Handbook of Propagation Effects for Vehicular and ... - Courses

6-4
High-Gain Antenna Fade (dB)
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Measured
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
Equal Values
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Low-Gain Antenna Fade (dB)
Figure 6-2: Fades measured by high- and low-gain systems at equi-probability levels.
6.4 Fade Reduction Due to Lane Diversity
We examine the extent by which fades are reduced (or increased) when switching lanes
for LMSS configurations. Figure 6-3 shows vehicles on the inner and outer lanes,
respectively, where the satellite is to the side and the propagation path passes through the
tree canopy on the side of the road. We note that the path length through the canopy is
greater when the vehicle is closest to the tree line (inner lane). Switching lanes from the
inner to the outer lanes should therefore produce a fade reduction. The authors measured
this effect at UHF (870 MHz) [Goldhirsh and Vogel, 1987], and L-Band (1.5 GHz)
[Goldhirsh and Vogel, 1989]. Repeated measurements were executed employing a
helicopter as the transmitter platform, and corresponding cumulative fade distributions
were derived for inner and outer lane scenarios at fixed path elevation angles of 30°, 45°,
and 60°. To characterize the increase in signal power by switching from the inner to the
outer lanes, a quantity known as the “fade reduction, FR” was defined. This quantity is
obtained is obtained by taking the difference between equi-probability fade values from
distributions pertaining to inner and outer lane driving.