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

12-10
12.6.5 Satellite Diversity
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
Figure 12-3 and Figure 12-4 have been derived from optical measurements and
simulations employing the Globalstar constellation of orbiting satellites for urban Japan.
The methods used to calculate these figures are summarized in Section 12-10. At the
20% level, the highest satellite fade at L-Band is noted to be 17 dB (Figure 12-3). A
diversity gain of 12 dB may be gained by sequential switching to the satellite giving the
smallest fading (highest signal level). Although percentages smaller than 20% give
improved diversity gains, the joint probability fade level may nevertheless be too great
for practical communications (e.g., at 1%, the joint fade level exceeds 20 dB). Figure
12-4 shows that, in general, one dB difference exists between the “hand-off” and
“combining” diversity modes of operation.
Percentage of Locations Fade > Abscissa
98
95
90
80
70
60
50
40
30
20
10
5
2
1
Satellite Scenario
Highest Satellite
Best Satellite
2 Best Satellites
3 Best Satellites
4 Best Satellites
-5 0 5 10 15 20 25 30 35
Fade Depth (dB)
Figure 12-3: Cumulative fade distributions at 1.6 GHz for the simulated Globalstar
constellation of satellites assuming combining diversity for urban Japan.