Global Positioning System Reference
In-Depth Information
not present because this quantity is not broadcasted by the GPS satellite and, as we stated
previously, the integrity data delivered by these satellites does not alter the Faulty section of
the HM P equation. For this reason, in this context, the above-mentioned probability does
not reach high values. Indeed, the statistics never exceed the Threshold.
x 10 -10
Integrity Risk
18
Alarms=0
16
14
12
10
8
6
IR Threshold
4
2
0
-2
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Time [s]
Fig. 14. IR algorithm combined constellation and bias on SISA, satellites GPS PRN3 and
PRN10
6. RAIM evolution: ARAIM
An interesting development of the described study is the analysis of the new RAIM
technique, the Advanced RAIM. ARAIM, proposed in 2010 by the GEAS (GNSS Evolutionary
Architecture Study), could be considered as an evolution of the classical RAIM. This new
solution takes advantage of the availability of different new navigation systems (i.e. Galileo)
in order to improve receiver performances.
ARAIM is an extension of the single-frequency RAIM. Both are based on an airborne
comparison of each satellite measurement to the consensus of the other available satellite
measurements (GEAS, 2010). However, the differences between the two techniques are
also important. ARAIM should be pursued for the worldwide vertical guidance of civil
aircraft based on two or more GNSS constellations radiating at two ARNS/RNSS
frequencies (L1 and L5). The main characteristic of the Advanced RAIM would support
vertical guidance to decision heights of 200 feet (LPV-200), whereas single-frequency RAIM
only supports LNAV guidance. As such, ARAIM must protect vertical errors at levels of
35 meters, while RAIM only needs to detect lateral errors of 200 meters or so. In addition,
LPV-200 corresponds to a severe major hazard level (10-7), and LNAV is only major (10-5).
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