[Discuss-gnuradio] Channel estimation in OFDM examples

[Jurgis Aleksandravičius]

Hi,

I am using the OFDM tx/rx example flowgraphs on USRP N210 radios to  
get complex channel coefficients from tags produced by OFDM Channel  
Estimation block.

When I record and plot the channel coefficient in time, I can see that  
its magnitude is constant, but phase is 'rolling' at a frequency of  
~100 Hz when center frequency is 2.4 GHz. I guess that is because of  
differences in clock frequency at transmitter and receiver. I tried  
using the MIMO cable for clock synchronization - that just made the  
phase of channel coefficient less noisy, but phase roll was still  
there. Also, my understanding was that OFDM should correct the  
frequency offset.
Does anyone have thoughts on what might going on here?

Thanks a lot,
Jurgis