Frequency response from fading simulator block not working as expected

GNU Radio
1

Hello,

In order to simulate a multi-path scenario, Im trying to validate the
“Frequency Selective Fading Model” block, but the results I found are
not
the ones I would expect.
The set up consisted of 2 taps delayed 20 microseconds each other, so
that
the frequency response should have very deep fadings spaced regularly in
frequency. The results I got showed a flat frequency response, as well
as
in other standardized power delay profile scenarios.
The blocks I used were a random source -> OFDM Mod -> Throttle ->
Frequency
Selective Fading Model -> WX GUI FFT Sink. Sample rate was set as 1MHz,
so
that in Freq. Selective block I set PDP Delays as [0, 20] and PDP
Magnitudes as [1, 1].
Please tell me if I misunderstood any of these parameters or this block
could be really improved.

Thanks and Regards,
Ricardo

2

On 02/28/2014 02:13 PM, Ricardo Yoshimura wrote:

and PDP Magnitudes as [1, 1].
Please tell me if I misunderstood any of these parameters or this block
could be really improved.

Did you increase the number of taps?
Also, note that this block provides a time-variant channel. If you
average, you might not see fades. For a static channel, use the “Channel
Model”.

If you use the default settings, you should see fades, right?

M

3

Hi Martin,

Thats right! As the number of taps was increased, the deep fadings were
visible, ranging until about 20dB.

Thanks and Regards,
Ricardo