OFDM equalization question

[thavamaran]

Hi guys, I am working on optical ofdm, its not much of a different from normal ofdm. I have a problem at the receiver side where my constellation shifts in phase.

So I did a very simple equalization, where the data before IFFT which will be in so call frequency domain, assume that as X. Then the data at receiver after FFT which will be in so call frequency domain, assume that as Y.

So I did the channel estimation by taking Y/X and I will get H which is the channel property. Then to get what I trasmitted at the receiver side, to compensate all the distortion, since H=Y/X, so to get back X at the receiver, I did X=Y/H and I got back my exact constellation at the receiver.

Im not sure whether this is correct or no, please someone advice me on this. Thank you very much.

 

[rameshrai]

can you show the block diagram of the simulation with IFFT and FFT blocks and the constellation diagram? Logically the H=X/Y process of finding the channel transfer function is correct but again you said you have problem at the output with shift in phase. You need to give us more information

Ramesh

 

[thavamaran]

Hi rameshraj. I have attached the block diagram and constellation, ignore the Rayleigh fading part of the block diagram cause Im designing both.

The shifted constellation is from my single carrier QPSK system, not OFDM, cause OFDM will take sometime to run in Matlab. But the result is same except for the constellation cloud, the pattern of the spots will be different, but the shift is same.

May I get your advice on how I can solve this. Thank you!