FFT of channel impulse response in python

Question

I have this channel impulse response. $h = [1,\,0.5,\,0.3+0.3j]$ The channel is like this by doing a FFT for h.

I resample (up-sample) my OFDM symbol to have smaller path delays and convolve it with my channel impulse response h. In the receiver side I estimate channel with my pilots and everything is Ok. when I want to see exact channel in frequency domain. So I do a FFT for h and the result is different from what I estimated from pilots.

The orange one is estimated channel. How can I have correct channel from h with doing a FFT?

Answer 1

To go from your four-tap channel to a frequency-continuous plot, you had to do some interpolation. I would check whether the assumptions for that really hold; lest you're literally zero-padding to the size of the FFT done in your FFT system, it won't.