Performance of Stand-Alone GPS - Understanding GPS: Principles and Applications - page 372

January 1, 2002-December 31, 2003

20

Average daily global performance:
4.5 meters (95%)

18

16

Average worst site performance:
7.2 meters (95%)

14

12

10

8

6

4

2

0

Jan-02 Apr-02 Jul-02 Oct-02 Jan-03 Apr-03 Jul-03 Oct-03 Jan-04

Date calendar years 2002-2003

95% 3D position error --
worst site

95% 3D position error --
Global median

ANALYSIS NOTES

- All-in-view PPS dual-frequency
receiver with five-degree mask
- 80 cm (1 ) receiver thermal noise
- One minute samples over 24 hours
- 95% sort on instantaneous 3D
position errors
- 1 1 degree equally spaced global
grid

σ

×

Figure 7.34 Global trend in GPS three-dimensional position error performance.

sample interval (1-minute samples). Worst-site performance understandably dem-
onstrates more variance but still trends to below 8m (95%).
Since GPS is a PNT system, it is appropriate to include time transfer perfor-
mance in our discussion. We consider time transfer performance from two perspec-
tives: dynamic and static. Dynamic time transfer is based on the time portion of the
navigation receiver's position solution. Static time transfer is the direct solution for
time, bypassing the position solution geometry, using a time transfer receiver from a
surveyed location. Figure 7.35 provides a 1-year trend of dynamic time transfer per-
formance, while Figure 7.36 provides a 1-year trend for static time transfer perfor-
mance. Note that static time transfer performance is generally better and more
consistent than dynamic time transfer. Static time transfer is computed from an