SSB-OOFDM

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I have been trying to plot EVM v/s Received power in a DD-OOFDM system. The constellation seems to be good. Also the BER shown by BER Test set is zero. But I can see that EVM is not zero, not an issue. Now my problem is, when I tried to plot EVM v/s Received power in the Report window of optisystem, the plot showed the EVM at zero too, which by seeing the EVM values given by OFDM demod is clear that it is showing wrong plot. Also, the eyediagram for OFDM system seems to be unusual. I am using optisystem Product Version: 13.0.3.474.

Thank you.

[Damian Marek]

Gokul,

I am not seeing this issue. When I use your project to make a plot of the EVM vs Transmitted Power I get the attached screen shot. It shows the EVM is non-zero and different for different carriers. Are you getting any warnings during the calculation?

Can you elaborate on the eye diagram not being correct? Is it possible you mean the constellation diagram? It seems normal to me!

Regards,
Damian

[Dr. Dhiman Kakati]

Hello Damian, I can mention here one issue. When we plot a graph as you have attached here for Rx power at the Rx input vs EVM (%). it is clearly noticeable that for lesser received power the EVM is less but according to me “for lesser received power the EVM should be more” i.e. for any system for lesser received power the EVM should be more and for greater Rx power the EVM should be less. (point to be noted that here I have considered that there is no fiber non-linearity because for much higher power the case will be opposite as I have mentioned above i.e. after a certain value of larger Rx power the EVM also start to increase)

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Hi Damian,
Thank you for the reply.
I have re-attached the screenshot that you have attached above after editing the picture, where I showed my point of confusion.
Since the EVM measurement shown by the OFDM block was never a zero in any of the iterations, the graph should not have been plot with points in the x-asis (power plot). But there are some points in the x-axis. Theoretically, for this system, the EVM should have been high at lower power and it should have been decreasing as the power is increased and then again EVM increases at a point where the fiber non-linearity come into play.
Please help.

[Damian Marek]

Thanks Gokul (and thanks Dhiman!). Clearly you are both correct and the plot is wrong, I am not sure what I was thinking when I wrote my first reply!!! This looks like a bug to me for iterations and the results calculation of the OFDM component. You can work around it by simulating a single iteration. Do not use a sweep. I, however, understand this is not a great fix when you want to simulate multiple power levels. Hopefully, we will get a fix for this soon.

Thanks again

[Dr. Dhiman Kakati]

Thanks Damian for your kind reply. the point to be noted is at any real system the EVM can not be zero except ideal system.

Regards,
Dhiman

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Thank you Damian, for making it clear. I was getting worried about this.

[Damian Marek]

Gokul,

Apparently the OptiSystem team was already aware of this bug and it will be fixed in OptiSystem 14.1.

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Hi Damian, thanks for the reply. But Optisystem 14 is already in already there in the website. Is is just 14?

[Dr. Dhiman Kakati]

Hi Gokul, I think 14.1 will be the updated version with bugs fixed, Hope for your problem solved soon

Regards,
Dhiman

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