Radio over fiber SCM ASK example problem

[Debanjan Sarkar]

hello all,
I have run the radio over fiber scm ASK. osd from examples given with the software. In this design when i change the power of cw laser the q-factor of the system change with a fraction only. the data that i have got are given below
cutoff frequency of am demodulator=0.6
cw laser power BER analyser1 q-factor value
0 dbm 8.42005
6 dbm 8.54212
12 dbm 8.42961
18 dbm 7.84567
24 dbm 8.14978

my question is ” am i able to plot BER curve with this value that is almost same and why the values of q -factor not change with the value of power??”
find the attachment of the file.
thank you

Attachments:

1. Radio-over-Fiber-SCM-ASK.osd

[alistu]

Hi Debanjan,

I ran the simulation for some values of laser and got results different from yours. What’s more, the results had slight changes by repeating the simulation. So I suggest you increase the sequence length (say, to 4096 or 2048) and do the simulations again. I did this for three laser values and the results showed constant yet rather small improvement by increasing the power.

Regards

[Debanjan Sarkar]

thank you alistu. i will try.

[Debanjan Sarkar]

For what reason this Q value is constant irrespective of any value of laser power. In practical scenario this should not occur. Can you suggest how I can plot the BER curves in this particular case.

[alistu]

To get an understanding of how to plot BER vs laser power I suggest refer to the following page where it has been explained in details for same same case (power vs BER). We can ask any further questions you may find here:

http://www.optiwave.com/resources/applications-resources/optical-system-lesson-4-parameter-sweeps-ber-x-input-power/

Regards

[Debanjan Sarkar]

thank you alistu. but can you tell me reason why Q value is almost constant??

[alistu]

Can you please upload the image of the plot you have acquired using sweep iterations? If you consider a wide range of launched power and do the simulations, changes in some input power areas must be evident. Otherwise, I am guessing the input power range has not been considered wide enough.

[Ravil]

Hi Debanjan,

If I am not mistaken and remember it correctly, I have such a problem of “not changing Q-factor” couple times. As Alistu recommended, I did increase the range of my power set and that gave me Q-factor dependence. At the same time, I would recommend you to look at the regime that you are working at for your launched powers. It is know that high values will increase the influence of non-linear effects in your system.

[Ravil]

On the other side, small values of launched power will decrease you power received and bring it close to the threshold of your receiver. Anyways, as it was recommended by Alistu, please upload the image of your plot and indicate the whole range of powers that you have worked with. It will definitely help us to better assist you with your question…

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