your statement and agree with that!

[Ashu verma]

Thank You Ravil Alessandro for making some good points.

[Author]

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