QAM Transmitter and Receiver

[Sasha]

Hi all,

I am trying to connect the optical fiber between QAM modulator and demodulator. Can anyone please help me out, what components should I use to connect optical fiber between them?

I tried to implement the QAM sample file given in optiwave tutorial.

Digital modulation – QAM

At the transmitter side, the constellation diagram is good as shown in the tutorial. I tried connecting the constellation diagram in the receiver side. I will attach the output screenshot. Please help me out whether it is right or not.

Thanks in advance.

Attachments:

1. 

   constdia.png
   

[alistu]

Hi Sasha,

Can you please upload your implementation osd file if it is possible? Thank you.

[Sasha]

Hi Alitsu,

I am working in Optisystem version4 and it is available in my school. You can find the file QAM – Transmitter and Receiver.osd in samples library. I will upload the file when I am in school.

Thanks in advance.

[Sasha]

Hello all,

I attached a file here. Please take a look at it.

Thanks in advance.

[Sasha]

Hello all,

I implemented the Coherent Optical Transmission Optical System given in optiwave tutorial.

Coherent Optical Transmission

I got the different constellation diagram at the receiver.

Can anyone please help me out.

Thanks in advance.

Attachments:

1. 

   const.png
   

1. Coherent-Optical-Transmission-system.osd

[Gokul Boro .]

There is always some issue if you simulate system designed in older version in a newer version. So what you can do is install the newer version and try it. If the problem still exists please do share.

Regards.

[alistu]

Hi Sasha,

I checked it by comparing it to the OptiSystem sample coherent 4-QAM and I must say I got really different constellations by the changes I applied to the implementations. By changing M-ary pulse generators bias and gain (gain=-2, bias=2) which were the main problem I think, I managed to get the constellation you can see. It was the best I could achieve although I tried make changes exactly according to the QAM sample. Here I have used coherent receiver component, even though yours was all right.

Regards

Attachments:

1. 

   constellation-qam.jpg
   

1. Coherent-Optical-Transmission-system-modified.osd

[Dr. Dhiman Kakati]

Hi Alistu,
I have seen in many cases that the constellation points gets elongated in a circular fashion as that you have attached in the comment above #27825, So can you tell me the reason for waht it happens so ??

in some another cases I have seen that if we do not connect the fiber the constellation comes quite good and clear points at the receiver side but when we add a fiber (Standard single mode fiber) the constellation points are shifted (not elongated) in anticlockwise direction. What may be the cause for this? Please anyone make me clear.

I need to mention that I don’t want to use DSP in this case as using DSP we can correct this. I don’t have the design file with me now, If anyone has faced the same problem as me please answer here.

With regards,
Dhiman

[alistu]

Hi Dhiman,

I really don’t know the problem with the above simulation, as I tried to change it according to the sample file but did not manage to get the proper result. As for the rotation, you can refer to the below topic which I had started a while ago to read a whole discussion:

Symbol Rotation in OFDM

Regards

[Author]

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