Link Budget

[Ranjeet Kumar]

Hi eveyone,

How i could calculate Link Budget in FTTx Networks. Is link budget and power budget is the same thing or different.
how could i calculate link budget in wdmPON. I am attaching osd file of WDM PON.

[ZULKARNAIN]

Hi Ranjeet..
Link budget and power budget are two different things but are related to eachother. A data link will only operate if the cable plant loss is within the power budget of the link.
The terms “power budget” and “loss budget” are often confused.

The power budget refers to the amount of loss that a datalink (transmitter to receiver) can tolerate in order to operate properly. Sometimes the power budget has both a minimum and maximum value, which means it needs at least a minimum value of loss so that it does not overload the receiver and a maximum value of loss to ensure the receiver has sufficient signal to operate properly.

The link budget is the amount of loss that a cable plant should have. It is calculated by adding the average losses of all the components used in the cable plant to get the total estimated end-to-end loss. The link budget has two uses, 1) during the design stage to ensure the cabling being designed will work with the links intended to be used over it and 2) after installation, comparing the calculated loss to test results to ensure the cable plant is installed properly.
For your reference i am attaching the link which might help you in calculating link budget in FTTH networks.
http://scialert.net/fulltext/?doi=rjit.2010.127.138&org=10

[ZULKARNAIN]

For your reference i am attaching the few more links which might help you.
http://www.thefoa.org/tech/lossbudg.htm
http://www.broadbandproperties.com/2007issues/jun07issues/corning_june.pdf
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0ahUKEwi14oa-86fLAhVBbY4KHWrmAWYQFgg1MAU&url=http%3A%2F%2Fresearch.ijcaonline.org%2Fvolume92%2Fnumber6%2Fpxc3895050.pdf&usg=AFQjCNH8rtQNHPwv9FoBXGfAAEcSR9n0Kg&sig2=ayqcAlNx2FHcTiAMnQW4sw&bvm=bv.116274245,d.c2E

[alistu]

Hi Ranjeet,

Link budget and power budget are the same. It involves calculating all the losses and gains in the transmission line to see how much power should be sent for the received signal power to have at least a certain power. In can be calculated this way:

Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB)

Regards

[Aabid Baba]

Hi Alistu,
You have mentioned gains and losses in the above mathematical expression. Can you please explain what these gains and losses correspond to.?
does the loss term include all the losses in the optical channel like dispersion, attenuation,scattering and all ??
Gain corresponds to what?

Regards

[alistu]

Hi Aabid,

Loss in the system corresponds to the attenuation of the fiber, as well as insertion loss of the connections and any other loss associated with components. Dispersion and nonlinearities cannot be considered loss, even though they deteriorate performance. For compensate for these effects, sometime power penalties are considered in the power budget equation.

Regards

[Aabid Baba]

hi alistu,
There must be some specific expression for in co operating the losses like insertion and attenuation. I guess the expression you mentioned above is a generalized expression. As far as i am concerned , we always calculate losses in a system in logarithmic domain. this is the reason i asked what losses and gains correspond to.
Anyways thanks.
Reagrds

[alistu]

Losses and gains very much depend on the components used i a system, and unless a specific system is being discussed, you would find the above relation for power budget. And as it can be seen, logarithmic scale is being used in the relation. I only wanted to clarify that dispersion and nonlinearities are not loss.

Regards

[Aabid Baba]

Hi alistu,
I got your point then only when you mentioned about it. I was just asking if you got a specific mathematical expression for calculation of power budget. i want to add this power budget to my research interest program. It is a good parameter that can be added to your thesis.
Anyway thank you much.
Regards

[alistu]

You’re welcome. Indeed power budget should always be taken into consideration in practical systems. All losses and gains can be calculated in the above formula. In case you want to expand it for a specific implementation, I would be happy to help.

Regards

[Aabid Baba]

Hi Alistu,
Once i am done with my majors i will definitely go for the cost analysis and power budget of my system design. I would definitely need some help and i would no doubt take suggestions and help over here. i hope you will be available then.
Anyways thanks again.
regards

[alistu]

I hope so too. And good luck with your research.

Regards

[Aabid Baba]

thank you Alistu!

[FAYIQA NAQSHBANDI]

Hi Ranjeet

Correctly mentioned by alistu..that link and power budget are the same.Term power budget is mostly used but u wil find a few papers using the term link budget too but anyway both have the same significance.
Now for calculating the power budeget of a WDM PON system you can use the formula

Power Budget = Transmitted power – Reciever sensitivity

Also calculate the total losses of your system.
Then make sure that the power budget you calculate using the above equation is higher than the total loss of your system.Take the losses due to MUX,Fiber and all other components into consideration to calculate the total system loss.

If your power budget comes out to be low than the total loss you can then make use of amplifiers at the OLT and ONU terminals to improve the reciever sensitivity of your system.

[Aabid Baba]

Hi fayiqa,
i want to know that where from did you get this mathematical expression for power budget??
Doesn’t it change as per our system designs? Or is it your are generalizing it ?
Also please can you explain further how do we calculate losses caused by each component??
Regards

[Ranjeet Kumar]

Thank you all for considering my queries and make me understand by providing good references and solutions.
Now, i am able to understand and able to find Link Budget of FTTx.

[FAYIQA NAQSHBANDI]

Hi Aabid

Since the question was asked for calculatinjg the power budget of WDM PON systems so my answer was specific to the particular systems.For other systems the formula might vary a bit but generaly for any system power budget is the difference between the transmitted power and the power level measured at the reciever end ( Reciever Sensitivity).

And for calculating the loss of each component check table 11.2 in the link i am posting.

http://ops.fhwa.dot.gov/publications/telecomm_handbook/chapter11.htm

Hope its helpful

Regards

[Aabid Baba]

Hi fayiqa,
Thank you so much. I was just inquiring about it. You mentioned it pretty right that for different systems the formula might vary a bit and i have myself seen lot of variation in the generalized mathematical model itself. And thank you for posting the link it seems to be very helpful.

Regards

[FAYIQA NAQSHBANDI]

You are welcome Aabid 🙂

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