- This topic has 10 replies, 6 voices, and was last updated 9 years, 5 months ago by Alessandro Festa.
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June 6, 2015 at 11:38 am #21429ferasParticipant
really what is the secret in this program , i designed tow same simulation and i got tow different result < what is the reason?
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June 6, 2015 at 9:42 pm #21435RavilParticipant
Hello Feras,
If I understood you situation correctly, you designed two the same schemes on two different layouts. If, according to your question, you have two different sets of results, then the main reason can be the sequence generated and transmitted by PRBS in your schemes. You can check this by disabling random sequences from PRBS’s properties. You should be able to get the same results for both of your schemes after disabling.
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June 6, 2015 at 11:20 pm #21436RavilParticipant
By the way, I have just check my previous guess with my old version of OptiSystem. I have noticed that each single time (by default) the simulation runs a random value is used for noise and the bit sequence generator (PRBS). Hence, theses random settings should make the resulting BER vary from one run to another! However, if you start increasing bit sequence length the difference between simulations decreases and you receive similar results for all your runs.
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June 7, 2015 at 9:35 pm #21442Dr. MohammadMahdi AriannejadParticipant
I have the same issue, my colleagues told me one thing can influence is the performance of your computer I mean your ram or even your CPU, cause is because we are using beam propagation method. if you found a way to solve this matter please share, thanks.
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June 8, 2015 at 1:16 am #21459Abhishek ShramaParticipant
Hello Feras and MohammadMahdi Ariannejad
the same has been discussed earlier. you can check for details: -
June 8, 2015 at 2:06 am #21462Alessandro FestaParticipant
If I may add: this should not be surprising. If you run a very short (= short bit sequence) BER test in the lab, you usually end up with different BERs every time…
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June 8, 2015 at 4:22 am #21466Ashu vermaParticipant
Hello, I am agree with Ravil completly.Also Alessandro gave a good point,in general low bit sequence also cause this type of problem.Please visit the link given by abhishek as Damian gave good points to disable the random seed and other parameters to get same results every time from same system.
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June 11, 2015 at 11:31 am #21609ferasParticipant
thank you all , i solved the problem by set the same prbs
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June 11, 2015 at 11:41 am #21610Alessandro FestaParticipant
You are welcome feras!
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June 11, 2015 at 11:57 pm #21628RavilParticipant
You are welcome, feras! And thank you for confirmation of my guess. Good luck with your work!
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June 17, 2015 at 11:04 am #21778Alessandro FestaParticipant
Now that I also discovered this issue, I thinkthat it is better to disable by default the Random Seed noise…I remember in the past many simulations made at small steps of OSNR where the BER did not have a monotonic relation with OSNR and I wondered why!
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