Designing a TDM-PON bidirectional system

[Jamal Rajabi]

Hi everyone.

I’m new to optical communication and to OptiSystem as well. I am to design a TDM-PON bidirectional system using OptiSystem. I could find some materials and even papers regarding this topic. There exists a sample in software named ‘PON bidirectional’ or something like that.
As I understood it’s most likely to be a WDM system rather that being a TDM, since it transmits different frequencies over transmission line!

It seemed to me totally different from what I had learnt in communication course about TDM. Moreover, there is another sample file in software for OTDM and it’s clear how it divide frames for multiple users but I really can’t get the point how the former sample use TDM!

Which is the part that we can conclude this sample is for TDM?
It may seem ridiculous to you but as I mentioned that I’m new and have no background experiences in this area, I’ve just got confused by obtained contents.

In advance I appreciate your attention.

[Damian Marek]

Hi Jamal,

You are correct that the sample file called “BPON Bidirectional” uses WDM to transmit data to users, but it is also a PON type network. A passive optical network is a telecommunications network that uses unpowered optical splitters to enable a single optical fiber to serve multiple users (this is heavily paraphrased from the link http://en.wikipedia.org/wiki/Passive_optical_network).

You’ll notice at the link provided they mention that time division multiplexing is most often used in these types of networks, but that doesn’t remove the possibility of other types of access systems (like WDM). You could also have a combination of WDM and TDM, mode division multiplexing, or code division multiplexing etc.

A passive optical network does not have to be time division multiplexed.

Hope this clears it up!

[Jamal Rajabi]

Hi Damian.

Thanks for your instructive answer.

Just for summing up, is the sample file entitled ‘PON bidirectional’ a kind of TDM network as well? This question was my main confusion, as I mentioned that I read somewhere this sample file is utilizing TDM along with WDM. But I still can not figure out its TDM part!

[Damian Marek]

Oh! I looked a bit closer this time and it looks like it is using both WDM and TDM. The backward and forward channels are centered at different frequencies while channels meant for different users are TDM. In this example though, there was no time division demultiplexer explicitly used. The BER for each separate user is calculated with all the bits, even the bits outside of their respective time window.

The upstream signal’s TDM nature can be seen if you open up the subcomponents for each user (ONU). They each have time controlled switches that only allow transmission in certain time windows.

Regards

[Jamal Rajabi]

Thanks Damian.

You showed me the aspects which I couldn’t find them out and I really appreciate your helps.
Hope you the best in both your personal and professional lives!

Regards

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