[Discuss-gnuradio] Understanding how CSI is measured with OFDM Channel Estimation block

[Ayaz Mahmud]

 

Hello,

 

I want to have a clear understanding on how the channel state information is being estimated in GnuRadio.

 

I have tried out the OFDM example of tx & rx which works fine and I am also able to extract the CSI. Now I want to understand how it is being actually measured.

 

From what I see & understand, OFDM carrier allocator has pilot carriers & Sync words defined. On the Rx end the same Sync words are present. The received symbols are then compared with these pre-defined sync word & CSI is calculated.

 

1. Why there are 2 sync words?
2. Are these sync word used to measure CSI ? Or is it the pilot symbols ?
3. How these sync words are being derived as shown in the example ? i.e what format has been followed for this?
4. What might happen if I change these values. (As it should work the same unless they are different at tx/rx)?