6
and 1.24 times per second, respectively.
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124 CHAPTER THREE
Normalized Level Crossing Rate (LCR)
0.01
0.1
1
10
??“40 ??“30 ??“20 ??“10 0 10
20*LOG(R) [dB]
Normalized LCR FIGURE 3.7 Level Crossing Rate (LCR) plot.
Using Fig. 3.8 along with the previous definition of the AFTD, we can extract the average time
we are below the 20-dB fading level. For maximum Doppler spreads of 200 and 5 Hz, the average
time durations are 200 sec and 8 msec, respectively.
Moreover, we plot the temporal variations of the received signal assuming a Rayleigh fading channel
(see Fig. 3.9). This plot aims to show that the time spent below the specified fading level varies
in duration, with the average value given above.
An equally important component of the multipath fading phenomenon is the phase variation. The
Rayleigh fading component will vary the signal envelope depending on fades and peaks present. The uniform
phase component will rotate the signal depending on the aggregate sum of the arriving signals. Note
although the Rayleigh and phase varying components have been called out or discussed separately, it is
quite common and acceptable to simply describe both effects when the phrase multipath fading is used.
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