All in view position solution with five degree mask

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Unformatted text preview: Availability 100% ANALYSIS CONDITIONS 99% - Current Operations Nominal 24 Satellite Constellation (as of 19 June 2000) 98% 97% - 5 x 5 degree global grid spacing with one minute sample steps over 24 hours 96% 95% - All-in-view position solution with five degree mask angle 94% 93% - 6 meter constellation RMS User Range Error (URE) 92% Global Vertical Availability 91% Worst Site Vertical Availability 2-10 3-22 10-26 2-27 22-25 22-31 11-29 2-26 2-11 7-26 7-20 4-7 11-25 2-20 11-31 21-29 1-20 3-31 7-11 1-25 90% - PREDICTED VERTICAL 95% ERROR USED FOR AVAILABILITY THRESHOLD: 77 meters GPS Satellite PRNs Removed Figure A-3-5. GPS Vertical Availability – Two Satellites Out Perhaps more important than the degradation of constellation geometry is the possibility of “DOP holes”, periods of time where the solution geometry is too marginal to use or not enough satellites are in view to generate an unaided solution. Periods of time up to 39 minutes in duration with less than four satellites were observed for some locations in the worst-case two-satellite out combination. In the worst-case combination, 13% of the world experienced periods of less than four satellites visible. For those locations that did experience less than four satellites with the worst-case 22-satellite constellation, the average amount of time was approximately seven minutes. Since this analysis was conducted with a five-degree mask angle, users can anticipate significantly worse effects when using mask angles greater than five degrees in the unlikely event the constellation degrades to 22 satellites. A-3.4 SIS URE Variation Effects on Service Availability Given a nominal constellation of 24 or more satellites, service availability can vary considerably based on variations in constellation URE performance. This variation can become even more significant when geometry is degraded to the worst-case conditions, as illustrated in Figure A-3-6 and Figure A-3-7. As shown in the figures, a constellation RMS URE of approximately 6 meters in a worst-case geometry scenario will by definition still support the service availability performance standard. With geometry variations over time, the maximum constellation RMS URE that supports the service availability may vary slightly. Given continuing consistency in the GPS program baseline and stability in managing constellation URE performance, this worst-case scenario is considered extremely unlikely to occur. Page A-16 October 2001 GPS SPS Performance Standard Horizontal Service Availability GPS Horizontal Availability Sensitivity to URE 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 Horizontal Availability 91% Worst Site Horizontal Availability - PREDICTED HORIZONTAL 95% ERROR USED FOR AVAILA...
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This document was uploaded on 09/26/2013.

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