How to Confirm OFDM constellation with USRP and GRC

Hi- all

I¡¯m now trying Transmission of the OFDM system with USRP and GRC

I use OFDM mod/demod block in GRC

I confirmed received spectrum by USRP receiver

But I want to confirm constellation of receive block

In my opinion, I have to spilt file before FFT.

Am I correct?

Do you have another method such as benchmark_ofdm? except using ofdm

Thank you