
285Statistical Simulation of Multipath Fading Channels
A second measure of interest is the RMS delay spread, which is dened as the square root of the
second central moment of the PDP:
−μ
=
{}
,
with the mean squared delay,
τ
, dened as
τ
τ
2
2
2
{}
=
∑
i
i
a
a
.
The RMS delay spread, σ
τ
, is a measure of the time dispersion of the channel’s impulse response
and serves to dene the key parameter for the frequency characterization of the channel: the coher-
ence bandwidth. The coherence bandwidth is a statistical measure of the range of frequencies over
which the channel can be considered at. The coherence bandwidth is inversely proportional to ...