ofdm ftth network

[Boyka]

Please help me ,

i’m trying to design a 32 users ofdma network using optisystem

but it seems like there is something wrong , all the constellations are wrong , also the min ber is 1

i think i have a problem in my design or in choosing the correct position array

my design is in the file attached

i’m using optisystem 13.0.3

please help me

Attachments:

1. O_f_d_m.osd

[alistu]

Hi Abdulla,

In OptiSystem 12 component, position array is defined as the initial position of the OFDM subcarrier for each subscriber, while you seem to have determined the exact position of the subcarriers in posision array. Please see if this is true. BTW, you can use new OFDM components which have offer the capability of determining the exact position of each subcarrier along with channel estimation and so on.

Regards

[Boyka]

hello alistu ,

thank you very much , so according to my understand ,in optisystem 13 i can connect the ofdm modulator and demodulator without defining the position arrays ?

another thing , can you please take a look at my design that i attached above , is this topology correct or i’m missing something here

[alistu]

You’re welcome Abdulla. In OptiSystem 13 OFDM component, you can define subcarriers position in any way you like whereas in OS 12 components you can only define the initial position on subcarriers, and the subcarriers will be placed one after another starting from that initial position.

At a cursory look at your design I couldn’t find anything wrong, but I suggest you troubleshoot it step by step.

Regards

[Boyka]

that’s very helpful thank you alistu,

well i’m trying to open the file attached that i found on the site , but it says failed to load document from storage

despite that i’m having the latest version of optisystem , what is the problem then ??

Attachments:

1. OFDM-basic-with-upconversion.osd

[alistu]

The file you have attached opens in my system without any problems. Please make sure that you have downloaded the last OptiSystem version by checking it after you open the software. Just choose ‘about OptiSystem’ from “help” in menu bar and see the version of OptiSystem in the opened window.

[Boyka]

ok , that’s a snap shot from the help of the program

Attachments:

1. 

   222.png
   

[alistu]

I am also using the same version and managed to open the file. Since we should expect your version to open the file and yet it doesn’t, I suggest you contact Optiwave via each of the two e-mails that can be seen in the screen shot you have attached and ask for their help mentioning your problem.

[Boyka]

ok , i have attached the file after the modifications you told me sir

Attachments:

1. O_f_d_m_2.osd

[alistu]

Still this is not the modification that I meant and explained in my comment. Please tell me how many subcarriers and how many fft points do you want your system to have and determine the initial position of the subcarriers so that I set the values in the OFDM components (if you don’t want to use OFDM 13 components).

[Boyka]

i will sir , but before that , can we give it a try , can you sir save the file by your program and upload it here again , i think it may solve the problem

[alistu]

Here I have attached the file that you uploaded last at your request. I don’t know why you wanted me to do this, but I think this way it can be seen if the problem with opening the file that you did not manage to open was actually from your software version (which it should not be) or it was an exception.

Attachments:

1. O_f_d_m_211.osd

[Boyka]

thank you very much sir , the file didn’t open and give me the same message i told you before , now i’m completely sure there is something wrong with my version

[alistu]

Indeed! Please see my screen shot from the window that I told you to open and you will see the difference (even though both show the same version and others have also attached screen shots from the same version which exactly looked like mine). I suggest you tell Optiwave about this problem.

Attachments:

1. 

   screenshot-version.jpg
   

[Boyka]

the 3rd party licence is colored with red not blue as your version , that may be the problem

[Boyka]

i installed the program on another computer and the files worked now lucky

[Boyka]

i have been trying for two days to find the problem with my design , i tried to increase the power , decreasing the fiber length , using optical and electrical gain , changing the position array as user defined or let it automatic .

but nothing of all that solved the problem

i don’t know what to do next ?

Attachments:

1. O_f_d_m2.osd

[alistu]

Please make the change that I have told you in my former comments and see if the system works well after the modifications are applied. As I mentioned, it is hard to check everything and find all the problems (if there are other problems than this) easily and therefore, you have to do it step by step.

[Boyka]

i tried the modifications you told me , but i faced the same problem

i know that i tired you with my continuous questions , but I am in desperate need of your help sir

[alistu]

I checked the last file that you have attached here in reply #28596 and the changes are not applied to it (unless you need me to explain again). After you have made the modifications, please upload the file in this topic page so that I would be able to check for other possible mistakes.

