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ptc-50085241-Visitor
1-Visitor
March 13, 2013
Question

OFDM Signal Reconstruction via DFT

  • March 13, 2013
  • 1 reply
  • 4236 views

I'm having trouble reconstructing an OFDM QAM signal using its amplitude and phase spectra obtained by using the DFT. The QAM signal is given in the image below.

qam+.PNG

I have tried to do it so far using the below equation.

lab6-1.PNG

This is the closest I have reconstructed it to the original. What am I missing?

I am using Mathcad 13.

1 reply

W
Werner_E25-Diamond I
25-Diamond I
March 13, 2013

You sure would get a better respones if you attach a worksheet. From the pic alone probably nobody would be able to determine what the problem ould be.

Would the following link be of any help?

http://www.comlab.hut.fi/users/tko/geta07/GETA fall 07- OFDM with MathCAD.ppt

P
ptc-50085241-VisitorAuthor
1-Visitor
March 13, 2013

No sorry that doesn't help. I was browsing through that just last night actually. I have attached my worksheet.

W
Werner_E25-Diamond I
25-Diamond I
March 13, 2013

Jonathan Mayers wrote:

1. Yes. The DC value is part of the reconstruction.

2. No. The last definition of X is what I'm supposed to use.

OK, so I'm not of much help. It was just that I thought that

1) the DC value could be (is) negative!?

and I noticed that

2) you are using just the first 10 values of the 200 element vector X in the definition of sDFT for reconstruction. Obviously thats supposed to be done.

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