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

6-14
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
implementation losses have been neglected. All diversity gains are shown to have a peak
at approximately 20% probability.
Diversity Gain (dB)
15
14
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10
9
8
7
6
5
4
3
2
1
0
50
40
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3 Best Satellites
Diversity Type
Combining
Handoff
20 10
Probability (%)
4 Best Satellites
2 Best Satellites
5
Best Satellite
Figure 6-10: Path diversity gains at f ≈ 1.6 GHz derived from distributions for the
simulated Globalstar constellation with combining diversity and handoff for Tokyo,
Japan [Vogel, 1997; Akturan and Vogel, 1997].
6.6.4 Satellite Diversity Measurements at S-Band Employing TDRSS
Direct orbital satellite mobile measurements were conducted by Vogel [1997] employing
a portable satellite receiver with a prototype personal antenna system using NASA’s
Tracking and Data Relay Satellite System (TDRSS). During three occasions, NASA
made available two TDRSS satellites for diversity measurements at ~2 GHz. The
receiver recorded simultaneously the signals from the two satellites located at different
azimuth and elevation angles. The mobile earth station (MES) was hand-carried to
several typical environments in Austin, Texas during the spring-summer period when the
deciduous trees were in full bloom. Figure 6-11 shows single and joint distributions for
three path states which are characterized as follows for the specific environments
considered: (1) “clear” denotes an open field with unobstructed line-of-sight paths to both
satellites, (2) “shadowed” denotes walking in the vicinity of a grove of tall and thin
deciduous trees, and (3) “blocked” denotes walking on the grounds of an apartment
complex with multiple three-story buildings set at various angles. The azimuths and
elevation pairs to the satellites denoted as T7 and T1 were respectively, 248°, 24° and
2
1