Spectral efficiency

[Dr. Dhiman Kakati]

Hello Everyone,
I need to plot Spectral efficiency vs SNR curve for different advanced modulation schemes such as QPSK, QAM, MSK. So is there any provision to directly plot the curves of all the modulation schemes above mentioned. we can directly see from power vs wavelength is that MSK is most bandwidth efficient scheme. But I need to plot Spectral efficiency VS SNR for all of these above from my own like in the attached figure below. Thanking you.

With regards,
Dhiman Kakati

[alistu]

Hi Dhiman,

As far as I am concerned, there is no such parameter as spectral efficiency in OptiSystem that can be plotted. About a month ago I also needed to plot spectral efficiency, so I calculated the spectral efficiency by estimating the bandwidth of the signal from the bandwidth of the filters or using spectrum analyzers.

Regards

[Dr. Dhiman Kakati]

Hi Alistu,
So also need to follow the steps as you have done. can you please elaborate a more in detail about how you calculated manually. Thanking you.

Regards,
Dhiman

[alistu]

Spectral efficiency is the data transmitted per bandwidth unit. So you need to calculate the following relation to find it:

Spectral efficiency (bits/sec/Hz) = Bit rate / Allocated bandwidth

The allocated bandwidth can be estimated by either using the bandwidth set for the filters or by using optical spectrum analyzer.

[Dr. Dhiman Kakati]

Hi Alistu,
I am very much clear about the theoretical concept. so for plotting the graph i need to have Spectral efficiency values for different values of Signal ti noise ratio (SNR). The allocated bandwidth can be found out by using the bandwidth set in the filters. but for a finally designed system the Bandwidth will be fixed. do I need to calculate for different bit rate by changing the bit rate in the PRBS generator. Thanking you..

Regards,
Dhiman

[alistu]

Hi Dhiman,

For the final system the bandwidth will be fixed as well as the bit rate. So you would only have one value for the spectral efficiency in this case. If you want to change the bit rate for the final design, the you would have to change the bandwidth, since bandwidth is determined chiefly by bit rate.

Regards

[Dr. Dhiman Kakati]

Hi Alistu,
As I mentioned before that I need to plot the Spectral efficiency VS SNR graph so I need to have different SNR value so that the respective spectral efficiency I can calculate. for that what parameter of the system should I change in order to get various points on the graph.

regards,
Dhiman

[alistu]

In order to change SNR you can change various parameters of the system including fiber parameters so as to change the noise value, or launched power or amplifiers parameters. However, these factors do not change the spectral efficiency, since it only depends on the bit rate and the allocated bandwidth.

Regards

[Dr. Dhiman Kakati]

Hi Alistu..

Thank you for the reply. I think the spectral efficiency is fixed for a fixed modulation scheme or a system.
please inform if I am wrong…

Regards

[alistu]

You’re welcome Dhiman. As it can be inferred from the relation that I formerly mentioned, you are absolutely right. A designed system has a fixed bit rate and a fixed allocated bandwidth (since both the bit rate and the symbol rate determined by the modulation or coding scheme are the same).

Regards

[FAYIQA NAQSHBANDI]

Hi

How can we measure SNR directly in optiwave.Like for BER measurement we use a BER analyser.Is there any component that can help us in giving the values of SNR directly ?

Regards

[Aabid Baba]

Hi fayiqa,
As far as i know if you are designing a WDM system , then i believe you can use WDm analyzer present in the visualizer library of the optisystem. I gives you the SNR/OSNR of each channel in addition to signal power and noise power. However, you can verify it if we are able to calculate SNR of whole deign as a whole. Kindly check the screenshot below. Hope it helps.
Regards

Attachments:

1. 

   Capture5.jpg
   

[alistu]

Hi Fayiqa,

You can directly calculate the BER in OptiSystem and plot it using 2D graph versus any other available parameter without the need for other softwares. Please refer to the answer given by Mohamed a while ago as a solution to see if it helps:

Graph between BER v/s SNR

Regards

[Aabid Baba]

hi Alistu,
i went through the link suggested by you but i could not get it clear. He has mentioned to put the electrical carrier analyser after NRZ pulse generator at the receiver side ?? Where exactly do we have to put it on the receiver side??
Can you please upload some screenshot of the design where you have done it?
I would appreciate your efforts.
Regards

[alistu]

Hi Aabid,

Mohamed is either referring to a specific design (which was attached but deleted after a while) or he merely wants to mention that electrical carrier analyzer should be on the receiver side. Otherwise, there is no need for NRZ component for the lelectrical carrier analyzer to determine SNR.

Regards

[Aabid Baba]

Hi Alistu,
Thank you so much for the response. I noticed the design has been removed but if you please try to put in simpler words it would be easy to understand and implement. I got confused with his statement there. He has kept it too short there. Now as you have implemented it i want your help here. I would be grateful.
Regards

[alistu]

You’re welcome Aabid. Please refer to the example available in OptiSystem samples regarding electrical carrier analyzer as an example. You would just need to put the component where you want to know the SNR for. there is nothing confusing about it. I don’t know how to put it in a simpler way!!

[Aabid Baba]

Hello Alistu,
Thank you for your concern. I will definitely go through the sample osd file and if i find any difficulty i would mention it here only. It may prove quite helpful if it is so. Anyway i will try to do it the same way as you and mohammad have mentioned. Hope it works fine.
Regards
Aabid

[Ranjeet Kumar]

Hi,

I agree with Alistu Sir, there is no such parameters like Spectral Efficiency in optisystem.
As far as i know Spectral efficiency (bits/sec/Hz) = Bit rate / Allocated bandwidth. For spectral efficiency we use WDM analyzer.

[Aabid Baba]

Hello ranjeet,
Can you please tell me where in WDM analyzer are we able to determine spectral efficiency of the system.
As far as i know there is nothing like spectral efficiency parameter in WDM analyzer , may be i have missed it or something like that. Can you please also attach a screenshot. I am not sure though.
Regards

[FAYIQA NAQSHBANDI]

Hi every one.

What I understand from the discussion is that while working with WDM systems we can use a WDM analyser as aabid suggested to check the SNR values.But for any system in general we can use an electrical analyser for calculating SNR.
But wht if we want to calculate the Optical signal to noise ratio for any system..WDM analyser does give the value of OSNR but cannot be used in a system where wavelength division multiplexing is not used.So is there any component which can be used to calculate OSNR for any system design nt just being specific to WDM systems.

Thanks and Regards

[Aabid Baba]

Hello fayiqa,
you have put forth a very important point. Actually i have used only WDM analyzer only in WDM systems i am not sure about rest of designs. However i have a slight idea that it has some option for changing ports though i am not sure. I am not having access to the tool right else i would have seen it. If you are on tool you could check it if possible.
regards

[FAYIQA NAQSHBANDI]

Hi aabid

Not a problem.You can check whenever its convenient for you and let me know if WDM can be used for measuring the OSNR for any general system or is thr any other component that can give the value of OSNR in optiwave.

Regards

[Aabid Baba]

Hi fayiqa,
surely i will do it.
As far as i am concerned as of now i have not come across any OSNR calculator ( talking about implementation of of my own case) , however , there may be some which we are unaware of. And the WDM analyzer i mentioned in above comment, i have used it for WDM system having 4 channels. We shall explore it hopefully.
regards

[FAYIQA NAQSHBANDI]

Hi aabid….
I just tried using WDM analyzer but i could use it for only two sources.
Anyways, thanks and regards

[Aabid Baba]

you are welcome fayiqa.

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