Slightly given continuing consistency in the gps

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Unformatted text preview: BILITY THRESHOLD: 90% 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 36 meters Constellation RMS URE (meters) Figure A-3-6. Horizontal Service Availability Sensitivity to URE, Worst-Case Geometry GPS Vertical Availability Sensitivity to URE Vertical Service Availability 100% ANALYSIS CONDITIONS 99% - Current Operations Nominal 24-Satellite Constellation (as of 19 June 2000) 98% 97% 96% - Worst two satellites removed 95% - 5 x 5 degree global grid spacing with one minute sample steps over 24 hours 94% 93% - All-in-view position solution with five degree mask angle 92% Global Vertical Availability 91% Worst Site Vertical Availability - PREDICTED VERTICAL 95% ERROR USED FOR AVAILABILITY THRESHOLD: 90% 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 77 meters Constellation RMS URE (meters) Figure A-3-7. Vertical Service Availability Sensitivity to URE, Worst-Case Geometry A-3.5 Representative Service Availability Characteristics As seen in Figure A-3-8, more than eight satellites are on average visible at the average location with the current operations nominal 24-satellite constellation. In the nominal 24-satellite case, less than six satellites are in view less than 0.1% of the time on average. With the current operational constellation, more than nine satellites are generally visible on a global basis. In the rare event the constellation is reduced to a worst-case 22 satellites, the average location will still see an average of seven satellites at any given time. With the normal range of satellite availability and UREs across the constellation, availability is generally much better than the performance standards, as shown in Figure A-3-9 and Figure A3-10. Both the global and worst-case site availability values are generally close to or at 100%. As satellites were removed from service later in the month, accuracy degraded slightly, but not enough to degrade service availability. Page A-17 GPS SPS Performance Standard Nominal 24-Satellite Constellation Worst Case Two Satellites Down out of Primary 24 50% Percentage of Time over 24 Hours Percentage of Time over 24 Hours October 2001 40% 30% 20% 10% 0% <4 4 5 6 7 8 9 10 11 12 13 50% 40% 30% 20% 10% 0% 14 <4 4 5 Number of Satellites Visible 6 7 8 9 10 11 Number of Satellites Visible 12 13 14 Figure A-3-8. Range of Average Global Satellite Visibility Distributions GPS Horizontal Service Availability -- June 2000 100.0% ANALYSIS CONDITIONS 99.9% 99.8% 99.7% 99.6% 99.5% 99.4% 99.3% 99.2% Global Horizontal Availability, 36 meter 95% Threshold 99.1% Worst Site Horizontal Availability, 36 meter 95% Threshold 99.0% 0 5 10 15 20 25 30 - Analysis conducted under normal constellation ops conditions - NANUs applied over intervals defined by 2 SOPS - Global 5 x 5 degree grid (1,666 locations) - 24 hour sample intervals - One minute sample steps - All-in-view NAVSOL - SPS signal-in-space UREs, with 50 cm of added noise to represent uncertainty due to Tgd - Five degree mask angle - Statistics are result of empirical sorts for each location over the...
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This document was uploaded on 09/26/2013.

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