modulation scheme

[Dr. Dhiman Kakati]

Hi all,
When we consider advanced digital modulation scheme such as DQPSK, QPSK, QAM etc. we see that Every modulation scheme has some advantages and some disadvantages, So for the design of Radio over Fiber (RoF) which one will give the best output in terms of High bit rate as well as transmission distance. which detection scheme will give better results for this irrespective of receiver complexity, I am asking for theoretical explanation and suggestion which modulation will be better for RoF. Thank you..

Regards

[alistu]

Hi Dhiman,

OFDM has better performance in terms of what you have mentioned somehow. In OFDM, the symbols are being sent through orthogonal frequency channels simultaneously, so the time length of the symbols can be extended and therefore, they can fight ISI caused by chromatic dispersion better. At the same time, the channels overlap and this results in better bandwidth efficiency.

Even though you haven’t asked about complexity, it is an important factor in general as we all know. Ignoring it would be like saying two channels transmit more data than one channel, so two channels are better than one. And OFDM is rather complex compared to other schemes you have mentioned. But it has become quite popular with researchers nowadays.

Regards

[Dr. Dhiman Kakati]

Yes I agree that Complexity is also a major factor for consideration, I mentioned it because once we design the system then we can modify the design to make it simpler.

With Regards

[alistu]

Indeed, you mentioned you were interested to know about the theoretical aspect. I also have to add OFDM scheme also requires a coding scheme such as QPSK to be adopted. So under any condition, it will be more complex than a simple coding scheme system (as it contains a coding part as well), and of course has better performance.

[Dr. Dhiman Kakati]

Thanks Alistu,
I have not designed any OFDM system till now, But yes I will try to go for it. I asked for theoretical concept because before going for practical implementation we should be very clear about the theory.

Regards

[alistu]

You’re welcome. As for what you asked about the type of receiver used in OFDM systems, I have only seen direct detection being adopted in RoF systems. I don’t know if actually RoF using coherent detection is feasible. You can go through a review paper named “Review – OFDM-RoF (Radio over Fiber) System for Wireless Network” if you are interested. All the cases discussed there also use direct detection.

Regards

[Dr. Dhiman Kakati]

Dear Alistu,
I will definitely go through the review paper you have mentioned, if you have the soft copy of he same please attach here.

Regards

[alistu]

Here I have attached the review pdf. I was not sure about the copyright before, but it is from an open access journal.

Regards

[Dr. Dhiman Kakati]

Thank you so much for providing me with the pdf.

Regards

[alistu]

You’re welcome Dhiman.

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