Re: Query about OFDM Receiver with USRP

On 17/11/2022 10:23, Al Amiri, Wesam (waalamiri42) wrote:

Hello,

I am working on the implementation of OFDM TX and  RX using USRP N210 and GNURadio.
I used the the grc flow graphs done by GNURadio workshops and I was able to receive the OFDM signal and demodulate it.
Also, I connected a constellation sink to the Palyoad Stream Virtual Source at the RX side (after demodulation), and I got 4 constellation points which is corresponding
to the QPSK similar to the Tx cosntellation.
However, when I removed the Smidl and Cox synchronization to check the phase rotation from the CFO (please see attached) , I still have the same 4 constellation points without phase rotation. Do you know why this happens?

You haven't described your physical setup, but if you have TX looped-back to RX, there won't be any phase rotation since
  the TX and RX are both phase-locked to the same master oscillator on-board the N210.  In "real-life" scenarios, of course,
  there will be phase rotation between the TX and RX.

One more thing please, is there any way to extract a certain subcarrier from the FFT at the receiver side. I need to do some post processing on one of the subcarriers?

Regards,
Wesam Al Amiri