# Doppler Model, how does it affect the fading impulse response?

I have been reading a paper that mentions Doppler model that may be included in the fading characteristics of impulse response. One example of bell shaped Doppler Spectrum is the following

$$S(f) = \frac{1}{1+A\frac{f}{f_d}}\,\,\,\,\,\,\,\, |f|\leq f_{\max}$$

where $f_d$ is the Doppler Spread, $A$ is a constant, $f_{max}$ is maximum frequency component of the Doppler power spectrum. Does anyone know how the following function affects the channel model?

Thanks

• thank you for the answer and the details therin. I am just wondering given $S (f)$ what can I learn from it? so if you give me $S (f)$ what can I tell about the fading model? – Tyrone May 14 '15 at 2:55
• @Tyrone The Doppler spread is approximately equal to $1/T_c$, where $T_c$ is the channel coherence time. For example, if the Doppler spread is 80 Hz, then the channel coherence time is approximately 1/80=12.5 ms. – MBaz May 14 '15 at 14:37