JPL's Wireless Communication Reference Website Slide Show

Coherence Bandwidth

When do we experience frequency selective fading?

When is frequency diversity effective?

Definition of Coherence Bandwidth:

Coh. BW is the frequency separation for which the correlation coefficient is down from 1 to 0.5

Insert: 1 = 4p(f₁ - f₂) T_RMS,

So Coh BW = 1 (4p T_RMS)

We derived this for an exponential delay profile

Another rule of the thumb

ISI occurs if T_b > 0.1T_RMS

Conclusion: keep transmission BW much less than Coh BW

JPL's Wireless Communication Reference Website © Jean-Paul M.G. Linnartz, 1993, 1995.