Performance of Stand-Alone GPS - Understanding GPS: Principles and Applications - page 354

The analysis considers both SA on and off cases. Although SA was turned off in
May 2000, TSO C129 receivers have the SA on pseudorange error hard coded into
the software. The availability results shown with SA on in Tables 7.7 and 7.8 still
apply to those receivers.
The availability of RAIM fault detection is well above 99% for the en route and
terminal phases of flight and 97.3% for nonprecision approaches. In order to
improve availability, the barometric altimeter can be included as an additional mea-
surement in the RAIM solution. With baro aiding, availability improves to 100%
for en route navigation with 99.99% availability for the terminal phase of flight and
99.9% for nonprecision approach. The maximum outage duration over the course
of the day decreases from over half an hour to 15 minutes for nonprecision
approach.
The availability of fault detection and exclusion with baro aiding ranges from
81.4% during nonprecision approaches to 98.16% for en route navigation (FDE
without baro aiding isn't considered in this analysis due to its low availability). For a
nonprecision approach, FDE outages can last for more than 1.5 hours at a location.
These results are summarized in Tables 7.7 and 7.8.
The availability of RAIM and FDE with SA off applying a 5º mask angle are
shown in Tables 7.9 and 7.10. As shown in Table 7.9, availability of the RAIM fault
detection function has nearly 100% availability with SA turned off and the use of
baro aiding. The removal of the SA noise allows better detection of a bias present on
a satellite.
The availability of FDE also improves substantially with SA off such that greater
than 99% availability can be achieved for en route navigation through nonprecision
approach. However, the outage duration for nonprecision approach can still be sub-
stantial, with outages lasting on the order of an hour.

Table 7.7 RAIM/FDE Availability with a 5º Mask Angle and

SA On

Nonprecision
Approach RAIM/FDE Function En Route Terminal

Fault detection 99.98% 99.94% 97.26%

Fault detection
with baro aiding

100% 99.99% 99.92%

Fault detection
and exclusion with
baro aiding

99.73% 97.11% 81.40%

Table 7.8 Maximum Duration of RAIM/FDE Outages with 5º Mask Angle

and SA On

Nonprecision
Approach RAIM/FDE Function En Route Terminal

Fault detection 5 minutes 10 minutes 35 minutes

Fault detection with
baro aiding

0 minutes 5 minutes 15 minutes

Fault detection and
exclusion with baro aiding

25 minutes 55 minutes 100 minutes