[Boyka]

ok sir , the file attached is the one with the modifications

Attachments:

1. O_f_d_m_21.osd

[alistu]

Please do as I have explained in reply #28617 and I will set the values for you.

[Boyka]

ok sir thank you

[Boyka]

i installed the programe on another computer and baaam , the above files worked with no error

now ,

i just need for the 32 user , the following values for both the ofdm modulator and demodulator :

1- the number of subcarriers
2- the position array
3- the number of fft
4- the number of cyclic prefix points

can you give me the appropriate values of those 4 variables ??

i will be very appreciated

thanks in advance

[alistu]

I don’t know about the appropriate values, but values of FFT points=1024, number of subcarriers=512 and position array= 256 were the default values for OS12 OFDM components and I have seen them being used in simulations, yet these are not the best. It depends, you may want to use short-FFT for example.

[Boyka]

yes i know , but that is for only one user , i need the modifications for 32 user that’s what confuses me

[alistu]

I haven’t worked much on OFDMA, so I think if you cannot find any values in the papers, you can go on with the values you have already chosen. System with so many users is really hard to troubleshoot, so I suggest first you implement it with only 2 users and see if it works (unless you have already done that).

[Mohamed Ben zegalam]

Hi all,

I have question regarding the design that attached, it is look likes all ONUs (end users) share the OFDM demodulation component. which means the signal will be distributed to 32 users after converter from optical to RF and demodulated from OFDM not before. and that is not FTTH concept unless your design is for the building.

is any one know if we can send the multi OFDM signal using one multi-port OFDM at transmitter, and using N single-port OFDM demodulation at the receiver side with specified the sub-carrier location.

[alistu]

Hi Mohamed,

It depends on what you mean by multi-OFDM. If you mean OFDMA (which is an access scheme), then you should use one block since each user is subscribed to some specific subcarriers. Otherwise, You can use OFDM modulators and demodulators, each corresponding to one certain user at each end.

Regards

[Mohamed Ben zegalam]

Hi Alistu,

thanks for your reply, please may I have more information about OFDMA.
I agree with you about OFDMA, we should use one block OFDM modulation with multi-ports at the OLT or CO, but if we use the same concept at the ONUs (which is one block OFDMA demodulation) that means we have to split the signals after the OFDM demodulation (in the electrical mode, not in optical mode). I think this is not full FTTH, because the optical to electrical converter and OFDM demodulation happened before the fiber reach the end users (homes or ONUs). Am I right or not?

[alistu]

You’re welcome. I understand. I also think the signals are being split in electrical domain as you have stated. However, this is Fiber-To-The-Home, and not Fiber-To-The-Desk. In FTTD signal is converted to electrical domain only when it reaches the user, whereas in FTTH the signal can be converted into electrical domain before entering home and getting to the user. Otherwise, there is no difference between these two.

[Mohamed Ben zegalam]

if I understand you, we should not use one optical-electrical converter and one block OFDM demodulation to all end users together, we have to split the optical signal to all users and then each end user has to converted to electrical and do the OFDM demodulation, correct or not

[alistu]

Let me put it this way: For FTTH, such a thing is not necessary; Optical signal can be converted to electrical signal and then be split between the users in FTTH (as is the case with Boyka’s simulation). However, in FTTD optical signal is converted to electrical signal after being split between the users.

[Mohamed Ben zegalam]

I think what is you explained for FTTH is for FTTC, please see the attached pictures that show the different between FTTC, FTTB, FTTH. and the FTTD is more advance than all of them, because as you explained before. it is stay optical until it reaches the PC or TV an so on.

Attachments:

1. 

   images.png
   

2. 

   Apps_FTTx_Fig3.png
   

3. 

   19c69dc1787797fce8ef8d7577d42777_f32.gif
   

[alistu]

You’re right. According to the images the conversion should take place in the last step. It is possile to use OFDMA in FTTH by using power splitter at the receivers, but this also causes a lot of power being wasted. I think it would be great it Boyka introduces any work based on which he has tried to implement OFDMA for FTTH.

[Author]

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