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

10-16
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
10.8.2 Diversity Gain Versus Probability for Tokyo, London, and Singapore
In Figure 10-13 is given the diversity gain versus probability for the “Best-Satellite” and
the joint distribution multiple satellite cases for Tokyo. Two types of diversity gains are
shown plotted; namely one corresponding to “handoff” (solid) and the other to
“combining” (dashed) as previously described. The diversity gain is defined here as the
fade difference between the highest satellite and any of the other scenario distributions at
a fixed probability level. For example, at the 10% probability in Figure 10-10, the
Highest-Satellite and Best-Satellite fade levels exceeded are approximately 22 dB and
15 dB, respectively. The difference in these fade levels corresponds to a diversity gain of
7 dB at a probability of 10% as noted in Figure 10-13. The diversity gains for the other
distributions are analogously derived.
The following results may be gleaned from Figure 10-13: (1) The diversity gain
differences (at any probability) between “handoff” and “combining” methodologies are
generally smaller than 1 dB. (2) For probabilities down to approximately 20%, the “Best
Satellite” diversity gain is within 1.5 dB of the other multiple satellite cases. (3) At the
10% level, the multiple satellite cases give 3 to 5 dB improvement in the diversity gain
relative to the Best Satellite.
The London diversity gain curves are similar to those of Tokyo except
approximately 1 to 2 dB lower because the “Highest” satellite reference distribution is
shifted to the left (as shown in Figure 10-6). This occurs predominantly because the
average satellite elevation of the highest satellite is 52° for London as compared to 40°
for Tokyo.
Diversity Gain (dB)
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3 Best Satellites
Diversity Type
Dashed: Combining
Solid: Hand-off
20 10
Probability (%)
4 Best Satellites
2 Best Satellites
Best Satellite
Figure 10-13: Path diversity gains at 1.5 GHz derived from distributions for the
simulated Globalstar constellation with “combining” and “handoff” diversity for Tokyo,
Japan.
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