1
Level Crossings and Fade
Durations
Instructor: M.A. Ingram
ECE4823
Normalized Fading Process
Begin with the channel fading process,
normalized to the local rms signal level
Local average in dB subtracted
[not real data]
Signal
Env.
in dB
0t
Normalized Threshold Level
ρ
Pick a level or threshold , where Ris
the unnormalized threshold and
[not real data]
Signal
Env.
in dB
0t
rms
RR /=
ρ
()
∑
−
=
== 1
0
2
2
)(
N
i
ibrms thER
α
ρ
(in dB)
Level Crossing Rate (LCR)
The LCR at threshold
ρ
is the expected
rate at which the normalized envelope
passes the value
ρ
with a positive slope
[not real data]
Signal
Env.
in dB
0t
............ .
.. ...
ρ
(in dB)
Trends
We expect the highest rate around
ρ
=0 dB, tapering
off gently for lower thresholds and abruptly for
higher thresholds
The maximum Doppler frequency just scales the
horizontal axis and therefore the rate
[not real data]
Signal
Env.
in dB
0t
ρ
.............
.....
(in dB)
LCR For Rayleigh Fading
For Rayleigh fading and isotropic
scattering (Clarke’s Model), the LCR is
given by
where fdis the maximum Doppler
frequency
2
2
ρ
ρπ
−
efd
