Using Fractional or Rational resampler to simulate Doppler

[Jose Ruvalcaba]

Hello,

I am trying to simulate an accurate representation of Doppler Shift in a channel and I was told that to do this I would have to multiply a complex signal with a cosine and implement a resampler block to simulate the signal samples that are coming closer or farther away from each other.

My question is this, can I use either the rational resampler or fractional resampler block in GNU Radio to dynamically simulate samples moving closer or farther than each other?  Or would I need to make my own OOT block to do this?

I tried using a QT GUI Range block to change the resampling ratio of a fractional resampler but my flowgraph froze. 

Any suggestions?

Thanks, 

Jose